Promoting root induction and growth of in vitro macadamia (<Emphasis Type="Italic">Macadamia tetraphylla</Emphasis> L. ‘Keaau’) plantlets using CO<Subscript>2</Subscript>-enriched photoautotrophic conditions

In this study, a rooting protocol was developed for macadamia plantlets with healthy roots and enhanced growth performance, along with enhanced photosynthetic capability. In vitro-grown shoots rooted in vented vessels containing vermiculite as the supporting material exhibited 100% frequency of root induction, whereas when shoots were grown in non-vented vessels containing a solidified Murashige and Skoog (MS) medium, the frequency of root induction was less than 30%. The formation of root with callus, hyperhydricity, and leaf necrosis was observed in this photomixotrophic closed system. The modification of the vented photoautotrophic system with different concentrations of CO₂ and sucrose were investigated using vermiculite as the supporter. The number of roots, root length, root surface area, fresh weight, and dry weight were significantly higher in plantlets grown in CO₂-enriched (1,000 μmol CO₂ mol⁻¹) photoautotrophic conditions. The water content in both root and shoot tissues of plantlets cultured under photoautotrophic conditions was maximized. In addition, shoot and leaf performances were enhanced in plantlets cultured under CO₂-enriched photoautotrophic conditions. The supplementation of sucrose (29–88 mM) to culture media in both ambient and elevated CO₂ conditions affected a reduction in the shoot and root performance of in vitro plantlets. Chlorophyll a, chlorophyll b, and total carotenoids in the leaf tissues of plantlets acclimatized in CO₂-enriched photoautotrophic conditions were enriched, leading to increasing photosynthetic abilities, including chlorophyll fluorescence and net photosynthetic rate. From this investigation, a root induction protocol was established and the production of healthy macadamia plantlets was successfully implemented using CO₂-enriched photoautotrophic conditions.     

An efficient procedure for embryogenic callus induction and double haploid plant regeneration through anther culture of Thai aromatic rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L. subsp. <Emphasis Type="Italic">indica</Emphasis>)

Anther culture is a biotechnology technique that can be used for the production of pure lines. The aims of this investigation were to induce embryogenic callus from major and minor culms of Thai aromatic rice cultivars and to subsequently regenerate double-haploid green plantlets by the application of exogenous polyamines. Embryogenic callus derived from anther culture was successfully induced in varieties KDML105, Homjan (HJ), and Pathumthani 1 (PT1). Production of embryogenic callus from anthers collected from the major culms was greater than those collected from the minor culms, especially in cultivar HJ. Plantlet regeneration in the three rice cultivars was observed from embryogenic callus and was highest, at 12.1%, from variety HJ treated with 0.5 mM spermidine. Plantlet regeneration from anther-derived embryogenic callus was dependent on the plant genotype, the types of exogenous polyamines, and the interactions of these factors. The percentage of haploid plantlets regenerated in PT1, KDML105, and HJ were 68.1%, 70.7%, and 78.5%, respectively. Only haploid plantlets were treated with colchicine for double-haploid production. This investigation has increased the knowledge of both embryogenic callus induction and plantlet regeneration in aromatic rice and has lead to the development of a pure, double-haploid line for the use in rice breeding programs in Thailand.