Cowpea Aphid Resistance In Cowpea Line CB77 Functions Primarily Through Antibiosis And Eliminates Phytotoxic Symptoms of Aphid Feeding

Abstract

Cowpea (Vigna unguiculata) is one of the most important crops in semiarid areas of the world, where it thrives in hot, dry conditions. While cowpea is able to withstand abiotic stresses, it suffers serious losses from biotic antagonists, including infestation by the cowpea aphid (Aphis craccivora). Cowpea aphid infestations are highly destructive, especially on young plants. However, it is unclear whether cowpea aphid damage is the result of aphids having phytotoxic effects on their hosts, or simple density effects. To better understand cowpea aphid damage and the potential for resistance traits to mitigate aphid impacts, we evaluated phenotypic changes in cowpea in response to variable aphid densities and systemic versus local infestations. Low aphid densities induced leaf distortions and pseudogalling, suggesting that cowpea aphids are phytotoxic to cowpea. Resistance to the cowpea aphid has been previously identified in an African cowpea germplasm, and near isogenic lines (NILs) containing resistance quantitative trait loci (QTL) were generated in the California blackeye cultivar background. Using a series of performance assays, we determined that resistance conferred by the two QTL counteracts aphid phytotoxicity and severely limits aphid growth and fecundity. Using choice assays, a preference by cowpea aphids for the susceptible NIL was observed. Electrical penetration graph analysis revealed that the resistance phenotype includes weak surface level deterrence and strong phloem based resistance that manifests during the sap ingestion phase. Our study provides evidence of phytotoxic traits in A. craccivora while identifying a viable means of counteracting aphid damage and reproductive potential through resistance.

Transcriptome analysis of aphid-resistant and susceptible near isogenic lines reveals candidate resistance genes in cowpea (Vigna unguiculata)

“…The first exploration of the phenotype of the NIL resistance mechanism reported a lack of aphid damage symptoms after two weeks of infestation [14]. In contrast, susceptible plants (e.g.…”

“…Antixenosis was identified as a secondary resistance mechanism through use of the electrical penetration graphing technique (EPG) and aphid choice assays. Cowpea aphids were deterred by the resistant NIL before phloem access and suffered reduced reproduction when forced to feed on the resistant NIL as the sole food source [14].…”

“…This time course included time points capturing early responses (1-day) and late responses following chronic damage (6-day). The early time point was chosen to elucidate responses underlying cowpea aphid nonpreference for resistant cowpea, identified previously by EPG recordings and choice assays [14]. The later time point captures gene expression responses during prolonged aphid feeding, which may provide insight into the mechanism of antibiosis (reduced population growth) seen previously.…”

Reactive Oxygen Species in Plant Interactions With Aphids

“… *Aphid species that cause marked morphological alterations or other severe, diagnostic symptoms are in bold. 1 This species is reported to be phytotoxic on amaranth ( Bayendi Loudit et al, 2018 ), cowpea ( MacWilliams et al, 2021 , preprint) and certain other legumes ( Quisenberry and Ni, 2007 ), but its status on soybean is not to our knowledge reported in published literature. 2 Phytotoxic symptoms described in Borowiak-Sobkowiak et al (2016) .…”

“… 1 This species is reported to be phytotoxic on amaranth ( Bayendi Loudit et al, 2018 ), cowpea ( MacWilliams et al, 2021 , preprint) and certain other legumes ( Quisenberry and Ni, 2007 ), but its status on soybean is not to our knowledge reported in published literature. …”