RHIZOCTONIA FOLIAR BLIGHT REACTIONS AND SEED YIELDS IN SOYBEAN

Rhizoctonia foliar blight (RFB) is caused by the fungus Rhizoctonia so lani Kuhn anastomosis group 1, intraspecific groups IA and IB. The dis ease affects more than half of the soybean [Glycine max (L.) Merr.] ac reage in Louisiana. Although less-susceptible cultivars are recommende d, reliable estimates of cultivar susceptibility have been difficult t o obtain because of several factors, including uneven distribution of RFB in fields, differences in plant developmental stage at time of inf ection, and the requirement for free moisture in RFD development. The objective of this study was to screen commercial soybean cultivars gro wn throughout the southern USA, as well as advanced breeding genotypes , for field reaction to RFB in south Louisiana. Ninety-one soybean gen otypes, representing Maturity Groups IV, V, VI, and VII, were evaluate d at two locations in 1993 and 1994. Disease ratings were made with a severity scale that included pods as well as foliage. A range of react ions to RFB was observed among cultivars, but most were severely damag ed. Significant negative correlations between RFB severity and yield o ccurred among cultivars I in all Maturity Groups. Results identified s everal cultivars, notably Buckshot 66 and Pioneer variety 9593, with p romising levels of resistance.