In situ estimation of outcrossing rate in sorghum landraces using microsatellite markers

We assessed the outcrossing rate of sorghum landraces sampled in situ from two fields under traditional cultivation in north-western Morocco using genotypic data from five microsatellite loci. Assuming a mixed mating model, we estimated outcrossing parameters by two methods that are based on progeny analyses. With both methods, the multilocus estimate of outcrossing rate for the overall sample was in the order of 0.1, meaning that sorghum landraces are predominantly autogamous, but with a significant proportion of outcrossing. The estimated outcrossing rate is about two times higher in field 1 (t(m) = 0.161) than in field 2 (t(m) = 0.069). This difference could be explained by distinct morphological characteristics of the inflorescence in the two fields, with predominance of loose panicles in field 1 and of very compact panicles in field 2. The distribution of outcrossing rate among progeny families showed that 30% of them were completely self-fertilized but some families showed substantial outcrossing. These results are at odds with the very low genetic differentiation observed previously among Moroccan landraces and suggest that morphological differences are maintained despite gene flow through seed exchanges among farmers.