(207) Sensitivity of Two Lettuce Genotypes to Abscisic Acid during Germination

Abstract

In many lettuce (Lactuca sativa L.) cultivars, temperatures above 30 °C can inhibit germination completely. Lettuce seeds imbibed at supraoptimal temperature for 72 hours or more will not germinate even when the temperature is returned to the optimal range. Sung et al. (1998) reported that thermosensitive `Dark Green Boston' and thermotolerant `Everglades' responded to temperature at seed maturation by being able to show greatly enhanced germination at 36 °C when seeds were matured at 30/20 °C. Abscisic acid (ABA) plays an important role relative to both dormancy and germination of many seeds and may contribute to lettuce seed thermodormancy. Therefore, sensitivity of `Everglades' and `Dark Green Boston' to ABA of seeds maturated at 30/20 °C and 20/10 °C in light and dark was determined. Seeds were germinated at 20 °C and 36 °C in light and dark. All seeds of `Dark Green Boston'and `Everglades' matured at 30/20 °C and 20/10 °C germinated similarly regardless of maturation temperature and light/dark condition at 20 °C. At 36 °C in dark, both genotypes matured at 30/20 °C germinated more than those matured at 20/10 °C. `Dark Green Boston' genotypes were more sensitive to ABA (0.5, 1, 10, 50, 100 μM) during germination at 36°C in dark. When ABA was added, seeds matured at 30/20 °C germinated better than those matured at 20/10 °C, regardless of genotype. At 36 °C in light, 40% of both genotypes were inhibited at 0.5 μM ABA. At 36 °C in dark, germination of all seeds but `Everglades' matured at 30/20 °C were completely inhibited at all ABA concentrations. Thus, seed maturation temperature has an influence on lettuce seed germination at high temperature and sensitivity to ABA.