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David M. Hunter and Martin F. Gadsby

Mature seedling trees of pear (Pyrus communis and interspecific hybrids), and fruiting trees of peach and nectarine (Prunus persica), apricot (Prunus armeniaca), and pear were relocated during the dormant season using tree spades. During the growing season immediately following, some signs of drought stress were noticed but all trees grew well enough that they could be used as a source of budwood for limited propagation purposes. When drip irrigation was supplied, supplemented by overhead irrigation as required, normal growth and production resumed within two growing seasons of the move. Some tree losses (less than 10% of trees moved) were reported from one site where the soil type was Fox sand with very poor water holding capacity. These tree losses were attributed to an inadequate water supply to the root ball, even though the site was irrigated. Our experience has demonstrated the feasibility of relocating relatively large trees, which can be beneficial for germplasm conservation in a tree fruit breeding program. However, it is probably not economically viable to relocate such trees for commercial production.

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David M. Hunter and John T.A. Proctor

Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced vegetative growth of `Seyval blanc' grapevines (Vitis spp.). At all rates, there was a reduction in internode length, while at rates higher than 10 μg a.i/g soil, there was also a reduction in node count. Leaf area produced following treatment declined in response to increasing rates, but specific leaf weight increased. Treatment with paclobutrazol delayed senescence and increased the retention of basal leaves that were nearly fully expanded at the time of treatment. Paclobutrazol application had no effect on fruit set or berry size, but the reduction in vegetative growth following treatment decreased the ability of the vine to supply sufficient photoassimilates for fruit maturation. Chemical name used: ß[(4-chlorophenyl)-methyl]-a-(1,1-dimethylethyl)1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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David M. Hunter and John T.A. Proctor

A system was developed to evaluate the response of grapes (Vitis spp. `Seyval') to soil-applied paclobutrazol. The youngest fully expanded leaf, and its axillary bud, on single shoots 6 to 9 nodes long developing on rooted softwood cuttings, were retained for use in a bioassay. The shoot that developed from the axillary bud exhibited a dosage-dependent growth inhibition following soil applications of paclobutrazol at 4 dosages between 1 and 1000 μg·g-1 soil. Other aerial components showed no response to paclobutrazol. This test plant system has potential for use in physiological studies with soil-applied plant growth regulators. Chemical name used: β -[(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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David M. Hunter and W. Gordon Bonn

The virulence of six strains of Erwinia amylovora used in combination for screening fire blight resistance of pear seedlings and advanced selections from the Harrow pear breeding program was evaluated by inoculating a standardized suspension (108 cfu/ml) of the six strains individually and in combination into actively growing shoot tips and measuring the lengths of the diseased shoots six weeks later. Three cultivars provided a range of resistance to fire blight: `Bartlett' was susceptible, HW-605 (`Seckel' × NJ-6) was moderately resistant, while `Kieffer' was resistant. On `Bartlett', one strain was consistently more virulent than the combination, while on HW-605, two strains were consistently more virulent than the combination. One strain was consistently less virulent than the combination on both `Bartlett' and HW-605. No strain was consistently more or less virulent than the combination when inoculated into `Kieffer'. Lesion lengths were greater in the susceptible cultivar `Bartlett' than in either HW-605 or `Kieffer'. These results suggest that a combination of strains of E. amylovora is appropriate for screening for fire blight resistance in pear genotypes.

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Richard E.C. Layne and David M. Hunter

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Richard E.C. Layne and David M. Hunter

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Richard E.C. Layne and David M. Hunter

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David M. Hunter and John T.A. Proctor

Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced photosynthetic CO2 uptake rate of leaves formed before paclobutrazol treatment within 3 to 5 days of treatment and the reductions were maintained for 15 days after treatment. The percentage of recently assimilated 14C exported from the source leaf was reduced only at the highest paclobutrazol dose, and there was little effect of treatment on the partitioning of exported 14C between the various sinks. In response to increasing doses of paclobutrazol, particularly at the higher doses, an increasing proportion of recent photoassimilates was maintained in a soluble form in all plant components. Reduced demand for photoassimilates as a result of the inhibition of vegetative growth may have contributed to a reduction in photosynthetic CO2 uptake rate, but this reduction in photosynthesis rate could not be attributed to a feedback inhibition caused by a buildup of starch in the leaves. Paclobutrazol had only a minor effect, if any, on photosynthetic electron transport. Chemical name used: β-[(4-chlorophenyl) methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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David M. Hunter and Cheryl A. Collucci

Fall-dug nursery trees stored in a jacketed cold storage were damaged by rodent feeding over Winter 2004–05. Damage was primarily confined to the lower trunk region of the scion cultivar, with very little feeding damage to the Bartlett seedling rootstocks. Damage ranged from slight nibbling of some buds to complete girdling and bark removal of considerable length of the trunk. Position of the tree bundle in the storage appeared to have no effect on severity of damage. An arbitrary 7-point scale was used to rate the incidence and severity of damage on 22 cultivars. The least damaged cultivars were Moonglow, Giffard, and Butirra Precoce Morettini, while Thornless Seckel, Conference, and AC Harrow Gold showed the most severe damage. In late Spring 2005, all trees were replanted back into a nursery row to allow trees to recovery rates. However, only trees with damage ratings in the slight to moderate range showed signs of recovery during the 2005 growing season.

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Richard E.C. Layne, Chin S. Tan and David M. Hunter

Three cultivars (`Garnet Beauty', `Harbrite', `Canadian Harmony'), two ground covers (temporary cover vs. permanent sod), and no irrigation vs. season-long trickle irrigation were studied in a high-density (633 trees/ha) peach [Prunus persica (L.) Batsch] orchard established on Fox sand in 1980. From 1985 to 1989, soil water content in the top 130 cm was similar in nonirrigated and trickle-irrigated plots except during the growing season (May to September). Total soil water was lowest in nonirrigated plots that had permanent sod strips in the row middles and fell below the-permanent wilting point for ≥11 months in summer but not at depths below 130 cm. Trunk cross-sectional area (TCA) was greater for `Canadian Harmony' and `Harbrite' than `Garnet Beauty', ground-cover treatments had no effect, and irrigated trees were generally larger than those not irrigated. Photosynthetic rate and stomatal conductance differed by cultivar, were unaffected by ground cover, and were enhanced by irrigation. Defoliation differed by cultivar, ground cover had little effect, and irrigation usually delayed defoliation. Flower bud and shoot xylem hardiness differed by cultivar but not by ground cover and were generally enhanced by irrigation. Tree survival was significantly affected by cultivar, being best with `Harbrite' and `Canadian Harmony' and poorest with `Garnet Beauty'. Permanent sod enhanced tree survival while trickle irrigation reduced it. Cumulative marketable yields were affected more by cultivar than by ground cover or irrigation. `Canadian Harmony' had the highest yield, followed by `Harbrite', then `Garnet Beauty'. Yields in sod were slightly higher than in temporary cover and yields with trickle irrigation were slightly higher than without irrigation. The best soil-management system when TCA, marketable yield, and tree survival were considered was a combination of permanent creeping red fescue sod strips in the row middles and trickle irrigation in the tree row. This system is being recommended to commercial growers in southwestern Ontario.