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Hein J. Gerber, Willem J. Steyn, and Karen I. Theron

shoot lengths (in terms of yield and fruit size) should be determined and strategies devised to maximize the number of these shoots on trees on an annual basis. It is therefore important to study the phenological characteristics of a cultivar to

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Morihiko Hamada, Takashi Hosoki, and Toshiyuki Maeda

Potted plants of `Taiyoh' and `Hanakisoi' tree peony (Paeonia suffruticosa Andr.) were treated with a foliar spray of uniconazole or paclobutrazol for shoot length control. Uniconazole sprays at 25 or 50 ppm upon sprouting effectively reduced shoot length in both cultivars. The retarding effect was greater in `Taiyoh' than in `Hanakisoi' at 25 ppm. Uniconazole treatment did not influence flower diameter or days to flowering in either cultivar. Paclobutrazol sprays at 500 and 1000 ppm were less effective in reducing `Hanakisoi' shoot length than uniconazole sprays at 25 and 50 ppm. Chemical names used: E-1-(4-chlorophenyl)-4,4-dimethyl-2-(l,2,4-triazol-l-yl)-l-pentan-3-ol (uniconazole); (1RS, 3RS)-1-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-l-yl)-l-pentan-3-ol (paclobutrazol).

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M.K. Ehlenfeldt, A.W. Stretch, and J.S. Lehman

Shoot growth of six blight-resistant highbush blueberry (Vaccinium corymbosum L.) cultivars and of one susceptible cultivar was manipulated during the primary infection period of mummy berry disease to determine if some portion of the observed resistance was based on disease avoidance. In experiments across 2 years, resistant cultivars either increased continually in susceptibility or exhibited a peak and then decreased in susceptibility as shoots elongated. In a larger experiment that included both susceptible and resistant cultivars, peaks of susceptibility were identified for `Bluejay', `Darrow', and `Jersey'. In contrast, general decreases in susceptibility were identified for `Duke', `Blueray', and `Croatan' as shoots elongated. Shoot lengths associated with peak susceptibility varied among and within cultivars across experiments. The increases in susceptibility observed at longer shoot lengths were generally small. This finding suggests that cultivars identified as resistant have intrinsic levels of resistance, but maturity and general condition of the plant tissue can also affect disease levels.

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John C. Neilsen and Frank G. Dennis Jr.

Chan and Cain (Proc. ASHS 91:63-68, 1967) demonstrated that seeded apple fruits inhibited flowering, whereas seedless ones did not. `Spencer Seedless' spurs bearing seeded or seedless fruits were defruited at various times after anthesis in 1989-1991 and fruit weight, seed number and bourse shoot length recorded, as well as repeat bloom. Similar defruiting treatments were also applied to entire `Paulared (all seeded fruits) trees in 1991 and 1992. In all years spurs bearing seedless fruits flowered the following year, regardless of defruiting time, shoot length or fruit weight per spur. Flowering of spurs bearing seeded fruits decreased as defruiting was delayed. In all years over 90% of spurs bearing fruits containing a total of 5 seeds or less flowered, whereas 90% of those with more than 5 seeds remained vegetative. Flowering was not correlated with shoot length or fruit weight. Bearing spurs of `Paulared' flowered when whole trees were defruited within 60 days after anthesis, but flowering was greatly inhibited when fruits were left on for 97 and 74 days in 1991 and 1992, respectively.

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M.T. Stevenson, K.A. Shackel, and L. Ferguson

Pistachio (Pistacia vera L.) is known to strongly exhibit alternate bearing. Over 19,500 individual shoots were measured on eight alternate bearing `Kerman' pistachio trees on P. atlantica Desf. rootstock. Average length of “on” year (5.4 cm) and “off” year new shoots (5.6 cm) were not significantly different. New shoot length distribution was skewed toward the shorter length categories, with a mode of 2 and 4 cm in “on” and “off” trees respectively. These results contrast with previous studies which have shown that “on” year new shoots of pistachio are much longer than “off” year new shoots. There were about twice as many “on” year new shoots in the 18 to 30 cm class as compared to “off” new shoots, and fruiting wood length was associated positively with fruit number. However, ≈80% of tree yield occurred on fruiting wood that was <10 cm long, with shoots longer than 15 cm contributing <5% to yield. We suggest that results from earlier studies regarding the bud abscission process in very long pistachio shoots should be confirmed on shorter shoots, which contribute significantly to yield. Shoots >30 cm in length may be important in establishing vegetative buds in a position above the main tree crown for canopy expansion during the following “off” year.

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Richard P. Marini and Donald L. Sowers

The relationship between peach [Prunus persica (L.) Batsch] fruit position and fruit weight (FW) was studied in experiments involving thinned vs. nonthinned fruiting shoots, shoots with and without axillary shoots, and trees with varying crop densities (CDs). FW was not consistently related to position on the shoot, and the influence of fruit position varied depending on the presence of axillary shoots on the fruiting shoot. FW was best related to fruiting shoot length and total shoot length per fruit (1-year-old plus current-season wood). Mean FW was also influenced by the number of fruit per shoot × CD interaction, a result indicating that FW depends on photosynthate from leaves in the immediate vicinity of the fruit as well as photosynthate from more distant parts of the tree.

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Charles J. Graham and J. Benton Storey

Pollarded `Wichita' pecan [Carya illinoensis (Wang) K. Koch] trees received 2 g uniconazol (UCZ) per tree using four application methods (trunk band, canopy soil injection, crown soil injection, and crown drench). All application methods increased trunk diameter but reduced shoot length, number of lateral shoots per terminal, nodes per terminal, internode length, and leaflets per compound leaf. Only the crown drench reduced leaf area. Area and dry weight per leaflet, and leaflet chlorophyll concentration were not affected by UCZ application. Effectiveness in growth reduction, as assessed by shoot elongation, was crown soil drench > crown soil injection > canopy soil injection > trunk band > control. All application methods increased viviparity. However, total yield per tree, nut size, and percentage of kernel were not affected. Chemical name used: (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (uniconazol).

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Frank G. Dennis Jr. and John C. Neilsen

The evidence for several hypotheses regarding the mechanism(s) controlling biennial bearing in apple (Malus×domestica Borkh.) are reviewed, citing relevant evidence from work with citrus (Citrus sp.) species and pear (Pyrus communis L.). The view that flowering is inhibited by withdrawal of nutrients, primarily carbohydrates, by apple fruit is questionable, given the effects of seed development in inhibiting flowering in facultatively parthenocarpic (normally seedless) apple cultivars. The hypothesis that seeds inhibit flowering by exporting hormones, chiefly gibberellins (GAs), is an attractive one, given a) the effects of application of GAs in inhibiting flowering and b) the high concentrations of GAs in seeds. However, an alternative hypothesis, namely that seeds compete with apices for hormones that are required for flowering, is equally tenable.

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Betsey Miller, Denny J. Bruck, and Vaughn Walton

root weight using destructive techniques. We measured shoot length from the lateral stem (or the soil level, if the shoot came from an underground lateral) to the tip of the most terminal leaf to the nearest millimeter. Leaf surface area (cm 2 ) was

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Claudia Negrón, Loreto Contador, Bruce D. Lampinen, Samuel G. Metcalf, Theodore M. DeJong, Yann Guédon, and Evelyne Costes

branching patterns and flowering. Thus, in this study specifically 1) branching patterns were modeled by a single hidden semi-Markov model of different shoot lengths for each cultivar; 2) the models of each cultivar were used to evaluate gradients in