Agriculture Reference
In-Depth Information
based on inoculum dynamics (Backhouse, 2003) have so far failed because of
insufficient data to develop the relationship for the production of new sclerotia based
on the size of infected bulbs. The maximum increase in numbers of sclerotia in the
soil occurs at the end of the onion growing season and this will affect the following
crop - but only if it is an onion crop.
Figure 19.5. Incidence of white rot in overwintered salad onions, Southfleet, UK (1976/1977)
(redrawn from unpublished data of A. R. Entwistle). Sampling dates were 5 April, 3 May,
2 June and 27 June, 1977. (°C) = Mean monthly soil temperatures at 100 mm depth.
In this respect the epidemiology of the white rot fungus is unlike that of an
airborne pathogen where inoculum increase and disease spread, within and between
like crops, can occur throughout the growing season.
Investigations of the epidemiology of this soilborne disease raise the question of
how the soil environment might be altered to the disadvantage of the pathogen, for
example, its sclerotia. Physical, chemical and biological approaches have been made
(Clarkson
et al.,
2004). The use of fungal antagonists or biocontrol agents (Adams
and Ayres, 1981; Ahmed and Tribe, 1977; Coley-Smith, 1987; Clarkson
et al.,
2002;
Kay and Stewart, 1994) has met with varying degrees of success dependent on the
limitations of the experimental systems used. The interaction between biocontrol
agent and pathogen is complex (Metcalfe and Wilson, 2001) and to model it, strict
control of the environment and of the inoculum (pathogen and biocontrol agent) is
necessary.
