Growth‐promoting S phingomonas paucimobilis ZJSH 1 associated with D endrobium officinale through phytohormone production and nitrogen fixation

Summary Growth‐promoting S phingomonas paucimobilis   ZJSH 1, associated with D endrobium officinale , a traditional C hinese medicinal plant, was characterized. At 90 days post‐inoculation, strain ZJSH 1 significantly promoted the growth of D . officinale seedlings, with increases of stems by 8.6% and fresh weight by 7.5%. Interestingly, the polysaccharide content extracted from the inoculated seedlings was 0.6% higher than that of the control. Similar growth promotion was observed with the transplants inoculated with strain ZJSH 1. The mechanism of growth promotion was attributed to a combination of phytohormones and nitrogen fixation. Strain ZJSH 1 was found using the K jeldahl method to have a nitrogen fixation activity of 1.15 mg l −1 , which was confirmed by sequencing of the nif H gene. Using high‐performance liquid chromatography‐mass spectrometry, strain ZJSH 1 was found to produce various phytohormones, including salicylic acid ( SA ), indole‐3‐acetic acid ( IAA ), Z eatin and abscisic acid ( ABA ). The growth curve showed that strain ZJSH 1 grew well in the seedlings, especially in the roots. Accordingly, much higher contents of SA , ABA , IAA and c‐ ZR were detected in the inoculated seedlings, which may play roles as both phytohormones and ‘Systemic Acquired Resistance’ drivers. Nitrogen fixation and secretion of plant growth regulators ( SA , IAA , Z eatin and ABA ) endow S . paucimobilis   ZJSH 1 with growth‐promoting properties, which provides a potential for application in the commercial growth of D . officinale .