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Use of Aeroponic Chambers and Grafting to Study Partial Resistance to Fusarium solani f. sp. glycines in Soybean

Several plant introductions (PIs) and cultivars have been classified as partially resistant (PR) to sudden death syndrome. However, little is known about the nature of resistance to this disease. Seedlings of two PR PIs and two susceptible cultivars were inoculated with Fusarium solani f. sp. glycines in aeroponic chambers. Plants were inoculated by taping two sorghum seeds infested with F. solani f. sp. glycines to the main root. Foliar symptoms of the susceptible cultivars were higher than those on the PR PIs and were associated with lower root and plant dry weight. Root lesion lengths of the four soybean lines differed (P < 0.05), but did not correlate with foliar disease or any other variable. To better understand the resistance mechanism by distinguishing between root and plant resistance, three partially resistant PIs (PI 520.733, PI 567.374, and PI 567.650B) and one susceptible soybean cultivar (GL3302) were compared using different grafting combinations in aeroponic chambers. Results of sudden death syndrome evaluation indicated that resistance is conditioned by both the scion and the rootstock. All three PIs evaluated had resistance associated with the scion; resistance in PI 567.650B also was associated with the rootstock. Although the PR PIs used appear to have little or no root resistance, an aeroponic system and grafting may help identify new sources of resistance to F. solani f. sp. glycines with root- or whole-plant resistance.