| Sugar beet is a main raw material for the sugar industry in the world. Endophyte can be in favor of the enhancement of leaf photosynthetic capacity, increasing stress resistance, delaying sugar beet senescence, prevention and control of main diseases of sugar beet, increasing yield and improving quality of the beet plants. Isolated endophytic bacteria has great potential for growth promotion, disease prevention and yield increasing of sugar beet, and is very significant in enhancing the management of beet cultivation, regulation of beet metablism and sustainable development of agriculture in Xinjiang.Endophytes, having characteristics of growth promotion, disease prevention and yield increasing, were isolated from sugar beet and identify by morphological and 16SrDNA sequence analysis. Endophytic bacteria yield-increasing mechanism involved in phytohormone levels, antagonism, nutrient absorption, photosynthesis, nitrogen and glucose metabolisms were investigated. The results were as follows:Using different separation medium and isolation methods,406 strains of endophytes were isolated from sugar beet materials in Xinjiang by surface disinfection using ethanol and mercuric chloride.380 bacteria and actinomycetes were identified by colony morphology, cultural characteristics, physiological and biochemical characteristics,16S ribosomal DNA sequence analysis; 26 fungus were identified by colony morphology, cultural characteristics, ITS sequence analysis. The results showed that endophytes in sugar beet were divided into 12 groups, as 7 genus bacteria,2 genus actinomycetes,3 genus fungus, separately. Bacteria were predominate in endophytes isolated from in beet.Three endophtic bacteria strain PG-1 (Bacillus flexus)、PG-2 (Pseudomonas plecoglossicida)、PG-3 (Chryseobacterium indologenes) isloated from beet plant has remarkable growth promoting effect. It was test by germination, wheat coleoptile growth, pot experiments experiments. Improving growth metabolisms of three strains were researched from phytohormone levels, phosphorus solubiliziog ability, nutrient absorption and colonization. The results showed that three improving growth endophtic bacteria could colonize within sugar beet, and enhance phytohormone levels and nutrient absorption. Three strains could increase yield and quality of beet, and best one was PG-3 among 3 strains. The quantity of four kinds of phytohormone (IAA、GA、ZR、ABA) in sugar beet were bosted 1.60、23.05、0.54、1.03 times than control after the strain PG-3 inculated sugar beet. The content of N,P,K,Mg elements and protein of in PG-3 increased by 0.18、0.51、0.08、0.33 and 0.60 times compared to CK, respectively. Endophyte colonization was composed of entering, reproduce and stabilization, which was a harmonious development process between endophyte and hostBased on the characteristics of pathogens identified, the beet root rot, seedling blight, brown patch and snake-eye disease are caused by Fusarium oxysporum, Rhizoctonia solan, Cercospora beticola and Phoma betae separately.45 endophytes strains were screened against the pathogens of beet by plate confrontation test. Three endophytic bacteria strains, AT-1, AT-2 and AT-3, showed relatively strong antagonistic against the pathogens. Three antagonistic strains could colonized into root of sugar beet by colonizing test. Strain AT-1 was identified as Paenibacillus polymyxa, while strains AT-2 and AT-3 were as Bacillus flexus and Stenotrophomonas sp. by their morphological, physiological and biochemical characteristics. Three antagonistic strains showed significantly control effect against the pathogens in field trail.The effects of endophytic PG-1, PG-2, PG-3 on photosynthetic parameters and yield of sugar beet were investigated. The results showed that three strains, PG-1, PG-2, PG-3 could obviously promote the photosynthesis of sugar beet, in which the net photosynthetic rate (Pn), stomatal limitation (Ls), transpiration rate (Tr) of sugar beet increased significantly (P<0.05) by 33.33%、21.43% and 12.31%, respectively, while stomatal intercellular CO2 concentration (Ci) decreased significantly (P<0.05) by 7.21%, maximum photochemical capacity (Fv/Fm) and quantum yield of PSⅡ(ΦPSⅡ) increased, while photochemical quenching (qP) and non-photochemical quenching (qN) decreased. It was shown that with the increasing of photo flux density, the net photosynthetic rate (Pn) increased at first and then decreased. The strain PG-3 could also increase the yield and the quality of beet, which biomass and sugar content in beet increased significantly (P<0.05) by 25.63% and 17.46%, respectively. It was concluded that the strain PG-3 not only affected photosynthetic parameters, but also promoted the yield and the quality of beet. We investigated the agronomic traits and determined the activity of key enzymes in sugar and nitrogen metabolisms in beet leaf and root with treatments of by using three strains, PG-1, PG-2, PG-3 solution seed soaking, leaf spraying and root watering. The results showed that the strains obviously promoted growth of beet seedlings, the effect with the better in root watering treatment than in others. The leaf fresh weight, content of chlorophyll, fresh weight per root, sugar content and sugar yield of beet increased significantly (P<0.05) by 16.7%, 55.3%,11.8%,22.1% and 27.9%, respectively; the three strains enhanced evidently the activities of key enzymes in sugar and nitrogen metabolisms of beet during whole growth period. The changes of activities of nitrate reductase (NR) and glutamina synthetase (GS) presented the changes of M-shape and parabola shape, respectively. The changes of activities of sucrose synthase (SS) and sucrose phosphate synthase (SPS) in beet displayed the single peak changes. The synthesis activity was much higher than the decomposition activity for SS in roots of beet at late growth stage. The activity of SPS was higher at early growth stage than at late growth stage, and the activity of SPS was the highest during phyllome formation period. It was concluded that the strains not only enhanced activities of key enzymes in sugar and nitrogen metabolisms of beet, but also promoted the growth, yield and sugar accumulation of beet. |
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