REACTIONS OF DRY BEAN, LIMA-BEAN, AND SOYBEAN CULTIVARS TO RHIZOCTONIA ROOT AND HYPOCOTYL ROT AND WEB BLIGHT

We evaluated the reactions of 15 soybean, 13 dry bean, and two lima bean cultivars to Rhizoctonia root and hypocotyl rot and web blight. Each cultivar was inoculated separately with Rhizoctonia solani isolates AG-2-2 and AG-4 to evaluate resistance to root and hypocotyl rot and with a dry bean isolate and a soybean isolate of AG-1 IB to evaluate resistance to web blight. Agar plate, potted plant, detached leaf, and whole plant assays were used to evaluate resistance. Data from agar plate and potted plant assays for hypocotyl and root rot were either not correlated or were only weakly correlated. This indicated that agar plate assays were not satisfactory for determining differences in host resistance and that investigations should be based on potted plant assays. With a few exceptions, all soybean cultivars were resistant or moderately resistant to hypocotyl and root rot in potted plant assays. Of the dry bean and lima bean cultivars tested, only Jackson Wonder was moderately resistant to both diseases. In potted plant assays, hypocotyl and root disease severities were positively correlated for soybean and dry bean (r = 0.67 and 0.71, respectively; P less-than-or-equal-to 0.01). Thus, cultivars may express a similar reaction to both diseases. Soybean cultivars were more resistant to web blight than dry bean cultivars. Web blight ratings from the detached leaf and whole p[ant assays were correlated for soybean but not for dry or lima bean.