Seasonality and lack of organic substrates suitable for the production of citrus rootstocks are the main problems in seedling production, coupled with the fact that these materials have alkaline pH. The objective of this study was to evaluate the effect of substrates composed of Pinus sp. needles and a commercial alkaline substrate at different concentrations on the growth and development of Poncirus trifoliata (L.) Raf rootstock. The development of ‘Trifoliata’ was assessed in different mixtures (v:v) of a commercial substrate (Vida®) based on eucalyptus bark and Pinus sp. needles (0, 25, 50, 75 and 100 %) with two particle sizes (3.5 and 8.0 mm). A randomized block experimental design with 10 treatments of seven plants each and four replications was used. During rootstock development, we monitored: the pH, electrical conductivity and stability of the substrates; the dry mass of the aerial part, roots and stem; and vegetative growth and development. Increasing the proportion of needles in the mixture with alkaline substrate reduced the pH, electrical conductivity and density. Treatments with 3.5 mm needles showed greater stability than those with 8 mm ones. The use of 25 % needles provided better results compared to 0 % (alkaline substrate only); however, the need for a specific fertilization and irrigation system for each treatment was detected, as each new substrate has its own physical and chemical characteristics.

The concentration of nutrient solution (NS) in soilless culture systems influences the accumulation of aerial biomass and nutrient contents. This research aimed to determine the optimal Steiner NS concentration for biomass production in Greek oregano (Origanum vulgare L. ssp. hirtum [Link] Ietswaart), and to quantify its nutritional requirement of nitrogen, phosphorus and potassium. A completely randomized design was established with five treatments and five replicates. The treatments were different NS concentrations: 25, 50, 75, 100 and 125 %. The experimental unit consisted of five bags (20 x 20 cm) with substrate (tezontle: 3 to 10 mm in diameter), with one plant each. The fresh and dry aerial matter and the concentration of N, P and K in the different samples were determined. The results showed significant statistical difference in the five variables. The highest fresh and dry matter production was obtained with the 50 and 75 % NS concentrations. While the lower concentrations did not meet the crop’s nutrient demand, the higher concentrations significantly decreased biomass production. The 50 % NS can be used in commercial hydroponic oregano production. The nutritional requirement of this crop is: 4.76 kg of N, 0.70 kg of P and 5.10 kg of K, per ton of fresh matter.

Solanum lycopersicum L. is one of the most consumed horticultural products in the world, due to its wide versatility in use (fresh and processed) and high nutraceutical value. The objective of this research was to evaluate the effect of preharvest spraying of ethephon, calcium prohexadione, iodine and sodium selenite on some physicochemical quality parameters in greenhouse-grown saladette tomato fruits. The experimental design was completely randomized and the evaluated variables were color, weight, equatorial and polar diameter, roundness index, firmness, total soluble solids (TSS), titratable acidity (TA) and lycopene concentration. Individual application of ethephon (1.6 mL∙L^-1) and iodine (5 mL∙L^-1) significantly increased fruit weight (133.71 g) and firmness (3.26 N), with respect to the control (80.36 g and 0.95 N). Fruits that showed the highest TA (0.34 % citric acid) were those sprayed with 125 mg∙L^-1 of sodium selenite. On the other hand, the equatorial and polar diameter, TSS and lycopene concentrations, brightness, hue and roundness index did not differ statistically among treatments. Preharvest foliar application of ethephon, iodine and sodium selenite could be considered as an agronomic management alternative in greenhouse tomato production systems.

Control of the environmental conditions inside a greenhouse is fundamental to obtain high yields and product quality. One of the tools to improve this control is the mathematical modeling of the system in question. Therefore, in this work a dynamic energy balance model was developed with the objective of predicting the air temperature inside a greenhouse. The model considers the process of plant transpiration, ventilation and condensation inside a greenhouse, outside climate conditions, crop characteristics (leaf area index, stomatal and aerodynamic resistance), cover properties and greenhouse characteristics. The information used was collected in a greenhouse located at the Universidad Autónoma Chapingo, Mexico (19° 29’ LN and 98° 53’ LW), with a polyethylene cover, natural ventilation and tomato cultivation. The model was calibrated in order to obtain optimal values for six parameters: infiltration coefficient, heat transfer coefficient through the cover, heat transfer coefficient through the soil, crop-specific transpiration and wind effect coefficient. After calibration, the efficiency of the model improved by 33.84 %. The performance of the model was quite acceptable when evaluated with another set of data.

The use of animal sex hormones in plants does not have a long history, but the presence of these hormones in plants has been proven. The aim of the research was to investigate the effects of gibberellic acid and progesterone on growth and development of Zinnia elegans flower in a factorial experiment based on a completely randomized design with three factors considering three replications. The first factor included application times (pre-sowing, four-leaf stage and two months after sowing), the second factor was progesterone rates (0, 5 and 10 mg·L^-1) and three gibberellic acid rates (0, 100, and 200 mg·L^-1). The measured traits were dry weight and fresh weight of aerial organ and root, number of nodes, number of flowers, number of buds, number of branches and leaves, the distance from the crown to the first leaf, the distance from the crown to the first branch, plant height, chlorophyll a, b and total chlorophyll and leaf area. Results showed that the highest fresh weight of aerial organ and root, maximum number of nodes, flower number, bud number, branch number, the highest plant height and the highest content of chlorophyll a occurred two months after planting. Overall, 10 mg·L^-1 progesterone had the best effects on the traits. The maximum leaf area was obtained by applying 5 mg·L^-1 two months after sowing.