New data completing the spectrum of the Ma, RMia and RMja genes for resistance to root-knot nematodes Meloidogyne spp. in Prunus.

Root-knot nematodes (RKN) Meloidogyne spp. are worldwide pests that affect a considerable number of plants among which stone fruits Prunus spp. are severely attacked. Prevalent RKN species are M. arenaria, M. incognita and M. javanica in stone fruits but the emergent M. ethiopica and M. enterolobii are also reported to challenge perennial crops. In Prunus, the complete-spectrum resistance (R) gene Ma from plum and the more restricted-spectrum R genes, RMia from peach and RMja from almond, completely inhibit nematode multiplication and gall formation of the RKN species that they control. This study aimed to update the resistance spectra of these three major genes by evaluating their activity towards one isolate of the yet untested RKN species mentioned above. To state whether a given gene controls a particular species, the principle of our experiment was to genotype with appropriate markers a number of individuals segregating for this gene and then to phenotype these individuals. A perfect matching of the genotype and of the phenotype of the individuals indicates that the gene of interest is active against and thus controls the corresponding isolate of this RKN species. Segregating materials used were a Ma F1 plum progeny, a RMia F2 peach progeny, and a RMja F2 almond progeny. In addition to previous data, our results establish a clear spectrum for each of the three genes towards isolates from both the three prevalent RKN species and the two emerging species. Ultimately, our results reveal that i) Ma controls all of them, ii) RMja controls all species except M. incognita and M. floridensis, and iii) RMia controls M. arenaria, M. incognita and M. ethiopica but not M. javanica, nor M. enterolobii. Our data should have wide implications in RKN resistance management and breeding and in deciphering the molecular mechanisms of the spectrum of RKN R genes.