DIFFERENTIATION BY MOLECULAR ANALYSIS OF ELSINOE SPP CAUSING SCAB DISEASES OF CITRUS AND ITS EPIDEMIOLOGIC IMPLICATIONS

Genetic differences among three citrus scab pathogens were investigate d. The three pathogens were (i) the cosmopolitan Elsinoe fawcettii cau sing citrus scab, (ii) E. australis from South America causing sweet o range scab, and (iii) Sphaceloma fawcettii var. scabiosa from Australi a causing Tryon's scab. In a companion study, we were unable to differ entiate these taxa morphologically, but were able to differentiate E. fawcettii, E. australis, and S. fawcettii var. scabiosa pathologically . Two pathotypes of E. fawcettii from Florida and two pathotypes from Australia were distinguished on the basis of host range. Restriction a nalysis of the amplified internal transcribed spacer (ITS) of ribosoma l DNA with several endonucleases and sequence analysis of the ITS read ily differentiated E. australis from E. fawcettii and S. fawcettii var . scabiosa. Random amplified polymorphic DNA (RAPD) analysis indicated that E. fawcettii isolates from Australia and from Florida were more closely related to each other than to E. australis isolates from Argen tina. However, all Australian isolates were separable from all Florida isolates by their RAPD profiles. There was a good correspondence betw een the RAPD profiles and the two pathotypes identified in Australia. Molecular analysis will be a rapid, useful tool in identifying exotic types of citrus scab on shipments of fruit and help reduce introductio ns of these types into new areas.