Screening Germplasm Highly Sensitive To Exogenous Ga₃and Mapping QTL For Flag Leaf Angle In Indica Rice （Oryza Sativa L.）

Hybrid rice seed production requires artificial pollination and leaf-cutting in order to enhance outcrossing rate. In the process of seed production, the blade of flag leaf was cut by1/3to1/2to eliminate obstacle to outcrossing in CMS lines and restorer lines with small flag leaf angle. This procedure of leaf-cutting requires not only high-intensity laborious work, but also a higher level of operative technique in order to avoid cutting young panicles being heading. In addition, wounds caused by leaf-cutting also had adverse effects on normal growth of rice plants. Identifying favorable alleles of flag leaf angle is a foundation for improving the traits relating to outcrossing of male sterile lines through pyramiding elite alleles. Exogenous gibberellin (GA3) application has been being a key technology in hybrid rice seed production. Improving flag leaf angle and sensitivity to GA3of male sterile lines will play an important role in increasing yield and lowering cost of hybrid rice seed production. In this thesis, two studies have been carried out. One was studies on sensitivities to exogenous GA3of6traits, including plant height(PH), panicle neck length (PNL), flag leaf angle (FLA), length of the1st internode from the top (LFI), length of the2nd internode from the top (LSI) and length of the3rd internode from the top (LTI) by using38accessions in Indica rice. Highly sensitive materials of PH, PNL and FLA were screened based on results of cluster analysis. Meanwhile BC1F2seeds were obtained from a cross of Huajing6and Xianhuil05for constructing their BIL population. The other was studies on QTL mapping of flag leaf angle in rice using BC1F1population derived from a backcross of Longtepu B (indica)/A7444(japonicd)//Longtepu B. BC2F2and BC1F3seeds of the combination were harvested for further constructing BIL population and NIL. The main results were as follows.1. The6traits mentioned above in the38accessions in Indica rice were all sensitive to exogenous GA3, but their sensitivities were different in different genetypes and traits. Materials with high sensitive to GA3in PH, PNL and FLA were identified. (1) Compared with control of spraying water, average values of treatment of all the6traits increased. Among them, PH increased by32.5±7.8cm, PNL3.5±3.3cm, LFI3.5±3.1cm, LSI16.4±4.4cm, LTI8.2±5.1cm, FLA12.8±10.8°.(2) In most accessions, LSI was more sensitive than LFI and LTI.(3)8accessions were clustered into the group of higher sensitivity for PH, such as Yangdao6, Rf838;18accessions were clustered into the group of lower sensitivity for PH, for example, Peiai64S, Yanhui559and Chuanxian5; the rest of12accessions were medium sensitivity for PH, such as Minghui63and Lungaihui.(4)3accessions were higher sensitivity for PNL, including Yangdao6, Zhongxian130and Zhongxiannuo;27accessions were lower sensitivity for PNL, for instance Minghui63and Yanhui559;8accessions were medium sensitivity for PNL, for example Peiai64S and Lungaihui.(5) Only one accession, Zhendian502xuanzao belonged to higher sensitivity for FLA. Up to34accessions belonged to lower sensitivity for FLA, Peiai64S, Minghui63, Yanhui559and so on; Chuanxian, Zhongxiannuo and Rf838were medium sensitivity for FLA.(6)405panicles of BC1F2derived from the cross of Huajing6and Xianhui105were harvested for further constructing BIL population.2. SSR polymorphic rate between Longtepu B and A7444was42.0%. The whole length of SSR linkage map constructed was1905.1cM. Three QTLs were detected for flag leaf angle in the BC1F1population derived from the cross of Longtepu B/A7444//Longtepu B.(1) Among350pairs of SSR primers used to screen polymorphism between Longtepu B and A7444,147pairs of primers amplified polymorphic products using total DNA of the two parents as templates. Chromosome9showed the lowest polymorphism rate (31.0%), while Chromosome3was the highest polymorphism rate (62.5%). With the147pairs of SSR markers, SSR marker genotypes of the116plants in BC1F1were identified. Heterozygous marker genotypes and homozygous marker genotypes of the BC1F1population consistented with the1:1overall segregation ratio, but14of147SSR markers were segregation distortion, accounted for9.5%. (2) Proportion of recurrent parent genome (PRPG) ranged from60.23%--84.47%, with an average of75.10%among116plants in the BC1F1population.(3) A SSR genetic linkage map was constructed by using Mapmaker3.0b software. The genetic map containing18linkage groups and130information loci has a total distance of1905.1cM with an average interval of14.7cM. Of the12linkage groups, there existed a gap on Chromosome3,4,5,6,8and11, respectively. And chromosome5,9and10carried8pairs of SSR makers at the least, while chromosome6harbored15pairs at the most.(4) Flag leaf angles of plants in BC1F1population were investigated at heading stage. Three putative QTLs associated with flag leaf angle were detected on chromosomes1and4by using composite interval mapping method in WinQTLCartographer2.5software, at5%probability level of genome-wide type Ⅰ error. Both qFLA-1a and qFLA-1b were located on chromosome1, in RM1-RM259and RM5-RM246, respectively. qFLA-1a was linked with RM1closely with a distance of0.01cM and explained12.62%of total phenotypic variation. The additive effect of qFLA-1a was23.83and positive allele was from A7444. qFLA-1b, located between RM5-RM246, and departed10.01cM from the nearest marker RM5, explained18.49%of total phenotypic variation. Its additive effect was--25.02and positive allel came from Longtepu B. qFLA-4was identified in the interval of RM6250-RM252on chromosome4near to marker RM2521.49cM and explained11.74%of total phenotypic variation, the additive effect was19.77, and the positive allel existed in A7444.(5) Panicles of105BC1F3and87BC2F2generations were harvested from the combination of Longtepu B and A7444.