Distribution and diversity of native isolates of Trichoderma Spp. of Kasaragod district

Abstract

The study entitled “Distribution and diversity of native isolates of Trichoderma spp. of Kasaragod district” was carried out in the Department of Plant Pathology, College of Agriculture, Padannakkad during 2021-23 with the objective of characterization of the native isolates of Trichoderma spp. from different agro ecological units of Kasaragod district to understand their distribution, diversity and antagonistic potential. A purposive sampling survey was conducted at different locations within the agro ecological units (AEU 2, 7, 11, 13 and 15) of Kasaragod district. The isolation of native Trichoderma spp. from the collected soil samples in Trichoderma Selective Medium (TSM) using the dilution plate technique yielded a total of fifty five isolates. Of these, ten isolates were from AEU 2 (Northern coastal plains), seventeen from AEU 11 (Northern laterites), four from AEU 13 (Northern foot hills) and twenty four from AEU 15 (Northern high hills). Notably, no isolate was obtained from AEU 7 (Kaipad lands). Correlation analysis between the different soil parameters and the occurrence of Trichoderma spp. demonstrated a positive but non-significant correlation with soil pH (r = 0.288, p = 0.246), organic carbon content (r = 0.274, p = 0.271), available P (r = 0.063, p = 0.804) and available K (r = 0.059, p = 0.817), whereas a negative non-significant correlation was observed with available N (r = -0.339, p = 0.168). The cultural characteristics of the isolates were examined on three different media, viz., PDA (Potato Dextrose Agar), RBA (Martin’s Rose Bengal Agar) and TSM (Trichoderma Selective Medium). Typically, the isolates exhibited the highest growth rate on PDA (3.02 cm per day), followed by RBA (2.18 cm per day) and TSM (2.08 cm per day). There was variation in colony morphology and spore characteristics among the isolates across the three media. The isolates produced conidia that were globose, sub globose, ellipsoidal and elongated. Additionally, flask shaped and pin shaped phialides were observed in clusters of two to three. Preliminary screening against Sclerotium rolfsii recorded more than 60 per cent inhibition in isolates Tr 5, Tr 12, Tr 37, Tr 38, Tr 40, Tr 41, Tr 43, Tr 48, Tr 52 and Tr 55, which were subsequently selected for further investigation. The antagonistic potential of these selected isolates against soil borne fungal pathogens, Pythium aphanidermatum, Phytophthora capsici, Rhizoctonia solani, Sclerotium rolfsii and Fusarium oxysporum f. sp. cubense was evaluated using the dual culture technique. The highest inhibition rate of 79.26 per cent against P. aphanidermatum was noticed in Tr 40, while cent per cent inhibition against P. capsici and R. solani was observed in the isolates, Tr 5, Tr 12, Tr 38, Tr 40, Tr 41 and Tr 43. The isolate, Tr 43 exhibited the maximum inhibition against S. rolfsii (82.96%) and Tr 40 exhibited the highest inhibition (73.33%) against F. oxysporum f. sp. cubense. All the isolates displayed cellulose hydrolyzing capacity, with Tr 43 recorded the highest value of 0.96. The compatibility of the isolates with the fungicides, copper hydroxide (0.1 %, 0.15% and 0.2 %), mancozeb (0.25 %, 0.3% and 0.35 %), carbendazim (0.15 %, 0.2% and 0.25 %), hexaconazole (0.15 %, 0.2% and 0.25 %) and metalaxyl (0.05 %, 0.1% and 0.15 %) and the insecticides, chlorpyriphos (0.05 %, 0.06% and 0.07 %) and carbosulfan (0.04 %, 0.05% and 0.06 %) was studied. The isolate Tr 55, showed relative compatibility with copper hydroxide and mancozeb at the concentrations, 0.15 and 0.3 per cent respectively. Carbendazim at all the tested concentrations exhibited cent per cent inhibition in all the isolates. The isolates exhibited more than 75 per cent inhibition with hexaconazole (0.2 %) and over 50 per cent inhibition with metalaxyl (0.1 %). The insecticides were relatively more compatible with the isolates. Particularly, isolates, Tr 5, Tr 12, Tr 41, Tr 43, Tr 48 and Tr 52 showed complete compatibility (zero inhibition) with carbosulfan at 0.05%. The molecular characterization of the isolates through ITS-PCR revealed Tr 5, Tr 12, Tr 38, Tr 41, Tr 43 and Tr 48 as Trichoderma asperellum; Tr 37, Tr 52 and Tr 55 as T. koningiopsis and Tr 40 as T. lixii. Furthermore, RAPD analysis employing six primers from the OPB series (OPB-1 to OPB-6) revealed the genetic polymorphism among the isolates. Out of the total 42 scorable bands, 41 were polymorphic and the per cent polymorphism was 97.62 per cent.