Epidemiological Factors Affecting Brown Spot (Physoderma maydis) Progression in Maize (Zea mays L.)

Brown spot of maize (Zea mays L.) caused by Physoderma maydis is an emerging disease whose development is influenced by several host- and pathogen-related factors. The present study was undertaken under controlled polyhouse conditions using a whorl inoculation technique to elucidate the role of host age, pathogen culture age, inoculum load, and sub-culturing on disease development. Host susceptibility increased with plant age with maximum disease progression in 50-days old plants, whereas, reduced severity at later stages suggested the onset of age-related resistance. Among varying culture ages, 14-days old culture exhibited peak virulence with disease severity (26.85%) and apparent infection rate of (0.04 r/day). A sporangial concentration of 1×106 sporangia/ml resulted in maximum average disease index (39.51%) and shortest average incubation period of 13.0 days establishing as optimal inoculum load. Among varying sub-culturing of the pathogen, highest average disease index (22.22%) was recorded in the maize plants inoculated with 1st sub-culture. Furthermore, these findings elucidate age-related resistance and define optimal inoculation factors, offering practical insights for timing of management interventions and supports the development of durable resistance through targeted breeding strategies in maize.