Natural occurrence of citrinin in rice grains and its biocontrol by Trichoderma hamatum

Paddy rice was sampled from El-Sharkia, El-Gharbia, El-Dakahlia and Kafr EI-Shekh governorates, Egypt. Of the 30 samples taken, ten were contaminated with the mycotoxin citrinin. An average of 6.79 x 10(4) fungal spores per gram rice was found. The isolated fungi represented 47 species and 28 genera. The predominant genera were Aspergillus, Cladosporium and Penicillium. Aspergilli were represented by 22 species; Aspergillus niger and A. flavus had the highest occurrence. Penicillium viridicatum produced the highest amount of citrinin on glucose ammonium nitrate salts broth and rice grains, and hence this isolate was selected as a good producer of citrinin in this study. The presence of Trichoderma hamatum reduced the amount of citrinin produced by P. viridicatum compared with its respective control. The excessive growth of T hamatum on P viridicatum was increased with time. Viability of R viridicatum conidia decreased by T hamatum with an increase in the incubation period. Chitinases and 1,3-beta-glucanase enzyme activity of T hamatum increased with extending the incubation period on P viridicatum mycelia up to maximum values at 72 and 84 h, respectively. T hamatum led to a decrease in the production of citrinin by P. viridicatum on rice grains compared with the respective control values.