Role of Root Colonizing Trichoderma Species in Management of Alternaria Leaf Blight of Asalio (Lepidium sativum L.) Caused by Alternaria alternata

Lepidium sativum an important medicinal plant with immense pharmacological properties has been observed to be generally affected by many fungal pathogens in India particularly Alternaria alternata characterized by the appearance of brown necrotic spots on the leaf margin affecting the herb yield. Root colonizing PGPF (plant growth promoting fungi) have been reported to produce substances such as plant hormones to allow plants to utilize decomposing organic matter through mineral solubilization and to suppress plant pathogens in the rhizosphere by antagonistic mechanisms, such as the production of hydrolytic enzymes, aggressive mycoparasitism, competition for saprophytic colonization, and the induction of plant systemic resistance. The effect of six species of Trichoderma isolated from different crops of rhizosphere and their efficacy was assessed under in vitro and in vivo conditions. Under in-vitro conditions, they were screened for their qualitative traits viz., IAA production, phosphorus solublizing activity and ammonia producing activity. Biomass determination and bioefficacy tests were performed against Alternaria alternata. The six Trichoderma species viz., T. koningii, T.ressei-1 and T.longibrachiatum produced higher quantity of IAA. The tri-calcium phosphate solublization activity was recorded only with T.asperellum and T. harzianum. The T. koningii and T.ressi-2 medium ammonium producer while rest four Trichoderma species were minimum ammonium producer. Out of six species of Trichoderma highest suppression was recorded with T.ressei-2 towards the Alternaria alternata. However, the highest inhibition was recorded by metabolite of T. asperellum isolates that corresponds to 38.75 percent reduction in mycelia growth when growth medium was non-amended with znso4. Similarly, the highest inhibition was recorded in metabolite of T.ressei-2 isolates when growth medium was amended with znso4. The highest biomass production of T. ressei-2 was recorded with znso4 amended medium while the highest biomass of T. ressei-1 was recorded with non znso4 amended growth medium. The effect of inoculation of fungal bioagent along with FYM and znso4 was found significant on relative water content (RWC), chlorophyll content, membrane stability index (MSI) and disease index under in-vivo conditions. The minimum disease incidence of Alternaria leaf blight was recorded with the soil application of either T.ressei-2+FYM + znso4 or T.ressei-1+FYM + znso4.