Elucidating the Innate Mechanisms of Resistance in Sorghum to Sorghum Aphid
Validating sorghum aphid (SA) resistance hinges upon an inherently subjective methodology that necessitates significant infestation. Moreover, this methodology is incapable of elucidating the mechanistic basis of aphid resistance. Failing to develop an objective methodology that can index resistance traits independent of infestation will hinder the creation of sustainable solutions. However, understanding the relationship between aphids and hosts provides a useful framework. This can be achieved by adopting an ecocentric approach that values both aphid and host, leading to an objective trait-based phenotyping platform. We conducted a three-year study to identify key traits of innate sorghum resistance, categorized into pre-contact, contact, and tolerance mechanisms, all analyzed under uninfested conditions. To ensure the best contrast, we implemented two reliable SA resistant sorghum lines (R. LBK1 and R. Tx2783) and two SA susceptible lines (R. Tx7000 and R. Tx430). Two distinct volatile organic compounds, 4-hydroxybenzaldehyde, and trans-β-ionone, were identified as biomolecular markers of innate SA resistance mechanisms. Meanwhile, stomatal density, trichome density, length, and chloroplast density were pinpointed as key indicators of contact resistance mechanism. Our results may promote the development of high-throughput platforms for objective determination of sorghum aphid resistance, regardless of infestation. However, these findings need validation across a diverse sorghum population before being considered true indicators of aphid resistance.