Only one species of Ramulispora is associated with eyespot disease of wheat in South Africa

Campbell G.F. ; Janse B.J.H. ; Marais G.F. ; Crous P.W. (1996)


Eighty-nine Ramulispora isolates were obtained from eyespot lesions on graminicolous hosts from different regions in the Western Cape of South Africa. Using verified isolates from England and Australia, and based on esterase isozyme electromorphs, all South African isolates were identified as R. herpotrichoides (W type). Single linkage cluster analysis of esterase banding patterns indicated that R. herpotrichoides isolates showed 23% similarity to the R. acuformis isolates. Intraspecific variation was observed within the R. herpotrichoides population and at 40% similarity 17 distinct groups could be identified. Restriction fragment length polymorphisms (RFLPs) and random amplified polymorphic DNAs (RAPDs) conducted on representative isolates of the 17 different groups confirmed their identity as R. herpotrichoides isolates. Using three different restriction enzymes, RFLPs revealed a high degree of homogeneity within the R. herpotrichoides population. Combined DNA fingerprints derived from banding patterns of four 10-mer primers could distinguish 13 of the 17 representative isolates. Similarity coefficients (F-values) using 25 RAPD bands were also determined. The average similarity coefficient obtained for pairwise comparisons of the 17 R. herpotrichoides isolates was 79% whereas the average value for pairwise comparisons of each R. herpotrichoides isolate with an R. acuformis isolate was 31%. These results suggest that R. acuformis is presently not associated with eyespot disease in South Africa, and probably does not occur here. Strict quarantine measures are required, therefore, to ensure that this fungus does not enter the country.

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