Protocol for assessing soybean antixenosis toHeliothis virescens

Abstract

Larvae of Heliothis virescens (Fabricius) (Lepidoptera: Noctuidae) often infest soybean crops, Glycine max (L.) (Fabaceae), causing significant yield losses in important soybean-producing regions. The use of soybean varieties resistant to lepidopteran larvae is a major approach in soybean integrated pest management. However, standardization and optimization of bioassays that are used to screen genotypes for insect resistance are essential for high-throughput phenotyping. Methodologies for screening were assessed to determine the most effective method for discriminating levels of antixenosis to H. virescens in soybean plants. Feeding and oviposition preference assays were performed to determine optimal densities of larvae and adults, and optimal plant structures and growth stages for conducting assays. In addition, trichome densities, and fiber and lignin contents were quantified in plant structures of soybean cultivars differing in resistance. Resistance levels of cultivars were best differentiated using nine neonate larvae and two 6-day-old larvae, and by using young leaves of plants at the vegetative stage. This was likely due to the more pronounced differences in lignin and fiber contents in young leaves of vegetative-stage plants. Density of adult pairs, plant structure, and growth stage did not affect ability to distinguish differences in oviposition preference by H. virescens. Higher numbers of eggs were found on the leaves, which were the plant structures that exhibited the lowest trichome densities. The protocol developed in this work will benefit future evaluations of soybean genotypes for antixenosis against H. virescens.

Soybean leaf age and plant stage influence expression of resistance to velvetbean caterpillar and fall armyworm

“…The results obtained here and in the study of Boiça Júnior et al (2015) for the differential responses of VBC and FAW on the older leaves from the lower part of resistant soybean plants indicate that effects of both antixenosis-and antibiosis-resistance are overlapped, as previously discussed by Stout (2013). This information coupled with the knowledge that leaf age and plant stage in uence the magnitude of resistance expression in soybean can bene t the design of speci c protocols of high-throughput screening assays for insect-resistance traits (Boiça Júnior et al 2015;Eduardo et al 2020).…”

Protocol for assessing soybean antibiosis toChloridea virescens

“…Tannins can reduce herbivory due to astringency, decreased nutrient assimilation, and damage to insect midguts, ultimately affecting their development (Sharma & Agarwal, 1983;Lattanzio et al, 2005;Sharma et al, 2009;Barbehenn & Constabel, 2011). Higher fiber and lignin contents can increase the hardness of plant structures (Coley, 1983), negatively influencing tissue digestibility for insects (Parra & Kogan, 1981;Miranda et al, 2002;Boiça Júnior et al, 2016), and causing feeding deterrence on immature stages of insects (Eduardo et al, 2020).…”

“…There have been several recent studies evaluating soybean cultivars for resistance to lepidopterans (Souza et al, 2014a,b; Boiça Júnior et al, 2015; Favetti et al, 2015; Wang et al, 2015; Chen et al, 2018; Freitas et al, 2018; Coelho et al, 2020; Queiroz et al, 2020), including C. virescens (Almeida et al, 2017a,b). However, studies aiming to develop an adequate, high‐throughput phenotyping protocol to evaluate soybean cultivars for resistance to lepidopterans are scarce in the literature (Eduardo et al, 2020), and to our knowledge, no studies have determined a protocol for antibiosis assays in soybean to lepidopterans. Choosing an appropriate protocol is important because there are various abiotic and biotic factors that can influence the expression of plant resistance, insect behavior, and herbivore biology (Smith, 2005).…”

“…Within this chemical group, tannins are noted for their insecticidal activity, and may negatively affect insect growth and development by causing lesions in the midgut, reducing consumption due to their astringent properties, and consequently reducing nutrient assimilation (Sharma & Agarwal, 1983;Lattanzio et al, 2005;Sharma et al, 2009;Barbehenn & Constabel, 2011). Fiber and lignin are also related to plant resistance; higher contents of these compounds can increase the hardness or toughness of plant structures (Coley, 1983), negatively influencing tissue digestibility in insects (Parra & Kogan, 1981;Miranda et al, 2002;Boiça Júnior et al, 2016), and causing feeding deterrence to lepidopteran larvae (Eduardo et al, 2020).…”

Soybean Leaf Age and Plant Stage Influence Expression of Resistance to Velvetbean Caterpillar and Fall Armyworm

“…The results obtained here and in the study of Boiça Júnior et al(2015) for the differential responses of VBC and FAW on the older leaves from the lower part of resistant soybean plants indicate that effects of both antixenosis-and antibiosis-resistance are overlapped, as previously discussed byStout (2013). This information coupled with the knowledge that leaf age and plant stage in uence the magnitude of resistance expression in soybean can bene t the design of speci c protocols of high-throughput screening assays for insect-resistance traits (Boiça Júnior et al 2015;Eduardo et al 2020).Differences in effects of genotype and leaf age/plant stage on the development of each insect species in this study were likely due to differences in their feeding behavior and adaptation to soybeans. Larvae of VBC are oligophagous and feed basically on leguminous plants(Kogan and Turnipseed 1987), while larvae of FAW are polyphagous and develop well on plants of taxonomically disparate families(Barros et al 2010).…”