Pathogenic Interactions between Macrophomina phaseolina and Magnaporthiopsis maydis in Mutually Infected Cotton Sprouts

The soil fungus Macrophomina phaseolina, the charcoal rot disease agent, poses a major threat to cotton fields. In Israel, highly infected areas are also inhabited by the maize pathogen Magnaporthiopsis maydis. This study reveals the relationships between the two pathogens and their impact on cotton sprouts. Infecting the soil 14 days before sowing (DBS) with each pathogen or with M. phaseolina before M. maydis caused a strong inhibition (up to 50-65%) of the sprouts' development and survival, accompanied by each pathogen's high DNA levels in the plants. However, combined or sequence infection with M. maydis first led to two distinct scenarios. This pathogen acted as a beneficial protective endophyte in one experiment, leading to significantly high emergence and growth indices of the plants and a ca. 10-fold reduction in M. phaseolina DNA in the sprouts' roots. In contrast, M. maydis showed strong virulence potential (with 43-69% growth and survival suppression) in the other experiment, proving its true nature as an opportunist. Interestingly, soil inoculation with M. phaseolina first, 14 DBS (but not at sowing), shielded the plants from M. maydis' devastating impact. The results suggest that the two pathogens restrict each other, and this equilibrium may lead to a moderate disease burst.