Reproduction and Pathogenicity of Three Isolates of Meloidogyne hapla Race A on Concord Grapes.

T h e nor thern root-knot nematode, Meloidogyne hapla Chitwood, 1949, parasitizes a number of impor tant crops in Washington (1). M. hapla is widespread on Concord grapes (Vitis labrusca L.), and heavy infestations have been associated with vines with poor growth. All the same, a greenhouse pathogenicity study with an isolate of M. hapla from alfalfa (Medicago sativum L.) showed that Concord grape was a poor host. Those observations indicated that at least two populat ions of M. hapla were present. Pathotypes are common in species of Meloidogyne (4, 5, 6), and five pathotypes of M. hapla are known from the Pacific northwestern United States (5). Pathotypes are generally differentiated by host range, pathogenicity, and mode of reproduct ion (6, 8). Chromosome numbers have recently been used to identify field populat ions of Meloidogyne spp. (2). T h e r e are at least two known races of M. hapla distinguished by type of chromosome reproduction (8). This study was done to measure the variation in reproduction, pathogenicity, and chromosome number of three Washington State field isolates of M. hapla on Concord grapes. Dormant three-node grape cuttings were rooted in peat moss in a greenhouse. Rooted cuttings were transplanted into methylbromide-fumigated sandy loam soil (72.4% sand, 22.6% silt, 5% clay) in 10-cm-diam plastic pots. After I0 weeks, established plants were transplanted into 7.5-liter plastic pots and inoculated with nematodes. Isolates of M. hapla taken from alfalfa, red currant (Ribes rubrum L.), and Concord grape in the field were increased and maintained separately on tomato (Lycopersicon esculentum Mill. 'T iny Tim' ) in a growth room. Second-stage larvae of M. hapla were