Effects of cold shock on the susceptibility of white lupins to fungal diseases

Experiments in controlled environments tested interactions between freezing soil (a compost-vermiculite mixture) and below-ground infection of white lupins with each of three pathogenic fungi (Botrytis cinerea, Fusarium avenaceum or Pleiochaeta setosa) on plant disease and death. Whilst soil freezing (up to 4 days at -1 degrees C) caused slight necrosis and increased the severity of disease symptoms, incidence of plant death was increased only after inoculation, before freezing, of the lower hypocotyl of the youngest plants (soil frozen at less than 17 days old) with P. setosa. It is concluded that the contribution of below-ground infection by pathogenic fungi to overwinter losses in autumn-sown white lupin crops is exacerbated to a negligible extent by soil freezing, the main primary cause of such losses.