Phytophthora boehmeriae: a new disease of cotton found in Greece
A new disease of cotton (Gossypium hirsutum) was observed for the first time in Greece in August 1993 in Larissa (at first localized in an area of 20 ha) and Volos countries, and in August and September 1995 in Trikala and Phthiotis counties. The disease is a severe boll rot. Initially, localized spots appear and progressively coalesce to cover the whole cotton boll. Infected tissues turn almost black. Infection is generally restricted to the lower half (or two-thirds) of cotton plants. Phytophthora boehmeriae was isolated from diseased plants. Colony morphology, growth rate, features of asexual and sexual structures, maximum growth temperatures were examined. The pathogenicity of the Greek isolates was confirmed by artificial inoculation of detached cotton bolls. In addition, the analysis of a-esterase isozyme revealed a unique pattern for P. boehmeriae when compared to P. cactorum and P. parasitica.
P. boehmeriae was first described in 1927 by Sawada as a new species on Boehmeria nivea (ramie – a fibre plant), in Formosa (Taiwan). This fungus is also reported to cause brown rot on citrus fruits in Argentina, root rot of Pinus patula in Australia, and cotton boll rot in China. Paper mulberry (Broussonetia papyrifera) is also reported as a host in China.
The geographical distribution of the fungus is the following:
EPPO region: Greece
Asia: China, Japan, Taiwan
South America: Argentina
Oceania: Australia (Queensland, New South Wales)
Chinese papers report that: 1) oospores of P. boehmeriae can overwinter in the soil and act as the primary infection source of cotton boll rot (Zheng et al., 1992); 2) sporangia or oospores can be detected on seeds from infected bolls and appear to be able to transmit the disease to plants (Zhang et al., 1995).
The authors stressed that this is the first report of Phytophthora boehmeriae in Europe, and that this disease could be a serious threat to cotton-growing countries.
Phytophthora boehmeriae boll root: A new threat to cotton cultivation in the Mediterranean region.
Phytoparasitica, 26(1), 20-26.
Zhang, X.Z.; Ling, P.L.; Ma, P., Chen, X.H. (1995) Studies on cotton seed-borne pathogen of Phytophthora boll rot and its lethal temperature.
Acta Phytophylactica Sinica, 22(1), 67-69 (abstract).
Zheng, X.B.; Lu, J.Y.; He, H., Wang, T.L., Wang, H.Y. (1992) Oospores of Phytophthora boehmeriae overwintered in soil as an infection source of cotton boll disease.
Acta Phytophylactica Sinica, 19(3), 251-256 (abstract).