Seed germination and in vitro propagation of three threatened endemic South African Aloe species

Abstract

Aloe modesta Reynolds (endangered), A. peglerae Schönland (critically endangered), and A. reitzii Reynolds (vulnerable) are endemic South African Aloe species valued for their horticultural and/or medicinal value, appearing on the Red List of South African Plants. Propagation is an important step in the cultivation of these species for their conservation. This study examined the effect of temperature (15, 20, 25, and 30°C) and photoperiod (constant dark, 16 h light, and constant light) on seed germination of these three species. The in vitro propagation of A. reitzii was also investigated by examining the effect of different cytokinins [kinetin, 6-benzyladenine (BA), meta-topolin (mT), and meta-topolin riboside (mTR)] on shoot multiplication. Germination percentage and mean germination rate of A. modesta were significantly inhibited when the seeds were incubated at a low temperature (15°C) in comparison to incubation at other temperatures (20 – 30°C). An increase in temperature significantly decreased mean germination time (MGT), as well as increased seedling chlorophyll and carotenoid contents in A. peglerae and A. reitzii. A reduction in germination speed, evident in increased MGT was observed in the three species when seeds were incubated under constant light and 16 h light as compared to constant dark. Medium with 5.0 µM meta-topolin produced the highest A. reitzii shoot proliferation (16 shoots) per shoot-tip explant after eight weeks of culture. This shoot multiplication rate translates to a potential production of 1 118 481 shoots per shoot-tip explant per annum, based on a geometric progression with six possible multiplication cycles per annum. Aloe reitzii shoots produced from BA and kinetin treatments had a high flavonoid content whereas all mT and mTR treatments gave reduced flavonoid content. Seed and/or in vitro propagation protocols of these threatened endemic Aloe species established in this study can be employed in the biodiversity conservation of Aloe species for their sustainable use.