Set by Dr Phil Taylor
Much of plant pathology is spent studying microorganisms in culture i.e. when they are growing on artificial media and not colonising a plant. However, it is always useful to know which microorganisms can be grown in culture and which are obligate biotrophs i.e. cannot be grown outside a host plant.
#1. Rust fungi are very common pathogens, but can they be grown in culture?
The correct answer is:
No they cannot be cultured externally to a host plant.
There are no media that can support the growth of rust fungi.
#2. Powdery mildew on the underside of an apple leaf. They are a very well-studied group of plant pathogens; they grow well on the surface of leaves but do they grow in culture?
The correct answer is:
They do not grow in culture.
Despite growing rapidly over the leaf surface powdery mildews cannot be cultured.
#3. Sooty mould is the black fungus often seen growing on the surface of leaves. The generic name describes a condition rather than a fungal species, but can the fungi be grown in culture?
The correct answer is:
Yes, the fungi that make up the sooty mould family can be grown in culture.
Sooty mould is not a true plant pathogen but is growing on the nutrient rich coating that may develop on leaves following a sucking insect attack. They are versatile and will grow on any nutrient rich media.
#4. The lesions on these bean leaves are due to Peronospora viciae in many regards it is a typical downy mildew. To what extent can the downy mildews be grown in culture?
The correct answer is:
It is not possible to grow any downy mildews in culture.
They have to be maintained as resting spores or actively growing on a susceptible host.
#5. Tobacco mosaic virus (virions seen here) is unusual in that it has considerable ability to survive on inanimate surfaces., how does it respond in culture?
The correct answer is:
Does not grow in culture:
Although TMV is able to survive outside a host plant cell the replication of the virus is intimately associated with the metabolism of the living cell, and it will never replicate in culture.
#6. The dwarfing of these poinsettias is due to a phytoplasma infection. Phytoplasmas are bacteria like organisms that are vectored by insects. Where can Phytoplasmas replicate?
The correct answer is:
In the host plant and the insect vector:
Phytoplasmas are vectored in a similar way to plant viruses but generally have a much more intimate relationship with the vector and usually replicate in both hosts. Unlike mycoplasmas phytoplasmas cannot be cultured.
#7. This is “white rust” on Salsify, this group are not true rusts (nor are they true fungi) they are oomycetes. Is it possible to grow this group of pathogens in culture?
The correct answer is:
Cannot grow away from a host plant.
The white rusts are not related to true rusts in any way, but they do have similar characteristics such as requiring a host plant to grow on.
#8. This is the stroma of Plasmodiophora brassiacae the causal agent of club root of brassicas. Originally considered a fungus it lacks hyphal type growth and is actually a protist. Can it be grown in culture?
The correct answer is:
Not it cannot be grown in culture.
It is not possible to culture this protist on artificial medium.
Photo credit: Eduardo Hidalgo
#9. This a young banana plant badly damaged by nematode attack. Can plant parasitic nematodes be grown in culture?
The correct answer is:
They cannot be cultured.
Nematodes are found in a great number of environments, but the plant parasitic nematodes do not grow without the presence of a living plant
#10. Xylella fastidiosa is a Xylem-Limited Bacterial Pathogen of Plants which has no capacity in the wild to survive outside a host plant or insect vector, however, can it be cultured?
The correct answer is:
It is possible to culture Xylella on special media.
There is special medium that will support the growth of Xylella, it grows slowly and produces small colonies..
Photo credit: John Hartman, University of Kentucky Bugwood.org
Results
We hope you enjoyed the quiz and learned something!
See how your score matches up…
1-3: You need to do a few more of these quizzes to become a field diagnostics expert.
3-5: You have made a start in your field diagnostics but there is some way to go…
5-7: You are getting more right than wrong so keep on learning!
7-9: Impressive you are getting pretty experienced in your field diagnostics!
10: Well done! But make sure you do the quiz again next month.
We hope you enjoyed the quiz and learned something!
See how your score matches up…
1-3: You need to do a few more of these quizzes to become a field diagnostics expert.
3-5: You have made a start in your field diagnostics but there is some way to go…
5-7: You are getting more right than wrong so keep on learning!
7-9: Impressive you are getting pretty experienced in your field diagnostics!
10: Well done! But make sure you do the quiz again next month.
