A Growth Chamber Test For Measuring Phytophthora Root Rot Tolerance in Soybean Seedlings

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Abstract
Soybean cultivars with high, moderate, and low tolerance to root rot caused by Phytophthora megasperma f. sp. glycinea, were grown in a growth chamber for 7 days, and then their taproots were inoculated with mycelial suspension. Six days later, elongation of the 1st internode and extent of tissue colonization in the hypocotyl were measured. The first internodes of the moderate- and low-tolerant lines were significantly shorter than those of uninoculated seedlings, and there were significant differences in hypocotyl tissue colonization among the 3 cultivars. Shortening of the 1st internode was not a reliable predictor of hypocotyl tissue colonization. Nonuniformity of root rot indicated that heterogeneity for tolerance may exist within cultivars, and high- or low-tolerant components can be selected for further evaluation after this nonlethal tolerance test.