Evaluation of perennial Glycine species for resistance to soybean fungal pathogens that cause Sclerotinia stem rot and sudden death syndrome

The cultivated soybean [Glycine max (L.) Merr.] has a relatively narrow genetic base and most commercial cultivars are susceptible to Sclerotinia sclerotiorum (Lib.) de Bary and Fusarium solani (Mart.) Sacc. f. sp. glycines, which, respectively cause Sclerotinia stem rot (SSR) and sudden death syndrome (SDS). The objective of this study was to screen all the available accessions of the perennial Glycine species for resistance to the pathogens that cause SSR and SDS. For SSR evaluations, five seedlings of each of 787 accessions were screened once in a series of eight non-replicated runs. Seedlings were inoculated with an agar plug cut from the edge of a 1-d-old fungal culture by placing the plug next to the stem. Of the 787 accessions, 183 had partial resistance with 144 of these accessions being G. tabacina (Labill.) Benth. A selected set of 53 accessions was further screened in two replicated trials with five plants per each of four replications. Glycine tabacina had several accessions that were consistently rated as partially resistant. For SDS evaluations, five plants of each of 767 accessions were screened once in a series of eight runs. Plants were inoculated by a layered technique in which infested sorghum seed were placed below the transplanted seedlings. In the initial evaluation of 767 accessions, 134 had partial resistance with 65 of these accessions being G. tomentella Hayata. In a replicated set of selected accessions, G. tomentella had several accessions that were consistently rated as partially resistant. These perennial Glycine species represent potential untapped sources for improving disease resistance in soybean.