Exploring the biocontrol efficacy of native isolates of Trichoderma spp. of Kasaragod district

Abstract

The study entitled “Exploring the biocontrol efficacy of native isolates of Trichoderma spp. of Kasaragod district” was carried out in the Department of Plant Pathology, College of Agriculture, Padannakkad during 2022-2024 with the objective of evaluation of selected native Trichoderma spp. of Kasaragod district for abiotic stress tolerance, plant growth promotion and biocontrol efficiency against damping off of brinjal. The evaluation of temperature tolerance of Trichoderma spp. revealed that the strains, Tr-5, Tr-12, Tr-41, Tr-43, KAU (T. asperellum), and Tr-40 (T. lixii) did not exhibit any mycelial growth or sporulation at 4°C, 10°C, 45°C and 55°C. At 15°C, the strain, Tr-40 showed the highest radial growth (0.85 cm), followed by Tr-41 (0.66 cm), while the KAU reference culture recorded the least growth (0.26 cm). All the strains demonstrated robust mycelial growth at the optimum temperature (30°C), almost on par with the control.

In drought and salinity tolerance assays, the strains displayed good mycelial growth and effective sporulation at 10 per cent polyethylene glycol (PEG) and 0.5 M NaCl concentration. However, at higher PEG levels (30% and 40%), radial growth was markedly reduced, and colonies exhibited irregular margins and a light fluffy texture, indicating stress. At 1.5 M NaCl concentration, the strains, Tr-5 (0.83 cm), Tr-12 (0.9 cm), and Tr-40 (0.8 cm) sustained mycelial growth with a light fluffy texture. None of the strains exhibited growth at 2.5 M NaCl. Compatibility of the strains of Trichoderma spp. with other biocontrol agents viz., Pseudomonas fluorescens, Metarhizium anisopliae, Lecanicillium lecanii, and Beauveria bassiana was assessed by the dual culture technique. The highest percentage compatibility (99.3%) was expressed by Tr-5 and Tr-12, followed by Tr-41 and Tr-43 (98.5%) with P. fluorescens. Regarding compatibility with fungal biocontrol agents, all the native strains of Trichoderma spp. and KAU culture showed good compatibility with B. bassiana, M. anisopliae and L. lecanii. But, the strain Tr-40 showed high per cent inhibition and less compatibility percentage with M. anisopliae (66.7%) and L. lecanii (33.58%). The root colonization of Trichoderma spp. on brinjal seedlings was visualised under a Zeiss compound microscope (400x, Axiocam 105 camera) at 15 DAS (days after sowing) under in vitro conditions. The presence of mycelia of these Trichoderma strains was observed on the surface of the roots of the brinjal seedlings. The effect of Trichoderma strains on plant growth was assessed using the paper towel method. The highest germination percentage was recorded in Tr-5 (83%) and Tr-41 (73%), and the least was in Tr-40 with 53%. The height of the seedlings (shoot + root length) was recorded as the highest in the Tr-5 (12.86 cm), followed by control (12.27 cm). Compared to other treatments, the Tr-5-treated seedlings showed good fresh weight (119.33mg), dry weight (20.66mg), and also vigour index (1072.66). Biocontrol efficacy of different strains of Trichoderma spp. in managing the damping off in brinjal was studied. In the seed application alone treatment (a1), germination of seeds was observed 3 DAS in treatments, a1t1, a1t2, a1t3, a1t5 and a1t9; and was 5 DAS in the control (t8). The highest germination percentage was observed in a1t3 (36.33%) and the lowest in t8 (13.33%). Here, the plants in control recorded the highest per cent disease incidence of 66.6% and in the case of a1t4 it was only 10 per cent. In the soil application alone treatments (a2), the germination of seeds was observed within 3 to 4 DAS, except the control (t8), where it was 5 DAS. Among all the treatments, the highest germination percentage was recorded in absolute control (59.9%) followed by treatments, a2t1, a2t2, a2t4, with 53.33 per cent. No disease incidence was recorded in a2t4. In the seed and soil combined application (a3), the highest germination percentage recorded was 66.67 in a3t1, in which no infected seedling was observed. The combined application of Trichoderma spp. showed a significant effect on the plant growth and the disease. The expression of defense-related genes in brinjal seedlings when exposed to Fusarium sp. was notably increased in the presence of T. asperellum strain Tr-5. There was a 3.47-fold increase in the expression of the PR-3 gene which codes for chitinase. This marked upregulation of the PR-3 gene highlights its role in enhancing defense responses and suppressing the pathogen