Water Stress Modulates Soybean Aphid Performance, Feeding Behavior, and Virus Transmission in Soybean

Abstract

Little is known about how water stress including drought and flooding modifies the ability of plants to resist simultaneous attack by insect feeding and transmission of insect-vectored pathogen. We analyzed insect population growth, feeding behaviors, virus transmission, and plant amino acid profiles and defense gene expression to characterize mechanisms underlying the interaction between water stress, soybean aphid and aphid-transmitted, Soybean mosaic virus, on soybean plants. Population growth of non-viruliferous aphids was reduced under drought stress and saturation, likely because the aphids spent less time feeding from the sieve element on these plants compared to well-watered plants. Water stress did not impact population growth of viruliferous aphids. However, virus incidence and transmission rate was lowest under drought stress and highest under saturated conditions since viruliferous aphids took the greatest amount time to puncture cells and transmit the virus under saturated conditions and lowest time under drought stress. Petiole exudates from drought-stressed plants had the highest level of total free amino acids including asparagine and valine that are critical for aphid performance. Aphids did not benefit from improved phloem sap quality as indicated by their lower densities on drought-stressed plants. Saturation, on the other hand, resulted in low amino acid content compared to all of the other treatments. Drought and saturation had significant and opposing effects on expression of marker genes involved in abscisic acid (ABA) signaling. Drought alone significantly increased expression of ABA marker genes, which likely led to suppression of salicylic acid (SA)-and jasmonic acid (JA)-related genes. In contrast, ABA marker genes were down-regulated under saturation, while expression of SA-and JA-related genes was upregulated. We propose that the apparent antagonism between ABA and SA/JA signaling pathways contributed to an increase in aphid densities under drought and their decrease under saturation. Taken together, our findings suggests that plant responses to water stress is complex involving changes in phloem amino acid composition and signaling pathways, which can impact aphid populations and virus transmission.

Location, location, location: Feeding site affects aphid performance by altering access and quality of nutrients

“…The soybean variety Asgrow AG3432 was used for all experiments. Plant growth and soybean aphid maintenance were as per Nachappa, Culkin (24). Briefly, plants were grown in Mastermix 830 soilless media (Mastermix, Quakertown, PA) in 15.24 cm diameter x 14.61 cm height plastic pots and watered three times per week.…”

“…In separate experiments, plants (variety AG3432) were grown in pots with a 30.5 cm diameter (Myers Industries Marysville, OH, USA) until the V1 growth stage. Vascular sap-enriched stem and leaf petiole exudates were collected as per Nachappa et al [24]. In order to prevent bacterial contamination, trifoliates were cut at the base of the petioles or stems cut 2 cm above the soil surface were immersed in 50% ethanol, and then immediately moved to 0.05% bleach solution for no more than 2-3 seconds to achieve surface sterilization of the petiole and stem cut surfaces.…”

Soybean Resistance to Soybean Mosaic Virus

“…SMV is a seed-and aphid-transmitted virus, and aphids uptake SMV in a non-persistent manner [47,76]. Aphid transmission depends on the interaction between HC-Pro and CP proteins.…”

Biology and Economics of Recommendations for Insecticide-Based Management of Soybean Aphid

“…To survive and reproduce, soybean aphids require specific nitrogen-rich amino acids that are present in plant fluids at low concentrations (Douglas and van Emden 2007;Mittler and Douglas 2003;Walter and DiFonzo 2007), which means they must ingest large quantities of plant fluids to fulfill their nutritional needs (Douglas and van Emden 2007). Nutrient (Myers et al 2005;Myers and Gratton 2006;Walter and DiFonzo 2007) and moisture (Nachappa et al 2016) status of soybean influences the composition of the plant fluids and, in turn, soybean aphid. In addition, quality of plant fluids likely influences location of soybean aphids within the canopy as plants age (McCornack et al 2008).…”