Date of Graduation
12-2024
Document Type
Thesis
Degree Name
Master of Science in Entomology (MS)
Degree Level
Graduate
Department
Entomology and Plant Pathology
Advisor/Mentor
Kariyat, Rupesh
Committee Member
Kud, Joanna
Second Committee Member
Jones, Austin
Keywords
Soybean; drought stress; water use efficiency; FAW feeding; insect resistance; wilting speed
Abstract
Soybean [Glycine max (L.) Merr.] is one of the most important food crops in the world due to its multiple uses in agriculture sector. A major limiting factor in soybean production system is drought stress, causing up to 80% reduction in yield. Due to climate change and associated rise in ambient temperatures, water scarcity is a major concern in crop production, and consequently researchers are turning to soybean accessions that demonstrate better water use efficiency (WUE) traits. However, field grown soybean is also under severe pressure from insect herbivores, often accounting for a 30% reduction in yield. Among these, Soybean looper (Chrysodeixis includens, SBL) and fall armyworm (Spodoptera frugiperda, FAW) are two major pests and have been found to reduce soybean yield by feeding on both foliar and floral organs.
The first part of this thesis aimed to investigate the impact of FAW feeding on soybean accessions that vary in their WUE traits, by examining FAW growth and life history parameters along with plant growth and response to FAW damage. Seventeen soybean accessions from the GRIN database provided by the USDA were grown in a greenhouse and exposed to feeding from second instar FAW for 48 hours at three different soybean growth stages: V3, R3, and R6. The growth and development of the soybean plants was monitored at each stage throughout the study. Once the soybean plants reached maturity, their pods were collected and counted. Following soybean exposure, the FAW were placed on artificial diet and allowed to pupate and emerge as adult FAW moths. Results showed that overall, fast wilting soybean accessions grow taller and have more leaves than slow wilting accessions, but slow wilting soybean accessions had a higher yield. Mid-stage (R3) soybean plants had the highest FAW mortality, but they gained the least mass on early stage (V3) soybean plants. FAW had higher mortality on fast wilting plants, potentially due to their increased trichome density. Overall, we observed significant variation in defense traits across soybean growth stages and wilting speeds with direct consequences on FAW development.
The second part of this thesis focused on understanding the intersection of WUE and insect resistance traits when exposed to pulsating drought and herbivory by FAW and SBL larvae. Using fast and slow wilting soybean accessions, we examined the interaction between physiological traits associated with WUE and insect resistance traits and how they influence soybean yield. Results showed that the soybean plants exhibited overcompensation regarding growth and development, but slow wilting genotypes yielded higher quality pods and seeds. Overall, FAW fed at a significantly higher rate than SBL despite being less specialized to feed on soybean. Fast wilting accessions had a higher pod yield than slow wilting accessions; however, slow wilting plants produced heavier pods with larger seeds. In terms of germination, there was no significant difference across wilting speeds and treatments.
These results advance our understanding in how plant insect-interactions at between soybeans with different wilting speeds various soybean growth stages can influence both FAW and SBL development. Overall, we show that different soybean wilting speeds have differential impacts on herbivore fitness. We also see that despite fast wilting plants overcompensating in terms of growth and pod production, slow wilting plants may still be more fit.
Citation
Ayala, J. (2024). Effects of Fast and Slow-Wilting Soybean Genotypes on Plant-Herbivore Interactions. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/5609
