Disease Note.

First Report of Phytophthora boehmeriae Causing Boll Rot of Cotton. E. J. Paplomatas, Benaki Phytopathological Institute, 145 61 Kifissia-Athens, Greece . K. Elena, and D. Lascaris, Benaki Phytopathological Institute, 145 61 Kifissia-Athens, Greece. Second author also at: National Agricultural Research Foundation, Athens, Greece. Plant Dis. 79:860. Accepted for publication 5 June 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0860C.

A severe boll decay was observed on cotton (Gossypium hirsutum L.) in Larissa County, Greece, in August 1993. The boll rot was restricted to the lower half to two-thirds of cotton plants. Diseased bolls were severely decayed, with the subtending dried carpels being dark-brown to black. White patches of fungal mycelium bearing numerous sporangia were present on the surface of the rotten bolls. Oospores were observed on the cotton lint and internal carpel surface of infected bolls. The disease was localized in an area of about 20 hectares in a field that was cropped to cotton the previous season, with the cotton residue being buried by plowing. During the 1993 growing season, the crop was irrigated 2 to 3 days before a heavy rainfall. Disease onset occurred on the lower bolls of the plants following these conditions, suggesting that the inoculum was splash-dispersed from the soil. The fungus was isolated from all diseased cotton bolls and identified as Phytophthora boehmeriae based on the following characteristics: sporangia ellipsoid to nearly spherical, mostly 39 to 48 × 29 to 35 μm, ratio 1.2:1.5, bearing papilla oogonia 29 to 40 ?m antheridia mostly amphigynous (with only a few paragynous an-theridia occasionally formed) maximum growth temperature 33°C. Artificially inoculated bolls developed symptoms similar to those observed in the field and the fungus was reisolated from infected bolls. This is the first report of P. boehmeriae causing boll rot of cotton in Europe (1).