Association analysis of sugar yield-related traits in sorghum [Sorghum bicolor (L.)]

Association mapping is widely used for detecting QTLs in higher plants. In the present study a synthetic sorghum population containing 119 representative samples, including 43 sweet and 76 grain sorghum accessions originating mainly from China, USA and India, were genotyped using 51 simple-sequence repeat (SSR) markers. Linkage disequilibrium (LD) of pair-wise loci and population structure were analyzed, followed by association analysis of SSR loci and 3 sugar yield related traits using the TASSEL general linear model program. Results showed that: (i) different degrees of LD occurred among syntenic markers and also among nonsyntenic markers, indicating historical recombination among sorghum linkage groups; (ii) significant LD extended up to 7.31 cM; (iii) the collection of accessions was composed of three subgroups; (iv) four marker loci were associated with stalk sugar concentration, fresh stalk weight and stalk juice weight measured in different growing environments and could be used, therefore, in future marker assisted breeding programs. Several loci were also associated with two or more traits simultaneously, which might be due to tight linkage between different genes affecting these traits and/or pleiotropy. In addition, some associated markers were located close to QTLs previously mapped in family-based linkage mapping analyses.