Isolation, morpho-physiological and molecular characterization, phylogenetic analysis of Trichoderma asperellum in Bangladesh.

Abstract

The experiment was conducted at the Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh to identify T. asperellum in a countrywide screening program and to evaluate its antagonistic effect against several soil borne pathogens. Samples were collected from the rhizosphere soil of 49 different crops in 107 different locations in Bangladesh, especially, considering the several isolates of T. asperellum for purification. Based on morphological and physiological features, fifteen isolates were selected. Of these, the isolates of TR27 and TR45 were grown and sporulated at 40 °C except all the isolates with 35 °C, and particularly, showing a decrease of mycelial growth across all the isolates for increasing pH. Meanwhile, T. asperellum showed significant antagonistic effects against Fusarium oxysporum, Sclerotium rolfsii and Pythium aphanidermatum, resulting in reducing foot and root rot, collar rot and damping off diseases, respectively. Four isolates were selected for molecular characterization among 15 isolates in terms of higher mycelial growth and spore density in-vitro condition, isolates of (TR27) Sadar, Moulvibazar (Rice), (TR45) Sadar, Mymensingh (Sweet gourd), (TR70) Chapra, Chapai Nawabganj (Sesame) and (TR85) Nayanpur, Lalmonirhat (Maize) were studied at ITS and TEF region. Isolates of TR45, TR70 and TR85 were observed with 98% homology, and TR27 exhibited 88% in their respective closest isolates at ITS sequences. Isolates of TR27 and TR85 also exerted their respective nearest homology (96%), while TR45 showed 99%, and 93% homology with TR70 in TEF sequences. Isolates TR45, TR70 and TR85 were evidently determined as T. asperellum of 100% bootstrap value, and TR27 isolate was also recognized with 72% bootstrap value in the phylogenetic tree. However, complementary effects of significant superior homology and the greatest bootstrap value in the identification of T. asperellum were found as noteworthy. In the phylogenetic analysis, magnificent differentiation among the Trichoderma isolates within and among the groups of closely related species was observed in Tef1 region than reflecting maximum variability in the isolates of rDNA at ITS region, whereas demonstrating a higher transversion ratio and evolutionary divergence.