Seed treatment with Trichoderma asperelloides, alone or in combination with Bacillus velezensis, attenuates Macrophomina phaseolina–induced physiological stress and promotes maize growth

Macrophomina phaseolina, the causal agent of charcoal rot, severely impairs maize development by disrupting essential physiological processes. This study aimed to evaluate the effects of seed treatment with Trichoderma asperelloides (Ta), Bacillus velezensis (Bv), and their combination (Ta + Bv) on the physiological responses of maize plants grown in substrate infested or non–infested with M. phaseolina. Gas exchange, chlorophyll a fluorescence, leaf water potential, plant growth, and disease severity were evaluated. Infection by M. phaseolina reduced leaf water potential, CO₂ assimilation, stomatal conductance, transpiration, and shoot and root biomass in untreated plants. In addition, infection impaired photosystem II photochemical efficiency and the electron transport rate, while increasing internal CO₂ concentration. Seed treatment with Ta and Ta + Bv mitigated these changes, reducing pathogen–induced damage to stomatal regulation and photochemical performance. Both treatments also increased stomatal conductance, CO₂ assimilation, and shoot and root biomass accumulation in maize plants grown in the absence of M. phaseolina. Disease severity was reduced by all treatments, with Ta and Ta + Bv showing the greatest efficacy, although no additive effect was observed for the combination. Overall, the results demonstrate that M. phaseolina disrupts primary metabolism in maize, whereas Ta and Ta + Bv attenuate the physiological effects of infection and promote plant growth.