Research Of Sensitivity Of Cold Resistance, Genetic Variation In Different Generations Of S. Perfoliatum

Silphium perfoliatum is a perennial herb belongs to Silphium genus of Compositae. It originated in humidity high grassland areas of central north America, introduced into China in 1979. It has high protein content,rich in inamino acid, high quality green fodder. Sensitivity of cold resistance, inheritance of domestication generation and fertilization effect of S. perfoliatum were researched to provide the theoretical and technical bases for new variety breeding and extension utilization of the species in Hohhot area in this paper. The main results were as follows:1 The conductivity, the soluble sugar content, the soluble protein content and the proline content of lateral root of S. perfoliatum increased at the beginning and then decreased following with temperature changes. The conductivity and the proline content of root crown also increased at the beginning and then decreased, but the soluble sugar concent and soluble protein content decreased with temperature changes. Tissue water content of lateral root and root crown decreased at the beginning and then increased following with temperature change. The conductivity and tissue water content of root crown were significantly higher than lateral root, but the soluble sugar content, the proline content and soluble protein content were lower than lateral root.2 The primary structure of lateral root of S. perfoliatum were composed of epidermis, cortex and stele. Primary xylem was fascicular alternated with primary phloem. The secondary structure were mainly composed of periderm, secondary phloem, vascular cambium and secondary xylem, secretory cavity was in the middle of secondary phloem . There were little starch granules in root of S.perfoliatum, which showed spheroidal, mainly existed in the epidermis and cortex cells. Starch granules were hydrolyzed gradually with the temperature decreased, and accumulated with the temperature increased until March next year. Protein particles showed ovoid and single grain, mainly existed in the primary phloem and cortex. Protein particles were accumulated with the temperature decreased.3 The low temperature of soil surface in January in Hohhot areas, the sensitivity to low temperature, the root crown situated nearly to the soil surface, and the little accum- ulateed osmotic regulation substances before winter was the main reasons caused the free -zing injury of S. perfoliatum. Returning green stage of S. perfoliatum could be advanced by irrigation before winter and returning green. Overwintering rate, overwintering buds and forage yield production were increased significantly by covering soil and irrigation before winter.4 The root crown length, root crown diameter, stem leaf width,basal leaf length, plant height and 1000-grain weight were varied significantly in different generations. Overwintering rate of S. perfoliatum was improved from 59.21% of original generation to 86.36% of second generation through natural and artificial selection in Hohhot area The variation degree of 6 phenotypic traits were smaller along with the generations alternation. The photosynthesis factors such as diurnal variations of photosynthetic curve, light response curve,net photosynthetic rate, transpiration rate and water use efficiency had also significant variation, and net photosynthetic rate had increased with the generations increasing.5 14 alleles and 5 loci were detected from 3 enzymes of 4 generations, and the percentage of average polymorphic loci was 64.29%. 265 loci and 203 polymorphic loci were detected by 6 AFLP primers, average polymorphic loci percent was 76.6%. Nei's gene diversity and Shannon's information index showed: S. perfoliatum had great genetic diversity, and genetic diversity was decreased with the increasing of generations. Genetic variation within generations was larger than that among generations, and mainly occurred within generations.6 Forage production, fresh and dry matter ratio, seed yield and seed quality of S. perfoliatum were improved significantly by fertilize N,P,K fertilizers. The maximal fertilizer combination for forage production, yield and quality of seed was the N 90kg/hm²,P2O5 60kg/hm²,K2O 25kg/hm² and N 90kg/hm², P₂O₅ 90kg/hm², K₂O 50kg/hm² respectively.