Novel sources of resistance to the soybean cyst nematode (Heterodera glycines) found in wild relatives of azuki bean (Vigna angularis) and their characteristics of resistance

Soybean cyst nematode (Heterodera glycines; SCN) is becoming a serious problem in azuki bean (Vigna angularis var. angularis) production in Hokkaido, Japan. To find sources of resistance to SCN, we screened wild relatives of azuki bean and calculated “female indices” (FIs) of 342 accessions from 8 Vigna species that are cross-compatible with azuki bean. Twenty-three accessions belonging to V. hirtella, V. minima, V. nakashimae, V. riukiuensis, and V. tenuicaulis were resistant to the most prevalent SCN race, race 3, but most of them were only moderately resistant or susceptible to race 5. Four promising accessions (V. minima JP205886, JP205891, and JP210806, and V. nakashimae JP107879) showed a high level of resistance to all SCN races found in Japan (1, 3, and 5) and race 2 (an experimentally derived race from race 5). Since the SCN-resistant soybean cultivars released in Japan are not resistant to races 2 and 5, these wild Vigna accessions may have resistance mechanisms different from that of soybean. Continuous culture of race 3 on promising accessions showed that it might be difficult to overcome the resistance of these accessions. The resistance sources found in this study will be useful in controlling SCN through the breeding of SCN-resistant azuki bean cultivars. This study also showed the effectiveness of using wild genetic resources for identifying novel resistance sources.