Wageningen, The Netherlands
August 7, 2008
Dutch, British and American
scientists have developed a method to more quickly identify and
isolate genes that can be used to make potatoes resistant to
Phytophthora infestans, the dreaded potato blight. With this
method, multiple resistance genes from different species of
potatoes can be isolated and possibly used simultaneously. This
offers the prospect of achieving sustainable resistance against
the pathogen because it is less capable of breaking the
resistance of the potato when multiple genes are involved.
According to researchers at
Wageningen University in the Netherlands, the Sainsbury
Laboratory at the John Innes Centre in the UK and Ohio State
University in the USA, the best strategy to make potatoes
resistant to the stubborn fungal pathogen Phytophthora is to
develop so-called broad spectrum resistance. In their article,
published on 6 August in the journal PLoS One, they explained
that the current methods to discover resistance genes are too
slow. Moreover, because they often concern only a single gene,
these methods do not lead to sustainable resistance because
Phytophthora can break single-gene resistance relatively quickly
and easily.
Interaction
The newly developed method is based on the interaction of genes
of the pathogen and genes of the potato. The response of the
potato involves resistance genes in the plant, and the response
of P. infestans involves so-called avirulence genes. The
avirulence gene produces proteins (effectors) that are
recognised by the resistance gene proteins of the potato; an
interaction then takes place. By using effectors (proteins that
are secreted by Phytophthora into the plant after infection
takes place), researchers can relatively quickly identify and
isolate the genes that are crucial to the interaction. Because
the pathogen (Phytophthora) cannot switch off these proteins,
but produces them constantly, genes that can recognise these
proteins can potentially serve as resistance genes.
In the study, a set of 54 effectors (of an estimated 500
effectors in total) were tested on a large set of wild potato
species. In many cases, this led to reactions from the wild
potato species (the hypersensitivity response: the location
where the effector protein was applied begins die off) and in
one case to the actual identification of the effector protein –
known as IPiO. This effector turned out to be directly
correlated with the resistance of three wild species, S.
stoloniferum, S. papita and S. bulbocastanum. This means that a
positive response against the effector always occurred in plants
that had the resistance gene. In additional studies, the
researchers were able to show that the effector in this case was
the avirulence gene of the resistance gene. Because the
researchers realised that the resistance genes from the three
species had to be very similar, they were quickly able to
isolate the resistance genes in S. papita and S. stoloniferum by
using their knowledge of the previously isolated resistance gene
from S. bulbocastanum.
Permanent threat
Since Phytophthora first ravaged the potato – an event
epitomised by the notorious Irish Potato Famine in the 19th
century – this pathogen has been a permanent threat, and has
repeatedly led to disastrous crop damage and high production
costs. Until now, a very labour-intensive process of searching
for sustainable resistance has yielded few or no results, and
the use of fungicides has been essentially the only way to
control the disease in modern agriculture.
The methods described in the article make it possible –
relatively quickly – to acquire an impression of the prevalence
and nature of resistance genes that would be very difficult or
even impossible for the pathogen to break. By combining several
of these potentially hard-to-break resistance genes, sustainable
resistance will come within reach. |
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