INTRODUCTION
Background
Soybean (Glycine max (L.) Merr.), originating from East Asia, ranks as the fourth most significant seed crop globally, following wheat, rice, and corn It serves as a crucial protein source for both humans and livestock In 2020, global soybean production reached approximately 368.5 million tons (FAOSTAT).
Soybean seeds are rich in essential amino acids, including tryptophan, leucine, isoleucine, valine, lysine, and methionine, making them a valuable protein source for the human body They also provide important minerals such as calcium, iron, magnesium, sodium, phosphorus, and potassium, along with vitamins B1, B2, D, K, and E The nutrient composition of soybean seeds per 100 grams includes 417 kcal, 12.5 g of water, 35.3 g of protein, 19.0 g of lipids, 28.2 g of carbohydrates, and 5 g of minerals Notably, the protein concentration in soybeans is approximately 4-5 times higher than that of rice, wheat, and corn, while their starch content is relatively low Additionally, soybeans are versatile and can be processed into over 600 different food products, including traditional items like tofu, soy sauce, and soy milk, as well as modern foods such as candy, bread, and cheese.
The soybean oil industry plays a crucial role in various sectors, including paint, ink, soap, plastics, and artificial rubber Additionally, soybeans serve as essential raw materials for the pharmaceutical and food processing industries Their use in crop rotation and intercropping enhances yields and soil nutrition, which is vital for the intensive agricultural growth in Vietnam As the demand for soybean products continues to rise, there is a pressing need to adopt new high-yielding varieties and efficient cultivation practices.
In Vietnam, soybeans are extensively grown across all seven ecological regions, with the Northern midland and mountainous areas having the largest cultivation zones In 2014, the northern mountainous region dedicated approximately 50,000 to 60,000 hectares to soybean farming, primarily in provinces such as Ha Giang, Cao Bang, Lao Cai, Dien Bien, and Son La, during the spring and summer-autumn seasons.
The rising demand for soybean products necessitates the research and development of new soybean varieties To achieve high yield, quality, and adaptability, it is essential to leverage scientific and technical advancements in breeding and selection The creation of new plant materials plays a crucial role in effective breeding Additionally, the diversity of genetic resources, particularly local varieties, is invaluable for acquiring desirable traits, including both quantitative and qualitative characteristics, as well as tolerance to adverse abiotic and biotic conditions.
For such importance of plant materials in soybean breeding, my research is titled “Evaluation soybean lines in the winter season 2020 in Gia Lam, Ha Noi”
Objectives
Evaluating soybean lines on morphological and agronomical traits to identify promising soybean lines
Soybean lines were grown in winter season 2020 in Gia Lam, Hanoi and evaluated for:
- Morphological and phenological traits of soybean lines
- Agronomical traits related to growth and development of soybean lines
- Yield and yield component traits of soybean lines
LITERATURE REVIEW
Origin, classification and distribution of soybeans
Soybean, a crop with a long history of cultivation, is believed to have originated in Asia, specifically China, where it was domesticated during the Shang Dynasty (1700-1100 B.C) Historical, geographical, and archaeological evidence supports this origin The cultivation of soybeans spread to Japan and Korea between 200 BC and 300 AD, with methods introduced from northern China Today, soybeans are a vital source of protein in many Asian diets and serve as valuable food and industrial products In Europe, soybeans were recognized only in the 18th century, while they flourished in the Americas during the 19th century.
Soybeans, when cultivated as seed crops in optimal water system zones in the US, have emerged as a significant agricultural product, particularly favored for mechanized farming (Hymowitz, 1988).
Research indicates that soybean cultivation in Vietnam dates back to the Hung dynasty, predating mungbean and black bean (Ngo The Dan et al., 1999) Recognized for its high nutritional value, soybean has significantly contributed to Vietnam's economy over the past few decades Nevertheless, the area dedicated to soybean cultivation and its productivity remain considerably lower than expected.
4 than those in other countries in the world Today, Vietnam still has to import soybeans from USA and China and some other countries
Glycine genus is subdivided into 26 perennial wild indigenous species of
Australia, along with the South Pacific Islands, the Philippines, Taiwan, and Southeast China, is home to various perennial crops The genome of these crops exhibits diverse ploidy levels, including 2n, 4n, and multiple deflates (40, 80, 38, 78) (Chung and Singh, 2008; Orf, 2010) Hybridization among species in this sub-family is largely unsuccessful, with the exception of Glycine canescens, which is cultivated for animal feed To facilitate hybridization, in vitro culture techniques are employed to obtain pre-embryo stages, aiming to produce viable fruit between diploid species of this subspecies and Glycine max While some crosses between G max and the tetraploid species G tomentella can yield hybrid and F1 seeds, the resulting F1 plants are often ineffective (Nguyen Van Hien, 2000).
In 1984, Hymowit and Newell identified the genus Glycine, which includes seven species of wild perennials, and the subsidiary subgenus Soja, comprising two species: the cultivated soybean Glycine max (L) Merr and an annual wild species.
During the first three decades of the 20th century, soybean production was largely confined to the Orient (China, Indonesia, Japan, and the Republic or Korea)
Nevertheless, in the 1940’s, the U.S overtook the entire Orient in production (mainly due to its cultivation being completely mechanized)
Soybeans are very sensitive to daylight, and in turn are grown in regions where light is available about 12-13 hours a day In the U.S over half of the
Approximately 5% of soybeans produced globally come from the Corn Belt region in the United States In Asia, China is a key area for soybean cultivation Both the U.S and China have their prime soybean production zones situated between 35° and 45° latitude.
Soybean production in the world
Soybeans are the leading oilseed crops globally, ranking fourth after wheat, rice, and maize They are cultivated in approximately 70 countries, with over 70% of production concentrated in the Americas, followed by Asia The world's soybean genetic resources are primarily stored in 15 countries, including Taiwan, Australia, China, France, Nigeria, India, Indonesia, Japan, Korea, South Africa, Sweden, Thailand, the USA, and Russia, totaling 45,038 varieties.
Soybean production situation in the world in recent years is shown in table 2.1
Table 2.1 Status of soybean production in the world in the period 2010-
(Source: Faostat, 2019; https://apps.fas.usda.gov/psdonline/circulars/production.pdf
Global soybean production has seen significant growth, with the cultivated area expanding from 102.8 million hectares in 2010 to 122.4 million hectares in 2019, marking an increase of 19.6 million hectares Yield also rose from 2.6 tons per hectare in 2010 to 2.8 tons per hectare in 2019 Between 2010 and 2019, production quantities increased due to both expanded acreage and improved productivity, reaching 336.6 million tons in 2020 However, despite rising demand for soybean products, the global soybean production area is declining, potentially due to outbreaks of animal diseases and reduced demand for raw materials in animal feed, particularly in China.
In 2020, global soybean cultivation covered 127.6 million hectares, yielding 2.9 tons per hectare and resulting in a total production of 368.5 million tons The Americas dominate soybean production, accounting for 87.1% of the world's total, followed by Asia, Europe, and Africa.
The leading countries in soybean production—America, Brazil, Argentina, India, and China—account for 90-95% of global output Brazil emerged as the top producer from 2015 to 2020, with 38.6 million hectares yielding 133.0 tons in 2020, followed by the USA (33.3 million ha, 116.2 tons), Argentina (17.3 million ha, 53.5 tons), and China (9.3 million ha, 17.5 tons) This success is attributed to advanced agricultural techniques, mechanization, high-yield transgenic varieties, and pest-resistant crops Additionally, countries have expanded soybean acreage by replacing other crops, such as sunflowers in Argentina and cotton in the US, as well as utilizing grasslands in Argentina and Brazil and replacing native plants in Brazil.
Table 2.2 Area, yield and production of soybeans of some countries in the period 2015-2020
Year USA Brazil Argentina China
(Source: Faostat, 2019; https://apps.fas.usda.gov/psdonline/circulars/production.pdf
The United States has developed new soybean varieties through selection methods, including mutagenicity and hybridization High-yield varieties serve as key breeding sources in these programs, contributing to advancements in soybean breeding research.
The United States has made significant advancements in soybean breeding, particularly in developing allergy-free varieties after extensive testing of thousands of options While the private sector leads most soybean variety development, public-sector breeders continue to play a crucial role in enhancing germplasm, improving breeding methodologies, and advancing molecular technologies Looking ahead, the future productivity of modern agriculture will heavily rely on the capacity to breed new varieties that can adapt to evolving environmental conditions and management practices.
China, a neighboring country of Vietnam, shares similar farming practices and is currently the 4th largest producer of soybeans globally The country has embraced scientific advancements, utilizing hybrid and imported varieties, and has implemented programs to enhance soybean varieties that are resistant to pests and weeds, tailored to the sub-regional climate Notable varieties include CN001, CN002, and YAT12 In recent years, China has also introduced new varieties through mutation, such as Tiefeng 18, which boasts high productivity, excellent quality, and resistance to high alum and lodging.
Recent years have seen a significant increase in global soybean production, driven by its nutritional and economic benefits Key factors contributing to this growth include advancements in soybean varieties Projections indicate that worldwide soybean production is expected to rise by 2.2%, reaching approximately 371.3 million tons by 2030 However, despite the growing production and demand for soybeans, the area of cultivated land is declining, highlighting the need for investment in research to enhance seed yields (Masuda and Goldsmith, 2009).
Soybean production in Vietnam
Soybeans are one of important legume crop in Vietnam Soy-based dishes became more popular in everyday dishes
Vietnam's soybean production has declined in recent years due to low yields and a reduction in growing areas, as farmers opt for more profitable crops like fruits and vegetables This decrease has resulted in soybean production falling significantly short of the demand from the food, livestock, and aquaculture feed sectors The data indicates a rapid decline in the country's soybean production area, which decreased from 109.4 thousand hectares in 2014.
In 2020, soybean production in Vietnam declined to approximately 50,000 hectares Official data from the Vietnamese General Statistics Office (GSO) indicates that for the marketing year 2016/17, soybean production reached 102.3 thousand metric tons (TMT) across 68,500 hectares, reflecting an 18% decrease compared to the previous year.
Table 2.3 Area, yield and production of soybean in Vietnam during 2010-
(Source: Faostat, 2019; https://apps.fas.usda.gov/psdonline/circulars/production.pdf )
The soybean breeding program in Vietnam is managed by eight research institutions, including the Institute of Agricultural Science and Technology, Southern Institute of Agricultural Science and Technology, Cuu Long River Delta Rice Research Institute, Maize Research Institute, Vietnam National University of Agriculture, Can Tho University, and the Institute of Oil Plants Between 1977 and 2010, a total of 45 new soybean varieties were registered, showcasing the program's significant contributions to agricultural development in the country.
Vietnam's soybean cultivation is inconsistent, meeting only 7–10% of the country's demand In 2020, the nation produced 76 thousand tons of soybeans from 50 thousand hectares, resulting in a yield of 1.53 tons per hectare.
Vietnam's domestic soybean production satisfies only 7% of the country's demand, primarily for soymilk and food products, while a staggering 93% is imported, mainly for animal feed This highlights the significant demand for soybean products in Vietnam, yet the area dedicated to soybean cultivation is declining Consequently, imports are essential to fulfill processing requirements.
In the first ten months of 2019, Vietnam imported 1,459,389 tons of soybeans, valued at approximately 579.92 million USD, as reported by the General Department of Customs (GCO) The primary sources of these imported soybeans are from various countries.
US, Canada, Argentina, Paraguay, Uzbekistan, Cambodia, the Philippines,
Soybean research and breeding
2.4.1 Soybean research and breeding in the world
Soybean was introduced to the United States in the 1700s, initially cultivated as a forage crop It wasn't until the 1920s and 1930s that soybeans began to be recognized and utilized as a grain crop, thanks to the efforts of early US plant breeders from Agricultural Experiment Stations and the United States Department of Agriculture.
The USDA played a crucial role in developing lodging and shattering-resistant soybean varieties, transforming soybeans from a forage crop to an oilseed crop While variety development has shifted predominantly to the private sector since the Plant Variety Protection Act of 1970, public sector breeders continue to contribute significantly, focusing on germplasm enhancement, breeding methodologies, and molecular technology The future productivity of agriculture will heavily rely on breeding's capacity to adapt new varieties to evolving environmental conditions and management strategies.
The success of soybean breeding relies on the availability of genetic variation in germplasm, effective selection strategies, and efficient resource management Breeders often create various crosses between different varieties or germplasm lines to enhance genetic variation through gene recombination and alterations in allele frequency within the breeding population Common selection methods employed include single-seed descent, pedigree, or a combination of both approaches.
Plant breeding is an essential and innovative endeavor aimed at addressing current and future food challenges amid decreasing arable land, population growth, and evolving consumer demands.
The objectives of soybean breeding vary by country and region In Thailand, the focus is on developing varieties that adhere to international standards, featuring large seeds, controlled growth, and reduced sensitivity to photoperiods, while also being resistant to significant diseases like rust, morning mist, anthracnose, and bacterial blight Conversely, Australian breeders prioritize enhancing yield, agronomic traits, and overall quality.
The primary objective of soybean breeding in the United States is to develop varieties that excel in intensive farming, exhibit responsiveness to photolysis, demonstrate resilience to challenging external conditions, possess high protein content, and are easy to preserve and process (Johnson and Bernard 1962).
Soybeans originated in China, but the United States has become the global leader in soybean acreage and production Through methods such as selection, mutation, and crossbreeding, the US has developed new high-yield soybean varieties Since the first experiment in 1804 in Pennsylvania, over 10,000 soybean seed samples have been collected by 1893 From 1928 to 1932, the US imported more than 1,190 soybean lines annually from various countries Today, over 100 soybean varieties are in production, including resilient types like Amsoy 71, Lee 36, Clark 63, and Herkey 63, which are adapted to different ecological regions The focus of breeding research is on utilizing hybrid combinations and imported varieties to enhance the genetic diversity of soybeans (Johnson and Bernard 1962).
Current research on soybeans in industrialized nations emphasizes genome integration and the development of genetic maps This approach enhances the understanding of gene functions, identifies candidate genes for specific traits, and employs molecular marker methods to select and develop new soybean varieties with desirable characteristics (Miladinovic et al., 2015).
In Vietnam, soybean breeding has predominantly relied on traditional methods, focusing on the selection and development of new varieties through importation, crossbreeding, and mutation techniques The integration of molecular applications is beginning to enhance these breeding practices.
13 marlcers to improve specific traits have only recently been studied (Nguyen Van Chuong et al 2013)
2.4.2 Soybean research and breeding in Vietnam
The objectives of soybean breeding in Vietnam focus on developing high-yield, stable varieties with strong growth, short growth duration, and high-quality seeds These varieties are designed to withstand both biotic and abiotic stresses, including drought, waterlogging, and resistance to pests and diseases Over the past 50 years, Vietnam has successfully developed several soybean varieties, including DT2001, VX93, M103, ĐT93, DT84, DT95, and ĐVN 5HL 203, as well as OMĐN.
The application of mutation techniques, as reported by the Joint FAO/IAEA, has significantly enhanced genetic variability, playing a crucial role in plant breeding and advanced genomics These techniques have led to the development of thousands of novel crop varieties across various species, resulting in billions of dollars in additional revenue globally.
Mutation breeding is a leading application of nuclear techniques in food and agriculture, resulting in the release of numerous mutant crop varieties that significantly enhance local and national food security The achievements of the IAEA Technical Cooperation Projects (TCPs) and Coordinated Research Projects (CRPs) have notably strengthened Vietnam's capacity, further bolstering the country's food security efforts.
Vietnamese Government officials are optimistic about extending their cooperation with the IAEA by integrating mutant crop varieties with effective agricultural practices, including efficient soil and water management, highlighting the significant potential of this collaboration.
The IAEA, via the Joint FAO/IAEA Division, plays a vital role in enhancing national food security by promoting sustainable agricultural practices This includes not only advancements in mutation breeding but also improvements in efficient soil and water management, livestock production, and the control of transboundary animal diseases.
With support from the IAEA through TCPs and CRPs, 30 mutant varieties were developed and released officially to farmers for their production, including
The Institute has developed 17 rice cultivars, 10 soybean varieties, two maize varieties, and one chrysanthemum variety, all of which are high-yielding and exhibit resistance to insect pests and diseases Notably, over 50% of the soybean cultivation area in Vietnam is comprised of mutant varieties developed by the Institute, significantly enhancing oil crop production The use of modern biotechnology techniques, including tissue culture and molecular marker-assisted selection, is further improving the efficiency of mutation breeding.
Botanical characteristics of the soybean plant
The soybean root system is distinct from that of herbaceous plants, featuring both primary and secondary roots The primary root can reach depths of 30-50 cm, and in some cases, it may extend over 1 meter Additionally, numerous secondary roots emerge from the main root, with the second and third levels concentrated in a soil layer approximately 7-8 cm wide and covering an area of 30-40 cm² (Nguyen Danh Dong, 1982).
The root system is shallow, deep, narrow, and the number of nodules is more or less dependent on variety, soil, climate and planting techniques
The development of the root system can be divided into 2 periods:
Stage 1: vigorous development of the first taproot and first secondary root usually lasts 30-40 days after growing
Stage 2: The first root layer grows slowly, the rootlets no longer sprout, even some of them dry At this time, near the root collar, small secondary roots extend and develop until near harvest This root layer is responsible for providing enough nutrients for the development of stems, leaves and fruit At this time, it is necessary to cultivate the soil so that this root layer is thriving
Soybean plants exhibit a significant presence of nodules on their roots, primarily concentrated in the topsoil layer of 0-20 cm As the depth increases to 20-30 cm, the number of nodules decreases substantially, with few or none found beyond this depth (Tran Van Dien, 2007) These nodules are the result of a symbiotic relationship between the soybean roots and the microorganism Rhizobium japonicum (Ngo The Dan et al.).
The formation of nodules in soybeans is significantly influenced by soil conditions and nutrient availability Optimal nodule development occurs when soybeans are grown in soils previously cultivated with soybeans, as this leads to earlier and more abundant nodule formation Soil pH plays a crucial role, with the ideal range for nodule formation being between 6 and 7; thus, selecting the right soil is essential Nutritional factors also impact nodule growth, as comprehensive NPK fertilization promotes thriving nodules, while the application of P2O5 specifically enhances nodule development, although the effect of potassium remains unclear (Tran Van Dien, 2001).
The symbiotic relationship between microorganisms and soybean nodules enhances plant growth; as the soybean plant supplies nutrients, microorganisms thrive and increase nitrogen accumulation, promoting optimal development.
Soybean stem belongs to the herbaceous plant, round in shape, with many small hairs on it The stem color when young is green or purple, the color of the
The color of a flower is closely linked to the color of its stem during its early growth stages Specifically, a green stem typically produces a white flower, while a purple stem results in a purple flower.
The average soybean plant has 14-15 internodes, with the lower internodes typically shorter than the upper ones due to rapid growth in the upper sections around 35-40 days The length of these internodes varies by variety and sowing season, generally ranging from 3 to 10 cm Notably, soybean plants grown in the summer tend to have longer internodes compared to those cultivated in spring and winter, which significantly contributes to the overall height of the plant.
Soybean stems typically range from 0.3 to 1.0 meters in height, while wild soybean varieties can reach 2-3 meters Large-stem varieties are generally upright, producing numerous seeds and demonstrating resilience against wind storms The stems are characterized by a short, thick undergrowth that extends from the base to the tip, with nearly hairless petioles Varieties featuring thick, dark hairs tend to exhibit strong resistance to diseases, drought, and cold conditions, whereas hairless varieties often struggle with growth and resilience The presence and characteristics of hair on the stems, whether long or short, thick or sparse, serve as key distinguishing features among similar soybean varieties.
Based on growth habits and the characteristics of the body, people are divided into 4 categories:
• Straight stem type: the trunk is hard, large stem diameter, not high stem, short internode, much-concentrated fruits, usually finite flower variety
The horizontal stem type features a main stem that branches out into numerous soft, smaller branches, which spread across the ground in clusters This structure results in a long stem with small fruits dispersed throughout.
• Half-horizontal type: is an intermediate between two types of straight and horizontal
The soybean plant features a climbing type characterized by a long, slender stem that can either crawl along the ground or ascend other surfaces Its stem is capable of branching from the axils of single or double leaves, enhancing its growth and adaptability.
Branches on the main stem of soybean plants are categorized into levels, with level 1 branches giving rise to level 2 branches The number of branches per plant varies based on factors such as variety, season, planting density, and cultivation conditions, typically averaging between 2 to 5 branches, although some varieties can exceed 10 branches under optimal conditions Soybean plants generally start to branch approximately 20-25 days after germination, with ideal branch positioning occurring at a height of over 15 cm to facilitate mechanization Additionally, a narrower branching angle is advantageous for increasing plant density.
Soybean has 3 types of leaves: cotyledons, single leaves and trifoliate leaves
Cotyledons: newly sprouted cotyledons are yellow or green The large seeds have more nutrients to feed the cotyledons When all of the nutrients are gone, the cotyledons dry up
Simple leaves: Whole leaves appear 2-3 days after the plant has grown and above the cotyledons Single leaves are symmetrical Large, glossy green leaves are a sign of good plant growth
Trifoliate leaf: each compound leaf has 3 leaflets, sometimes 4-5 leaflets The leaflets are alternate, usually green, and turn yellow-brown as they age
There is also a variety that, when the fruit is ripe, retains its green color, these varieties are suitable for growing as fodder
Many leaves exhibit a hairy texture and come in various shapes depending on the plant variety Smaller leaves typically yield less, while larger varieties, although less drought-tolerant, often produce higher yields.
The quantity and size of compound leaves significantly impact yield and are influenced by the planting season Leaves adjacent to flower clusters are crucial for supplying nutrition to those clusters Yellowing of these leaves often leads to fruit drop or deformity in that area.
Soybean breeders provide the basis for improving soybean yield by enhancing photosynthesis and in order for photosynthesis to be highly efficient, choose plants with a small egg leaf, thick, vertical
During the flowering period, the presence of large leaves indicates the plant's health and productivity Healthy plants exhibit big, wide, thin, flat, and bright green leaf blades, which are signs of their capability for high yields.
The soybean plant features small, flavorless butterfly-type flowers that typically come in purple, light purple, or white, with most varieties displaying purple hues Notably, soybean varieties with white flowers tend to have a higher oil content compared to their purple counterparts These flowers emerge in clusters from leaf axils, branches, and the head stem, with each cluster containing 1 to 10 flowers, usually averaging 3 to 5 Despite blooming, the fruiting rate of soybean flowers is relatively low, ranging from 20% to 30%.
Soybean flowers are usually pollinated before flowers bloom and are self- pollinated, the rate of delivery is very low, accounting for an average of 0.5 - 1% (Ngo The Dan et al., 1999)
Ecological requirements of soybean plants
Light significantly influences the morphology of soybean plants, altering their flowering and ripening times, as well as impacting height, leaf area, and various other characteristics, including seed yield (Doan Thi Thanh Nhan et al., 1996).
Light plays a crucial role in photosynthesis, nitrogen fixation, and the yield of dry matter, significantly affecting various photosynthesis-dependent properties Soybeans respond to light in two key ways: the duration of daylight and the intensity of light Additionally, the length of the day influences the overall impact of light on soybean growth.
Soybean is a short-day crop that exhibits a significant response to day length The seedling stage is particularly sensitive to shorter daylight hours, with this sensitivity decreasing during the bud stage and nearly ceasing at the flowering stage.
For optimal flowering and seed formation, plants require 6-12 hours of light per day If the lighting duration is less than 12 hours, late-ripening varieties or those that flower shortly after 25-30 days of growth will bloom Conversely, in long-day conditions with more than 18 hours of light daily, plants tend to grow indefinitely without flowering.
Day length significantly influences both the fruiting rate and growth rate of soybeans Shorter days enhance bean production and accelerate dry matter accumulation in the fruit However, prolonged high temperatures after flowering can lead to fruit loss and reduced seed count In Vietnam, the soybean seed variety is diverse, with late-maturing varieties being more sensitive to light conditions compared to early-maturing ones.
In Vietnam, soybean varieties are categorized into three groups: early ripening, medium ripening, and medium late-ripening Early ripening varieties, which show minimal response to day length, can be cultivated in all three seasons In contrast, late ripening varieties exhibit a significant response to day length, necessitating careful crop planning for optimal growth (Doan Thanh Nhan et al., 1996).
Light intensity significantly impacts soybean growth, with a light saturation point of 23,680 lux, equivalent to 20% of midday sunlight Flower bud differentiation occurs when light intensity exceeds 1,706 lux Insufficient light leads to elongated plants that tend to climb, resulting in lower seed yields A 50% reduction in light intensity can decrease branch numbers and increase fruit burning, potentially halving the yield Conversely, optimal light conditions promote robust plant growth and higher yields.
The distribution of soybeans ranges from 48o to 30o south So, depending on the variety, distribution of the appropriate planting area
Early-ripening plants cultivated in low latitude regions tend to flower prematurely, which can lead to lower yields due to insufficient stem growth Conversely, late-ripening varieties planted at 400 North latitude experience prolonged flowering periods, making them vulnerable to adverse weather conditions such as rain and wind before harvest, ultimately resulting in reduced productivity (Doan Thi Thanh Nhan et al., 1996).
Soybeans thrive in temperate climates but are not resistant to cold The total temperature range for soybean growth varies between 1888°C and 2700°C, depending on whether the variety is early or late ripening Temperature significantly influences the growth, development, and physiological processes of soybean plants.
The best temperature for germination is about 18°C - 26°C Above 30oC, seeds germinate quickly but germinate is weak Low temperatures will slow the plant growth and make it susceptible to disease
The single leaf period can withstand temperatures below 0°C, the double- leaf period grows at temperatures from 12°C, but the coefficient of leaf area increases with the temperature from 18- 30°C
The flowering and fruiting stages are negatively impacted by temperatures below 18°C, while high temperatures exceeding 40°C hinder internode formation, growth, and flower differentiation These extreme conditions also disrupt nutrient transport to the seeds, resulting in poor grain quality.
In the final stage of plant growth, low temperatures can hinder seed ripening, leading to uneven maturation and negatively impacting seed quality.
Temperature plays a crucial role in the nitrogen fixation process of soybean plants, particularly affecting the activity of Rhizobium jabonocum bacteria, which are inhibited at temperatures exceeding 33°C Optimal nodule bacteria activity occurs between 25°C and 27°C Additionally, lower temperatures slow down substance transport within plants, halting it entirely at 2°C to 3°C Furthermore, soil temperature significantly influences nutrient uptake in soybean roots, with varying minimum temperature requirements for different cations.
Soybean is a shallow-rooted crop with significant water requirements, which are a major limiting factor in its production The water needs of soybeans fluctuate based on climate conditions, farming practices, and the growth stage of the plant Throughout the growing season, from sowing to harvest, soybeans require between 350-600 mm of rainfall The water efficiency of soybeans ranges from 600 to 1000 grams of water per gram of dry matter (Doan Thi Thanh Nhan et al., 1996).
During the germination and seedling stages, water utilization is minimal due to the small canopy, with most water lost through ground evaporation For successful seed germination, seeds must absorb water until their moisture content reaches 50%, as dry soil significantly reduces germination rates As soybean plants progress to the 3-5 trifoliate leaf stage, their water requirements gradually increase, peaking during the flowering to full fruit growth stage Once the fruit begins to ripen, water needs decrease as leaf decay occurs and evaporation diminishes Overall, plant growth is closely linked to photosynthesis intensity, efficiency, total leaf area, and photosynthetic potential, all of which are adversely affected by insufficient water.
Adequate water supply is crucial for soybean growth, particularly during the flowering and fruiting stages, where rainfall and humidity significantly impact yield Insufficient water during this period leads to a substantial loss of flowers and fruit, resulting in decreased yields primarily due to lower grain weight Additionally, dehydration hampers nitrogen fixation, which is affected by reduced photosynthetic products in the roots and the direct influence of water potential in the nodules.
MATERIALS AND METHODS
Plant materials
Plant materials included 29 soybean lines which were developed by mutation and hybridization Control variety was DT84 (Table 3.1)
Table 3.1 Soybean lines evaluated in winter season 2020
No Line Origin No Line Origin
Experimental design
The experiment was carried out in the winter season, from September
2020 to January 2021 in the open field of Faculty of Agronomy
The experimental plots were established with a planting density of 30 plants per square meter, arranged in two rows per bed The rows were spaced 50 cm apart, while individual plants were positioned 15 cm apart within the rows, covering a total area of 1 square meter.
Cultural practices
Soil was prepared carefully and cleaned weeds before sowing
Fertilizer application rates per hectare included 250 kg of Song Gianh microbiological fertilizer, 85 kg of nitrogen (N), 300 kg of phosphorus pentoxide (P₂O₅), and 80 kg of potassium oxide (K₂O) The application was conducted in three stages: the basal dressing occurred after seed bed preparation and before sowing, incorporating the full amounts of microbial fertilizer and superphosphate; the first top dressing took place when the plants had 2-3 fully expanded leaves, applying half of the nitrogen and potassium; and the second top dressing was performed when the plants had 4-6 fully expanded leaves, utilizing the remaining nitrogen and potassium.
The field was meticulously maintained to prevent weeds, ensuring consistent plant growth and development through effective cultural practices Regular moisture levels were monitored, and the area was routinely inspected for insect pests and diseases.
Trait measurements
Traits were evaluated according to QCVN 01-58: 2011/BNNPTNT by Ministry of Agriculture and Rural Development for soybean
Morphological characteristics were evaluated in terms of color, stem color, flower color, etc and pod and seed characteristics (Table 3.2)
Table 3.2 Qualitative morphological and seed traits observed in soybean
No Trait Evaluation stage Definition and Expression
1 Hypocotyl colour Germination Anthocyanin pigment: Green/ Purple
2 Flower color Flowering White /purple
Spear/Triangle/Oval /Round Egg-shaped acute
(on main stem) Light Green/ Medium Green/ Dark Green
Flowering -pod and seed ripening
Flowering -pod and seed ripening
Flowering -pod and seed ripening
9 Dry pod colour Pod and seed ripening Light brown /Medium brown /Dark brown
10 Testa colour Pod and seed ripening Yellow/Yellow green/Green
11 Seed shape Pod and seed ripening Oval/round/flat round/flat
12 Hilum color Pod and seed ripening White /Grey/ Ligth brown/
Yellow/Dark brown/ Other color
Germination, flowering, end of flowering, and physiological maturity dates were meticulously documented, with flowering defined as the appearance of the first fully open flower The end of flowering was noted when significant flowering ceased, leaving only sporadic blooms, while physiological maturity was recorded when over 95% of the pods had ripened (see Table 3.3).
Table 3.3 Phenological traits observed in soybean
Time from sowing to the first flowers appear
2 Time to flowering end Time from sowing to the end of flowering
3 Growth duration Time from sowing to harvesting
Morphological and yield related traits
Table 3.4 presents the measured traits for soybean lines, with data collected from 10 plants per line Key vegetative traits assessed include plant height (cm), leaflet dimensions (length in cm and width in mm), stem diameter (mm), internode length (mm), and the count of leaves and nodes on the main stem Leaf size was determined by measuring the terminal leaflet, while stem diameter was recorded at the 5th and 6th nodes using a Vernier caliper Internode length was calculated by measuring the distance between the 5th and 6th nodes and averaging it per node These measurements were taken at week 8 post-sowing, with additional traits such as the number of main branches per plant and nodes on the stem recorded at physiological maturity.
Table 3.4 Morphological and yield related traits observed soybean lines in winter season 2020
1 Plant height Cm Measure when the plant flowers and get mature
2 Pod closed height Cm Measure the height of first node that has filled pods
3 Total number of leaf on main stem Leaf Count the number of leaves on main stem
4 Total number of nodes on main stem Node Count the nodes on main stem
5 Stem diameter Mm Measure the stem diameter of 5 th and 6 th node
6 Node length Cm Measure the length of 5 th and 6 th node
7 Total number of branches Branch Counting the total number of branches when harvesting
8 Leaf size Cm Measure the length and width of 5 th and
9 Total number of pods/plant Pod Count the total number of pods/plant,
10 Number of 1-seed, 2-seed, 3- seed pods/ plant Pod Count the number of 1-seed, 2-seed, 3- seed pods/ plant
11 Weight of 100 seeds Gram Weight of 100 seeds
12 Individual yield g/plant Weight of all seeds/ plant
13 Theoretical yield quintal/ha Individual yield x density
14 Harvest index (HI) Individual yield/ Weight of dry stem
The study assessed various pod and seed traits, including the total number of pods per plant, the total number of seeds per pod, and the distribution of pods with one, two, or three seeds Additionally, the weight of 100 seeds was measured to determine seed size in grams.
Traits were recorded for 10 plants/line
Evaluation of disease and pest damage and lodging resistance of soybean
Table 3.5 outlines the methods for assessing pest damage and lodging resistance in soybean varieties The primary pests affecting soybeans include the pod borer (Eitiella zinekenella), stem borer (Melanesgromyza sojae), and rust (Phakopsora pachyrhizi Sydow).
Table 3.5 Evaluation of disease and pest damage and lodging resistance of soybean lines in winter season 2020
Very mild (5% - 25% infected number of fruit) Severe (> 25% - 50% infected number of fruit) Very severe (>50% infected number of fruit)
Incidence of pod borer = Number of damaged pods / total number of surveyed pods Investigate 15 plants using 5-point angular method
Very mild (5% - 25% infected leaf area) Severe (> 25% - 50% infected leaf area) Very severe (>50% infected leaf area)
Investigate 15 plants using 5-point angular method
No falling (Almost plants stand straightly) Low (75% plants fall down)
Count the fallen plants in a plot
Statistic parameters including means, variance and CV% were calculated for each lines
RESULTS AND DISCUSSION
Phenological characteristics of soybean lines in winter season 2020
Plants experience two key growth stages: vegetative and reproductive, both influenced by genetic factors and external conditions like temperature, humidity, and farming techniques In a controlled experiment, these external conditions were kept constant to assess their impact on different plant lines The phenological timing, determined by the lines, helps differentiate between short and long growth period varieties, which is crucial for selecting appropriate crop seasons and rotations Soybean varieties are categorized based on growth duration into short (≤ 85 days), medium (86-100 days), and long (> 100 days) growth durations.
Table 4.1 Means for phenological phases of soybean lines in winter season
No Line Days to flowering (days)
No Line Days to flowering (days)
After the vegetative growth stage, soybean plants enter the reproductive growth stage, which lasts from the appearance of the first flowers to the emergence of the last flower The timing of flowering varies by variety and environmental conditions, with early flowering varieties typically blooming 30 to 40 days after sowing, while late varieties flower after 45 to 50 days.
In this experiment, the days to flowering for the tested lines varied between 30 and 41 days, while the control variety flowered at 31 days after sowing, showing no significant difference Notably, among the 29 lines evaluated, the lines LSB23-6-2, LSB62-2-3, LSB70-30-1, and LSB17-10-3 were highlighted for their performance.
14-4, LSB17-21-3-12-10, LSB17-22-2-1-8, LSB17-27-3-16-5 flowered latest with 41 days Most lines flowered in 32 – 36 days after sowing (Table 4.1)
The flowering period is crucial for determining the number of effective flowers, pods, and overall yield Adverse conditions can lead to a shortened flowering time, while an excessively long flowering period may result in unsynchronized pod ripening, complicating machine harvesting.
The flowering period plays a crucial role in determining the number of effective flowers, pods, and overall yield of the plant Adverse conditions can lead to a shortened flowering time, while an excessively long flowering period may result in unsynchronized flowers and uneven pod ripening, ultimately impacting the harvesting process.
In winter season 2020, almost lines had a growth duration longer than DT84 except for LSB17-12-1-3-3(9 days) due to unfavorable weather and short photoperiod (Table 4.1)
The total growth duration of soybeans, spanning from sowing to harvest, is categorized into three groups: short growth (≤ 85 days), medium growth (86-100 days), and long growth (> 100 days) This classification aids in recommending suitable crop rotations for different ecological regions based on their specific growth durations.
The growth duration of all lines in this experiment ranged from 75 days to
The study observed that the ripening period for the control variety was 83 days, while the LSB33-5-4, LSB32-50-10, LSB32-54-3, and LSB36-65-2-4 varieties ripened earlier at 102 days and were classified as having a short growth duration of 85 days or less In contrast, the LSB17-10-3-14-4, LSB17-22-2-1-8, LSB17-22-2-1-3, and LSB17-24-2-6-9 lines exhibited the longest growth duration, while the remaining lines fell into the medium growth category.
4.2 Morphological characteristics of soybean lines in the winter season
The morphological characteristics of soybean varieties provide insights into traits such as hypocotyl color, flower color, stem hair color, stem hair density, leaflet shape, and growth type Distinct differences in these morphological traits were observed among soybean lines, as illustrated in Table 4.2.
Table 4.2 Morphological characteristics of soybean lines in winter season
Egg-shaped Acute Brown Dense
Egg-shaped Acute Brown Sparse
Egg-shaped Acute Grey Dense
Egg-shaped Acute Grey Dense
Egg-shaped Acute Grey Dense
Egg-shaped Acute Brown Dense
Dark Egg-shaped Grey Dense Determi
Egg-shaped Acute Brown Sparse
Egg-shaped Acute Grey Sparse
Egg-shaped Acute Grey Sparse
Egg-shaped Acute Grey Sparse
Egg-shaped Acute Grey Dense
Egg-shaped Acute Grey Sparse
Egg-shaped Acute Brown Sparse
Egg-shaped Acute Grey Dense
Egg-shaped Acute Grey Sparse
Egg-shaped Acute Grey Dense
Egg-shaped Acute Brown Dense
Egg-shaped Acute Grey Sparse
Egg-shaped Acute Grey Sparse
Egg-shaped Acute Brown Dense
Egg-shaped Acute Brown Dense
Egg-shaped Acute Grey Dense
Egg-shaped Acute Grey Dense
Egg-shaped Acute Grey Dense
Egg-shaped Acute Brown Dense
Egg-shaped Acute Brown Dense
Egg-shaped Acute Brown Dense
Soybean hypocotyls exhibit two distinct colors: green and purple, which are linked to flower color; specifically, green hypocotyls correspond to white flowers, while purple hypocotyls are associated with purple flowers In the study, the hypocotyls of the lines LSB10-4-3, LSB23-6-2, LSB36-65-2-4, LSB62-11-5, and LSB70-23-3 were found to be green, whereas all other lines, including the control variety DT84, displayed purple hypocotyls (Table 4.2).
The number of lines exhibiting white and purple flower colors corresponded to the lines with green and purple hypocotyl colors, respectively (Table 4.2) Among the varieties, LSB10-4-3, LSB23-6-2, LSB36-65-2-4, LSB62-11-5, and LSB70-23-3 displayed white flowers, while the control variety DT84 exhibited purple flowers.
In this experiment, the majority of soybean lines and the control variety DT84 exhibited a dark green leaf color, while three specific lines—LSB32-7-4, LSB32-46-3, and LSB17-14-1-9-2—displayed a lighter leaf color.
The observed soybean lines, along with the control DT84 variety, exhibited an egg-shaped acute leaf shape, while only the LSB27-5-5 line displayed a lanceolate leaf shape All lines, including the control DT84 variety, demonstrated a determinate growth type and a dense stem hair structure (Table 4.2; Fig 4.1).
The color and density of hair in soybeans reveal distinct characteristics, with brown and dense hair providing better resistance to diseases, drought, and cold compared to grey stem hair with sparse density.
Figure 4.1 Leaf and flower characteristics of soybean lines evaluated in
Pod and seed characteristics of soybean lines in winter season 2020
In this experiment, soybean lines were distinguished based on dry pod color, seed characteristics, and other morphological traits Notably, the seed characteristics play a significant role in determining the commercial value of these lines.
The color of dry pods is influenced by carotene and xanthophyll pigments, while young pods appear green and hairy, with hair color affected by anthocyanin As the pods ripen, they transition to shades of light brown, medium brown, or dark brown.
Soybean lines in this experiment were distinguished by the dry pod colours, ranged from light to dark brown (Table 4.3; Figure 4.2)
Table 4.3 reveals that the soybean lines exhibited variations in testa color, with most lines and the control DT84 variety displaying a yellow testa Notably, LSB62-2-3 and LSB62-11-5 were characterized by a green testa color.
4, LSB23-6-2, HSB0059-D2-4 and HSB0059-D1-2 had yellow-green testa colour
The soybean lines exhibited notable variations in pod color, hilum color, and seed shape Among the lines, five distinct hilum colors were identified, with the majority displaying light brown, dark brown, and brown hues Additionally, there were two white lines (LSB32-46-3 and LSB28-13-10) and two black lines (LSB32-45-7 and LSB32-54-3) as detailed in Table 4.3 and illustrated in Figure 4.2.
Soybean seeds exhibit a variety of shapes, including oval, round, flat round, and flat Their testa colors range from yellow, yellow-green, and green to light brown, brown, and even black, as illustrated in Table 4.3 and Figure 4.3.
In this experiment, the soybean lines exhibited significant variations in pod color, hilum color, and seed shape Four distinct seed shapes were identified across all lines: round, flat, oval, and flat round Notably, only the line LSB36-65-2 displayed these characteristics.
The DT84 variety and four other lines exhibited a flat round seed shape, while three lines, namely LSB10-4-3, LSB10-12-2-3, and LSB17-27-3-16-5, displayed an oval seed shape Additionally, eight lines, including LSB28-9-2, LSB32-7-4, LSB32-46-3, LSB33-5-4, LSB62-11-5, and two instances of LSB17-22-2-1-8, also had a flat seed shape The remaining lines were characterized by an oval seed shape, as detailed in Table 4.3.
Table 4.3 Pod and seed characteristics of soybean lines in winter season
No Lines Dry pod colour Testa colour Hilum colour Seed shape
1 HSB0059-D1-2 Dark brown Yellow Green Brown Oval
2 HSB0059-D2-4 Dark brown Yellow Green Brown Oval
3 LSB10-4-3 Dark brown Yellow Light brown Round
4 LSB10-12-2-3 Medium brown Yellow Brown Round
5 LSB23-6-2 Medium brown Yellow Green Dark Brown Oval
6 LSB27-5-5 Medium brown Yellow Dark Brown Oval
7 LSB28-9-2 Medium brown Yellow Brown Flat shape
8 LSB28-13-10 Medium brown Yellow White Oval
9 LSB32-7-4 Medium brown Yellow Light Brown Flat shape
10 LSB32-45-7 Medium brown Yellow Black Oval
11 LSB32-46-3 Medium brown Yellow White Flat shape
12 LSB32-50-10 Dark brown Yellow Brown Oval
13 LSB32-54-3 Dark brown Yellow Black Oval
14 LSB33-5-4 Light brown Yellow Green Light brown Flat shape
15 LSB36-65-2-4 Medium brown Yellow Brown Flat round
16 LSB62-2-3 Dark brown Green Dark Brown Oval
17 LSB62-11-5 Dark brown Green Dark Brown Flat shape
18 LSB70-23-3 Dark brown Yellow Brown Oval
19 LSB70-30-1 Dark brown Yellow Brown Oval
20 LSB17-10-3-14-4 Light brown Yellow Brown Oval
21 LSB17-12-1-3-3 Light brown Yellow Brown Oval
22 LSB17-14-1-9-2 Dark brown Yellow Dark Brown Oval
No Lines Dry pod colour Testa colour Hilum colour Seed shape
23 LSB17-20-1-15-3 Dark brown Yellow Brown Oval
25 LSB17-22-2-1-8 Light brown Yellow Light brown Flat shape
26 LSB17-22-2-1-3 Light brown Yellow Light brown Oval
27 LSB17-24-2-6-9 Dark brown Yellow Dark Brown Oval
28 LSB17-27-3-16-5 Light brown Yellow Dark Brown Round
29 LSB17-28-1-17-8 Dark brown Yellow Dark Brown Flat shape
30 DT84 Medium brown Yellow Dark brown Flat round
Figure 4.2 Pod characteristics of some soybean lines
Vegetative and morphological traits of soybean lines in winter season
4.4.1 Plant height, number of leaves and number of nodes at flowering and harvesting stage of soybean lines in winter season 2020
Significant difference in all lines were observed for plant height, number of leaves and number nodes at two different stages, flowering and harvesting
Plant height is a key indicator of the growth and development of varieties under specific conditions, influencing lodging resistance and other yield components External factors like temperature, light, soil, and nutrition significantly affect the growth of the main stem, which is also linked to various quantitative traits, including the number of leaves.
47 of branches, numbers of effective nodes, number of pods and flower differentiate in plant
The height of soybean lines at the flowering stage ranged from 16.1 cm to 39.2 cm, with the control variety DT84 measuring 33.7 cm The line LSB32-50-10 exhibited the tallest height at 39.2 cm, followed by LSB70-30-1 and LSB27-5-5 at 35.3 cm and 35.1 cm, respectively In contrast, LSB17-10-3-14-4 was the shortest, measuring only 16.1 cm.
At the harvesting stage, plant height varied significantly among different lines, ranging from 36.2 cm to 93.9 cm, while the control DT84 variety measured 41.7 cm The shortest plant was LSB17-22-2-1-8 at 36.2 cm, whereas LSB70-30-1 reached the tallest height of 93.9 cm Additionally, LSB62-11-5 and LSB62-2-3 measured 89.6 cm and 79.8 cm, respectively, making these three lines notably taller than the other soybean lines in the experiment.
Leaves play a crucial role in plant photosynthesis, directly influencing crop productivity The quantity and surface area of leaves significantly impact overall productivity Notably, in the evaluation of various soybean lines, there were significant differences observed in the number of leaves among the different lines.
At the flowering stage, the number of leaves of soybean lines varied from
The study revealed that the number of leaves varied among different soybean varieties, with LSB27-5-5 exhibiting the highest count at 10.6 leaves, followed by LSB36-65-2-4 with 9.7 leaves and LSB32-54-3 with 9.3 leaves In contrast, the control DT84 variety had an average of 7.2 leaves, while the soybean line LSB17-22-2-1-8 recorded the lowest number at just 5 leaves (Table 4.4).
At the harvesting stage, the number of leaves ranged from 9.4 to 20.2, with a notable increase observed across all lines and varieties due to their defoliation ability All experimental lines surpassed the control variety DT84, which had 9.1 leaves The line LSB17-12-1-3-3 exhibited the highest leaf count at 20.2 leaves per plant, followed by LSB17-22-2-1-3 with 18.7 leaves and LSB10-4-3 with 13.6 leaves Conversely, LSB17-10-3-14-4 recorded the lowest number of leaves at 9.4.
Table 4.4 Plant height, number of leaves and number of nodes at the flowering and harvesting stages of soybean lines in winter season 2020
Flowering stage Harvesting stage Plant height (cm)
The number of nodes per soybean plant is essential for yield, as each node is responsible for the production of flowers and pods The variety of soybean determines the number of nodes, which directly influences the number of pods formed Generally, a higher node count leads to an increased pod quantity Additionally, the number of nodes is associated with plant height and has an indirect effect on the height of the first pod.
During the flowering stage, the number of nodes varied between 6 and 10.2, with the control DT84 variety averaging 9.8 nodes The LSB33-5-4 line exhibited the highest count at 10.2 nodes, followed closely by LSB32-54-3 and LSB32-45-7, which had 9.8 and 9.7 nodes, respectively In contrast, the LSB17-22-2-1-8 line recorded the lowest number of nodes at 6.
During the harvesting stage, the number of nodes in soybean lines increased compared to the flowering stage, ranging from 11.3 to 17.1 nodes The control variety, DT84, had an average of 12.1 nodes Notably, LSB62-2-3 exhibited the highest node count at 17.1, followed by LSB70-30-1 with 16.6 nodes, and both LSB27-5-5 and HSB0059-D1-2 with 15.2 nodes each In contrast, LSB17-10-3-14-4 recorded the lowest number of nodes at 11.3.
4.4.2 Other vegetative and morphological traits of soybean lines in winter season 2020
In soybean breeding research, key growth indicators include first pod insertion height, the number of first-level branches, effective nodes, stem diameter, node length, and leaf size.
* First pod insertion height (cm)
First pod insertion height (FPIH) is a crucial agronomic trait for the mechanical harvesting of soybeans, yet it has garnered limited attention from breeders compared to other traits FPIH is positively correlated with plant height, while exhibiting negative correlations with the number of pods, seeds per plant, seeds per pod, and seed weight (Oz et al 2009).
In the experiment, the FPIH of the lines varied between 8.9 cm and 18.9 cm The control variety, DT84, exhibited the shortest FPIH at 8.9 cm, while the LSB27-5-5 variety recorded the highest FPIH at 18.9 cm Following closely were the LSB10-12-2-3 and LSB32-46-3 varieties, with FPIH measurements of 15.9 cm and 15.7 cm, respectively (Table 4.5).
The size of soybean leaves is primarily determined by the genetics of each variety, while also being affected by climatic conditions, nutrient availability, and cultivation practices Varieties that exhibit a greater number of leaves, larger leaf size, flat and broad leaf structure, and vibrant green color tend to show better growth and development, leading to higher productivity compared to those with smaller leaves.
In the experiment, soybean lines exhibited leaflet widths ranging from 5.2 cm to 8.9 cm, with the control variety DT84 measuring 7.6 cm The line HSB0059-D1-2-3 had the widest leaflets at 8.9 cm, while LSB27-5-5 had the narrowest at 5.2 cm The length of the leaflets recorded varied from 8.7 cm.
The leaf length of the LSB27-5-5 variety reached 13 cm, making it the longest among the tested varieties, followed by LSB36-65-2-4 at 12.3 cm and LSB33-5-4 at 12.2 cm In contrast, the control DT84 variety measured 9.8 cm, while the shortest leaf length was recorded for HSB0059-D2-4 at 8.7 cm (Table 4.5).
Yield related traits of soybean lines in winter season 2020
* Total number of pods/plant
The number of pods/plant is a direct component to plant productivity and yield The number of pods/ plant depends on the characteristics of the variety
55 and the environmental conditions such as temperature, humidity and light The plant with the high total number of pods/plant would be high yield
In this experiment, soybean lines exhibited a range of pod counts per plant from 22.2 to 59, with the control variety DT84 averaging 36 pods per plant The line LSB62-2-3 recorded the highest pod count at 59, followed by LSB62-11-5 with 54.9 pods and LSB70-30-1 with 54 pods Conversely, the line HSB0059-D2-4 had the lowest count at 22.2 pods.
The filled pod ratio is crucial during the fruiting stage and is closely linked to the accumulation of dry matter in seeds High percentages of filled pods are indicative of high-yielding soybean varieties In a study, soybean lines exhibited a wide range of filled-seed pod percentages, from 79.7% to 99.5% The control variety, DT84, had the lowest filled-seed pod percentage at 79.7%, while LSB62-2-3 achieved the highest at 99.5%, closely followed by LSB17-21-3-12-10 with 99.3%.
* Percentage of 1-, 2-, 3- and 4 seed pod (%)
The ratios of 1-seed, 2-seed, 3-seed, and 4-seed pods are closely linked to the number of seeds in a plant and significantly influence individual yield Varieties with a high ratio of 3-seed and 4-seed pods are desirable in soybean breeding programs, as they tend to exhibit higher individual yields Additionally, the ratios of 3-seed and 4-seed pods are affected by the genetic traits of the variety, environmental conditions, and plant density.
Table 4.6 showed a great fluctuation in the percentage of 1-seed pod of the soybean lines, ranged from 5.2% to 20% while that of control DT84 variety
The analysis of 29 soybean lines revealed three distinct groups based on the percentage of 1-seed pods The first group, with less than 10% 1-seed pods, included 11 lines, notably LSB62-2-3, which had the lowest percentage at 5.2% The third group, characterized by more than 15% 1-seed pods, contained five lines, with LSB32-45-7 showing a percentage of 20% The remaining soybean lines fell into the second group, which had a 1-seed pod percentage ranging from 10% to 15%.
Experimental results indicate that the 2-seed pod ratio remains the highest among the different pod types, ranging from 25.9% to 90%, compared to the 1-seed, 3-seed, and 4-seed pods, while the control DT84 variety recorded a rate of 68.3% The line LSB33-5-4 achieved the highest ratio at 90%, followed by LSB28-9-2 and LSB32-50-10 with rates of 83.9% and 82.7%, respectively Conversely, the lowest ratio was observed in the line LSB62-11-5 at 25.9% Notably, 26 out of the 29 lines examined exhibited a 2-seed pod rate exceeding 50.1%.
The percentage of 3-seed pods among the tested lines ranged from 6.1% to 56.1%, with the control DT84 variety showing a percentage of 26.4% The line LSB62-11-5 exhibited the highest percentage of 3-seed pods at 56.1%, followed by LSB17-20-1-15-3 and LSB36-65-2-4, which had percentages of 47.5% and 42%, respectively In contrast, LSB17-28-1-17-8 recorded the lowest percentage of 3-seed pods at 6.1%.
Especially, only two lines with 4-seed pod were LSB62-11-5 and LSB23- 6-2, with 12.6% and 0.29% respectively (Table 4.6)
Table 4.6.Yield related traits of soybean lines in winter season 2020
Total no of pods / plant
Percentag e of filled- seed pod (%)
Percenta ge of 1- seed pod (%)
Percenta ge of 2- seed pod (%)
Percenta ge of 3- seed pod (%)
Percent age of 4-seed pod (%)
The 100-seed weight is one of the most important traits that control soybean yield and is generally positively correlated with yield (Burris et al.,
The weight of 100 seeds is crucial for assessing seed size, classifying them into small (< 16 g), medium (16 - 19 g), and large (> 20 g) categories This measurement serves as a key productivity component and a significant indicator of seed quality in the market.
The 100-seed weight of soybean lines ranged from 11.9 g to 24.2 g, with the control DT84 variety averaging 15.1 g Among the 29 soybean lines, most exhibited small to medium seed sizes Notably, LSB10-12-2-3 had the largest seed size, boasting the highest 100-seed weight of 24.2 g, followed closely by LSB10-4-3 at 22.9 g and LSB17-14-1-9-2 at 22.8 g In contrast, LSB23-6-2 recorded the smallest 100-seed weight at 11.9 g.
Individual yield, theoretical yield and harvest index of soybean lines in
Beside the quality traits, yield is the important indicator to select potential varieties for the production
Individual yield, calculated as the seed yield per plant, serves as the foundation for determining theoretical yield Varieties exhibiting high individual yields are expected to correspond with high theoretical yields, and this relationship is reciprocal.
Experimental results indicated varying individual yields among the lines, ranging from 7.4 to 18 g/plant, compared to the control DT84 variety, which yielded 9.1 g/plant Notably, LSB33-5-4 recorded the lowest yield at 7.4 g/plant.
3 had the highest individual yield with 18 g/plant, followed by LSB10-12-2-3 (17.6 g/plant) and LSB17-22-2-1-3 (17.7 g/plant) (Table 4.7)
The harvest index (HI) measures the yield of a crop relative to its total biomass Plant breeders have focused on selecting for a high harvest index to enhance seed yield in various crops However, in soybean [Glycine max (L.) Merrill], inaccuracies in estimating the harvest index can arise due to factors such as maturity interactions and seeding dates.
60 harvest index measured at maturity does not include leaf and petiole dry weights
The heterosis index (HI) of the evaluated lines ranged from 0.349 to 0.588, with LSB32-7-4 exhibiting the lowest HI at 0.349 In contrast, LSB17-20-1-15-3 recorded the highest HI of 0.588, followed closely by LSB17-10-3-14-4 and the control DT84 variety, both sharing a HI value of 0.561 (Table 4.7).
Theoretical yield shows the yield potential of each variety Theoretical yield is the basis for building appropriate technical measures to maximize the yield potential of the variety
The theoretical yield of soybean lines varied between 12.6 and 30.6 quintals per hectare, while the control DT84 variety yielded 17.7 quintals per hectare The highest yield was recorded for LSB70-23-3 at 30.6 quintals per hectare, followed closely by LSB17-22-2-1-3 and LSB10-12-2-3 with yields of 30.1 and 29.9 quintals per hectare, respectively In contrast, LSB32-46-3 exhibited the lowest yield at 12.6 quintals per hectare.
Table 4.7 Individual yield, harvest index and theoretical yield of soybean lines in winter season 2020
Evaluation of disease and pest damage and lodging resistance of soybean
soybean lines in winter season 2020
Soybeans can be attacked by pests at any stage from seedlings to harvest, but are most attractive to insect pests from flowering onwards The soybean
Pest management significantly affects soybean yield, with various pests including fungi, bacteria, and insects posing challenges Over time, strategies and costs associated with pest control have evolved, highlighted by a staggering 130-fold increase in insecticide usage in the North-Central US since 2001.
Soybean crops are commonly threatened by foliage-feeding pests, particularly Lepidopteran and Coleopteran species, including the soybean looper, velvet bean caterpillar, beet armyworm, bean leaf beetle, stem borer, pod borer, and soybean leaf miner During the winter season of 2020, all soybean lines experienced significant attacks from pod borer, although the extent of damage varied among them.
Pod borer (Etiella zinckenella Treitschke) can lead to significant yield losses of up to 80% However, among the observed lines, all exhibited a pod borer infestation level classified as level 1, indicating less than 5% damage (Table 4.8).
Soybean production in Vietnam faces significant challenges due to the spread of soybean rust (SBR) caused by the fungus Phakopsora pachyrhizi In the winter of 2020, the drier weather resulted in most soybean lines remaining healthy, although some, such as LSB32-7-4, LSB32-46-3, and LSB17-22-2-1-8, experienced severe rust infections, with infected leaf areas reaching levels of 5 (over 5% to 25%) Other lines, including LSB32-45-7, LSB32-54-3, LSB70-23-3, and the control variety DT84, showed moderate infection levels of 3 (1% to 5%) Additionally, five lines (LSB28-13-10, LSB33-5-4, LSB17-14-1-9-2, LSB17-21-3-12-10, and LSB17-22-2-1-3) exhibited minimal infection at level 1 (less than 1%), while the remaining lines remained unaffected by rust.
Lodging resistance (LR) is an important trait for high yield and combine- harvesting efficiency in soybean [Glycine max (L.) Merr.] Numerous studies
Numerous studies have explored the impact of lodging on crop yield, revealing that complete lodging during the seed maturation stage can reduce yield by over 30% (Noor and Caviness 1980; Saito et al 2012; Weber and Fehr 1966; Woods and Swearingin 1977) Additionally, research has shown that lodging significantly affects combine-harvesting efficiency, with losses in soybean harvesting estimated at around 20% due to lodging (Ono et al 1990; Uchikawa et al 2006; Weber and Fehr 1966).
In winter season 2020, all 29 soybean lines and control DT84 variety were at level 1 of lodging resistance (no falling) This is an important characteristic required for mechanical harvesting (Table 4.8)
Table 4.8 Disease and pest damage and lodging resistance of soybean lines in winter season 2020
No Lines Pod borer (0-5) Rust