Abstract
Although the blue dye indigo has been chemically synthesized for over a century, there is an increasing interest in the indigo plant (Polygonum tinctorium) as a source of natural dyes and medicines. To maintain a stable supply of P. tinctorium throughout the year, we examined the effect of two harvesting methods on the leaf yield of this plant under a closed-cultivation system. With method 8c-M, all shoot branches >8 cm of the stem bottom were harvested and under method 2b-M, all branches, but two, were harvested at the stem bottom. Both methods enabled sustainable leaf yields from the same plants over 1 year. The total weight of shoot branches harvested by 8c-M was 1.86–3.11 times higher that of shoot branches harvested by 2b-M. Harvesting by 8c-M resulted in shoot branch weights lower than those from plants harvested with the 2b-M. Leaf/shoot ratio was increased in plants harvested by 8c-M. The content of indican, the precursor of indigo, in leaves was not significantly different between the two harvesting methods. Our data may provide a new continuous cultivation method of leaf crops all over years in controlled-cultivation systems.
Highlights
To maintain a stable supply of P. tinctorium throughout the year, we examined the effect of two harvesting methods on the leaf yield of this plant under a closed-cultivation system
Indigo is a blue dye that was being extracted from the indigo plant (Polygonum tinctorium) until the end of the 19th century, when chemically synthetized indigo almost completely replaced natural indigo (Bechtold et al, 2002)
Indigo is used in traditional Chinese medicines to treat systemic psoriasis and leukemia (Koo & Arain, 1998; Xiao et al, 2002)
Summary
Indigo is a blue dye that was being extracted from the indigo plant (Polygonum tinctorium) until the end of the 19th century, when chemically synthetized indigo almost completely replaced natural indigo (Bechtold et al, 2002). New cultivation methods for the continuous production of P. tinctorium without flowering might be required. The production of indican and related compounds in vitro has been attempted in cell and root-hair cultures of P. tinctorium (Chung et al 1996; Kim et al 1996; Young-Am et al, 2000), these approaches yield indican concentrations that are much lower than those present in fresh leaves (Minami et al, 2000; Campeol et al, 2006). We designed and tested two harvesting methods for the continuous leaf production of this annual plants in a closed-cultivation system
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