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David C. Ferree

`Melrose'/M.26 apple (Malus domestics Borkh.) trees were mechanically root-pruned annually for 9 years at bloom to a 25-cm depth at 80 cm from the trunk on two sides. An evaluation of the number of roots of four size categories on the exposed wall of a 1.2 x 2-m trench located 1 m from the trunk indicated that root pruning caused a reduction in all root size categories. Roots < 1 mm in diameter were reduced 20% by root pruning, while the reduction in larger roots was nearly double this amount. The effect of root pruning on root distribution was greatest in the top 30 cm of soil, parallel to the location of the root-pruning cut. Roots below 30 cm were unaffected. The number of roots in all size categories in samples taken parallel and perpendicular to the row decreased linearly with soil depth.

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Steven J. McArtney and Li Shao Hua

A single spray of either GA3 or GA4+7 at full bloom reduced the severity of the alternate bearing cycle of `Braeburn' apples, measured as the proportion of flowering spurs over the 2 years following treatment. Increasing the concentration of GA3 applied in the light-flowering year linearly reduced the proportion of flowering spurs in the following year and linearly increased the proportion of flowering spurs 2 years after treatment. Application of GA3 or GA4+7 at full bloom inhibited flower bud formation on spurs only, whereas, in a separate experiment, GA3 or GA7 applied later than 8 weeks after bloom inhibited flower bud formation on 1-year wood only. Thus, delayed GA treatments may provide suitable technology for the selective removal of fruit from 1-year wood in apple.

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John Warner

`Sturdeespur Delicious', `MacSpur`, `Summerland McIntosh', `Idared', and `Empire' apple trees (Malus domestics Borkh.) planted in 1986 on various size-controlling rootstock were used to determine the effect of rootstock on primary scaffold branch crotch angle. There were differences in crotch angle depending on rootstock. Rootstock effects were more pronounced with the upright growing `Sturdeespur Delicious' than with `Idared' and `Empire', which have a spreading growth habit. Ottawa 8 rootstock had a tendency to produce primary branches with wider crotch angles than other semidwarf to standard rootstock.

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M. Meheriuk

`Newtown' apples (Malus domestics Borkh.) treated weekly with urea at 10 g·liter-l or Ca(NO3)2 at 7.5 g·liter-1 for 5 consecutive weeks from late August were greener at harvest and during storage than comparable control fruit. A postharvest dip in Nutri-Save, a polymeric coating, was better for retention of skin greenness than a dip in diphenylamine and both gave greener apples than control (nondipped) fruit. Fruit treated with Ca(NO3)2 displayed lesions that were larger and more numerous than typical bitter pit in the control fruit.

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A.R. Biggs

Three apple (Malus domestics Borkh.) cultivars varying in susceptibility to Erwinia amylovora (Burr.) Winslow et al., the causal agent of tire blight, were inoculated at biweekly intervals during the growing season. Data were collected on percent infection, canker length, and canker margin quality (a reflection of the overwintering status of the infection). There was a significant cultivar × noculation date interaction, indicating that cultivars that are more susceptible to the pathogen are more likely to develop cankers with indeterminate margins. For `Cortland' and `Jonathan', but not `Delicious', there was a significant linear trend toward forming indeterminate cankers as inoculations were made later in the season. Cankers initiated earlier in the season were more likely to be determinate, which suggests that later-season infections on susceptible cultivars carry over inoculum to the following season. No specific switch-over period from determinate- to indeterminate-type cankers could be identified, and canker margin qualities changed gradually during the growing season. As expected, `Delicious' appeared resistant to tire blight in this study, based on percent infection, canker length, and canker margin type, whereas `Cortland' and `Jonathan' appeared moderately and highly susceptible, respectively. `Delicious' was more likely to form cankers with determinate margins, which suggests that cankers formed on this cultivar are less likely to produce inoculum in the spring than the other two cultivars.

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Mervyn C. D'Souza, Morris Ingle, and Suman Singha

Chromaticity values (L*, a*, b*) of `Rome Beauty' apples (Malus domestics) were measured at weekly intervals during maturation periods in 1988 and 1989. Chromaticity was measured using a Minolta Chroma Meter CR-200b calorimeter on four quadrants of the fruit at locations midway between the stem and calyx ends. The apples continued to develop red color through the maturation period. After storage, the peel areas where chromaticity was measured were evaluated for scald intensity. The L* value at harvest was correlated positively with scald intensity, while the a* value was correlated negatively. An equation has been developed to describe the relationship between chromaticity values at harvest and scald intensity after storage.

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Shiow Y. Wang and Miklos Faust

Ethylene biosynthesis and polyamine content were determined in normal and watercore-affected apple (Malus domestics Borkh. cv. Delicious). Fruit with watercore produced more ethylene and contained higher amounts of putrescine (PUT), spermidine (SPD), 1-aminocyclopropane-1-carboxylic acid (ACC), and 1-(malonylamino) cyclo-propane-1-carboxylic acid (MACC). The activities of ACC synthase and ethylene-forming enzyme (EFE) in watercore-affected fruit were also higher than in normal fruit. The EFE activity in severely affected flesh was inhibited, resulting in ACC accumulation and low ethylene production. S-adenosylmethionine (AdoMet) was maintained at a steady-state level even when C2 H4 and polyamides were actively synthesized in normal and affected fruit.

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Eric Young

Budbreak and root and shoot extension growth of apple trees (Malus domestics Borkh. MM.111) were affected by exposure to 500 hours of higher temperatures (15, 20, or 30C) during the first, second, or third 500 hours of a 1500-hour, 5C chilling period. Exposure to 15C during the third 500 hours had a significantly positive effect on budbreak, 20C at this time had no effect, and all other treatments had a negative effect on budbreak and new root and shoot growth.

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Richard J. Campbell, Richard D. Fell, and Richard P. Marini

Flowering spurs located at interior and exterior canopy positions of `Stay-man' and `Delicious' apple (Malus domestics Borkh.) trees were girdled and/or defoliated to determine the influence on nectar production and composition. Nectar volume was less at exterior than interior canopy positions for `Delicious', but not for `Stayman'. Girdling suppressed nectar production by 92% and reduced the sugar concentration of the remaining nectar. Defoliation of nongirdled spurs had no effect on nectar sugar concentration, but defoliation of girdled spurs reduced nectar sugar concentration by 24%. Relative percentages of sucrose, glucose, and fructose, and the sucrose: hexose ratio were unaffected by any treatment. Nectar production of nongirdled spurs did not depend on the presence of spur leaves.

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Errol W. Hewett and Christopher B. Watkins

The incidence of external and internal bitter pit in `Cox's Orange Pippin' apple (Malus domestics Borkh.) fruit sprayed with normal therapeutic sprays either with or without Ca salts at 2-week intervals during the growing season was determined after 6 weeks of storage over 7 consecutive years. Following harvest, fruit was either vacuum-infiltrated with CaCI2 or received no further treatment. Although there was a tendency for fruit that had been sprayed and vacuum-infiltrated with Ca to exhibit the greatest degree of bitter pit control, this treatment was not significantly superior to Ca sprays alone. Vacuum infiltration alone reduced the disorder to a lesser extent than Ca sprays and was more effective in reducing external than internal bitter bit. The results suggest that Ca applications over the growing season are superior to postharvest vacuum-infiltration with Ca in the prevention of bitter pit.