Dry-Season Survival of Rhynchosporium oryzae in Rice Leaves and Stored Seeds

Abstract

Rhynchosporium oryzae Hashioka & Yokogi causes leaf scald disease in many rice varieties in West Africa (1, 7, 8). Preliminary data suggest that R. oryzae does not survive in soil (6). A secondary host of R. oryzae has not been identified at the University Farm (UF), University of Liberia (unpublished data). Rhyncho? sporium oryzae is seedborne and rice seeds might be important in spreading leaf scald disease (4, 6). Very little is known about dry-season survival of R. oryzae in lowland tropical ecosystems. The objective of this study was to determine if R. oryzae can survive in rice leaves and seeds during the dry season (November to April) in Liberia. After harvest on October 18, 1982, all rice plants ofthe variety Lac 23 in three of several 4.5 m x 2.4 m plots at UF were either left standing, placed on soil surface, or buried 10 cm deep in soil, respectively. In October, 1983, after harvest, plants in one plot were left standing. Sets of 25 leaves with leaf scald symptoms from another plot were placed on the surface of the soil and held in place at the proximal end with wooden stakes. Other sets of 25 leaves with leaf scald symptoms from a third plot were placed between nylon mesh and buried 10 cm deep in soil. Ten leaves were retrieved periodically from each ofthe three treatments for each year and kept separate. Five 4 mm diam disks per leaf from scald lesions for each ofthe 10 leaves from each treatment were surface-sterilized