Evaluation of Okra Accessions with Reported Resistance to Root-knot Nematodes for Reaction to Southern Root-knot Nematode

Abstract

Forty-seven of the 53 plant introductions (PI) in the U.S. Plant Germplasm System okra [Abelmoschus esculentus (L.) Moench] collection with reported resistance to root-knot nematodes [Meloidogyne incognita (Kofoid and White) Chitwood or unidentified Meloidogyne spp.] were evaluated in replicated greenhouse tests for reaction to the southern root-knot nematode (M. incognita). (Four of the 53 PI were unavailable and two accessions failed to germinate.) Preliminary evaluations identified a serious problem in evaluating this subset of okra germplasm for resistance to root-knot nematodes. The seed coats of most of the accessions were hard, and this trait delayed germination, which caused many of the seedlings to escape infection when the seeds were inoculated at planting with M. incognita eggs. A seed disinfection, scarification, and germination procedure was developed to ensure uniform seedling emergence. Except for two PI that failed to germinate, all available okra accessions with reported resistance were evaluated using these procedures. All tested accessions were susceptible to M. incognita race 3. Based on these results, we conclude that none of the accessions in the okra PI collection with reported resistance to root-knot nematodes is useful as M. incognita—resistant parental material in okra breeding programs.