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James W. Olmstead, Amy F. Iezzoni and Matthew D. Whiting

defined, the genetic differences in cell division and enlargement contributing to the wide range in fruit size that can occur between genotypes are not. Wild forms of forest sweet cherry have small (≈1–2 g) fruit consisting predominantly of the pit

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Lisa Klima Johnson, Anish Malladi and D. Scott NeSmith

processes may be key factors determining fruit size. Dissecting the relative contribution of these factors is essential to develop a clear understanding of fruit size regulation. Variation in fruit size is often associated with differences in cell number

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Jun Matsumoto, Hideyuki Goto, Yasutaka Kano, Akira Kikuchi, Hideaki Ueda and Yuta Nakatsubo

melon fruit ( Kano and Fukuoka, 2006 ), and increased numbers of larger cells in japanese pear ( Pyrus serotina Rehd.) treated with gibberellic acid also showed increased sucrose accumulation ( Kano, 2003 ). In contrast, restricting fruit size by

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Yasutaka Kano

, sucrose accumulation has been demonstrated to occur in response to cellular enlargement if cell size is increased by auxin treatment during early fruit development ( Kano, 2002 ) as well as in response to heating fruits ( Kano, 2006 ). Conversely, sucrose

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Yahya K. Al-Hinai and Teryl R. Roper

The effects of rootstock on growth of fruit cell number and size of `Gala' apple trees (Malus domestica Borkh) were investigated over three consecutive seasons (2000-02) growing on Malling 26 (M.26), Ottawa-3, Pajam-1, and Vineland (V)-605 rootstocks at the Peninsular Agricultural Research Station near Sturgeon Bay, WI. Fruit growth as a function of cell division and expansion was monitored from full bloom until harvest using scanning electron microscopy (SEM). Cell count and cell size measurements showed that rootstock had no affect on fruit growth and final size even when crop load effects were removed. Cell division ceased about 5 to 6 weeks after full bloom (WAFB) followed by cell expansion. Fruit size was positively correlated (r 2 = 0.85) with cell size, suggesting that differences in fruit size were primarily a result of changes in cell size rather than cell number or intercellular space (IS).

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James W. Olmstead, Amy F. Iezzoni and Matthew D. Whiting

Although maximizing fruit size is critical for profitable sweet cherry (Prunusavium L.) production, little is known about the cellular differences among and between cultivars that contribute to fruit size differences. A wide range of fruit size exists among sweet cherries, and, due to cultural and environmental differences, significant variation exists among genetically identical fruit from the same cultivar. To determine the relative contributions of flesh cell number and cell size to final fruit size in sweet cherry, equatorial sections of three cultivars with a wide range in final average fruit size [`New York 54' (NY54; 1.4 g fresh weight, 11.8 mm diameter), `Emperor Francis' (EF; 6.1 g, 21.0 mm), and `Selah' (12.8 g, 25.5 mm)] were created from mature fruit. Cells intersecting a transverse line were counted and average cell length was calculated. The average cell numbers were significantly different (P ≤ 0.05) between `NY54', `EF', and `Selah' (26.7, 47.4, and 83.2, respectively), indicating that flesh cell number is the major contributor to differences in fruit size between cultivars. Flesh cell numbers of `NY54', `EF', and `Selah' were similar at bloom and increased rapidly for a short duration after fertilization, suggesting a key developmental period for fruit size differences. To determine the contribution of cell number differences to variation in fruit size within a cultivar, fruit from `Bing' and `Regina' trees exhibiting a range of size due to cultural and environmental differences were measured. In both cases, average cell number was not significantly different (P = 0.9, P = 0.3, respectively), while average cell size was (P ≤ 0.05), further indicating fruit flesh cell number is a genetically controlled trait.

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E.T. Maynard, C.S. Vavrina and W.D. Scott

Muskmelon (Cucumis melo L. cvs. Superstar and Mission) transplants were grown in seedling flats with individual cells ranging in volume from 7 to 100 cm3. The smallest cells were in a 338-cell polystyrene flat 33 cm wide × 66 cm long × 4.75 cm deep; the largest cells were in a 32-cell plastic flat 30.5 × 50.8 × 6.5 cm. The study was conducted in Florida and Indiana during the 1993 and 1994 growing seasons. Seedlings of uniform age were transplanted to the field and grown to maturity using standard cultural practices. Early yield of `Superstar' muskmelon, measured as number of fruit per plot or percentage of total yield, increased as transplant cell volume increased. In one trial, plants from 7-cm3 cells produced no early yield, while plants from 100-cm3 cells produced 40% of the total yield in the first three harvests. In three of the four trials, total yield of `Superstar' increased as cell volume increased. Marketable early yield of `Mission' muskmelon, measured as number or weight per plot, increased as cell volume increased in three of four trials. In Florida, total yield of `Mission' also increased as cell volume increased. Size of `Superstar' fruit was not influenced by cell volume. In Florida, size of early `Mission' fruit increased as cell volume increased.

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Paul T. Wismer, J.T.A. Proctor and D.C. Elfving

Benzyladenine (BA), carbaryl (CB), daminozide (DM), and naphthaleneacetic acid (NAA) were applied postbloom as fruitlet thinning agents to mature `Empire' apple (Malus domestica Borkh.) trees. BA, NAA, and CB reduced fruit set and yield per tree, and increased fruit size, percent dry weight, soluble solidscontent and return bloom. Fruit size was reduced, return bloom, length: diameter ratio and flesh firmness were increased, and fruit set and yield unaltered by DM. Although fruit set and yield were similar for BA, NAA, and CB, BA treated fruit were larger, indicating that BA increased fruit size beyond the effect attributable to chemical thinning alone. BA increased the rate of cell layer formation in the fruit cortex, indicating that BA stimulated cortical cell division. NAA, CB and DM had no effect on cell division rate. Mean cortical cell diameter at harvest was increased by NAA and CB and reduced by DM. Cell diameter at harvest in BA-treated fruit was similar to the control. These data support the hypothesis that BA-induced fruit size increase in `Empire' apple results from greater numbers of cells in the fruit cortex, whereas the fruit size increase due to NAA or CB is a consequence of larger cell size. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)]; 1-napthaleneacetic acid (NM); 1-naphthalenyl methylcarbamate [carbaryl (CB)]; butanedioic acid mono (2,2dimethyl hydrazide) [daminozide (DM)].

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Paul T. Wismer, J.T.A. Proctor and D.C. Elfving

Benzyladenine (BA), carbaryl (CB), daminozide (DM), and naphthaleneacetic acid (NAA) were applied postbloom, as fruitlet thinning agents, to mature `Empire' apple trees. Although fruit set and yield were similar for BA, NAA, and CB, BA-treated fruit were larger, indicating BA increased fruit size beyond the effect attributable to thinning. BA applied at 100 mg·liter–1 increased the rate of cell layer formation in the fruit cortex, indicating that BA stimulated cortical cell division. The maximum rate of cell division occurred 10 to 14 days after full bloom (DAFB) when fruit relative growth rate and density reached a maximum and percent dry weight reached a minimum. Cell size in BA-treated fruit was similar to the control. Cell division ended by 35 DAFB in the control and BA-treated fruit when percent dry weight and dry weight began to increase rapidly and fruit density changed from a rapid to a slower rate of decreased density. These data support the hypothesis that BA-induced fruit size increases in `Empire' apple result largely from greater numbers of cells in the fruit cortex, whereas the fruit size increase due to NAA or CB is a consequence of larger cell size.

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Guiwen W. Cheng and Patrick J. Breen

Fruit size, number of receptacle cells, and mean cell size were determined throughout development of secondary fruit of three day-neutral strawberry (Fragaria ×ananassa Duch.) cultivars grown in a greenhouse. Cells were counted after enzymatic separation of receptacle tissue, and mean cell volume was estimated from cell count and receptacle tissue volume. Size of mature fruit was small (3.8 g) in `Tillikum', medium (11.5 g) in `Tristar', and large (15.6 g) in `Selva'. Fruit size was correlated with the number of achenes per berry. Mature fruit of `Tillikum' had a lower fruit fresh weight per achene and lower achene population density (achenes per square centimeter) than the larger-fruited cultivars. The average number of cells per mature fruit was 0.72 × 106, 1.96 × 106, and 2.94 × 106 for `Tillikum', `Tristar', and `Selva', respectively. The relative difference among cultivars in the number of receptacle cells was established by the time of anthesis. In all cultivars, cell division was exponential for 10 days following anthesis and ceased by the 15th day. Mean cell volume increased slowly during active cell division, but rose rapidly and linearly for 10 days after cell division halted. Mean cell volume of all cultivars increased > 12-fold after anthesis and was ≈ 6 × 106 μm3 in mature fruit. The genotypic variation in the size of mature fruit was not the result of large differences in either duration of cell division after anthesis or mean cell volume, but rather was primarily due to differences in the number of receptacle cells established by anthesis.