Studies of the cause of blindness in brassicas

The effects of temperature, duration of temperature, growth stage, rate of cooling, daylength during raising, shading, seed quality, moisture stress and sowing date on blindness in calabrese cv. Marathon were investigated in eight experiments over three years. Of these only batches of plants raised throughout the winter produced appreciable levels of blindness. The incidence of the disorder varied from zero to 80% in plants which received no specific supplementary cold treatment. High levels of blindness were strongly associated with low solar radiation in the period just before plants went blind and were less well associated with low temperatures in the same period. However, it is not possible to separate effects of light and temperature in these data. There are suggestions that competition between leaves for limited assimilate may be responsible for switching off leaf production.