Fusaric acid instigates the invasion of banana by Fusarium oxysporum f. sp. cubense TR4.

Siwen Liu,Yong Zhang,Cunwu Zuo,Guiming Deng,Ganjun Yi,Altus Viljoen,Chunhua Hu,Tao Dong,Li‐Jun Ma,Qiaosong Yang,Ou Sheng,Huijun Gao,Na Liu,Diane Mostert,Jian Li,Fangcheng Bi,Tongxin Dou,Chunyu Li

doi:10.1111/nph.16193

Abstract

Summary Fusaric acid (FSA) is a phytotoxin produced by several Fusarium species and has been associated with plant disease development, although its role is still not well understood.Mutation of key genes in the FSA biosynthetic gene (FUB) cluster in Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) reduced the FSA production, and resulted in decreased disease symptoms and reduced fungal biomass in the host banana plants.When pretreated with FSA, both banana leaves and pseudostems exhibited increased sensitivity to Foc TR4 invasion. Banana embryogenic cell suspensions (ECSs) treated with FSA exhibited a lower rate of O2 uptake, loss of mitochondrial membrane potential, increased reactive oxygen species (ROS) accumulation, and greater nuclear condensation and cell death. Consistently, transcriptomic analysis of FSA‐treated ECSs showed that FSA may induce plant cell death through regulating the expression of genes involved in mitochondrial functions.The results herein demonstrated that the FSA from Foc TR4 functions as a positive virulence factor and acts at the early stage of the disease development before the appearance of the fungal hyphae in the infected tissues.

Highlights

Banana (Musa spp.) is one of the most important economic crops for many Asian and African countries
Foc race 4 is divided into the Foc ‘subtropical’ race 4 (STR4) and the Foc ‘tropical’ race 4 (TR4) strains that affect the Cavendish bananas in the subtropics and tropics, respectively
Fusaric acid (FSA) is a phytotoxin produced by several Fusarium species and other fungal pathogens (Fakhouri et al, 2003), and known to have strong phytotoxicity to both animal and plant cells

Summary

Introduction

Banana (Musa spp.) is one of the most important economic crops for many Asian and African countries. Foc race 3 is only virulent on the ornamental Heliconia spp. but does not affect the Musa spp. It is not considered cubense anymore (Ploetz et al, 2015b). Foc race 4 is divided into the Foc ‘subtropical’ race 4 (STR4) and the Foc ‘tropical’ race 4 (TR4) strains that affect the Cavendish bananas in the subtropics and tropics, respectively. Between these two strains, Foc TR4 is the more virulent one as it can infect Cavendish bananas under both stressed and nonstressed conditions (Li et al, 2013). A lack of effective quarantine measures has resulted in Foc TR4 spreading from the Asia-Pacific region, where it was restricted for more than two decades, to the Middle East and countries of the Greater Mekong Subregion

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