The production of lettuce, a cool-season leafy vegetable, in high tunnels the year around is a challenge for growers in subtropical regions. The aims of this research done by HortScience were to characterize the growth of locally grown lettuce cultivars, develop a new high-yielding cultivar by crossing romaine-type lettuce ‘Jhih Li Wo’ and Batavia type lettuce ‘Fu San’, and determine the relationships between climatic variables, temperature, and daylength, and days to harvest for maximum marketable yield (DMMY) in individual cultivars in high tunnels. 

Nine cultivars were grown in high tunnels in the spring and winter of 2008 and summer of 2009 to evaluate growth and maximum marketable yield (MMY), the latter being defined as the aboveground fresh weight of 5 ± 0.7 cm of plant stem. Romaine lettuce ‘Jhih Li Wo’ had a higher growth rate during the initiation of plant growth in the spring of 2008.

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