田菁内生菌定殖及其与多糖混合浸种的耐盐促生效果

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

摘要:

【背景】土壤盐渍化已经成为日益严重的世界性问题，盐渍化不仅影响作物的产量，还会影响土壤的理化性质，抑制种子的萌发，阻碍植物正常生长，以及种子对水分和养分的吸收，进而影响作物的产量。【目的】玉米在盐渍土壤上生长受限，探究在中、高盐浓度下田菁种子内生菌与田菁胶混合浸种对玉米发芽的影响，为促进盐渍土玉米生长提供技术支持。【方法】利用LB液体培养基测定田菁种子内生菌贝莱斯芽孢杆菌ZH60的耐盐性；分别利用1%浓度田菁胶、OD₆₀₀为0.8的ZH60菌悬液及两者混合液对玉米浸种3 h，自然风干后分别置于0、100和200 mmol/L NaCl的0.8%琼脂培养基上培养，测定玉米种子发芽势、发芽率、根长及芽长。将两叶一心期的玉米幼苗移至装有蛭石的花盆中培养，用荧光标记的内生菌ZH60灌根，分别于1、5、11、17、25 d取玉米根系研磨，利用平板菌落计数法测定内生菌在玉米根部的定殖量；利用激光共聚焦显微镜观察第28天ZH60在玉米根部的定殖情况。【结果】菌株ZH60耐11%的NaCl盐浓度，在中、高盐浓度下混合浸种的发芽势较对照组分别提高了28%、22%、30%；芽长提高了158%、163%、150%；根长提高了36.8%、21.4%、42.9%。ZH60能够在玉米根部定殖，定殖量从第1天的2×10⁴ CFU/g提高到第25天的2.5×10⁴ CFU/g。【结论】田菁种子内生菌贝莱斯芽孢杆菌ZH60具有较高的耐盐性，在盐浓度下与田菁胶共混浸种均明显提高了玉米发芽势及根长、芽长，且能在玉米根部定殖，为实现盐渍土上提高玉米出芽和生根提供了菌株资源。

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.