Pulsating Drought and Insect Herbivory Cause Differential Effects on Soybean (Glycine max) Genotypes That Vary in Canopy Wilting Speed

Abstract

As a result of climate change, global temperatures are increasing, and water scarcity is on the rise. Soybean [Glycine max (L.) Merr] is one of the most important crops in the world due to its importance as food and feed. One of the major limiting factors for soybean production is drought, which can cause up to 80% reduction in yield. Therefore, growers and plant breeders are turning to soybean accessions that demonstrate better water use efficiency (WUE). However, in addition to drought, insect herbivory by soybean looper (Chrysodeixis includens, SBL) and fall armyworm (Spodoptera frugiperda, FAW) can also reduce soybean yield by feeding on foliar and floral organs. Using soybean accessions that differ in their wilting speed, we examined the relationship between physiological traits associated with WUE, and how they affect both herbivore and host plant growth and development. Results showed that both fast- and slow-wilting genotypes displayed strong overcompensation in terms of growth and development, but slow-wilting genotypes produced higher-quality pods and seeds. Regardless of treatment effects, FAW fed at a significantly higher rate than SBL despite being less specialized to feed on soybeans. While fast-wilting plants produced more pods than slow-wilting plants regardless of treatment, slow-wilting plants produced heavier pods with larger and heavier seeds. Collectively, we show that despite fast-wilting plants overcompensating in pod production and growth traits, slow-wilting plants may still be better fit through seed functions.