The effects of applications of gibberellins to the parent plant, harvest date and harvest method on seed yield and mean seed weight of crisp lettuce

SUMMARY The effects on bolting and flowering of treating crisphead lettuce plants cv. Pennlake with gibberellins 4 and 7 (GA4+7) at the rosette stage were compared with cutting open the mature heads in three experiments (1981–83). In addition, to the effects of GA4+7 treatment, those of two methods of harvesting (‘shake’ and ‘windrow’) and time of harvest on seed production were examined. Compared with plants induced to produce flowering shoots by cutting the mature heads, GA4+7‐‐treatment increased the proportion of plants surviving to produce flowers. It gave more synchronous flowering and it increased seed yields by between 11 and 278% for the ‘shake’ method and by between 33 and 125% for the ‘windrow’ method. There was no consistent effect of method of harvest on seed yield. For windrow harvests, maximum yields were obtained from plants cut between 30 and 45 days after the appearance of the first flowers. Mean seed weight varied between 1. 25 and 1. 62 mg depending on the year of production and harvest date. In 1982 and 1983, the differences in seed weight within any one year were positively associated with differences in mean temperature during the period of seed growth but temperature could not account for the differences in mean seed weight between years.