Damping-off of asparagus caused by Rhizoctonia solani KÜHN

Abstract

A fungal disease was observed on seedling of asparagus grown under vinyl house conditions in the spring of 1989 in Nagasaki Pref., Japan. The common symptom was damping-off of seedlings. The mycelium, suggestive of Rhizoctonia sp., was found on chlorotic, water soaked or brownish host substrate. The isolate (NR-59) formed dilutery brown colonies with aerial hyphae and sclerotia, but without clear zonation on culture media. The fungus grew well on potato dextrose agar over a temperature range of 15-34°C, optimum near 28°C. The hyphal branches arised at approximately right angles with septum near to the junction. The width of the mature main hyphae was 6-10 μm (mean 8 μm) and the number of nuclei per cell was 4-6 (mean 5.2) . The fungus was identified as Rhi;octonia solani KUHN. According to the anastomosis grouping by J. R. Parmeter, Jr. et al. (1969), the isolate belonged to AG 4. The cultural type of the isolate by B. Watanabe et al. (1966) was type III A. This appears to be the first record of damping-off on cultivated asparagus in Japan.