Doctor of Philosophy (PhD)
Plant Pathology and Crop Physiology
Comparative reproduction and pathogenicity of reniform nematode (Rotylenchulus reniformis) populations derived from single-egg masses and collected form West Carroll (WC), Rapides (RAP), Morehouse (MOR), and Tensas (TEN) parishes in Louisiana were evaluated in microplot and greenhouse trials. Data from microplot trials showed significant differences among isolates of reniform nematode in both reproduction and pathogenicity on upland cotton (Gossypium hirsutum) cultivars Phytogen 499 WRF, Deltapine 1133 B2RF, and Phytogen 333 WRF. Across all cotton cultivars, MOR and RAP isolates had the greatest and the least reproduction values 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 isolate, respectively. The reproduction and pathogenicity of WC and TEN isolates were intermediate. In the greenhouse experiment, reproduction of MOR and RAP isolates across all cotton genotypes (three cultivars used in microplot experiment, cultivar Stoneville 4946 GLB2, and two resistant germplasm lines MT2468 Ren3 and M713 Ren5) was the greatest (reproduction value 10.7) and the least (reproduction value 7.9), respectively. Although reproduction values 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. In order to determine genetic variability in reniform nematode populations, 31 KASP SNP primers sets were evaluated against 13 reniform nematode isolates that include MOR and RAP isolates from Louisiana as well as other 11 isolates from Mississippi, Arkansas, Hawaii, and Alabama. Twenty-six SNP assays amplified genomic DNA of reniform nematode isolates while five failed to successfully amplify. Five SNP assays identified genetic differences within and among populations of reniform nematode from Louisiana, Mississippi, and Arkansas. Similarly, eight SNP assays identified genetic differences among samples from Hawaii, and Alabama. The SNP markers developed in this study will be useful in resistance breeding programs as well as in the assessment of the genetic diversity, origin, and subsequent distribution of this nematode.
Khanal, Churamani, "Virulence Phenotypes of Rotylenchulus reniformis: Evaluation of Host Status of Cotton and Utility of Single Nucleotide Polymorphisms (SNPs) for Identification" (2017). LSU Doctoral Dissertations. 4129.
Mcgawley, Edward C.