1a. Objectives (from AD-416):
Obj 1. Determine soybean yield loss associated with infection by Macrophomina phaseolina and charcoal rot development in the North Central U.S. Obj 2. Assess seasonal progress of charcoal rot (pathogen colonization and disease development) in the North Central U.S. Obj 3. Evaluate high-yielding commercial soybean varieties adapted to the North Central U.S. for field resistance to charcoal rot.
1b. Approach (from AD-416):
Obj 1 and 2. Four commercial soybean varieties (maturity group-MG 2.0-2.5) will be planted on 1-2 research farms in IN, WI, and MI. Treatments will be irrigated/infested, irrigated/non-infested, non-irrigated/infested, and nonirrigated/non-infested and arranged in a split-randomized complete block design with irrigation being the main plot. Soil populations (colony forming units-CFUs) of M. phaseolina will be assessed post-planting and pre-harvest. Disease development and colonization by M. phaseolina (plant CFUs) will be assessed at soybean growth stages VC, V5, R2, R4, R6, and R8. Yield will be assessed at maturity. Obj 1. Commercial farms in OH with a history of charcoal rot will be grid-sampled for soil CFUs of M. phaseolina to determine areas of high and low disease pressure. A commercial variety will be grown and yield and plant CFUs assessed at maturity. Comparisons will be made between plants grown in high disease pressure areas versus low. Obj 3. Twenty commercial soybean varieties will be planted on 2 research farms in IN (MG 2.5-3.5), WI (1.0-2.0), and MI (2.0-2.5). Plots will be irrigated or non-irrigated and all will be artificially infested with M. phaseolina. Soil CFUs will be determined postplant and pre-harvest and disease developed at stages VC, V5, R2, R4, R6, and R7. At maturity, varieties will be assessed for yield and plant CFUs.
3. Progress Report:
Objective 1. In collaboration with scientists at The Ohio State University, four commercial soybean varieties, two resistant and two susceptible to charcoal rot, and all with resistance to the soybean cyst nematode (SCN), were planted on two production farms in Ohio. After planting, fields were grid-sampled (450 samples total) to determine soil populations of both Macrophomina phaseolina, casual agent of charcoal rot, and SCN. Fields will be sampled again after harvest to assess how populations of both pathogens may have changed over the season. Root rot ratings for charcoal rot will be evaluated at soybean growth stage R7 and yield determined at harvest. In addition, each of the four varieties were planted at variable seeding rates (120,000; 160,000; 200,000 seeds/acre) to determine the influence of plant population density on severity of charcoal rot. Soil samples were taken following planting, and will be taken again at harvest, to determine soil populations of M. phaseolina and SCN. Severity of charcoal rot (root rot) will be assessed at R7.