RESISTANCE VERIFICATION IN PRUNUS SELECTIONS TO A MIXTURE OF 13 MELOIDOGYNE ISOLATES AND RESISTANCE MECHANISMS OF A PEACH-ALMOND HYBRID TO MELOIDOGYNE-JAVA']JAVANICA

Thirteen root-knot nematode isolates from Spain that included Meloidogyne incognita (four), M. arenaria (six), and M. javanica (three) were used to verify the resistance level of twelve Prunus rootstocks. The majority of the rootstocks were peach-almond hybrids in the process of selection. In a first trial, the hybrids G x N Nos 3, 7, 14, 15, and Cachirulo, the almond D-3-5, and the peach Nemared exhibited different levels of resistance to a mixture of twelve isolates of Meloidogyne. Cv. Garrigues was susceptible, In a second trial, the hybrids G x N Nos 2, 9, and Nemaguard were highly resistant to ten isolates of Meloidogyne, although the almonds D-3-5 and Moncayo, the peach GF-305 and the hybrid GF-677 were susceptible. A nematode penetration and development bioassay indicates that an hypersensitive reaction is involved in the resistance mechanism of G x N No 9 infected with M. javanica. The nematode induces a necrotic reaction in the surrounding cortical parenchyma isolating the dead tissue by a compact barrier formed by several cell layers in which callose was detected in its cell walls. In F2 progenies of a seedling population of G x N, 92% of the plants showed resistance.