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M. McLean, G.S. Howell and A.J.M. Smucker

An experiment was conducted to evaluate interrelationships between differing crop loads and water stress on physiology and root dynamics of 3 year old Seyval grapevines grafted to 5-BB, Seyval and Seyval own-rooted stock grown under a rain exclusion shelter. Treatments were: 1) cropping level, either 0 (defruited) or 6 clusters/vine (heavily cropped) and 2) irrigation level, either 2.5 (stress) or 10 liters (control) of water/plant/week. Vines had significantly different root dynamics in regards to crop load, water status and rootstock. Water stressed vines had significantly fewer and smaller leaves (area cm 2 lighter trunk weights (g) and shorter shoot length compared to control vines. Heavily cropped vines had significantly fewer mature nodes, shorter shoot growth and higher bud mortality (winter injury) compared to defruited vines.

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D.P. Miller, G.S. Howell and J.A. Flore

Chambers were constructed to measure gas exchange of entire potted grapevines (Vitis vinifera L.). The plant enclosures were constructed from Mylar film, which is nearly transparent to photosynthetically active radiation. Maintaining a slight, positive, internal pressure allowed the Mylar chambers to inflate like balloons and required no other means of support. The whole-plant, gas-exchange chamber design and construction were simple and inexpensive. They were assembled easily, equilibrated quickly, and did not require cooling. They allowed for the measurement of many plants in a relatively short period. This system would enable the researcher to make replicated comparisons of treatment influences on whole-plant CO2 assimilation throughout the growing season. While CO2 measurement was the focus of this project, it would be possible to measure whole-plant transpiration with this system.

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David P. Miller, G. Stanley Howell and James A. Flore

The measurement of whole-plant CO2 uptake integrates leaf-to-leaf variability, which arises from such sources as angle of incident radiation, source/sink relationships, age, and biotic or abiotic factors. Respiration of above-ground vegetative and reproductive sinks is also integrated into the final determination of whole-plant CO2 assimilation. While estimates of whole-plant CO2 uptake based on single-leaf determinations have been used, they do not accurately reflect actual whole-plant assimilation. Chambers were constructed to measure gas exchange of entire potted grapevines. The design and construction are simple, inexpensive, and easy to use, allowing for the measurement of many plants in a relatively short time. This enables the researcher to make replicated comparisons of the whole-plant CO2 assimilation of various treatments throughout the growing season. While CO2 measurement was the focus of this project, it is also possible to measure whole-plant transpiration with this system.

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M. McLean, S. Howell, J.A. Flore and A.J.M. Smucker

Both berries and roots of grapevines are powerful carbohydrate sinks. However, during periods of soil-moisture stress, the relative strength of these two sinks is not known. This experiment was conducted to evaluate interrelationships between differing crop loads on carbohydrate partitioning for above and below-ground tissues. Root development, depth, and rate of turnover were determined by quantifying root images from video recordings taken to depths of 75 cm at two week intervals throughout the growing season. Two-year old own rooted Seyval grapevines, and Seyval grafted to 5-BB and Seyval, were grown under a rain exclusion shelter and provided with 10 or 2.5 liters of water/plant/week. Treatments were cropping level, either 0 or 6-clusters/vine. Shoot length, number of mature nodes, and dry leaf weight of vines under high cropping level were significantly reduced compared to vines growing under the low cropping level; so was root number and depth of root penetration. These data suggest that conditions of low soil moisture result in carbohydrate partitioning in favor of the clusters at the expense of the roots.

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A. Howell, W. Kalt, J.C. Duy, C.F. Forney and J.E. McDonald

It is now widely held that the antioxidants contained in fruit and vegetables can provide protection against certain human degenerative conditions that are associated with oxygen free radical damage. This view is supported by epidemiological, in vitro, and more recently, in vivo evidence. Phenolics (polyphenolics) contribute substantially to the antioxidant complement of many small fruit species whose ripe fruit are red, purple or blue in color. Fruit containing high levels of phenolic antioxidants would be attractive to health conscious consumers, therefore optimization of production and processing factors affecting small fruit antioxidant capacity is desirable. In many small fruit crops, antioxidant activity [measured as oxygen radical absorbing capacity (ORAC)] is positively correlated with their content of anthocyanins and total phenolics. Genera, species, and genotypes vary with respect to phenolic content. Both annual and geographical factors appear to influence ORAC, although many years of study are needed to distinguish these effects from other biotic and abiotic factors that influence fruit phenolic content. Antioxidant capacity due to phenolics is decreased by food processing practices, such as heat or aeration.