INTERSPECIFIC HYBRIDIZATION OF MEIOTIC PARTHENOGENETIC MELOIDOGYNE CHITWOODI AND M-FALLAX

Hybridization between two meiotic parthenogenetic species of root-knot nematodes, Meloidogyne chitwoodi and M. fallax, was investigated in t wo different crossing experiments on tomato plants grown in sand. The first experiment was a controlled cross between the two species. The s econd experiment was a bulk mating in a 1:1 mixture of two isolates. T he haploid chromosome number of the parental isolates was n = 18. Succ essful interspecific hybridization was obtained, and the resulting hyb rids produced egg masses. In eggs, cell division was observed, but mos t of them were without clear differentiation and consequently were ste rile. Hatched F-2 juveniles were small in number, not viable, and show ed morphological distortions. In the progeny of the isolate mixture of the bulk mating experiment, parental-type females of the two isolates were present in equal numbers, and 10% of all females were nonviable hybrids. Similar ratios of parental-type and hybrid females were detec ted in roots of test plants grown in soil from a field sample that con tained a mixture of M. chitwoodi and M. fallax populations. In the con trolled cross experiment, isozyme electrophoresis of malate dehydrogen ase was applied to distinguish the two species and their hybrids. In t he bulk mating experiment, malate dehydrogenase, esterase, and glucose 6-phosphate dehydrogenase were used as markers, two by two simultaneo usly on the same individual females, providing conclusive evidence for the occurrence of hybrids. This is the first report on interspecific hybridization in Meloidogyne. The possible role of interspecific hybri dization in species differentiation and interspecific exchange of gene tic material within Meloidogyne is discussed.