Doctor of Philosophy (PhD)


Plant Pathology and Crop Physiology

Document Type



Experiments were conducted to evaluate soybean, Glycine max (L.) Merr., responses to indigenous isolates of the reniform nematode (Rotylenchulus reniformis) in Louisiana and to understand the genetic variability of these native isolates. Microplot and greenhouse experiments were conducted to evaluate the comparative reproduction and pathogenicity of single egg-mass populations of R. reniformis isolated from West Carroll (WC), Rapides, Tensas and Morehouse (MOR) parishes of Louisiana. Data from full-season microplot trials, displayed significant differences in reproduction and pathogenicity of the nematode with the commercial soybean cultivars REV 56R63, Pioneer P54T94R, and Dyna-Gro 39RY57. Significantly low population density was observed in the isolate from the MOR parish compared to that of the least reproducing WC isolate. The MOR isolate was also the most pathogenic and resulted in significantly less soybean plant and pod weights compared to the control. In 60 day greenhouse trials, susceptible cultivar Progeny P4930LL and the resistant germplasm lines PI 90763 and PI 548316 were added together with the same cultivars used in the microplot trials. Similar to the microplot trials, the MOR isolate had the least level of reproduction compared to that of WC and presented the greatest level of pathogenicity. In both microplot and greenhouse trials, the soybean cultivar REV 56R63 had a significant reduction in reniform numbers compared to cultivars Pioneer P54T94R and Dyna-Gro 39RY57. The second set of experiments were conducted to understand the amount of genetic variability present in the 13 reniform nematode isolates from Louisiana, Mississippi, Arkansas, South Carolina and Georgia with the use of Single Nucleotide Polymorphism (SNP) analysis. Thirty one chosen SNPs were tested against the reniform nematode isolates using kompetitive allele-specific PCR genotyping assay. Out of the 31 SNPs tested, 26 SNPs amplified genomic DNA of the reniform nematode isolates. Four SNPs out of all tested were able to distinguish genetic differences between and among tested geographic isolates of reniform nematode from Louisiana, Mississippi, and Arkansas. Even with limited numbers of samples, a genetic variability was observed with 3 SNPs between South Carolina, and Georgia isolates. The results obtained in this study might be extremely useful in resistance breeding programs as well as providing soybean cultivar recommendations for growers in different geographical locations.



Committee Chair

Overstreet, Charles