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Y. M. Moreno, A. A. Gardea and A. N. Azarenko

`Lovell' peach seeds were stratified for 0 to 13 weeks at 4C under moist conditions. Heat of metabolism and CO2 evolution, measured by Differential Scanning Calorimetry, increased with stratification time. The calorespirometric ratio increased between 0 and 6 weeks and then remained constant until 13 weeks. Germination percentages paralleled this ratio and reached 80% only after 6 weeks of stratification.

After radicle emergence, seedlings from different stratification treatments were grown for 3 weeks. Increasing stratification time resulted in taller seedling growth. Calorimetrically measured CO2, evolution and the calorespirometric ratio of the apex (one cm) of the seedling increased with longer stratification time. Contrary to the observations of the seeds, metabolic heat rates decreased as stratification time increased. Yet, seedling sustained higher growth rates. These data suggest that the stratification treatment resulted in an improvement in metabolic efficiency.

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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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E. Carvajel-Millan, A.A. Gardea, V. Guerrero-P, F. Goycoolea and C. Rivera

Apple embryos from moist seeds kept at 4 °C were used for a calorimetric characterization of Red and Golden Delicious apple seed dormancy. Seeds were sampled at 100-h intervals during 1200 h. The metabolic response of such samples was compared to that from chilled Golden Delicious seeds (>1200 h) stored under controlled atmosphere (CA). Isothermal calorimetry at 25 °C, evaluated metabolic activity (q), respiration rate (RCO2), metabolic 65 °C estimated activation energy (Ea) in a 10 to 20 °C range, and respiration coefficients (Q10) from 10 to 50 °C at 10 °C intervals. Data showed a direct relationship between chilling exposure and embryo metabolic responses from both cultivars. Once chilling requirement was satisfied, Red and Golden Delicious seeds presented a significant increase (P ≤ 0.05) in q, 0.94 and 0.98 μW/mg dry weight (dw); RCO2, 9.9 and 7.6 mmol CO2/mg dw; and RSG·ΔHB, 3.6 and 2.5 μW/mg dw, respectively. On the other hand, q/RCO2 did not follow a definite pattern, neither in Red nor Golden Delicious cultivars. Ea decreased 19.2 and 23.4 J/mol per °K per mg dw in Red and Golden Delicious, respectively, as a function of seed chilling. Q10 showed a significant response to temperature, but not to chilling exposure. Golden Delcious seeds from CA showed a significant reduction on q, RCO2, and RSG·ΔHB of 0.28 μW/mg dw, 2.47 mmol CO2/mg dw, and 14 μW/mg dw, respectively. Results show that calorimetry is a sufficiently sensitive, fast, and precise tool to quantify metabolic responses during seed chilling, as evolving energy.

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J. Antonio Orozco, A.A. Gardea, E. Valenzuela, V. Guerrero-P and E. Carvajal-Millan

Table grapes grown in the Sonoran Desert of Mexico are mostly an export commodity directed to early season markets. In order to define the effect on canopy management on light use and berry ripening, `Perlette' vines planted along eastwest rows (typical in such a region) were trained under four systems: slanted pergolas (SP), CIAD, lyre (LY), and T-trellis with open canopies (TTOC). They were compared with traditional closed-canopy T-trellis (TT). Variables evaluated were photosynthetic active radiation (PAR), photosynthesis (PH), stomatal resistance (SR), chlorophyll content (CC), and berry total soluble solids (TSS). At harvest, PAR values for LY, SP, CIAD, TTOD, and TT were 2192, 2076, 1900, 885, and 771 μmol·m-2·s-1, respectively. In the same order, PH at veraison was 12.5, 12.7, 11.0, 10.5, and 5.1 μmol CO2/m2 per s, while in recently harvest vines it decreased to 9, 9, 8.1, 5.1, and 3.7 μmol CO2/m2 per s. SR at veraison was 3.4, 2.6, 2.8, 3.9, and 4.2 s/cm, but, after harvest it was 2.5, 3.5, 2.3, .2.9, and 6.8 s/cm. No significant differences in CC were found among treatments. TSS on 27 Apr. reached 14.9, 15.3, 15.7, 14.5, and 12.2 °Brix; on 29 Apr. they increased to 15.9, 15.5, 16.3, 15.1, and 13.1 °Brix. Based on the above, we demonstrated that canopy management and sunlight cropping represent a useful tool to advance table grape ripening, thus allowing an early harvest and therefore access to the high prices typical of early season markets.

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A.R. Dixon, R.B. Boone, A. Gardea, L.S. Daley and T.L. Righetti

A microcomputer-based image processing system was used to simplify the large number of visual comparisons required to identify various Corylus spp., cultivars, and clonal accessions using polyacrylamide gel electrophoresis isozyme patterns. Photographs of gels stained for peroxidase, acid phosphatase, and phenol oxidase were digitally captured and selected lanes were enhanced and scanned. The scan data were analyzed to locate bands and normalize their position to that of standards. Such data were plotted and a computer-generated isozyme pattern was displayed. Compressed image data were then stored in a database for subsequent automated isozyme pattern comparisons. Photographic records that were previously used in published reports were reevaluated with the computerized system. Species, cultivars, or clones that were characterized in visual evaluations were similarly characterized using the computer method. Computer evaluations usually identified more bands. Band positions were only rarely different and probably resulted from better normalization relative to standard bands when using the computerized procedure.

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A.A. Gardea, Y.M. Moreno, A.N. Azarenko, P.B. Lombard, L.S. Daley and R.S. Criddle

The pattern of respiratory changes during dormancy and development of `Pinot noir' primary grape (Vitis vinifera L.) buds through the broken-bud stage was determined using differential scanning calorimetry. Metabolic heat rates [μJ·s-1·mg-1 dry weight (dw)] decreased during endodormancy and increased during ecodormancy and bud development. Respiration of ecodormant buds was at its minimum (≈1 μJ·s-1·mg-1 dw) in January. Respiration steadily increased, beginning in February and continuing as buds passed through the four developmental stages: ecodormant, initial swelling, fully swollen, and broken bud. Heat of metabolism increased from 5 to 18, 28, and 29 μJ·s-1·mg-1 dw as the buds developed from ecodormant to broken-bud stage. Carbon dioxide evolution from respiring buds increased from 15.9 to 22.2, 57.9, and 68.3 × 10-6 μmol·s-1·mg-1 dw as bud development advanced. Metabolic inefficiency, as quantified by heat (kJ) released per CO2 (mol) produced, was lowest in ecodormant buds, then increased at initial bud swelling and declined again in fully swollen and broken buds. The temperature coefficient of metabolism (μ) [apparent activation energy (Ea)/gas constant (R)] was lower at low temperatures (5 to 15C) in ecodormant buds than at the three more advanced stages. At higher temperatures (20 to 35C), buds at the ecodormant and initial swelling stages had a higher μ than the fully swollen and broken buds. These results suggest there may be a major change in metabolic pathways between the ecodormant bud stage and bud swelling.

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A. A. Gardea, Y. M. Moreno, A. N. Azarenko, P. B. Lombard, L. S. Daley and R. S. Criddle

The increasing respiration of breaking `Pinot Noir' buds was measured by Differential Scanning Calorimetry. Bud development was classified into ecodormant, initial swelling, fully swollen, and breaking buds. Metabolic and CO2 evolution heat rates increased as the buds developed. Activation energy decreased steadily as development proceeded, which implied that less energy was required for metabolism to continue at later bud stages. A decrease in metabolic efficiency noted by a low calorespirometric ratio was observed during the transition from ecodormant to the initial swelling stage. From the second stage on, metabolic efficiency increased. The responsive nature of grape buds to warm temperatures was explained by increasing Q10 (10-20C) values from 2.8 to 3.8, 3.2, and 3.6 for the four developmental stages described above.

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A. A. Gardea, P. B. Lombard, R. L. Kohnert, A. N. Azarenko, Y. M. Moreno and L. S. Daley

Changes in water content of `Pinot Noir' endo- and ecodormant primary buds were gravimetrically partitioned into extracellular (ECW) and intracellular water (ICW). During endodormancy, water status remained unchanged with values of 0.6 and 0.1 mg/mg dw for ICW and ECW, respectively. Ecodormant buds, prior to budbreak, increased in ICW from 0.5 to 4.4 mg/mg dry weight for Jan. and Apr., respectively. Liquid water in the buds was determined by H-NMR. The spin-spin relaxation time (T2) at -30C represented the bound fraction, which peaked in Jan. at 0.3 mg/mg dw followed by a decrease to 0.2 mg/mg dw in March. During the dormant season the free fraction was always larger than the bound fraction. No vascular connection between bud and stem was observed by mid Jan. Changes in bound water indicated that there is a transient fraction changing to the free form. These changes were not strictly related to the bud's dormancy status.

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R. Báez-Sañudo, E. Bringas, J. Mercado, M. Báez, J. Siller and A. Gardea

Dehydration limits bell pepper postharvest life. Research had focused on waxes and individual sealed packages used to prolong shelf-life. Even though, the fruit natural package -the cuticle- is unknown; besides, cuticle functions as a barrier to protect fruits against excessive water loss. The objective of this work was to characterize cuticle changes and their relationships with fruit quality during postharvest handling. Green `Wonder' bell peppers were stored under marketing conditions (20C; 65-70% RH). Following cuticle isolation determinations included weight changes (CW), permeability and soluble cuticular lipids (SCL). In addition, quality characteristics like firmness, total soluble solids (TSS), titratable acidity (TA) and CO2 production were monitored every other day. CW and SCL decreased from 2798 to 1398 and 145 to 48 μg/cm2, respectively. Permeability was also reduced from 11 to 10 mg/cm2*h. CO2 climateric was reached between the 9 and 12th day peaking with 25 mg/kg*h. Firmness decreased from 2.1 to 1.1 Kg*f, while no noticeable changes were observed on TSS and TA.

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Alfonso A. Gardea, Miguel Martinez, Alfonso Sánchez, Manuel Báez and Gustavo González

Weight loss and dehydration arc major problems limiting shelf life of early-season seedless grapes grown in the Sonoran Desert. This research was conducted to assess conditions improving cluster performance in cold storage (4C±1,. 90% R.H.). Clusters were packed: 1) loose, 2) wrapped in perforated plastic bags, 3) loose and water supplement added, and 4) in plastic bags + water supplement. After 12 days in storage, weight losses accounted for 7.0, 5.6, 8.5, and 4.0% of initial fresh weight for treatments in ascending order. In another experiment, individual clusters were stored in modified atmospheres using a high gas-permeability film with two different gas-exchange areas of 25 and 75 mm2. Cluster weight and gas composition significantly interacted with storage period. During the first 30 days, weight loss was not higher than 0.5% on every sampling date. Gas composition was affected by the effective exchange area After 47 days, CO2 concentration was 2.22% and 0.8% in the 25 and 75mm2 treatments. At any given time, oxygen content followed the opposite trend with final values of 18.9 and 20.0% for the same treatments. Although cluster quality was highly preserved, eventually rots developed.