Improving micropropagation: effect of Azospirillum brasilense Sp245 on acclimatization of rootstocks of fruit tree

The effect of Azospirillum brasilense Sp245 on the micropropagation of three fruit rootstocks: Mr. S 2/5 plum (Prunus cerasifera x P. spinosa), GF 677 hybrid (Prunus persica x P. amigdalus), and MM 106 apple (Northen Spy x M1) was assessed. Rooted shoots were treated with 3 x 10(7) of Sp245 cells during transplantation from in vitro cultures to the acclimatization phase. After 60 days, growth parameters were positively affected by Sp245 inoculum. In the case of Mr. S 2/5, an increase in rootstock stem length and node number by 37% and 42%, respectively, compared to the control was noted. In the case of GF 677, the bacterial inoculum increased stem length and node number by up to the 75% and 65%, respectively, compared to the control. The inoculum did not exert on MM 106 for both parameters suggesting that the effects of Sp245 could depend on a specific clone-microbe association. In all cases, however, a higher vigor, consistent with a wider leaf area, was present in the inoculated plantlets demonstrating that the use of Azospirillum can significantly contribute to optimize plant performance during the phase of adaptation of plants to post-vitrum conditions.