| Adzuki bean?Vigna angularis?is one of important legume crops,and widely grown in more than 30 countries in the world.Adzuki bean,as an important source of starch,digestible protein,mineral elements and vitamins,is consumed by at least a billion people.In China,the main production area of adzuki bean is semi-arid region,Identification of the drought resistance of germplasm resources is important for drought trait genetics research and improvement of adzuki beans.In this research,the germplasm resources of cultivated adzuki bean?Vigna angularis?and wild adzuki bean?Vigna angularis var.nipponensis?were used to explain the characteristics of drought resistance at seedling stage by drought stress.The resistant drought and sensitive accessions with dominant difference were selected for physiological and biochemical analyses.The phenotypic traits under drought stress at seedling was used for genome-wide association study.To explore drought resistance characteristics of adzuki bean at the seedling stage,325 accessions of wild adzuki bean and cultigen from different countries and were stressed under drought by pot cultivation assay.The nine traits including root morphology,plant height,biomass and canopy wilting etc.were assayed.The subordination function method,principal component analysis?PCA?,and cluster analysis were used to comprehensively assess drought resistance.The result showed that the total root surface area,total root volume,shoot dry mass,root dry mass,plant dry mass,and plant height were lower than those of the controls under drought treatment.The correlation analysis on the subordination function values of each trait showed the most significant correlation between the total root surface area and average values of subordination function.The first principal components were mainly contributed by total root surface area in PCA.These accessions were classified into three types,composing of drought-resistant,intermediate and drought-sensitive,which accounted for 30%,28%and42%of total accessions,respectively.Integrating the subordination function value,PCA and root morphology of different types,the total root surface area was thought as a major index for assessing drought resistance in the seedling stage of adzuki bean.Twenty drought-tolerant accessions were identified,and will lay the foundation for further drought-resistant breeding and drought resistance gene mining in adzuki bean.Basing on the screening result of drought resistance,10 accessions of wild adzuki bean and cultivated adzuki bean with different drought resistance were selected to assay relative water content,malondialdehyde content,proline content,photosynthetic index,and physiological-biochemical indexes of under polyethylene glycol simulated drought stress at seedling stage.The results indicated that the higher drought-resistant accessions had stronger water-maintaining capacity,smaller water deficit,larger increase multiple of proline,higher relative integrity of the cell membrane,smaller decline rate of net photosynthetic,larger decline rate of stomata conductance and transpiration,and higher water use efficiency.The drought-resistant subordination function values exhibited that the drought resistance of the assayed accessions was wild drought-resistant>cultivated drought-resistant>wild drought-sensitive>cultivated drought-sensitive accessions.Integrating the data of resistant-drought phenotypes and re-sequencing of the 325 accessions,the genome-wide association study was carried out using 1,110,535 SNP markers.Forty SNP sites significantly associated at the P<3.07×10-7 level using the optimized compression mixed linear model.A total of 771 genes were searched by identifying genes in the 500 kb region upstream and downstream of the significantly associated locus.The genes associated with drought resistance were further analyzed,and the DREB and EPF genes on chromosome5 were thought to be candidate genes. |
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