Abstract:

Aims Endophytes are found in the root systems of various plants and play beneficial roles in root growth and function maintenance, especially when plants are under biotic or abiotic stress. Xanthoceras sorbifolia is a unique woody plant that grows in the northern part of China and is resistant to cold and drought and highly tolerant to poor soil. Moreover, it is considered a promising candidate for bio-diesel and bio-lubricant production. Our objective was to investigate endophytes in the roots of X. sorbifolia. Results will help in the selection and development of bacterial fertilizer to improve the growth and yield of X. sorbifolia, which grows in marginal lands.

Methods We examined root systems of field-grown one- and two-year-old plants. After surface sterilization, endophytes were isolated with yeast-malt extract agar (YMA) and Ashby media respectively. Seven representative single colonies were selected according to their macro-morphology. After DNA extraction and purification, 16S rDNA PCRs were carried out with the universal bacterial primers. The PCR products were separated with electrophoresis, collected and purified. The 16S rDNA sequence similarity search of different bacteria was performed by Blast on NCBI against GenBank, and a similarity of 97% was set as the criterion for identity. Nitrogenase activity of the selected strains was assayed with ethylene production by GC.

Important findings The number and type of colonies on YMA medium were significantly more than those on Ashby medium, as YMA medium contains a small amount of nitrogen and is more suitable for bacteria growth. The number and species of endophytes in one-year-old X. sorbifolia roots were slightly more than those in two-year-old plants. This may be because the roots of one-year-old plants were as a whole younger than those of two-year-old plants and were more suitable for the infection and survival of endophytic bacteria. The main bacteria species isolated from the roots of one-year-old plants were Pantoea agglomerans, Agrobacterium tumefaciens and Klebsiella oxytoca, while those from two-year-old plants were of the Pseudomonas genus. Six of seven strains demonstrated nitrogenase activity, including the activity of 9.688 nmol·mg^-1·h^-1 in K. oxytoca, which is significantly higher than other strains. This report on endophytes of X. sorbifolia roots provides the basis for bacteria fertilizer strain selection.

Key words: endophytes, identification, isolation, Xanthoceras sorbifolia