Touchy-feely fungi: sensory recognition by fungal plant pathogens

Fungi A single spore (inset) grows from a germling into a colony in just 5 days.

Professor John Lucas, Dr Paul Bowyer and Dr Raffaella Carzaniga.
Rothamsted Research.

Dr Tim Carver.
Institute of Grassland and Environmental Research.

Dr Sarah Gurr.
University of Oxford.

When fruit in your kitchen goes mouldy, you are probably in more of a hurry to throw it out before the rot spreads than you are to look at what is causing it. But if you were to examine it closely, the chances are that you would discover different kinds of mould or fungi infecting specific kinds of fruit. A set of experiments from Rothamsted Research, the Institute of Grassland and Environmental Research and the University of Oxford has shown that each species of fungus is uniquely adapted to invade a particular plant or crop.

Many fungi are parasitic organisms, which means they depend on other living organisms (hosts) for the food and protection they need to grow and reproduce. They produce thousands of tiny spores that distribute the fungus by infecting new plants. These spores can recognise not only particular plant species, but also specific parts of the plant, where they can enter with least risk of triggering the plant's defence mechanisms.

Scientists have been looking at the physical cues used by the spores to sense surfaces, orientate themselves, and infect the correct plant species in the right place. Achieving this as efficiently and stealthily as possible is crucial for the fungus, as the spores can only survive a short time without the host's resources. Once in the right place, the spores sprout tubes that penetrate the plant. They then develop feeding structures so the spore can profit from the new food supply.

'Our exhibit will illustrate some of the ingenious ways that parasitic fungi locate, break and enter the host plant without triggering its alarm system,' says Professor John Lucas. 'A live video link-up lets you spy on fungi infecting plants in the laboratory. And you can pretend to be a fungus yourself and test your reaction skills to different physical stimuli.'

Some fungi use the physical surface of the plant to find the right place to infect. By watching Downy mildew (Peronospora) spores penetrate cabbage leaves, scientists now know that it is ridges and troughs of a particular size (0.9 microns) on the leaf surface that trigger infection. These ridges mark the break between two cells, which might offer less resistance to the spore's infection tubes as they push into the leaf.