This paper provides an overview of the biological, ecological, epidemiological and management aspects of Candidatus Liberibacter, a bacterium recently introduced into Mexico that is associated with diseases such as citrus Huanglongbing, Zebra chip and chili pepper variegation. Plants affected with Ca. Liberibacter have multiple swellings located in the necrotic phloem and dispersed throughout the vascular system, massive accumulation of starch, aberrations in cambial activity and excessive formation of phloem. It is suggested that phloem necrosis causes blockage of the nutrient translocation stream, which leads to anatomical changes such as mottling and vein yellowing. Ca. Liberibacter control focuses on reducing inoculum sources, such as the use of healthy plants, removal of symptomatic trees and chemical control of the insect vector to reduce the transmission of the bacterium.

Among the acid limes produced in Mexico, the Mexican lime is the most important in the domestic market; however, because of the heterogeneous quality of the fruit at harvest time, the export volume is limited. Due to the thin epicarp, the fruits are sensitive to weight and green color loss, so their shelf life is short. Three varieties have recently been registered, namely Colimex, Colimón and Lise, whose response to the use of plant hormones to slow senescence and maintain quality is unknown. The aim of this research was to study the effect of pre-harvest treatment with gibberellic acid (GA3) on the quality and shelf life of the fruit of the above-mentioned varieties. In two periods of fruit growth, spraying with GA3 (30 mg∙L-1) was performed. After the harvest, a wax was applied to fruits with and without GA3; in addition, there were fruits without any treatment (control). The fruits were stored for 10 days at 22 ± 2 °C. At the end of this time, the following variables were evaluated: weight loss, color index, and concentration of chlorophyll, citric acid, TSS and ascorbic acid. AG3 treatments decreased weight loss and delayed changes in color, chlorophyll, TSS and citric acid, with ascorbic acid remaining unchanged. This response was more consistent in the Colimex and Lise varieties. We conclude that pre-harvest treatment with GA3, in combination with wax, maintains fruit quality for a longer period.

Semi-closed greenhouses are more efficient in water and energy use than conventional ones. However, one of the challenges is the humidity control. This paper is based on experimental data generated during the 2012 tomato production cycle in a semi-closed greenhouse located at the Humboldt University of Berlin. The aim was to generate two models for simulation of the humidity behavior. In the first model, the greenhouse was completely closed and only transpiration and condensation processes were taking place. In this model, after calibration, a mean absolute error (MAE) of 1.94 and a correlation coefficient (r) of 0.87 were obtained, with the boundary layer resistance and the radiation extinction coefficient being the most varying parameters. The second model, in addition to the processes considered in the first, had natural ventilation, so a sensitivity analysis was performed before calibration, resulting in a MAE = 2.17 and r = 0.85, with the latent heat of vaporization and the radiation extinction coefficient being the most sensitive parameters. The developed models allow for a quantitative comparison of the processes involved in the water balance in the open and closed system, and will thus enable us to improve control over this factor. Both models were implemented using Simulink in Matlab®.

One of the main characteristics that plant growth-promoting rhizobacteria (PGPR) must have is good rhizosphere colonization. This study evaluates the ability of five PGPR separately and together (Bacillus-Pseudomonas), including four strains of Pseudomonas fluorescens (UM16, UM240, UM256 and UM270) and one of Bacillus thuringiensis (UM96), to colonize the rhizosphere of maize (Zea mays L.) plants. Additionally, the promoting effect of the bacterial consortium on green tomato (Physalis ixocarpa Brot. ex Horm.) seedlings was assessed. The results showed that the five strains analyzed are highly competent to colonize the rhizosphere, in addition to not presenting antagonism in vitro between them. The recovered strains were analyzed by means of their natural resistance to carbenicillin and by means of random amplified polymorphic DNA. Also, by assessing the growth-promoting effect of inoculating the strains together, only the combination of B. thuringiensis UM96 and P. fluorescens UM16 significantly improved the total fresh weight of the tomato seedlings and increased hypocotyl and root length. The P. fluorescens strains, separately, were the only ones that showed a beneficial effect on seedling development. The results showed that only the UM96-UM16 consortium had beneficial interaction with the plant, while separately the strains showed broad potential for colonizing the rhizosphere and promoting tomato plant growth.

Scion-rootstock selection plays an important role in determining orchard performance. Pyrus communis and Cydonia oblonga are the most widely cultivated rootstocks for European pear cultivars. The lack of rootstocks adapted to different edaphoclimatic conditions and scion cultivars is widely acknowledged in pear culture. Hence, this study was designed to investigate the growth characteristics and performance of the ‘Shahmiveh’ pear grafted onto six rootstocks including Quince A, B, C, BA29, ‘Konjoni’, and generative seedling. The experiment was conducted during two consecutive years, 2013-2014, at the Agricultural Research Center of Kabutarabad, Isfahan, Iran. The experimental design was based on a randomized complete block design including three replications of six trees each. The assessed variables were trunk diameter, current season shoot length, tree height, leaf dimensions, the number of flowers and abscised flowers, and also the number and percentage of fruit set. Cumulative data from a 7- to 8-year-old pear orchard showed that rootstock selection markedly influenced trunk diameters, current season shoot growth, leaf length, and fruit set of the endemic ‘Shahmiveh’ pear. The largest trunk diameters were obtained from the ‘Konjuni’ rootstock, whereas the highest current season shoot length was observed on the generative seedling. PQBA29 exhibited the largest leaf length, number of fruits per current season shoot, and percentage of fruit set, whereas Q. A rootstock had the second highest cropping efficiency. This experiment demonstrates the significantly higher performance and compatibility of PQBA29 as a rootstock for endemic ‘Shahmiveh’ pear in the arid condition of Iran.