Functional and ecological investigations in Cucurbita: factors mediating fruit infections and insect interactions

Bacterial spot disease of cucurbits, caused by Xanthomonas cucurbitae, poses a significant threat to pumpkin production. This study aimed to investigate the role of the exocellulase gene cbhA in disease development by comparing a wildtype IL 234 4R isolate to a ΔcbhA mutant in greenhouse fruit inoculation trials. Eight experiments were conducted, including four with the wildtype isolate alone, and four comparing wildtype and mutant strains. Regression analysis of wildtype-inoculated fruit revealed a significant age-related resistance trend, with disease severity peaking at 10–12 days post-pollination. A quadratic model showed fruit age and bacterial concentration were strong predictors of disease area. Mutant-inoculated fruit exhibited weak, non-significant associations with age. Analyses indicated no statistically significant difference in disease severity between wildtype and mutant strains across experiments. Our results suggest cbhA is not essential for fruit pericarp infections but may play a role in vascular pathogenesis or possibly be compensated for by alternative virulence factors. Cucurbit‐feeding beetles such as western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), spotted cucumber beetle Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae), and the striped cucumber beetle, Acalymma vittatum Fabricius (Coleoptera: Chrysomelidae). are major pests of pumpkins and related Cucurbita crops. We evaluated how floral resource availability and cultivar identity influenced beetle abundance across two field seasons on 16–21 pumpkin cultivars. Each season, randomized blocks of pumpkin cultivars were planted and sampled weekly over six weeks. We used statistical models to assess the effects of weekly flower count and sampling week on beetle abundance. We also screened greenhouse‐grown flowers of cultivars by ultra-performance liquid chromatography to quantify cucurbitacin B levels. Both flower availability and cultivar identity strongly influence beetle abundance. Although flowers provide essential feeding sites, inherent cultivar traits significantly modify attraction. These findings demonstrate selecting cultivars with lower beetle‐attraction profiles or pairing high‐cucurbitacin lines as trap crops could reduce pesticide reliance.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Lee, Iris

Contributors dc:contributor

• Hind, Sarah Refi
• Jamann, Tiffany
• Seiter, Nicholas

• Xanthomonas
• plant pathology
• entomology
• cucurbits
• cucurbitae

Statement dc:rights

• Copyright 2025 Iris Lee

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132722

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132722