The effect of five shade levels (30, 48, 58, 78, and 92 %) imposed 15 days after transplant on stem elongation, mesophyll thickness, foliar area, bract area, shoot dry weight, CO2 fixation rate and chlorophyll content of poinsettia (Euphorbia pulcherrima Will. ex Klotzsch) cv. Subjibi was studied under greenhouse conditions. Stem length and foliar area increased and reached in average 325.5 mm and 0.216 m2, respectively, under 48, 58 and 78 % shade while bract area reached the maximum value under 48 % shade. Mesophyll thickness increased up to a value of 151.34 mm under 30 %, but it was significantly reduced at 92 % shade. Shoot dry weight increased under 48, 58 and 78 % shade but decreased significantly at 30 and 92 % shade. At 60 days after transplant the rate of CO2 fixation increased steadily from 30 % shade reaching a maximum value under 58 % shade, from this point CO2 fixation rate diminished and reached the lowest rate at 92 % shade. Chlorophyll content was determined twice, 90 and 128 days after transplant, in the first date the concentration of chlorophyll a, b and total raised steady as the shade intensity was increased and 92 % shade induced the maximum chlorophyll concentration; 128 days after transplant the absolute values of chlorophyll a, b and total were higher than 90 days after transplant, but the raise in chlorophyll content observed as the shade intensity increased was not significant. This study makes clear that as the shade intensity increased a delay in development of color in the bracts occured. Among the five shade treatments tested, 48 % shade produced the best quality plant.

To observe the influence of leaf cover on frost damage, the potato cultivar Atlantic was sown at three spacing distances (20, 30, and 50 cm between tubers). Of the variables recorded, plant height, number of leaves, number of tubers, weight of tubers, and weight of frost damaged leaf were affected significantly (P£0.05). Spacing at 20 cm between plants resulted the least damage to foliage per plant. The largest number of tubers was obtained with the widest spacing between plants. Although at 20 cm fewer tubers were produced, yield was higher considering the variable weight of tuber.

To determine the effectiveness of floating row covers alone or combined with plastic mulch in the control of whiteflies and in yield of zucchini squash, seven treatments were set up in a design of random blocks with four replications: control, black plastic mulch (BPM), white plastic mulch (WPM), black on white co-extruded plastic mulch (BWCM), white on black co-extruded plastic mulch (WBCM), Kimberly Farm row cover alone (KFC), black plastic mulch plus Kimberly Farm row cover (BPM+KFRC), and black plastic mulch plus Vispore row cover (BPM+VRC). The treatments of mulch alone or mulch plus row cover induced significantly lower values for days to harvest and higher values for plant cover relative to the control (P£0.05). WPM, BPM, and BWCM resulted in the highest yields (P£0.05) with 35.4, 35.2 and 31.1 t×ha-1, respectively, while the control produced only 21.4 t×ha-1. The treatments with floating row covers had practically zero incidence of whitefly, while WPM, although it had the highest yield, also had the highest number of whiteflies (P£0.05), relative to the rest of the treatments.

The objective of this study was to confirm field observations on differences in susceptibility to white rot (Sclerotium cepivorum Berk.) shown by white, red and pink types of garlic cultivars planted in Mexico. Pink cultivars of garlic were the most susceptible followed by red and white cultivars. White rot induced the higher yield reductions on the pink cultivars (75 to 99 %), red varieties 65 to 90 %, and white cultivars 23 to 55 %. The white cultivars Perla and Blanco de Cortazar together with ‘Massine’ and ‘Taiwan’ types of red and pink cultivars, respectively, showed the lowest susceptibility to S. cepivorum.

The karyotype was studied in six genotypes of pitahaya (Hylocereus spp.). The chromosomes were observed in cells from root tips pretreated in a watery solution saturated with p-dichlorobenzene for 5:30 to 6:00 hours and fixed in Carnoy. Chromosomes were stained in Feulgen and 1.8 % propionic orcein. Chromosomes were measured on scanned photographs of cells and processed in Image Tool, version 1.8, software. The six genotypes of pitahaya were diploid, exhibiting a chromosome number of 2n = 2x = 22. Chromosome length varied from 2.46 to 5.06 µm. The karyotypes of the pitahayas were uniform in length and arm relationships. Two cytotypes were distinguished, both with metacentric (m) and submetacentric (sm) chromosomes. Cytotype A (10 m + 1 sm) was present in five genotypes (BHA, BV22, A28, A39, and Rojo), and cytotype B (9 m + 2 sm) in only one (Solferino). The karyotypes showed two to three secondary constrictions in the short arms of metacentric chromosomes. The similar karyotype characteristics of the genotypes studied could indicate that they belong to the same species, Hylocereus undatus.

To study the biological activity of endogenous gibberellins in the apple flower, a quantitative analysis of these hormones in petals and embryo sac was performed in the cultivars Golden Delicious, Rome Beauty and Red Delicious, using lettuce hypocotyl bioassay. It was found that gibberellin activity is present in both petals and embryo sacs. However, the concentration varies within floral tissue and among cultivars. The level of these hormones in petals was 0.78, 14.47, and 1.8 µg·g-1, dry weight for Golden Delicious, Rome Beauty, and Red Delicious, respectively, whereas, in the embryo sac it was 0.4, 0.18, and 10.8 µg·g-1 dry weight in the same order. The results show that the presence and levels of gibberellins vary among floral parts and cultivars of apple.

The purpose of this research was to study the relationship between the amounts of amino acids and starch found in the mango buds, and flowering induction. Five treatments were applied: KNO3 g×liter-1, NH4NO3 20 g×liter-1, ethrel ml×liter-1, girdling on stems, and control. Anatomic mango bud cuts were realized, from these data, they were classified into three growth stages: vegetative, flowering initiation, and inflorescence differentiation. Starch and amino acids concentrations were also measured in these buds. It was observed that the buds under nitrogen treatments had a faster transformation from the vegetative to the reproductive stage. It was not found a relationship between the starch concentration and the flowering initiation; therefore, it is quite possible that the starch found in buds is not an important factor that promotes flowering in mango trees. The analysis of amino acids in apical buds showed high level of glycine, asparagine, glutamine, alanine, serine, arginine, leucine, lysine, and treonine; while the analysis also showed that histidine, tyrosine, valine, phenylalanine, and isoleucine, were found in much lower levels. The greater amino acids concentration was found during the flowering initiation, while the lowest levels were identified in vegetative buds. These results indicate that high amino acids’ levels might be related to the mango’s flowering initiation.

The investigation was carried out in the Practice Fields of the Superior Technical School of Agricultural Engineers, Polytechnic University of Madrid in 1993, in an apple orchard of ‘Starkrimson’/M-26 and /MM-106 and ‘Golden Spur’/MM-111, at 10,000 and 13,000 tree·ha-1, respectively, using different products for the chemical thinning of fruits, and sprayed when the fruits had around 25 mm of diameter. The area of the trunk, height of the tree and number of vegetative shoots bigger than 10 cm of length, had a positive effect with the total number of fruits, number and weight of the commercial fruits per tree, as effect of the chemical thinning of fruits in the two apple cultivars. The maximum number of commercial fruits per tree and the maximum yield of the same quality of fruits, was bigger in ‘Starkrimson’, with the products ethephon (0.18 and 0.60 g·litro-1), carbaryl (2.55 g·litro-1) and urea (6 %); in ‘Golden Spur’ the products that induced the best results were NAA (16 mg·litro-1) and carbaryl (1.27 and 2.55 g·liter-1). The ethephon in the used concentration induced a high abscission of fruits. The reddest and uniform, less yellow colors and with smaller brightness in ‘Starkrimson’, were induced by the treatments with ethephon (0.30 g·liter-1) and hand thinning; in ‘Golden Spur’ the fruits from hand thinning and with ethephon, were with more yellow coloration of fruit peel and more brightness. The firmness of the pulp of the fruits, in ‘Starkrimson’ didn’t have effect by the chemical products; contrarily in ‘Golden Spur’, the control, hand thinning and NAA (16 mg·liter-1), were more consistent in relation to the fruits with ethephon (0.30 g·liter-1). The quantity of total soluble solids of the fruits (TSS; ºBrix) in ‘Starkrimson’ was higher only in the hand thinning, and in ‘Golden Spur’ the maximum of TSS was found it the fruits with hand thinning and with ethephon (0.18 g·liter-1); only in this cultivar the higher content of TSS was present in the commercial fruits (³65 mm of diameter).

The investigation was carried out in 1994 in the Experimental Farm of the Community of Navarra, Spain, with the objective of inducing chemical and hand thinning of fruits in ‘Royal Gala’ apple, established in a density of 6,600 trees×ha-1, using different useful chemical products in the agriculture, and the evaluation of the interaction between the tree vigor of the trees and the efficiency of the thinning of fruits. Of the used chemical products, the carbaryl was the one that showed, in its three concentrations the higher abscission of fruits per tree, without affecting tree production. As the carbaryl concentration was increased the quantity of fruits by tree was redused and the quantity of commertial quality fruits was in creased. The hand thinning leaving a single fruit each 15 to 20 cm of shoot lenght showed that the quantity of fruits for tree was the appropiate having commercial quality without affecting production and neither the yield. One fruit per corymb left, showed high quantity per tree, but quality decreases. It was found that for each one tenth in the increment of the index of productivity of commercial fruits,as a result of the increase of the area of the traverse section of the trunk, the production of commercial fruits per tre is increased in 1.9 kg×tree-1 and in consequence, the yield is increased in 12.5 t×ha-1.

The quality of non waxed (control) and waxed ‘Valencia’ oranges was evaluated during a storage at 2 °C and 6 °C, and after marketing conditions (20 °C for six days). Every week during the cold storage, the fruits were evaluated for: Maturity index (total soluble solids/titratable acidity), color (a/b ratio), weight loss, chilling injury (CI), and decay. The maturity as determined by the SST/TA ratio varied during storage at 2 and 6 °C, with values that ranged from 8.7 to 18.8 on the control, and from 10.9 to 17.6 on waxed oranges. Waxing reduce weight loss during cold storage and under marketing simulated conditions (except those fruits stored previously at 6 °C). A weight loss of 9.1 % was registered on the oranges after they were stored for ten weeks at 6 °C. Waxing did not reduce chilling injury (CI). The symptoms of chilling injuries began to appear on the waxed oranges after five weeks of being kept under temperatures ranging from 2 to 6 °C, with values of 14 and 2 %, respectively. Non-waxed fruits showed lower incidence for the same storage time. It was observed that these symptoms increased during cold storage, reaching values up to 46 % after 10 weeks at 2 °C. Higher CI values were observed when oranges were transferred to the simulated marketing conditions. Rotting incidence was low during cold storage. Rotting was not observed until the 9th week in up to 16 % of the non-waxed fruits. However, rotting notably increased when the oranges were transferred to environments with higher temperatures (20 °C) for 6 days, reaching values up to 60 % of the non-waxed fruits previously stored for 10 weeks at 2 °C. A lower rotting incidence was observed on waxed fruits during cold storage and simulated marketing conditions. CI is the most important quality disorder that limits the orange shelf life during low temperature storage.

Mexico is the world´s most important mango exporting country. Approximately 165,000 tons of mangos are exported every year. About 25 % of these exportations belong to the Tommy Atkins cultivar. Due to the fact that the price of mango depends on supply and demand, an early harvest can double or even triple its price. The ammonium and/or potassium nitrates have been used successfully to promote early flowering of several mango cultivars, but there is no success with the Tommy Atkins cultivar. Paclobutrazol (PBZ) has been applied as a soil drench, and has promoted early flowering in the Tommy Atkins cultivar for about 40 days. However, the United States has established a set or restrictions to use this substance due to its high persistence in soil, and because it has been identified as a possible cause of irrigation water pollutant, that could have tralocation in to the fruits. These facts may reduce this fruit exportation to the United States, which produces an income of 40 million dollars per year to Mexico. This research was established with the purpose of determining if PBZ’s residues affect the ‘Tommy Atkins’ mango fruits harvested from trees treated with this plant growth retardant. Commercial ‘Tommy Atkins’ orchards treated with PBZ during 1996, 1997 or during both years were sampled from the 1998’s mangos production season in the states of Michoacán and Colima. PBZ residues were identified by gas chromatography. No PBZ residues were detected when the treatment was applied for a year. When the treatment was applied during two consecutive years, very low levels of PBZ were detected (levels below the detection level).