Powdery Mildews under the microscope

Since the visit of powdery mildew expert Dr. Roger Cook in mid-August I have been pressing on in order to successfully culture colonies of the Erysiphales. This has involved experimentation with various methods, including infection of both detached leaves and fresh cotyledons, enabling an ongoing stock of powdery mildews on fresh plant material to be maintained. Whilst also collecting and pressing various species of infected plant material, which may well be paramount come the winter, I have been able to begin advanced microscopic analysis.

Delphinium (Osmium) 6

Delphinium leaf at magnification of 700 x showing the hyphal network of the powdery mildew along with several conidia.

An intricate method of powdery mildew identification is that of using high power microscopes in order to view the surface patterns of powdery mildew spores. These spores are rarely larger than 20 microns (0.02 of a mm) and as such it is necessary to use a Scanning Electron Microscope (SEM) to see the level of detail necessary. Fortunately the people at the university’s Centre for Advanced Microscopy (CfAM) have been very helpful and trained me suitably so that I will be able to continue this research largely unassisted.

Conidial side and end walls come in various forms which, when distinguished, can be used to determine the tribe and genus of the specimen within the Erysiphaceae family. While much of this work has been done before, but there are gaps in the knowledge which include the potentially important step of studying Microidium phyllanthi, a powdery mildew of the Phyllanthus family and transferring the technique from the one place it havs been used previously. I therefore aim to become familiar with these superficial features to determine which group of powdery mildew the intermediate Microidium are most related in order to support this relatively new method of classification.

Acer 2

Conidium at magnification of 3000 x showing typical ‘dendritic’ side wall patterning of the genus Sawadaea

Acer 3

Conidium at magnification of 9500 x showing typical ‘whorled’ end wall patterning of the genus Sawadaea







My research project is jointly funded by BBSRC and the Royal Horticultural Society under a BBSCR CASE award.

About Oliver Ellingham

PhD student at the University of Reading. Working on ID techniques of powdery mildew Fungi. Interested in mycology, plant pathology and arboriculture.
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5 Responses to Powdery Mildews under the microscope

  1. stephen ellingham says:

    Great microspy pics. Do the hypha grow from one end of the Conida? While your pics show Sawadaea, just wondered to which family they belong. 9500x must be max limit, no way of seeing inside? Thanks for going to Berks Record Library, M very appreciative. SDE.

    • Oliver Ellingham says:

      Stephen, the pics are good, but I need to do more to see better surface patterns as these are still not of a high enough resolution. Experimenting with preparation methods will help this, but this can be a long (or quick but expensive) process. The SEM is able to x-ray the specimen, but this is not necessary.
      I am unsure if the initial orientation of hypha from a conidium is known, but ‘…a germ tube protrudes from the spore, elongating to form a hypha. Appressoria will then grow or swell laterally from the hypha, and penetration pegs will protrude from the appressoria to penetrate host cells via turgor pressure and enzymatic activity.’
      All the PMs are of the order Erysiphales and the family Erysiphaceae, there are then five ‘tribes’ and Sawadaea falls within the Cystotheceae, you can have a look here, but their grouping is actually not quite right…

  2. Pingback: Powdery mildew taxonomy | Culham Research Group

  3. pratikshya says:

    structure is different from that what i have observed here in my context.

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