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F.M. del Amor, V. Martinez and A. Cerdá

The shortage of good quality water in semiarid zones necessitates the use of saline water for irrigation. In order to simulate the usage of brackish irrigation water in greenhouse melon (Cucumis melo L. cv. Galia) culture in perlite, plants were supplied with nutrient solutions containing 0 (control), 20, 40, and 60 mm NaCl applied at four different times. Treatments were applied during early vegetative growth [14 days after transplanting (DAT)], beginning of flowering (37 DAT), beginning of fruit set (56 DAT), and beginning of fruit ripening (71 DAT). All vegetative and fruit yield parameters were significantly reduced when salinization was started 14 DAT. This inhibitory effect of salinity was progressively lessened when salinity was imposed at later dates. This suggests that the response of melons to salinity depends on the duration of exposure to saline water. Salinity treatments increased fruit reducing sugars, acidity, and total soluble solids. Fruit yield reduction at each salinization time was correlated with salinity levels, but there was some evidence of a nutrient imbalance, since leaf concentrations of N-NO3, and especially K, were low at higher salinities. These results indicate that brackish waters can be used for growing melon with minimum yield losses if concentration and duration of exposure are carefully monitored.

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F.M. del Amor, V. Martinez and A. Cerdá

In order to simulate the usage of brackish irrigation water in greenhouse tomato (Lycopersicum esculentum Mill. cv. Daniela) culture in perlite, plants were supplied with nutrient solutions containing 0, 20, 40, and 60 mm NaCl. The three highest salinity treatments were applied at three different plant growth stages, during early vegetative growth [16 days after transplanting, (DAT)], beginning of flowering (36 DAT), and starting fruit development (66 DAT). Salt tolerance of tomato plants increased when the application of salinity was delayed. Salinity significantly decreased size and number of marketable fruits, but increased fruit quality by increasing total soluble solids and sugar content. Leaf and fruit calcium and potassium concentrations were decreased significantly by increasing salinity levels. This was compensated for the accumulation of sodium. Anion accumulation was increased by increasing chloride concentration. These results indicate that it is feasible to use brackish water for growing tomato with minimum yield losses if salt concentration and duration of exposure are carefully monitored.

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A. Rascon-Chu, A.A. Gardea, V. Guerrero-P, J. Martinez-T, C. Rivera and R. Garcia

The effect of epiphytic bacteria population with different ice nucleation activity (INA) on the extent of supercooling of in vitro and leaf tissue disks of greenhouse-grown Capsicum annuum L. plants was determined. Bacterial strains were isolated on PDA and King's B medium from foliar samples of weeds from commercial apple orchards in Cuauhtemoc, Chihuahua, Mexico. Bacteria were screened by colony morphology, fluorescence under UV light, while growin on King's B medium plates and screened for ice-nucleating capability at -5 °C in suspensions of 108 cfu/mL. Ice nucleating (Ice+) and non-ice-nucleating (Ice-) active strains with fluorescent capacity were isolated from symptomless leaf samples. Four bacterial strains were used with different ina as epiphytic population models. Two Pseudomonas syringae strains, Pss29A and PD, from Oregon State Univ., with high Ice+ capability; P. fluorescens A-506, in its Blight Ban™ commercial lyophilized presentation; and UC001, a native fluorescent strain from CIAD-Cuauhtemoc; both Ice-strains. Freezing tests were carried out under controlled conditions. The high Ice+ strains Pss29A and PD increased the temperature of supercooling 2 and 1 °C compared to control samples. The non-inoculated tissue showed damage over 50% at -3 °C and below. Inoculated tissue with Ice+ strains (P. syringae 29A and PD), showed damage superior to 50% at -1 and -2 °C, respectively. Conversely, at none of the temperatures assayed, Ice-strains surpassed 50% damage. These results are of interest for further development of passive strategies towards minimizing damage due to low-temperature exposure of tropical vegetable crops.

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Ángel V. Domínguez-May, Mildred Carrillo-Pech, Felipe A. Barredo-Pool, Manuel Martínez-Estévez, Rosa Y. Us-Camas, Oscar A. Moreno-Valenzuela and Ileana Echevarría-Machado

Amino acids, a major fraction of the low-molecular-weight organic nitrogen in soil, act as signaling molecules that indicate the presence of nutrient-rich patches to the roots. To characterize the effects of amino acids on root growth, we used seedlings of habanero pepper (Capsicum chinense), one of the most widely cultivated annual spice crops in the world. We tested the effect of L-glutamate, L-aspartate, and glycine on the primary root of seedlings grown aseptically under different conditions of pH and light. L-glutamate and L-aspartate did not inhibit the root growth of habanero pepper. In contrast, glycine inhibited the growth of roots, stimulated root hair growth, and induced a significant accumulation of starch grains in the root apex. The use of aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis, and the evaluation of 1-aminocyclopropane-1-carboxylic acid oxidase expression provided evidence of a role for ethylene in the root responses to glycine. We suggest that these changes in the root apex in response to exogenous glycine could be an important adaptive response that allows plants to efficiently access the fluctuating availability of nutrients in the soil.

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J. Llamas, A.A. Gardea, J.J. Martinez-Tellez, V. Guerrero-P, E. Carvajal-Millan, J.A. Orozco and A. Rascon-Chu

Potted 1-year-old `Starking Spur' and `Golden Delicious' trees on MM.106 were used to characterize the metabolic changes in lateral buds and rrots during their transition from para- to endodormancy. Sampling period was from 4 Sept. to 25 Nov. 1999 at 10-day intervals. Well-formed lateral buds were collected from the apical section of current growth; while root samples were white rootlets. Isothermal calorimetry at 25 °C was used to evaluated metabolic activity (q), respiration rate (RCO2), metabolic efficiency (q/RCO2), and growth rate (RSG·ΔHB). In both cultivars, q from buds showed significant differences (P ≤ 0.05) among sampling dates; `Starking' rose from 1.8 to 3.7 μW/mg dry weight (dw), while in `Golden' change was from 2.1 to 3.3 μW/mg dw. RCO2, q/RCO2, and RSG·ΔHB showed a pattern similar to q. On each sampling date, cuttings were also forced to break and, in all dates, buds broke after 21 days, demonstrating a paradormant condition. MM.106 root tips q behave differently depending on the variety they were grafted on to. When grafted with `Starking', root tips produced a small, but significant, increase in q (from 9.1 to 15.7 μW/mg dw) as the season progressed. RCO2 and RSG·ΔHB behaved similarly, increasing from 27.6 to 57.6 mmol CO2/mg dw and 3.4 to 8.3 μW/mg dw, respectively. These conditions agreed with a dynamic root growth. A small decrease in q/RCO2 was observed. However, when grafted with `Golden' root tips metabolic responses did not increase; furthermore, q decreased while RCO2, q/RCO2, and RSG·ΔHB did not show a defined pattern. Four complete 2-year-old trees of each variety, kept in 1-m3 containers, were sampled. The relation of root/wood dry matter was estimated, with difference found between varieties.