REPRODUCTION AND PATHOGENICITY OF ENDEMIC POPULATIONS OF ROTYLENCHULUS RENIFORMIS ON COTTON
Keywords: pathogenicity, reniform nematode, reproduction, Rotylenchulus reniformis, upland cotton, virulence phenotypes
AbstractThe reniform nematode (Rotylenchulus reniformis) is the predominant parasitic nematode of upland cotton (Gossypium hirsutum) in the southern United States. Little is known about variability in geographic isolates of reniform nematode. In order to evaluate the comparative reproduction and pathogenicity of reniform nematode populations endemic in Louisiana, a series of microplot and greenhouse experiments were conducted. Reniform nematode populations derived from single-egg masses collected from West Carroll (WC), Rapides (RAP), Morehouse (MOR) , and Tensas (TEN) parishes were used in full-season (150 days) microplot, and 60-day greenhouse experiments, each repeated once. Data from two microplot trials, averaged over 2 yr, showed significant differences among isolates of reniform nematode in both reproduction and pathogenicity on upland cotton cultivars Phytogen 499 WRF, Deltapine 1133 B2RF, and Phytogen 333 WRF. Across all cotton cultivars, the MOR and RAP isolates had the greatest and the least reproduction value of 331.8 and 230.2, respectively. Reduction in plant dry weight, number of bolls, seed cotton weight, and lint weight was the greatest and the least for MOR and RAP isolates, respectively. MOR and RAP isolates lowered plant dry weights of cotton by 55%, and 9%, respectively. Reproduction and pathogenicity of the WC and TEN isolates were intermediate. Data from greenhouse trials showed results similar to that of microplot trials. In greenhouse experiments, reproduction of MOR and RAP isolates across all cotton genotypes was the greatest (reproductive value of 10.7) and the least (reproductive value of 7.9), respectively. Although reproductions of reniform nematode were lower in the germplasm lines than the cultivars, the germplasm lines sustained greater plant weight loss. The variability in reproduction and pathogenicity among endemic populations of reniform nematode in both the microplot and greenhouse experiments adds further support to the hypothesis that virulence phenotypes of R. reniformis exist.