Effects of phosphorus solubilizing bacteria on nursery tree growth and expression of phosphorus transporter SPX gene family in apples

In this study, the aim was to test whether high-quality apple nursery trees could be produced by reducing the chemical phosphorus usage rate with the help of phosphorus solubilizing bacteria. Additionally, the study aimed to determine which treatment or treatments most effectively enhance nursery tree quality. Furthermore, the study sought to identify and characterize the SPX gene family, which plays crucial roles in phosphorus transport in apples. The study was conducted at Burdur Mehmet Akif Ersoy University, using the 'Granny Smith' apple cultivar grafted onto M.9 rootstock as the plant material. Five different treatments focusing on the chemical phosphorus fertilizer dose and the use of Bacillus megaterium, a phosphorus solubilizing bacteria, were examined, including (1) 100%P (phosphorus fertilization according to soil analysis), (2) 50%P (half of the phosphorus recommended in soil analysis), (3) 50%P with phosphorus-solubilizing bacteria (PGPR), (4) 0%P, and (5) 0%P with PGPR. The 50%P+PGPR treatment showed a relatively higher leaf phosphorus content (%±standard deviation) of 0.1631±0.0156 compared to other treatments. On the other hand, the 100%P treatment exhibited better results in terms of tree height and total leaf area. In the study, genes containing seven MdSPX (Malus domestica SPX) domains, distributed across five different chromosomes, were identified. Additionally, the phylogenetic tree analysis identified seven different subfamilies with 72 SPX proteins from various plant species. The expressions of these seven MdSPX genes were measured in leaf tissues using RT-qPCR under different phosphorus treatments. Notably, the analysis revealed a significant decrease in MdSPX2 expression in the 50%P+PGPR treatment, despite an increased amount of phosphorus in the leaf. Consequently, MdSPX2 has been identified as a promising candidate for future investigations into phosphorus metabolism and functional characterization studies in apples. Keywords: bacillus megaterium, malus domestica, phosphorus deficiency, apple