Abstract: Abstract Aims Many factors can influence the growth of plants and their adaptability to the growing environment, among which plant growth promoting rhizobacteria (PGPR) may play a key role. Thus, the aim of this study is to explore the rhizosphere microbial resources with good aluminum tolerance and investigate their role in alleviating aluminum toxicity of sugarcane. Methods We isolated and screened the dominant strains of aluminum-tolerant PGPR from the rhizosphere soil of sugarcane (Saccharum officinarum) and studied their effects on sugarcane growth. By measuring the aluminum accumulation, physiological metabolism and expression changes of aluminum-tolerant genes in the aboveground and underground parts of sugarcane after aluminum stress, we compared the aluminum tolerance of sugarcane inoculated with aluminum-tolerant bacteria and those without aluminum-tolerant bacteria. Important findings Three strains of dominant sugarcane rhizosphere bacteria, Burkholderia A1, A23 and X6, have strong acid resistance (pH 3.8) and aluminum tolerance (4 or 5 mmol·L–1). All the three strains have the ability to dissolve phosphorus, secrete extracellular polymeric substances (EPS), fix nitrogen and remove Al3+. X6 can produce low level indole-3-acetic acid (IAA), A1 and X6 can secrete more iron carriers, and A23 and X6 have aminocyclopropane-l-carboxylic acid (ACC) deaminase activity. The combined bacteria of A1, A23 and X6 improved the plant height, leaf area and fresh weight of aboveground part of sugarcane. Although the bacteria combinations showed no obvious effect on the contents of nitrogen, phosphorus and potassium in aboveground and underground parts of the plant, but significantly increased the aluminum content in aboveground part of sugarcane under 0.5 and 1 mmol·L–1 aluminum stress and significantly reduced the aluminum content in underground part of sugarcane under 1 mmol·L–1 aluminum stress, and the overall performance was reducing the total aluminum content in sugarcane. The inoculation treatment showed no significant effect on the activities of superoxide dismutase (SOD) and peroxidase (POD), and the contents of proline (Pro) and soluble protein (SP), but it significantly reduced the malondialdehyde (MDA) content and significantly increased the catalase (CAT) activity in root tips under aluminum stress, and significantly increased the expression of MAPK and GST genes in root tips and PEPC gene in leaves of sugarcane. These results showed that Al-tolerant Burkholderia had significant effects on sugarcane growth, aluminum absorption and accumulation, plant antioxidant defense ability and aluminum-tolerant gene expression, which together improved the aluminum tolerance of sugarcane.

Key words: Burkholderia, Saccharum officinarum, aluminum stress, physiological?adaptation, aluminum resistance genes