Development of micropropagation system of Zingiber officinale var. rubrum Theilade using different spectrum light-emitting diode (LED) irradiation

Abstract

Halia Bara, a popular variety of Zingiber officinale Theilade in Malaysia valued for medicinal values was successfully micropropagated using light-emitting diodes (LEDs) to produce disease-free planting materials. This study aimed to establish LED-induced organogenesis of Halia Bara and to evaluate their biochemical profile. Basal part explants were irradiated with white (400−700 nm), far-red (720 nm), blue (460 nm), green (530 nm), red (660 nm), and purple (400–660 nm) LEDs to study the impact of light quality on vegetative growth of 12-week-old Halia Bara plantlets and their biochemical profile such as superoxide dismutase antioxidant enzyme, pigmentation in addition to total carbohydrate content and accumulation of proline amino acid. Generally, shade avoidance syndrome driven growth by red (660 nm) LED significantly promoted shoot length to 12.07 cm producing taller plants with long and thin leaves. The number of shoots (5.57) and leaves (20) were significantly higher on plants irradiated with dichromatic purple (400–660 nm) LED. Root formation of Halia Bara was also significantly promoted by monochromatic red (13.29). However, microshoot formation was fairly enhanced by white, far-red (720 nm), and blue (460 nm) LEDs in the range of 5–5.9 while exhibiting the insignificant difference in green, red, and purple irradiance. First-line defense by superoxide dismutase (SOD) enzyme was significantly upregulated on Halia Bara plantlets irradiated by blue (460 nm) (0.186 ± 0.001 SOD U/mg) and green (530 nm) (0.183 ± 0.001 SOD U/mg). In general, pigmentation such as total chlorophyll (0.516 to 0.541 μg/mL) and carotenoid (1917–2109 μg/g) were notably higher in Halia Bara plants irradiated by white, blue, green, and purple LEDs than the red and far-red irradiation meanwhile porphyrin (14.143 ± 1.930 μg/g) was highly produced following green LED irradiation. Light-regulated accumulation of total carbohydrate and proline were the highest in far-red (109.098 ± 3.223 mg/g) and control white (0.101 ± 0.008 mmol/mg) LED irradiated Halia Bara plants, respectively. In short, vegetative traits and biochemical profile of in vitro Halia Bara is differentially influenced by the quality of light. Based on the photomorphogenetic and physiological traits, the present study emphasizes the suitability of adoption of the LED irradiance for the sustainable production of micropropagated Halia Bara plants to be supplied to small-scale farmers.