Screening of Aphid-Resistant Faba Bean Germplasm and Identification of Key Physiological and Biochemical Indicators Associated with Aphid Resistance

Aphis craccivora is a major piercing–sucking insect pest in faba bean (Vicia faba L.) production and severely restricts yield and quality. To identify aphid-resistant genetic resources and clarify the key physiological and biochemical mechanisms underlying resistance and susceptibility, 937 faba bean germplasm accessions were evaluated using a stepwise strategy comprising natural field screening, precise net-house re-screening, laboratory validation based on aphid life-table parameters, and physiological and biochemical characterization of representative resistant and susceptible accessions. After final laboratory validation, three resistant and three susceptible accessions were selected and subjected to aphid feeding for 0 h (CK), 36 h, and 72 h. Eleven physiological and biochemical traits were dynamically analyzed, including the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and phenylalanine ammonia-lyase (PAL), as well as the contents of soluble protein, soluble sugar, free amino acids, tannins, total phenolics, flavonoids, and lignin. Three stable aphid-resistant accessions were ultimately identified. Laboratory life-table analysis showed that the net reproductive rate of aphids on resistant accessions was significantly lower than that on susceptible accessions, with R0 decreasing from 53.63 to 25.08, representing a reduction of 53.2%. The intrinsic rate of increase decreased by 26.7%, whereas the mean generation time increased by 10.7%, confirming the reliability of the screening results. Physiological and biochemical analyses showed that aphid feeding induced significant and time-dependent increases in SOD, POD, CAT, and PAL activities and in tannin, total phenolic, flavonoid, and lignin contents in resistant accessions, whereas these defense responses were weak in susceptible accessions. In contrast, susceptible accessions showed abnormal accumulation of soluble sugars and free amino acids, whereas resistant accessions maintained these nutrients at low levels. Lignin exhibited both constitutive and inducible defense characteristics in resistant accessions and emerged as a prominent candidate indicator for aphid resistance in faba bean. This study establishes an effective technical pipeline for screening aphid-resistant faba bean germplasm and reveals a coordinated defense network involving antioxidant enzymes, phenylpropanoid metabolism, secondary metabolites, and physical barriers. These findings provide elite parental germplasm and theoretical support for aphid-resistance breeding in faba bean.