Resistance to QoI Fungicides Is Widespread in Brazilian Populations of the Wheat Blast Pathogen Magnaporthe oryzae

Abstract

Wheat blast, caused by Magnaporthe oryzae, is an important disease across central and southern Brazil. Control has relied mainly on strobilurin fungicides (quinone-outside inhibitors [QoIs]). Here, we report the widespread distribution of QoI resistance in M. oryzae populations sampled from wheat fields and poaceous hosts across central and southern Brazil and the evolution of the cytochrome b (cyt b) gene. Sequence analysis of the cyt b gene distinguished nine haplotypes, with four haplotypes carrying the G143A mutation associated with QoI resistance and two haplotypes shared between isolates sampled from wheat and other poaceous hosts. The frequency of the G143A mutation in the wheat-infecting population increased from 36% in 2005 to 90% in 2012. The G143A mutation was found in many different nuclear genetic backgrounds of M. oryzae. Our findings indicate an urgent need to reexamine the use of strobilurins to manage fungal wheat diseases in Brazil.

Wheat blast research: Status and imperatives

“…Blast pathogen has also evolved to acquire resistance to fungicides extensively used to manage the disease . Similar findings of widespread distribution of QoI (group of fungicides used for controlling blast) resistance in M. oryzae populations sampled from wheat fields and Poaceous hosts across central and southern Brazil were reported by Castroagudin et al (2015). This resistance is a result of mutation of G143A which led to evolution of cytochrome b gene.…”

“…Literature now accepts M. oryzae pathotype Triticum as the correct name for wheat blast pathogen (Maciel, 2016;Castroagudin et al, 2015, Perello et al, 2015Maciel et al, 2014) although recently, a new species named Pyricularia graminis-tritici was proposed to cause wheat blast by Castroagudin et al (2016). Ever since its first report, blast pathogen was variously named by researchers for example, Pyricularia oryzae Oliveira et al, 2015;Cruz et al, 2015a;Silva et al, 2015), Pyricularia grisea (Filha et al, 2011;Kohli et al, 2011;Rocha et al, 2014), Magnaporthe grisea (Urashima and Kato, 1994;Peng et al, 2011;Pagani et al, 2014) and M. oryzae Triticum (Cruz et al, 2015a).…”

Emergence of wheat blast in Bangladesh was caused by a South American lineage of Magnaporthe oryzae

“…This finding calls for intensive monitoring and surveillance of the wheat blast pathogen to limit its further spread outside South America and Bangladesh. In addition, our finding indicates that the knowledge acquired to manage wheat blast in Brazil using disease resistant cultivars [35][36][37] and fungicides [38,39] can be directly applied to the Bangladeshi epidemic.…”

Wheat blast disease: danger on the move

“…Extensive use of strobilurin (QoI) fungicides in Brazil has led to widespread distribution of cyt b mutations conferring resistance in strains isolated from wheat and other grasses (Castroagudín et al 2014). Therefore, fungicide resistance in the MoT population should be routinely monitored.…”