Study On The Resistance Mechanism Of Nine Astragalus Adsurgens Varieties To Yellow Stunt Root And Rot And Comprehensive Evaluation For Germplasm Characteristics

Standing milkvetch is a leguminous forage and also used as sand fixation plant, which is only cultured in China. Yellow stunt and root rot of standing milkvetch(YSRR) caused by Embellisia astragali, a systematic fungal disease, is a key limiting factors in the forage production. Planting varieties resistant is a feasible strategy to manage the disease. However, it is not available to use in China. Screening high quality germplasm from plant material is a fundamental work for resistance breeding. The object of this thesis is to evaluate the resistant grading for 9 varieties in 3 inoculation experiments with detached leaves and potted seedlings by spraying conidia inoculation, and with field plants by natural inoculation. In order to determine high resistant varieties in further breeding process, the relationship between resistance level and biological characteristics were analyzed. The variety features of 9 varieties includes storage protein in seeds assayed by SDS-PAGE, genetic relationship determined by rDNA-ITS, content of 5 kind endogenesis hormone and activity of 4 kind protective enzyme tested by HPLC. The main results were as follows:1. In this study, the taxonomic status of standing milkvetch is identified by molecular method. The phylogenetic tree based on ITS showed that cultured and wild standing milkvetch were same species, Astragalus adsurgens. And the relationship between cultured standing milkvetch is closer than that of wild one. The varieties of Zhongsha No. 1 and Shanaxi Yulin are of significant difference than other varieties. The species Astragalus adsurgens was closed to A. austrosibiricus and both were belong to sect. Onobrychium Bunge.2. All the species were provided with purple spica and erect type except Zahua(white spica) and Zhongsha No. 1(creeping type). Storage protein in seeds of Liaoning Fuxin was similar to Zhongsha No. 1.3. The inocula for the natural experiment were from infected seeds but not from field outside. Conidia of the disease produced from died plants and invade into leaf blades during the shooting stage. Percentage of infected plants increased anally to 100%. This founding finally clarified the disease cycle.4. According the evaluation standard and based on data from 3 experiments, resistance level of Inner Mongolia Zaoshu and Shanaxi Yulin were high resistant(HR) to the disease, in which the former was stronger than the later; others ranged from strong to weak was Zahua, Ordos, Guyuan and Henan, all were resistant varieties(R); Ningxia Pengyang was moderate resistance(MR); Liaoning Fuxin and Zhongsha No. 1 were low resistance(LR). Disease resistance mechanisms of Inner Mongolia Zaoshu and Shanaxi Yulin were invasion-resistance and extension-resistance, and later variety also had damag-resistance. In contract, Zhongsha No. 1 was the lowest in the 3 resistance mechanism. Hay yield of Inner Mongolia Zaoshu, seed production and nutrient of Zhongsha No. 1, pasture resistance of Liaoning Fuxin was the strongest were the best among the 9 varieties.5. Significant differences(P<0.05) of the content of all tested endogenesis hormone and the activity of all tested protective enzyme were found among the 9 varieties in healthy seedlings(without inoculation). Contracted with free inoculated seedlings, content of IAA in inoculated seedlings for all varieties were increased significantly(P<0.05), and activity of POD were significantly decreased(P<0.05). Content of SA and ABA, and activity of SOD were decreased(significantly or not), whereas, content of CTK and activity of CAT in all seedling of all varieties were increased(significantly or not). More content of IAA or higher activity of SOD, stronger resistance for standing milkvetch varieties, therefore, IAA and POD likely would be used as indicators in screening material resistant to yellow stunt and root rot of standing milkvetch.6. The alcohol extract from Ledebouriella seseloides, walnut green husk and garlic could inhibit Embellisia astragali strongly. Embellisia astragali and its fermented products have antagonism effect to some plant pathogenic fungi and the antibacterial material of E. astragali is worthy of development and utilization.The features of Zhongsha No. 1 would be absorbed in the resistance breeding such as early seed maturity and high nutrient content although it was low resistance to the disease, beside Inner Mongolia Zaoshu and Shanaxi Yulin are obliged to be used as they both have high resistance to the disease, and high yield.