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| Isolation and Identification of Sphingomonas sp. CL01 and Its Promoting Effects on Watermelon (Citrullus lanatus) in Continuous Cropping Soil |
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Abstract Phosphorus Solubilizing bacteria (PSB) can improve utilization of phosphorus in soil, increase soil fertility, promote plant growth, and alleviate continuous cropping obstacle. In this study, four PSB strains were screened from the rhizosphere soil, and all of them had phosphorus solubilizing ability. By the analysis of comparisons, one of them was screened and classified as Sphingomonas sp., named strain CL01. Further, the efficiency of phosphorus-solubilizing and the secreting level of indole acetic acid (IAA) were determined for the strain CL01, meanwhile, the effects on the root growth of watermelon (Citrullus lanatus) seedling were studied. The results showed that the strain CL01 was the strongest one on the capacity of phosphorus solubilizing than the other strains. Its maximum amount of phosphorus solubilizing was 642.60 mg/L, and the secretion level of IAA was up to 22.87 mg/L, which could promote the development of roots and growth of plants. The watermelon seedlings were treated with the bacterial suspension (in LB medium, OD600=0.5), for 30 d, the underground dry weight, root length, root volume, the number of root tips and the proportion of fibrous roots of watermelon seedlings were increased significantly compared with the controls (CK1, sterilized continuous cropping soil; CK2, unsterilized continuous cropping soil). The underground dry weights of the seedlings were increased by 27.04% and 103.90% compared with CK1 and CK2, respectively, The root length of the seedlings were increased by 83.60% and 63.75% compared with CK1 and CK2, respectively. The root volume of the seedlings were increased by 14.29% and 100% compared with CK1 and CK2, respectively. The number of root tips were increased by 15.16% and 85.45% compared with CK1 and CK2, respectively. The proportion of fibrous roots were increased by 47.81% and 26.80% compared with CK1 and CK2, respectively. Also the average diameter of roots was decreased by 47.89% and 66% compared with CK1 and CK2, respectively. Noticeably, if the concentration of the bacterial suspension was doubled (OD600=1.0), the similar results were obtained, but they were not as good as the lower ones. Based on the results mentioned above, we proposed that strain CL01 had the capacities to dissolve organic phosphorus efficiently and secrete IAA. While the watermelon seedling continuous cropping with the bacterial suspension (OD600=0.5), the growth of root was promoted, root morphology was optimized and the composition of root was improved. The strain CL01 is an excellent candidate for reducing continuous cropping obstacle.
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Received: 19 March 2015
Published: 24 July 2015
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