GENETIC VARIATION IN A WORLDWIDE COLLECTION OF THE SUGARCANE SMUT FUNGUS USTILAGO SCITAMINEA

THE sugarcane smut fungus, Ustilago scitaminea, first appeared in Australia in the Ord River Irrigation Area (ORIA) in July 1998. The most likely source of this infection was thought to be wind blown spores from Indonesia. Currently, the sugar industries of eastern Australia, Fiji and Papua New Guinea are still free of the disease. However, the risk of a smut incursion into eastern Australia is very high. Australian sugarcane cultivars are currently being screened in Indonesia and the ORIA to obtain smut resistance ratings, and results show that 70% of Australian cultivars are susceptible. As the use of resistant cultivars is the best option for long-term control of smut, a high priority of Australian sugarcane breeding programs is to increase the level of smut resistance in commercial cultivars. However, successful disease control requires an understanding of the level of diversity in the pathogen population. Information on the smut pathogen present in Australia and neighbouring sugar industries will enable plant breeders to select appropriate breeding strategies, including germplasm selection, for increased resistance in Australian sugarcane. The DNA fingerprinting technique of amplified fragment length polymorphisms (AFLPs) was used to assess genetic variation between isolates of the sugarcane smut fungus. The fungal collection comprised 38 isolates from 13 countries with some isolates collected from the same sugar industry 15 years apart. The technique revealed a low level of variation at the genomic DNA level, but a divergent group of isolates from Southeast Asia was identified. Sugarcane smut spores from this region could show different virulence patterns on Australian cultivars and could constitute another incursion threat to the Australian sugar industry.