progress in super hybrid rice breeding

Progress in super-hybrid rice breedingLongping Yuan China National Hybrid Rice Research and Development Center, Changsha 410125, China a r t i c l e i n f o Article history: Received 25

Progress in super-hybrid rice breeding

Longping Yuan

China National Hybrid Rice Research and Development Center, Changsha 410125, China

a r t i c l e i n f o

Article history:

Received 25 July 2016

Received in revised form 8 August 2016

Accepted 2 November 2016

Available online xxxx

Keywords:

inter-subspecific heterosis

indica

japonica

morphological characteristics

yield increase

© 2017 Crop Science Society of China and Institute of Crop Science, CAAS Production and hosting by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Contents

1 Introduction 0

2 Technical approaches 0

2.1 Morphological improvement 0

2.2 Raising the level of heterosis 0

3 Conclusions 0

References 0

1 Introduction

To meet the food demand of the Chinese people in the 21st century,

a super-rice breeding program aimed at increasing rice yield was

initiat-ed by the Ministry of Agriculture of China in 1996 It is dividinitiat-ed into four

phases, with the following yield targets: 10.5 t ha−1(phase I, 1996–

2000), 12 t ha−1(phase II, 2001–2005), 13.5 t ha−1(phase III, 2006–

2015), and 15 t ha−1(phase IV, 2016–2020)[1] The average yield of

super-rice should be verified in two locations of 6.7 ha each in two

con-secutive years

Through morphological improvement and the use of

inter-subspe-cific (indica/japonica) heterosis, much progress in developing super

hy-brid rice varieties has been achieved By 2000, several pioneer super

hybrids that met the phase I yield target had been developed, and

they were released for commercial production in 2001 In recent years

the planting area of these hybrids has been approximately

1 million hectares and their average yield has been 8.3 t ha−1 The phase II breeding objective of super-hybrid rice was achieved in 2004 The planting area of phase II hybrids was close to 1 million hectares in

2014 and their average yield was 9 t ha−1

A yield breakthrough in super-rice varieties has been rapidly real-ized with the great efforts of Chinese rice breeders since 2011 The aver-age yield of the super-hybrid rice Y-U-2 reached 13.9 t ha−1in a 7.2-ha demonstration trial in 2011 Another new super-hybrid, Y-U-900, yielded 14.8 and 15.4 t ha−1, respectively, in 6.8-ha demonstration trials evaluated in Longhui county, Hunan province in 2013 and in Xupu county, Hunan in 2014 These experimental results mean that the phase III and phase IV breeding objectives of the super-rice breeding program have been achieved Accordingly, the phase V breeding pro-gram for super-hybrid rice has been proposed in 2015, with a yield tar-get of 16 t ha−1 The current landmark variety of super-hybrid rice, Super-1000, was developed, with yield reaching 16.0 t ha−1in a 6.8-ha demonstration trial in Gejiu county, Yunnan province in 2015

The Crop Journal xxx (2017) xxx–xxx

E-mail address: lpyuan@hhrrc.ac.cn.

CJ-00214; No of Pages 3

http://dx.doi.org/10.1016/j.cj.2017.02.001

2214-5141/© 2017 Crop Science Society of China and Institute of Crop Science, CAAS Production and hosting by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Contents lists available atScienceDirect

The Crop Journal

2 Technical approaches

To date, morphological improvement and heterosis use are the only

two effective approaches to increasing yield potential in rice breeding,

as verified by long-term crop improvement practice[2] Increases in

yield potential are very limited without these two approaches Any

other breeding approaches and methods, including modern breeding

technologies such as genetic engineering, must be combined with

favor-able morphological characters and strong heterosis; otherwise, there

will be no actual contributions to yield increase[3]

2.1 Morphological improvement

A plant ideotype is the foundation for super-high yield in rice

breed-ing[4] For example, the high-yielding combination P64S/E32, with

striking characteristics, achieved a yield record of 17.1 t ha−1 Based

on our studies, a super-high-yielding rice variety displays the following

morphological features[5]:

(1) Tall erect-leaf canopy[6,7]: The upper three leaf blades should be

long, erect, narrow, V-shaped, and thick Long and erect leaves

usually present a larger leaf area They can receive light on both

sides and will not shade one other from sunlight Thus, light is

used more efficiently, and air ventilation is also better within

such a canopy Narrow leaves occupy a relatively small space

and thus allow a higher effective leaf area index V-shaped leaves

make the leaf blade stiffer so that the leaf is not prone to droop

Thick leaves have higher photosynthetic function and do not

readily senesce These morphological features afford a large

source of assimilates that are essential to super-high yield

(2) Lower panicle position[8–10]: The tip of the panicle should be

only 70 cm above the ground during the ripening stage With

this architecture, the center of gravity of a plant is low, making

the plant highly resistant to lodging Lodging resistance is also one of the essential characters required for breeding super-high-yielding rice

(3) Greater panicle size[8]: Grain weight per panicle should be around

7 g, and the number of panicles about 250 per square meter The-oretically, the yield potential is about 15 t ha−1in this case

2.2 Raising the level of heterosis Our studies indicate that the heterosis level in rice shows the follow-ing general trend[11]: indica/japonicaN indica/javanica N japonica/ javanicaN indica/indica N japonica/japonica Indica/japonica hybrids pos-sess a very large sink and rich source, of which the yield potential is 30% higher than that of indica/indica hybrids used commercially For this rea-son, the use of indica/japonica heterosis has become our focus in devel-oping super hybrid rice However, there are many challenges in developing indica/japonica hybrids, a key one being low seed set[12]

By use of the wide compatibility (WC) gene (S5) and the intermedi-ate-type male parent instead of typical japonica varieties[13], several inter-subspecific hybrid varieties with stronger heterosis and normal seed set have been successfully developed

Grain yield is the product of harvest index (HI) and biomass As HI has already reached a very high level (above 0.5), further improvement of the rice yield ceiling should rely on an increase in biomass[2,14] From a morphological viewpoint, increasing plant height is an effective and fea-sible way to increase biomass Our experience in super-hybrid rice breed-ing has indicated a general trend: the greater the plant height, the higher are the biomass and grain yield, provided that the HI remains above 0.5 and the plant is resistant to lodging[15] This trend is illustrated inFig 1 Another effective approach to increasing biomass is increasing the thickness of the stem Comparing a promising new hybrid,

Super-1000, with a super-hybrid, Y-U-900 (Table 1), we found that the height

of Super-1000 was 7.2 cm less than that of Y-U-900, its biomass per culm was almost the same as that of Y-U-900, and Super-1000 had thicker and heavier stems The advantage of this approach is that the de-veloped hybrids are highly resistant to lodging However, it is more dif-ficult to increase stem thickness than plant height

3 Conclusions The development of science and technology is endless Pursuing higher and higher crop yields is an eternal theme Rice still has great

Table 1

Comparison of agronomic traits between Super-1000 and Y-U-900 (Changsha, Oct., 2014).

(t ha−1)

HI Plant height (cm)

Biomass per culm

Stem weight (g 100 cm−1)

Y-U-900 (CK) 14.14 0.57 125.20 12.26 7.53

Difference (%) 0.35 1.75 –5.75 0.16 11.82

HI: harvest index.

HI ≈0.3 >0.5 >0.5 >0.5 >0.5 >0.5 Yield level

(t ha –1 ) 3–5 6–8 8–12 12–18 18–20 >20

Tall (traditional)

Dwarf Semi-dwarf

Semi-tall

Super tall Tall

(new type)

(actual) (actual) (actual)

2.0

1.5

1.0

0.5

Fig 1 Trend in plant height for development of super-high-yielding hybrid rice [3].

potential for yield increases Our further objective is to achieve a yield of

17 t ha−1within two or three years Super-hybrid rice has a very bright

future and can make a great contribution to world food security and

peace

References

[1] L.P Yuan, Developing super hybrid rice for the food security of China, Hybrid Rice 30

(3) (2015) 1–2 (in Chinese).

[2] G.H Ma, L.P Yuan, Hybrid rice achievements, development and prospect in China, J.

Integr Agric (2015) 197–205.

[3] L.P Yuan, Conceiving of breeding further super-high-yield hybrid rice, Hybrid Rice

27 (6) (2012) 1–2 (in Chinese with English abstract).

[4] C.M Donald, The breeding of crop ideotypes, Euphytica 7 (1968) 385–403.

[5] L.P Yuan, Breeding of super hybrid rice, in: S.B Peng, B Hardy (Eds.), Rice Research

for Food Security and Poverty Alleviation, International Rice Research Institute, Los

Baños, Philippines 2001, pp 143–149.

[6] E.H Murchie, Y Chen, S Hubbart, S.B Peng, P Horton, Interactions between

senes-cence and leaf orientation determine in situ patterns of photosynthesis and

photoinhibition in field-grown rice, Plant Physiol 119 (1999) 553–564.

[7] P Horton, Prospects for crop improvement through the genetic manipulation of photosynthesis: morphological and biochemical aspects of light capture, J Exp Bot 51 (2000) 475–485.

[8] S.B Peng, G.S Khush, P Virk, Q.Y Tang, Y.B Zou, Progress in ideotype breeding to increase rice yield potential, Field Crops Res 108 (2008) 32–38.

[9] T.L Setter, E.A Conocono, J.A Egdane, M.J Kropff, Possibility of increasing yield po-tential of rice by reducing panicle height in the canopy I Effects of panicles on light interception and canopy photosynthesis, Funct Plant Biol 22 (1995) 441–451 [10] T.L Setter, E.A Conocono, J.A Egdane, Possibility of increasing yield potential of rice

by reducing panicle height in the canopy II Canopy photosynthesis and yield of iso-genic lines, Funct Plant Biol 23 (1996) 161–169.

[11] L.P Yuan, Recent Progress in breeding super hybrid rice in China, in: Y.X Lu (Ed.), Science Progress in China, Elsevier Science Ltd., Oxford 2003, pp 231–236 [12] L.Y Chen, Y.H Xiao, W.B Tang, D.Y Lei, Practices and prospects of super hybrid rice breeding, Rice Sci 14 (2007) 71–77.

[13] Q Ji, J.F Lu, Q Chao, M.H Gu, M.L Xu, Delimiting a rice wide-compatibility gene S 5

to a 50 kb region, Theor Appl Genet 111 (2005) 1495–1503.

[14] J.F Ying, S.B Peng, Q.R He, H Yang, C.D Yang, R.M Visperas, K.G Cassman, Compar-ison of high-yield rice in tropical and subtropical environments: I Determinants of grain and dry matter yields, Field Crops Res 57 (1998) 71–84.

[15] H.F Deng, Studies on the Objective Traits of Super Hybrid Rice in the Yangtze River BasinPh.D Dissertation Hunan Agricultural University, 2008.

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