Trinexapac-ethyl effect on eucalyptus primary metabolism under drought stress conditions

Author(s)

Allan Lopes Bacha

• Document type: Doctoral Thesis
• Press: Jaboticabal. 2022-01-17.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências Agrárias e Veterinárias. Jaboticabal
• Defense date: 2021-11-30
• Advisor: Pedro Luis da Costa Aguiar Alves

Abstract

Eucalyptus plants are sensitive to interference imposed by stress factors during their initial growth, with water deficit being the most common among them. Previous studies reported that trinexapac-ethyl can have a positive effect on the growth of eucalyptus seedlings, but there are no studies that have proven the occurrence of hormesis for this chemical compound. Hormesis is a stimulatory effect caused by the application of low doses of a chemical that would be toxic in high amounts. Thus, the objective of this study was to verify the possible hormetic effect of trinexapac-ethyl on Eucalyptus urograndis (Clone 1407) seedlings, under normal conditions and with water deficit, and its effects on the primary metabolism of eucalyptus plants. For this, two experiments were conducted under semi-controlled conditions, in 25 L and 15 L pots, for 90 and 81 days after planting (DAP) of eucalyptus, respectively for experiments 1 and 2. The first experiment consisted of the application of eight doses of trinexapac-ethyl, namely: 0, 15, 30, 60, 90, 120, 150 and 300 g a.i. ha-1, and two water conditions (normal condition and under water deficit, maintained at 40% of field capacity) in eight repetitions. Trinexapac-ethyl was sprayed one day before eucalyptus planting. Evaluations of gas exchange, photosystem II quantum efficiency (Fv/Fm) and total relative chlorophyll content from 9 to 15 DAP were carried out. Every two weeks, eucalyptus height and stem diameter assessments were carried out. At the end of the experimental period (90 DAP), the eucalyptus leaf area was determined, followed by the dry mass of leaves and stems. The second experiment was carried out in six replications, in the same places and conditions as the first experiment, with the doses established by the results found; they were: 0, 90 and 150 g a.i. ha-1. Destructive assessments were performed (along with the collection of materials for primary metabolism analyses) at 8, 14, 21, 42 and 81 DAP. Destructive evaluations consisted of measuring height, diameter, leaf area and dry mass of leaves and stems. From 02 to 06 DAP, evaluations of gas exchange, Fv/Fm and the total relative chlorophyll content were carried out at the following times: 9:00 am; 11:00 am; 1:00 pm; 3:00 pm; and 5:00 pm. In both experiments, the data were submitted to analysis of variance by the F test and the means were compared by the Tukey test at the 5% probability level, as well as submitted to regression analysis. For the analysis of compounds from primary metabolism, plant materials were prepared in extracts for isolation and profiling of metabolites, and the collected fractions were analyzed by 1H Nuclear Magnetic Resonance. The collected data were subjected to principal component analysis. Trinexapac-ethyl had a stimulatory effect on eucalyptus seedlings, and the dose of 150 g a.i. ha-1 provided greater plant growth. Nevertheless, this product did not provide complete hormesis in eucalyptus (i.e., the biphasic effect, being stimulatory at low doses, followed by deleterious effect at high doses), thus, not being toxic to plants at doses up to 300 g a.i. ha-1. Water restriction was a limiting condition for eucalyptus growth, thus, plants under these conditions did not suffer a stimulatory effect of trinexapac-ethyl. Trinexapac-ethyl caused alterations in the primary metabolism of plants cultivated without water restriction, possibly resulting in a greater production of carbohydrates. However, more researches aiming to study the effects of this plant growth regulator in the eucalyptus crop must be carried out, mainly works that evaluate the hormonal alterations in the plants. (AU)

• FAPESP's process: 18/04376-9 - Effect of trinexapac-ethyl in eucalyptus primary metabolism and hormonal balance under drought stress
• Grantee: Allan Lopes Bacha
• Support Opportunities: Scholarships in Brazil - Doctorate