Aspectos do crescimento e desenvolvimento de plântulas de Cattleya walkeriana Gardner visando sua aclimatação ex vitro para reintrodução e conservação

Abstract

In vitro propagation of plant species is a biotechnological tool widely used in the conservation of rare, endangered, or difficult-to-propagate species, such as Orchidaceae. Orchids produce small seeds with limited reserves, often depending on mycorrhizal fungi for germination and initial establishment. Although in vitro cultivation enables overcoming these limitations, plantlets develop under highly controlled conditions, including high humidity, low irradiance, supplementation with sugars and growth regulators, and restricted gas exchange, resulting in individuals poorly adapted to external environments. Therefore, the acclimatization phase represents one of the main bottlenecks in propagation. Many orchids are epiphytic and, in nature, establish themselves on host trees, whose bark physical and structural characteristics may influence germination and the early development of new plantlets. In addition to the substrate, light availability and dependence on atmospheric water sources are determining factors for epiphytes. Cattleya walkeriana Gardner is an epiphytic orchid endemic to Brazil, threatened with extinction and associated with environments characterized by strong seasonal water availability and high light variability. In this context, this study aimed to understand how abiotic factors influence the survival and initial performance of C. walkeriana plantlets during ex vitro acclimatization. In the first chapter, the effects of different substrates on the morphophysiological performance of micropropagated plantlets were investigated, including commercial substrates and a native-origin substrate, as well as the potential role of foliar water uptake as a compensatory mechanism. In the second chapter, the combined effects of irrigation regimes and irradiance on growth, water status, photochemical efficiency, chlorophyll indices, photoprotective mechanisms, and crassulacean acid metabolism (CAM) were evaluated