Agriculture Reference
In-Depth Information
Fig. 5.13.
Microclimate effects on the development of sporangia by onion downy
mildew,
Peronospora destructor
. (a) The effect of temperature on relative
sporulation rate, derived by combining data from the authors listed in the graph
(from Friedrich
et al
., 2003. Courtesy of the
European Journal of Plant Pathology
).
(b) The effect of relative humidities (range 93-100%) on the relative number of
sporangia produced on onion leaves in two separate experiments (
) after
14 h at 12°C in darkness (from Gilles
et al
., 2004. Courtesy of
Plant Disease
).
and
The means by which leaf pathogens survive and spread in the absence of
growing crops vary, and detailed knowledge of the biology of each pathogen is
needed. Several can survive as long-lived, dormant structures in the soil - for
example, onion smut chlamydospores, leek white tip oospores and the sclerotia of
Botrytis
leaf blights (see Table 5.5). Knowledge of the conditions for survival and
germination of these dormant stages is important for disease management. For
example,
Botrytis squamosa
forms dark-coloured, irregular, roughly ellipsoidal
sclerotia 3-10 mm long on decaying onion waste. In a study on organic soil in
