Heterosis Performance Of Indica-japonica Intersubspecific Cross Combinations Of JXY Series

Rice is one of the most important food crops in the world,of which hybrid rice plays a important role in rice production.Since the 1970s,the use of rice heterosis has made a huge contribution to increasing rice yield.Indica and japonica are two subspecies of Asian cultivated rice（Oryza sativa L.）,and have been considered to have strong heterosis.However,a series of problems such as hybrid sterility have always restricted the development of indica-japonica hybrid rice.This study use 29 excellent japonica-compatible indica restorer lines bred by predecessors in our laboratory and 63 excellent japonica sterile lines collected from multiple breeding units across the country were used to assemble cross combinations named JXY series indica-japonica hybrid rice.The F₁ hybrids were planted in multiple seasons and stages.The main agronomic traits and quality traits of each combination were investigated,and combining ability analysis was performed to select high-yielding and high-quality hybrid combinations and evaluate the overall performance of parents.The effects of different planting periods on indica-japonica hybrid rice were explored.The main results are as follows:（1）Study on the seed setting rate and yield of the indica-japonica hybrids rice participating in the test for the third consecutive season.Compared with the control variety,more than 75%of the combinations reached the normal seed setting rate,the hybrid sterility barrier was basically overcome.There are some combinations showed significant yield advantages compared with the excellent indica hybrid rice.（2）Using the HJX74 and high-quality indica hybrid rice varieties as controls,through a multi-season production test,a number of combinations with significant yield advantages compared with the control varieties were selected from the JXY series indica-japonica hybrid rice combinations.These combinations have significant advantages in tillering and grain weight,and generally exhibit short heading date characteristics.Some of the combinations with high-quality restorer lines as parents showed significantly better quality traits than HJX74,which were similar to high-quality indica hybrid rice,but chalky quality was slightly worse than those of high-quality indica hybrid rice varieties.These advantageous combinations are expected to be applied in production.（3）The test cross was conducted on three candidate families of the strong heterosis restorer line HJH27.The test results show that the test offspring of candidate line 27-3 show strong advantages in yield and thousand-grain weight.In combination with the field performance of each offspring,27-3 was selected as the strong heterosis japonica-compatible indica restorer lines and renamed HJH27.（4）In a multi-season test,the japonica-compatible indica restorer lines was used to perform a mating test with multiple japonica sterile line.The test results show that F₁ of most restoer lines could maintain normal seed setting rate,and reached the goal of overcoming infertility of indica-japonica hybrids.Among them,HJH05 showed the best affinity for japonica rice.Although HJH27 tested F₁ had a lower seed set rate than HJH05,it showed a strong heterosis in yield.The yield of progeny of tested restorer lines,represented by HJH28,was slightly lower,but the quality was significantly improved.The two high-quality restorer lines HJH28 and HJH33 have the highest performance and stable yield.HJH30 has a long grain length improvement effect and can be used as a long-grain,high-quality indica-japonica hybrid rice parent.（5）HJH27 and HJH28 were used as test parents to evaluate the assembling effect of male japonica sterile lines and japonica-compatible indica restorer lines.The result showed that most of the male sterile lines show good combining ability with japonica-compatible indica restorer lines.Among them,the sterile lines 01,04,52,61 and other materials performed the best,and the heterosis on yield of F₁ was significant.Sterile lines 06,07,60,63 and other materials performed poorly,mainly due to low cross seed F₁ seed set rate,less tillering,and hybrid sterility problems still existed between the restorer lines.In addition,a batch of japonica sterile line with unique advantages in thousand-grain weight and grain shape were selected to provide a basis for subsequent larger-scale test cross experiments.（6）The combining force analysis were be performed within the incomplete diallel cross in the test materials of each season.The result show that the parental combining effect of participating combination is greater than the special combining effect,and the parental effect dominates.Screened a number of parents with high combining effect on different traits,and comprehensive analysis of the combining abilities of some main parents was made.Although the special combining ability is not as high as the general combining ability,it also plays a major role in breeding.An analysis of multi-season data screens out a number of combinations with high special combining ability in various traits as a reference in the breeding process.（7）The traits of indica-japonica hybrid rice planted at different seeding periods were compared,and the effects of different planting periods on the comprehensive performance of indica-japonica hybrid rice and its parents were studied.The results showed that compared with the early season,the yield,seed setting rate,thousand-grain weight,effective spike,alkali elimination value,amylose content,and chalkiness were higher in the late season,while the spike length,plant height,heading date,and gel consistency low.Comparing the differences between the two materials of late sowing and early sowing in the late season,different combinations showed different adaptations in late sowing and early sowing.Late sowing materials generally had more effective ears,higher plant height,longer heading period,and lower chalky grain rate and chalkiness.In this study,the yield,agronomic traits and quality of multiple indica-japonica hybrid rice combinations and their parents were evaluated comprehensively through multiple season experiments.A selection of outstanding indica-japonica hybrid rice parent materials was screened out.These results will provide guidance for future breeding practices of indica-japonica hybrid rice.The selected combination of advantages is expected to stand out in the subsequent comparison tests and be applied in production.