Virulence in Meloidogyne hapla differentiated by resistance in common bean (Phaseolus vulgaris)

A diverse collection of seven Meloidogyne hapla isolates, all identified as cytological race A, were studied for their host-parasite interactions with several common bean (Phaseolus vulgaris L.) genotypes. The M. hapla isolates showed significant (P < 0.01) differential interactions of ability to reproduce on resistant common bean cultivars. Based on the nematode egg mass production on susceptible cv. Yolano and resistant cv. NemaSnap beans, the isolates formed three groups. Four isolates produced many egg masses on both susceptible and resistant cultivars and were defined as virulent to resistance in cv. NemaSnap. Two isolates produced many egg mass numbers on susceptible cv. Yolano, but very few on resistant cv. NemaSnap, and were defined as avirulent to the resistance in NemaSnap. One isolate, WI, produced fewer egg masses on susceptible cv. Yolano than on resistant cv. Nemasnap and was defined as virulent to resistance in cv. NemaSnap. The three types of host-parasite interaction indicated a transagonal reaction for a gene-for-gene relationship between M. hapla and resistant common bean (cv. NemaSnap). Analysis of an F-2 population from crosses between cultivars NemaSnap and Yolano revealed a single dominant gene pattern of segregation for a major form of resistance in cv. NemaSnap. According to an allelism test, the resistance to M. hapla in cv. NemaSnap was not derived from the line PI165426, which is the pedigree source of M. incognita resistance in ev. NemaSnap. However, PI165426 was found to have M. hapla resistance but may not be homozygous for these factors.