Abstract
Endophytes are rich in plant tissues and play important roles in plant-microbial interactions and plant-growth regulation. Here, endophytic bacteria from two closely related tea cultivars of Zijuan and Yunkang-10 were isolated, and the diversities were compared. Plant-growth promoting (PGP) activities were determined on the dominant groups or nitrogen-fixing genera from the two cultivars. Endophytic bacteria were isolated by using of different selective media and methods, and the PGP activities were investigated by analytical and molecular technologies. A total of 110 isolates of 18 genera belonging to three phylums (Proteobacteria, Firmicutes, and Bacteroidetes) were obtained from Zijuan, while 164 isolates of 22 genera belonging to two phylums (Proteobacteria and Firmicutes) were obtained from Yunkang-10. PGP screening indicated that Herbaspirillum spp., Methylobacterium spp., and Brevundimonas spp. showed different PGP abilities. The PGP ability decreased in order of Herbaspirillum spp., Brevundimonas spp. and Methylobacterium spp., and the majority of Methylobacterium spp. did not showed PGP activity of nitrogen-fixation, P-solubilization, siderophore, indole-3-acetic acid (IAA) production or 1-aminocyclopropane-1-carboxylate (ACC) deaminase. The study of bacterial community and PGP activities confirmed that endophytes in tea plants are constantly changing in different seasons and tea cultivars, and the PGP bacteria in Zijuan are much abundant than those of Yunkang-10.
Highlights
Endophytes are a group of microorganisms that reside in healthy plants, but not result in plant disease, and endophytes have attracted increasing attention to microbiologist (Qin et al, 2011)
For the Zijuan results, a total of nine isolates were obtained in spring, and the dominant groups were Variovorax spp. (44.4%) and Herbaspirillum spp. (22.2%), the other groups were only obtained one isolate for each genus; 70 isolates were obtained in summer, the dominant groups including Herbaspirillum spp. (44.29%) and Bacillus spp. (15.7%), and the other groups were less than 10% for each genus; 27 isolates were obtained in autumn, and the dominant groups were Methylobacterium spp. (51.9%), Bacillus spp. (25.9%) and Serratia spp. (14.8%), and the other groups were less than 4.0% for each genus; 4 isolates were obtained in winter, the 3 isolates were Bacillus spp. and the other was Brevundimonas sp. (Figure 2 and Supplementary Table S1)
For the Yunkang10 results, a total of 34 isolates were obtained in spring, and the predominant group was Sphingomonas spp. (82.4%), and the other groups were less than 10% for each genus; 41 isolates were obtained in summer, the dominant groups were Bacillus spp. (26.8%), Methylobacterium spp. (17.1%), Staphylococcus spp. (12.2%), and the other groups were less than 10% for each genus; 25 isolates were obtained in autumn, the dominant groups were Methylobacterium spp. (44.9%), Serratia spp. (32%), and the other groups were less than 10% for each genus; 64 isolates were obtained in winter, the dominant groups were
Summary
Endophytes are a group of microorganisms that reside in healthy plants, but not result in plant disease, and endophytes have attracted increasing attention to microbiologist (Qin et al, 2011). Numerous studies indicated that endophytes play important roles in plant disease resistance, secondary metabolites synthesis, plant growth regulations, and environmental stressors withstand (Coombs and Franco, 2003; Qin et al, 2009, 2011, 2015, 2017; Glick, 2014; Mora et al, 2014; Zhao et al, 2016). Plenty of studies showed that endophytes can regulate plant growth by means of nitrogen-fixation, phosphate solubilization, siderophore, 1aminocyclopropane-1-carboxylate (ACC) deaminase activity and indole-3-acetic acid (IAA) synthesis. Qin et al (2014) assessed the PGP functions (i.e., ACC deaminase, IAA synthesis and nitrogen fixation) of 126 endophytic isolates from the medicinal plant Limonium sinense (Girard) Kuntze, and found many isolates showed PGP activities, but no further study was made on the PGP mechanisms Endophytic isolates from rice plants (Oryza sativa) were the earliest investigated plant endophytes, and the endophytes showed versatile PGP activities of nitrogen-fixation, phosphate solubilization, siderophore and IAA synthesis (Ji et al, 2014). Qin et al (2014) assessed the PGP functions (i.e., ACC deaminase, IAA synthesis and nitrogen fixation) of 126 endophytic isolates from the medicinal plant Limonium sinense (Girard) Kuntze, and found many isolates showed PGP activities, but no further study was made on the PGP mechanisms
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