Abstract:Abstracts:Pseudomonas fluorescens Q2-87 and 1M1-96 were applied to Pinus elliottii seedlings,which were one year old,two years old and three years old respectively,and after one growth peak stage the growth rhythm of the seedlings under the natural condition was analyzed and the height and basal diameter of the seedlings before and after the treatment of the bacterial agents were contrasted. The results showed as following: ①The growth rhythm of the seedlings under the natural condition accorded with that the previous researchers summarized;②The height growth rates of all of the seedlings inoculated with the two strains were not raised obviously;③The basal diameter growth rates of the seedlings,which were one year old,inoculated with the two strains were raised extremely obviously;the basal diameter growth rates of the seedlings,which were two years old,inoculated with two strains were raised obviously;the basal diameter growth rates of the seedling,which were three years old,inoculated with two strains were not raised obviously.Through the analysis,we think the reason that the basal diameter growth rates of the seedlings, which were three year old,were not raised obviously was that the seedlings at this age were not sensitive to 2,4-DAPG.We concluded that the low age seedlings of slash pine,which were younger than two years old, turned thick by 2,4-DAPG, which is produced by Pseudomonas fluorescens Q2-87 and 1M1-96 and acts on the seedling similar to the effect of auxin.