Evaluation and characterization of aphid (Aphis craccivora) resistance in selected alfalfa genotypes

Abstract

Aphis craccivora Koch, 1854, a major pest of alfalfa, causes severe crop damage not only through direct feeding but also, and more critically, as a vector for devastating plant viruses, causes severe crop damage due to its rapid reproduction and high resistance to pesticides. This study aimed to identify alfalfa cultivars with natural resistance to A. craccivora and to elucidate the underlying resistance mechanisms by testing the hypothesis that specific plant nutrients and secondary metabolites are key drivers of aphid resistance. To evaluate the suitability of alfalfa cultivars for cultivation in southern China in terms of their resistance to A. craccivora, life tables were constructed for aphids reared on different cultivars. In addition, the nutrient and secondary metabolite contents of the alfalfa were quantified, and their correlations with aphid life-history parameters were analyzed. The results showed that alfalfa cultivars significantly influenced the life history of A. craccivora, with the Algonquin cultivar exhibiting the strongest negative effects. Integrating life table parameters with chemical profiling revealed that tannins and total phenols are key biomarkers for resistance. Elevated levels of these compounds were strongly associated with a cascade of detrimental effects on A. craccivora, including reduced adult longevity, shortened oviposition periods, and a decreased net reproductive rate, ultimately leading to suppressed population growth. Algonquin was identified as a cultivar with strong natural resistance to A. craccivora, while also elucidating the physiological and biochemical characteristics underlying resistance among alfalfa cultivars. These findings provide a theoretical basis for breeding insect-resistant alfalfa and for developing integrated pest management (IPM) strategies.