Potatoes… - Bayer CropScience

“Phytophthora
infestans will
continue to adapt
more rapidly in the
coming years. We
must therefore
outsmart the
pathogen and
attack it in all
possible ways.”
Huub Schepers
mating types are endemic throughout
Europe.
Oospores (which develop via sexual
reproduction) are now found in virtually
all Western and Northern European countries.
In the Netherlands, 60 to 70 % of all
potato-growing areas have mixed populations
of A1 and A2, according to long-term
surveys by the PPO Research Centre. Early
infection caused by oospores occurs mainly
in lighter soils and areas with very short
rotations. This applies particularly to the
North-East of the Netherlands, where
starch potato cultivation is concentrated.
In the period 1999 – 2005, about 32 percent
of all early infections in that region
appeared to be caused by oospores.
Oospores are a considerable
threat
Sexual reproduction via oospores is a serious
threat for potato cultivation, because it
provides for greater variation in the
pathogen population. Laboratory tests and
field studies have shown that the sexuallyreproducing
populations can be considerably
more aggressive than their asexual
predecessors. Research has shown that
the new, mixed populations adapt more
rapidly to temperatures that are normally
unfavourable for Phytophthora; the
pathogen used to be inviable at temperatures
below 10°C and above 25°C, but
this is not the case for the new variants.
Newly-collected isolates are also often
able to survive better on the tuber, as they
tend to damage the tuber less severely: the
tuber rots less rapidly, and is consequently
less easy to sort out on the basis of external
symptoms.
The new population also has a considerably
shorter latent period, meaning that
the life-cycle of Phytophthora infestans
can be completed more rapidly than
before. This, in turn, allows the fungus to
adapt more rapidly through sexual reproduction.
Under favourable conditions, two
generations a week are now possible, compared
with one generation before. It is thus
important to have short intervals in the
spraying programme in areas where
oospores are being formed.
Further threats presented by the new,
mixed populations include the fact that
they often have high spore production
rates, and can break through varietal genetic
resistance more easily. In addition, they
have a broader range of host plants compared
with the ‘old’ Phytophthora: for
example, it is known that the new mixed
populations can also infect green night-
Phytophthora infestans – symptoms
If “Phytophthora-weather“ prevails,
potato tubers can be infected as soon
as they are formed in the middle of
the season.
Above-ground parts of the plant must be
adequately protected right from the start,
in order to prevent inoculum from being
washed down into the soil.
Severe infection of foliage leads to
significant yield losses.
1/08 COURIER 19