Endogenous resistance to insect pests in alfalfa: engineering for enhanced resistance

摘要: Alfalfa (Medicago sativa) is a valuable forage crop grown throughout the World. While resistant to attack by many insect pests, it subject potentially severe losses through action of several specific which are adapted alfalfa as host. The most economically damaging these pests weevil, Hypera postica. This thesis investigates endogenous defences against insects, responsible for its resistance non-pest species, and develops strategy increasing towards pest specifically weevil. role saponins in species has been investigated using successive bioassays, carried out with extracts, mixtures compounds, purified identify compounds present tissues toxicity insects. Crude saponin 80% methanol, from seedling were bioassayed cowpea seed Callosobruchus maculatus. Both extracts shoot root caused larval mortality delayed development when incorporated into an artificial diet at levels comparable those found alfalfa, but lower showed probiotic effects, whereas still toxic. Hydrolysis decreased their toxicity. Purified prepared butanol partition ether precipitation, potato aphid (Aulacorthum solani) liquid diet, allowed quantitative effects be accurately assayed. Shoot concentration-dependent toxic effect, decreasing survival over initial 5 day period, growth, inhibiting fecundity (measured nymph production) no deleterious below threshold level, complete above this level. separated fractions chromatography on reverse phase column. Bioassays that was associated only containing saponins, component identified soyasaponin I more aphids than others. Finally, two medicoside A, These assays consistently mortality, growth fecundity. It concluded particular I, major factors aphid, other A mixture another sugar beet {Beta vulgaris) also aphids, supporting view have general Inhibition digestive proteolysis expression foreign protein protease inhibitor selected protect transgenic activity larvae msect shown due cysteine proteases, could inhibited cystatins. Rice cystatin produced large quantity recombinant system E. coli use "proving" experiment. Incorporation rice weevil survival, showing approach feasible.