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

Thirteen root-knot nematode isolates from Spain that included Meloidog yne incognita (four), M. arenaria (six), and M. javanica (three) were used to verify the resistance level of twelve Prunus rootstocks. The m ajority 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 C achirulo, the almond D-3-5, and the peach Nemared exhibited different levels of resistance to a mixture of twelve isolates of Meloidogyne. C v. Garrigues was susceptible, In a second trial, the hybrids G x N Nos 2, 9, and Nemaguard were highly resistant to ten isolates of Meloidog yne, 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 nem atode induces a necrotic reaction in the surrounding cortical parenchy ma isolating the dead tissue by a compact barrier formed by several ce ll layers in which callose was detected in its cell walls. In F2 proge nies of a seedling population of G x N, 92% of the plants showed resis tance.