Two distinct Guignardia species associated with citrus in South Africa

Abstract

of the PCR products clearly distinguished the two species, provid- ing a quick yet reliable identification tool. Growth rate in culture also corresponded with the two species. The first species, G. citricarpa, is confirmed as the causal organism of CBS and is restricted to citrus. This fungus occurs in all major citrus-producing areas of South Africa, except the Western Cape. The pathogen can be isolated from hard spots, virulent spots, freckled spots and false melanose lesions from sweet orange, grapefruit, lemon and tanger- ine. The second species, which is harmless to fruit, can be isolated from symptomless citrus products, but also from avocado, mango, banana, cabbage tree and kumquat, which occur in various geo- graphical areas. Phytosanitary measures may be used against the export of citrus fruit suspected of being infected with CBS. The DNA tests we have devised are able, for the first time, to distinguish the pathogenic from the harmless endophyte of citrus and other plants.