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S. Kaan Kurtural, Lydia F. Wessner and Geoffrey Dervishian

) further reported that decreasing shoot density did not provide any further benefit to canopy function. Increasing the severity of shoot thinning resulted in a lack of physiological response as a result of vegetative compensation by the grapevine generating

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Desmond R. Layne and J.A. Flore

The leaf surface area of l-year-old, potted `Montmorency' sour cherry (Prunus cerasus L.) trees was reduced by punching disks from some or all leaves to determine the threshold level of leaf area removal (LAR) necessary to reduce net CO2 assimilation (A) and whole-plant growth. Removal of 30% of the leaf area of individual leaves reduced A on a whole-leaf basis between 1 and 3 weeks following LAR. Less than 30% LAR was compensated for by higher estimated carboxylation efficiency and ribulose-l,5-bisphosphate (RuBP) regeneration capacity. The threshold level of LAR based on gas exchange of individual leaves was 20%. Although whole-plant dry weight accumulation was reduced at all levels of LAR, a disproportionately large decrease in dry weight occurred as LAR increased from 20% to 30%. This result indicates that 30% LAR exceeded the threshold LAR level that was noted for A (20% LAR). Wound ethylene production induced by leaf-punching ceased after 24 hours, which indicated that wounds had healed and that ethylene, therefore, did not influence A significantly. The observed threshoId of 20% LAR represents a significant compensation ability for sour cherry, but this threshold may change with crop load, environment, or both.

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Chieri Kubota and Toyoki Kozai

A storage method of transplants in vitro was developed using light compensation points in conjunction with low temperatures. Broccoli (cv. Ryokurei) plantlets, aseptically germinated and cultured for three weeks in vitro, were used as model transplants. Culture conditions were: 23C air temperature, 160 μmol m-2s-1 PPF, and 3.6 air exchanges per hour of the vessel. Prior to storage, light compensation points were determined at 3, 5, 10, and 15C for the plantlets cultured with or without 20 g liter-1 sugar in the medium. Plantlets were stored for six weeks at 5, 10, and 15C under either 0 or 2 μmol m-2s-1 continuous PPF. The light compensation points varied with air temperature and with medium sugar level. Plantlet dry weight during storage was best maintained by keeping CO2 exchange rate of the plantlets close to zero throughout the storage period. High transplant qualities were successfully preserved at light compensation points: 2 μmol m-2s-1 PPF at 5-10C without sugar, and at 5C with sugar in the medium. This method may be applicable for storage of other crop transplants, plug seedlings and cuttings as well.

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Juliet Mann and Bernadine C. Strik

Mature `Kotata' and `Marion' trailing blackberry plants were studied in 1994. In `Kotata', canes were subjected to 0%, 25%, 50%, 75%, or 100% primary bud removal in Feb. 1994. In `Marion' 0, 55, or 100 primary buds were removed per dm2 from fruiting sections (panels). Primary bud removal did not subsequently affect yield per cane or per dm2 in either cultivar. Yield compensation occurred through production of secondary laterals, which were as fruitful as primary laterals.

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Jeffrey A. Leshuk and Mikal E. Saltveit Jr.

A method is described for the rapid determination of the anaerobic compensation point (ACP) of plant tissue, i.e., the O2 concentration at which CO2 production is minimum. The rate of CO2 production is measured from tissue exposed to an exponentially declining O2 concentration produced by a flow of N2 into a dilution bottle initially containing air. Too rapid a rate of O2 decline produces abnormal data because of the time required for the tissue to respond to changes in O2 concentration. The ACP is easily determined from a plot of CO2 production vs. O2 concentration. Rates of CO2 production and ACPS calculated using the exponentially declining system are similar to those calculated from traditional methods of continuously holding tissue under various O2 concentrations.

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Jorge M. Fonseca, James W. Rushing and Robert F. Testin

The influence of temperature and O2 concentration on respiration and shelf life of fresh-cut watermelon was investigated. Product stored at selected temperatures from 1 to 30 °C showed increasing respiration and reduced shelf life with increasing temperature. Oxygen depletion and CO2 evolution were measured using a closed system method and rates of O2 consumption and CO2 production were computed. A mathematical model found to predict the CO2 production as function of temperature and O2 showed an elevated rate of CO2 production at about 14% O2 or lower. A modified atmosphere trial that compared product stored at 7 to 9 °C in air with product at either 14% or 8% O2 revealed increased respiration in the latter treatments, suggesting a relatively high anaerobic compensation point (ACP) at >14% O2. Our results suggest limited applicability of modified atmosphere packaging (MAP) for this product. Fresh-cut watermelon had extended shelf life and reduced respiration rate when stored at 1 to 3 °C and in >14% O2 atmospheres.

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Norman A. Gundersheim and Marvin P. Pritts

A factorial arrangement of 48 treatments was used to evaluate the effects of cane density, time of cane density adjustment, primocane tipping, and cane or branch length on yield components in `Royalty' purple raspberry [(Rubus occidentals × R. idaeus) × R. idaeus] over 2 years. Yield was positively related to cane density and length, while fruit size and fruit count per lateral were negatively related to cane and branch length. When branches on tipped canes were shortened in late winter, more buds became fruitful at the proximal end of the branch, but fruiting laterals did not have more flowers or fruit. Fruiting laterals were longer on shortened canes, resulting in a decrease in the fruit: wood ratio. Plants performed similarly whether floricane density was adjusted in late winter orprimocane density was adjusted in late spring. Although potential yield was higher when primocanes were tipped in late spring, harvesting was more difficult because of branch orientation, and the incidence of cane blight infection was higher. Our study suggests that maintaining at least 12 canes per meter of row, avoiding primocane tipping, retaining full cane length, and providing adequate light, moisture, and nutrient levels can result in high yields of large fruit.

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Marvin Pritts, Mary Jo Kelly and Greg English-Loeb

The strawberry bud weevil (Anthonomus signatus Say; clipper) is considered to be a serious early-season pest in perennial matted row strawberry (Fragaria ×ananassa Duchesne) plantings in North America. Adult females damage flower buds in early spring by depositing an egg in the bud, then clipping the bud from the pedicel. Action thresholds are low (two clipped buds/meter of row) because pest managers and growers have assumed that one clipped flower bud results in the loss of one average-sized fruit. Fields with a history of clipper damage are often treated with insecticides during the first period of warm weather that coincides with inflorescence development, without scouting for clipped buds or evaluating damage. We examined 12 strawberry cultivars and found that most can compensate for a significant amount of flower bud loss, provided that the loss occurs early in the development of the inflorescence. A new threshold is proposed in which the potential loss of fruit per inflorescence is considered, along with the total number of severely damaged inflorescences. We believe that in most circumstances and with most cultivars, clipper injury will remain below the damage threshold.