Abstract
Plant resistance can provide effective, economical, and sustainable pest control. Tolerance to the soybean aphid has been identified and confirmed in the soybean KS4202. Although its resistance mechanisms are not fully understood, evidence suggests that enhanced detoxification of reactive oxygen species (ROS) is an active system under high aphid infestation. We further explored tolerance by evaluating the differences in constitutive and aphid-induced defenses in KS4202 through the expression of selected defense-related transcripts and the levels of the phytohormones abscisic acid (ABA), jasmonic acid (JA), JA-isoleucine (JA-Ile), cis-(+)-12-oxo-phytodienoic acid (OPDA), and salicylic acid (SA) over several time points. Higher constitutive levels of ABA and JA, and basal expression of ABA- and JA-related transcripts were found in the tolerant genotype. Conversely, aphid-induced defenses in KS4202 were expressed as an upregulation of peroxidases under prolonged aphid infestation (>7 days). Our results point at the importance of phytohormones in constitutive defense in KS4202 tolerance to the soybean aphid. Understanding the underlying mechanisms of tolerance will assist breeding for soybean with these traits, and perhaps help extend the durability of Rag (Resistance to Aphis glycines)-mediated resistance genes.
Highlights
Hemipterans, within the family Aphididae, are one of the most economically important insect pests on plants worldwide, representing 26% of the 45 major crop pests of main food crops in temperate climates[3]
Consistent with previous studies[17,47], aphid population numbers were similar between soybean genotypes and the brief duration of soybean aphid infestation did not result in visual damage for either tolerant or susceptible soybean
Our results indicate that constitutive levels of salicylic acid (SA) do not appear to be different between tolerant and susceptible genotypes (Fig. 2e; P = 0.21); aphid infestation resulted in higher SA levels at 6 hpi in all soybean genotypes (Fig. 2e; KS4202: P = 0.0168; K03-4686: P = 0.0041; Wyandot: P = 0.0421)
Summary
Hemipterans, within the family Aphididae, are one of the most economically important insect pests on plants worldwide, representing 26% of the 45 major crop pests of main food crops in temperate climates[3]. Redox control is governed by enzymes and antioxidants that rapidly detoxify ROS Environmental stressors, such as insect feeding, may cause oxidative bursts leading to ROS accumulation, and cell toxicity and death. The current literature on compatible and incompatible interactions between plants and several aphid species has uncovered that plants defend themselves using a variety of defense signaling pathways. Many of these interactions are dependent on several hormonal pathways, including but not limited to salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) signaling[20,21,22]. Abscisic acid (ABA) plays an important role in abiotic stress tolerance and pathogen resistance though its role in insect-plant interactions is less understood
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