Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 14, 1997
Publication Date: N/A
Interpretive Summary: Okra, a popular vegetable in the southern U.S., is extremely susceptible to the southern root-knot nematode (Meloidogyne incognita). These soil-borne microscopic roundworms invade and feed on roots of susceptible plants. In response to this feeding, large knots (or swellings) develop on the roots. Nutrients are drawn away from the plant leaves to support this abnormal root growth; consequently the plant becomes stunted and yellow, and yields poorly. Pesticides are often used for nematode control in okra, but environmental concerns may limit pesticide use in the future. Host plant resistance would be the most economical and environmentally safe method for controlling root-knot nematodes. Fifty-three okra lines from the U.S. Plant Germplasm System okra collection have been reported resistant to root-knot nematode. We re-evaluated the 49 available okra lines for the purpose of identifying nematode-resistant okra lines that could be used as parents in okra breeding programs. All of the okra lines that we tested were susceptible to southern root-knot nematode. Based on these tests, none of the lines in the U.S. okra collection with reported resistance to root-knot nematodes has any potential for use as root-knot nematode resistant parental material in okra breeding programs.
Technical Abstract: Forty-nine of 53 plant introductions (PI) in the U. S. Plant Germplasm System okra (Abelmoschus esculentus) collection with reported resistance to root-knot nematodes (Meloidogyne spp.) were evaluated in replicated greenhouse tests for reaction to two isolates of M. incognita race 3. Seed of four PI with reported resistance were unavailable from the U.S. Plant Germplasm System. Preliminary evaluations identified two serious problems in evaluating this subset of okra germplasm for resistance to root-knot nematodes: (1) the seed coats of most of the accessions were hard, and this trait resulted in both delayed and erratic germination, and (2) late emerging seedlings often escaped infection when the seeds were inoculated at planting with M. incognita eggs. A seed disinfection, scarification, and pre-germination procedure was developed to ensure uniform seedling emergence. Except for two PI that failed to germinate, all 49 available okra accessions with reported resistance were successfully evaluated using these procedures. All of the tested accessions were very susceptible to both M. incognita isolates. Based on these tests, none of the accessions in the okra PI collection with reported resistance to root-knot nematodes has any potential for use as root-knot nematode resistant parental material in okra breeding programs.