Factors affecting mass production of Duosporium yamadanum in rice grains.

Duosporium yamadanum (Matsuura) Tsuda & Ueyama is a pathogenic fungus that attacks purple nutsedge, Cyperus rotundus, L. in Brazil. Occasionally, it is found causing severe natural epiphytotics of leaf blight on that host in the field. Exploratory studies have already indicated that this fungus has potential for the development of a mycoherbicide. To help confirm its potential, we studied mass production of inoculum of D. yamadanum in solid fermentation using polished rice as the substrate for cultivation of D. yamadanum. The effects of the following factors were investigated for their influence on conidial production: water content, length of incubation period before the opening of the plastic bags containing the substrate and addition of supplements to the substrate. Maximum production of conidia was obtained with a water content of 40–60% in the substrate (w/v), with average production at each harvest of 2.5 ́ 105 conidia per gram of substrate. Water contents above 60% inhibited growth and sporulation. Opening bags containing the inoculated substrate after 3 to 4 days resulted in the highest levels of sporulation; average of 3.0 ́ 105 conidia per gram of substrate. The supplementation of the substrate with calcium carbonate did not significantly increase the sporulation levels compared to controls, whereas the addition of urea or sucrose led to a significant reduction in sporulation; average of 9.0 ́ 104 conidia per gram of substrate.