Evaluation location: Illinois, United States
Brown Stem Rot Resistance in Soybean Germ Plasm from Central China. Based on field results, putatively resistant lines were selected and evaluated in the greenhouse from Oct. 1994 through May 1996, using the root-dip inoculation method of Willmot and Nickell. Sixty-four accessions, 3 susceptible, and 3 resistant standards were replicated 6 times in a randomized complete block design. The resistant standards were L78-4094 (Rbs1), PI 437833 (Rbs2), and PI 437970 (Rbs3). The susceptible standards were cvs. Century 84, Resnik, and Flyer. Entries were inoculated with a monoconidial type I isolate of P. gregata, PgOh2. Plants were evaluated for BSR reaction after 8 to 9 weeks (R1 to R3 growth stages). Individual pots were rated for incidence of foliar (percentage of plants with foliar symptoms) and stem symptoms. Stem symptoms were measured by splitting each stem lengthwise and recording the proportion of total nodes exhibiting internal browning. Accessions were classified as resistant if the foliar and stem symptoms were significantly lower than the corresponding means of the susceptible standards and not significantly different from the corresponding means of the resistant standards.