Microplot research supports the existence of virulence phenotypes in populations of reniform nematode endemic in Louisiana

Abstract

Microplot studies were conducted to assess virulence phenotypes of populations of reniform nematode (Rotylenchulus reniformis) endemic in Louisiana. Reniform nematode populations were derived from single egg mass collected from West Carrol, Rapides, Morehouse, and Tensas parishes in Louisiana. Trials were conducted using the upland cotton cultivars (Gossypium hirsutum) Phytogen 499 WRF, Deltapine 1133 B2RF, and Phytogen 333 WRF that are recommended for use in Louisiana. Experiments were established as a 3 X 4 X 5 design (cotton cultivars X isolates of reniform nematode X replications) with inoculum level of 50,000 vermiform life stages of nematodes. After 165 days, nematodes were extracted and enumerated from a 250 cc subsample of soil from each microplot. Plant data collected include number of bolls, seed cotton weight, lint weight, and plant dry weight. A significant difference in reproduction among the reniform nematode isolates was observed. Of the four isolates and across all varieties, the Morehouse isolate displayed the greatest level of reproduction; Tensas and West Carroll were intermediate; and Rapides had the least. Reproduction of Morehouse isolate was 31% greater than that of Rapides isolate. A significant reduction in plant dry weight, numbers of bolls, seed cotton weight, and lint percentage were observed for the nematode inoculated plants when compared with uninoculated controls. Plant dry weight losses caused by West Carrol, Rapides, Morehouse, and Tensas isolate was 26%, 9%, 55%, and 21%, respectively. Number of bolls, seed cotton weight, lint weight, and lint percentage reduction by the most damaging Morehouse isolate were 66%, 59%, 65%, and 14%, respectively. Similarly, number of bolls, seed cotton weight, lint weight, and lint percentage reduction by the least damaging Rapides isolate were 14%, 15%, 19%, and 4%, respectively. Results suggest that endemic populations of reniform nematode behave differently on cotton indicating virulence phenotypes. Cotton varieties, across all isolates, did not differ significantly in terms of reproduction of reniform nematodes. Nematode reproduction in DP1133 was approximately 3% higher than in PHY333, and PHY499. Data obtained from this research supports previous reports of the existence of virulence phenotypes of reniform nematode.