Tospoviruses Infecting Capsicum and Tomato in Australia
Sharman M1,2, Persley D1,2, McMichael L2, Thomas J2
1Cooperative Research Center for Tropical Plant Protection, St Lucia, Queensland, Australia 4072.
2Department of Primary Industries, Plant Pathology Group, 80 Meiers Road, Indooroopilly Australia 4068
Correspondence: murray.sharman@dpi.qld.gov.au
Tomato spotted wilt virus (TSWV) has caused serious sporadic epidemics in capsicum and tomato crops in all major growing regions of Australia since it was first described in the 1920s. The frequency and distribution of outbreaks increased in the 1990s, with the arrival and dispersal of the western flower thrips being one factor favoring this situation. During 2002 in South Australia, TSWV caused crop failures of up to 100% in glasshouse crops of capsicums with the Tsw gene for resistance to TSWV. These Tsw virulent strains were shown to cause severe systemic infection on Capscium chinense genotypes PI 152225 and PI 159236, which have the Tsw gene. Minimal differences were found between the nucleocapsid (N) gene amino acid sequences of the Tsw virulent and avirulent TSWV strains from Australia. Other biological and serological similarities were also shown between Tsw virulent and avirulent TSWV strains, including a hypersensitive reaction on TSWV resistant tomatoes with the Sw-5 gene. This is the first field record of Tsw virulent strains of TSWV in Australia. Capsicum chlorosis virus (CaCV) was first detected in Australia in 1999 (McMichael LA et al. 2002. Australasian Plant Pathology 31: 231¨C239). In the state of Queensland it has caused epidemics and symptoms, in capsicum crops, similar to those caused by TSWV. However, in most instances it infects up to 5¨C10% of capsicum plants in a crop. It is a distinct member of serogroup IV, with N gene nucleotide and amino acid sequence identities of <85% with other members of this group, and is most closely related to Watermelon silver mottle virus. CaCV infects all capsicum and tomato cultivars tested, including those with the TSWV resistance genes Tsw and Sw-5. However, resistance has been found in one C. chinense PI line from the USDA germplasm collection. Natural hosts are capsicum (pepper), tomato, groundnut and Hoya spp. CaCV is transmitted by Thrips palmi and Frankliniella schultzei. Transmission tests with WFT have been negative. CaCV affects all capsicum production areas in Queensland and recent records from other states (Western Australia and New South Wales) and Thailand, suggest a wide distribution in northern Australia and South East Asia.
