Sugars and cuticular waxes impact sugarcane aphid (Melanaphis Sacchari) colonization on two different developmental stages of sorghum

Authors: CARDONA, JUAN - University Of Nebraska; GROVER, SAJJAN - University Of Nebraska; Bowman, Michael; BUSTA, LUCAS - University Of Minnesota; Sarath, Gautam; Sattler, Scott; LOUIS, JOE - University Of Nebraska

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2023
Publication Date: 2/18/2023
Citation: Cardona, J.B., Grover, S., Bowman, M.J., Busta, L., Sarath, G., Sattler, S.E., Louis, J. 2023. Sugars and cuticular waxes impact sugarcane aphid (Melanaphis Sacchari) colonization on two different developmental stages of sorghum. Plant Science. 330. Article 111646. https://doi.org/10.1016/j.plantsci.2023.111646.
DOI: https://doi.org/10.1016/j.plantsci.2023.111646

Interpretive Summary: Aphids feed on plant sap and can wreak significant economic damage to crops. The sugarcane aphid (SCA) is a newly emergent pest of sorghum across wide swaths of the US. SCA can infest and damage sorghum plants at different stages of maturity, although why SCA prefers one stage of plant development versus another is not known. Plants have a waxy coating on their leaves and stems, and the characteristics of this waxy layer can differentially influence aphid settling and feeding. Additionally, the complex composition of this waxy layer changes significantly between the juvenile and adult stages of the sorghum plant, suggesting that the composition of the waxy layer could influence SCA behavior. In this study, SCA preferences for juvenile versus adult plants were monitored using analysis of their feeding behavior and changes in plant waxy components and select sugars responding to aphid herbivory. Data indicated that SCA preferred the more adult plants as a source of food, but grew more rapidly on the juvenile plants. Juvenile plants contained more sucrose which might account for these findings. Two specific chemicals components of the leaf surface waxes were increased by SCA feeding only in the adult plants. Notably, SCA feeding depressed many of the compounds present in the waxy layer in juvenile plants relative to the more adult plants. Overall, these findings indicate a complex interaction between the aphids and the plants, and manipulating the waxy coating of leaves or the sugars in sorghum may represent new ways to strengthen plant resistance to this economically injurious pest for which there are currently limited control options.

Technical Abstract: Sugarcane aphid (SCA; Melanaphis sacchari) is a devastating pest of sorghum (Sorghum bicolor) and colonize sorghum plants at different stages of growth. Leaf surface characteristics and sugars often influence aphid settling and feeding on host plants. However, how changes in cuticular waxes and sugar levels affect SCA establishment and feeding at two different development stages of sorghum are not explored. In this study, two- and six-week-old BTx623 plants, a reference line of sorghum, was used to evaluate plant-aphid interactions. Monitoring aphid feeding behavior using Electrical Penetration Graph (EPG) technique revealed that aphids spent more time in the sieve element phase of six-week-old plants compared to two-week-old plants. Significant differences were found in the pathway phase and time spent to reach the first sieve element phase between the two-week and six-week-old plants. However, no-choice aphid bioassays displayed that SCA population numbers were higher in two-week-old plants compared to six-week-old plants. Differences in the abundance of the wax components and sugar contents were analyzed to determine how these plant components influenced aphid feeding and proliferation. Among the cuticular wax compounds analyzed, a-amyrin and isoarborinone, increased after aphid infestation only in six-week-old plants. Trehalose content was significantly increased by SCA feeding on two- and six-week-old plants. Furthermore, SCA feeding depressed sucrose content and increased levels of glucose and fructose in two-week-old but not in six-week-old plants. Overall, our study indicates that plant age is a determinant for SCA feeding, and subtle changes in triterpenoids and available sugars influence SCA establishment on sorghum plants.