Evidence of a new gene for high resistance to Meloidogyne spp. in Myrobalan plum, Prunus cerasifera

The Myrobalan plum Prunus cerasifera clones 'P.2175' and 'P.1079' carry sin gle major genes (Ma1 and Ma2, respectively) for resistance to the predomina nt root-knot nematode (RKN) species Meloidogyne arenaria (MA), Meloidogyne incognita (MI) and Meloidogyne javanica (MJ). The Myrobalan plum clone 'P.2 980' is another complete-spectrum source bearing favourable agronomic Featu res. The genetics of its resistance to MA, MI, MJ and to the population Mel oidogyne sp. Florida has been investigated from G1 crosses with the host My robalan plum clone 'P.16.5' (recessive for both Ma genes), the resistant cl one 'P.2175' (heterozygous for Ma1) and the 'Nemared' peach (homozygous for resistance to MA, MI and MJ but a host for M. sp. Florida). The segregatio n of the G1 hybrids from the intraspecific crosses into two significantly s eparated resistant and host classes, independent of the RKN species, indica tes that resistance to all four species in 'P.2980' is also controlled by a single major dominant (heterozygous) gene. This gene is designated Ma3 bec ause it shares the same spectrum and efficiency as Ma1 and Ma2, and its rel ationship with these last two genes is discussed. The first hybrids between 'P.2980' and 'Nemared' tested only segregated for resistance to M. sp. Flo rida. These results illustrate the possibility of cumulating (pyramiding) M a3 and the 'Nemared' peach resistance gene(s) into new interspecific rootst ocks.