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F. Kultur, H.C. Harrison and J.E. Staub

Muskmelon (Cucumis melo L.) genotypes, Birdsnest 1 [`Qalya' (BN1)], Birdsnest 2 (BN2), and `Mission' (V) were used to determine the effects of differing plant architecture and spacing on fruit sugar concentration and yield. The BN1 and BN2 genotypes possessed a highly branched growth habit specific to birdsnest melon types, but not characteristic of standard indeterminate vining types (e.g., `Mission'). Experiments were conducted at both the Hancock and Arlington Experimental Farms in Wisconsin, where plant response to two within-row spacings [35 cm (72,600 plants/ha) and 70 cm (36,300 plants/ha)] in rows on 210-cm centers was examined. Genotypes were grown in a randomized complete-block design with four replications at each location and evaluated for primary lateral branch number, fruit number per plant and per hectare, average fruit weight, yield per plant (g), yield per hectare (t), and fruit sugar concentration. Yield, fruit number, and sugar concentration were higher for all genotypes at Arlington than at Hancock. The main effect of genotype was significant for all traits examined. Genotypes BN1 and V had higher mean fruit weight, yield per plant and per hectare, and fruit quality (fruit sugar concentration) than did BN2. Spacing affected all traits, except primary branch number and fruit sugar concentration. Fruit number and yield per plant and average fruit weight were higher with wider spacing, but yield (t·ha-1) and fruit number per hectare were lower.

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F. Kultur, H.C. Harrison and J.E. Staub

Muskmelon (Cucumis melo L.) genotypes, Birdsnest 1 [`Qalya' (BN1)], Birdsnest 2 (BN2), and `Mission' (V) were used to determine the effects of plant architecture and spacing on fruit sugar concentration and yield. The BN1 and BN2 genotypes possessed a highly branched growth habit specific to birdsnest melon types but not characteristic of standard indeterminate vining types (e.g., `Mission'). Experiments were conducted at the Hancock (sandy soil, <1% organic matter) and Arlington (heavy, praire loam soil, >4% OM) Experimental Farms in Wisconsin. Plant response to two within-row spacings [35 cm (72,600 plants/ha) and 70 cm (36,300 plants/ha)] in rows on 210-cm row centers was examined. Genotypes were grown in a randomized complete-block design with four replications at each location and evaluated for primary lateral branch number, fruit number per plant, fruit number per hectare, average fruit weight, yield (g) per plant, yield (MT) per hectare, and fruit sugar concentration. All genotypes produced higher yield, fruit number and sugar concentration on the mineral soil at Arlington compared to the sands at Hancock. The main effect of genotypes was significant for all traits examined. BN1 and V genotypes had greater yield (gram per plant, yield per hectare, and average fruit weight) as well as higher fruit quality (fruit sugar concentration) than the BN2 genotype. Spacing affected all traits examined except primary branch number and fruit sugar concentration. As withinrow spacing increased from 35 to 70 cm, fruit number per plant, yield per plant and average fruit weight increased. However, yield (MT) per hectare and fruit number per hectare decreased. Fertility was adjusted according to soil tests for the two different soil types at the two farm locations.

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N. Georgelis, J.W. Scott and E.A. Baldwin

Small-fruited cherry tomato accession PI 270248 (Lycopersicon esculentum Mill. var. cerasiforme Dunal) with high fruit sugars was crossed to large-fruited inbred line Fla.7833-1-1-1 (7833) that had normal (low) fruit sugar. Sugars in the F2 were positively correlated with soluble solids, glucose, fructose, pH, and titratable acidity, and inversely correlated with fruit size. Earliness was not significantly correlated with sugars but was negatively correlated with fruit size. Thus, the lack of a sugar-earliness correlation indirectly indicates a trend for early tomato plants to be lower in sugars than later maturing plants. Sugars were not correlated with yield or pedicel type. Fruit from indeterminate plants had significantly more sugars than from determinate plants. Six random amplified polymorphic DNA (RAPD) markers linked to high sugars were found, five dominant (OPAE 4, UBC 731, UBC 744, UBC 489, UBC 290) and one co-dominant (UBC 269). Five of the markers were also linked to small fruit size and one of these also was linked to low yield (UBC 290). The sixth marker (UBC 269) was linked to indeterminate plant habit. UBC 731, UBC 489, and possibly OPAE 4 were in one linkage group, while UBC 744 and UBC 290 were in another linkage group. Combinations of all the markers together explained 35% of the sugar variation in the F2 grown in Spring 2002.

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Zhifang Gao, Sastry Jayanty, Randolph Beaudry and Wayne Loescher

In apple (Malus ×domestica Borkh.), where sorbitol is a primary photosynthetic product that is translocated throughout the plant, accumulation of sorbitol in sink cells appears to require an active carrier-mediated membrane transport step. Recent progress in isolation and characterization of genes for sorbitol transporters in sour cherry (Prunus cerasus L.) and mannitol transporters in celery (Apium graveolens L.) suggested that similar transporters may be present in apple tissues. A defect in these transporters could also explain the occurrence of the fruit disorder watercore, characterized by the accumulation of fluids and sorbitol in the apoplasmic free space. Our objectives therefore included isolation and characterization of genes for sorbitol transporters in apple tissues and comparisons of expression of transporter genes, especially in various sink tissues including watercored and non-watercored fruit tissues. We have isolated and characterized two sorbitol transporter genes, MdSOT1 and MdSOT2. Sequence analyses indicated that these are members of the major facilitator transporter superfamily that gives rise to highly hydrophobic integral membrane proteins. Heterologous expression and measurement of sorbitol uptake in yeast indicated that these are specific and with high affinities for sorbitol, with Kms for sorbitol of 1.0 and 7.8 mm for MdSOT1 and MdSOT2, respectively. Sorbitol transporter expression was evident in all sink tissues tested with the exception of watercore-affected fruit tissues. Sorbitol accumulation in apple sink tissues thus involves an apoplasmic active membrane transport step and watercore results from a defect in that process.

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John R. Stommel and Kathleen G. Haynes

Fruit of the cultivated tomato (Lycopersicon esculentum Mill.) store predominantly glucose and fructose whereas fruit of the wild species L. hirsutum Humb. & Bonpl. characteristically accumulate sucrose. Reducing sugar and sucrose concentrations were measured in mature fruit of parental, F1, F2, and backcross (BC1) populations derived from an initial cross of L. esculentum `Floradade' × L. hirsutum PI 390514. Generational means analysis demonstrated that additive effects were equal to dominance effects for percentage of reducing sugar. It was determined that a single major gene, dominant for a high percentage of reducing sugar, regulates the percentage of reducing sugar in tomatoes. We propose that this gene be designated sucr. Only additive effects were demonstrated to be important for glucose: fructose ratios. Using L. hirsutum as a donor parent for increasing total soluble solids concentration in the cultivated tomato is discussed.

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I-C Wen, W.B. Sherman and K.E. Koch

Peach-to-nectarine mutations are associated with broad pleiotropic effects. The present study addresses the heritability of nectarine-specific effects in three hybrid families. A comparison of peach and nectarine siblings showed that nectarine fruit were smaller (less fresh weight), rounder, darker, redder, and had higher levels of sugars and organic acids. These heritable characteristics are similar to effects of spontaneous peach-to-nectarine mutations described previously.

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Ien-Chi Wen, K. E. Koch and W. B. Sherman

Two peach-to-nectarine mutants were compared with their peach progenitors to quantify physical and biochemical characters associated with this conversion. Both nectarine mutants showed pleiotropic effects that included smaller, rounder, and more-dense fruit with redder skin and altered sugar and organic acid composition relative to those found in their peach progenitors. In addition, one of the nectarine mutants exhibited a later bloom time, a less pronounced change in fruit size, a shorter fruit development period, and an associated capacity to develop red fall leaf color.

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Gerhard C. Rossouw, Jason P. Smith, Celia Barril, Alain Deloire and Bruno P. Holzapfel

maturity ( Van Leeuwen et al., 2009 ). A depletion of root TNC coincided with rapid fruit sugar accumulation ( Table 3 ), and root TNC reserves were seemingly not used toward structural development in the fruited vines ( Fig. 1 ). In the absence of fruit

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Gene E. Lester, Luis Saucedo Arias and Miguel Gomez-Lim

Muskmelon [Cucumis melo L. (Reticulatus Group)] fruit sugar content is the single most important consumer preference attribute. During fruit ripening, sucrose accumulates when soluble acid invertase (AI) activity is less then sucrose phosphate synthase (SPS) activity. To genetically heighten fruit sugar content, knowledge of sugar accumulation during fruit development in conjunction with AI and SPS enzyme activities and their peptide immunodetection profiles, is needed. Two netted muskmelon cultivars, Valley Gold a high sugar accumulator, and North Star a low sugar accumulator, with identical maturity indices were assayed for fruit sugars, AI and SPS activity, and immunodetection of AI and SPS polypeptides 2, 5, 10, 15, 20, 25, 30, 35, or 40 (abscission) days after anthesis (DAA). Both cultivars, grown in the Fall, 1998 and Spring, 1999, showed similar total sugar accumulation profiles. Total sugars increased 1.5 fold, from 2 through 5 DAA, then remained unchanged until 30 DAA. From 30 DAA until abscission, total sugar content increased, with `Valley Gold' accumulating significantly more than `North Star'. During both seasons, sucrose was detected at 2 DAA, which coincided with SPS activity higher than AI activity, at 5 through 25 DAA, no sucrose was detected which coincided with SPS activity less than AI activity. At 30 DAA when SPS activity was greater than AI activity, increased sucrose accumulation occurred. `Valley Gold' at abscission had higher total sugar content and SPS activity, and lower AI activity than `North Star'. `North Star' had AI isoforms at 75, 52, 38, and 25 kDa (ku) that generally decreased with maturation, although the isoform at 52 ku remained detectable up to anthesis (40 DAA). `Valley Gold' had the same four AI isoforms, all decreased with maturation and became undetectable by 20 DAA. Both `Valley Gold' and `North Star' had one SPS band at 58 ku that increased with DAA, and coincided with SPS activity. `Valley Gold' had a more intense SPS polypeptide band at abscission than `North Star'. Thus, netted muskmelon fruit sugar accumulation may be increased, either by genetic manipulation or by selecting for cultivars with a specific number of down-regulated AI isoforms, and higher SPS activity during fruit ripening.

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N. Georgelis, J.W. Scott and E.A. Baldwin

Small-fruited cherry tomato accession PI 270248 [Lycopersicon esculentum Mill. var. cerasiforme (Dunal) A. Gray] with high fruit sugars was crossed to large-fruited inbred line Fla.7833-1-1-1 (7833) (L. esculentum) that had normal (low) fruit sugars. The F1 was crossed to PI 270248 and 7833 to obtain BCP1 and BCP2, respectively, and self-pollinated to obtain F2 seed. The resulting population was used to study the inheritance of high sugars from PI 270248. Continuous sugar level frequency distributions of BCP1, BCP2, and F2 suggest that the trait is under polygenic control. Additive variation was significant, but dominance variation was not. There was a heterozygote × heterozygote type of epistasis present that likely caused the F1 sugar level to skew nearly to the level of the high sugar parent. The F2 mean sugar level was lower than the midparent level. Broad-sense heritability was 0.86. There was a significant line × season (fall, spring) interaction where lines with higher sugars were affected more by seasons than lines with lower sugars. Sugar level, in general, was higher in spring. Higher solar radiation in spring than in fall may explain the sugar level difference between the seasons.