Screening for Resistance and Assessment of Soil Temperature Driven Reproduction Biology in Nematodes
Date of Award
8-2026
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Plant and Environmental Science
Committee Chair/Advisor
Dr. Churamani Khanal
Committee Member
Dr. William Rutter
Committee Member
Dr. Sandra Branham
Abstract
Rotylenchulus reniformis and Meloidogyne incognita are among the most economically important plant-parasitic nematodes affecting agricultural production. Although selected citron melon-derived rootstocks have been evaluated for their response to R. reniformis, broad-scale screening of Citrullus amarus plant introductions for variation in nematode reproduction has not been well characterized. To evaluate the response of C. amarus plant introductions to R. reniformis, we screened a core set of 126 C. amarus accessions from the USDA-ARS Genebank along with a watermelon cultivar (Charleston Gray) and a resistant rootstock (Carolina Strongback) as reference controls in a greenhouse environment. We further characterized nematode penetration, establishment, and development within roots of selected C. amarus PIs through microscopic observations and morphometric measurements of nematode growth at successive stages after inoculation. Significant variation in nematode reproduction, ranging from 1,080 to 98,094 eggs/g root, and reproduction factors (ratio of final population and initial inoculum) from 0.1 to 9.8 were observed among accessions at 60 days after inoculation (DAI). Microscopic observations revealed that R. reniformis juveniles were present within roots at 3 DAI, while vermiform females were observed at 6 DAI and 15 DAI. In contrast, only juveniles were detected at 30 DAI. Although nematodes successfully penetrated roots and exhibited limited growth within host tissues until 30 DAI, swollen kidney-shaped females characteristic of reproductive maturity were not observed. These findings indicate that C. amarus supports initial infection by R. reniformis but may limit sustained nematode development and reproduction. Similarly, soil temperature is among the major environmental factors that influences nematode distribution, life cycle, and survival. This study was conducted to assess the impact of four soil temperatures [26 °C (control), 28 °C, 30 °C, and 32 °C] on reproduction and virulence of M. incognita and percent hatch rate of the next generation in a greenhouse environment at two different sampling dates, 30 DAI and 45 DAI. Higher soil temperatures led to increased egg production and abundance of second-stage juveniles (J2) in the soil at both 30 and 45 DAI, resulting in higher gall severity. The highest reproduction and gall index were consistently observed at 32 °C at both time points. At 45 DAI, percent egg hatch remained unchanged between the control (26 °C) and 28 °C (48%) but increased to 56.8% at 30 °C and 67.4% at 32 °C. Percentage of eggs hatched at 32 °C was significantly greater than at all lower temperature regimes at both 30 and 45 DAI. Interactions between nematode inoculation and soil temperature did not significantly affect plant biomass or growth parameters. However, higher soil temperature of 32 ℃ supported 1.8 times higher reproduction at 30 DAI and 1.8 times higher gall index at 45 DAI compared to the control (26 °C), which suggests that rising soil temperatures driven by climate change will likely exacerbate crop losses to nematode damage.
Recommended Citation
Dhakal, Aarti, "Screening for Resistance and Assessment of Soil Temperature Driven Reproduction Biology in Nematodes" (2026). All Theses. 4814.
https://open.clemson.edu/all_theses/4814