MORPHOLOGICAL AND CYTOLOGICAL STUDIES OF SCLEROSPORA SPECIES ON CORN IN THAILAND

Abstract

The downy mildew (DM) diseases reported thus far on corn (Zea mays L.) in Thailand are sorghum DM (Sclerospora sorghi Weston and Uppal) and brown stripe DM (Sclerophthora raysseae var. zeae Payak and Renfro). The former is of greater economic importance. It occurs in 24 provinces and 50 to 100% loss in yield has been reported in the main corn-growing areas (2). Morphological studies of the corn DM pathogens have been made by many workers. They found that conidia were spherical, measured 16-29 x 11-21 µ (av. 22.3 x 14.3 µ) and germinated by forming a germ tube. No oospores have been observed in corn tissue. The conidia of S. sorghi reported by Weston and Uppal (7) were suborbicular, hyaline with thin walls, germinted by hyphae and measured 15-28.9 x 15-26.9 µ. Conidiophores were erect, had basal cells and a main axis and were dichotomously branched. The basal cell was approximately 100-150 µ on length, with 7-9 µ in width. The main axis was extended by 80-150 µ.