Biweekly cold hardiness and water content were measured on 1-year-old field cuttings of bearing Concord grapevines at the Horticultural Teaching and Research Center at MSU from Sept. 1998 to Apr. 1999. Cold hardiness index LT50 (temperature at which 50% of the sample was killed) was determined by three viability tests after laboratory controlled sub-freezing treatments. Weather data were obtained from the MSU agricultural weather automatic system. Average maximum and minimum air temperatures of 1, 3, 5, and 7 days prior to each field sampling were regressed against the LT50 of the tissues. Our results suggested that: 1) Tmin1 (minimum air temperature of the preceding 1 day of each sampling) had the most significant correlation with LT50 and cane water content among all air temperatures analyzed. 2) While cane water content was significantly related to its bark water, the water content of periderm and pith did not. 3) When comparing the effects of Tmin1 and bark water content on cane LT50 together, bark water had significant higher coefficient of determination (R 2). This research provided additional information about the mechanisms of plant dormancy and cold hardiness.
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.
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.
Francis X. Mangan, Charles S. Vavrina and John C. Howell
The effects of transplant depth on lodging and yield were evaluated in five experiments in Florida and Massachusetts. `Cherry Bomb', `Jupiter', and `Mitla' pepper (Capsicum annuum L.) transplants were set at three depths so that the soil surface was even with the top of the rootball, the cotyledon leaf, or the first true leaf. Seedlings set to the depth of cotyledon leaves or to the first true leaf lodged less than did those set to the top of the rootball. No yield differences were recorded among treatments in Massachusetts; however, total weight of red fruit was greater in treatments that lodged less in 1 of the 2 years, suggesting that lodging delayed maturity. Soil temperature in Massachusetts declined at the level of the rootball as planting depth increased.
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.
Daren S. Mueller, Mark L. Gleason, Nicholas P. Howell and Edward M. Moran
Recently, roses (Rosa spp.) that require relatively little maintenance have gained in popularity in the United States. One group of these roses is the Griffith Buck roses, which were selected to survive the extremely cold winters of the north-central United States. Many of these roses were rated qualitatively as having disease resistance when they were released, but their resistance levels to black spot (Marssonina rosae) have not been quantified, compared with each other, or rated against other resistant or susceptible roses. In a field trial in Iowa in 2005 and 2006, 24 Griffith Buck roses that were originally described as disease resistant were compared with susceptible and resistant control cultivars for susceptibility to black spot. No fungicides were applied in either year. Plants were rated five times each year for black spot incidence, and also to assess overall plant appearance. Griffith Buck roses ‘Carefree Beauty’, ‘Aunt Honey’, ‘Honeysweet’, ‘Earthsong’, and ‘Pearlie Mae’ had significantly less black spot than many of the other cultivars. In addition, these cultivars also remained attractive and could be used in low-maintenance landscapes in the north-central United States, even under moderate black spot pressure.