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Kevin Maloney, Marvin Pritts, Wayne Wilcox, and Mary Jo Kelly

Various soil amendments and cultural practices were examined in both a phytophthora-infested (Phytophthora fragariae var. rubi) (+PFR) and uninfested field (–PFR) planted to `Heritage' red raspberries. Although plants in the +PFR field did not exhibit typical disease symptoms due to unseasonably dry weather, their growth was less than those in the –PFR field. After 2 years, plants in the +PFR site had the highest yields in plots treated with phosphorous acid or amended with gypsum, whereas compost-amended plots had the lowest yields in both +PFR and –PFR sites. A second field study confirmed the positive effect of gypsum on growth and yield of raspberries in an infested site. In a third study, `Titan' raspberries grown under greenhouse conditions in pots containing unamended soil from the infested site, then flooded, exhibited severe disease symptoms; however, pasteurization of the soil, treatment with phosphorous acid and metalaxyl fungicide, or gypsum amendment mostly prevented symptoms from developing. These three studies suggest that a preplant soil amendment containing certain readily available forms of calcium, such as found in gypsum, can help suppress phytophthora root rot and increase survival, growth and yield of raspberries in sites where the pathogen is present.

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Shiow Wang* and Wei Zheng

The effects of preharvest methyl jasmonate (MJ) application on fruit quality, flavonoid content and antioxidant capacity (ORAC) in black raspberry cv. Jewel (Rubus occidentalis L) were studied under field conditions. Raspberries treated with 0.1 mm methyl jasmonate had 20% higher soluble solids content, 20% higher total sugars, 16% higher fructose, 34% higher glucose and 30% lower titratable acids, 31% lower malic acid and 17% lower citric acid than untreated fruit. El-lagic acid, quercetin 3-glucoside, kaempferol 3-glucoside, kaempferol 3-glucuronide, cyanidin 3-glucoside and cyaniding 3-rutinoside were found in raspberry fruit extract. Cyanidin 3-rutinoside was the most dominant anthocyanin and was the major contributor to antioxidant activity in Jewel raspberries. MJ treatments significantly enhanced the content of anthocyanins by 92%, total phenolics by 53%, flavonoids by 98% and the antioxidant capacities by 74% in the fruit. The ORAC value was positively correlated with anthocyanins and total phenolics. In this study, the correlation coefficient for ORAC (y) vs anthocyanins (x) was 0.977 (y = 0.056x + 27.874), and that for ORAC (y) vs. total phenolics (x) was 0.988.

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Eric T. Stafne, John R. Clark, and Curt R. Rom

Net CO2 assimilation (A), evapotranspiration (ET), and stomatal conductance (g s) were determined in two experiments for 14 and 18 raspberry (Rubus sp.) genotypes, respectively, grown in 4-L containers and exposed to 35 °C daytime temperatures 2 weeks and 4 weeks after placement in growth chambers. Measurements were taken on two successive leaves on the same primocane between the third and seventh node (≈75% to 85% of full leaf expansion). In Expt. 1, selections from Louisiana exhibited higher A (3.10-5.73 μmol·m-2·s-1) than those from Oregon (0.50-2.65 μmol·m-2·s-1). In Expt. 2, the genotype × time interactions were nonsignificant, and time of measurement did not affect A or ET (P ≤ 0.05). Assimilation ranged from 2.08 to 6.84 μmol·m-2·s-1 and varied greatly among genotypes, indicating that diverse A levels exist at high temperatures in raspberry germplasm. NC 296, a selection of R. coreanus Miq. from China, and `Dormanred', a southern-adapted raspberry cultivar with R. parvifolius Hemsl. as a parent, had the highest A rates. Evapotranspiration and g s did not differ among genotypes. Average g s for all genotypes declined from 234 mmol·m-2·s-1 in week 2 to 157 mmol·m-2·s-1 in week 4. Our findings, coupled with plant performance under hot conditions, can be used to identify potential parental raspberry germplasm for breeding southern-adapted cultivars.

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P. Chowdary Talasila, Arthur C. Cameron, and Dennis W. Joles

Natural variation of product respiration rate and temperature variation during shipping and marketing influence the atmosphere inside MA packages. Respiration rate variation data was collected at 0C and 5.5C for `Allstar' and `Honeoye' strawberries and at 5.5C for `Heritage' raspberries. Coefficient of variation was 8% for raspberries and ranged from 6.5% to 12.5% for strawberries. To determine package-to-package variations, steady-state O2 partial pressures were measured in 100 similarly designed packages and frequency distributions were constructed. For `Honeoye' variety, `O2 partial pressures ranged from 3.5 kPa to 13.7 kPa with a median of 7.5 kPa in one set of packages and from 0.4 to 1.65 kPa with a median of 0.6 kPa in another set of packages with different design. Large variations were also observed for `Allstar' variety and raspberries. The results compared well with package O2 distributions predicted by a mathematical model that was constructed based on respiration rate variation. A modeling approach was used to predict frequency distributions and changes in gas levels in strawberry and raspberry packages for several possible temperature variation situations and for different types of package designs.

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J.A. Sullivan, B.A. Hale, and D.P. Ormrod

Factorial experiments in two growing seasons in open-top field chambers with two or three O3 concentrations and two primocane-fruiting raspberry (Rubus idaeus L.) cultivars were used to obtain dose-response relationships describing the effects of seasonal O3 exposure on raspberry plant vegetative and reproductive growth. At the lower concentration (0.12 μl·liter-1), the response to O3 was nonsignificant. However, at 0.24 μl·liter-1, `Heritage' showed a significant decline relative to the control in cane height, node count, cane diameter, and dry weight. These changes were accompanied by a 52% decrease in yield, caused mainly by a reduction in fruit count. In contrast, vegetative and yield characters of the `Redwing' were not affected by O3.

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Pauliina Palonen, Danielle Donnelly, and Deborah Buszard

Low tissue-water content and increased osmotic concentration of cell sap are associated with frost resistance. Changes in total osmotic concentration of cell sap are due mainly to changes in concentration of sugars. Generally, sugar content increases with hardening and decreases with dehardening. This study examined the effect of elevated sucrose levels (3% to 15%) in the medium on the cold hardiness of `Festival' red raspberry (Rubus idaeus L.) shoots in vitro. To determine whether expected hardening is caused by elevated sucrose levels or by osmotic stress, different levels of mannitol in the media have been tested. After growing raspberry shoots on media with different levels of sucrose and mannitol for 2 weeks, shoot moisture content (percent) was determined. Cold hardiness of the shoots was determined by using differential thermal analysis or artificially freezing the shoots and assessing the survival by regrowth test and visual rating.

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Marvin Pritts, Eric Hanson, Joseph Fiola, and Mary Jo Kelly

Studies were conducted over eight location-years to evaluate the effects of rowcover material, time of application, and time of removal on `Heritage' red raspberry cane growth, flowering, and fruiting. We anticipated that rowcovers would accelerate fruit maturity so that more of the crop could be harvested before the onset of cold temperatures in autumn. In seven of the eight experiments, rowcovers either increased yields or accelerated harvest. With a March application, harvest began 3 weeks earlier, and August yields of covered plants were 42 times higher than those of noncovered plants. Responses were observed with spunbonded polypropylene and polyester covers, but not with polyethylene covers. Rowcovers placed over the row before primocane emergence and removed when canes were ≈50 cm tall resulted in the greatest plant response. The use of polyester or polypropylene rowcovers with primocane-fruiting raspberries appears to be economically feasible in most years in northern climates.

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M.A. Ellis and S.A. Miller

A commercially available serological assay kit (flow-through enzyme-linked immunosorbent assay, Phytophthora F kit) was compared to a culture-plate method for detecting Phytophthora spp. in apparently diseased (phytophthora root rot) and apparently healthy red raspberry (Rubus idaeus subsp. strigosus Michx.) plants. During 4 years of testing, 46 tests were conducted on apparently diseased roots. All diseased plants gave a strong positive reaction, a result indicating that Phytophthora spp. were present. Of the 46 plants that tested positive, Phytophthora spp. were recovered from all but one using a selective medium for Phytophthora and the culture-plate method. When the same test was conducted on 27 apparently healthy plants, all had a negative reaction for the presence of Phytophthora except one sample, which had a slight positive reaction. No Phytophthora spp. were isolated from any apparently healthy plants. Our results indicate that the serological test kit enables rapid, dependable, on-site diagnosis of raspberry phytophthora root rot.

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Hans Spalholz, Mary Jo Kelly, and Marvin Pritts

The use of high tunnels is a technology that can be implemented just about anywhere for a modest cost, and can be used to bring crops on earlier or extend them later in the season. Raspberries are a high value crop that, in season, sell for more than $3.00/lb. In the middle of winter, raspberries can sell for more than $10.00/lb. Our goal was to produce raspberries in October and November, after the field season ends from frost and rain, and when the selling price of raspberries doubles. Our project examined primocane-fruiting varieties and methods of managing plants to delay their production beyond the normal late August-September season. The first part of the study was to monitor the growth and productivity of several late varieties that typically fruit too late for the New York climate. One selection (NY01.64) and one cultivar (Josephine) appeared very promising for high tunnel production. The second set of treatments manipulated `Heritage' so that it fruits later than the normal September season. The five treatments were an unmanipulated control, applying straw over plots in late February at the rate of 6 tons/acre after a period of cold weather, mowing canes to the ground in early June shortly after they emerge, pinching primocanes (removing the top 4–6 inches) when they reach a height of about 2½ ft, and pinching when canes were 3½ ft tall. Each of these 4 treatments delayed flowering and shifted production to later in the season. The late pinching treatment appeared to provide the best yield curve under the high tunnel.

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Pauliina Palonen and Leena Lindén

Canes and flower buds of selected red raspberry cultivars (Rubus idaeus L. `Maurin Makea', `Muskoka', and `Ottawa') were sampled from a field (latitude, 61 °20'N; longitude, 24 °13'E) at 1-month intervals during Winter 1996-97 to study the interaction of dormancy and cold hardiness, hardiness retention, and rehardening capacity. One set of canes was subjected to dehardening (3 days) and two sets to dehardening + rehardening (3 and 7 days) treatments before cold hardiness determination. Maximum midwinter hardiness occurred in January, after breaking of endodormancy. Cold hardiness of canes and buds reached -28.6 to -37.2 °C and -24.2 to -31.6 °C, respectively. Throughout the winter, raspberry canes were hardier than buds. Endodormancy had a greater influence on dehardening and rehardening in buds than in canes, and cultivars differed in their response. Dehardening of `Maurin Makea' canes and buds, and `Muskoka' buds was slightly enhanced by breaking of dormancy, whereas dehardening in `Ottawa' was not affected by dormancy. Raspberry canes and buds could reharden even after dormancy release. Rehardening capacity was affected by the state of dormancy only in `Maurin Makea' buds. Changes in dormancy status failed to explain cultivar differences regarding dehardening and the capacity to reharden suggesting other factors may be involved.