Abstract
High solar radiation in tropical regions can affect the development, physiology, and biochemistry of plants. Our aim with this research was to evaluate the biochemical responses and production of iceberg lettuce cultivars under environments with different shadings. An experiment under field conditions was installed in a 4 × 4 factorial scheme. Four cultivars of iceberg lettuce (Great Lakes, Winslow, Delicia, and Balsamo) and four environments with different shadings (three types of shading screens: red, ChromatiNet®, and black; and treatment under the full sun) were evaluated. Forty-five days after transplanting, the plants were harvested, and the biomass was weighed to obtain the fresh consumable part (FCP) and the biochemical parameters: total soluble sugar (TSS), reducing sugar (RS), and the activity of SOD, CAT, and POD. We found that shading modulates biochemical and productive responses of iceberg lettuce, and the main microclimatic factor related to these responses was solar radiation. We observed a negative correlation between RS and FCP. The solar radiation between 16 and 18 MJ·m−2·day−1, observed in the environments with a black screen and ChromatiNet®, promoted the highest activity of the SOD enzyme and average levels of TSS and RS, providing higher FCP of the cultivars Delícia and Balsamo in high temperatures period.
Highlights
Iceberg lettuce production is directly influenced by temperature since it is a species from temperate regions
The shading screens that we used in this research caused microclimate changes in the environments, mainly in solar radiation
This factor was predominant in the modulation of the iceberg lettuce cultivars biochemical and productive responses
Summary
Iceberg lettuce production is directly influenced by temperature since it is a species from temperate regions. High temperatures stimulate its bolting, which is accelerated as this climatic factor increases [1]. This is why the production of this vegetable in high-temperature regions, mainly semi-arid, is still not very expressive. In these regions, the weather conditions are characterized by high solar radiation (average 21.6 MJ·m−2 ·day−1 ), high temperatures (average 26 ◦ C), low relative humidity, and reduced rainfall (average 700 mm per year) [2]. A recent study shows that is the temperature a limiting factor for head formation in this type of lettuce, but mainly solar radiation, with a range of 17.6 to
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