Differentiation by Molecular Analysis ofElsinoespp. Causing Scab Diseases of Citrus and Its Epidemiological Implications

Genetic differences among three citrus scab pathogens were investigated. The three pathogens were (i) the cosmopolitan Elsinoe fawcettii causing citrus scab, (ii) E. australis from South America causing sweet orange scab, and (iii) Sphaceloma fawcettii var. scabiosa from Australia causing Tryon's scab. In a companion study, we were unable to differentiate 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 analysis of the amplified internal transcribed spacer (ITS) of ribosomal DNA with several endonucleases and sequence analysis of the ITS readily 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 Argentina. However, all Australian isolates were separable from all Florida isolates by their RAPD profiles. There was a good correspondence between 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 introductions of these types into new areas.