Identification Of Alfalfa Rhizobia And Their Correlations With Soil Physical And Chemical Properties

Grass and livestock industry is one of the advantageous and characteristic industries of agriculture in Ningxia.With the vigorous development of grass and livestock industry,the planting area of forage is gradually expanded.Alfalfa,as the "king of forage crops",is one of the most important forages legumes in the development of grass and livestock industry in Ningxia.Previous studies suggested that alfalfa rhizobia symbiosis can improve both the alfalfa quality and productivity.However,alfalfa rhizobia symbiosis system has symbiotic specificity and is greatly affected by the environment.In addition,due to the arid climate and high degree of land salinization in Ningxia,the existing alfslfs rhizobia are not suitable for Ningxia,so the study of Ningxia indigenous rhizobia can better improve the uapplication efficacy of rhizobia in the field.In this experiment,rhizobial strains isolation and identification,growth and adaptability to adversity of indigenous rhizobia in Yinchuan area were studied by using potted plantsassays and natural nodulation of different varieties of alfalfa.The correlations between natural nodulation efficacy and soil physical,chemical properties were analyzed,in order to select rhizobia with good symbiotic effect suitable for alfalfa planting in Ningxia Yinchuan region,so as to improve the utilization efficiency of rhizobia,and provide scientific basis for the application of rhizobia in alfalfa production.The specific research results are as follows:1.The field studies of root nodules of different alfalfa varieties showed that the numbers of nodules per plant of varieties ’Suntory’,’WL326HQ’ and ’Queen’ were less than 10,and the number of nodules per plant of other alfalfa varieties was more than 10;The heaviest nodule is 233.03mg for’A dina’ and 72.43 mg for ’WL326HQ’,with long diameter ranging from 4.83 to 8.43mm and short diameter ranging from 1.17 to 5.20mm.By comparing the nodule numbers per plant,nodule size and quality,’Adina’,’Nanmu 701’and ’Surprise’ are better than the other six alfalfa varieties.The shape of root nodules is mainly rod-shaped,coral shaped or nearly spherical,and the colors are mainly white,meat pink or yellowish brown.Nodules are found in the main root and lateral root of alfalfa.2.A total of 21 rhizobial strains were isolated and purified in vitro,and the Gram staining was G-.The average growth time of rhizobial colony was 3-5d,and the colony diameter is 2mm-6mm.The appearance of the colony is milky white and translucent,with neat edges,flat and convex,producing mucus and luster.3.The Sanger sequencing technology was applied to identify the isolated rhizobia species.Results suggested that 21 isolates were identified into 1 genus and 2 species,belonging to Sinorhizobium kummerowiae and Sinorhizobium meliloti.4.The correlation analysis between the quality and size of alfalfa root nodule and soil physical and chemical properties showed that there was a very significant positive correlation between root nodule quality and soil total potassium(P<0.01).The higher the content of total potassium,the heavier the root nodule quality.Root nodule quality was significantly positively correlated with organic matter and total phosphorus(P<0.05).There was a significant positive correlation between nodule size and soil available molybdenum(P<0.01).The content of available molybdenum in nodule was in the range of 69.52-82.86mg/kg,and the nodule length and diameter increased with the increase of available molybdenum content.Among them,the interpretation quantities of soil available molybdenum,organic matter,total potassium and total phosphorus to the quality and size of root nodules were 37.1%,23.9%,6%and 1.9%respectively,with a total interpretation amount of 68.9%.5.The results of Rhizobium salt and alkali stress showed that most Rhizobium strains had high salt tolerance,acid and alkali resistance,wide temperature adaptation range,and better resistance to erythromycin,chloramphenicol and ampicillin than neomycin.Cluster analysis categorized all isolates into three groups.The first category was A-1,J-2,etc.The stress resistance of strains was relatively weak.The second type is G-1,S-3,etc.The strain has general resistance to stress,and the third type is N-3,S2,etc.The strain has relatively good resistance to salinity stress.