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Plant growth regulators are widely used in modern agriculture, horticulture and viticulture. “True” plant growth regulators interfere directly with the plant’s hormonal status. They are represented by plant hormones or their synthetic analogs, by inhibitors of hormone biosynthesis or translocation and by hormone receptor blockers. “Atypical” plant growth regulators act by displaying a local and/or transient phytotoxic effect. Approximately 40 active ingredients are in use, applied either as a single component or as combinations. Many plant developmental processes can be actively regulated in cultivated plants, for example, acceleration or delay of seed germination, dormancy breaking in woody perennials, stimulation or reduction of shoot elongation, induction of flowering and fruiting, reduction or increase of fruit set, acceleration or delay of senescence processes including fruit ripening and defoliation. The achieved benefits range from facilitating crop management to increasing and securing yield and quality of the harvested produce and improving its storage and shelf life. Systematic use of plant growth regulators started in the 1930s. Current global annual sales are in the range of US$ 1.2 billion.

Salt stress severely limits the productivity of crop plants worldwide and its detrimental effects are aggravated by climate change. Due to a significant world population growth, agriculture has expanded to marginal and salinized regions, which usually render low crop yield. In this context, finding methods and strategies to improve plant tolerance against salt stress is of utmost importance to fulfill food security challenges under the scenario of the ever-increasing human population. Plant priming, at different stages of plant development, such as seed or seedling, has gained significant attention for its marked implication in crop salt-stress management. It is a promising field relying on the applications of specific chemical agents which could effectively improve plant salt-stress tolerance. Currently, a variety of chemicals, both inorganic and organic, which can efficiently promote plant growth and crop yield are available in the market. This review summarizes our current knowledge of the promising roles of diverse molecules/compounds, such as hydrogen sulfide (H 2 S), molecular hydrogen, nitric oxide (NO), hydrogen peroxide (H 2 O 2 ), melatonin, chitosan, silicon, ascorbic acid (AsA), tocopherols, and trehalose (Tre) as potential primers that enhance the salinity tolerance of crop plants.

The exogenous application of salicylic acid can induce plant resistance against pathogens. However, little is known about the potential uses of this bioregulator for controlling coffee diseases. In this study, we assessed the effect of applying salicylic acid (SA – 150 mg L-1) on the management of coffee rust (Hemileia vastatrix) in a 7-year-old coffee plantation with low crop load (651.6 kg ha-1 in 2017). For comparison, plants were sprayed with protectant fungicide (copper hydroxide – CH) and standard fungicides (SF) used by local farmers (boscalid, pyraclostrobin + epoxiconazole, and copper hydroxide). Non-treated plants were included as a negative control. Five monthly applications were performed from November 2016 to March 2017. Rust incidence and severity, defoliation, and growth of plagiotropic branches were evaluated monthly. The activity of catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD) and total proteins was assessed one day after the first, third, and fifth product applications. Compared to untreated plants, SA reduced the severity and incidence of rust from 36.3 to 54.7%, while CH and SF reduced disease from 31.8 to 54.6% and from 83.8 to 88%, respectively. SA reduced defoliation by 54.1%. SA increased the concentration of CAT, APX, and SOD after the first application. However, this effect was not observed after subsequent applications. Foliar application of SA reduces the severity and incidence of coffee rust and defoliation in plants with a low crop load.

Water deficiency is a threat to food security and limits the yield of vegetables, including arugula ( Eruca sativa Mill.). Despite the increasing use of amino acid-based bioregulators to mitigate water stress, the effects of carnitine as a water deficit mitigation agent have not yet been elucidated. Here, the effects of different carnitine concentrations on the morphophysiology of arugula plants under different water deficit conditions were evaluated. Plants were irrigated to 100%, 80%, 60%, or 20% field capacity (FC) with water alone (control) or water with carnitine at concentrations of 100 µM or 100 mM. Forty days after sowing, the photosynthetic pigment content, gas exchange, chlorophyll a fluorescence, electrolyte leakage, relative water content, and growth parameters were measured. The application of 100 µM carnitine to well-watered plants (80%-FC) and plants under moderate water stress (60%-FC) resulted in greater photosynthetic plasticity, as demonstrated by the unaltered maximum quantum yield of photosystem II. However, under severe water deficit (20%-FC), plants treated with carnitine exhibited a reduced maximum quantum yield of photosystem II, indicating damage to photosystem II. Application of 100 µM carnitine increased the shoot biomass of arugula plants exposed to 80%-FC conditions and reduced electrolyte leakage in plants receiving 60%-FC irrigation. In contrast, 100 mM carnitine was toxic to arugula, hampering overall plant growth. The results suggest that low carnitine concentrations have the potential to mitigate the effects of moderate water stress on arugula, maintain membrane integrity and photosynthetic plasticity, and enhance shoot growth, which indicates this amino acid as a promising biostimulant in plants.

Aphids (Hemiptera: Aphididae) are serious pests of pecan foliage (Carya illinoinensis [Wangenh.] K. Koch). The black pecan aphid, Melanocallis caryaefoliae (Davis) (Hemiptera: Aphididae), feeds on pecan foliage and elicits leaf chlorosis that can cause defoliation. In contrast, the blackmargined aphid, Monellia caryella (Fitch) (Hemiptera: Aphididae), and yellow pecan aphid, Monelliopsis pecanis Bissell (Hemiptera: Aphididae), feed on pecan foliage but do not elicit chlorotic feeding injury. Application of gibberellic acid (GA3) to pecan foliage reduces chlorotic foliar injury and nymphal populations of the black pecan aphid. GA3 has potential to manage black pecan aphid later in the season when broad-spectrum insecticides are used to control direct pests of pecan nuts but also inadvertently induce aphid outbreaks. Here, broad-spectrum insecticides were used with GA3 or aphicides in orchard trials for 2 yr. Populations of aphids and natural enemies along with chlorotic feeding injury on foliage were assessed. When used concurrently with GA3 or aphicides, broad-spectrum insecticides did not flare black pecan aphid populations. However, combined populations blackmargined aphids and yellow pecan aphids were higher in treatments with GA3 than with an aphicide or in the control treatment during one of two years. Application of GA3 or the aphicide often led to significantly less chlorotic injury than observed in the control. Surprisingly, natural enemies were not significantly affected by broad-spectrum insecticides when applied concurrently with GA3. These results show that GA3 can be used as part of a late-season IPM strategy to protect foliage from localized chlorotic leaf injury elicited by the black pecan aphid.

Maize is a crop of global economic importance and is widely cultivated throughout the Brazilian territory. The use of biostimulants can increase yield and improve crop yield. Unmanned aerial vehicles can be employed in arable areas, allowing their use in an economically way. This study to evaluate the use of biostimulant and the best application timing using photogrammetric indexes in maize, and indicate the most suitable plant index for yield increase through a Pearson's correlation. The DJI Drone coupled with RGB camera was used, and the images were processed through the AgisoftPhotoscan® software to generate the orthomosaic, and the QGIS® software version 3.4.15 with GRASS was used to generate thematic maps with the classification of the indexes of vegetation (NGRDI, EXG, SAVI, TGI, GLI, RI). A matrix of Pearson correlation coefficients between the variables was also created, and the results were analyzed with the R software. In general, the products Pyroligneous Extract (PE) and the hormonal product (HP) were the best for the two seasons studied. However, the HP was the best product to mitigate plant water stress in the dry period. Application at phenological stage V3 showed the lowest growth in the rainy season and in application to the seeds in the dry season. Dose 4 of the pyroligneous extract increased productivity in the rainy season and level 3.4 for the hormone product. Among the indexes evaluated, only the SAVI index showed significant differences between the others and showed significance for productivity in the two periods.

Aim: To investigate the influence of nutrients and bioregulators on the vegetative growth, flowering and productivity of Litchi. Methodology: The vegetative growth, flowering and productivity of litchi cv. Bombai was assessed through application of nutrients and bioregulators. Results: The plants receiving treatment with @ 0.5% Borax (T1) showed the highest percentage increase in canopy volume (7.56 %) and plant height (2.46 %) in litchi, outperforming all other treatments. The maximum productivity (38.69 kg per plant) was registered in plants under treatment T2 (0.3% Borax), which was found to be statistically at par (36.68 kg per plant) with plants treated with 0.1% Seaweed extract (T10) . The percentage increase in the plant height, plant spread in East-West and North-South direction, canopy volume, , fruit weight and fruit set capture positive correlation in both PC-1 and PC-2. The total contribution of PC-1 and PC-2 was 60.857 %. Interpretation: Among all the treatments, T2 (0.3% borax) and T4 (ZnSO4 @ 0.4%) treatments proved superior over other treatements with respect to vegetative growth, flowering and productivity parameters in litchi. However, further investigation need to be carried out with combination of these applied nutrients and bioregulators for getting acceptable results. Key words: Bioregulators, Flowering, Growth, Litchi, Nutrients

There are documentary records referring to paclobutrazol (PBZ) as a growth bioregulator that inhibits the gibberellin synthesis and its application increases yields in fruit and vegetable crop productions. Its agronomic management includes it as an emerging technology to reduce vigour, promote flower induction and flower development in fruit trees with increased economic returns. Its use is banned in some countries because of concerns about residues that can cause harmful effects on the environment. Therefore, the aim of this article was to collect, analyse and summarise relevant information on the use of PBZ in fruit tree production and its possible risks to the environment. The results obtained indicated that the application of PBZ can be effective in solving some problems related to flowering if it is applied in the right amount and at the right time. However, it is necessary to elucidate the physiological processes with which it is associated and its response to be taken into account to increase yield. PBZ is currently used in fruit trees such as mango, lime, apple and guava, increasing their productivity. However, some studies have shown its residual effect on the environment. Therefore, PBZ is a viable strategy, because it presents a series of advantages in the production of fruit trees. However, it is vital to generate protocols that seek its regulation with a rational and sustainable approach.

Abiotic stresses such as salinity and drought severely affect plant growth and productivity. Plants employ various defence strategies, including antioxidant responses and osmotic adjustment, to cope with these stresses. Carnitine, a compound found in many organisms, has been linked to osmoprotection and stress mitigation. In this study, the effects of exogenous carnitine (5 μM) on antioxidant responses in Arabidopsis thaliana Col-0 under short-term salt (80 mM NaCl) and drought (150 mM mannitol) stress were evaluated. Carnitine application mitigated reductions in relative water content, shoot fresh weight, and rosette diameter. It also alleviated stress-induced damage, as indicated by decreased lipid peroxidation and H₂O₂ levels. Interestingly, enzyme activity responses differed between stress types: Catalase (CAT) and Ascorbate Peroxidase (APX) were predominantly upregulated under salt stress, while Peroxidase (POX) and APX increased under drought. In addition, total glutathione content was enhanced, suggesting support for redox homeostasis. While limited in scope, the findings indicate that carnitine may contribute to short-term stress tolerance through modulation of antioxidant metabolism. These results support the potential role of carnitine as a bioregulator under abiotic stress, though further studies are required to clarify its mechanisms and broader applicability.

Coffee berry borer (CBB) Hypothenemus hampei is the major pest of coffee fruits worldwide. Bioregulators have been applied in crop plants with the aim of changing their physiology and metabolism for better yield and quality of produce, but little knowledge exists on the effects on insect pests. This study evaluated application of ethylene synthesis inhibitor in arabica coffee on CBB field infestation, preference, and performance in function of application time and dose. Field experiments were conducted in Lavras, Brazil, and the effects of ethylene synthesis inhibitor Mathury™ on CBB were evaluated using five treatments: control (water); Time1 + Dose1; Time1 + Dose2; Time2 + Dose1; and Time2 + Dose2. The first and second applications were performed at 80 and 110 days after flowering, respectively, using the doses of 2 and 15 L ha −1 . CBB field infestation was recorded through time as the percent bored fruits, and the colonization in the beans and degree of fruit maturation were evaluated at harvest. CBB preference and colonization were assessed in dual-choice bioassay and the performance under no-choice condition in the lab. Plants treated with the bioregulator overall presented fruits less suitable for CBB preference and performance in terms of females choice and survival in the lab, but varying effects were found between field experiments for bored fruits (%), which increased with fruit maturation. In the second field experiment, reduced larvae and pupae infestations were found in bioregulator-treated fruits. Application of ethylene synthesis inhibitor is promising to complement CBB management in sustainable coffee crops. Future research should evaluate the underlying induced-resistance mechanisms.