Sweet basil is a globally important herb crop grown for its unique aroma and flavor (Akbari et al., 2018). Basil is in the mint family (Lamiaceae) and comprises more than 60 species native to tropical regions (Satpute et al., 2019). Field-grown basil is sensitive to cold stress during early spring and fall in temperate regions. Temperatures below 10 °C lead to significant leaf necrosis and brown discoloration, resulting in significant crop loss due to leaf damage (Ribeiro and Simon, 2007). Cold stress also impacts the essential oil composition, affecting taste, flavor, and marketability (Akbari et al., 2018; Senji and Mandoulakani, 2018). The postharvest shelf life of basil is also negatively impacted by cold temperatures if appropriate temperatures are not maintained during shipping and postharvest handling and can result in significant losses (Cantwell and Reid, 1993).
Datnoff et al. (2007) proposed that plant nutrition could be improved by adding Si fertilizer. Although Si is not classified as a plant-essential element, studies have shown that Si can be beneficial to some crops, including barley, cucumber, melon, pumpkin, rice, soybean, strawberry, sugarcane, and wheat (Datnoff et al., 2001; Liang et al., 2015). The availability of Si usually does not affect plants when grown under optimum conditions. However, when plants are under biotic or abiotic stress, Si can strengthen the plant’s defense system, thereby increasing crop productivity (Datnoff, 2014).
The effects of Si on stress resistance are likely to comprise a combination of changes in plant physiology and the accumulation of Si in the epidermis (Datnoff et al., 2001). The major effects of Si deposition include increased rigidity and enhanced protection from insect or fungal penetration (Bakhat et al., 2018; Datnoff et al., 2001; Epstein, 1994, 2009; Liang et al., 2006, 2015). Recent studies have indicated that Si can alter the stress responses at the physiological and molecular levels (Adrees et al., 2015; Debona et al., 2017; Etesami and Jeong, 2018; Gu et al., 2011; Shi et al., 2016). Si has also been shown to be effective against cold stress in some macroaccumulator species (Liu et al., 2009).
Based on their mode of Si uptake (active, passive, exclusive, or combined), plant species can be divided into high-, intermediate-, low-, and nonaccumulators of Si. Si in plants can accumulate to a macronutrient level (>0.1%) or micronutrient level (<0.1%). Many important food crops are Si microaccumulators, including most leafy greens and basil (Datnoff et al., 2001; Li, 2020; Takahashi et al., 1990). Recent research has shown that under certain stress conditions, some microaccumulators such as potato (Vijaya et al., 2016) and tobacco (Zellner et al., 2011, 2019) can absorb and benefit from Si. Because we suspected that Si may be beneficial to some microaccumulator species, the objective of our study was to evaluate the effects of Si amendments on sweet basil grown hydroponically at a constant air temperature of 23 °C.
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