Differential responses to Melanaphis sorghi (Hemiptera: Aphididae) reveal diverse resistance mechanisms across sorghum genotypes.

Sorghum aphid (Melanaphis sorghi  Theobald) is a major constraint to sorghum production, making the identification of resistant germplasm essential for sustainable management. Understanding plant resistance mechanisms is crucial for developing effective pest management strategies. This study assessed resistance mechanisms in a panel of sorghum genotypes representing broad geographic origins and possible genetic diversity using antixenosis, antibiosis, and tolerance assays. Antixenosis assays demonstrated that the genotypes ICRISAT 29, ICRISAT 218, Lunuo 45A, and Tx2783 possessed strong antixenotic resistance, as evidenced by low aphid colonization. Antibiosis screening demonstrated that PI 656025, Lunuo 45A, PI 542718, ICRISAT 218, and ICRISAT 29 significantly reduced aphid reproduction, maintained higher chlorophyll content, and sustained low damage scores (≤3.0) at 15 days post-infestation (dpi). In contrast, Tx7000 and other susceptible genotypes were completely desiccated by this time point. Tolerance was moderate in ICRISAT 218, PI 656025, ICRISAT 29, and Lunuo 45A, but no highly tolerant genotype was identified. Integration of these resistance traits through the Plant Resistance Index (PRI) highlighted Lunuo 45A, ICRISAT 29, ICRISAT 218, PI 656025, and Tx2783 as the most promising lines, while multi-trait genotype-ideotype distance index (MGIDI) analysis identified PI 656025, ICRISAT 218, Lunuo 45A, and ICRISAT 29 as strong multi-trait candidates. Overall, this study reveals distinct resistance mechanisms within the sorghum germplasm panel and identifies several genotypes with strong potential for sorghum breeding programs. The integration of antixenosis, antibiosis, and tolerance provides a robust framework for developing sorghum cultivars with durable resistance to sorghum aphids.