Effect of Magnaporthiopsis maydis inoculum density on late wilt disease development and maize yield

Powder of Magnaporthiopsis maydis diseased plants (Mm-PDP) was employed as an inoculum for soil infestation instead of M. maydis-colonized sorghum seeds (Mm-CSS). Inoculum density levels of 5~100g /pot (0.071 m²) and 10~200g/box (0.15 m²) were used in the greenhouse and 150~3000 g Mm-PDP /row/2.1 m² in the field. Mm-CSS were used in the positive control (PC) and un-infested treatments served as negative control (NC). Pioneer; SC3062 late wilt-sensitive maize hybrid was used and the disease incidence (DI%) was assessed at the age of 90 and 104 days, and yield component at 115 days. In the greenhouse, plants that emerged from PDP-infested soil (20g-100g or 40-200g, respectively) were insignificantly different in their DI % at the two assessing dates (DI ranged from 86.7-100 to 76.7-100%, respectively). On the other hand, use of 3000g Mm-PDP /row/2.1 m² exhibited the highest DI (34 and 59 % at the age of 90 and 104 days, respectively) in the field. Ear weight (EW), net kernels weight (NKW), and 100 kernels weight (100 KW) loss following this density were 47.5, 49.1 and 17.7%, respectively. Moreover, DI% resulted from 600g Mm-PDP was higher than that obtained from both 1200g Mm-PDP and 600g Mm-CSS (PC). In this study, the optimal Mm-PDP densities for obtaining more than 50% of DI were 3000g followed by 600g and 1200g, respectively. Fortunately, 50% of DI or more are acceptable to differentiate among maize genotypes when screened for resistance against the disease. So, the use of 600g Mm-PDP is less cost than the other densities (600g Mm-CSS as well as 1200g and 3000g Mm-PDP) and adequate for this purpose.