New taxonomy of Alternaria species from citrus
The taxonomy of citrus diseases caused by Alternaria species has been subject to controversy for many years, which has led to some confusion in the literature. A recent taxonomic revision of some Alternaria pathogens found on citrus has been done by Simmons (1999), with emphasis on pathogens associated with brown spot of tangerine and related hybrids and cultivars (also called brown spot of Minneola tangelo - EPPO Alert List) and leaf spot of rough lemon (Citrus jambhiri). Morphological characteristics of 135 isolates originating from citrus-growing regions of Colombia, Israel, Turkey, South Africa and USA (Florida) and taken from citrus lesions were examined under controlled culture conditions. This study showed that none of the isolates studied could be attributed to Alternaria alternata (although in many earlier studies, brown spot of Minneola tangelo was attributed to A. alternata). 77 isolates could be assigned to 10 new species of Alternaria, the remainder were unique or unstable in culture and could not be assigned to a species. Results showed that most isolates causing brown spot of Minneola tangelo in Florida and Colombia belong to A. tangelonis sp. nov. (20 isolates), and that brown spot of Minneola tangelo in Israel, Turkey and South Africa (15 isolates) is mainly caused by A. turkisafria sp. nov. The following new species have also been described from tangerines (C. reticulata) and tangelos (C. paradisi x C. reticulata) showing brown spot: A. citriarbusti sp. nov. (tangelo in Florida, US, 4 isolates), A. toxicogenica sp. nov. (tangerine in Florida, US, 1 isolate), A. colombiana sp. nov. (tangelo in Colombia, 1 isolate), A. perangusta sp. nov. (tangelo in Turkey, 1 isolate), A. interrupta sp. nov. (tangelo in Israel, 1 isolate), A. dumosa sp. nov. (tangelo in Israel, 1 isolate). In this study, it has also been found that leaf spot of rough lemon in Florida is essentially caused by A. limoniasperae sp. nov., and to a lesser extent by A. citrimacularis sp. nov. It is concluded that the disease called 'brown spot of Minneola tangelo', observed in many citrus-growing regions of the world, is caused by several distinct species of Alternaria.
Note: this paper mentions the occurrence of Alternaria brown spot in Colombia, which is a new record according to the EPPO Secretariat.
Sources
Simmons, E.G. (1999) Alternaria themes and variations (226-235). Classification of citrus pathogens.
Mycotaxon, 70, 263-323.