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Wesley T. Watson*, David N. Appel, Michael A. Arnold, Charles M. Kenerley, and James L. Starr

Phymatotrichopsis omnivora (Duggar) Hennebert (syn. Phymatotrichum omnivorum Duggar) is a recalcitrant soilborne pathogen that causes serious root rot problems on numerous plant species in the southwestern United States and northern Mexico. Apple trees [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. (syn. M. domestica Borkh. non Poir.)] are highly susceptible to P. omnivora with most tree death occurring in the summer months. Studies were conducted from 1996 to 1999 to examine when and at what rate infection and colonization of roots of apple trees by P. omnivora actually occurs. In three-year-old trees growing in orchard soils in 45-gallon containers (171,457 cm3) and inoculated with sclerotia in August 1997, infection occurred in the nursery after 12 weeks. For trees inoculated with sclerotia in February 1998, infection occurred within 15 weeks. After 18 weeks, 100% of trees were infected after inoculation in August and 80% of trees were infected after the February inoculation. This information is vital to understanding the epidemiology of Phymatotrichum root rot in apple orchards.

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Amos Naor, Moshe Flaishman, Raphael Stern, Aharon Moshe, and Amnon Erez

The relative contribution of various temperatures to dormancy completion of lateral vegetative apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] buds was studied quantitatively on whole container-grown trees. Trees were exposed continuously to 10 different temperatures and also to daily alternating temperatures in a 24-hour cycle. In addition, fully chilled vertically and horizontally positioned shoots were compared under forcing conditions. No budbreak occurred in shoots chilled above 12.5 °C. There was a steep increase in budbreak as the chilling temperature fell from 12.5 to 7.5 °C. There was little difference in the level of budbreak on shoots chilled between 7.5 and 0 °C. The relative contribution of temperature to chilling accumulation in apple found in our study differs from what has been proposed for stone fruit and for apple in previous studies, especially at temperatures <6 °C. The length of exposure to forcing conditions required to initiate budbreak diminished as the chilling temperature was reduced. No additional bud-break was apparent on shoots chilled longer than 2100 chilling hours. The chilling requirement found here for lateral vegetative buds is much higher than that needed for terminal vegetative and flower buds. Trees that were exposed to daily alternating temperatures had lower levels of budbreak when the high temperature in the diurnal cycle was greater than 14 °C. Practically no budbreak was apparent on trees that were exposed to diurnal cycles with a high temperature of 20 °C for 8 hours. Budbreak on horizontally positioned trees was more than twice that on the vertically positioned trees, emphasizing the magnitude of the apical dominance effect and its strong masking of the chilling effect on lateral buds in vertically grown apple trees. Based on the data collected here we propose a new response curve for vegetative budbreak in `Golden Delicious·apple, within a temperature range between 0 to 15 °C.

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Iwan F. Labuschagné, J.H. Louw, Karin Schmidt, and Annalene Sadie

Significant response to selection for budbreak number (NB) based on data recorded on 1-year-old shoots of young apple (Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.) seedlings (Expt. I) and branches from adult seedling trees (Expt. II) has been demonstrated in clonally propagated seedling trees. Between family variation for NB was low and masked by year × family interaction effects. Realized heritability for NB was estimated as 40% to 60%. Correlated response in uniformity and position of budbreak, and in the number and length of side shoots, was found. Association between the time of budbreak (TB) and NB, according to midparent and cross groupings, and according to the parental means, indicate a positive genetic correlation between these traits. Where data on adult trees were used as a measure of selection response and tested on young clonal trees, significant response and genetic variation was shown, confirming the presence of utilizable genetic variance and that this procedure may be successfully applied as an early screening method for increased budbreak in adult trees. Combined selection utilizing genetic variance between crosses as well as within crosses is proposed as the best procedure to increase the frequency of seedlings with increased budbreak and to improve adaptation to low winter chilling conditions.

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Richard K. Volz, F. Roger Harker, and Sandy Lang

Puncture force was measured in `Gala'apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] fruit from 16 to 175 days after full bloom over 2 years using a range of circular flat-tipped probes (1 to 11 mm diameter) to test the firmness of each fruit. The area-dependent (Ka) and perimeter-dependent (Kp) coefficients of puncture force were determined and were used to calculate the indicative puncture force approximating a standard 11.1-mm-diameter Effegi/Magness-Taylor probe for even the smallest fruit. Ka declined exponentially throughout fruit development with much greater changes occurring closer to bloom. In contrast, maximum Kp occurred at 107 to 119 days after full bloom before declining progressively. Estimated firmness (using a 11.1-mm-diameter probe) declined constantly from 16 days after full bloom. Ka was associated with developmental changes in cortical tissue intercellular air space, cell volume and cell packing density although relationships changed throughout fruit growth. However seasonal change in Kp was not associated with any obvious anatomical change in the cortex.

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Martin Harz, Moritz Knoche, and Martin J. Bukovac

Water conductance of the cuticle of mature fruit of apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf., `Golden Delicious' Reinders/`Malling 9' (M.9)], sweet cherry (Prunus avium L., `Sam'/`Alkavo'), grape (Vitis vinifera L.), pepper (Capsicum annuum L. var. annuum Fasciculatum Group, `Jive'), and tomato (Lycopersicon esculentum Mill.) was de ter mined using excised epidermal segments (consisting of epidermis, hypodermis, and some cell layers of parenchyma) and enzymatically isolated cuticular membranes (CM) from the same sample of fruit. Segments or CM were mounted in diffusion cells and transpiration was monitored gravimetrically. Conductance (m·s-1) was calculated by dividing the flux of water per unit segment or CM area (kg·m-2·s-1) by the difference in water vapor concentration (kg·m-3) across segments or CM. Transpiration through segments and through CM increased with time. Conductance of segments was consistently lower than that of newly isolated CM (3 days or less). Conductance decreased with increasing time after isolation for apple, grape, or sweet cherry CM, and for sweet cherry CM with increasing temperature during storage (5 to 33 °C for 4 days). There was no significant effect of duration of storage of CM on conductance in pepper or tomato fruit. Following storage of CM for more than 30 days, differences in conductance between isolated CM and excised segments decreased in apple, grape, and sweet cherry, but not in pepper or tomato. Use of metabolic inhibitors (1 mm NaN3 or 0.1 mm CCCP), or pretreatment of segments by freezing (-19 °C for 18 hours), or vacuum infiltration with water, had no effect on conductance of apple fruit segments. Our results suggest that living cells present on excised segments do not affect conductance and that epidermal segments provide a useful model system for quantifying conductance without the need for isolating the CM. Chemical names used: sodium azide (NaN3); carbonylcyanide m-chlorophenylhydrazone (CCCP).

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M. Virtudes Andrés, José M. Durán, and Eusebio Rodríguez-Almazán

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Daniel Ferreira Holderbaum, Tomoyuki Kon, Tsuyoshi Kudo, and Miguel Pedro Guerra

Apples ( Malus × sylvestris var. domestica ) are an important source of polyphenols (phenolic compounds) in the human diet ( Hertog et al., 1992 ) and a classic example of fruit susceptibility to enzymatic browning, which is a major problem for

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Kevin R. Kosola, Beth Ann A. Workmaster, James S. Busse, and Jeffrey H. Gilman

roots from apple trees [ Malus sylvestris var. domestica (Borkh.) Mansf.] at the University of Wisconsin Peninsular Agricultural Experiment Station near Sturgeon Bay (lat. 44°52′51.96″ N, long. 87°20′7.8″ E) on 13 May 2004. The soil type was an Emmet

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Bradley J. Rickard, David R. Rudell, and Christopher B. Watkins

costs if fewer materials are needed in storage. Here, we focus specifically on firm flesh browning of the ‘Empire’ apple ( Malus sylvestris var. domestica Borkh.), which is a major cause of revenue loss for growers and storage operators in New York

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Gerry Henry Neilsen, Denise Neilsen, and Linda Herbert

concentration and timing on performance of five different apple cultivars. Materials and Methods In Apr. 1998, five apple [ Malus sylvestris (L.) Mill var domestica (Borkh.) Mansf] cultivars (Ambrosia, Cameo, Fuji, Gala, and Silken) on the dwarfing