Agriculture Reference
In-Depth Information
The presence or absence of sexual reproduction in the pathogen population is
especially significant to the epidemiology of tomato late blight. In temperate zones
where there is a crop-free period, isolates of
P. infestans
adapted to tomatoes are less
certain to survive from one season to the next than are isolates adapted to potatoes.
This is because tomato pathogens have no effective means to survive the inter-
cropping period. Potato pathogens, on the other hand, survive on tubers (in storage,
in fields, or in clamps.) The pathogen appears unable to survive from one season to
the next on tomato seeds, and other parts of the tomato plant typically die between
seasons. Survival of
P
.
infestans
in infected tomato tissue (leaflets, stems, and green
fruits) either kept on the soil surface or buried 10 cm deep, under field conditions in
Brazil, was limited. No viable structures were found after 30 days (Fig. 17.1) (M.A.
Lima, L.A. Maffia and E.S.G. Mizubuti, unpublished data).
Figure 17.1. Survival of
Phytophthora infestans
in infected tomato tissues: leaves, stems or
tomato fruit. Samples were kept either buried or on the soil surface, under field conditions
(Spring to Summer) in Brazil. Survival was estimated by periodically sampling infected tissue
and subjecting samples to a bioassay modified from Drenth
et al
. (1995).
There are survival mechanisms even if potatoes are not involved. If hosts of
P. infestans
are growing in a region, these can be a source of the pathogen. In
temperate regions, some glasshouse or greenhouse production can be a source.
Tomatoes are an expected host, but recently it has become clear that petunias and
calibrachoas can also be hosts to
P. infestans
(Becktell
et al
., 2005b)
.
Transplants
produced in one region, transported to and subsequently planted in another can
certainly be a source of the pathogen. In the highland tropics where potatoes are
