Biological control of onion basal rot disease using Trichoderma harzianum and induction of antifungal compounds in onion set following seed treatment

Trichoderma harzianum KUEN 1585 (commercial product, Sim®Derma) was tested to determine its effect on the mycelial growth of Fusarium oxysporum f. sp. cepae (FOC) in dual culture and its control of basal rot disease in pot- and field-grown onion sets. The abilities of T. harzianum to induce the production of antifungal compounds in sets and to increase onion set diameter were also studied. In pot experiments, where the soil was inoculated with a pathogenic isolate of FOC, seeds were coated with T. harzianum at the dosage of 10 g kg−1 seed. In field experiments, seeds coated with T. harzianum were sown in soil naturally infested with the pathogen. T. harzianum inhibited mycelial growth of the pathogen in vitro. Seed treatment with T. harzianum decreased disease incidence comparable to the imidazole fungicide, prochloraz in both pot and field experiments. It also enhanced bulb diameter of sets, especially in the pot experiment. Extracts from onion sets grown from treated seeds under both conditions were fractionated by thin-layer chromatography for their antifungal compounds. Most of the fractions obtained from the sets of T. harzianum-treated seeds showed high antifungal activity against the pathogen. This study suggests the possible role of T. harzianum in the induction of antifungal compounds against F. oxysporum f. sp. cepae in onion sets.