Abstract The adoption of growth regulators can be an alternative method to modulate the quality of the propagation material and obtain reproductive precocity. The objective was to evaluate if a gibberellin biosynthesis inhibitor affects the morphophysiological, biochemical and anatomical parameters of sour passion fruit seedlings and if such alterations affect the reproductive period. Two trials were conducted. In trial I, 40 days after emergence, the seedlings were immersed up to the substrate level in paclobutrazol (PBZ) solutions at concentrations of: 0, 40, 80, 120 and 160 mg L-1. At 45 days after the application of PBZ - DAA, the morphophysiology, biochemistry and anatomy were evaluated. Trail II was conducted in pots, using seedlings from trail I with 45 DAA of PBZ. At 200 days after transplanting, accumulation of shoots and roots fresh and dry mass (g), flowering speed index, total number of reproductive organs and SPAD index were evaluated. In seedlings, restriction of shoot growth induced by PBZ was associated with root increment, seedling quality, photosynthetic pigments and optimization of gas exchange. A shorter period of transition from the juvenile – vegetative phase to reproductive is observed when the seedlings were submitted to PBZ concentrations.

Resumo A adoção de reguladores de crescimento pode ser um método alternativo para modular a qualidade do material de propagação e obter precocidade reprodutiva. Objetivouse avaliar se os parâmetros morfofisiológicos, bioquímicos e anatômicos de mudas de maracujazeiro azedo são afetados por um inibidor da biossíntese de giberelina e, se tais alterações afetam o período reprodutivo. Foram conduzidos dois ensaios. No ensaio I, aos 40 dias após a emergência, as mudas foram imersas até o nível do substrato em soluções de paclobutrazol (PBZ) nas concentrações de: 0, 40, 80, 120 e 160 mg L-1. Aos 45 dias após a aplicação de PBZ – DAA, avaliou-se a morfofisiologia, bioquímica e anatomia. O ensaio II foi conduzido em vasos, utilizando mudas do ensaio I com 45 DAA de PBZ. Aos 200 dias após o transplantio, foram avaliados acúmulo de massas fresca e seca da parte aérea e raiz (g), índice de velocidade de florescimento, número total de órgãos reprodutivos e índice SPAD. Em mudas, a restrição do crescimento da parte aérea induzida pelo PBZ foi associada à incremento radicular, qualidade de mudas, pigmentos fotossintéticos e otimização das trocas gasosas. Menor período de transição da fase juvenil – vegetativa para reprodutiva é observado quando as mudas foram submetidas a concentrações a PBZ.

ABSTRACT The aim of this study was to verify if a growth reduction of yellow passion fruit seedlings’ growth morphophysiology and quality could be changed by paclobutrazol applied through seedling immersion. The experiment was conducted in a greenhouse, with seedlings grown in polyethylene tubes (290 cm3), with substrate. At 40 days after sowing, the seedlings were immersed in an aqueous solution of paclobutrazol at concentrations of 0, 50, 100, 150, and 200 mg L-1. The experiment was conducted in a randomized block design, with five treatments (paclobutrazol concentrations) and four replicates. At 15 and 30 days after treatment, growth characteristics were evaluated. At the end of the assay, destructive evaluations related to mass determination, total leaf area, and seedling quality index were performed. Paclobutrazol treatment induced restrictions in seedling growth, except for fresh and dry mass of root and total fresh mass. Based on these characteristics, the increase in values induced by paclobutrazol was verified. The seedling quality, defined by the major value of the Dickson quality index and a smaller robustness index, was higher when submitted to paclobutrazol treatment.

RESUMO A restrição do vigor vegetativo de mudas pode ser uma estratégia para otimização da modulação frente à estresses bióticos e abióticos após o transplantio. O objetivo desse estudo foi verificar se os parâmetros morfológicos de mudas de maracujazeiro amarelo (Passiflora edulis) são afetados pela restrição do crescimento com aplicação de inibidor da biossíntese de giberelina. O ensaio foi realizado em casa de vegetação a partir de mudas cultivadas em tubetes de polietileno com capacidade de 290 cm3. Aos 40 dias após a emergência, as bandejas com as respectivas mudas foram imersas em soluções de paclobutrazol (PBZ) com concentrações de 0, 40, 80, 120 e 160 mg L-1 de ingrediente ativo, até a saturação do substrato. Foi utilizado o delineamento experimental em blocos casualizados, com cinco tratamentos (concentrações de PBZ) e quatro repetições. Aos 15, 30 e 45 dias após a aplicação do PBZ (DAA), foi mensurado o diâmetro basal; aos 45 dias foram avaliados o diâmetro do caule, área foliar individual, área foliar específica, diâmetro e volume das raízes, conteúdo de lignina parte aérea e a anatomia da folha, caule e raiz. As alterações anatômicas induzidas pela restrição de crescimento por triazol condicionaram modificações na estrutura morfológica e estimulou a biossíntese de compostos secundários em mudas de maracujazeiro amarelo.

ABSTRACT Inhibiting seedling vegetative growth may be a strategy for improving modulation against biotic and abiotic stresses after transplanting. The objective of this study was to evaluate morphological responses of yellow passion fruit (Passiflora edulis) seedlings to growth inhibition resulted from the application of an inhibitor of gibberellin biosynthesis. The experiment was carried out in a greenhouse using seedlings grown in 290 cm3 polyethylene tubes. At 40 days after emergence, trays containing the seedlings were immersed in solutions at concentrations of 0, 40, 80, 120 and 160 mg (Paclobutrazol) PBZ L-1 up to substrate saturation. These five treatments were laid out in a randomized block design with four replicates. At 15, 30 and 45 days after PBZ application (DAA), basal stem diameter was measured; at 45 DAA, stem diameter, individual leaf area, specific leaf area, root diameter and root volume were measured, lignin content and the anatomy of leaves, stems, and roots were analyzed. Triazole-induced anatomical alterations in stems, leaves and roots cause morphological traits and intensify the specific reagent staining of phenolic compounds and lignin in yellow passion fruit (Passiflora edulis) seedlings.