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Todd C. Einhorn, Debra Laraway and Janet Turner

Sweetheart is valued for its late-season harvest timing, precocity, and high productivity ( Lane and MacDonald, 1996 ). However, ‘Sweetheart’ has medium to small fruit size ( Lane and MacDonald, 1996 ) and propensity for surface pitting (B. Bailey, personal

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Todd C. Einhorn, Yan Wang and Janet Turner

fruit and tree response to GA; of those studied, the emphasis has been on ‘Sweetheart’ ( Horvitz et al., 2003 ; Kappel and MacDonald, 2002 , 2007 ) and ‘Lapins’ ( Choi et al., 2002 ). Although similar conclusions were reached for these two genotypes

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M. Meheriuk, D.-L. McKenzie, B. Girard, A.L. Moyls, S. Weintraub, R. Hocking and T. Kopp

Kilogram quantities of `Sweetheart' cherries were stored in HDPE perforated bags (1993, 50.8 μ thickness, OTR = 750 ml·m–2·day–1) or in nonperforated bags (1994, 11 μ thickness, OTR = 5196 ml·m–2·day–1) at 0C. Samples were removed at 1, 2, 4, and 6 weeks of storage and evaluated for fruit and sensory quality. Bag atmospheres after 6 weeks of storage were 10% CO2 and 4.6% O2 for the perforated bags and 3.5% CO2 and 6.6% O2 for the nonperforated bags. Fruit brightness, firmness, and titratable acidity declined during storage. Skin color tended to be redder with the longer storage periods. Sensory evaluation in 1993 showed a decline in overall appearance and flavor with time, but texture and juiciness did not change. Acceptability remained high for the first 4 weeks of storage but dropped at week 6. Surface pitting was noticeable at weeks 4 and 6, particularly from stem bruising.

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Amal de Silva, Keith Patterson and James Mitchell

Growth of strawberry (Fragaria ×ananassa Duch. `Sweetheart') seedlings inoculated with six spore levels ranging from 0 to 12,000 spores/plant of the mycorrhizal fungi Glomus intraradices Schenck and Smith was studied in the greenhouse and with greenhouse plants subsequently moved to the field. Plant height, leaf area, and number of leaves increased significantly with inoculum spore densities ranging from 750 to 12,000 spores/plant in relation to control plants in the greenhouse and field. In the greenhouse, there was a linear relationship between percent infection and spore density, although the relationship was cubic in the field. In the field study, control plants were infected with indigenous mycorrhizae, but inoculated plants produced more runners than the control plants, and foliar Cu and Ca increased linearly with increased spore density. Inoculated plants contained significantly more dry matter than the controls. For inoculated plants, root dry weight increased linearly with increased spore density. We conclude that a minimum spore density of 750 spores/plant is sufficient for a positive growth response.

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Frank Kappel, Michel Bouthillier and Rob Brownlee

`Sweetheart' sweet cherry trees (Prunus avium L.) were summer-pruned for four summers (1991-94) either before or after harvest and at two levels, removing 1/3 or 2/3 of current-season growth by heading cuts. In an additional postharvest treatment, some current-season growth was removed by thinning cuts. The preharvest 1/3 treatment had the highest cumulative yield during the experiment. Higher yields were obtained following preharvest than postharvest treatments, and following less severe treatments (removing 1/3 of current-season growth) than more severe (removing 2/3) treatments. These increased yields were for the early stages of orchard production. Average fruit mass was not affected by any of the treatments. The summer-pruned trees had smaller trunk cross-sectional area (TCSA) increments over the trial and their final TCSA was smaller than that of the control trees.

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Roberto Nunez-Elisea and Lilia Caldeira

We tested two severities and four timings of summer pruning in 2-year-old `Sweetheart' (P. avium L.) trees on seedling mazzard (P. avium L.) rootstock to evaluate growth and precocity responses. Trees were planted at 3.6 m × 5.6 m (497 trees/ha). Canopies consisted of three to four scaffolds and about 20 current-season shoots. All shoots on summer-pruned trees (n=6) were either headed or tipped on 24 June, 9 July, 26 July, or 9 Aug. 2004. Control trees were trained as steep leaders, with comparative current season shoots left intact. Trees had no bloom in 2004 and negligible bloom or fruiting in 2005. All 2005 shoots were headed in late July, except for controls, where only leaders were headed. By late Fall 2005, controls were 3.4 m tall with a canopy diameter of 3 m, while headed and tipped trees were about 65% and 75% the size of controls, respectively. Growth modules consisting of the original shoot and subsequent growth showed distinct responses to summer pruning treatments. Control shoots did not branch in 2004 and modules had an average of 17 spurs. Headed shoots branched in 2004 (except those headed 9 Aug.) and produced compact modules with a similar amount (24 June) or about 25% fewer (later heading treatments) spurs than controls. Shoots tipped in 24 June or 9 July branched in 2004 and produced modules with about 50% more spurs than controls. Shoots tipped in 26 July or 9 Aug. produced no new growth in 2004 and modules had about 30% the spurs of controls. Selective summer pruning produced compact trees which are expected (based on spur number) to yield at least 15 kg of fruit in 2006 (4th year) and appear suitable for densities of about 750 trees/ha. Yields, fruit quality, and future canopy management will be discussed.

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Thomas Gradziel, Bruce Lampinen, Franz Niederholzer and Mario Viveros

Sweetheart’ is a new almond [ Prunus dulcis Miller (D.A. Webb)] cultivar from the breeding program of the University of California at Davis, CA. ‘Sweetheart’ kernels have a cordate shape and very high oleic acid content and so are similar to the

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Peter M.A. Toivonen, Frank Kappel, Sabina Stan, Darrell-Lee McKenzie and Rod Hocking

A convenient and reliable method that used a specially designed tool to apply a uniform bruising force in situ was developed to assess the relative susceptibility to fruit surface pitting in sweet cherry. Assessment of pitting with a visual scale after 2 weeks of 1 °C storage was found to be in close agreement with measurements of pit diameter. Using this method `Bing' showed the greatest susceptibility to pitting in both years of the study and `Bing', `Lapins', and `Sweetheart' cherries showed a decline in susceptibility as fruit matured. The predictive value of fruit firmness at harvest, fruit respiration at harvest, and weight loss in storage was assessed in relation to the severity of pitting. The model to best describe pitting was found to include all three physiological variables (firmness, respiration, and weight loss). While an acceptable model was obtained when combining all three cultivars, the best models were achieved when each cultivar was considered separately. It was concluded that there are likely unmeasured variables involved in determining susceptibility to pitting. Hence the best approach to predicting pitting susceptibility is the application of the pit-induction method described in this work.

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Paul A. Wiersma, Deniz Erogul and Shawkat Ali

mRNA of the cultivars Sweetheart and three of its offspring Staccato ® , Sovereign™, and Sentennial™ with a TruSeq kit (Illumina, San Diego, CA) according to the manufacturer’s instructions. Two lanes of HiSeq Illumina sequence data were obtained from

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Penelope F. Measham, Audrey G. Quentin and Nicholas MacNair

varieties: ‘Sweetheart’ and ‘Kordia’. ‘Kordia’ is generally considered to have a high chill requirement, ≈1300 chill hours ( Brown, 2011 ; Thomas et al., 2012 ). One study ( Guak and Neilsen, 2013 ) was sourced regarding chill requirements for ‘Sweetheart