Division of Plant Health, Environment and Biotechnology
Plant Pathology

IKEDA, K. Associate Professor

ASUKE, S. Assistant Professor

Introduction of research results

1. The final goal of plant pathology is to reveal causes of plant diseases, and to develop effective methods for controlling them. In this laboratory we have been working on wheat blast, a devastating wheat disease. Wheat blast, caused by a subgroup (Triticum pathotype) of Pyricularia oryzae, first emerged in Brazil in 1985 and spread to neighboring countries in South America. In 2016 it suddenly appeared in Bangladesh and caused a significant loss of wheat production. Wheat blast is now becoming a pandemic disease. The first question is how this important plant pathogen evolved in Brazil. Genetic analysis revealed that the incompatibility between Lolium isolates of P. oryzae (pathogenic on ryegrass) and common wheat is governed by an avirulence gene, PWT3, and its corresponding resistance gene Rmg6 (Rwt3). We isolated PWT3 through map-based cloning. When PWT3 of a Lolium isolate was disrupted, the resulting strain gained virulence on wheat cultivars carrying Rwt3. These results indicate that mutations or deletions of PWT3 would lead to a gain of virulence on a majority of wheat cultivars.　 Among local landraces of common wheat collected worldwide, Rwt3 carriers accounted for ~77% and the remaining were lacking Rwt3. Historical data on wheat cultivation in Brazil suggest that the wheat blast fungus evolved due to widespread deployment of rwt3 wheat followed by the loss of function of PWT3. This implies that the rwt3 wheat served as a springboard for the host jump to wheat. Resistance genes against this new pathogen are very rare in common wheat populations. However, we found two major genes against the wheat blast fungus, Rmg8 and RmgGR119. We are now introducing these genes into leading varieties in Japan.
   

   Wheat blast disease (Provided by Dr. A. S. Urashima）

2. Elucidation of infection strategies based on morphological study
   Fungal adhesion to host cells is an initial important step to establish infection, which is considered to be a universal mechanism across plant pathogenic fungi. The fungal surface is covered with de novo synthesized compounds collectively called the extracellular matrix, which might be involved in host adhesion. After the establishment of host adhesion, the germ tube differentiates into appressorium. We try to elucidate molecular mechanisms of infection process.
   

   Appressorium on the wheat leaf (left) and extracellular matrix (right)．
3. Development of novel disease protection measures
   （１）Detachment action
   

   Based on our finding that adhesion is one of the pathogenicity factors, we try to develop novel biological control. The glycoproteinase family was able to degrade fungal extracellular matrix. Therefore, we try to utilize gelatinolytic bacteria to detach fungal pathogen from the leaf.

   

   The glycoproteinases (e.g., collagenase and gelatinase) were able to degrade extracellular matrix and
   detach fungal pathogen from host plant (left).
   We try to develop novel biological control by detachment action of the pathogen (right).

   （２）Virocontrol (Virological Control)
   Certain mycoviruses cause hypovirulence in fungal pathogens. We try to develop a biological control strategy by utilizing a hypovirulent mycovirus, virocontrol.

   

   Certain mycoviruses affect virulence of phytopathogenic fungi (left).
   We try to introduce an effective mycovirus to a fungal pathogen for virocontrol (right).

Plant Pathology Web Site