| Salinity and drought are the most serious contrains influenceing rice production.Breeding rice varities with single or multiple resistances is the most effective way to promise high and stable productions of rice.Rice salt tolerance is quantitatively inherited controlled by multiple genes/QTL,thus deeply understanting genetic mechanisms of rice resistant to salinity could considerably facilate to salt tolerance molecular breeding.Therefore,the study was design to?1?screen high yield,drought and salinity tolerant rice materials using recurrent selection populations facilitated by dominant male sterile line;?2?detect QTL for targeted traits using salinity tolerance,drought tolerance and high yield selected breeding populations;?3?dissect QTL and candidate genes affecting rice salt toleranc at seedling stage;?4?genetically dissect rice yield and related traits under whole growth salinity stress condition;?5?obtain breeding materials with high yield,multiple resistances as well as high grain quality.The main results were summarized as follows:1.Developing high-yielding materials with tolerances of drought and salt stresses using recurrent selection populationsTwo different kinds of recurrent selection populations facilitated for outcrossing using dominant male sterile line‘Jiabuyu'?controlled by single dominant male sterility gene?were developed.After two cycles of recurrent selection through natural outcrossing,the seeds from male fertile progeny plants were screened for higher grain yield under normal irrigated,drought and salt stressed natural field conditions,followed by two seasons of replicated yield trials in International Rice Research Institute?IRRI?.Finally,we identified 11 promising high yielding lines under irrigated conditions.Another 12drought and 12 salt tolerant lines were identified.Interestingly,we identified one line that gave higher grain yields across all the three conditions and three lines that yielded high in both irrigated and drought conditions while another three lines that gave high yields in both drought and salt stressed conditions.2.Utilizing selective breeding population to genetically dissect yield and its related traits under salinity,drought and normal irrigated conditionsA F2 population derived from cross between GPDQ3 and GPDQ4 was carried out salinity–salinity directional screening?S–S?,and crossover screening including salinity–drought?S–D?and salinity–high yield?S–Y?in salinity,drought and normal irrigated field conditions.In total,91,45 and 27 plants were selected for S–S,S–D and S–Y,respectively.Simultaneously,a random population with 200 F4 lines was obtained by single seed descent method.In 2016 dry season and wet season,all of these materials were replicated planted in the above three conditions to evaluate the yield and its related traits.In total,2,188 SNP markers genotyped by tunable genotyping-by-sequencing?tGBS?were used for genetic analysis.Segragation distortion method was applied for selected population to identify QTL for targeting traits,and 18,9 and 10 chromosome regions showing significant segregation distortion was detected in S–S,S–D and S–Y populations,respectively.Furthermore,four QTL regions were verified in random population affecting yield,panicle number,heading date and plant heigh identified.Taking advantage of high density SNP markers of three grandparents generated in 3K Rice Genome Project,we found the genes located in the confidence interval of the QTL having non-synonymous SNP among grandparents,followed by analyzing graphical genotypes of parents,which led to the discovery of 293candidate genes for eight important QTL regions,and 15 most like candidate genes were inferred by comparied their functional annotation with known genes.3.Mapping QTL for rice seedling stage salt toleranceThe materials including 200 F4 lines and their two parents?GPDQ3 and GPDQ4?and three grandparents?WTR1,Khazar and BG300?were replicated to evaluate salt tolerance at seedling stage.In total,28 lines with salt stress score?evaluated by standard evaluation system,SES?ranging from 1 to 3were identified.Interval mapping was applied using 2,188 SNP markers,and two QTL for SES?qSES2and qSES4?and two QTL for leaf chlorophyll content?qChlo1 and qChlo4?were identified.The qSES4and q Chlo4 were located in same chromosome region.What's more,the two QTL for SES were also identified by selective genotyping method.Finally we discoved 87 candidate genes of the three QTL.According to their functional annotation,12 most likely candidate genes were inferred.4.Mapping QTL associated with yield and its component traits of rice under whole growth duration salinity stressThe whole plant growth duration salinity tolerance was studied through genotyping and phenotyping eight populations of BC1F5 introgression lines?ILs?with the same recipient for grain yield and its five component traits under severe natural saline stress condition in two consecutive years.A joint multiple-population analysis method was applied to perform QTL mapping and estimate allelic effects of each parents.In total,25 QTL regions affecting the six traits were identified with each having multiple alleles.Eight QTL regions harbored previously detected ST related genes/QTL and 17 were novel.Five QTL were commonly detected across the two years.Through analysising proper ILs coupled with 0.4M SNP markers,two stable QTL qGY2 and qSSR2 were fine mapped into 93 kb and168 kb region harboring 16 and 29 functional annotation putative genes,respectively.5.Eating and cooking quality traits analysis for high yield-multiple resistances breeding materialsWe analyzed the eating and cooking quality?ECQ?traits including amylsoe content,gelatinization temperature and RVA?Rapid Viscosity Analysis?properties for 671 high yield with multiple resistances materials developed by Grain Super Rice project in IRRI,and obtained many matierls having similar ECQ parameters with known famous high quality varieties by cluster analysis,providing valuble sources for high quality,multiple resistances as well as high grain quality rice varieties breeding. |
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