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A Quantitative Technique for Evaluating Cotton for Root-Knot Nematode Resistance. Raymond L. Shepherd, Research Agronomist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Auburn, AL 36830; Phytopathology 69:427-430. Accepted for publication 17 October 1978. This article is in the public domain and copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1979. DOI: 10.1094/Phyto-69-427.

A technique was developed for evaluating cotton (Gossypium spp.) for resistance to the root-knot nematode (Meloidogyne incognita acrita). Resistance was based on egg production (a nematode response to the plant) and root galling (a plant response to the nematode). To assess root galling and egg production on test plants, individual plants were inoculated with 8,000 eggs in a greenhouse and evaluated 3545 days later by counting egg masses and rating root galling. Plants almost free of egg masses and root galls were selected and their progeny tested. Final selection for resistance was based on actual numbers of eggs per plant. By using this technique, levels of resistance to egg production were differentiated among upland cultivars, F3 lines, and G. hirsutum races. These levels could not be detected by rating root galling alone. Selection for resistance to root galling and egg production was necessary to develop cotton lines with high resistance to both processes. Cotton accessions exhibited higher levels of resistance and more levels of resistance (ranging from highly resistant to highly susceptible) than has been reported previously in cotton. Selecting highly resistant germplasm by this technique should result in development of agronomically desirable cotton cultivars capable of preventing economic loss from root-knot nematodes.

Additional keywords: Gossypium hirsutum races, G. barbadense race, breeding for resistance.