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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 phosphorus transporters are involved in glyphosate uptake by plants, so phosphorus fertilization might act as an attenuator of glyphosate effects on a possible drift. The objective of this study was to evaluate the influence of phosphorus fertilization on the initial growth of Pinus taeda genotypes submitted to glyphosate subdoses applied during two growing seasons, warm and cold. Four experiments were conducted in an open area using 10-L pots, two in the warm season (during 180 days after application on Genotypes 1 and 2) and two in the cold season (during 81 days after application on Genotypes 3 and 4). The treatments consisted of a 2 × 4 factorial scheme, with presence or absence of phosphorus fertilization (25.2 kg ha−1 P2O5) and four subdoses of glyphosate (0, 72, 144 and 288 g ha−1 acid equivalente), using five replicates. For warm season, glyphosate subdoses provided a stimulatory effect on the plant growth of both P. taeda genotypes independently of the fertilization condition. The supplementary phosphorus fertilization increased plant growth characteristic in both warm and cold season, regardless of the exposure to glyphosate subdoses. However, the plant response is dependent on the genotype. Glyphosate subdoses did not negatively affect P. taeda genotypes growth at both experimental seasons, regardless of phosphorus fertilization. [ABSTRACT FROM AUTHOR]

In order to understand the physiological effects of ripeners in sensitive crops, the objective of this work was to evaluate the effect of subdoses of the ripeners glyphosate, trinexapac-ethyl and sulfometuron methyl commonly used in sugarcane, in the growth of lettuce cultivar 'Lucy Brown' and 'Vanda'. To address the effects of the products in the lettuce physiology, analyses of fresh weight, dry weight, number of leaves, chlorophyll content, quantum efficiency of photosystem II, lipid peroxidation (MDA), hydrogen peroxide (H2O2), glutathione reductase (GR), guaiacol peroxidase (GPOX) were performed. We observed that among the products tested, glyphosate had minor impact on plant growth, compared to trinexapac-ethyl and sulfometuron methyl. All products induced a decrease in chlorophyll content for both cultivars. Chlorophyll A fluorescence suffered a major reduction with trinexapac-ethyl and sulfometuron methyl in 'Vanda' and no differences were observed for 'Lucy Brown'. MDA content and enzyme quantification varied by cultivar and the sugarcane ripener tested. By disturbing chlorophyll content and quantum efficiency of photosystem II, through these sugarcane ripeners did not have direct mode of action affecting photosystem II, they can cause some level of damage and activate different mechanisms and at different times, in response to stress. In this sense, it is possible to observe that reduced doses of glyphosate, trinexapac ethyl, and sulfometuron methyl affect the development of lettuce at different levels and trigger an oxidative response that was cultivar dependent. [ABSTRACT FROM AUTHOR]

In silvopasture system, the coexistence of eucalyptus seedlings with other species may result in growth reduction, especially during eucalyptus early development. Therefore, studies elucidating how forage species affect the eucalyptus growth can provide important information for their rational management aiming to obtain the maximum gain of the system. The aim of this work was to evaluate the effect of increasing densities of Urochloa brizantha cv. Marandu in the early development of Eucalyptus urograndis. An experiment was conducted in 20 L pots, in an open and semi-controlled area, during 90 days after planting of eucalyptus. A completely randomized design with four replications was used, in a 6 × 7 factorial system, meaning six evaluation periods and seven densities of U. brizantha: 0 (control), 22, 33, 44, 67, 89 and 111 plants m−2. Fortnightly, eucalyptus height, stem diameter and chlorophyll fluorescence (Fv/Fm) were evaluated. At the end of experimental period, the net assimilation rate, stomatal conductance and transpiration rate of eucalyptus plants were determined, in addition to the dry matter of eucalyptus (leaves and stem) and U. brizantha (leaves). In coexistence with 111 plants m−2, eucalyptus had reduction of 63.9% on total dry matter and 72.7% on leaf area, compared to the control. From the density of 22 plants m−2, U. brizantha negatively interfere significantly the growth of E. urograndis. Up to 8 plants m−2 there are no reductions greater than 5% in eucalyptus height and stem diameter. [ABSTRACT FROM AUTHOR]

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