BluGen - the Blumeria Sequencing Project

Powdery mildew fungi

by Prof. Sarah Gurr, Plant Sciences, University Of Oxford.

Powdery mildews are amongst the most commonplace, widespread and recognizable of all plant diseases. They are aptly named, for infection produces a white lawn of fungal mycelium that covers the plant surface, while chains of aerial conidia give the characteristic powdery appearance

Mildew on a barley leaf.

Powdery mildews can infect a wide range of hosts, including over 9000 dicotyledonous and over 650 monocotyledonous plant species. The cereals, particularly wheat and barley are among the most important agricultural crops that suffer from powdery mildew disease. Indeed, in temperate regions barley powdery mildew can cause yield losses of some 5-20% and occasionally as much as 40%. Other plants that succumb to severe powdery mildew infections include cucurbits (cucumbers, squashes and cantaloupe melons), legumes, strawberries, grapes, roses, apples and oak trees. Curiously, powdery mildews do not infect maize, carrots or celery. Taken collectively, powdery mildews cause greater losses in terms of crop yield than any other single “type” of plant disease.

The powdery mildew diseases are caused by many species of Ascomycete fungi, grouped into several genera. They are true obligate biotrophs, which means that growth and reproduction of these fungi depends on their parasitising living host plants. Despite the lack of a robust and reliable DNA-mediated transformation studies and mutational analysis, significant progress has been made over the past decade towards understanding powdery mildew-host interactions at both the cellular and molecular level.

Blumeria graminis conidia growing on a barley leaf.

As yet, the most intensively studied powdery mildew-host systems have been those which are important as crop diseases. Blumeria graminis DC. [syn. Blumeria graminis (DC.) Speer] f.sp. hordei Marchal infects barley and is one such powdery mildew fungus. More recently, however, the interaction of Bgh and Arabidopsis thaliana L and of the powdery mildew Erysiphe cruciferarum Opiz & Junell with Arabidopsis have emerged as good systems to study. Whilst a vast amount of genetic information is now available for A. thaliana following the Arabidopsis genome sequencing initiative, far less is known about its fungal pathogen.