Selection against Pratylenchus vulnus populations attacking Prunus rootstocks

Twenty-nine commercial and experimental Prunus rootstocks, most with incorp orated root-knot nematode [Meloidogyne javanica (Traub.) Chitwood] resistan ce, were evaluated against mixtures comprising nine populations of the root -lesion nematode Pratylenchus vulnus Alien and Jensen. Nearly all tested ma terials were susceptible. Five cultivars with high resistant levels were fu rther challenged with seven P. vulnus populations individually. 'Redglow' ( Prunus salicina Lindl. x P. munsoniana Wight and Hedrick) was the only root stock that showed broad resistance to all populations. The rootstocks 'Tori nel' (P. domestica L.), AC-595 (P. domestica x P. insititia L.),'Marianna 4 001' (P. cerasifera Ehr. x P. munsoniana), and 'Felinem' [P. dulcis (Mill.) D. A. Webb x P. persica (L.) Batsch] showed resistance to one or a few P. vulnus populations. Several supposedly resistant sources proved to be susce ptible. Tests of crosses made between parents of diverse genetic background with partial resistance to P. vulnus indicate that a descendant with poten tial P. vulnus resistance is difficult to obtain. Pathogenic diversity amon g P. vulnus populations appears to be high.