Comparisons of yield performance and nitrogen response between hybrid and inbred rice under different ecological conditions in southern China

In order to understand the yield performance and nitrogen （N） response of hybrid rice under different ecological conditions in southern China, field experiments were conducted in Huaiji County of Guangdong Province, Binyang of Guangxi Zhuang Autonomous Region and Changsha City of Hunan Province, southern China in 2011 and 2012. Two hybrid （Liangyoupeijiu and Y-liangyou 1） and two inbred rice cultivars （Yuxiangyouzhan and Huanghuazhan） were grown under three N treatments （N1,225 kg ha-l; N2, 112.5-176 kg ha-l; N3, 0 kg ha-1） in each location. Results showed that grain yield was higher in Changsha than in Huaiji and Binyang for both hybrid and inbred cultivars. The higher grain yield in Changsha was attribut- ed to larger panicle size （spikelets per panicle） and higher biomass production. Consistently higher grain yield in hybrid than in inbred cultivars was observed in Changsha but not in Huaiji and Binyang. Higher grain weight and higher biomass production were responsible for the higher grain yield in hybrid than in inbred cultivars in Changsha. The better crop perfor- mance of rice （especially hybrid cultivars） in Changsha was associated with its temperature conditions and indigenous soil N. N2 had higher internal N use efficiency, recovery efficiency of applied N, agronomic N use efficiency, and partial factor productivity of applied N than N1 for both hybrid and inbred cultivars, while the difference in grain yield between N1 and N2 was relatively small. Our study suggests that whether hybrid rice can outyield inbred rice to some extent depends on the ecological conditions, and N use efficiency can be increased by using improved nitrogen management such as site-specific N management in both hybrid and inbred rice production.

Changes in Some Physiological Characteristics After Full Heading Stage in Flag Leaves of Super High-Yielding Inbred Rice

In a field experiment, rice cultivar Shanyou 63 was used as a check cultivar to investigate the changes in activity of peroxidase and contents of malondialdehyde and soluble protein after full heading stage in flag leaves of two super high-yielding inbred rice, including Shengtai 1 and Yuxiangyouzhan. The results showed that the peroxidase activities and soluble protein contents in the leaves of the three cultivars tended to increase gradually to peak values and thereafter descended during stage after full heading. Moreover, both the peroxidase activities and soluble protein contents of Shengtai 1 and Yuxiangyouzhan peaked at 8 days after full heading, which was compared with that of Shanyou 63 at 4 days later. Meanwhile, the malondialdehyde contents in the leaves of the three cultivars increased gradually after full heading stage. In addition, activities of peroxidase and contents of malondialdehyde and soluble protein in different cultivars were various at the same time. In general, for Shengtai 1 and Yuxiangyouzhan, the peroxidase activities and soluble protein contents were higher than those of Shanyou 63, whereas the malondialdehyde contents were lower compared with that of Shanyou 63. And these features could make the senescence of leaf become later and slower and photosynthetic product was more in Shengtai 1 and Yuxiangyouzhan than that in Shanyou 63.

Comparison of agronomic performance between inter-sub-specific hybrid and inbred japonica rice under different mechanical transplanting methods

Mechanical transplanting has been applied to rice cultivation to save labor costs and ease labor shortages in Asian countries, especially in China. However, little information is available related to the characteristics of agronomic performance when comparing inter-sub-specific hybrid rice(IHR) and inbred japonica rice(IJR) under mechanical transplanting method. In 2013 and 2014, field experiments were conducted using IHR(Yongyou 2640) and IJR(Wuyunjing 24) under two cultivation patterns, that is, pot seedlings mechanically transplanted(PS) and carpet seedlings mechanically transplanted(CS). Grain yield, yield components, leaf area index(LAI), leaf area duration(LAD), aboveground biomass, crop growth rate(CGR), nitrogen(N) uptake, and N accumulation were investigated. When compared with CS, PS displayed significantly increased grain yield for both varieties because the larger sink size allowed higher N accumulation from panicle initiation to maturity. Moreover, total aboveground biomass under PS increased significantly compared with that under CS; that is, higher photosynthetic productivity resulted from a greater LAI and higher LAD during the grain filling stage. Higher N absorption capacity in the middle and late growth periods resulted in significantly enhanced total N uptake under PS. When compared with IJR for both treatments, IHR generated 75.2% more grain yield. However, the characteristics creating high yield of IHR were different from those of IJR. Greater aboveground biomass production as well as higher N uptake and accumulation created higher grain yield in IHR than in IJR. These results suggest higher yield could be achieved using PS with IHR, attributing to exploit both yield superiority and productive potential.

QTL mapping of grain appearance quality traits and grain weight using a recombinant inbred population in rice(Oryza sativa L.)

supported by a grant from the National High-Tech R＆D Program of China （2014AA10A603, 2014AA10A604）;a grant from the Youth Foundation in Sichuan, China （2011JTD0022）;the special fund for China Agricultural Research System （CARS-01-08）;the Provincial Specialized Funds for Innovation Ability Promotion in Sichuan, China （2013GXJS005）

Critical Yield Factors for Achieving High Grain Yield in Early-Season Rice Grown under Mechanical Transplanting Conditions

Double-season rice cropping systems occupy a large portion of the rice production area in southern China.Because the problem of insufficient labor,mechanical transplanting(in contrast to the manual transplanting)was become more attractive in double-season rice system.However,the decisive yield factors which resulting in high grain yield of early-season rice are unclear under mechanical-transplanted conditions.In present study,the field experiments were conducted in the early season in 2017 and repeated in 2018 in Santang Town,Hunan Province,China.Ten early season rice cultivars(Zhuliangyou 819,Lingliangyou 268,Lingliangyou 104,Luliangyou 996,Xiangzaoxian 24,Xiangzaoxian 32,Xiangzaoxian 45,Xiangzaoxian 42,Zhongjiazao 17,and Zhongzao 39)were used as materials in this study.The difference in grain yield and closely-related agronomic and physiological traits of ten tested cultivars were compared.The range of yields(t ha^(–1) at 86%dry matter)in 2017 was 6.2 to 8.7(mean 7.8)and in 2018 was 6.5 to 8.4(mean 7.8).Grain weight and pre-heading biomass accumulation had potent significant positive correlations with the grain yield.The greater pre-heading biomass accumulation was major attributed to higher apparent radiation use efficiency.Our results suggested that early-season rice cultivars to achieve the high grain yield in mechanical-transplanted conditions depends on apparent radiation use efficiency in the pre-heading period and higher grain weight.

Reduced nitrogen application rate with dense planting improves rice grain yield and nitrogen use efficiency: A case study in east China

Dense planting could be a feasible method for reducing nitrogen(N) application rates without compromising rice grain yield in northeast and central China. It is still unclear whether reduced N application with dense planting(RNDP) can achieve higher rice yield and N use efficiency(NUE) in Jiangsu, east China. Three japonica inbred rice(JI) and three indica hybrid rice(IH) cultivars were grown in a field experiment. Their grain yield, NUE, and related traits were compared under two cultivation treatments:conventional high-yielding practice(CHYP) and RNDP. JI showed similar yields under the two treatments,while IH showed lower yield under RNDP than under CHYP, and the partial factor productivity of N and N use efficiency for grain yield increased(P < 0.05) in both JI and IH under RNDP. Compared with CHYP,RNDP reduced spikelets per panicle but increased panicles per m2 and filled-kernel percentage of JI and IH, and JI's kernel weight was increased(P < 0.05) under RNDP. Shoot biomass weight and nonstructural carbohydrate(NSC) content in the stem at heading and maturity of JI and IH were reduced under RNDP, while harvest index and NSC remobilization reserve were increased(P < 0.05) under RNDP, especially for JI. Our results suggest that RNDP could achieve a higher rice grain yield and NUE, particularly for JI, a dominant rice cultivar type in Jiangsu. For JI, the increased panicles per m2, sink-filling efficiency, harvest index, and NSC remobilization after heading under RNDP contributed to a grain yield similar to that under CHYP.

Comparison of Morphological and Genetic Differentiations in Filial Generation of Cross Between Indica and Japonica Rice

A recombinant inbred line （RIL） population of F8 and F9 generations derived from a cross between a typical indica rice （Qishanzhan） and a typical japonica rice （Akihikari） was used to study the difference between morphological differentiation based on phenotype characters and genetic differentiation using indica and japonica specific SSR markers, and to evaluate the relationship between vascular bundle characters and morphological and genetic differentiations. The results showed that the frequency distributions of morphological and genetic differentiations were all inclined to japonica type in the filial generation. The population was more inclined to japonica type based on genetic differentiation than on morphological differentiation. The consistent degrees of classification based on the Cheng’s index, the ratio of large vascular bundle number to small vascular bundle number in panicle neck （RLSVB） and the ratio of large vascular bundle number in the second internode from the top to that in the panicle neck （RLVB） were all about 50% compared with the genetic differentiation, and the consistent degree of the total scores of the Cheng’s index combined with the vascular bundle number ratios was significantly increased to about 80% compared with the genetic differentiation. Therefore, the vascular bundle characters could be used as a helpful supplement for subspecies classification.

Effect of Environment and Genetic Recombination on Subspecies and Economic Trait Differentiation in the F_2 and F_3 Generations from indicajaponica Hybridization

indica and japonica are the two most important subspecies of Asian cultivated rice. Identifying mechanisms responsible for population differentiation in these subspecies is important for indica-japonica hybridization breeding. In this study, subspecies and economic trait differentiation patterns were analyzed using morphological and molecular （InDel and Intron Length Polymorphism） data in F2 and F3 populations derived from indica-japonica hybridization. Populations were grown in Liaoning and Guangdong provinces, China, with F3 populations generated from F2 populations using bulk harvesting （BM） and single-seed descent methods （SSD）. Segregation distortion was detected in F3-BM populations, but not in F3- SSD or in F2 populations. Superior performance was observed with respect to economic traits in Liaoning compared with that in Guangdong and 1 000-grain weight （KW）, seed setting rate （SSR） and grain yield per plant （GYP） were significantly correlated with indica and japonica subspecies types. Analysis of molecular and morphological data demonstrated that the environment is the main factor giving rise to population differentiation in indica-japonica hybridization. In addition, we also found that KW, SSR and GYP are related to subspecies characteristics and kinship, which is possibly a significant factor resulting in economic trait differentiation and determining environmental adaptability. Our study has provided new insights into the process of population differentiation in these subspecies to inform indica-japonica hybridization breeding.