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Gina E. Fernandez and Marvin P. Pritts

The objective of this experiment was to determine the effects that altering the probable source-sink relationships would have on subsequent growth and yield components under field conditions. The balance between vegetative and reproductive growth was altered by imposing light stress (shading) on various growth phases, or removing primocanes, floricanes or fruit. Removal of primocanes significantly increased yield the year of removal. However, if primocane removal coincided with canopy shading, this increase in yield was not achieved. Overall, a significant negative correlation existed between 1991 and 1992 yields. Treatments with high yields in 1991 had low yields in 1992, and visa verca. This evidence-suggests that: 1) primocanes and floricanes are competing for light, not photosynthates during the flowering and fruiting period and 2) altering the balance of vegetative and reproductive growth one year had a significant effect on growth the subsequent year.

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Maria E. Cramer, Kathleen Demchak, Richard Marini, and Tracy Leskey

relocated, so there were three replicates of all six treatments. Two primocane-fruiting red raspberry cultivars, Josephine and Polka, were used in 2016 and 2017. These cultivars were double-cropped and were chosen for their ability to provide fruit

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G. Fernandez and M. Pritts

Seasonal changes in growth, photosynthetic rates, temperature, and light response curves of `Titan' red raspberry (Rubus idaeus L.) were obtained from potted plants grown under field conditions. Primocane dry weight accumulation underwent two phases of linear growth at the beginning and the end of the season, but growth slowed during fruiting. This slower rate of dry weight accumulation also coincided with an increase in root dry weight. Primocane NAR and SLA were highest early in the season. Light response curves differed depending on cane type and time of year. Floricane photosynthetic rates (A) were high during the fruiting period, while primocane A rates remained steady throughout the season. Both primocane and floricane leaflets displayed a midday drop in A rate, with a partial recovery in late afternoon. Photosynthetic rates of both primocane and floricane leaves were very sensitive to high temperatures. Temporal convergence of sink demand from fruit, primocanes, and roots occurs when plants experience high temperatures. This may account for low realized yields in raspberry and the high level of yield component compensation typical of source-limited plants.

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Gina E. Fernandez and Marvin P. Pritts

Seasonal changes in growth, mean maximal photosynthetic rates, and the temperature and light response curves of `Titan' red raspberry (Rubus idaeus L.) were obtained from potted plants grown under field conditions. Primocane dry weight accumulation increased steadily at the beginning and the end of the season, but growth slowed midseason during fruiting. The slower midseason dry-weight accumulation rate coincided with an increase in root dry weight. Primocane net assimilation rate (NAR) was highest early in the season. Floricane photosynthetic rates (A) were highest during the fruiting period, while primocane A remained steady throughout the season. Primocane and floricane leaflets displayed a midday depression in A under field conditions, with a partial recovery in the late afternoon. Photosynthetic rates of primocane and floricane leaves were very sensitive to temperature, exhibiting a decline from 15 to 40C. Light-response curves differed depending on cane type and time of year. A temporal convergence of sink demand from fruit, primocanes, and roots occurs when plants experience high temperatures. These factors may account for low red raspberry yield.

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Fumiomi Takeda

NAA at 0.25% to 1.0% applied in late May on the basal portion of thornless blackberry (Rubus, subgenus Eubatus) primocanes inhibited lateral shoot growth in the treated area and reduced the number of primocanes. However, regrowth occurred near or below ground from axillary buds not contacted by NAA. Rates of (0.25% and 0.12570 NAA did not affect the terminal or lateral growth above the treated area. The reduced number of basal lateral shoots facilitated machine harvesting. Chemical name used: napthaleneacetic acid (NAA).

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Herbert D. Stiles

Static-V trellis increases raspberry yield, but fruiting shoots grow toward its center making harvest difficult. Shading causes early leaf abscission and it favors fungus diseases inside the V. Static training of floricanes and primocanes to opposite sides of a V trellis prevents neither harvest difficulty, nor primocane injury during harvest. In 1988-89 harvest difficulties were reduced by bloom-time shifting of floricanes on a V-trellis. Over 90% of fruiting shoots were oriented to the trellis ' exterior, but primocane shading and early leaf abscission continued. The 'bent fence' trellis was designed and tested in 1989. It shifts floricanes from horizontal orientation to an upright position on one side of a V-shaped trellis, thus retaining outward display of fruiting shoots and achieving unobstructed display of primocanes on the opposite side. Harvest efficiency, disease reduction, accurate deposition of pesticides, avoidance of solar injury (sun scald), and adaptation of mechanical pest control procedures are potentiated by this system. It also reduces impediments to studies of carbohydrate partitioning, photosynthetic efficiency, yield efficiency, and intraplant competition.

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Eric Hanson, Steven Berkheimer, Annemiek Schilder, Rufus Isaacs, and Sasha Kravchenko

Seven primocane-fruiting and 15 floricane-fruiting raspberry varieties (Rubus idaeus) were compared for three fruiting seasons on a loamy sand soil in southwest Michigan. The earliest primocane-fruiting varieties (`Autumn Bliss', `Autumn Britten', `Polana') began ripening 3 weeks before the standard variety, `Heritage'. `Autumn Bliss' was the most productive early primocane-fruiting variety. `Caroline' and `Dinkum' ripened about 1 week earlier than `Heritage', and `Ruby' was 2 days later. `Caroline' was the most productive of this group and also had large fruit that were somewhat resistant to rot caused by Botrytis cinerea. `Caroline' also received the greatest leaf feeding from rosechafer beetles (Macrodactylus subspinosus). Most primocane-fruiting varieties were fairly resistant to leaf spot (Sphaerulina rubi), while `Dinkum' was highly susceptible to spur blight (Didymella applanata). Floricane-fruiting varieties were evaluated based on fruit production and quality as well as winter injury to canes, disease resistance, and feeding injury from two-spotted spider mites (Tetranychus urticae). The floricane-fruiting varieties showing minimal winter injury were `Boyne', `Killarney', `Latham', `Nova', and `Prelude'. `Canby', `Encore', `Glen Ample,', `Qualicum', `Reveille', `Titan', and `K 81-6' were moderately hardy; while `Tulameen', `Malahat', and `Lauren' were not hardy enough for this location. `Reveille', `Killarney', `Boyne', and `Prelude' were the most productive floricane-fruiting varieties. `Nova' and `Qualicum' had low levels of botrytis rot. `Nova' was most resistant to leaf spot and also had resistance to spur blight. Injury from mites was greatest on `Glen Ample' and lowest on `Malahat', `Prelude', `Qualicum', and `Tulameen'. `Caroline' (primocane-fruiting), `Prelude', and `Nova' (floricane-fruiting) were promising newer varieties.

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Gina E. Fernandez and Marvin P. Pritts

Stomatal and non-stomatal limitations to photosynthesis were determined for both primocanes and floricanes of “Titan” red raspberry. Limitations to photosynthesis were determined from the relationships between rates of photosynthesis (A), stomatal conductance (g), and the internal CO, concentration (Ci) of the leaf. We generated this data (A, g and Ci) using steady state gas exchange. Calculation of limitations were determined from A/Ci and A/g curves, second order polynomial regression and computer simulation. Using methods developed by Farquhar & Sharkey (1982), stomatal limitation during and after fruiting in both primocane and floricane leaves was approximately 28%. Non-stomatal limitations were determined through computer modeling and expressed as the maximum rates of carboxylation, Vcmax, and of electron transpont, Jmax.

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P. Manjula Carter and John R. Clark

Chilling requirement, (the number of hours below 7 °C necessary to break dormancy) has been shown to vary with genotype in blackberry (Rubus subgenus Rubus). Previous work has demonstrated that the chilling requirement of field-grown plants could be accurately determined from stem cuttings of lateral shoots taken at 100-hour intervals of chilling up to 1000 hours, by placing them in a mist chamber maintained at 26 °C with a daylength of 16 hours, and observing budbreak over a period of 5 weeks. This technique has previously demonstrated clear differences in the chilling requirements of thorny and thornless floricane-fruiting cultivars. In the current study, a comparison of floricane-fruiting and primocane-fruiting blackberries using the stem-cutting technique illustrated a lower chilling requirement associated with the primocane-fruiting trait. The use of the stem-cutting technique can be a simple and effective tool for assessing blackberry adaptation to different hardiness zones.

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Justine E. Vanden Heuvel, J. Alan Sullivan, and John T.A. Proctor

Treatments of either staked (stabilized) or not staked (control, freestanding) canes were applied to Rubus idaeus L. `Boyne' and `Regency' during the 1997 and 1998 seasons to determine the effect of stabilizing fruiting canes in a windy environment. Treatments were applied in late April of each year, and canes were removed following harvest for growth analysis. Stabilizing (staking) floricanes increased yield per cane in `Boyne' by 68% and in `Regency' by 189%, primarily through increases in fruit number per cane. Leaf area of the staked canes was 41% larger for `Boyne' and 159% for `Regency' than that of the control canes, suggesting that more leaf area was retained for photosynthesis, resulting in greater yield. Primocane diameter in `Boyne' and primocane height in `Regency' were also increased by staking, but floricane structure was unaffected.