Ploidy stability of somatic embryo-derived plants in two ecological keystone sedge species (Lepidosperma laterale and L. concavum, Cyperaceae)

Abstract

We report on the development of a somatic embryogenesis system for Lepidosperma concavum R.Br. and L. laterale R.Br. and the determination of ploidy stability of plants derived from somatic embryos. These keystone Lepidosperma species cannot currently be returned to restoration sites because of propagation difficulties (i.e. seed dormancy, low seed fill and recalcitrance to vegetative propagation). Three explant types (in vitro-germinated seedlings, immature seed and immature inflorescences) were used for the assessment of callus production potential. Embryogenic callus was induced and multiplied on 1/2MS medium with 2,4-D either alone, or in combination with zeatin. Over 90% of seedling explants of L. laterale produced regenerative calli after 6 weeks and 53% of seedling explants of L. concavum produced calli after 16 weeks on media containing 2,4-D and zeatin. Inflorescence material appeared to be least responsive. High rates of conversion to plants were achieved on medium containing activated charcoal, followed by thidiazuron medium. Acclimatisation success of plants ranged from 86% to 95%. Acclimatised plants grew vigorously under standard nursery conditions. The DNA ploidy level of 486 somatic embryogenesis-derived plantlets was analysed by flow cytometry. Only one plant (=0.2% of all plantlets tested) was found mixoploid. All other plants showed a stable ploidy level and stable C-values within the species. There was a small but significant C-value difference between the two Lepidosperma species. Five variegated plants (=0.3%) were observed among a total of ~1600 plants acclimatised. The application of tissue culture techniques such as somatic embryogenesis brings large-scale production of Lepidosperma plants for revegetation and horticultural purposes closer to commercial feasibility.