Condições hídricas e térmicas para o desenvolvimento ex vitro e in vitro de Acmella oleracea (L.) R.K. Jansen (Jambu).

Abstract

Jambu, Acmella oleracea (L.) R.K. Jansen, is a native vegetable from the Amazon with high socioeconomic value for small producers in Pará and other regions of Brazil. In this context, the generation of strategic information is essential to support future genetic breeding programs aimed at developing cultivars adapted to environments with greater climatic adversity. The present study aimed to evaluate the response to thermal and water stress in two jambu varieties (“yellow” and “purple”) under in vitro and ex vitro conditions to guide management strategies and improve the production system. In the water stress experiment, five irrigation levels (40, 70, 100, 130, and 160% of field capacity) were applied in a nursery, evaluating morphological variables (shoot length, root length, number of leaves, number of branches, number of nodes, number of roots, bud opening, and inflorescences) and biomass of leaves, roots, inflorescences, and shoot length. In the thermal stress assay, germination and initial seedling development morphology in vitro were analyzed under temperatures of 25, 33, and 41 °C. A completely randomized design (CRD) was used in both experiments. It was evidenced that water availability and temperature distinctly modulate the phenotypic expression of plants. The purple variety demonstrated high phenotypic plasticity under ideal irrigation conditions (100% and 130% of field capacity). PCA confirmed this trend, associating the variety with greater reproductive investment and leaf area expansion. The yellow variety adopted a conservative morphological strategy, prioritizing physiological stability. Severe water deficit restricted vegetative growth in both varieties and predisposed plants to mite attacks. In in vitro cultivation, 25 °C proved ideal for germination and seedling development, while 33 °C induced significant stress, with etiolation, reduced leaf area, and compromised rhizogenesis. The temperature of 41 °C completely prevented germination. It is concluded that jambu cultivation is highly dependent on proper management of water and thermal conditions, with recommended irrigation levels close to 100–130% of field capacity and 25 °C in in vitro cultivation. In the face of extreme climatic events, the purple variety stood out as the most suitable for intensive cultivation systems due to its greater phenotypic plasticity and productive stability in the face of environmental variations.