Changes in Tobacco Root Exudates Under Acidic Conditions Aggravate Soil Acidification, Attract Pathogens and Increase Plant Infection

ABSTRACT

Soil acidification reduces crop production and exacerbates soil‐borne diseases. Root exudates play important roles in the interaction between plants and soil microorganisms, yet changes in root exudates under acidic soils and their influence on plant resistance are unknown. Here, root exudates secreted by tobacco plants grown under strongly acidic, weakly acidic or neutral conditions were investigated in relation to infection by
Ralstonia pseudosolanacearum
, which causes a soil‐borne bacterial wilt disease resulting in economic losses worldwide. Root exudate profiles changed under acidic conditions, with weakly and strongly acidic treatments revealing 354 and 580 differential metabolites, respectively. Organic and phenolic acids accumulated under acidic conditions, including
p
‐coumaric acid ethyl ester, hydroxycitric acid, 1‐naphthyl acetate,
trans
‐cinnamic acid and 3,4,5‐trimethoxycinnamic acid, which attracted and promoted
R. pseudosolanacearum
root colonisation. Exogenous addition of
p
‐coumaric acid ethyl ester, ethyl ferulate, 1‐naphthyl acetate,
trans
‐cinnamic acid and 3,4,5‐trimethoxycinnamic acid acidified soil and inhibited seed germination and plant growth. Soil pH declined by 0.34–0.66 units when treated with
trans
‐cinnamic acid, 3,4,5‐trimethoxycinnamic acid,
p
‐coumaric acid ethyl ester and 1‐naphthyl acetate. The cell number of
R. pseudosolanacearum
in roots increased by 7.9–232.2 times when tobacco plants were treated with hydroxycitric acid, 1‐naphthyl acetate,
trans
‐cinnamic acid, 3,4,5‐trimethoxycinnamic acid and
p
‐coumaric acid ethyl ester. The decrease in plant hormones abscisic acid, indole‐3‐butyric acid, IAA‐Asp and
trans
‐zeatin‐riboside may hinder plant growth and reduce plant resistance to pathogen attack. Overall, the up‐regulated exudation of organic and phenolic acids aggravates soil acidification, promotes bacterial wilt disease and hinders plant growth in acidic soils.