The spotted alfalfa aphid, , is one of the most important pests of alfalfa, . Previous studies have revealed a significant difference in aphid numbers between the aphid-susceptible cultivar WL343 and the aphid-resistant cultivar Zhongmu No.1. To explore the reasons for this phenomenon, we constructed life tables for reared on these two alfalfa cultivars, and analyzed the changes in jasmonic acid (JA), salicylic acid (SA), secondary metabolites (total phenolic compounds, tannic acid, total flavonoids, and saponin), the activities of catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) in both cultivars following the introduction of aphids. In addition, we measured the gastric toxicity of secondary metabolites (tannic acid and saponin) against . Results revealed a lower fitness of on the resistant cultivar compared to the susceptible cultivar. The concentrations of JA, phenolic compounds, tannic acid, flavonoids, saponin, and the activities of CAT, SOD, and POD in the resistant cultivar were significantly higher than those in the susceptible cultivar. Subsequently, it was confirmed that tannic acid and saponin have direct gastric toxicity against . This indicated that the aphid-resistant cultivar inhibited aphid growth and fecundity by producing more defense substances, i.e., JA, secondary metabolites, and enhanced activities of protective enzymes including tannic acid and saponin found in alfalfa leaves directly associated with toxicity to , while reducing the content of SA. This study provides important support for breeding insect-resistant varieties while elucidating plant-resistant responses to insect herbivory.

中文翻译：

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抗蚜虫苜蓿品种通过上调植物防御化合物来最大限度地减少斑点苜蓿蚜虫的存活

苜蓿斑点蚜虫是苜蓿最重要的害虫之一。前期研究表明，易感品种WL343和抗蚜品种中牧1号的蚜虫数量存在显着差异。为了探究这一现象的原因，我们构建了这两个苜蓿品种的生命表，分析了茉莉酸（JA）、水杨酸（SA）、次生代谢产物（总酚类化合物、鞣酸、总黄酮、和皂苷），以及引入蚜虫后两个品种中过氧化氢酶（CAT）、超氧化物歧化酶（SOD）和过氧化物酶（POD）的活性。此外，我们还测量了次生代谢产物（单宁酸和皂苷）对 的胃毒性。结果显示，与感病品种相比，抗性品种的适应性较低。抗病品种JA、酚类化合物、鞣酸、黄酮类、皂苷含量以及CAT、SOD、POD活性均显着高于感病品种。随后，又证实单宁酸和皂甙对胃毒具有直接的胃毒性。这表明，抗蚜品种通过产生更多的防御物质，即JA、次生代谢产物，以及增强苜蓿叶中与蚜虫毒性直接相关的单宁酸和皂苷等保护酶活性，抑制蚜虫生长和繁殖，同时降低蚜虫的毒力。 SA 的内容。该研究为抗虫品种的选育提供了重要支持，同时阐明了植物对食草昆虫的抗性反应。