Physiological and molecular mechanisms of moisture stress in soybean: Impacts on soybean aphid populations and virus infection
Soybean (Glycine max (L.) Merr.) is an important crop due to its versatility as a food source, and applications in industries such as biofuel and textiles. Drought stress is a major environmental concern causing reduced yields, as well as, promoting outbreaks of insects and pathogens. Soybean aphid (Aphis glycines Matsumura) is an invasive pest that not only reduces yields by feeding, but also transmits economically-important viruses such as the Soybean mosaic virus (SMV). The objectives of my study were to: (1) determine effects of drought stress on aphid populations and SMV infection and (2) determine plant physiological and molecular mechanisms underlying the interaction. Soybean plants were subjected to varying levels of moisture stress (drought, well-watered, and saturated) and exposed to non-viruliferous aphids and viruliferous aphids. Plants subjected to well-watered conditions harbored highest aphid populations, whereas drought stress reduced aphid populations. Aphid populations were lowest on saturated plants. Moisture stress did not affect viruliferous aphid populations, but virus replication was significantly reduced in well-watered and drought-stressed plants. Interestingly, saturated plants had highest SMV titer. Artificial feeding assays using petiole exudates from moisture-stressed plants indicated a major impact on plant nutritional status. Drought stress caused a significant increase in concentrations of total free amino acids. Additionally, there were significant differences were observed in several individual amino acids essential to aphid development and fecundity. Gene expression analysis revealed that drought stress caused up-regulation of RD20A, a marker for Abscisic acid. In contrast, drought stress reduced SARK expression which is a marker gene for Ethylene and Auxin. Moisture stress significantly affected expression of Salicylic acid (SA) and Jasmonic acid (JA) -related genes. Nevertheless, antagonistic crosstalk was evident between the SA and JA pathways. These results suggest that during moisture stress a complex interplay between plant nutritional status and defense responses influence outcomes between soybean aphids, SMV, and host plants.
Nachappa, Purdue University.
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