In Chapingo, Mexico, two evaluations of potato genotypes were carried out in different years with the purpose of knowing the behavior of flowering and sexual seed production, and to determine the physiological quality of recently harvested seed. Number of flowers per plant, pollen viability, fruit set, and number of mature berries per plant varied widely among genotypes. Only between 10 and 31 % of genotypes, en each year of testing, had seed yields from 9 to 139 kg·ha-1, where cv. Tollocan was outstanding in seed number per berry and weight of 100 seeds were 242 and 32 mg, respectively. Due to dormancy, recently harvested seed only reached 79 and 72 % germination, respectively. Best seed physiological quality was shown by genotypes ‘San Jose’, ‘Greta’, ‘Tollocan’, ‘C-171836’, and ‘C-575049’.

In order to accelerate the introduction of new potato cultivars (Solanum tuberosum L.) with durable resistance to late blight (Phytophthora infestans Mont. De By), and within the framework of standard international field trials, in the summer of 1999 twenty five potato cultivars were planted in plots with and without fungicides in the Valley of Toluca, México. Plots without chemical protection against the disease showed final disease severities ranging from 5 to 15 % (‘Norteña’ and ‘Pampeana’-INTA, respectively) with no statistical differences in this parameter. There were differences among genotypes, though, when comparing the area under the disease progress curve. This provided evidence for the presence of the oomycete in spite of fungicide spraying. Tuber yields averaged 1200 g per plant for the highest yielding cultivar Stirling, and 100 g per plant for ‘Monserrate’; there were statistical differences among genotypes. In plots without fungicides the least disease severity (22 to 27 %) was observed in ‘Norteña’, ‘LBr-20’, ‘Cruza-148’, and ‘Idiafrit’. On the other hand, the highest incidences (90 to 100 %) occurred in ‘Pampeana’-INTA, ‘Teena’, and ‘Bionta’. ‘Stirling’, with 53 % final foliar infection, produced the highest yields (933 g per plant) in plots without fungicide, followed by ‘Norteña’ (22 % infection, 675 g per plant), and ‘Rosita’ (38 % infection, 418 g per plant). The rest of the materials yielded less than 350 g per plant, and no direct relationship was detected between degree of disease severity and tuber yield. That is, genotypes resistant to the disease did not necessarily yield the most.

Water productivity and watermelon (Citrullus lanatus Thunb.) yield were measured as quantity of fruit produced (kg) per unit of water consumed (m3) in plots established by direct sowing (SD) or transplant, with or without plastic mulch, and irrigated considering two irrigation criteria using underground drip irrigation. Results show that establishing the crop by transplanting at “initial handlebar” (IG) or “two true leaves” (HV) stages, with plastic mulch (CA), and irrigated at 50 % pan evaporation (E), productivity was 9.0 and 9.1 kg×m-3, respectively. In contrast, crop established by direct sowing, without mulch, and irrigated at 50 % E had a water productivity of 4.0 kg×m-3. The highest fruit yields of 52.0 and 51.5 t×ha-1 were obtained in plots established with HV and IG respectively, with mulch, and irrigated at 60 % E. The lowest yield (22.7 t×ha-1) was obtained in plots established by direct sowing, no mulch, and irrigated at 60 % E. Plastic mulch allowed harvest to begin seven days earlier than control treatments. Using transplant at IG allowed harvest to begin 7 to 14 days earlier than transplant at HV or SD, and 22 days earlier than treatments with direct sowing and no plastic mulch.

In this study, resistance to single and mixed infections to pepper golden mosaic virus (PepGMV) in Capsicum chinense Jacq. individuals were evaluated. Plant inoculation was carried out by biolistics and grafting. To 140 plants from seven accessions of C. chinense Jacq., inoculations were preformed with PepGMV. Of these plants, 99 were asymptomatic, although the virus was detected by ELISA and PCR techniques. Additionally, resistance to geminivirus (PepGMV and Pepper huasteco virus or PHV) mixed infections, was evaluated in these accessions. Thirty-one plants from the accessions with the best characteristics of resistance to single infections by PepGMV were evaluated, and 15 individuals displayed resistance in different degrees. Resistance to geminivirus mixed infections was grouped as: delayed symptoms, symptom remission and asymptomatic plants. DNA levels of both geminiviruses correlated positively with symptom severity.

IIn this study the effect of gamma rays on bulbs of Tigridia pavonia (L.f.) D.C. variety Sandra was determined. The bulbs were irradiated in the Gammacell 220 in the Instituto Nacional de Investigaciones Nucleares (ININ). The doses were 0, 5, 10, 15, 20, 25 and 30 Gy. The experiment was established in a rustic greenhouse at Campus Universitario El Cerrillo, Toluca, México. The experimental design was completely randomized with three replications (7 x 3 = 21 experimental units), with a total 336 bulbs. The results indicated that gamma rays affected: a) days to emergence, b) plant height, c) number of stems per plant, d) stem length, e) number of leaves per stem, f) leaf length, g) number of stems per bulb, h) number of flowers per bulb, and i) flower diameter. The gamma rays did not affect: a) days to flower stem apparition, b) number of branches per stem and c) number of fruits per flower stem. Doses higher than 15 Gy induced deformation of flowers. Three color mutations were observed in Tigridia pavonia generated by irradiation between 15 and 25 Gy.

With the purpose to study the lack of seed germination in Annona purpurea Moc y Seesé, mature seeds were immersed during five days in a solutions of GA3 (0, 100, 500 and 1000 mg·liter-1). Seed germination and seedling development was evaluated under greenhouse conditions. Gibberellins and ABA in seeds were measured using the lettuce hypocotyl bioassay whereas identification of endogenous gibberellins was conducted using the gas chromatography and mass spectrometry technique. It was found that any concentration of GA3 promotes seed germination. Control seed showed 8 % of total germination whereas GA3 treatments showed 55.3, 62 and 68 % at 100, 500 and 1,000 mg·liter-1 respectively. Seedling development showed the same pattern as in seeds germination. Control plants reached a final height of 0.32 mm in comparison with 44.4, 65.3 and 71.2 mm with 100, 500 and 1,000 mg·liter-1 of GA3, respectively. More gibberellin activity than ABA was found in seeds although not enough to provoke germination. Gibberellins A1, A20, and A53 were identified. It is concluded that the lack of seed germination in Annona purpurea Moc. Sossé is related to low levels of endogenous gibberellins in seeds.

Rootstocks ‘Volkamerian’ lemon (Citrus volkameriana Pasq.), ‘Cleopatra’ tangerine (C. reshni Hort. ex Tanaka), and ‘Amplycarpa’ tangerine (C. amblycarpa Oche) are tolerant to Citrus Tristeza Closterovirus and could be utilized to substitute sour orange (C. aurnatium L. Osbeck). We studied fruit characteristics, polyembryony, and the relationship between them in three rootstocks (‘Volkamerian’ lemon, and ‘Cleopatra’ and ‘Amblycarpa’ tangerines) in fruits harvested in the fall-winter periods of 1998-1999 and 1999-2000. ‘Volkamerian’ lemon presented 154.7 g fruits with 8 to 10 carpels, and 37.9 % polyembryony with 2 to 5 embryos per seed. ‘Cleopatra’ tangerine fruits weighed 74.8 g, with 10 to 14 carpels, and 84.8 % polyembryony with 1 to 26 embryos; and ‘Amblycarp’ tangerines weighed 20.1 g, with 7 to 11 carpels, and 82.1 % polyembryony with 2 to 15 embryos per seed. Fruit morphological characteristics and polyembryony varied according to rootstock and harvest year. The latter significantly affected ‘Volkamerian’ lemon and ‘Cleopatra’ tangerine, but not ‘Amblycarpa’. Number of embryos per seed showed high correlation to number of carpels; while embryo length was positively correlated to fruit weight and equatorial diameter, but negatively to number of embryos.

En un ambiente subtropical se estudió en Spondias purpurea L. la variación diurna en las tasas instantáneas de asimilación neta de CO2 (An) y conductancia estomática (Ce) y su relación con el flujo fotónico fotosintético (PPF) y la temperatura del aire (TA) durante el verano de 1998. Las hojas de S. purpurea L. son delgadas (137.0 µm); esta característica foliar está asociada con ambientes con baja disponibilidad de luz. Los valores diarios del PPF en campo abierto fueron 49.01 mol·m-2·día-1 en julio; 42.12 mol·m-2·día-1 en agosto y 16.73 mol·m-2·día-1 en septiembre; sin embargo, 80 % de los valores de An fueron registrados con niveles bajos de PPF (<500 μmol•m-2•s-1), e inferiores al punto de saturación lumínica (660 μmol•m-2•s-1). No obstante, en algunas hojas se registraron valores de An que oscilaron de 10 a 20 μmol•m-2•s-1. Las tasas más altas de An fueron de 10.7 μmol•m-2•s-1 en julio, 16.2 μmol•m-2•s-1 en agosto y 7.5 μmol•m-2•s-1 en septiembre. Los patrones de asimilación neta diaria de CO2 mostraron que la An se incrementó durante la mañana, disminuyendo al atardecer. No se encontró relación entre la reducción durante el día de la An con Ce, TA y PPF. Los valores de asimilación neta diaria de CO2 fueron de 359 mmol•m-2•día-1 en julio; 647 mmol•m-2•día-1 en agosto y 200 mmol•m-2•día-1 en septiembre. Los valores de An registrados en S. purpurea L. son cercanos a los más altos reportados para árboles tropicales. La ganancia de carbono registrada en S. purpurea L. puede ser considerada alta, no obstante que esta especie prospera en suelos pedregosos de baja fertilidad, con un manejo agronómico mínimo.

A research was conducted in Arteaga, Coahuila, Mexico in 2002 with the purpose of evaluating the effect of the retardant prohexadione-Ca on vegetative and reproductive growth of apple trees. Applications of this compound were done in the spring of 2002, when new buds reached a length of 5 cm, with 0, 125, 175, and 250 mg·liter-1 on cultivars Royal Gala and Golden Delicious. A second application with the same concentrations was carried out 15 days after the first spraying. Results showed that the three concentrations used for this retardant had a noticeable reduction in branch growth and internode length for both cultivars. The number of leaves per branch decreased for both cultivars at all concentrations; however, petiole length tended to decrease without significant effect. Fruit setting was higher at concentrations of 175 and 250 mg·liter-1 in ‘Royal Gala’ while this was observed for ‘Golden Delicious’ only at 250 mg·liter-1. Different concentrations of the retardant caused a higher production per tree in both cultivars. At harvest, fruit weight and radius tended to be higher for the control; while fruits treated with prohexadione-Ca showed a lower content of total soluble solids and higher firmness in both cultivars. We concluded that prohexadione-Ca, at different concentrations studied in apple cultivars Royal Gala and Golden Delicious, reduces vegetative growth, increases fruit production per tree, reduces total soluble solids content, and increases firmness of harvested fruits.

Substrates used in commercial seedling production are made from peat moss and pine bark; however, in different agricultural regions substrates are obtained from local by-products. Chemical analysis of mineral content and availability in organic substrates has been difficult. There are no standardized methods of analysis and methodologies used in the analysis as mineral soils analysis are used, resulting in imprecise data and erroneous interpretation. In this study, mixtures of three kinds of substrates: hog manure, sisal pulp and soil, were used as substrate to obtain papaya seedlings. The objectives were: to analyze the content of macronutrients using three chemical methods: total contents, water soluble elements, and those extractable by chemical agents; with these a ratio between concentration and availability was obtained and to determine the best mixture of sisal pulp, hog manure and Rodic Luvisol soil for use as substrate for the development of papaya seedlings in nursery. A better relationship resulted when K was analyzed with the soluble method; P and Mg by the three methods, and Ca did not have a positive relationship with any of the methods. Total N results were used to obtain the C:N ratio, which had an inverse relationship with biomass production. The best mixtures for seedling production were all those containing 25 to 100 percent hog manure.

Performance of ‘Brazos’, ‘Comanche’, and ‘Cherokee’ blackberry was studied in tropical conditions in Santiago Ixcuintla, Nayarit, Mexico. In this environment, and without the application of stimulants for budbreak, blackberry showed good development and vegetative growth. The latter occurs all year long, and plants do not show a dormancy period. ‘Brazos’ produces up to 20.7 lateral shoots per plant, while ‘Cherokee’ produces 13.8 and ‘Comanche’ 9.7. Flowering and production occur from April to September, and average yield per plant is 1.5 to 2 kg year-1 in cultivars Cherokee and Brazos, and less than one kilogram for cv. Comanche. Soluble solids content was 10.5 °Brix for ‘Comanche’, 8.5 for ‘Brazos’, and 8.7 for ‘Cherokee’.

Two experiments were conducted in a Mexican lime [Citrus aurantifolia (Christm) Swingle] orchards in Tecomán, Colima, México to compare the effectiveness of several insecticides in the control of citrus leafminer (Phyllocnistis citrella Stainton) and to compare different concentrations of Abamectin to Diaflubenzuron and Clorpirifos. In the first experiment nine insecticides were sprayed on the foliage. Abamectin and Imidacloprid greatly reduced the number of live larvae and pupae and were superior to the other products. In the second experiment, the treatments evaluated in two sites (El Llano and Cerrito de Aguilar) were 1.8 % Abamectin CE in concentrations of 300, 400, and 500 ml·ha-1 plus mineral oil, Diaflubenzuron 0.5 kg·ha-1, Clorpirifos 48 % 3.0 liter·ha-1, and an absolute control. In the El Llano site, the applications of the insecticides reduced the number of live larvae by 80 and 98 %, compared to the control. Where Abamectin was applied there was a reduction of 86 to 89 % in percentage of deformed leaves and 85 to 88 % in percentage of mined leaf area, relative to the control. Diaflubenzuron reduced percentage of deformed leaves by 68 % and percentage of mined leaves by 72 %. However, Abamectin and Diaflubenzuron were statistically equal in these variables. Cloropirifos was the least effective. Although in the Cerrito de Aguilar site there was less leaf miner infestation than in El Llano, the performance of the treatments was similar. A single application of Abamectin or Diaflubenzuron was sufficient to protect a surge of vegetative budding infested with leaf miner. There were no differences among the treatments with Abamectin, and a lower concentration can be recommended for application, alternating with Diaflubenzuron on 5- to 7-day-old vegetative buds.

We evaluated levels of ascorbic acid, b-carotene, lycopene, and total carotenoid concentration in guava fruits from the cultivar Hawaii-74 and the clone Java. Fruits were harvested at the physiological maturity state and stored at 20 °C and ± 85 % relative humidity to simulate marketing conditions. Ascorbic acid content increased throughout storage in both types of guava, where cv. Hawaii-74 and clone Java reached values of 130 and 230 mg×100 g-1 of fresh weight (f.w.), respectively, at the end of the study. The highest concentration of b-carotene was quantified at harvest, with values of 56.4 and 42.2 µg×100 g-1 of f.w. in the fruits of cv. Hawaii-74 and clone Java. b-carotene degraded during storage; fruits of cv. Hawaii-74 lost 98.7 % at 10 days, while fruits from clone Java lost it entirely at the second day of storage. During maturation, lycopene content increased only for cv. Hawaii-74, reaching 8.2 mg×100 g-1 by day 10. Ninety five percent of carotenoids present in these guava fruits was due to lycopene content.

In this research, the mechanical behavior of papaya fruits cv. Maradol Roja under static compression was analyzed. The mechanical variables determined were stress relaxation and strain relaxation. Testing of stress relaxation consisted of subjecting the fruits to constant deformation of 5 % with an Instron Universal Testing Machine Model 1130 and registering the decrease in stress as a function of time. In this case, relaxation time (time taken to decrease the initial stress 36.8 %) and relaxation range were registered. For strain relaxation, the fruits were deformed with static compression of 250 N during 24 hours with a compress-meter. In this test the increase of the deformation as a time function was registered. In each experiment three maturity stages (M1, Chroma 16.1; M2, Chroma 22.0 and M3, Chroma 27.7), and three compression positions (horizontal, vertical and inclined) were evaluated. Fruits in M1 and M2 stages had the highest values in relaxation time and the lowest values in relaxation range; these parameters indicate that the fruits in M1 and M2 had more resistance to compression, relative to fruits in M3 stage. Fruits in horizontal position registered the lowest index of relaxation and more resistance to static compression, with relationship to vertical and incline positions.