Growth and physiology of ornamental sunflower under salinity in function of paclobutrazol application methods

Rafaela F B Guimarães,Jailma R De Andrade,Ronaldo Do Nascimento,Sebastião De O Maia Júnior,Robson F De Lima,Allesson R De Souza

doi:10.1590/1807-1929/agriambi.v25n12p853-861

Abstract

ABSTRACT The ornamental sunflower has great importance in the floriculture sector due to the color and vitality of its flowers. However, the production and quality of flowers decrease under salt stress, which can be mitigated with paclobutrazol application. The objective of the present study was to evaluate the effects of different application methods of paclobutrazol in ornamental sunflower ‘Sol Noturno’ irrigated with brackish waters. The experimental design was randomized blocks arranged in a 5 × 3 factorial scheme, corresponding to five electrical conductivities of irrigation water - ECw (0.4; 1.9; 3.4; 4.9, and 6.4 dS m-1) and three paclobutrazol application methods (foliar application, via soil and a control treatment - without paclobutrazol), with four replicates. The increase in salinity of irrigation water reduced gas exchange, photosystem II photochemical efficiency, SPAD index, plant height, and chapter diameter. The paclobutrazol application via soil or foliar increased stomatal conductance and transpiration by 21.09 and 17.80%, respectively, in comparison to plants without application, whereas photosynthesis and instantaneous carboxylation efficiency increased by 28.33 and 31.18% via soil and 14.40 and 16.12% via foliar, respectively. The paclobutrazol application, mainly via soil, favored ‘Sol Noturno’ sunflower plants under salt stress, increasing chlorophyll SPAD index and external chapter diameter, and keeping the number of the petals.

Highlights

The ornamental sunflower is a highly valued plant as a flower for cultivation in vases, mainly due to the different colors and exuberance of its inflorescence (Brito et al, 2016)
While for photosynthesis, application via soil promoted higher A followed by the foliar application, corresponding to 28.33 and 14.40%, respectively higher than without PBZ (Figure 1E)
These effects on the gas exchange may be associated with the improvement promoted by the application of PBZ over stomatal density on both the adaxial and abaxial surfaces of leaves of plants under salt stress (Waqas et al, 2017), which favors stomatal conductance, transpiration, and photosynthesis, as observed in the sunflower plants

Summary

Introduction

The ornamental sunflower is a highly valued plant as a flower for cultivation in vases, mainly due to the different colors and exuberance of its inflorescence (Brito et al, 2016). The plant has a large size, difficult for the production and commercialization of this species for ornamental purposes, considering that small architectural plants are sought for cultivation in vases with a mean height of 35 cm (Wanderley et al, 2014). The first is characterized by reduced growth independent of ions, which occurs within minutes or days, cause stomatal closure and inhibition of cell expansion, mainly the aerial part. The second phase occurs over days or even weeks and relates to increased levels of cytotoxic ions, which delay metabolic processes, cause premature senescence, and, cell death (Isayenkov & Maathuis, 2019; Lima et al, 2019; Alves et al, 2020). Cultivation alternatives have been used to minimize the deleterious effects of salinity, such as the use of paclobutrazol (Hu et al, 2017; Waqas et al, 2017; Xia et al, 2018)

Objectives

Methods

Results