Colonization of sesbania seed endophytic bacterium and salt-tolerant and growth-promoting effect of mixed seed soaking with endophytic bacterium and polysaccharide

Abstract:

[Background] Soil salinization has become an increasingly serious problem worldwide, affecting not only crop yield but also the physical and chemical properties of soil. It can inhibit seed germination and hinder the normal growth and the water and nutrient uptake of crops, thereby reducing crop yield. [Objective] Maize growth is limited in saline soil. We studied the effects of mixed soaking with sesbania seed endophytes and sesbania gum on the germination of maize seeds exposed to medium and high concentrations of salt, aiming to provide technical support for improving maize growth in saline soil. [Methods] The LB liquid medium was used to determine the salt tolerance of the sesbania seed endophytic bacterium Bacillus velezensis ZH60. Maize seeds were soaked with 1% sesbania gum, ZH60 suspension (OD₆₀₀=0.8), and their mixture for 3 h. After natural drying, the seeds were cultured on 0.8% agar plates containing 0, 100, and 200 mmol/L NaCl, respectively. The germination rate, root length, and bud length of maize were measured. The maize seedlings at the two-leaf stage were transplanted to the pots filled with vermiculite and irrigated with fluorescence-labeled ZH60 suspension. The maize roots were collected after 1, 5, 11, 17, and 25 days, and the colonization of endophytic bacteria in maize roots was determined by plate colony counting. The colonization of ZH60 in maize roots on day 28 was observed under a scanning confocal microscope. [Results] The strain ZH60 can tolerate 11% NaCl. Compared with the control group, the mixed soaking of maize seeds with 1% sesbania gum, ZH60 suspension, and their mixture increased the germination potential by 28%, 22%, and 30%, the bud length by 158%, 163%, and 150%, and the root length by 36.8%, 21.4%, and 42.9%, respectively, under medium and high concentrations of NaCl. ZH60 could colonize maize roots, and the colonization increased from 2×10⁴ CFU/g on day 1 to 2.5×10⁴ CFU/g on day 25. [Conclusion] The endophytic bacterium B. velezensis ZH60 has high salt tolerance. The germination potential, root length, and bud length of maize are increased by mixed seed soaking with ZH60 and sesbania gum. B. velezensis ZH60 can colonize the roots of maize, which provides strain resources for improving germination and rooting of maize in saline soil.