| Rapeseed is the most important oil crop in China.The safe production of rapeseed is of great significance to guaratee the supply of edible vegetable oil in China.Drought stress is one of the most severe abiotic stresses that harm agricultural production on a global scale.Drought severely affects the normal growth and development of oilseed rape.Therefore,selecting drought-resistant germplasm,studying drought tolerance of rapeseed and cultivating new varieties of drought-tolerance rape is important for dealing with drought hazards.This study established an effective and reliable phenotyping method for drought tolerance in Brassica napus L.,by using this method screeded 107 Brassica napus mini-core germplasms for drought tolerance from across the globe.We used Genome-wide Association study(GWAS)to explore drought-tolerant candidate genes in Brassica napus,to provide drought tolerance gene resources and markers for molecular breeding of drought tolerance in B.napus.The main research contents and results are as follows:1.Establishment of identification method for drought tolerance in Brassica napus L.In this study,we used a method of simulating drought in a dry shed in a pot experiment,using drought-rehydration-drought-rehydration treatment.The first,drought stress-rehydration treatment was implemented by using normal water supply after emergence,and five plants per pot in three leaf stage.The water supply to the treatment group was stopped and the drought stress treatment was started.The control group received normal water supply.After the first drought stress for 43 days,the treatment group and the control group were all rehydrated with 300 ml water.The day before rehydration,the wilting index(WI)was investigated.The second drought-rehydration treatment: After the first rehydration,the treatment group stopped water supply and began to drought stress.The control group received normal water supply.After the second drought stress for 30 days,the treatment group and the control group all rehydrated for 300 ml.After 6 days,we investigated 7 indicators of drought tolerance,such as the shoots fresh weight stress index(SFWSI).The chlorophyll content variation was measured once a week for all test materials using the SPAD-502 plus instrument throughout the test.2.Optimization of evaluation index system for drought tolerance in Brassica napus L.and screening of germplasm resources with high drought tolerance.In this study,seedlings of 107 accessions of rapeseed mini-core collection were screened for drought tolerance.Drought stress was implemented by treating seedlings with dehydration-rehydration-dehydration-rehydration procedures.The variations of drought tolerance in these germplasms were evaluated and ideal indicators of drought tolerance were selected by measuring several drought-tolerance-related indicators such as drought resistant index(DI),wilting index(WI),shoots fresh weight stress index(SFWSI),shoots dry weight stress index(SDWSI),root fresh weight stress index(RFWSI),root dry weight stress index(RDWSI),plant fresh weight stress index(PFWSI)and plant dry weight stress index(PDWSI).Our analysis indicated that shoot fresh weight stress index,plant fresh weight stress index,and droughtresistant index were remarkably correlated with each other and these indicators can be used as the major evaluation indicators for drought tolerance of B.napus seedlings.Among these indicators,shoot fresh weight stress index was suggested to be the simplest,most accurate and effective index.By integrative utilization of the three selected indices,the drought tolerance of 107 accessions of mini-core collection of B.napus were verified and two highly-tolerant B.napus accessions were selected among the mini-core collection.3.Genome-wide association analysis for drought tolerance candidate genes in Brassica napus L.In this study,we conducted a genome-wide association analysis of drought tolerance traits in 107 Brassica napus microcore germplasm resources and used 3,473,777 SNP loci selected from resequencing analysis to detect 36 candidates marks were remarkably correlated to drought tolerance.We found drought tolerant associated signals in whole genomes,and we found 21 drought tolerance candidate genes such as BnaC09g32050 D.They mainly regulate the expression of drought-resistant genes and signaling regulatory proteins,including transcription factors,protein kinases,and other signaling molecules such as calmodulin binding protein and other processes to regulate plant drought tolerance. |
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