Auxin, Abscisic Acid and Jasmonate Are the Central Players in Rice Sheath Rot Caused by Sarocladium oryzae and Pseudomonas fuscovaginae

K J Peeters,M Höfte,K Audenaert,K Demeestere,M Ameye

doi:10.1186/s12284-020-00438-9

Abstract

Sheath rot is an emerging rice disease that causes severe yield losses worldwide. The main causal agents are the toxin producers Sarocladium oryzae and Pseudomonas fuscovaginae. The fungus S. oryzae produces helvolic acid and cerulenin and the bacterium P. fuscovaginae produces cyclic lipopeptides. Helvolic acid and the lipopeptide, fuscopeptin, inhibit membrane-bound H+-ATPase pumps in the rice plant. To manage rice sheath rot, a better understanding of the host response and virulence strategies of the pathogens is required. This study investigated the interaction of the sheath rot pathogens with their host and the role of their toxins herein. Japonica rice was inoculated with high- and low-helvolic acid-producing S. oryzae isolates or with P. fuscovaginae wild type and fuscopeptin mutant strains. During infection, cerulenin, helvolic acid and the phytohormones abscisic acid, jasmonate, auxin and salicylic acid were quantified in the sheath. In addition, disease severity and grain yield parameters were assessed. Rice plants responded to high-toxin-producing S. oryzae and P. fuscovaginae strains with an increase in abscisic acid, jasmonate and auxin levels. We conclude that, for both pathogens, toxins play a core role during sheath rot infection. S. oryzae and P. fuscovaginae interact with their host in a similar way. This may explain why both sheath rot pathogens cause very similar symptoms despite their different nature.

Highlights

Rice sheath rot is an emerging disease that affects all rice growing areas worldwide
We have shown before that the S. oryzae population is very diverse in its toxigenicity and virulence with the most pathogenic isolates producing the highest amounts of helvolic acid in the rice sheath
Disease Assessment, Phytohormone and Toxin Levels during Sarocladium oryzae Infection To study the interaction of S. oryzae with its host and the role of its toxins cerulenin and helvolic acid rice plants were inoculated with four isolates (Table 1) that were earlier shown to differ in virulence and toxin production (Table S1; Peeters et al 2020)

Summary

Introduction

Rice sheath rot is an emerging disease that affects all rice growing areas worldwide. Breeding for resistant varieties is difficult because there are various sheath rot pathogens and there is a lack of knowledge about their infection strategies (Bigirimana 2016; Sakthivel 2001; Ayyadurai et al 2005; Chauhan et al 2017a; Mvuyekure et al 2017). Different Fusarium spp., such as Fusarium andiyazi, F. proliferatum, F. verticillioides and F. fujikuroi can cause sheath rot symptoms (Bigirimana 2016; Wulff et al 2010). Both S. oryzae and P. fuscovaginae are seed-borne which could explain the fast spreading of these pathogens (Batoko et al 1997; Ayyadurai et al 2005; Adorada et al 2015).

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