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Baby salad leaves of salad roquette, arugula in the U.S. (Eruca vesicaria ssp. sativa) had an increased postharvest shelf life of 2 to 6 days, while lollo rosso lettuce (Lactuca sativa L. `Ravita') and red chard [Beta vulgaris L. var. flavescens (Lam.) Lam] baby salad leaves had increased shelf life of 1 to 2 days when harvested at the end of the day compared with leaves harvested at the start of the day. We have shown that improved shelf life of salad roquette and lollo rosso following end-of-day harvest was correlated with altered biophysical characteristics of the cell walls, with increased cell wall extensibility (percent plasticity and elasticity) measured at end of day. Leaf turgor pressure (P, MPa) was also highest in salad roquette and red chard at the end of day. Improved shelf life following `end of day' harvest was also associated with the accumulation of leaf sucrose in salad roquette but not lollo rosso and red chard following daily photosynthesis. Diurnal alterations of leaf starch concentration were detected in lollo rosso and red chard but not in salad roquette. The degree of leaf shelf life extension in salad roquette and red chard was further associated with the peak rates of leaf photosynthetic activity. These data suggest that, depending on species, significant improvements to postharvest shelf life could be achieved through the rescheduling of time of day for harvest and also provide relevant information on the selection of traits for future genetic improvement.
Grapes grown in West Texas are especially susceptible to freeze damage during spring deacclimation and budbreak. This experiment was undertaken to evaluate whether refrigeration of the root zone would delay budbreak in two grape cultivars, `Chardonnay' and `Cabernet Sauvignon'. The experiment was conducted under greenhouse conditions using 1-year-old grafted plants planted into containers in water bath chillers to cool the root zone. Three root-zone temperatures were maintained: 7.2 °C, 1.7 °C, and a nonchilled control. The experiment followed a randomized split plot, with main plots being temperatures and the sub-plots being genotype, and the experiment was repeated once. Evaluation of budbreak was performed on a daily basis. Other data collected included shoot dry weight and root dry weight with soil, water, and air temperatures recorded using type T thermocouples (copper-constantan) attached to a datalogger. The experiments indicated that budbreak could be delayed in both varieties by the refrigeration of the root zone by an average of 1 to 2 days when comparing the 1.7 °C treatment with the nonchilled control. The refrigerated treatments of `Chardonnay' also tended to show a prolonged budbreak over time. This finding may be significant since `Chardonnay' generally exhibits budbreak relatively early compared to other grape varieties and a prolonged budbreak may allow some buds to escape spring frost injury.
Abstract
Isozyme phenotypes were used to identify two (P2 and P3) of the six monosomic alien addition lines that have been isolated from a Cucurbita moschata × C. palmata hybrid. Phenotype P2 displayed the C. palmata fumarase isozyme, whereas P3 exhibited two glucose phosphate isomerases and an aspartate aminotransferase derived from C. palmata. P2 also possessed the hard rind trait characteristic of C. palmata. Both the biochemical and the morphological phenotypes were inherited in a non-Mendelian fashion, and no recombination was observed within either the P2 or P3 set of characters. It was concluded that the loci coding fumarase and hard rind were situated on the alien chromosome in P2 trisomics and that the other three loci were on a 2nd C. palmata chromosome possessed by the P3 line. The loci responsible for other C. palmata isozymes either were not expressed or were not located on any of the five C. palmata chromosomes represented in the alien addition lines.
The use of potential evapotranspiration (PET) estimates to identify irrigation timing for greenhouse tomatoes (Lycopersicon esculentum Mill.) grown in peat-based substrate was evaluated for a spring and fall crop. PET (using the Penman equation) was calculated from leaf, wet and dry bulb temperatures, and incident and reflected photosynthetic photon flux. Substrate matric potential (SMP) was monitored continuously using electronic tensiometers. Two irrigation starting setpoints (-4.5 and -6.5 kPa SMP) and two nutrient solution electrical conductivity (EC) treatments (1.5 and 3.0 dS·m-1) were factorially combined in a completely randomized design. Irrigation frequency was greater in treatments irrigated at -4.5 than at -6.5 kPa. The integral of calculated PET values was correlated with SMP for both experiments. Accumulated PET values were higher at the start of irrigation in the -6.5-kPa treatments for spring and fall crops. Nutrient solution EC did not influence irrigation frequency. Leaf pressure potential (LPP) was correlated to PET-predicted LPP (r 2 > 0.56) in plants subjected to high EC, low (-6.5 kPa) matric potential setpoint, or both treatments. PET and electronic tensiometer technology can be used jointly to improve irrigation management for tomatoes grown in peat-based substrates by more accurately responding to crop needs for water and nutrients.
Abstract
Ethylene dibromide (EDB) fumigation of fruit of tomato (Lycopersicon esculentum Mill.) reduced red color development in the outer pericarp, although the inner tissues remained unaffected at EDB doses as high as 35 g/m3. Carotene accumulation was enhanced by EDB at 4 g/m3, but at higher doses the carotene content of the tomato pericarp was reduced. Skin puncture force was reduced in green fruit fumigated at 4 g/m3, but not in breaker or pink fruit; higher skin puncture forces were recorded at higher doses for the three fruit maturities tested, EDB stimulated the respiration of preclimacteric fruit, but fruit fumigated just prior to the climacteric showed a normal respiration peak, although a 4 g/m3 treatment resulted in partial climacteric respiratory rise.
An automatic irrigation system was designed for use on green-house tomatoes growing in peat-based substrates. This system uses electronic tensiometers to monitor continuously substrate matric potential (SMP) in peat-bags. The system also uses the Penman equation to evaluate potential evapotranspiration (PET) through the acquisition of many greenhouse environmental parameters. Through a series of linear equations, estimates of PET are used in a computer-controller system to vary the electrical conductivity (EC) of irrigated nutrient solutions, as well as SMP setpoints at which irrigations are started. Such modifications to current irrigation management systems may improve fruit quality and reduce the risk of water stress during periods of high PET by irrigating more frequently with less-concentrated nutrient solutions. Conversely, during periods of low PET, irrigation is less frequent with more-concentrated nutrient solutions. Although no differences were found in fruit number or overall yield using variable nutrient solution EC, plant fresh weight was higher in those treatments. It is concluded that an integrated tensiometer-PET system may give increased precision to irrigation management and the control of crop growth in the greenhouse.
This paper describes the climatic and cropping conditions in the major peach [Prunus persica (L.) Batsch] producing areas in the southeastern United States in 1996. The peach and nectarine crop was the smallest since 1955 due to a series of unusually cold temperatures in February, March, and April. Crop set was not strictly a function of late blooming. No variety produced a full crop across the region. Many reputedly hardy peaches cropped poorly. The only peach or nectarine varieties that produced substantial crops in multiple locations were `La Premiere', `Ruston Red', and `Contender'. Cropping ability of some breeding selections shows that peach frost tolerance may be improved further.