Abstract
Plant propagation via in vitro culture is a very laborious and time-consuming process. The growth cycle of some of the crop species is slow even in the field and the consistent commercial production is hard to maintain. Enhanced methods of reduced cost, materials and labor significantly impact the research and commercial production of field crops. In our studies, stem-segment explants of Brassica species were found to generate adventitious roots (AR) in aeroponic systems in less than a week. As such, the efficiency of rooting from stem explants of six cultivar varieties of Brassica spp was tested without using any plant hormones. New roots and shoots were developed from Brassica alboglabra (Kai Lan), B. oleracea var. acephala (purple kale), B. rapa L. ssp. chinensis L (Pai Tsai, Nai Bai C, and Nai Bai T) explants after 3 to 5 days of growing under 20 ± 2°C cool root zone temperature (C-RZT) and 4 to 7 days in 30 ± 2°C ambient root zone temperature (A-RZT). At the base of cut end, anticlinal and periclinal divisions of the cambial cells resulted in secondary xylem toward pith and secondary phloem toward cortex. The continuing mitotic activity of phloem parenchyma cells led to a ring of conspicuous white callus. Root initials formed from the callus which in turn developed into ARs. However, B. rapa var. nipposinica (Mizuna) explants were only able to root in C-RZT. All rooted explants were able to develop into whole plants, with higher biomass obtained from plants that grown in C-RZT. Moreover, explants from both RZTs produced higher biomass than plants grown from seeds (control plants). Rooting efficiency was affected by RZTs and explant cuttings of donor plants. Photosynthetic CO2 assimilation rate (Asat) and stomatal conductance (gssat) were significantly differentiated between plants derived from seeds and explants at both RZTs. All plants in A-RZT had highest transpiration rates.
Highlights
Green leafy vegetables, known for their high nutritional content, are consumed by humans for good health and dietary benefits
As previous studies (Weathers and Giles, 1988; Zobel, 1989; Luo et al, 2012) have suggested that aeroponics is the optimum system for growing intact plants or excised roots and tissue cultures, this research explores the possibility of vegetative propagation of temperate Brassica species (Asian greens) in an aeroponic system within a tropical greenhouse, with the manipulation of only RZTs He et al (2013)
The adventitious roots (AR) formation is of great importance for vegetative propagation, but difficult to achieve in many crop species
Summary
Known for their high nutritional content, are consumed by humans for good health and dietary benefits. A quick alternative in the commercial field would be to use vegetative propagation via stem cuttings This minimizes seed usage while allowing for new plants to be developed within a week shorter time interval. As previous studies (Weathers and Giles, 1988; Zobel, 1989; Luo et al, 2012) have suggested that aeroponics is the optimum system for growing intact plants or excised roots and tissue cultures, this research explores the possibility of vegetative propagation of temperate Brassica species (Asian greens) in an aeroponic system within a tropical greenhouse, with the manipulation of only RZTs He et al (2013). This study describes a rapid and efficient rooting and whole plant regeneration methodology for six Brassica species This method of root and shoot development using aeroponics can be applicable to all commercial Brassica cultivars. The findings of this study could be applied in the mass propagation of vegetable crops, shortening the growth cycle as seed germination and seedling development periods can be eliminated
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