Resistance to greenbugs in the sorghum nested association mapping population

Authors: GROVER, SAJJAN - University Of Nebraska; WOJAHN, BRADEN - University Of Nebraska; VARSANI, SURESH - University Of Nebraska; Sattler, Scott; LOUIS, JOE - University Of Nebraska

Submitted to: Arthropod-Plant Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2019
Publication Date: 4/1/2019
Citation: Grover, S., Wojahn, B., Varsani, S., Sattler, S.E., Louis, J. 2019. Resistance to greenbugs in the sorghum nested association mapping population. Arthropod-Plant Interactions. 13(2):261-269. https://doi.org/10.1007/s11829-019-09679-y.
DOI: https://doi.org/10.1007/s11829-019-09679-y

Interpretive Summary: The aphids called greenbugs are a serious pest of sorghum, and can contribute to economically significant losses of both grain and forage yields. For the past several decades, greenbug-resistant sorghum hybrids have been used to manage these aphids in farm fields. However, greenbug-resistant hybrids are continuously challenged by the ability of greenbugs to overcome resistant plants through the evolution of new aphid strains. Thus, there is a continuous need to identify new sources of sorghum resistant in order to manage this pest. In this study, a diverse set of sorghum lines were evaluated through a series of experiments to identify aphid-resistant plants and the genes behind sorghum resistance to greenbugs. These experiment identified SC265 and Segaolane as resistant and susceptible sorghum lines, respectively. The Electrical Penetration Graph (EPG) analysis was used to examine their feeding behavior on the resistance and susceptible sorghum plants. The greenbugs spent significantly lesser time feeding on the resistant line, SC265 as compared to the susceptible line Segaolane or standard line RTx430. The EPG results suggest that resistance factors are present in the veins of SC265 plants, which contribute to resistance mechanisms against greenbugs. Overall, SC265 affected both the greenbug feeding behavior and the health of the aphids after feeding, and both these components contribute to greenbug resistance of this plant line.

Technical Abstract: The greenbug, Schizaphis graminum, is a serious pest of sorghum (Sorghum bicolor). For the past several decades, resistant sorghum hybrids have been used to control greenbug populations. However, the durability of plant resistance is frequently challenged by evolution of new greenbug biotypes, and there is a continuous need for screening of resistant germplasm for its effective management in the field. Natural variation in sorghum plants/populations provides distinct approaches to identify novel sources of resistance against greenbugs. In this study, we used the recently developed sorghum nested association mapping (NAM) population parental lines to understand sources of sorghum resistance to greenbugs. Using choice and no-choice assays, we have identified SC265 and Segaolane as the resistant and susceptible lines, respectively, to greenbugs compared to the wild-type plants. The Electrical Penetration Graph (EPG) analysis revealed that the greenbugs spent significantly lesser time in the xylem and sieve element phases while feeding on the resistant NAM parental line, SC265, compared to the susceptible (Segaolane) and wild-type (RTx430) sorghum lines. In addition, the EPG results indicated that there is no significant difference in the time to first probe, time to reach first sieve element, pathway phase, and non-probing phase among the three sorghum plants, which suggests that the resistance factors present in the vascular tissues of the resistant line (SC265) potentially contribute to the resistance mechanisms against greenbugs. Overall, SC265 NAM parental line showed a combination of antixenotic and antibiotic-mediated resistance mechanisms against greenbugs, whereas the susceptible line Segaolane displayed the least resistance to greenbugs.