| Indoleacetic acid(IAA),as an important plant growth regulator,affects plant growth and development.In addition to the synthesis of IAA by plants,microorganisms can also synthesize and secrete IAA.The application of IAA producing bacteria in agricultural production is mainly to promote crop growth and increase crop yield.In this study,IAA-producing strains were screened from the inter-root soil of maize and rice crops,identified,and their medium components and culture conditions were optimised to further analyse the effect of their bodies,fermentation broth and supernatant on the germination of tomato seeds and the growth of tomato seedlings.This study can provide technical reference for the application of IAA-producing bacteria in crops.The main research results are as follows:(1)110 strains of bacteria were isolated from the inter-rhizosphere soil of maize and rice crops,among which 36 strains were IAA-producing,and three strains with strong and stable IAA-producing ability were obtained after re-screening: NL5,NL50 and NH3.the bacteria belonged to Enterobacter sp.,Ochrobactrum sp.and Klebsiella sp.(2)Single-factor optimization was carried out for three strains.The optimum carbon source for IAA production by strain NL5 was starch and the optimum nitrogen source was ammonium sulphate;the optimum carbon source for both strains NH3 and NL50 was glucose and the optimum nitrogen source was ammonium chloride;the optimum tryptophan concentration for indoleacetic acid production by strains NL5,NL50 and NH3 was 0.3 g/L.(3)The optimal fermentation conditions for indole acetic acid production by strain NL5 were optimized by single-factor and response surface tests: p H 6.93,incubation time 4.19 d,incubation temperature 26.73°C and inoculum level 2.33%,and the IAA content could reach 99.72 mg/L.The optimal conditions for IAA production by strain NL50 were p H 7.02,incubation time 4.06 d,incubation temperature 32.46°C and inoculum level 2.32%,and the IAA content could reach 94.39mg/L.The optimal conditions for IAA fermentation of strain NH3 were p H 6.08,incubation time4.17 d,incubation temperature 30.78°C and inoculum level 2.45%,and the IAA content was115.41 mg/L.The optimized IAA content of the fermentation broth of the three strains was 1.17 times,1.19 times and 1.12 times higher than that before optimization,respectively.(4)Tomato seed germination tests were conducted using prepared NL5,NL50 and NH3 fermentation broth,supernatant and bacteriophage.the fermentation broth of the three strains had the most significant effect on tomato seed germination promotion,followed by supernatant and then bacteriophage.Shoot length and root length in the NL5 fermentation broth treatment increased by 27.34% and 46.56%,respectively,compared with the control;shoot length and root length in the NL50 fermentation broth treatment increased by 68.35% and 94.10%;shoot length and root length increased by 23.02% and 11.05% in the NH3 fermentation broth treated group.(5)The tomato seedlings were treated with the prepared three strains of bacteria fermentation solution,and it was found that the three strains of bacteria fermentation solution significantly promoted the growth of tomato seedlings.Compared with the control group,the tomato plant height of NL5,NL50 and NH3 fermentation solution was increased by 40.17%,36.32% and49.82%,respectively.The promotion effect of NH3 fermentation liquid treatment group was the most significant.Stem diameter,leaf number,above-ground fresh weight and underground fresh weight of tomato in NH3 fermentation liquid treatment group increased by 66.67%,60.78%,75.19% and 80.64%,respectively. |
