Professor Kansas State University Manhattan, Kansas, United States
Abstract Text: Charcoal rot, caused by Macrophomina phaseolina (Mp), is a major soilborne disease affecting sorghum, soybean, and corn. Microsclerotia, the pathogen's primary survival structures, vary in size depending on host source, isolate, and carrier medium, influencing pathogen persistence, inoculum potential, and disease severity. However, the extent to which these factors interact to impact microsclerotia dimensions remains unclear. This study used multivariate analysis of variance (MANOVA) to assess the effects of host source, isolate, and carrier on microsclerotia length and width. Mp microsclerotia, from three isolates each from three crop sources, were grown on sterile Japanese millet (JM), white sorghum (WS), and oatmeal (OATS) inoculum carriers. For each isolate*carrier combination (4 reps ea.), a microclerotia wetmount was made. For each rep, the length and width of 50 microsclerotia were measured under a microscope. Significant effects were observed for source-isolate (VPillai = 0.259, P < 0.0001) and carrier (VPillai = 0.141, P < 0.0001), with a significant source-isolate*carrier interaction (VPillai = 0.061, P</em> < 0.0001). Tukey’s HSD indicated that MP57 (corn) grown on OATS produced the largest microsclerotia, while MP334 (sorghum) grown on JM yielded the smallest. These findings highlight pathogen-environment interactions influencing microsclerotia development and inoculum potential. Understanding these factors can improve soil-based screening methodologies by ensuring consistent artificial inoculations, ultimately aiding in disease assessment and management strategies.
