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Elden J. Stang and John Klueh

Spunbonded polypropylene fabric covers were applied over mature `Searles' cranberry (Vaccinium macrocarpon Ait. in the field during dormancy in 1989. Covers were selectively removed at 3 week intervals in April, May and early June after onset of growth. Plant canopy air temperatures under fabric were 5 to 6C higher than in exposed controls. Temperature differences up to 17C were measured in early June. Soil temperatures did not differ from the control until late May. Earlier greening of leaf tissue resulted in increased photosynthetic rates earlier in the growing season under fabric covers. Subsequent shoot dry weight was increased 5%; leaf size was not affected. A trend to increased fruit set (4 to 6%) with fabric cover treatments was observed when covers were applied for 6 or 9 weeks. Total fruit yield and anthocyanin content were not appreciably influenced by fabric covers.

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Teryl R. Roper and John S. Klueh

The dwarfing potential of apple interstems has long been recognized. This study was undertaken to examine the relationship between the dwarfing effect of apple interstems and interstem starch concentration. In 1981 apple trees with P2 or P22 interstems on clonal Antonovka rootstock using Jerseymac or Starkspurmac as scion were planted. In 1989 and 1990 core samples from the interstems and root samples were analyzed for starch concentration. Roots always had higher starch concentrations than interstems. In the spring, P22 interstems had higher starch levels than P2 interstems, but in the fall the reverse was found. No difference in starch concentration was found between the Antonovka rootstock under the same interstem. However, root starch concentration was more stable under P22 than P2. Further, roots under P22 were lower in starch in the fall than in the spring. This suggests that P22, the more dwarfing interstem, may interfere with the transport of carbohydrates through the trunk, which may be a factor in dwarfing.

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Teryl R. Roper and John S. Klueh

The source of photosynthate for developing cranberry (Vaccinium macrocarpon Ait.) fruit can be partitioned spatially among new growth acropetal to fruit, 1-year-old leaves basipetal to fruit, and adjacent uprights along the same runner. Cranberry uprights were labeled with 14CO2 in an open system with constant activity during flowering or fruit development. When new growth acropetal to fruit was labeled, substantial activity was found in flowers or fruit. Little activity was found in basipetal tissues. When 1-year-old basipetal leaves were labeled, most of the activity remained in the labeled leaves, with some activity in flowers or fruit. Almost no labeled C moved into acropetal tissues. When new growth of adjacent nonfruiting uprights on the same runner were labeled, almost no activity moved into the fruiting upright. These data confirm that new growth acropetal to developing flowers and fruit is the primary source of photosynthate for fruit development. Furthermore, they show that during the short time studied in our experiment, almost no C moved from one upright to another.

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Teryl R. Roper, John Klueh, and Marianna Hagidimitriou

Cranberry (Vaccinium macrocarpon Ait.) vines were shaded with either 72% or 93% shadecloth (28% or 7% of full sun) for 1 month before flowering, after flowering, or before harvest. Fruit set was reduced by heavy shade (93%) before flowering in 1991 but not in 1992 or 1993. Heavy shade following flowering reduced fruit set in 1991 and 1992 but not 1993. The number of flowers per upright was generally not affected by shading but was reduced by prebloom shading at either level in 1993. Mean berry weight was usually conserved. Yield was reduced by shading at either level following flowering in 1991 and 1992. Shading just before harvest had no effect on the characteristics measured. Total nonstructural carbohydrate concentration was reduced to about half relative to the controls by either shading level at all treatment dates. Carbohydrate concentrations recovered to control levels by 4 to 8 weeks following removal of shading. Shading always reduced carbohydrate concentrations but did not always reduce fruit set or yield.

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Teryl R. Roper and John S. Klueh

The sources of photosynthate for fruit growth in cranberry (Vaccinium macrocarpon Ait.) can be spatially partitioned as new growth, old leaves and woody stems, or adjoining uprights. New growth, l-year-old leaves, or both were removed at the time of fruit set and following fruit set. Removing new growth at the time of fruit set reduced fruit set, fruit count, and yield. Removing old leaves at fruit set generally did not reduce fruit set, fruit count, or yield. Removing both often had an additional effect. Removing new leaves after fruit set did not affect fruit set or count, but did reduce fruit size. Removing old leaves after fruit set did not reduce fruit set, fruit count, or size. These data suggest that new growth is an important source of photosynthate for fruit set.

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Eric L. Zeldin, Brent H. McCown, Elden Stang, and John Klueh

A project to determine the comparative growth response of micropropagated (MP) and field propagated (FP) cranberry plants was conducted in field plots at a commercial cranberry marsh. Microcuttings were derived from shoot culture and rooted in either plugs or peat pots filled with peat. Replicated 1 m2 plots of MP plants and 15 cm FP cuttings were planted in June. Survival of MP plants after one month was significantly greater than that of the FP plants. Significant growth differences were observed later in the season. The MP plants produced more branches and greater runner elongation, resulting in a much greater ground cover. Many of the FP plants flowered and produced fruit, while the MP plants produced neither. Far fewer new flower buds were set in the fall on the MP plants. Potential advantages of MP cranberries include the fast, uniform establishment of new marshes and consequently earlier achievement of full productivity, and the rapid introduction of new genotypes from breeding or genetic engineering.