Physiological Responses of Phaseolus vulgaris to Damping-Off Disease Control Using Mutant Trichoderma spp.

The effectiveness of biological control agents is increasingly recognized in sustainable agriculture, particularly in combating soil-borne pathogens such as Rhizoctonia solani , which causes damping-off disease in beans. This study investigates the potential of mutant Trichoderma species to enhance plant resistance and improve physiological responses in Phaseolus vulgaris . Five species of Trichoderma ( T. harzianum NAS110, T. aureoviride NAS106, T. atroviride NAS112, T. afroharzianum NAS107, and T. lixii NAS114) were subjected to gamma irradiation to induce mutations, and their effects on the growth of R. solani were assessed. The experimental design included a completely randomized setup with statistical analyses to determine the significance of differences in disease incidence. Key physiological parameters, including peroxidase enzyme (POD) and polyphenol oxidase (PPO) activities, chlorophyll a and b levels, carotenoid concentrations, proline content, and lipid peroxidation were meticulously measured. The analysis revealed that treatment with mutant Trichoderma significantly increased POD and PPO activities compared to controls, indicating a heightened defense response. Moreover, treated plants exhibited higher chlorophyll and carotenoid levels, along with increased proline accumulation, which collectively contribute to enhanced photosynthetic efficiency and stress tolerance. Notably, the reduction in malondialdehyde (MDA) levels and lipid peroxidation in mutant-treated plants suggests decreased oxidative damage and improved cellular integrity. The evaluations showed that the mutant isolates decreased disease incidence (DI) more than the corresponding wild-type Trichoderma species, and the use of a mixture of Trichoderma spores (mutant or wild type) showed better efficacy. Overall, mutant Trichoderma species effectively suppress R. solani growth and enhance beneficial physiological changes in bean plants, supporting their use as biocontrol agents for managing damping-off disease sustainably.