Lipoxygenase-related defense response induced by Trichoderma viride against Aspergillus niger Van Tieghem, inciting collar rot in groundnut (Arachis hypogaea L.)

Groundnut varieties grown in non-infested soil (T-1), pathogen (Aspergillus niger)-infested soil (T-2), and seed treatment with Trichoderma viride JAU60 followed by challenge with fungal pathogen (T-3), showed significant differences in percent disease incidence of collar rot in pot culture. Percent disease incidence was higher in GG-13, GG-20 (susceptible) followed by GAUG-10 (moderate), and minimum in J-11, GG-2 (tolerant varieties) in A. niger-infested pot culture at 15 days after sowing (DAS). Seed treatment (T-3) of T. viride reduced approximately 51% to 58% disease incidence in different groundnut varieties. The lipid peroxidation product - malondialdehyde (MDA) - content was found to be higher in susceptible varieties grown in pathogen-infested soil (T-2) and it was significantly reduced to 56% under T. viride treatment (T-3) at 12 DAS. However, tolerant varieties reduced the MDA content by 60% in T-3 as compared with the T-2 at an earlier stage (9 DAS). The lipoxygenase (LOX) activity rose approximately 3.5-fold in tolerant varieties upon infection (T-2) and groundnut seed treated with T. viride (T-3) at 12 DAS. Trichoderma treatment (T-3) maintained a high level of LOX compared with T-2, particularly in tolerant varieties. The pathogen infection ability was positively correlated with LOX activity in tolerant and moderately tolerant varieties of T-2 seedlings. MDA content was positively correlated with disease incidence in susceptible varieties followed by induction of LOX activity under T. viride JAU60 treatment (T-3). T. viride JAU60 signifies induction of a LOX-related defense response to combat the collar rot disease incidence in groundnut seedlings.