Klebsiella pneumoniae SnebYK Mediates Resistance Against Heterodera glycines and Promotes Soybean Growth

Soybean is an important economic crop that is often adversely affected by infection in the field with the soybean cyst nematode . Biological control is an eco-friendly method used to protect the crop against disease. The bacterium has been reported to protect rice from sheath blight and seedling blight, but its role in the control of nematode is unclear. In this study, the effect of SnebYK on the control of was assessed. Potting experiment results showed that coating soybean seeds with SnebYK not only reduced the infection rate of but also decreased the proportion of adult female nematodes. Field experiment results showed that SnebYK reduced both the number of in soybean roots and the number of adult females. However, SnebYK caused low juvenile mortality in an assay. To further analyze the role of SnebYK in the inhibition of infection, split root experiments were conducted. The results indicated that SnebYK controls via induced systemic resistance, which reduces penetration. SnebYK treatment also significantly increased the proportion of second-stage juveniles and decreased the proportions of third- and fourth-stage juveniles in the population. Moreover, 48 h after inoculation with , the expression levels of , and were significantly higher in soybeans pretreated with SnebYK than in control soybeans. Interestingly, besides providing protection against nematodes, SnebYK fixed nitrogen, produced ammonia, solubilized phosphate, and produced siderophores, leading to well-developed root system and an increase in soybean seedling fresh weight. These results demonstrate for the first time that SnebYK not only promotes soybean growth but also inhibits the invasion and development of by inducing systemic resistance.