Effects of cultivar and storage duration on emergence and yield of fluid-drilled pregerminated lettuce seed

Abstract

Storage (2°C) duration (0, 3, 6 and 9 days) of pre-germinated lettuce ( Lactuca sativa L., cultivar ‘Ithaca’) seed had no effect on time to 50% emergence ( T-50), final percentage emergence, head size or yield. Earlier work indicated that storing pre-germinated seed for as little as 3 days delayed and reduced the uniformity of emergence. Discrepancies between studies may simply reflect cultivar (genetic) -related differences in sensitivity to chilling temperatures. A controlled-environment study was thus conducted to investigate the effects of cold-storage duration on growth response of pre-germinated seed of different lettuce cultivars. Radicles of pre-germinated seeds of ‘Ithaca’, ‘Green Lake’ and ‘Montello’ continued to elongate during a 12-day storage interval at 2°C. Elongation rate of radicles from ‘Green Lake’ was 42% higher compared to those from ‘Ithaca’ and ‘Montello’. Following storage, pre-germinated seed from all three cultivars emerged earlier and final percentage emergence was higher compared to non-germinated seed (when grown under a 12 7° C , day/night regime). Moreover, within a cultivar, storage duration did not affect T-50 or final percentage emergence. However, T-50 of pregerminated ‘Montello’ seed was delayed compared to ‘Green Lake’ and ‘Ithaca’. Percentage emergence of seedlings from dry seed was 42, 27 and 12% for ‘Ithaca’, ‘Green Lake’ and ‘Montello’, respectively. Percentage emergence of seedlings from pre-germinated ‘Montello’ seed was more varialbe, ranging from 23 to 67%, compared to 83–100% from the other cultivars. These results clearly demonstrate a genetic basis for resistance to cold in iceberg-type lettuce. Compared to ‘Montello’, ‘Green Lake’ and ‘Ithaca’ would be the preferable cultivars when planting into colder soils. Furthermore, seeds of ‘Ithaca’ and ‘Green Lake’ can be safely stored for up to 12 days at 2°C with no apparent decrease in time to emergence or final percentage emergence.