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Variability in Root-Knot Nematode Resistance within the Genus Alysicarpus¹

Root-knot nematodes (Meloidogyne spp.) are a major limiting factor in the establishment and growth of many forage legumes, including alyceclover [Alysicarpus vaginalis (L.) DC.], which is highly susceptible to three Meloidogyne species. An extensive collection of Alysicarpus germplasm was evaluated for variability in Meloidogyne susceptibility to determine the feasibility of developing resistant cultivars. Germplasm was evaluated in two field (Arredondo fine sand) and two greenhouse tests. Variation in response to Meloidogyne spp. was identified in the Alysicarpus germplasm. Accessions FL-1, FL-4, FL-5, and FL-7 had overall mean gall scores of less than 2.0 (0 = no galls; 5 = more than 100 galls) when infested with M. incognita race 3. Accessions FL-1, FL-3, and FL-4 received mean gall scores of less than 1.0 in response to M. javanica, while FL-2, FL-5, and FL-7 had ratings of less than 2.0. M. arenaria race 1 was the most aggressive pathogen as only FL-3 had a mean gall score of less than 2.0. No one line was highly resistant to all three Meloidogyne spp., suggesting the need for hybridization. Galling was highly correlated (r = 0.98) with egg mass production in the a!yceclover germplasm. Greenhouse and field results were also highly correlated (r = 0.61 to 0.89), so accessions resistant in the greenhouse were also field resistant. The level of Meloidogyne infestation achieved in Field Experiment 2 did not adversely affect yield, nodulation, or crude protein percentages. Broad sense heritabilities (47 - 78%) indicate a large percentage of the existing variation is genetic. Thisuggests that hybridization and selection programs to improve populations could be successful.

Key Words: Alysicarpus vaginalis (L.) DC. Alyceclover • Broad-sense heritability • Meloidogyne arenaria race 1 (peanut-root-knot nematode) • M. incognita race 3 (southern root-knot nematode) • M. javanica (javanese root-knot nematode) • Meloidogyne resistance • Resistance breeding

² Graduate research assistant, assistant professor, and associate professor, Dep. of Agronomy; and associate professor, Dep. of Entomology and Nematology, Univ. of Florida, Gainesville, FL 32611.

³ The views and interpretations in this ptiblication are those of the authors and should not be attributed to the U.S. Federal Government or to any individual acting in its behalf.

Received for publication May 10, 1985.