Jicama [Pachyrhizus erosus (L.) Urban] is a species recently introduced to Venezuela and is a possible alternative for human and animal food because of its high yields and nutritional value, among other reasons. To evaluate the effect of weeds and their control on yield of tuberous roots of jicama (P. erosus), an experiment was conducted in the Experimental Station of the National Center of Agricultural Research, located 423 m above sea level in Maracay, Aragua, Venezuela, in 1996 to 1997 (November to May). The treatments evaluated were no weed control (control), control with manual labor cultivation (manual), and control by grazing sheep in an experimental area of 100 m2, with a density of 50,000 plants·ha-1. The statistical analysis was performed with an analysis of variance and the means were compared with the Duncan test. The results indicated that weed control with sheep increased root yields (36 t·ha-1), and weeds were controlled in the crop (12.9 % at the end of the cycle). It is concluded that sheep as weed controllers increased jicama yields by more than 15 %.

During the days following germination, when the seed’s reserves run out and root growth is slow, stress may occur due to a deficit of phosphorus (P), which has repercussions in later development of the plant and its yield. Plant species differ in their ability to absorb P, and this depends on the amount of available P in the soil and the capacity of the root system to acquire it. The objective of this study was to compare, under controlled conditions, the absorption of P, the morphological (length, surface area, and density) and physiological (intensity of P absorption) root characteristics of maize seedlings (cv. Batán-92) and potato (cv. FL795) when phosphate fertilizer is applied locally. The soil used in the experiment was a sandy loam-textured Andisol. The treatments were P localized at 2, 5, and 8 cm to one side of the seed (L), below the seed at 2, 5, and 8 cm deep (Pr), incorporated (I), and a control without P. The amounts of P were 81 and 54 mg.kg-1, in function of the forms of application. The maize was harvested at 17 and 30 days after germination, and potato was harvested 34 days after germination. The growth behavior of the maize and potato roots treated with P localized in the different forms was not the same. Potato developed an average ratio of radical density in the fraction fertilized with P, compared to the rest of the soil, 2.2 times higher than maize, i.e. potato depends more on P applied as a fertilizer than maize. The accumulation of P and the production of dry matter in maize and potato were in function of the root characteristics and the availability of P in the soil. The total mean root density in maize was 2.7 times higher than in potato. To compensate the lower root density and rate of root lengthening, potato required more available P in the soil than maize and developed a greater intensity of absorption of this element [100 nmol.cm-1 (34 days) vs. 24 nmol.cm-1 (30 days), respectively].

This research was carried out in a glasshouse located in Cuautlalpan, Texcoco, Estado de Mexico from March to September of 1995, with the purpose of extending the period from sowing to planting up to 60 days and, consequently to shorten the period from planting to final harvest of tomato and so to achieve more cycles per year and higher annual yield. The effect of a single application of the growth retardant cycocel (2-cloroetil trimetilamonia chloride) and B-9 (N-dimetil-amine succinamic acid) on tomato seedlings in two dates (25 or 45 days after sowing) and three concentrations (250, 500 and 100 mg·liter-1) was evaluated. The evaluated parameters were plant height, stem diameter, number of flowers per cluster and yield of tomato cv. Floradade cultivated with a hydroponic production system based in decapitation of plant tips to leave two clusters per plant conducted with high population densities. A randomized block design with 13 treatments, four replications and 10 plants for experimental unit was used. Both products significantly reduced plant height at the age of planting (60 days after sowing) facilitating this work. None of the treatments affected the fruit size or yield in relation to the control without application. The reduction in height of the plant was greater with cycocel than with B-9; the effect was greater at the highest concentration (1000 mg·liter-1) and with earlier application.

This study was conducted to observe the postharvest performance of five cultivars of eggplant so as to make it possible to conserve quality and prolong shelf life. Eggplant fruits of the cultivars ‘Classic’ or ‘Typical’, ‘Italian’, ‘Philippine’, ‘Chinese’ and ‘Thai’ were studied. The fruits were stored at 20 °C for eight days, every two days pH, titratable acidity, soluble solids, weight loss, color (peel and pulp), weight, diameter, and length were recorded, and respiratory activity was recorded every day. The ‘Classic’ type eggplant was the largest in weight and volume, while the ‘Thai’ type was the smallest. After eight days of storage at 20 °C, the eggplant ‘Thai’ had lost the most weight, 8.58 %, while the ‘Italian’, ‘Philippine’ and ‘Chinese’ were not significantly different in this variable. Most of the eggplants showed stable values of pH, titratable acidity, and soluble solids during the entire storage period; however, the ‘Italian’ type suffered a considerable reduction in soluble solids. External and internal color of the fruits was different among the types of eggplant, but with no considerable changes during postharvest. The ‘Thai’ type eggplants had the highest respiratory activity, shortening considerably its shelf life. The characterization of the types of eggplant contributes knowledge of postharvest composition and performance, which could be used to find alternatives that maintain fruit quality, prolong postharvest life, and offer possibilities of reaching more distant markets.

Micropropagation of cacti from the areola has generated an important option for the multiplication and preservation of many species, especially those in which seed production is limited, or when there is no plant material available. Areolas of Cephalocereus senilis Haworth Pfeiffer were cultivated in Murashige and Skoog (MS) medium supplemented with naphthaleneacetic acid (NAA) only, and in combination with 6-benzyladenine (BA) and kinetin (K) in concentrations of 0.0, 0.3, 1.0, and 3.0 mg·liter-1. After 21 days, areola activation began with NAA 0.3 + BA 3.0 mg·liter-1, and 61 days later, when plantlets reached 2.5 cm in height, they were subcultivated for multiplication under three conditions: whole plantlets, plantlets without apex, and fractional plantlets (apical, middle, and basal). After 40 days, the best response in number of buds was achieved with fractional plantlets, obtaining 11 shoots with a height of 0.9 cm and a diameter of 0.6 cm, on average, and vigorous, healthy appearance. Later, the shoots were transferred to an environment without regulators, where they formed roots spontaneously after 30 days of incubation.

In experiments carried out at Chapingo, México (highlands) seedlings of Tagetes erecta L. as breeding dwarf experimental plant genotype were sown on March 10th, April 12th, May 11th, June 17th and July 26th of 1999 year, at four planting densities (15 x 15, 20 x 20, 25 x 25, 30 x 30 cm between plants). In all planting dates, smallest plant hight and greatest flower bud number per plant were given at plant density of 30 x 30 cm. As transplanting date was later several plant characteristics such as: plant hight, stem internode number, basal and top lateral branches lenght, number of flowers per plant and time to flowering decreased. Early (75 days), intermediate (95 days) and late (110 to 120 days) flowering responses correspond to June-July, May and March-April transplanting dates, respectively, showing a photoperiodic response of the genotype.

The purpose of this study was to describe the process of senescence in the species: alstroemeria, aster, lilium, limonium, minigerbera, and rose in bouquets wrapped in plastic films that differ in their absorption of ethylene. During the experiment, average temperature was 23 °C, light was 3 mm×m-2×s-1, and RH was 42.8 %. The species that kept their quality characteristics (shape, color, fresh weight), in order of importance were: minigerberas, alstroemeria, and aster. Those that lost these characteristics more rapidly were, in order of importance were: rose, lilium, and limonium. This last species, although it lost fresh weight rapidly, kept its esthetic characteristics. It was found that the use of plastic film helps to conserve fresh weight and the characteristics of each species. The plastic wrap PEAKfreshâ was that which best conserved fresh weight of the bouquets and reduced the level of ethylene present in their microenvironments, only during the first few days. Cellophane also conserves fresh weight, although it was not statistically different from the treatment without plastic wrap.

Coadjutants of somatic embryogenesis, such as malt extract and glycerol, induced formation of 50 % of the embryogenic structures in calluses of Citrus sinensis cv. Jaffa after 6 weeks of in vitro culture. The calluses of different cultivars were obtained from nucellar tissue in a Murashige and Skoog (1962) culture medium (MS), with 1.0 mg×liter-1 dichlorophenoxyacetic acid (2,4-D) and 1 mg×liter-1 kinetin. Adding coadjutants and reducing sources of both ammonium and nitrates in the medium were also tested in in vitro culture of calluses of different cultivars of Citrus. Combining treatments of L-proline and L-glutamine, the subcultured calluses of Citrus cv. Valencia Late had the best embryogenic response to the treatments with 150 mg×liter-1 L-proline, with the source of ammonium reduced to 75 %, and the Murashige and Skoog salts diluted to 50 %. The treatments with MS salts and ammonium in the different treatments with L-glutamine promoted the formation of globular, or embryogenic, structures in the calluses of C. sinensis L. Osbeck cv. Parson Brown C. sinensis L. Osbeck cv. Jaffa, and, C. sinensis L. Osbeck cv. Valencia Late. In cell suspension culture, the calluses taken from the cultivar C. sinensis x C. reticulata cv. Monica, developed embryogenic structures after eight weeks, and later, green embryos in liquid mediums to which 46 g×liter-1 of galactose and 38 ml×liter-1 of glycerol plus 500 mg×liter-1 of malt extract were added. There was no response in cell cultures with mediums in which abscisic acid and L-proline were used.

‘Cayena’ Lisa is the pineapple cultivar most widely used in Mexico. However, the study of other cultivars before introducing them into our country is imperative. In this study some features related to drought resistance were determined under two growth conditions: plastic mulch and bare soil. In each treatment the cultivars ‘Cayena Lisa’, ‘Champaka’ and ‘Oro’ were evaluated under a randomized block design with four replicates, in split plot. Samples were collected in the dry season, at the beginning of the rainy season, just before floral induction and during flowering. The results showed that the pineapple cultivars behaved as a typical CAM plant. In the early development stage and during blooming, CO2 fixation was similar in plastic mulch and bare soil treatments; however, at floral induction, the plastic mulch treatment had higher values. In the early development stage cv. Oro was more efficient in the CO2 fixation, but this happened only in the early morning. There was also an inverse relationship between pH and malic acid content. During the dry season, RWC (relative water content) was lower in bare soil than in the plastic mulch treatment. RWC values obtained for ‘Cayena Lisa’ and ‘Champaka’ were higher than those obtained for cv. Oro. The cv. Oro had the higher chlorophyll content and the fewer stomata, but larger in size, than in the other cultivars.

This study was conducted to evaluate the apples ‘Anna,’ ‘Elba,’ ‘Ma´ayan,’ and ‘Agua Nueva II’ (self-pollination) as pollinators. ‘Agua Nueva II’ apple trees grafted onto the rootstock MM106 were used. Conduction was a trellis system, with distances between plants of 2, 3, and 4 m. Three experiments were set up: in Experiment 1 branches with flowers from each of the pollinators were placed inside the crowns of the ‘Agua Nueva II’ trees, while in Experiments 2 and 3 pollination was done manually. The flowering period of ‘Ma´ayan’ apple was that which best overlapped with that of ‘Agua Nueva II,’ and it was found that the cultivars ‘Anna,’ ‘Elba,’ and ‘Ma´ayan’ are compatible with ‘Agua Nueva II.’ with 18.7; 12.9 y de 13.4 a 19.0 % fruit set, respectively. In the cultivar Agua Nueva II, a response of self-incompatibility was found, with between 0 and 0.85 % fruit set after self-pollination.

Mature sapote mamey (Pouteria sapota Jacq. H.E. Moore & Stearn) fruit were stored at 20 °C for 6 days and 5, 10 and 15 °C for 14 days to determine the effect of storage on ripening. Sapote mamey fruits exhibited typical climacteric behavior, with increases in production of CO2 and ethylene, weight loss, reduction in acidity, total phenols, firmness, and increases in total sugars and carotenoids. Pulp color changed, and synthesis of soluble protein was high, and there were large increases in catalase, peroxidase and polyphenoloxidase activities. Fruit stored at 5 and 10 °C showed lower ethylene production and respiration, protein synthesis, and enzymatic activities. A lower total carotenoid content was observed at low temperatures and some aspects related to ripening like total sugars, total phenols, firmness, flesh color and acidity were delayed, once transferred to room temperatures, without affecting normal ripening. The stage of fruit ripening affected sensitivity to chilling injury. Storage at 15 °C did not stop the ripening in sapote mamey.

Mature-green and commercial harvest stage guava fruits were picked in a commercial orchard in Zitacuaro, Michoacán, México. They were wrapped in polyethylene plastic film bags (PF), that had pores of 10 mm diameter pores, and stored at 5 and 10 °C during 6, 12 and 18 days. The results were compared with a control stored at temperate room (20 °C and 70% relative humidity). CO2, O2, and ethylene were determined in the internal atmosphere generated by the PF; the characteristics evaluated were weight loss, firmness, total soluble solids, titratable acidity and fruit color at the above mentioned storage days and 6 days after the removal of fruits from the cold storage. The PF modified the internal atmosphere in function of both temperature and stage of ripeness stage of the fruit. Fruit stored at 5 and 10 °C in PF had good physiological and biochemical characteristics, and good quality up to 18 days of storage. The best results were found with guavas harvested at the mature-green stage followed by 6 days after removal from storage at 5 °C for 6 days, chilling injury was not observed. The fruit stored at room temperature showed color and weight loss, and attack of Colletotrichum gloeosporioides Penz. after 18 days of storage.