A low cost mass culture medium for Trichoderma spp. to be used in the control of damping off disease of big onion (Allium cepa L.).

Abstract

Big onion (Allium cepa L.) is a condiment grown for its flavorful bulbs in Sri Lanka. The most common soil-borne seedling disease of big onion seen at the nursery stage is damping off caused by Fusarium solani which results in severe seedling mortality. As Trichoderma spp. are widely used bio control agents of many fungal pathogens, Trichoderma spp. present in fifty-five onion fields in Sri Lanka were isolated and identified with a view to use in the control of Fusarium solani. Frequently isolated Trichoderma spp. (Trichoderma virens, Trichoderma asperellum) were evaluated for their ability to control the growth of Fusarium solani using dual culture assays. Both tested Trichoderma spp. suppressed the mycelial growth of Fusarium solani significantly (P < 0.05). Two low cost mass culture media i.e. rice bran + saw dust, molasses + yeast were evaluated to mass produce the Trichoderma isolates for field applications. Both Trichoderma spp. showed a significantly (P < 0.05 ) high level of spore production in molasses + yeast medium 14 days after inoculation producing 1.15  0.05  1010 and 1.36  0.03  1010 spores/ ml (n=3) for T. virens and T. asperellum respectively as compared to 1.92  0.07  108 and 2.23  0.23  108 spores/ml (n=3) in the rice bran + saw dust medium. The results obtained were analyzed using t test with Minitab 16. Data indicated that molasses + yeast medium is more suitable for mass production of the two Trichoderma spp. The mass cultured Trichoderma spp. were then added to a carrier medium consisting of Talc at a rate of 1: 2 (v/w). Trichoderma asperellum alone or Trichoderma asperellum and Trichoderma virens combination were inoculated as seed coating or soil treatment at a concentration of 107 CFU/g under greenhouse conditions and the inocula reduced the incidence of damping off disease significantly (P ≤ 0.05) It could be concluded that the two Trichoderma spp. could be effectively used in the management of damping off disease.