For the publicTouchy Feely Fungi: Sensory recognition by fungal plant pathogens

Powdery mildew on leaf surface
Powdery mildew on leaf surface
 
Eyespot lesion on a stem base
Eyespot lesion on a stem base
 
Downy mildew looks for a groove
Downy mildew looks for a groove
 
Cereal eyespot infection plaque
Cereal eyespot infection plaque

This exhibit was presented at the Royal Society Summer Science Exhibition in 2003.

Fungal diseases of plants affect both food production and quality, destroying up to 30 % of our crops. Studies at Rothamsted Research, the University of Oxford and the Institute of Grassland and Environmental Research are investigating the infection processes of these fungi. This research is revealing them to be selective foragers that touch, feel and taste their way to the right location for germination

Fungi reproduce by means of thousands of tiny spores. These spores can sense not only when they are on the correct plant but also when they are on the right part of the plant to infect. When spores land in the wrong place they will be unable to infect the plant and rapidly die. In the right place they produce infection structures to help them invade the plant.

But how do they know when they are in the right place?

Much is known about chemical recognition cues from plants but new research is demonstrating that physical cues are also important in helping the fungus determine whether it has found a suitable infection site.

Leaf surface topography

Some fungi show thigmotropism, that is, the ability to feel surface features. For example, downy mildew (Peronospora parasitica) sends out spore tubes, searching for a groove of precisely 0.9 microns. This groove width (which is about 10,000 times smaller than the width of your fingernail) corresponds to the ridges found at cell boundaries, enabling the spores tubes to penetrate the plant tissue between the cells, which may help to avoid triggering the plant's defences before the infection has become established.

Pressure between leaves

Experiments have recently revealed that cereal eyespot fungus (Tapesia yallundae and Tapesia acuformis) have a pressure-sensing mechanism enabling them to find the best place for penetration by detecting the right pressure between the leaves in the leaf sheath. This is the first time that such a sensory mode has been found to operate.

Waxy surfaces

Powdery mildew (Erysiphe or Blumeria) spores can respond within a minute of contacting the right plant. How it does this is not yet properly understood but it seems that the instantaneous release of adhesive material is involved. The growing fungus then recognises plant surface features, including water-repellent leaf waxes, and this controls development of special infection structures.

Understanding the infection processes of these economically important diseases may help in devising new strategies to control them without the need for chemical pesticides.

Animations

Cereal eyespot: Under pressure
Downy mildew: Get in the groove

PowerPoint slideshow

PowerPointConfusing a powdery mildew spore

Links

Royal Society Web page