Effect of pesticides on the seed-borne fungi and fungal succession on rice in Malaysia

Abstract

Three fungicides (thiophanate methyl, thiram and 2-methoxyethyl mercury chloride) and two insecticides (carbaryl and malathion) were used to study the effects of each of the pesticides on the seed-borne fungi of rice. A total of over 40 species in 23 genera of fungi, including several pathogenic forms was isolated from the untreated flowers and seeds. Fewer fungi were encountered on flowers still enclosed within the sheaths and the largest number of fungi was isolated from seeds just before harvest. Storage of the seeds for 6 months eliminated a large number of field fungi that was originally present on freshly harvested rice seeds. The fungi that persisted on the stored seeds, however, were species reported to be capable of grain deterioration and mycotoxin production. With the pesticide-treated seeds, fewer fungi were isolated from those treated with thiram or 2-methoxyethyl mercury chloride than with any of the other chemicals. Species of Curvularia were isolated as the principal fungi on seeds treated with any of the chemicals.