A Quantitative Technique for Evaluating Cotton for Root-Knot Nematode Resistance

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Abstract
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 inocualted with 8000 eggs in a greenhouse and evaluated 35-45 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 germ plasm by this technique should result in development of agronomically desirable cotton cultivars capable or preventing economic loss from root-knot nematodes.

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