Genetic differentiation and gene flow in Colletotrichum sublineolum in Ethiopia, the centre of origin and diversity of sorghum, as revealed by AFLP analysis

Isolates of Colletotrichum sublineolum were collected from different sorghum-producing regions of Ethiopia and divided into five groups based on their geographic origin. The growth rate of 50 isolates showed considerable variation: 1 center dot 7-5 center dot 8 mm day(-1), mean 3 center dot 3 mm day(-1). However, the isolates displayed little variation in colony colour and colony margin, except for isolates from the north, which were different from the others. Amplified fragment length polymorphism analysis of 102 isolates revealed much greater variations among the different groups. Dice similarity coefficients ranged from 0 center dot 32 to 0 center dot 96 (mean 0 center dot 78). Cluster analysis and principal coordinate analysis revealed a differentiation of the isolates according to their geographic origin, and both methods clearly indicated a genetic separation between the southern, the eastern and the other isolates. Analysis of molecular variance (amova) indicated a high level of genetic variation both among (42%) and within (58%) the C. sublineolum sampling sites in Ethiopia. The amova also indicated a high level of genetic differentiation (F-ST = 0 center dot 42) and limited gene flow (Nm = 0 center dot 343). The results of this study confirmed the presence of a highly diverse pathogen, which is in agreement with the existence of diverse host genotypes and widely ranging environmental conditions in sorghum-producing regions of the country. Such diversity should be taken into account in future breeding programmes to achieve an effective and sustainable disease management strategy.