Curvularia Leaf Spots of Yams (Dioscorea spp.)

Abstract

Leal spots caused by Curvularia geniculata, C. eragrostidis and C. sp. were found and identified on Dioscorea rotundata and D. alata yams in Puerto Rico. In pathogenicity tests and field trials, C. eragrostidis caused more lesions than either C. geniculata or C. sp. C. geniculata and C. eragrostidis caused round to oval spots with irregular margins (3 x 3 mm) scattered on yam foliage. C. sp. caused blotches (42 x 27 mm) on leaf margins. C. geniculata spores are falcate with five cells measuring 18 x 8 H (min), 27 x 14 µ (max), and 25.3 x 11.1 µ (mean); those of C. eragrostidis are oval with four cells and measured 18 x 11 µ (min), 37 x 20 M (max) and 26.1 x 15.4 µ (mean); and those of C. sp. spores are oval to round with four cells measuring 20 x 9 µ (min), 24 x 11 µ (max) and 21.9 x 9.8 µ (mean). In field trials, the D. rotundata cultivars Guinea Blanco and Guinea Negro and the D. alata yams Florido, Binugas, Forastero and Purmay were found susceptible, whereas Gemelos, Gunung, Kinampay and Moresby were resistant to Curvularia leaf spots. Curvularia spp. were found to be tuber borne, infecting both cortex and internal tissues. In Guinea Blanco cultivar more than half of the plants were infected 240 days after planting, with a maximum foliar necrosis of 31%.