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Although recent studies have reported stimulatory effect of trinexapac-ethyl (TE) on eucalyptus growth, there is no consensus regarding the best dose to promote this response. Since TE acts in the gibberellin (GA) biosynthesis pathway, the study of hormonal crosstalk between the leaves and the shoot apical bud (SAB) can provide important information for understanding the positive effect previously reported. We evaluate the TE dose–response curve for eucalyptus growth in different soil moisture conditions (well watered—WW and 40% of field capacity—40-FC) and its effects on plant physiology, as well as the hormonal crosstalk between the leaves and SAB. TE caused a 49% increase in WW eucalypt growth, but not to plants under 40-FC. Estimated dose for the greatest stimulatory effect on WW eucalypt plants is 202 g a.i. ha−1. TE did not cause an increase in the plants' photosynthetic characteristics up to 15 days after application (DAA), suggesting a later increase in the eucalypt's primary metabolism. Conversely to what have been reported for monocot crops, TE caused a fivefold increase in leaf GA1 as a short-term effect (05 DAA), but significantly decreased SAB-GA1 concentration. Leaf concentrations of indole-3-acetic acid, salicylic acid, abscisic acid and N6-isopentenyladenine also increased. TE caused changes in both 13-hydroxylated (GA20, GA1 and GA8) and non-13-hydroxylated (GA9, GA4 and GA34) GA metabolic pathways in an organ-specific manner. Our results provide information to support the use of this plant growth regulator in eucalyptus plantations, as well as insights into the hormonal crosstalk between leaves and SAB in response to TE. [ABSTRACT FROM AUTHOR]

Eucalyptus are trees sensitive to interference imposed by weeds mainly during the early growth phase. The repetitive use of herbicides with the same mechanism of action has led to the selection of resistant weeds, and Digitaria insularis stands out for its resistance to glyphosate. Due to its occurrence in eucalyptus plantations, knowledge regarding D. insularis interference in eucalyptus early growth is needed to develop management strategies. This study aimed to confirm D. insularis glyphosate-resistence; and also to evaluate the effect of densities and distances of glyphosate-resistant D. insularis, seeded and in regrowth, on the early growth of Eucalyptus urophylla × E. grandis (Clone AEC-144). Prior to eucalyptus' experiments, D. insularis glyphosate-resistance was confirmed through a dose–response curve experiment. After that, two experiments [one for weed's first growth (seeded) and other for second growth (regrowth)] were carried out in an open area, in 700 L pots, for 105 days after planting eucalyptus seedlings. The treatments consisted of increasing densities of D. insularis (0, 1, 2 and 3 plants m−2) planted at 10, 20 or 30 cm from the eucalyptus seedlings. Eucalyptus height, stem diameter, leaf area and dry matter were evaluated. The eucalyptus variables most sensitive to interference were leaf and stem dry matter, with reductions of 45% and 88.4%, respectively for weeds seeded and regrowth. Weed second growth (regrowth) interfered more aggressively in eucalyptus growth. The coexistence with D. insularis, regardless of density and distance, negatively interfered early tree growth. [ABSTRACT FROM AUTHOR]

Previous studies have reported that trinexapac-ethyl (TE) stimulates growth of well-watered (WW) eucalypt plants. However, the physiological and hormonal changes in response to this chemical remain unclear. Furthermore, there are reports that this chemical attenuates drought responses in grasses. This research investigated the hormonal and physiological response of Eucalyptus urograndis (Clone 1407) plants treated with TE, cultivated under WW and drought conditions. The experiment was carried out in a greenhouse up to 42 days after application of 0, 90 and 150 g ha−1 of TE. Eucalypt growth, hormone concentration, gas exchange, maximum quantum yield of photosystem II and total relative chlorophyll content were evaluated. TE increased growth of WW plants by up to 65%. Drought restricted the stimulatory effects of TE on eucalypt growth, despite an increase of at least 102% in gibberellin A 4 (GA 4), trans -zeatin (tZ) and N 6-isopentenyladenine (iP) concentrations after application. GA 4 stood out as an indicator of drought stress as it increased almost 6-fold compared to WW eucalypt. TE caused a hormonal imbalance in eucalypt up to 42 days after application, increasing GA 1 concentration as a short-term effect (8 days) and GA 8 as a medium-term effect (42 days). Gibberellin homeostasis was not reestablished until 42 days after TE treatment. These results provide insights into eucalypt hormonal response to TE. Future research should be conducted under field conditions to understand how long such positive effects would be detected over time in short-rotation eucalypt plantations. • Trinexapac-ethyl increased well-watered eucalypt growth by up to 65%. • Trinexapac-ethyl increased GA 1 biosynthesis as a short-term effect, followed by GA 8. • Gibberellin A 4 stood out as a drought stress indicator, increasing almost 6-fold. • Under drought, trinexapac-ethyl increased cytokinin biosynthesis, which may lessen the stress. • Drought restricted stimulatory effects of trinexapac-ethyl on growth. [ABSTRACT FROM AUTHOR]

Eucalyptus plants are sensitive to abiotic stresses in their initial growth, and nutritional deficiency is one of the most recurrent among them. Trinexapac-ethyl, which is a plant growth regulator, can positively affect eucalyptus, a response known as hormesis, possibly providing plants with greater tolerance to stress. The objective of this study was to evaluate the effect of trinexapac-ethyl at two application times, before planting (BP) or after planting (AP), in Eucalyptus urophylla under conditions of nutritional deficiency (NPK). Two experiments (one for each application time) were conducted simultaneously during 81 days after planting of eucalyptus in 15 L pots. The treatments consisted of three doses of trinexapac-ethyl (0, 30, and 60 g a.i.·ha−1) and four variations of nutrient supply: complete solution (NPK) and solutions without nitrogen (−N), without phosphorus (−P), and without potassium (−K). The variables of gas exchange, growth, and dry matter were evaluated. For both application times, trinexapac-ethyl had a positive effect on the root-shoot ratio of plants grown in −N and also positively affected some eucalyptus photosynthetic characteristics. In the AP application, the compound provided gains in height and dry matter, regardless of the nutrient supply. Under phosphorus deficiency, trinexapac-ethyl provided gains in total dry matter (BP) and leaf area (AP). [ABSTRACT FROM AUTHOR]