Oryzae pathotype of Magnaporthe oryzae can cause typical blast disease symptoms on both leaves and spikes of wheat under a growth room condition

Abstract

Blast diseases of rice and wheat are known to be caused by the specific pathotypes of Magnaporthe oryzae (syn. Pyricularia oryzae), M. oryzae Oryzae (MoO) and M. oryzae Triticum (MoT), respectively. Rice blast disease has been seen in Bangladesh from a very ancient time. However, Bangladesh’s first epidemic outbreak of wheat blast was recorded in 2016. This study aimed to investigate the cross-infection reactions of MoO and MoT in rice and wheat in a growth room condition. Artificial inoculation was done at vegetative and reproductive phases of both wheat and rice plants in a completely randomized design using virulent isolates of MoO and MoT. Artificial inoculation with MoO resulted in foliar symptoms with typical eye-shaped lesions as well as partially bleached or completely white head symptoms in both wheat and rice plants. On the other hand, MoT produced blast symptoms only on the leaves and spikes of wheat. Molecular analyses using PCR amplification (with Pot2, MoT3 and MoT6099 primers) and a recently developed rapid detection PCRD strip confirmed the presence of MoT and MoO pathotypes in the symptomatic plant samples. Our results demonstrated that MoO pathotype can infect the leaves and spikes of wheat but MoT is unable to infect rice plants under the same controlled environment in Bangladesh. This study has revealed the vulnerability of wheat to MoO pathotype and an urgent need to understand the molecular mechanism underlying host-specificity of the blast fungus M. oryzae. Our results also provided evidence for a potential wheat blast epidemic by MoO in many rice–wheat inter-cropping regions as climate change intensifies. A comprehensive study is needed to have a better understanding on the variability in virulence of MoO and MoT isolates in infecting wheat and rice under controlled environment by the inclusion of a large number of isolates and crop varieties/genotypes.