1a.Objectives (from AD-416):
To idenify new sources of charcoal resistance in adapted and exotic germplasm.
1b.Approach (from AD-416):
A uniform cultivar screening protocol will be developed and implemented. A set of standard susceptible cultivars will be used. These standard susceptible cultivars will represent early and late cultivars with in maturity groups 3 through 5. Tests will be established in naturally infested fields supplemented with adding inoculum at planting. Disease will be evaluated by rating the development of foliar symptoms of charcoal rot, rate of premature plant death, and by splitting the stems at harvest, visually determining the extent of stem colonization and quantifying colonization by determining the colony forming unit of M. phaseolina. Yields will be taken. Test cultivars will be selected based on previous observations and from other charcoal rot screening tests in the field and in greenhouse and laboratory assays. Soil temperature and moisture and rainfall data will be taken and related to disease development.
The regional cultivar test consisting of 18 soybean lines planted in Tennessee on May 18th. These lines represent three genotypes from Maturity Group (MG) III, five from MG IV and seven from MG VII all planted in artificially infested and in non-irrigated soil. Ten samples from each plot were taken for measuring stem severity rating and colony forming unit (CFU) assessments. Five of the breeding lines developed under the Crop Genetics and Research Unit in Stoneville, MS, showed resistance across multiple environments. In addition among the 649 PIs evaluated in 2010, four lines showed a consistent resistance. Seeds for three of these lines will be increased in Costa Rica and may be included for testing in multiple environments by 2013. The test plots in Tennessee are inoculated each year with infested millets to reduce plot to plot variability. Soil, air temperature, soil moisture relative humidity, rainfall, and solar radiation were all recorded.