Evaluation of Tetraploid Switchgrass (Poales: Poaceae) Populations for Host Suitability and Differential Resistance to Four Cereal Aphids

Abstract

Switchgrass, Panicum virgatum L., is being developed as a bioenergy feedstock. The potential for large-scale production has encouraged its evaluation as a host for important grass pests. Eight no-choice studies were performed for two developmental stages of two switchgrass cultivars ('Kanlow' and'Summer') and two experimental strains, K x S, and S x K produced by reciprocal mating of these cultivars followed by selection for high yield. Plants were evaluated for host suitability and damage differences to herbivory by four important cereal aphids, Sipha flava (Forbes), Schizaphis graminum (Rondani) (biotype I), Rhopalosiphum padi (L.), and Diuraphis noxia (Mordvilko). All switchgrasses were found to be unsuitable feeding and reproductive hosts to R. padi and D. noxia, which were unable to establish on the plants. However, both S. flava and S. graminum were able to establish on all switchgrasses tested. Differential levels of resistance to S. flava and S. graminum were detected among the switchgrasses by both cumulative aphid days (CAD) and plant damage ratings. Kanlow was consistently rated as highly resistant based on CAD and damage ratings for both aphid species, while Summer was consistently among the most susceptible to both aphids at both developmental stages, with relatively high damage ratings. The resistance of the K x S and S x K populations in relationship to their Summer and Kanlow parents indicted that they inherited some resistance to S. graminum and S. flava from their Kanlow parent. These studies provide valuable baseline information concerning the host suitability of switchgrass to four cereal aphids and the plant-insect interactions within a system that has been largely overlooked and indicate that there are genetic differences among switchgrass populations for resistance to some insects.

Categories of Resistance to Greenbug and Yellow Sugarcane Aphid (Hemiptera: Aphididae) in Three Tetraploid Switchgrass Populations

“…Plants were grown to the V-1 stage [23] in Cone-tainers essentially as described earlier [19]. Each Cone-tainer had a single plant.…”

“…Attempts were made to condition aphids on the same switchgrass population and developmental stage they were to be tested on for at least 1 week; however, efforts to condition enough of either aphid species on Kanlow were unsuccessful. As a result, all aphids were conditioned for at least 1 week prior to the beginning of each study on Summer, which had preliminarily been identified as the susceptible population [19], in the V-1 stage.…”

“…Dowd and Johnson [9] noted that the apparent lack of insect pest problems in switchgrass suggested that insect resistance genes are present. Differential resistance has been documented among switchgrass populations to potential insect pests including, S. frugiperda [9,10], as well as S. flava and S. graminum [19]. Further, Dowd et al [10] were able show that multiple resistance mechanisms may be at work; however, the categories and relative levels of resistance being expressed among these populations have remained undocumented.…”

Characterization of Greenbug Feeding Behavior and Aphid (Hemiptera: Aphididae) Host Preference in Relation to Resistant and Susceptible Tetraploid Switchgrass Populations

“…The origin of these cultivars and experimental strain has been published [26,27]. The experimental strain was developed by Dr. Kenneth Vogel, USDA-ARS (retired), Lincoln, NE, who also provided seeds of the cultivars.…”

“…Recently, Koch et al [26,27] have shown that tetraploid switchgrasses can serve as suitable hosts for two different aphids, namely the greenbug, Schizaphis graminum (Rondani), and the yellow sugarcane aphid, Sipha flava (Forbes). Both aphids can be found across the USA and have been well characterized as pests of many cultivated and native grasses [6,7,24,31].…”