Influence of adjuvants on spore germination, desiccation tolerance and virulence of Fusarium anthophilum on barnyard grass (Echinochloa crus-galli)

Spores of Fusarium anthophilum isolate 16c, a pathogen of barnyard grass, were harvested from 10 day old semi-defined culture medium with a C:N ratio of 5:1 and suspended in pure white coconut oil, diethanolamine, PZ, RG(22) or volk, each at 0.2, 0.5, 1 or 2% Spore suspension in distilled water was considered as the control. Droplets (3-mu L) of spore suspensions were separately placed on semi-permeable membrane and stored at 25 degrees C with 15% RH for 0, 6, 12 or 38 days. At each interval, four replicated discs of each treatment were place on PDA for 8 h to evaluate germination rate and germ tube elongation. In glasshouse experiments, spores suspended in the above mentioned adjuvants were sprayed onto seedlings of barnyard grass to determine their influence on the virulence of the pathogen. For nondesiccated spores, the highest germination was achieved with coconut oil 2%. After 6-, 12- or 38-day desiccation period, the germination of spores suspended at each concentration of coconut oil or volk at 1% was significantly higher than those suspended in the other adjuvants or water Germ tubes of non-desiccated spores which were suspended in each concentration of volk, 0.2 or 0.5% PZ, 0.5% diethanolamine or 0.5% coconut oil were significantly longer than other treatments. The enhancing effect of coconut oil 0.5% on germ tube elongation was more pronounced after 6, 12 and 38 day desiccation periods. All adjuvants used in this study significantly enhanced disease expression, compared with water, but the effect of coconut oil 1%, PZ 0.5% and RG 0.2% was higher than diethanolamine at 2% and volk at 1%.