Small Fruit Size Research Articles

518 Regulating Fruit Set and Maturity of `Macoun' Apples

`Macoun' is a high-value apple cultivar in the northeastern United States that is very difficult to produce. It is difficult to thin and prone to alternate bearing. `Macoun' is also prone to preharvest drop. Small fruit size, bruising, and lack of red color are additional obstacles to profitable production. The objective of this study was to compare the efficacy of two chemical thinning treatments—accel plus carbaryl, or NAA plus carbaryl—with an untreated control. A second objective was to evaluate the efficacy of ReTain for delaying `Macoun' fruit maturity and to determine if there was an interaction between ReTain and thinning treatment on fruit characteristics at harvest. Both thinning treatments were effective in reducing fruit set in 1997. Accel plus carbaryl was effective again in 1998, while NAA plus carbaryl over-thinned. Accel increased fruit size in 1997 compared to unthinned controls, and both thinning treatments increased fruit size in 1998. Accel increased fruit firmness in both years. ReTain reduced preharvest drop and delayed fruit maturity both years. In 1997, firmness was greatest for fruit treated with accel and ReTain, while ReTain had no effect on firmness of fruit from NAA thinned trees. ReTain had no effect on fruit firmness in 1998.

657 Relationship between Intensity of Flowering and Cropping in Fruit and Nuts

The relationship between intensity of flowering and various aspects of cropping will be reviewed for fruit and nuts. Clearly, relatively light flowering can limit yield in most fruit and nut species. This commonly occurs before mature bearing commences and in “off” years for varieties that display alternate bearing. During mature bearing, many species will carry fruit numbers that exceed commercially desired levels, resulting in excessively small fruit and accentuating alternate bearing. The economic disadvantages of excess cropload have resulted in considerable research on fruit thinning and widespread commercial application of this practice. Heavy flowering intensity in some crop species results in economic disadvantages beyond the problems of excessive cropload and resultant small fruit size. Many species flower profusely and have initial fruit set far in excess of final tree capacity, resulting in abscission of numerous flowers and fruitlets. Abscised organs can represent a substantial investment in carbohydrates and nutrients, compromising availability at critical periods in flower and fruit development. The potential implications of this process are best exemplified in navel orange, where an increase in flowering beyond intermediate intensity results in a reduction in both initial fruit set and final fruit yield at harvest. In several crops, there is evidence that fruit size may be reduced by excessive flowering, even when cropload is quickly adjusted to an acceptable level. These data suggest that further research on the advantages of controlling flowering intensity is warranted.

Shoot Growth and Fruit Development as Affected by Warming the Soil in Forcing Culture of 'Tonewase' Persimmon under Restricted Root Volume.

Effects of warmed and non-warmed soils on shoot growth and fruit development were compared by using in seven-year-old 'Tonewase' persimmon (Diospyros kaki L.) in forcing culture under restricted root volume condition. The warmed soil was maintained at 20°C by circulating warm water in the pipes laid in the ground from Jan.12 to Apr.15. The time of bud burst and anthesis by warming was advanced slightly, compared with plants in the non-warmed treatment. Warming the soil increased shoot growth and accelerated maturation and TSS accumulation of fruit, but the yield was reduced because of low fruit set and small fruit size.

Fruit Removal and Continual Defoliation Altered Papaya Fruit Production and Quality

The source size and sink strength were modified by continual defoliation and fruit removal in `Sunset' papaya. Flower and fruit set, mature fruit mass, and TSS was recorded weekly. Fruit at four different stages of development were harvested at the end of the experiment. Fruit mass, respiration, sugar content, and sucrose phosphate synthase (SPS), sucrose synthase (SS), and invertase enzyme activities were compared. Continual defoliation resulted in lower new fruit set (25% of control), smaller fruit size (77% of control), and lower TSS (85% of control) in the 24-week experimental period. In contrast, there were 52% and 100% more new fruit when fruit were removed than in the control within the first 8 weeks and 24 weeks, respectively. Larger fruit size, earlier fruit development, lower respiration, and higher sugar contents were observed when fruit were removed at 140, 154, and 175 days from anthesis. No significant difference was found in TSS level in the mature fruit compared to the control. Fruit removal plus defoliation gave the same number and mass of new fruit as the control and slightly lower TSS in mature fruit than in the control. Fruit sugar was higher with increased fruit invertase activity and fruit age. Data confirmed that source–sink balance was critical for fruit set, development, and sugar accumulation in papaya.

Effects of AVG, NAA, Ethephon, and Summer Pruning on Preharvest Drop and Fruit Quality of `McIntosh'

Ethylene production increases dramatically during maturation and ripening of `McIntosh' apples, frequently resulting in preharvest drop and accelerated fruit softening. As harvest approaches, commercial growers must balance the need for color development with minimizing fruit softening and drop. The effects of plant growth regulators and summer pruning on this balance were evaluated in this study. Treatments were applied to trees in the Mid-Hudson in 1995 and 1996 and a subset of growth regulator treatments was applied in the Champlain Valley in 1996. NAA (naphthalene acetic acid) significantly reduced drop on only one sample date in only one of the three trials. Ethephon (2-chloroethylphosphonic acid) at 150 ppm plus 10 ppm NAA, accelerated ripening and permitted harvest before substantial drop occurred, but earlier harvest resulted in smaller fruit size. AVG (aminoethoxy vinyl glycine) at 124 gram a.i./ha, on otherwise untreated trees, significantly delayed drop compared to the controls in two of three trials and resulted in better fruit firmness out of storage. Use of ethephon on AVG-treated trees significantly enhanced red color but also accelerated drop, although drop was reduced compared to ethephon only treatment. Late summer pruning significantly accelerated red color development, drop and ripening in both years. Pruning 16 Aug. 1996 significantly accelerated drop compared to pruning 1 Aug. 1996. Combining AVG application and pruning on 16 Aug. 1996 resulted in improved color without increasing drop compared to controls.

EFFECTS OF DIFFERENT IRRIGATION LEVELS ON APPLE FRUIT QUALITY

Irrigation scheduling for deciduous fruit trees is an unresolved matter. Methods available do not respond satisfactorily to the demands of fruit grower. On the other hand productivity and quality criteria established to decide which is the best irrigation treatment do not necessarily coincide. Maximization of fruit production may be contradictory with maximum high quality production and optimization of certain horticultural practices such as reduction of pruning time or tree vigor control. An irrigation experiment was set up to validate the water budget method for irrigation scheduling with estimation of water usage using crop Evapotranspiration. As expected, treatments with lesser quantity of irrigation water applied, resulted in a higher frequency of fruits in the small size fruit classes. On the contrary, increasing amount of water applied, resulted in a statistically significant tendency of lower fruit firmness and fruit refractometric index (RI). However, the decrease in fruit firmness and RI has been variable with years and on average has no practical significance on today's industry mode of operation.

The stunted fruit disorder—A physiological anomaly in mango (Mangifera indica L.) caused by a fluorine pollutant

SummaryThe stunted mango fruit disorder (SFD) is characterized by small-sized fruit, stiffened pulp tissue and failure to ripen at harvest. A cabinet fumigation trial with potted fruiting mango trees was carried out to investigate the cause of this disorder. Treatment with hydrogen fluoride (12 μg HF m–3 and 24 μg HF m–3) succeeded in inducing the typical symptoms of SFD, while treatment with sulphur dioxide (800 μg SO2 m–3) failed. Inhibition of cell expansion growth was observed in SFD fruits. The cells of affected fruits were much smaller than those of normal fruits at the same growth stage. Although reduction of photosynthesis of mango leaves was seen under both HF and SO2 fumigation treatments, it did not seem to limit fruit growth. The leaf and fruit fluorine (F) or sulfur (S) contents increased in HF or SO2 fumigation treatments. Fluorine pollutant in the smoke emitting from brick-kilns or aluminum factories must be the direct cause of SFD.

Inheritance of Resistance to Anthracnose Caused by Colletotrichum coccodes in Tomato (Lycopersicon esculentum)

Anthracnose, caused by Colletotrichum coccodes, is a serious ripe tomato fruit rot disease. Genetic resistance to anthracnose is not available in commercial tomato cultivars, but has been reported in small-fruited Plant Introductions (P.I.), and with lesser intensity in a number of breeding lines. Transfer of high levels of resistance from these breeding lines or P.I.s to elite materials has proven difficult. Inheritance of resistance has been described as complex with at least six loci influencing resistance reactions. Segregating populations originating from a cross between a susceptible tomato breeding line and a large-fruited breeding line (88B147) with resistance derived from Lycopersicon esculentum var. cerasiforme P.I. 272636, were evaluated for anthracnose resistance. Analysis of anthracnose resistance in puncture-inoculated fruit indicated small, but significant, additive genetic effects for resistance. Additional populations were developed from crosses of a susceptible inbred processing tomato cultivar with: 1) the resistant P.I. 272636, 2) an unadapted small-fruited resistant line developed from P.I. 272636, and 3) the large-fruited breeding line 88B147, also with resistance derived from P.I. 272636. Small additive effects identified in large-fruited material, in comparison to the resistant P.I., suggests that resistance loci have been lost during germplasm development. This is consistent with the relatively larger lesions observed in large-fruited lines derived from P.I. 272636. Positive correlations were noted between small fruit size and high levels of anthracnose resistance. Identification of molecular markers linked to resistance genes in the respective populations will be discussed.

Monopotassium phosphate as a phosphorus and potassium source for greenhouse‐winter‐grown cucumber and muskmelon1

Glasshouse experiments were conducted at the Newe Ya'ar Research Center in the winter seasons of 1992/93 and 1993/94 to examine a phosphorus/ potassium (PK) fertilizer for cucurbit crops. Monopotassium phosphate [(MKP), KH2PO4] was found to be very effective as a P and K source for cucumber (Cucumis sativus L.) and muskmelon (Cucumis melo L.) plants grown in soilless container conditions. The efficiency of MKP was essentially not different from that of the combination of phosphoric acid (H3PO4) and potassium chloride (KCl) which is widely used in the commercial production of vegetables. Appropriate fertilization of cucumbers with MKP in 1992/93 affected late‐season yield more than early‐season yield. Deficiency of P and K in Gala muskmelon inhibited vegetative growth and decreased yield. The reduced yield resulted from both less fruit‐setting and smaller fruit size. The MKP rates required by cucumber plants in 1993/94 depended primarily on growth medium composition. Generally, plants grown in inert tuff (volcanic gravel) and sandy media responded more significantly to MKP than did those grown in media rich in organic matter. There are at least three reasons for preferring the use of MKP, first it is much safer to handle than is H3PO4, second it is highly soluble and can be easily incorporated in fertigation systems, and third it has a high PK content.

Carbohydrate Contribution to Fruit Development in Two Phenologically Distinct Rabbiteye Blueberry Cultivars

Rabbiteye blueberry (Vaccinium ashei Reade) cultivars differ in timing of floral and vegetative budbreak and in final fruit size. For example, `Bonita' exhibits concomitant floral and vegetative budbreak and has relatively large fruit size, while floral budbreak precedes vegetative budbreak in `Climax' and fruit size is smaller. Mobilization of carbohydrate before and during fruit development in `Bonita' and `Climax' rabbiteye blueberries was examined to determine if differences in carbohydrate availability between these two cultivars were correlated with differences in fruit size. Root dry mass (DM) of both cultivars decreased from dormancy (31 days before anthesis) through fruit development. Sugar concentrations in roots and stems of both cultivars decreased significantly between dormancy and anthesis, then remained relatively steady throughout fruit development. Starch concentrations in roots and stems of `Bonita' decreased significantly between dormancy and anthesis. The extent of total starch depletion in `Climax' was similar; however, the decrease was more gradual, extending from dormancy to 28 days after anthesis (DAA); at which time, vegetative budbreak in `Climax' occurred. Thus, although total reserve carbohydrate pool sizes were similar between the two cultivars, remobilization patterns were different, resulting in increased starch mobilization in `Bonita' compared to `Climax' in the period leading up to anthesis. Concentration of 14C from reserve carbon sources was similar in flowers of both cultivars at anthesis. These values declined throughout fruit development as a result of dilution of the labeled carbon by unlabeled carbon from current photosynthesis. There was a sharper decline in 14C concentration of `Bonita' fruit compared to `Climax' fruit between anthesis and 51 DAA. This, coupled with differences in timing of vegetative budbreak between the two cultivars, suggests that `Bonita' fruit were accessing current (unlabeled) assimilate earlier (i.e., before 51 DAA) than `Climax' fruit. Smaller fruit size in `Climax' compared to `Bonita' may be a consequence of a decrease in reserve carbohydrate mobilization to `Climax' flower buds before anthesis relative to `Bonita', as well as a delay or reduction in the availability of current carbohydrates to developing `Climax' fruit between anthesis and 51 DAA.

Influence de la fertilisation azotée, des bâches et des cultivars sur la productivité des fraisiers à production continue au Québec

The effects of two nitrogen sources and a row cover were studied for 2 day-neutral strawberry cultivars covered with different row covers and grown for 3 yr at two sites at Lavaltrie and L’Acadie. The nitrogen sources did not significantly (P ≤ 0.05) affect yield and fruit size at either site. However, the black polyethylene mulch combined with cultivar Tribute increased yield and fruit size at both sites. The use of a row cover in the fall did not prevent early frosts or lengthen the picking season. Despite a smaller fruit size and 5–8 d of earliness, good total yields appear possible from a second year crop of day-neutrals. Key words: Strawberry, nitrogen, NH4, sulphur-coated urea, mulching, yield, fruit size.

A Comparison of Pseudomonas solanacearum- resistant Tomato Cultivars as Hybrid Parents

Seven tomato Lycopersicon esculentum lines, `Venus', `Saturn', `Rodade', `Rotam 4', `Hawaii 7998', `UC-82B', and `Stevens', and their 21 crosses were evaluated for their ability to resist infection by seven virulent strains of Pseudomonas solanacearum E.F. Sm. representing race 1 biovars 1 and 3. The Gardner and Eberhart model III analysis was used to evaluate the response of lines in crosses to P. solunaceurum infection. General combining ability mean squares were significant for all strains and in 5 of 7 instances specific combining ability mean squares were significant. In four instances the parent vs. cross contrast was significant. `Hawaii 7998' was resistant to all seven strains of P. solanacearum, whereas `Rotam 4' and `Rodade' were resistant to biovar 3 and two races of biovar 1. `Venus' and `Saturn' were resistant to two other biovar 1 strains. `Hawaii 7998' transmitted greater resistance than the other resistant parents, but its small fruit size and indeterminate growth habit make it a poor choice for a hybrid parent.

EFFECT OF NAA OR ACCEL SPRAYS ON YIELD AND FRUIT SIZE OF `EMPIRE' APPLE ON THREE ROOTSTOCKS

`Empire' is a popular new apple with fruit growers in the northeastern United States, noted for producing small-sized fruit. To test the efficacy of chemical thinners and rootstocks for increasing fruit size of `Empire', three-tree plots containing trees on M.7 EMLA, MM. 111, and seedling rootstocks were chemically thinned at petal fall with 10 ppm NAA or 85 ppm 6 BA, applied as Accel. Both NAA and Accel reduced fruit set. Trees on M.7 EMLA had higher set than trees on seedling. Yield was highest on M.7 EMLA and lowest on seedling. Fruit diameter after final set in July was increased by both chemical thinners and was greater for both clonal rootstocks than for seedling. Fruit on seedling trees were delayed in maturity relative to the two clonal rootstocks. Accel increased the number of fruit 70 mm or greater in diameter, while NAA increased the number of fruit in the 64- to 69-mm-diameter class. Analysis of covariance with crop load suggested that the increase in fruit size associated with Accel was a direct effect rather than a secondary effect from thinning.

Sensitivity of Yield and Fruit Quality of French Prune to Water Deprivation at Different Fruit Growth Stages

The sensitivity of French prune (Prunus domestica L. syn. `Petite d'Agen') to water deprivation at various fruit growth stages was studied over 3 years in a drip-irrigated orchard. The soil was a poorly drained Rocklin fine sandy loam with a hardpan that varied from 4.75 to I m from the surface at the northern end of the orchard (shallow soil condition) to no hardpan apparent to 2 m below the surface at the southern end of the orchard (deep soil condition). Water deprivation during a) the first exponential phase of fruit growth or stage I, b) lag phase of fruit growth or stage II, c) first half of stage II, d) second half of stage II, e) second exponential fruit growth phase or stage III, and f) postharvest was compared to a fully watered control. Water deprivation caused the most severe reduction in tree water status when it was imposed over longer periods of time and during periods of high evaporative demand and also had mm-e severe effects under shallow soil conditions. Compared to the control treatment, deprivation during all of stage II (the most severe deprivation treatment) was associated with increased Ilowering, reduced fruit hydration ratio, and smaller fruit size under all soil conditions. Under deep soil conditions, deprivation during all of stage II resulted in increased return bloom, which was reflected in higher fruit loads and dry t-ha-' fruit yield. However, under shallow soil conditions, even though return bloom was increased with this treatment, fruit loads and dry t·ha-1 fruit yields were the lowest of all treatments. These differences in treatment effects in shallow vs. deep soil conditions were most likely the result of increased fruit drop, which occurred under shallow soil conditions as a result of rapid onset and increased severity ofstress. Treatments that had parallel effects in shallow and deep soil conditions resulted in statistically significant overall treatment effects, while those that had opposing effects in shallow vs. deep soil conditions did not show significant overall treatment effects. Substantial alternate hearing occurred, and, in general, dry fruit yields above ≈9 dry t·ha-1 resulted in a decrease in fruit load the following year, while loads below this value showed a subsequent increase. Based on a separate estimate of the theoretically stable value for each treatment, all deprivation treatments resulted in a higher sustainable fruit load compared to the fully irrigated control. This suggests that, for the purpose of prune fruit production, there may be an optimal level of tree water stress.

482 PB 414 A COMPARISON OF Pseudomonas solanacearum-RESISTANT TOMATO CULTIVARS AS HYBRID PARENTS

Seven tomato lines and their 21 hybrid populations were evaluated for their ability to resist infection by 7 virulent strains of Pseudomonas solanacearum representing race 1 biovars 1 and 3. In all cases the Gardner and Eberhart model III analysis found GCA values to be significant. In 5 of 7 cases SCA was significant. In 4 cases the parent vs. cross contrast was significant. We conclude that resistance to Pseudomonas solanacearum is predominantly controlled by additive gene action and to a lesser degree by dominant gene effects. Hawaii 7998 was found to be resistant to all 7 strains, while Rotam 4 and Rodade were resistant to biovar 3 and one race of biovar 1 (UW 275). Venus and Saturn were resistant to 3 other biovar 1 strains. Hawaii 7998 transmitted disease resistance better than the other resistant parents but its small fruit size and indeterminate growth habit make it a poor choice for a hybrid parent.

745 PB 079 SINK SIZE IN GAs-TREATED AND POLLINATED RABBITEYE BLUEBERRY FRUITS

Exogenous applications of GA, have induced pathenocarpic fruit set in blueberry; however, size of GA,-treated fruit is smaller than pollinated fruit. The small fruit size in GA3-treated fruit may be related to either cell number and/or cell size. Thus, these parameters were examined throughout development in pollinated, non-pollinated and GA3-treated fruits. Fruit growth followed a double sigmoid pattern. During Stage I (0-25 DAA), fruit size in GA,-treated, pollinated, and non-pollinated fruits averaged 0.33, 0.39, and 0.16 g, respectively. There was little change in fruit size in Stage II (25-45 DAA). At ripening, fruit size averaged 1.7 g for GA,-treated and 2.6 g for pollinated fruits. Non-pollinated fruit abscised in Stage II. At anthesis, mesocarp cell number averaged 9910 cells per median cross sectional area and remained constant up to ripening. In Stage I, cell size in G A3-treated and pollinated fruits increased 7X and 9X respectively. Cell size in both fruit types increased 1.5X and 2.8X during Stage II and Stage 111, respectively. Fruit cell number was set at anthesis and differences in fruit size were due to differences in cell ellongation in Stage I.

INHERITANCE AND HERITABILITY OF SEED SIZE IN HULLLESS SEEDED STRAINS OF CUCURBITA PEPO

Genetic experiments were initiated to assess the potential for combining large seed size from PI 285611, a large-fruited, hullless seeded accession, with small fruit size from a hullless seeded breeding line (NH29-13-5-4). An F2 population and parental line were field-grown during Summer 1993 to determine inheritance and heritability of large seed size and the relation between fruit and seed size. Seed size variables of weight, width, length, and thickness were regressed against fruit weight. There was a moderate, positive correlation between large fruit and seed length (R2 = 0.46). However, seed thickness, a major determinant of seed weight, was not correlated with fruit size. In an F2 population of ≈450 plants, there was a small number of plant selections with fruit under 1.5 kg and seed size approaching that of PI 285611.

FIELD PERFORMANCE AND SENSORY ANALYSIS OF EARLY TO MIDSEASON TOMATO CULTIVARS

Twelve early to midseason ripening tomato cultivars were evaluated for early and total marketable yield, fruit size, and external characteristics under the cool, short growing season of northern New England. The acceptability of external and internal color, texture, and flavor of four cultivars was evaluated by a sensory panel of 50 members. There was little difference between cultivars in total yield. This was probably due to an early frost that destroyed much of the later ripening fruit. `Summerset' had the highest early and overall yields but the smallest fruit size. `Johnny's 361` had high overall yield and large fruit with good early yields. `Pilgrim' had high early yield, good overall yield, and fair fruit size. `Jetstar' and `Daybreak' fell into the middle of the range for total yield and fruit size, but `Jetstar' had very low early yield. `Pik Red' and `Pik Rite' had low early and total yields but good fruit size. `Moreton Hybrid' had fair early and total yields and small fruit size. In the sensory analysis, `Sunrise' had the highest rated external color, while `Moreton Hybrid' had the lowest rating. Internal color ratings did not vary greatly, although `Sunrise' was least acceptable in this characteristic. `Jetstar' was rated highest for flavor and texture, followed by `Moreton Hybrid', `Sunrise', and `Valley Girl'.

734 (PS 7) FRUIT GROWTH RESPONSES IN `HEDELFINGEN' SWEET CHERRY WITH FIVE ROOTSTOCK CULTIVARS, BLOSSOM THINNING, AND IRRIGATION

Small fruit size reduces fresh-market value and potential net income in sweet cherry. Several new rootstock cultivars for sweet cherry induce greater precocity, heavier blossom density, and a range of dwarfing but also may reduce fruit size. A field study was undertaken with sixth leaf `Hedelfingen' scions grown on Prunus avium L. `Mazzard' seedling rootstock or on one of 4 new rootstock cultivars: `Damil,' `Gi 148/1,' `Gi 172/9,' and `Gi 196/4.' Factorial treatments included (+/-) trickle irrigation when soil tensiometer readings reached 20 k Pa and (+/-) hand thinning to single fruits/cluster aat 7 days after full bloom. High natural precipitation reduced irrigation effect but fruit size was increased significantly by thinning. Yield differences were also seen between rootstock cultivars.

The Use of Full Length 'Festival' Rasberry Canes in a Scheduled Planting and Harvesting System

Late planted full length 'Festival' raspberry canes cropped from early August to mid-October, 2-3 months after planting. The June 1 planting gave the highest yield in 1989 but a smaller fruit size compared to the June 20 planting. Large canes were more productive in 1988 and 1990 but had no effect on fruit size. Excessive amounts of nitrogen fertilization and trickle irrigation after planting appeared to be detrimental to yield.