High Humidity Causes Abnormalities in the Process of Appressorial Formation of Blumeria graminis f. sp. hordei.

Koreyuki Sugai,Masamichi Nishiguchi,Mayuko Sato,Kappei Kobayashi,Kiminori Toyooka,Mayumi Wakazaki,Takashi Yaeno,Chie Inoue,Hiroshi Inoue,Naoto Yamaoka

doi:10.3390/pathogens9010045

Koreyuki Sugai, Masamichi Nishiguchi + Show 8 more

Open Access

https://doi.org/10.3390/pathogens9010045

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Abstract

High humidity decreases the penetration rate of barley powdery mildew Blumeria graminis f. sp. hordei. However, the mechanism is not well understood. In this study, the morphological and cytochemical analyses revealed that substances containing proteins leaked from the tip of the appressorial germ tube of conidia without the formation of appressorium under a high humidity condition. In addition, exposure to high humidity prior to the formation of appressorium caused the aberrant formation of the appressorial germ tube without appressorium formation, resulting in failure to penetrate the host cell. These findings suggest that the formation and maturation of the appressorium requires a low humidity condition, and will be clues to improve the disease management by humidity control.

Highlights

Powdery mildew is a major fungal disease of barley, caused by Blumeria graminis f. sp. hordei (Bgh)
When barley leaves inoculated with Bgh were exposed to the high humidity condition
To examine in detail whether the penetration process is affected by the humid condition, the humid condition, the coleoptiles were kept at about 70% relative humidity (RH) or more than 95% RH

Summary

Introduction

Powdery mildew is a major fungal disease of barley, caused by Blumeria graminis f. sp. hordei (Bgh). An obligate biotrophic pathogen Bgh can make a success of the asexual life cycle only on the living host cells, resulting in the spread of airborne conidia through the formation of conidiophores. The appressorium mounts the formation of a penetration peg at the side contacting with the host surface, using the mechanical force by turgor pressure and the enzymatic degradation of the cell wall [4]. In case of failure to penetrate it through the appressorium, Bgh forms the second lobe from the lateral part of AGT as another attempt to penetrate a neighbor cell. Penetrating Bgh forms a haustorium surrounded by a host-derived extrahaustorial membrane and establishes infection

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