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Save【Objective】The indica-japonica super hybrid rice breeding technology innovation and practice had been carried out in to improve with problematic characters, such as longer growth period, lower seed setting rate and lower seed yield existing in the utilization of heterosis between indica rice and japonica rice. 【Method】Japonica maintainer lines with early flowering and high rates of stigma exsertion were developed by indica-japonica intergression crossing. Using these materials, high outcrossing rate japonica CMS lines were bred. Indica-japonica intermediate type restorer lines with wide compatibility were bred by means of indica-japonica intergression crossing, molecular marker assisted selection of wide compatibility gene and directional selection of indica and japonica components. The main agronomic traits of these type’s Cheng’s index, wide compatibility and gene restoring spectrum were compared with the japonica restorer line. The light-temperature reaction type and the outcrossing rate were also compared between japonica-indica hybrid rice and indica-japonica hybrid rice. The japonica-indica hybrid rice and indica-japonica hybrid rice were bred from japonica CMS line Chunjiang 16A, indica CMS line Wufeng A and the indica-japonica intermediate type restorer lines CH58, C84 and C927 with wide compatibility. 【Result】The japonica CMS lines Chunjiang 16A, Chunjiang 99A and Chunjiang 23A with early flowering and/or high rate of stigma exsertion were developed by indica-japonica intergression crossing, and their seed yield increased significantly. The indica-japonica intermediate type restorer lines CH58, C84 and C927 with wide compatibility were bred, which had characteristics of large panicles, strong stems, good wide compatibility and wide restoring spectrum. The F1 of late season japonica CMS lines/indica-japonica intermediate type restorer lines with wide compatibility showed stronger photoperiod-sensitivity, while the F1 of middle season japonica CMS lines/indica-japonica intermediate type restorer lines with wide compatibility had increased temperature-sensitivity, but the light-temperature reaction type F1 were different between early season indica CMS lines/indica-japonica intermediate type restorer lines with wide compatibility. Larger stigma exsertion rates of CMS lines and smaller differences in spikelet flowering rates before noon of parents were beneficial in increasing the outcrossing rate of the japonica-indica hybrid rice and indica-japonica hybrid rice. Chunyou 84 and Wuyou 84 which developed from japonica CMS line Chunjiang 16A, indica CMS line Wufeng A and the indica-japonica intermediate type restorer line C84, and showed the advantage of large panicle, strong heterosis, high yield potential, high lodging resistance, high seed setting rate and strong cold tolerance. These two were released provincially.【Conclusion】 Japonica CMS lines with early flowering and high rates of stigma exsertion were developed by indica-japonica intergression crossing. The indica-japonica intermediate type restorer lines with S5-n gene and wide restoring spectrum were different from the ordinary japonica restorer line. The F1 of middle season japonica CMS lines/indica-japonica intermediate type restorer lines with wide compatibility were temperature-sensitive, with a marked benefit to shorten the whole growth period. Larger stigma exsertion rates of CMS lines and smaller differences on spikelet flowering rates before noon of the parental lines were effective in increasing the outcrossing rates of the japonica-indica hybrid rice and indica-japonica hybrid rice. The indica-japonica super hybrid rice Chunyou 84 was released provincially.
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Save【Objective】With the development and improvement of breeding technology in indica-japonica hybrid rice, it has been possible to explore inter-subspecific heterosis directly to develop high-yielding rice varieties. It is highly significant to be able to detect gene frequencies of indica or japonica accurately, identify indica-japonica attributes and cultivar classification, and to predict competitive heterosis by genetic distance for indica-japonica hybrid rice breeding and cultivar classification using InDel molecular mark and sophisticated technology. 【Method】Twenty-four indica-japonica hybrids or japonica-japonica hybrids, recently bred by different breeding units in Zhejiang province, were collected to analyze using eighteen pairs of primers selected from the InDel molecular marker. The gene frequencies of japonica genomics were detected by the Wang’s reported method, and tested materials were judged for different attributes. Genetic distance (GD) among tested materials was assessed by InDel molecular markers using Nei’s calculation method.. The genetic similarity (GS) was assessed using UPGMA cluster analysis of genetic similarity. Principal component analyses (PCA) were conducted using SPSS 17.0 statistical analysis software to assign InDel bands, then, on the basis of the average values of the eigenvectors of the first and second principal components, a scatterplot was created. Ten agronomic important characteristics, i.e. period duration, plant height, spikelet number per panicle, seed setting, 1000-grain weight and grain weight per plots were investigated for analysis of competitive heterosis. The relationships of competitive heterosis of japonica-japonica hybridsor indica-japonica hybrids with GD values to control cultivar were determined. 【Result】Eighteen pair of InDel primers could amplify all materials to obtain special indica bands, japonica bands and indica-japonica hybrid bands. According to calculated frequencies of japonica genes, these materials were accurately judged different to have indica-japonica attributes, and were divided into six clusters, twelve hybrids belonging to indica-japonica hybrids, and another thirteen hybrids placed into japonica-japonica hybrids. Again, using cluster analysis of InDel markers, this distribution was verified. With the results of PCA analysis, we show that all varieties classify into three non-overlapping tzones, an indica zone, typical japonica -japonica zone, and a japonica cline-intermediate type zone. Comparison of the average of plot yields in two-year trials, we found that the yieldsof indica-japonica hybrids increased by 12.5% and 14.9% over that of japonica-japonica hybrids, expressing outstanding yield advantages. Upon analysis of ten agronomic characters between the two type hybrids, total spikelet numbers and fertile spikelet numbers of indica-japonica hybrids were significantly increased by about 30%. We suggest that the attribute of larger panicles is the major contribution factors to yield increases. After comparative analyses of the genetic distances (GD) relationship of tested varieties to the control Jiayou 2, we found no significant relations the group of japonica-japonica hybrids, whereas have most significant positive relations with traits of panicle length and 1000-grain weight, but has a significant negative relations with the grain density. 【Conclusion】Using InDel molecular mark technology is powerful and effective in its ability to detect gene frequencies of japonica in various types of cultivars, and to identify their indica-japonica attributes or classify their cultivar types. The indica-japonica hybrid rice expressed significant competitive heterosis in grain yield, the major contribution of heterosis was more spikelets per panicle.
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Save【Objective】 This study was conducted to determine quantitative trait loci (QTLs) associated with the standard heterosis of yield traits and to analyze the genetic basis of standard heterosis in rice. 【Method】 A recombinant inbred line (RIL) population was derived from crosses between rice restorer lines Teqing and six IRBB lines that are near isogenic lines in the genetic background of IR24. A testcross population was also constructed by crossing the 204 RILs to male sterile line Zhong 9A. The 204 sets of RILs and corresponding F1 were grown side by side for two years in the same trial site. They were planted in two replications. At maturity, the middle four plants of each replication for each line were harvested together. The number of panicles per plant (NP), number of grains per panicle (NGP), number of spikelets per panicle (NSP), spikelet fertility (SF), 1000-grain weight (TGW) and grain yield per plant (GY) were measured. Mean values over the two replications were used for data analysis. A data set derived by subtracting the trait value of a RIL from that of its corresponding F1 was used for QTL analysis using QTLNetwork 2.0. A putative QTL was claimed using a genome-wise type I error of P<0.05 determined by 1000 permutations. 【Result】 Significant positive correlations between the RILs and F1s were observed for all the six traits. The correlation coefficients were highest for TGW (0.903), lowest for NP (0.333) and GY (0.357), and intermediate for SF (0.406), NGP (0.448) and NSP (0.680). A total of 16 QTLs distributed on chromosomes 2, 3, 5, 6, 8 and 10 were detected, including three (3) for NGP, four (4) for NSP, three (3) for SF, four (4) for TGW, and two (2) for GY. The phenotypic variance explained by a single QTL ranged from 1.7 % to 22.1 %. All three QTLs affecting NGP showed higher standard heterosis for Zhong 9A/IR24 than Zhong 9A/Teqing. For NSP, SF and TGW, three, two and two QTLs had higher standard heterosis for Zhong 9A/IR24 than Zhong 9A/Teqing, and one, one and two QTLs were higher in standard heterosis for Zhong 9A/Teqing than Zhong 9A/IR24. Of the two QTLs associated with GY, qGY2 overlapped with qNGP2 for NGP and qNSP2 for NSP, and qGY10 overlapped with qNGP10 for NGP and qSF10 for SF. All six QTLs showed higher standard heterosis for Zhong 9A/IR24 than Zhong 9A/Teqing. 【Conclusion】 F1 performance was correlated with both parental performance and F1 heterosis. QTLs for standard heterosis play an important role in the genetic control of F1 performance of yield traits in rice.
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SaveChina’s super rice research project was initiated by the Ministry of Agriculture in 1996. In the past 20 years, China has been a leader in super rice research, including genetic and physiological basis of super-high yielding or theory and practice for super rice breeding, and indica super hybrid rice in south or conventional japonica super rice in north. These research provided scientific and technical basis for improving production potential and converting sciences and technology to realistic productivity, and made outstanding contribution for maintaining China the international advanced level on rice science. Research progress of japonica super rice in Northern China, including the development of super rice, establishment of technical route, new variety breeding and demonstration promotion, basic research in physiological and genetic were reviewed in this paper. Meanwhile, some related physiological and genetic issues of Northern japonica super rice were discussed: The Northern japonica rice in recent years kept high levels on yield and quality, and the chalk white character and other appearance qualities have been improved, without significant contradiction between yield and main quality traits when yield no more than 9 t·hm-2, and the yield and quality can reach a new balance at a higher level. Analysis of Northern japonica rice regional test results showed that extending growth period to increase yield was unsatisfactory, also not work by increasing plant height, while improving the resistance to rice blast was one of the important breeding targets for Northern japonica rice. The seed density of Northern japonica rice is generally high, but the negative impact on the yield components and the main quality traits is relatively small, which can be thought that Northern japonica rice seed density is in an appropriate range through the untiring efforts of the breeders. Grain length-width ratio is a main factor determining indica and japonica rice milling quality, and less impact on the appearance quality difference between subspecies. Chinese indica rice milling quality has been improved significantly in recent years, difference between indica and japonica rice decreases. The appearance quality of indica and japonica rice has improved significantly, but the difference still exists between indica and japonica. On the basis of full summarizing Chinese super rice research achievements and experience in the past 20 years, the super rice research directions and goals in the future should be determined. Long-term stability research support mechanism according to the ecological regions should be established instead of stage yielding goals; small area yield evaluation should be changed to the assessment of large area stable yield increase. The basic theory and key technology research should be targeted according to the ecology, production and varieties of Northern japonica rice, such as the genetic and physiological and ecological mechanism of indica and japonica yield and quality. From the molecules, cells, tissues, organs, individual and population levels, comprehensive evaluation of erect panicle gene EP1 function should be further studied to effectively improve quality of both indica and japonica hybrid varieties with big and erect panicles. We should make full use of the research achievements of molecular biology and technology, and make a breakthrough on rice blast resistance, cold resistance and salt-tolerant germplasm innovation and breeding.
