Nematode and Fusarium Population Densities at the Regional Cotton Fusarium Wilt Nursery

J. L. Starr, K. M. Glass, W. S. Gazaway, and J. D. Mueller


The Regional Cotton Fusarium Wilt Nursery at the E. V. Smith Research Center, Shorter, AL has screened cotton genotypes for resistance to Fusarium wilt for breeders and others interested in the development of cotton genotypes with improved resistance to wilt since 1951. An important component of this nursery is the root-rot nematode, Meloidogyne incognita. The presence of the nematode is necessary for the identification of resistance that is effective when plants are infected by the nematode, as concomitant infection by root-knot nematodes can breakdown the resistance to Fusarium wilt in cotton genotypes resistant to the wilt alone. Despite the importance of root-knot nematodes to this nursery, data on structure and densities of nematode populations in the nursery are lacking. Three separate composite soil samples were systematically collected from each of the four replications of the nursery in August 1993. A 500-cm3 subsample of each sample was processed by elutriation-centrifugation to extract plant-parasitic nematodes. Populations of Fusarium oxysporum were determined by dilution plating of duplicate 5-g subsamples of air-dried soil on to Komoda's medium. Population densities of M. incognita ranged from 7,250 to 10,230 eggs & J2/500 cm3 soil across all four replications. Other nematodes present were Hoplolaimus galeatus (mean of 440 individuals/500 cm3 soil), Paratrichodorus spp. (90/500 cm3 soil), and Tylenchorhynchus spp (130/500 cm3 soil). Population densities of F. oxysporum ranged from 790 to 1,880 colony forming units/g air-dried soil across the four replications. Six plants were sampled from each of five arbitrarily selected plots of Auburn 56 (the wilt-resistant standard cultivar) and Rowden (the wilt-susceptible standard cultivar) for a comparison of root galling and final percentage of wilted plants. Root-gall indices did not differ between the two cultivars; on a 0 to 5 scale with 5 being severe galling, Auburn 56 had a mean gall index of 3.7 whereas Rowden has a mean gall index of 4.2. Final percentage wilt was 50% for Auburn 56 and 93% for Rowden in these plots. Populations of both pathogens were judged to be sufficient to induce the Fusarium wilt/root-knot nematode complex. Data confirm previous reports that resistance to Fusarium wilt in the presence of root-knot nematodes does not imply concomitant resistance to the nematodes

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pg. 278
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998