Date of Award
5-2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Plant and Environmental Science
Committee Chair/Advisor
Churamani Khanal
Committee Member
Christopher Saski
Committee Member
John Mueller
Committee Member
Christopher McMahan
Abstract
Management of the reniform nematode (Rotylenchulus reniformis Linford and Oliveira) in cotton (Gossypium hirsutum L.) is a challenge since the resistant cultivars lack uniformity in nematode suppression when tested across multiple geographical regions. The central hypothesis of this study was that regional variability in performance of resistant cotton cultivars is associated with unique reproduction biology (reproduction and virulence) of R. reniformis from distinct geographic origins. Greenhouse studies were conducted to assess differential reproduction biology among nine geographic population of R. reniformis originated from South Carolina (SC), Alabama (AL), Florida (FL), Arkansas (AR), Georgia (GA), Louisiana (LA), Texas (TX), Mississippi (MS), and Tennessee (TN) using a resistant (DP 2141NR B3XF) and a susceptible (DP 2317 B3TXF) cotton cultivar. Substantial variability in reproduction was observed among R. reniformis isolates, with the AR isolate having the greatest reproduction factor (Rf) of 19.7 and the AL isolate having the lowest Rf of 3.3. The resistant cultivar suppressed the reproduction of R. reniformis by 85% relative to the susceptible cultivar. The root biomass of nematode inoculated plants were reduced relative to the non-inoculated control, implying nematode virulence. The AR isolate was the most virulent while the AL isolate was the least virulent. Further studies were conducted to assess genetic diversity among the isolates via multiple genomic approaches including phylogenetic relationship, principal component analysis (PCA), single nucleotide polymorphism (SNP) summary, pairwise genetic distance, and admixture analysis. A total of 26 SNPs from mitochondrial genome and 4,596 SNPs from nuclear genome were obtained for downstream analysis. The phylogentic analysis grouped R. reniformis isolates into four distinct clusters while the PCA explained up to 43% variation among the isolates. The TX (218), LA (127) and MS (115) isolate had the greatest numbers of private SNPs suggesting greater divergence among these isolates. The pairwise genetic distance was also higher for LA and MS (64.05) followed by LA and FL (59.34), LA and SC (58.29) and LA and TN (57.73). The admixture analysis revealed five distinct ancestral lineages among the R. reniformis isolates. The TX, LA and MS isolates were identified as the most genetically distinct populations while the TN, AL, FL, SC, AR, and GA isolates more closely related as evident from their closed clustering. To assess the impact of warmer soil temperatures [26 °C (control), 28 °C, 30 °C, and 32 °C] on three geographically distinct populations of reniform nematode (Rotylenchulus reniformis) originating from AL, AR, SC and non-inoculated control, a series of greenhouse experiments were established. The AR isolate had consistently higher reproduction (egg production on root and vermiform life stages, or VLS, in soil) at all temperature regimes. Reproduction of the SC isolate was greater at higher temperature regimes, but this trend appeared to be the opposite for the AL isolate. The AR isolate was consistently the most virulent among the isolates across all soil temperatures. A significant increase in nematode virulence was observed at 30 °C and 32 °C, but not at 28 °C relative to the control for SC while it was the opposite for the AL isolate. Plants grown in soil infested with R. reniformis had significantly reduced plant heights, plant height-to-node ratios and number of leaves relative to the control in all temperature regimes. At 30 °C and 32 °C , plant height and number of leaves were increased by up to 14% and 36% for the AL isolate, while they decreased by 17% and 20% for the SC isolate respectively. The AR isolate consistently reduced plant height, plant height-to-node ratio and number of leaves across all soil temperatures. Plant height-to-node ratio was reduced by the SC isolate only, the reduction being 13% at 32 °C compared to the control. Results from the current study imply that R. reniformis populations of distinct geographic origin have unique reproduction biology and genetic make-up, suggesting the inherent variability in R. reniformis should be considered by breeding programs for the development of durable resistance. The current study also reported that the changes in soil temperature further influenced reproduction biology of R. reniformis, implying a need for the development of reproduction biology-informed niche-specific management programs in cotton.
Recommended Citation
GC, Sagar, "Understanding Variability in Geographic Isolate of Rotylenchulus Reniformis Across the US Cotton Belt" (2026). All Dissertations. 4249.
https://open.clemson.edu/all_dissertations/4249