Agriculture Reference
In-Depth Information
Fig. 7.13.
The important factors, processes and interactions within an onion store
that can influence bulb sprouting and disease.
and cooled by contact with colder bulbs, the temperature may decline below the
dew point of the incoming air and water may condense on the bulbs.
If the base plate of bulbs is wetted, rooting will occur rapidly and this will
accelerate sprouting which, as we have seen, will favour increased water loss
from bulbs. Therefore, a loss of control, leading to excessive humidity and wetness
within the store, can trigger a vicious circle of positive feedback events leading to
rapid deterioration of the stored bulbs. High humidity, particularly if combined
with high temperatures, favours the spread of pathogens within the store.
In warm storage conditions the rate of deterioration due to pathogens -
e.g. black mould,
Aspergillus niger
- usually outweighs the importance of
sprouting (Currah and Proctor, 1990). The breakdown of bulbs by rotting will,
in itself, probably increase the permeability of the skins to water vapour, and
thus increase the rate of transfer of water from bulbs to the store atmosphere.
So, various chains of causation are possible, with physical store conditions
