Variation in flowering time in sorghum core collection and mapping of QTLs controlling flowering time by association analysis

A wide range of variation in flowering time was observed within a diversity research set of 107 sorghum accessions ranging from 56 to 133 days. Accessions were classified into early medium and late flowering groups. 45 accessions were grown under three different environments of photoperiod (11, 12 and 15 h). Sorghum accessions gradually responded to the decreasing of day-length. The 12 h of photoperiod could be considered as a threshold above which day-length delays the flowering time in sorghum. Association analysis was performed to identify the QTLs controlling flowering time and photoperiod sensitivity using 107 accessions of sorghum grown under natural condition and 45 accessions grown under controlled conditions. Four QTLs controlling flowering time were detected under natural condition of day-length at threshold 2.5 using K model. A total of seven flowering time loci were detected under controlled conditions of day-length. One QTL controlling photoperiod sensitivity was detected on chromosome 1 and one QTL controlling photoperiod insensitivity was detected on chromosome 4.