| Plant growth promoting rhizobacteria (PGPR) can colonize in the rhizosphere, improve soil nutrition structure, inhibit pathogens and promote the absorption of nutrients and water through a variety of mechanisms, thus promote the growth of plants. The growth-promoting effect of PGPR has been recognized, however, as the mechanism of plant growth promotion by PGPR is complex and there are so many different strains, the research and development of PGPRs is still lack of theoretical guidance. Therefore it needs to evaluate and analyze the growth-promoting effects of these strains and to study the mechanism of their interactions with plants in depth.Based on the results of the previous studies,24 strains were selected, which had significant growth-promoting effects on wheat, rice and cotton, respectively. Wheat, rices and cotton, inoculated with 24 PGPR strains respectively, were cultured in semi-solid medium and/or pot soil, respectively, to analyze and evaluate the growth-promoting effects of these strains on rice, wheat and cotton. The aim of this paper is to find the growth-promoting rule of the PGPR strains on different crops and screen excellent strains. Using wheat as a mode, the influences of test strains on nine parameters of wheat roots and stem were observed in detail. The growth-promoting effects of 24 PGPR strains on wheat were evaluated and analyzed. The relationships between various indexes and the relationships between wheat roots and shoots were analyzed, and the mechanism of plant root development and plant growth promoted by PGPRs were revealed to provide data to explain the growth-promoting mechanism of PGPR. The main results are as following.1. In semi-solid (12 d) test of wheat, strains WS03, WS04, WS24, WS32 and r-K2915 significantly promoted more than 4 parameters. Strain WS03 had the most significant growth-promoting effect, made the height of wheat stem increased by 17.25%, the length of wheat root increased by 52.37%, the dry weight of wheat shoot and the dry weight of wheat root increased by 30.87% and 67.86%, respectively. While in the 30 d pot experiment WS32 and r-P5350 were excellent strains, significantly promoted the height of wheat stem increased by 7.78% and 5.42%, respectively, the length of wheat root increased by 10.07% and 15.95% respectively, the dry weight of wheat shoot increased by 14.98% and 8.98%, respectively, the dry weight of wheat root increased by 14.49% and 28.28%.2. The semi-solid test (12 d) and pot experiment (38 d) of rice showed that the strains WS26, WS31, r-K7808, r-P1201 and r-P5304 had significant growth-promoting effects in more than 4 parameters, among which r-P1201 was the best one. In semi-solid test, r-P1201 significantly increased the length of rice root, the height of rice stem, the dry weight of rice shoot and the dry weight of rice root by 42.06%,19.09%,51.67% and 43.24%, respectively. In pot experiment strain r-P1201 significantly increased the length of rice root, the height of rice stem, the dry weight of rice shoot and the dry weight of rice root by 73.12%,36.97%,102.87%and 57.67%, respectively.3. The results of 30 d pot experiment of cotton suggested that strains c-P1 and c-P1108 had the most significantly growth-promoting effects, significantly promoted the height of cotton stem increased by 17.25% and 14.85%, respectively, the length of cotton root increased by 55.03% and 58.86%, respectively, the dry weight of cotton shoot increased by 47.55% and 46.57%, respectively, the dry weight of cotton root increased by 89.89% and 105.99%, respectively.4. Strains which had the best growth-promoting effects on wheat, rice and cotton were wheat PGPRs, rice PGPRs and cotton PGPRs, respectively. Compared with cotton PGPRs, wheat PGPRs and rice PGPRs had less difference. As the nutrients and culture conditions were different, the results of semi-solid test and pot test had difference.5. The effects of PGPRs on the development of wheat root were studied. It was showed that the total length of wheat root, the total surface area of wheat root, the number of root tips and root fork had the significant correlations with the dry weight of wheat root, the height and the dry weight of wheat stem. The growth-promoting effects of PGPRs on the total length of root, the total surface area of root, the total volume of root, the average diameter of root, the number of root tips and root forks were analyzed. The study showed that strains WS32, WS26, r-P1201, c-P1, c-P1108 and c-N3101 significantly promoted more than 4 parameters in both tubes and pots experiments, among which strains WS32, r-P1201, c-P1 and c-P1 108 were Pseudomonas spp. with strong phosphorus solubilization ability, indicating that the Pseudomonas spp. had better growth-promoting effects on wheat root development. |
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