The Biological role of glycosides in alfalfa (Medicago sativa L.) as a resistance factor against alfalfa weevil (Hypera postica Gyll.)

After the identification of resistant, semi-susceptible, and susceptible genotypes among 42 alfalfa (Medicago sativa L.) genotypes concerning farm traits, nine genotypes were selected. Saponins obtained as a result of homogenous suspension of alfalfa tissue under maximum alfalfa weevil (Hypera postica Gyll.) attack were extracted using methanol and were purified using water-saturated butanol. The resulting solution was immobilized using the active enzyme extracted from the midgut of the pest and the thermally deactivated enzyme. In addition to the isolation of secondary glycosidic metabolites extracted from alfalfa, the enzymatic hydrolysis activity of the pest in the glycosides of genotypes were monitored using thin layer chromatography. The results of the enzymatic digestion test using TLC indicated that other than glycosides1 epigenin, other compounds were digested in the solution. The flavonoidal band of epigenin glycoside1 in all five resistant genotypes, including Tak Buteh and Ranger, was high in density and nearly equal. While maintaining the stability of the molecular structure, this compound was isolated and revealed at Rf=0.45 on a TLC plate. Therefore, midgut enzymes of alfalfa weevil were not able to digest the above compound in alfalfa. In two susceptible genotypes of Poly Cross Shiraz and Mahali Neyshaburi, the saponin band of soysaponin1 at Rf=37 had the highest density. In natural field conditions and at the time of biological stress, the lowest concentrations of saponin, soysaponin 1, and the highest concentration of flavonoids, epigenin glycoside 1, had a significant biological role in resistance to pests, and reduced damage to the cultivars under study.