A Study On The Inheritance Of Stigma Exsertion Rate And Genotypical Variation Of Stigma Vitality In Rice

Rice is an important food crop in China,our huge population calls for high demands on rice.The application of hybrid rice technology has significantly increased rice yield and has played an important role in ensuring food security.In hybrid seed production,the outcrossing characteristics of male sterile lines,especially stigma exsertion rate（SER）and stigma vitality,has a great impact on seed yield and quality.Male sterile lines with a high stigma exsertion rate and stigma vitality is a vital to improve yield and quality in hybrid seed production.In this study,firstly,we observed the genetic segregation of SER in several genetic populations.Secondly,we analyzed the distribution of the SER QTL--qSER-3.1 in rice breeding parent lines and a segregating population and its correlation with SER.Then,two rice lines with the same qSER-3.1 allele but having different SERs were used as parents to create a doubled haploid（DH）population and used for QTL mapping of SER.Finally,we explored and established a method for measuring rice stigma vitality based on catalase activity,after which we analyzed the variation of it in different rice genotypes.The main findings are as follows:1.The SER performance in F₁ and F₂/DH₂ populations of different rice lines.To clarify the rice SER performance of filial generation from diverse materials,we analyzed the SER of F₁ and F₂/DH₂ populations derived from crosses of 3 high SER lines[TS848（81.1%）,TS849（75.7%）,Hupper 616S（98.3%）]and 6 low SER lines[C703（0%）,SD2620（10.7%）,1350（0%）,B732（0.6%）,TS846（0%）and Xidao No.1（0%）].It was found that the SER of F₁ plants was higher than that of the parents with the low SER,but was more inclined to the parents with low SER.The SER of F₂ plants of Hupper 616S/Xidao No.1 and the F₂/DH₂ plants/lines of TS849 crossed to TS846and B732 showed normal distribution.However,there were only a few F₂ plants/DH₂lines derived from TS848 having a high SER,majority of its F₂ plants/DH₂ lines had very low SERs.The above results indicate that there are two different inherited separation pattern,the genetic mechanism of rice SER is complicated.2.The distribution of SER QTL qSER-3.1 in diverse parents and in a F₂ population.qSER-3.1 is a SER QTL identified by our team,but the distribution in diverse varieties and the relation with SER in other genetic populations remained unclear.Consequently,we analyzed the SER and qSER-3.1 genotype of 100 F₂ plants developed from cross of Hupper 616S/Xidao No.1 initially,it was found that the SER of lines carrying qSER-3.1-ZS allele was 72.6±6.9%（with the range 12.7～89.7%）,and 19.5±9.9%（with a range 0～28.2%）carrying the qSER-3.1-DS allele.Subsequently,the SER and genotype of qSER-3.1 of 180 parental lines were analyzed,it was found that 20 carried the qSER-3.1-ZS allele,158 carried the qSER-3.1-DS one.The former lines showed higher SERs（47.7%±18.7%）as compared to the latter ones（3.1%±10.3%）.The above results indicate it is universal that the SER of qSER-3.1-ZS lines is significantly higher than qSER-3.1-DS ones.3.Mapping of high SER QTLs in TS849.TS849 is a high SER material,but it carries the qSER-3.1-ZS allele the same as TS846,a line with low SER,which indicates that they may carry new QTLs other than qSER-3.1.A total 93 DH₂ lines were developed from the of TS846/TS849 F₁ plants and analyzed for SER.Out of them,10 lines with extremely low SER（<12.6%）and 10 with extremely high SER materials（>74.2%）were selected for the development of 2 sequencing pools,of which the genomes were sequenced using next generation sequencing.Four QTLs related to SER were identified through SNP-index:qSER-8.1（20.48-22.46 Mb of Chr 8）,qSER-10.1（14.91-19.25 Mb of Chr 10）,qSER-11.1（20.03-23.38 Mb of Chr 11）,qSER-12.1（24.06-25.12Mb of Chr12）.Among them,qSER-8.1,qSER-10.1,qSER-12.1 are overlapped with previously reported SER QTLs,while qSER-11.1 is a new one.4.Establishment of a method for measuring rice stigma vitality and its use for analysis of different rice varieties.The determination of rice stigma vitality by crossing and examination of seed set rate was a commonly used method,but it has several drawbacks.In this study,we analyzed the catalase activity and seed set rate after manual pollination of TS948,TS992,TS9211,DH9070,TS256 and TS248 for 6consecutive days after flowering,it was found that the correlation between the two methods is extremely significant,hence a method for measuring stigma vitality based on the determination of catalase activity was established.Using this method to analyze the difference in stigma vitality between varieties,it was found that the stigma vitality decreased gradually after flowering,but the stigma vitality of the purple stigma material decreased slower than that of the white stigma material.Spraying 30mg/L gibberellin at 5:00 pm on the flowering day can delay the decline of stigma vitality.In this thesis,through the study on the inheritance of stigma exsertion rate and genotypical variation of stigma vitality in rice,we revealed the genetic characteristics of SER in different populations,verified the validity of qSER-3.1 to breed rice with a high SER,identified new SERQTLs in TS849,and established a new method for measuring stigma vitality of rice,which together will have a positive impact on improving outcrossing characteristics of male sterile rice for improving yield in hybrid seed production.