ARTICULO POR INVITACIÓN

Sechium edule (Jacq.) Swartz is a neotropical species that is notable for its diverse uses since ancient times. The commercial success of the chayote has motivated an increase in farming area for its cultivation in atypical agro-climatic areas. This study determined the diurnal pattern of gas exchange, water relationships, and morphological characteristics of the chayote leaf related to the gas exchange process. Observations were performed once a month during the production cycle (four months). It was observed that S. edule has amphistomatous leaves with five types of trichomes. The gas exchange pattern showed partial stomatal closure induced by an increase in leaf temperature, as a consequence, the transpiration and the assimilation rate were also affected. Changes in pH in the leaf xylem sap were related directly to the changes in stomatal conductance. The xylem sap analysis showed that K+ and Ca2+ were the most abundant ions and that they maintained a proportion of 3:1 up to 6:1. It was concluded that under atypical field conditions Sechium edule restricts its physiological processes related to gas exchange and water relations by partial stomatal closure.

Recent research has shown that the seeds of Erythrina americana Miller are high in proteins and an adequate content of lipids, giving it possibilities as a human food. The E. americana flowers and seeds are known in Mexico as "Colorín", and are highly appreciated for their flavor; in some countries they are used as a protein complement. In several regions of Mexico, traditionally the flowers are cooked, but the seeds are not consumed because the presence of alkaloids makes them highly toxic. The alkaloids affect the peripheral nervous system: muscular relaxation and a strong sedative effect on the central nervous system. The objective of the present study was to determine the alkaloid content in some parts of the flowers (calyx and corolla) and where the most toxic alkaloids are located. By liquid chromatography and mass spectrometry of the extract, it was observed that alkaloid content was higher in the calyx than in the petal, although the toxic alkaloids a- y b-erythroidine were detected in both tissues.

The in vitro establishment and sprouting of axillary buds and shoot apex of Ginkgo biloba L. was evaluated using as a basic medium the inorganic salts of Murashige and Skoog (1962) MS, supplemented with thiamine-HCl (0.5 mg·liter-1), myo-inositol 100 mg·liter-1, 3 % sucrose, Aguilar (1993) vitamins, 2 g·liter-1 of activated charcoal, 0.7 % agar-agar, Benomyl (400 mg·liter-1), and with a pH of 6.0±0.1. In sprouting and proliferation, the medium described above was used without the addition of activated charcoal and Benomyl. Different concentrations of BA (0, 5, 10, 15 y 20 mg·liter-1) were evaluated. Incubation was done under a light intensity of 50.48-59.83 mmol·m-2·s-1 and a photoperiod of 16 h of light and 8 h of dark with a temperature of 26/24 ºC (day/night). The results demonstrated that the season of the year in which the explants were collected influences establishment, while the age of the explant and its position on the branch influence sprouting. The best responses were obtained in one-year-old explants taken from apical regions. Sprouting in the control was 25 %, contrasting with sprouting and proliferation in the 15 mg·liter-1 treatment which was 60 % and in the 20 mg·liter-1 treatment it was 80 %.

Several nutrient solutions modified from Steiner´s were evaluated in tomato (Lycopersicon esculentum Mill.) under field conditions with a drip irrigation system. Treatments were combinations of three NO3-:anion and three K+:cation ratios in a factorial design with two factors and three levels plus a control treatment (common fertilization used by growers). Harvest was done on ten picking dates. The highest yield and the best fruit quality were obtained on the first picking date with the highest N level and on the fourth picking date with the intermediate concentration as well as on the third picking date, and in total yield, with the intermediate K concentration. The control was not significant different from the mean of the factorial. These results should allow a great reduction in fertilization rate and in costs for growers and a reduction in soil and groundwater pollution. Also, the results show that nutrient concentration should be administered in accordance with phenological stage of the crop. Fruit quality declined in the final third of the harvest period; this was related to an excessive K concentration in the fruit.

The purpose of this study was to present integrated information on Taxus, particularly the Mexican species T. globosa. The study is based on a review of literature, laboratory and field work, and herbarium study. The existing information shows that the species are morphologically similar, but are relatively unknown in terms of their biology, and taxonomically they are classified by their geographic distribution. T. globosa is distributed, unevenly, from northern Mexico (Tamaulipas and Nuevo León) to Honduras. It flowers from January to March and produces fruit from May to November. In nature, it reproduces by seed, although it produces sprouts from the stem, an important potential for vegetative propagation. All of the plant's parts are poisonous except for the arilo, which is edible and attracts birds. It is in its toxic nature that its economic importance lies. It produces a pseudo-alkaloid called taxol, which acts against various types of cancer, among these ovarian cancer, and thus a considerable increase in its demand is expected. Bibliographic information on Taxus is very scarce, especially on the Mexican species, which is rare and has not been studied, and its biological characteristics, its population and habitat are unknown. The paper concludes with a description of its potential for use and the need to investigate it in order to protect, propagate, conserve, and possibly cultivate it.

The objective of this study was to determine the effect of the time under floating row cover on growth and yield of muskmelon (Cucumis melo L.). The experiment was established in Saltillo, Coahuila, Mexico. The experimental design was a randomized complete block design with four replications. The treatments were 1) control, 2) plants under row cover for 7 days after emergence (DRC), 3) 14 DRC, 4) 24 DRC, 5) 31 DRC, and 6) 41 DRC. Throughout the experiment temperatures inside the covers were above 35 ºC; however, the frequency of days the temperatures were above 40 ºC increased as the period under cover increased. The number of days when temperature inside the cover was > 40 oC were 2, 5, 12, 18, and 25 for treatments 2, 3, 4, 5, and 6, respectively. Row covers increased (P£ 0.01) the number of perfect flowers, stem length, and number of fruits per plant, relative to the control. The total yield increased as the period under row cover increased. The highest yield (77.8 t×ha-1) was obtained with 41 DRC, in which heat accumulation was 1134 heat units. Yield was higher in the covered treatments relative to the control (43.1 t×ha-1) because plants under cover retained more heat.

In this study, tomato (Lycopersicon esculentum Mill.) demand changes are estimated through the estimation of elasticity (-0.587) within the Almost Ideal Demand System (AIDS). Such estimation is compared to the elasticity (-0.10) obtained in other research, all referred to foreseeing changes in quantity demanded. The results showed that there is an underestimation of 17 % in quantities obtained through the elasticity proposed by such research; it is stated that underestimation is due to the lack of economic choice axioms.

Tolerance to anthracnose (Colletotrichum gloeosporioides) was measured by evaluating quality in Cera type, cv. Maradol and cv. Sunset papaya fruit, inoculated or not, during postharvest storage at 18 ± 3 °C. Biochemical and/or biophysical variables were determined, and pathological lesion diameter was measured. It was found that the pathogen does not influence weight loss, firmness, malic acid, ascorbic acid, total soluble solids, or color changes. However, it does affect the appearance of the fruits' peel and flesh. The cultivar most tolerant to C. gloeosporioides was cv. Maradol, which showed more firmness. The cultivar judged to have the highest quality was cv. Sunset, having a higher content of ascorbic acid and total soluble solids and better peel and flesh color.

The aim of this study was to determine when black flesh ("pulpa negra") begins to appear in ‘Haden’ mango fruits during postharvest storage and its relationship to fruit quality. ‘Haden’ mango fruits were stored for 37 days at 13 ±1 °C and 85-90 % relative humidity. Samples were taken at 6, 13, 16, 19, 22, 25, 28, 31, 34 and 37 days of storage (treatments), to determine the time of black flesh development. The experimental unit consisted of one fruit with 10 replicates. The experimental design was random blocks. The variables were incidence and severity of black flesh; weight loss, firmness, total soluble solids and malic acid. Incidence of black flesh was observed in mango fruits starting 22 days after harvest. The incidence and severity of black flesh increased with time after harvest. Soluble solid concentration increased during storage, and firmness and malic acid content decreased. The fruits that developed black flesh showed marked weight losses, less firmness and lower concentration of malic acid.