| Aflatoxins, the high carcinogenic secondary metabolites of Aspergillus flavus Link, is possess of serious health hazards to human and domestic animals because it frequently contaminates agricultural commodities.Peanut (Arachics hypogaea L.) is one of most susceptible host crops to A.flavus invasion and subsequently aflatoxin production. Development of host resistance to A.flavus invasion and aflatoxin producing is the best and most widely explored strategy to control aflatoxin contamination. About 20 resistance genotypes have been identified since 1970's, but progress toward developing resistance variety is the slow and the mechanism and inheritance of resistance were not clear, especially the specifics markers responsible for resistance.The objectives of this thesis were: ?to identified the main factors responsible for resistance in peanut seed; (2) to detect the difference of defense response between resistant and susceptible peanut seed after A.flavus invaded; (D to analyze the performance of resistant characters in progeny of resistant X susceptible genotype.To gain these informations above mentioned, 5 resistant genotypes (J-ll, VRR245, PI337494-F, UF71513 and Zhangqui 48) and 4 susceptible genotypes (Yueyou 5, Yueyou 114, Shanyou 523 and Zhanyou 30) were used. The experiment results are outlined below.1. The aflatoxin content of broken seeds was higher than intact seeds after inoculation with A.flavus. The account, distribution, bioassays in vitro of wax and cutin layers in peanut seeds was investigated. The datum revealed that there were significant differences between genotypes tested. The kernel wax contents of resistant genotypes were higher than susceptible genotypes. The bioassays in vitro showed that no significant test-by-treatment interactions were detected for wax bioassay data. Scanning electron microscopy of kernel wax revealed distinct differences between seed of resistant and susceptible genotypes. Most of resistant kernels were thick and coarse in appearance and had rich wax deposits on seed surfaces. Thin and a small amount of surface wax deposits were observed on most susceptible seeds.Removing of wax with chloroform, and removing of cutin with KOH and cutinase or both can increase the susceptibility of peanut seeds but don't reducing their germination. The infected rate of intact seeds after removing both wax and cutin were nearly equal to those in wounded control seeds in both genotypes.These results indicated wax and cutin layers of peanut seed might play a role in resistance to A.flavus invasion and colonization.2. In attempt to search for zn\\-A.flavus protein, peanut seeds proteins extracted at pH2.8 and pH7.5 were analyzed with PAGE and SDS-PAGE. Consistent differences in protein profiles were detected only in proteins extracted at pH2.8 buffer among genotypes. A protein of 38kDa was unique or presented in higher concentration in resistant genotypes, whereas absent or in low concentration in susceptible genotypes. Protein extracted at pH2.8 from seed showed markedly antifungal activity against A.flavus in vitro. By means of (NH)4SO4 precipitation and chromatography, 14.2 and 26.3 kDa proteins were isolated and purified. 14.2 and 26.3 kDa proteins can inhibit spores germination and hypha extending of A.flavus in vitro. The peptide mass fingerprinting and database search showed 14.2 and 26.3 kDa proteins may be new proteins.3. A trypsin inhibitor in peanut seeds was purified by acetone fractionation, followed by passing through DEAE-Sephadex A50 ion-exchange column. The purified inhibitor consisted of two subunits with molecular weight of 10.3 andlTkDs respectively. The inhibition of germination and hypha growth of A.flavus were observed in protein concentration 10 u g on Czapek medium. The content and activity of trypsin inhibitor were relative to genotypes resistance. The content and activity of trypsin inhibitor in resistant genotypes were significantly higher than that in susceptible genotypes.4. The activities of perox...
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