Insights into the Genetics Underlying the Resistance to Root-Knot Nematode Reproduction in the Common Bean Ouro Negro

Root-knot nematodes (RKNs, Meloidogyne spp.) have become the major yield-limiting biological factor in common bean production in many warmer-climate regions such as the south of Europe. Broadening the genetic base of resistance in elite common bean cultivars is the most effective and environmentally friendly method for managing this disease. Toward this goal, F₁, F₂, and F₃ populations from crosses between susceptible snap beans (Helda and Perona) and the resistant Ouro Negro cultivar were phenotyped for M. incognita and M. javanica-induced root-galling (GI) and egg mass production (EM) in controlled growth chamber infection assays. F₁ progenies showed a susceptible response to both RKN isolates, with high GI and EM values, indicating a recessive inheritance of nematode resistance. The estimates for broad-sense heritability for GI and EM in the F₂ Helda × Ouro Negro population infected with M. incognita were 0.62 and 0.54, respectively. RKN resistance in Ouro Negro is largely controlled by partial to overdominant genetic effects and that susceptibility factor leads recessive resistance. The minimum number of genes involved in nematode resistance was estimated to be about two or three. In agreement, genetic analysis of F₂ segregating populations supported duplicate recessive epistasis as the inheritance pattern involved in the resistance provided by the Ouro Negro cultivar. Ouro Negro is an important resource for broadening RKN resistance in elite common bean cultivars.