An Influence of Water Stress at Different Growth Stages on Yield and Quality of Lettuce Seed1

The effects of soil moisture deficit on yield and quality of head lettuce seed ( Lactuca sativa L.) were studied. Three moisture levels (−0.3, −0.8 and −5.0 bars) were imposed upon lettuce plants continuously or in various combinations during vegetative and reproductive growth. Highest seed yields were obtained from treatments of intermediate water deficit during vegetative growth. Severe stress significantly reduced seed yields when introduced during either vegetative or reproductive growth. These treatments resulted in the lowest average number of seeds/seed head and seed heads/plant. Average seed weights were highest from plants exposed to severe stress for extended periods. Lowest average seed weights were produced on plants grown in adequate moisture treatments. Seed length, width, thickness and volume correlated with seed weight in response to soil moisture deficits. Germination was high in all treatments (97-100%). The lowest percentage abnormal seedlings observed during germination were obtained from seed developed on plants in severe and intermediate water deficit treatments. Seeds from these same treatments also produced the most vigorous seedlings, based on radicle length. Moisture levels conducive to highest seed yield generally produced lower quality seeds. Intermediate water deficits during vegetative and reproductive growth of lettuce plants appear to produce highest seed yields together with adequate seed quality.