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Genetic Variability Within and Among Mycelial Compatibility Groups of Sclerotium rolfsii in South Africa

Isolates of Sclerotium rolfsii, the causal organism of stem rot or southern blight of groundnut, can be placed in mycelial compatibility groups (MCGs) based on hyphal interactions between isolates. The aim of this study was to determine whether amplified fragment length polymorphism (AFLP) analysis was a suitable technique to assess genetic variability between isolates and MCGs of S. rolfsii. For preliminary genetic analysis, 10 isolates were selected from each of two MCGs and compared with each other using the restriction enzymes EcoRI and MseI and 4 primer pairs. The number of polymorphisms ranged from 10 to 36 per primer combination, with an average of 22.5. AFLP analysis clearly showed genotypic differences (22%) among MCGs B and C, with a maximum variation of 6.41% between any two isolates per group using four primer pairs. Certain isolates could not be distinguished from each other. A more in-depth study of 10 isolates from MCG B, using 8 additional primer pairs, showed small genetic differences (maximum of 4.2% and minimum of 0.2%) between isolates. These results suggested that DNA could be pooled for comparison of MCGs. Pooled DNA from isolates within groups using 20 primer pairs confirmed differences between 9 MCGs. This technique effectively differentiated MCGs of S. rolfsii from each other and also detected differences between isolates within a single MCG.