Date of Award
12-2024
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Plant and Environmental Science
Committee Chair/Advisor
Dr. Daniel J. Anco
Committee Member
Dr. John D. Mueller
Committee Member
Dr. Anthony Keinath
Committee Member
Dr. Sachin Rustgi
Abstract
Peanut ring nematode, Mesocriconema ornatum is a nematode pest of peanut which can cause necrotic lesions on pods, pegs, and roots. It has been reported to facilitate secondary infections in peanut and other crops resulting in more significant losses in yield and quality. Aspergillus flavus is a ubiquitous facultative saprophyte that produces aflatoxin, the most problematic mycotoxin for global health and economy. Experiments were conducted at the Edisto Research and Education Center of Clemson University to examine the relationship of ring nematode populations at pegging and harvest with aflatoxin concentration in peanut kernels due to infection by A. flavus. In four field-years, pesticide treatments were applied to create varying ring nematode densities from which relationships with pod yield and kernel aflatoxin contamination were examined. Pesticide applications were ineffective in reducing aflatoxin levels. In 2022, ring nematode populations were not significantly different from the non-treated control among treatments across all sampling times. However, Admire Pro, with or without Velum, followed by Propulse had the least number of ring nematodes (0 nematodes per 100 cc soil) while Thimet applied with Admire Pro or Velum had significantly greater ring nematodes/100 cc in one of two examined sites. Aflatoxin levels were variable and not affected by ring nematode populations at the time of pegging or harvest. However, a small positive relation was found in the pooled field data with regard to ring nematode soil quantities at pegging In 2023, nematode populations did not differ among treatments in either field except approximately 45 days after planting in one field where Orthene-treated plots had the least number of ring nematodes (0 nematodes/100 cc soil) and all the other treatments had similar ring nematode populations compared to the non-treated control. The ring nematode counts from soil and lesion nematodes extracted from roots or pods were negatively correlated (ρ=-0.27, pvalue=0.01 and ρ=-0.38, pvalue < 0.001 on roots and pods, respectively). Increases in ring nematode populations during the growing season ranged from 3.4 to 8.6 times from near 45- to 80-days after planting; however, this was not associated with a significant corresponding negative impact on pod yield. Ring nematode populations in the irrigated field further increased until harvest, whereas ring nematode numbers measured in the non-irrigated field subsequently decreased by the time of harvest. Peanuts grown in irrigated fields had significantly lower aflatoxin compared to the non-irrigated fields. Results from greenhouse experiments examining co-inoculation of ring nematode and A. flavus were consistent with those from the field showing the lack of a direct or consistent relationship between ring nematode and A. flavus incidence in terms of subsequent aflatoxin contamination.
In a survey conducted in SC peanut fields, 59% of the sampled fields had Peanut ring nematode (M. ornatum) which was confirmed by DNA sequencing on ribosomal genes. Increased numbers of M. ornatum were associated with higher sand content and lower clay content.
This work adds new data to the current understanding on the presence of ring nematode species in SC as well as the relationship between ring nematode and A. flavus in peanut.
Keywords: Aspergillus. Flavus; Mesocriconema ornatum; Aflatoxin; SC Peanut fields
Recommended Citation
Giri, Sarala, "Field Prevalence of Ring Nematodes in South Carolina and Its Potential to Predispose Peanut Pods to Aflatoxin Contamination" (2024). All Theses. 4420.
https://open.clemson.edu/all_theses/4420
