Influence of post‐flowering temperature on seed development, and subsequent performance of crisp lettuce

Abstract

Crisp lettuce plants cv. Saladin were grown from the time they started flowering, at 20/10 "C (16 h day, 8 h night), 25/15 "C and 30/20 "C in glasshouses on two occasions in 1985.Yields of seed increased from, on average, 15 g to 27 g and then fell to 20 g per plant with progressive increases in temperature. The number of mature florets per plant increased with temperature but the number of seeds per mature floret was lower at 20/10 "C and 30/20 "C than at 25/15 "C. An increase in temperature reduced mean seed weight by up to 45%, seed volume by 15%, cell numerical volume density (N,) by 27% and the number of cells per seed by 39%. Percentage seed germination reached a maximum early in seed development at the stage when the pappus appeared through the involucral bracts. Differences in percentage germination and vigour of seeds (slope test) from different temperatures were accounted for largely by the effects on mean seed weight. However, when germinated at 30 "C seeds produced at 30/20 "C germinated more readily than those produced at 25/15 "C or 20/10 "C. Seed vigour gradually increased with an increase in the length of storage after harvest, reaching a maximum after 260 days. In general, seeds produced at 25/15 "C exhibited a greater variation in numbers of seeds per floret, N,, seed weight, times of seedling emergence, seedling and mature head weight than seeds produced at lower or higher temperatures.

Environmental and genetic effects on tomato seed metabolic balance and its association with germination vigor

“…It has been shown in numerous studies that environmental conditions, such as temperature, light [56] and possibly others, during lettuce seed maturation have an effect on seed germination and plant growth. Lettuce seeds that developed at higher temperatures had reduced weight but germinated at higher percentages [57], specifically under higher than optimal germination temperatures [58, 59]. In Arabidopsis, temperature during development was found to have a strong influence on germination [33, 34], and higher light intensity, photoperiod, nitrate and phosphate also increased germination under stress conditions [32].…”

Expression of9-cis-EPOXYCAROTENOID DIOXYGENASE4Is Essential for Thermoinhibition of Lettuce Seed Germination but Not for Seed Development or Stress Tolerance

“…Lettuce seeds that mature at lower temperatures or in far-red light exhibit lower maximum germination temperatures than those that develop at warmer temperatures or in red light (Gray et al, 1988;Contreras et al, 2009). Similarly, Arabidopsis seeds that develop and mature at lower temperature exhibit higher dormancy, while higher temperature during seed development and maturation results in reduced dormancy (Donohue et al, 2005;Chiang et al, 2009).…”

Genetic Variation for Thermotolerance in Lettuce Seed Germination Is Associated with Temperature-Sensitive Regulation of ETHYLENE RESPONSE FACTOR1 (ERF1)

“…Seeds shed in the summer will not germinate if unseasonable rain falls while temperatures are still high; when rainfall coincides with cooler temperatures in the autumn, the seeds will germinate and the plants overwinter as rosettes followed by flowering the following spring. The upper temperature limit for lettuce seed germination is genotype dependent and influenced by the seed production environment (Gray et al, 1988;Kozarewa et al, 2006). Seeds of most lettuce cultivars, including cv Salinas (Sal), are thermosensitive and fail to germinate when imbibed at 29°C or greater, while seeds of some thermotolerant genotypes can germinate above 90% at 36°C (Thompson et al, 1979).…”