Abstract
The plant growth-promoting and antagonistic fungi Trichoderma contain a large number of strains that are beneficial to agriculture mainly as biological control agents (BCAs) against a wide range of plant pathogens. This study was intended to corroborate the positive relationships of molecular and morphological characteristics as well as the physiological and biochemical features of Trichoderma species. Nineteen Trichoderma isolates, collected from different locations in Bangladesh, were characterized using morphological, physiological, biochemical and molecular means. Among the Trichoderma isolates, 14 isolates (TR01, TR07, TR08 and TR10-TR20) were identified as T asperellum, three isolates (TR02, TR04 and TR06) were identified as T. virens, and the other three isolates (TR03, TR05 and TR09) were identified as T. harzianum based on the different morphological characteristics. These results matched the molecular characterization using ITS region and tefl nucleotide sequencing. Additionally, their antifungal actions were assessed in vitro through dual culture and culture filtrate assay. Dual culture and culture filtrate assays against six phytopathogens revealed that nine of the nineteen isolates showed significant antifungal activities. The isolate T. harzianum TR05 showed the highest inhibition against Fusarium oxysporum (79.9% and 87.8%), Rhizoctonia solani (76.9% and 86.7%), Fusarium circinatum (74.3% and 86.8%) and Phomopsis vexans (74.3% and 86.8%) in dual culture and culture filtrate assay, respectively, and followed by T. asperellum TR08 and T. virens TR06. TR08 had the highest inhibition against Sclerotium rolfsii (73.7% and 88.5%) and Pythium aphanidermatum (76.9% and 85.7%) in dual culture and culture filtrate assay, respectively, and followed by TR05 and TR06. These findings were in agreement with the activities of their extracellular hydrolytic enzymes, including chitinase, B-1,3-glucanase and proteinase. The highest level of chitinase activity was found from TR08 (12.8 U/ml), followed by TR06 (10.6 U/ml) and TR05 (7.63 U/ml); the maximum level of B-1,3-glucanase (13.9 U/ml) was observed from TR05, followed by TR08 (7.67 U/ml); and; the highest level of proteinase activity was recorded from TR05 (10.5 U/ml) followed by TR08 (6.70 U/ml). In a pot experiment under greenhouse conditions, tomato seeds inoculated with TR05 (seed treatment) showed the lowest disease incidence (5.36%) and the highest germination rates (90.3%), as well as providing superior results in root length (12.2cm), shoot length (12.5cm), dry weight (5.40g) and seedling vigor (2,430) than seeds inoculated with TR08 and TR06. In case of soil treatments, TR08 showed the lower disease incidence (9.78%), as well as providing greater results in root length (13.8cm), shoot length (20.2cm), dry weight (5.93g) and seedling vigor (3,350) than TR05 and TR06. Our results indicate that isolates TR05 and TR08 have the potential to be effective biocontrol agents against these phytopathogenic fungi, using as seed and soil treatments under pot condition.