Resistance to Brown Stem Rot in Soybeans¹

A total of 2,060 soybean strains, screened for resistance to brown stem rot, revealed no immune lines. However, PI 84946‐2, a strain of unknown origin selected from an introduction from Korea, had a very high proportion of disease‐free plants through 12 seasons. When crosses of PI 84946‐2 were made with several commercial varieties, the segregating generations averaged more healthy plants than did the commercial varieties. Lines with resistance similar to that of PI 84946‐2 have been selected from these populations. We observed that early‐maturing varieties tended to escape infection; locally adapted varieties planted in late June did likewise. Irradiating the seeds of six soybean varieties with thermal neutrons failed to induce resistant mutants in progeny tests.