AUTHOR=Liu Dan , Chen Le , Zhu Xiaofeng , Wang Yuanyuan , Xuan Yuanhu , Liu Xiaoyu , Chen Lijie , Duan Yuxi 

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

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.01134

DOI=10.3389/fmicb.2018.01134

ISSN=1664-302X

ABSTRACT=<p>Soybean is an important economic crop that is often adversely affected by infection in the field with the soybean cyst nematode <italic>Heterodera glycines</italic>. Biological control is an eco-friendly method used to protect the crop against disease. The bacterium <italic>Klebsiella pneumoniae</italic> 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 <italic>K. pneumoniae</italic> SnebYK on the control of <italic>H. glycines</italic> was assessed. Potting experiment results showed that coating soybean seeds with <italic>K. pneumoniae</italic> SnebYK not only reduced the infection rate of <italic>H. glycines</italic> but also decreased the proportion of adult female nematodes. Field experiment results showed that <italic>K. pneumoniae</italic> SnebYK reduced both the number of <italic>H. glycines</italic> in soybean roots and the number of adult females. However, <italic>K. pneumoniae</italic> SnebYK caused low juvenile mortality in an <italic>in vitro</italic> assay. To further analyze the role of <italic>K. pneumoniae</italic> SnebYK in the inhibition of <italic>H. glycines</italic> infection, split root experiments were conducted. The results indicated that <italic>K. pneumoniae</italic> SnebYK controls <italic>H. glycines</italic> via induced systemic resistance, which reduces <italic>H. glycines</italic> penetration. <italic>Klebsiella pneumoniae</italic> SnebYK treatment also significantly increased the proportion of second-stage juveniles and decreased the proportions of third- and fourth-stage juveniles in the <italic>H. glycines</italic> population. Moreover, 48 h after inoculation with <italic>H. glycines</italic>, the expression levels of <italic>PR1, PR2, PR5</italic>, and <italic>PDF1.2</italic> were significantly higher in soybeans pretreated with <italic>K. pneumoniae</italic> SnebYK than in control soybeans. Interestingly, besides providing protection against nematodes, <italic>K. pneumoniae</italic> 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 <italic>K. pneumoniae</italic> SnebYK not only promotes soybean growth but also inhibits the invasion and development of <italic>H. glycines</italic> by inducing systemic resistance.</p>