Effects of domestication and agronomic selection on phytoalexin antifungal defense in Phaseolus beans

Abstract

Systems of wild and cultivated relatives are good experimental systems to test chemical defense theory because they provide closely related varieties that differ in discrete traits. To determine the relationship between resistance and chemical defense diversity among wild, landrace and cultivar accessions of Phaseolus vulgaris, we measured resistance to fungal infection in laboratory and field experiments, quantified phytoalexin diversity, and assessed the effectiveness of phytoalexin mixtures extracted from live tissue. Results show a gradient of resistance to fungal infections between wild, landrace and cultivar varieties. In the laboratory, wild seedlings were more resistant (93% non‐infected) than landrace seedlings (80% non‐infected) and modern cultivar seedlings (68% non‐infected). Under field conditions wild seedlings were more resistant (97% non‐infected) than cultivar seedlings (71% non‐infected). Wild seedlings presented the highest phytoalexin diversity (H′ = 1.11), while those of the landrace presented an intermediate level (H′ = 0.97) and cultivar seedlings presented the lowest diversity (H′ = 0.93). No differences were found in total concentrations. The in vitro inhibitory properties on hyphal growth of the isoflavonoid mixtures produced by individual seedlings showed a similar trend. Our results are consistent with similar gradients in other species of Phaseolus beans and resistance to Colletotrichum sublineolum in sorghum.