High Crop Load Research Articles

Source and sink limitations in vascular flows in peach fruit

SummaryThe daily patterns of vascular and transpiration flows to and from peach fruit were compared between heavily-thinned (LCL) and unthinned (HCL) trees, in order to assess when these flows were limited by resource availability (source-limited) or by the genetic potential of the fruit (sink-limited) during the day. Minute variations in fruit growth and in phloem, xylem, and transpiration flows were determined at cell division (stage I) and at cell expansion (stage III) during fruit development on several fruit per treatment, using highly sensitive fruit gauges. During cell expansion, the thinning treatments were also compared for their effects on fruit water potential. At stage I, no difference between treatments was found in any of the flows, suggesting that fresh matter (FM) import from phloem and xylem is sink-limited during early fruit development. At stage III, HCL fruit were smaller and had higher specific transpiration rates during the day. Xylem flow did not show any source limitations due to high crop load. However, it was “sink-strengthened” in the afternoon, in HCL, as these fruit reached lower water potentials during the day. Phloem flow to HCL fruit was source-limited during the afternoon, and at night, due to fruit-to-fruit competition. However, HCL fruit appeared to take advantage of their lower water potential at midday, when they showed higher rates of phloem flow. Although daily growth in HCL fruit undergoes periods of source limitation, this study showed how, at certain times of day, fruit may be more active sinks in attracting resources in high cropping conditions than at low crop loads.

Responses of apple fruit size to tree water status and crop load

The combined effects of irrigation rate and crop load on apple yield and fruit size were examined in two commercial apple orchards (cv. Golden Delicious) in a semi-arid zone. The irrigation rates applied were 1, 3 and 7 mm day(-1), and the two fruit thinning treatments involved adjusting crop load to 100 and 300 fruits per tree at Ortal and 50 and 150 fruits per tree at Matityahu. Unthinned trees served as the control. The fruit from each tree was picked separately, and fruit size distribution was determined with a commercial grading machine. Midday stem water potentials varied from -0.9 to -2.8 MPa, crop load varied from 80,000 to 1,900,000 fruit ha(-1) and crop yield varied from 10 to 144 Mg ha(-1). Midday stem water potential decreased with increasing crop load in all irrigation treatments at Matityahu, but only in the 1 mm day(-1) treatment at Ortal. The extent of the lowering of midday stem water potential by crop load decreased with increasing soil water availability. At both orchards, a similar response of total crop yield to crop load on a per hectare basis was observed. Mean fruit mass and relative yield of fruit > 70 mm in diameter increased with midday stem water potential, with the low crop loads having similar but steeper slopes than the high crop load. The responses of mean fruit mass and relative yield of fruit > 70 mm in diameter to midday stem water potential were similar at both orchards, perhaps indicating that thresholds for irrigation scheduling are transferable to other orchards within a region. Factors that may limit the transferability of these thresholds are discussed.

Plant and Environmental Factors Influencing the Pattern of Pigment Accumulation in ‘Honeycrisp’ Apple Peels Using a Novel Color Analyzer Software Tool

One of the most important factors determining apple (Malus pumila P. Mill.) market acceptance is peel color. Coloring of ‘Honeycrisp’ fruits can adopt two patterns: blushed or striped. This is an unusual phenomenon in apple. The objective of this study was to compare ‘Honeycrisp’ fruit from trees that were propagated from buds occurring on branches carrying only blushed or striped fruit. We concluded that blushed trees tend to produce a higher percentage of blushed fruit than striped trees, indicating a mechanism conserved through cell division. The percentage of blushed fruit on any given tree changed from year to year. Blushed and striped fruit occurred together on the same branch, and even on the same spur, with fruits located in the outer canopy being more likely to be striped. Higher crop loads were associated with a lower percentage of blushed fruit on the tree. Blushed and striped fruit do not consistently differ in their maximum pigment accumulation before ripening. The comparison of average hue angle for the whole peel at harvest indicates that blushed fruit are redder on average. Stripes were caused by reduced anthocyanin accumulation in certain portions of the peel and not by deeper localization. We speculate that an epigenetic mechanism regulates the pattern of anthocyanin accumulation in ‘Honeycrisp’ apple. Increased production of blushed, redder apples may be achieved through clonal selection and crop load regulation. A software tool for efficient relative color evaluations was developed and is freely available to the community.

Carbohydrate availability affects growth and metabolism in peach fruit

Along with sucrose, sorbitol represents the main photosynthetic product and form of translocated carbon in peach. This study aimed at determining whether peach fruit carbohydrate metabolism is affected by changes in source-sink balance, and specifically whether sorbitol or sucrose availability regulates fruit enzyme activities and growth. In various trials, different levels of assimilate availability to growing fruits were induced in vivo by varying crop load of entire trees, leaf : fruit ratio (L:F) of fruiting shoots, or by interrupting the phloem stream (girdling) to individual fruits. In vitro, fruit tissue was incubated in presence/absence of sorbitol and sucrose. Relative growth rate (RGR), enzyme activities and carbohydrates were measured at different fruit growth stages of various peach cultivars in different years. At stage III, high crop load induced higher acid invertase (AI, EC 3.2.1.26) activities and hexose : sucrose ratios. Both sorbitol and sucrose contents were proportional to L:F, while sorbitol dehydrogenase (SDH, EC 1.1.1.14) activity was the only enzyme activity directly related to L:F in both fruit growth stages. Girdling reduced fruit RGR and all major carbohydrates after 4 days and SDH activity already after 48 h, but it did not affect sucrose synthase (SS, EC 2.4.1.13), AI and neutral invertase (NI, EC 3.2.1.27). Fruit incubation in sorbitol for 24 h induced higher SDH activities than in buffer alone. In general, assimilate availability affected both sorbitol and sucrose metabolism in peach fruit, and sorbitol may function as a signal for modulating SDH activity. Under highly competitive conditions, AI activity may be enhanced by assimilate depletion, providing a mechanism to increase fruit sink strength by increasing hexose concentrations.

Growth, Yield, Fruit Composition of 24 Wine and Table Grape Cultivars and Selections

ABSTRACT Eight American (Vitis labrusca L.); eight European (Vitis vinifera L.), including four Eastern European selections; four hybrids; and four table grape cultivars planted in 2002 were evaluated for yield components, berry composition, berry split, and frost damage from 2004 to 2006 in south-central Kansas. Over the three years, harvest started in July, although summer of 2006 was the warmest year, which accelerated maturity, reduced titratable acidity (TA), and increased soluble solids concentration (SSC). Earliest-and latest-ripening grapes, respectively, were ‘Valiant’ and ‘Catawba’ (American), ‘Nero’ and ‘Bromariu’ (European), ‘LaCrescent’ and ‘Traminette’ (hybrids), and ‘Reliance’ and ‘Marquis’ (table grapes). In 2005, hybrids were the most productive grapes, with highest crop load, whereas American grapes were the least productive, with the lowest crop load. Table grapes produced the largest clusters (160 g). ‘LaCrescent’ was the least productive hybrid, with the smallest cluster (65 g). ‘Toldi’, produced the largest berry (4 g), whereas ‘Cabernet Sauvignon’ produced the smallest berry (1.2 g). The highest mean SSC was recorded for the hybrids at 21.7°Brix, followed by European grapes at 20.3°Brix. Titratable acidity was reduced for most of the grapes in 2006 by more than 20%. Hybrid berries, especially ‘Swanson Red’, were the most susceptible to hail damage, whereas American and table grapes were the least susceptible. Frost damage was greatest on European grapes and least on American grapes. ‘Cabernet Franc’ was the most sensitive cultivar, whereas ‘Valiant’ was the least sensitive American cultivar to frost.

Fertigation and Crop Load Affect Yield, Nutrition, and Fruit Quality of ‘Lapins’ Sweet Cherry on Gisela 5 Rootstock

‘Lapins’ sweet cherry (Prunus avium L.) on Gisela 5 (Prunus cerasus × Prunus canescens) rootstock were subjected to a factorial combination of two crop load and eight fertigation treatments from the sixth to the eight growing seasons. Crop load treatments included full crop and dormant spur thinning to remove and maintain 50% of fruiting spurs. The eight fertigation treatments, which had been maintained since the first growing season, included low (42 mg·L−1), medium (84 mg·L−1), and high (168 mg·L−1) concentrations of N applied by sprinkler fertigation of Ca(NO3)2 annually ≈8 weeks postbloom. The medium N concentration was also applied with P fertigated in early spring or K fertigated in June. A standard N treatment involved broadcast application of NH4NO3 in early spring at 75 kg·ha−1 also followed with medium N sprinkler-fertigated postharvest in August. The medium N concentration was also supplied for 8 weeks postbloom through drip emitters. Removal of 50% of fruiting spurs decreased annual yield on average by only 10%. Average fruit size could be increased in years of high crop load (greater than 400 g fruit/cm2 trunk cross-sectional area), but in a year of low crop load (less than 100 g fruit/cm2), fruit size was very large (averaging greater than 14 g) and unaffected by crop load adjustment. Minimal effects on fruit and leaf NPK concentrations, fruit firmness, soluble solids concentration (SSC), and titratable acidity (TA) were associated with yield reductions of 10%. Fertigation treatments resulted in a large range in tree vigor and yield during the experiment. High N applications reduced tree and fruit size and fruit TA and were undesirable. Annual P and K fertigation by sprinklers was generally ineffective, having minimal effects on tree PK nutrition and fruit quality with the exception of increased fruit firmness associated with P fertigation in 2005, when yield was low. Drip-fertigated trees were small, frequently had fruit with elevated SSC, but had deficient leaf K concentrations in 2004 implying a need to fertigate K when drip-irrigating.

Rootstock effects on salt tolerance of irrigated field-grown grapevines (Vitis vinifera L. cv. Sultana). 3. Fresh fruit composition and dried grape quality

Field-grown vines of cv. Sultana on either their own roots or grafted to a range of rootstocks, were drip-irrigated at one of three salinity levels (0.40, 1.75 and 3.50 dS/m) over a five year period. Rootstocks were Ramsey, 1103 Paulsen, J17-69 and 4 hybrids (designated R1, R2, R3 and R4) derived from parentage involving Vitis champini, V. berlandieri and V. vinifera. Grape juice total soluble solids, titratable acidity and pH were measured at harvest, while colour of dried fruit was measured before and after processing and again after six months storage. Damage index (an indicator of skin damage) was measured post-processing; sugar crystal formation in dried grapes and dried grape compaction were measured post-storage. There was a strong salinity x rootstock interaction for grape juice soluble solids concentration, soluble solids yield (the product of soluble solids concentration and fruit yield) and pH, but not for titratable acidity when analysed on the basis of 5 year means. Small increases (< 5%) in juice soluble solids concentration were recorded at medium salinity (1.75 dS/m) for the low vigour genotypes, Sultana on own-roots and on J17-69 rootstock, based on the 5 year means and Fisher's protected (interaction) LSDs. Moderate increases (< 10%) also occurred in years of low crop load e.g. 1993 at high salinity for the high vigour rootstock R2 and in 1995 at medium salinity for Sultana on own roots and at high salinity for Sultana on R1 rootstock. By contrast, decreases in soluble solids concentration occurred with increasing salinity for the high vigour rootstocks (Ramsey, 1103 Paulsen and R2) in years of high crop load e.g. 1992. Small (< 2%) increases in grape juice pH were recorded at high salinity for Sultana on R3 rootstock and moderate increases (< 7%) in grape juice titratable acidity were recorded at high salinity for Sultana on own roots and Sultana on J17-69, R1, R2 and R4 rootstocks. Dried grapes from all treatments achieved a light amber colour (quality grade termed 5 crown light) and were generally of high quality. Sultanas from own-rooted grapevines were redder (higher ‘a-value’) than sultanas from 1103 Paulsen and Ramsey when assessed as unprocessed fruit, after processing (both years) and after 6 weeks storage. While soluble solids yields per vine were 23–31% lower at high salinity for Sultana on own roots and on R1, R3 and R4 rootstocks, they were unaffected by high salinity for Ramsey, 1103 Paulsen and R2 rootstocks. Moreover, soluble solids yields for Sultana on Ramsey, 1103 Paulsen and R2 rootstocks were 1.4 to 2.5-fold higher than for Sultana on the other rootstocks at high salinity. This study has shown that over a 5 year period rootstocks such as Ramsey, 1103 Paulsen and R2 grafted with Sultana were tolerant of salinity, producing dried grapes of generally high quality.

Predicted Crop Value for Nectarines and Cling Peaches of Different Harvest Season as a Function of Crop Load

Several field experiments to assess the effect of tree size and crop load on fruit size and yield efficiency were conducted in cling peach and nectarine orchards of different harvest seasons in Chile. Trees were randomly selected in each orchard and then hand-thinned at the beginning of pit hardening to a wide range of crop loads. The fraction of above-canopy photosynthetically active radiation (PAR) intercepted by the canopy (PAR i) was determined at harvest. All fruits were counted and weighed and average fruit weight calculated. Crop load and yield were normalized by tree size measured by intercepted PAR i. For each orchard, the relationship between crop load and fruit size or crop load and yield efficiency was assessed by regression analysis. Fruit size distribution was calculated from fruit size adjusted for fruit load assuming a normal fruit size distribution and valued according to shipment date and price obtained from a Chilean export company. Using crop load as a covariate, fruit size adjusted for crop load was compared for nectarine and peach cultivars. Fruit size adjusted for fruit load and yield efficiency was greater with late season cultivars than the early or midseason cultivars. Predicted crop value (PCV), normalized in terms of PAR intercepted, was calculated for all the cultivars. Large differences in predicted crop value were found for early, midseason, and late ripening nectarines. Early and late ripening cultivars had the highest predicted crop value, especially at lower crop loads and larger fruit sizes. The early season cultivars had high crop value as a result of higher fruit prices, whereas the late season cultivar had high crop value as a result of higher production. With cling peaches, the early season cultivar ‘Jungerman’ had a lower predicted crop value than the late season cultivars ‘Ross’ and ‘Davis’. For cling peaches, the highest PCV was achieved at a relatively high crop load with high yield and small fruit size.

Effects of potassium and early-season nitrogen applications on young ‘Keisie’ canning peach trees on a sandy, infertile soil

The effects of different rates of potassium (K) and early season nitrogen (SN) were investigated in a ‘Keisie’ canning peach orchard on a sandy, infertile soil, at 1111 trees ha−1, in the Western Cape Province, South Africa. Over the first four reasonably consistent bearing seasons (tree age 4 to 7 years) vegetative growth (trunk circumference) and yield were found to be sensitive to both × and SN. To sustain a crop of approximately 301 ha−1, annual × applications, in spring, at the rate of 124 g tree−1 were required. Nitrogen applications at full bloom (FB) at 133 g N tree−1, 42 days after FB at 67 g N tree−1, and again after shoot growth had ceased in autumn gave the best results (at 67 g N tree−1). At higher crop loads (c. 35.5 tons ha−1) × application rates of 300 g tree−1 season−1 may be required on similar sandy soils, possibly in association with rates of N application which exceed 267 g tree? season−1 (297 kg ha−1). Fruit quality was neither beneficially nor adversely affected by × and N fertilisation over the range of application rates utilised. High and low rates of application of K and N were nevertheless reflected by their concentrations in the leaves and fruit.

着果量と環状はく皮がブドウ‘安芸クイーン’の果実品質および根の伸長に及ぼす影響

The effects of trunk girdling and crop load levels on skin color, juice composition, and root elongation of a red table grape, ‘Aki Queen’ (Vitis labrusca L. × V. vinifera L., tetraploid) were investigated. The treatment of a low crop load with girdling significantly elevated the anthocyanin concentration in berry skin compared to that of a high crop load without girdling. The total soluble solid content of berries was significantly greater in a low crop load with girdling than in other treatments. Titratable acidity was not different among treatments. Root elongation stopped for two weeks as a result of the girdling treatment, regardless of the crop load level. Root elongation after girdle healing was vigorous when the crop load was low.

(463) Grapefruit Crop Load Affects Net Gas Exchange of Leaves, Tree Growth, and Fruit Quality

Effects of crop load on leaf characteristics, shoot growth, fruit shape, fruit quality, and return bloom were investigated in 13-year-old `Ruby Red' grapefruit (Citrus paradisi Macf.) on `Swingle' citrumleo rootstock. Trees were hand thinned in June 2003 and 2004 at the end of physiological fruit drop to establish three to four levels of crop load ranging from normal (high crop load without thinning) to extremely low (near 90% fruit removal). Leaves on high crop load trees had higher net assimilation of CO2 (ACO2) than those on low crop load trees. Crop load enhancement of ACO2 continued until harvest. In 2004, however, the effects were diminished in October just prior to the beginning of the harvest season, after leaf and fruit loss from three consecutive hurricanes. There was no difference in leaf dry weight per leaf area and leaf nitrogen among treatments. Nonfruiting branches of high crop load trees produced fewer, but longer, summer flushes than those of low crop load trees. Fruiting branches generally produced few summer flushes with similar shoot lengths among treatments. High crop load trees developed a greater percentage of vegetative shoots, whereas low crop load trees developed more inflorescences. Crop load adjustments did not affect fruit size and total soluble solid content, but low crop load trees produced a higher percentage of irregular shape (sheepnosed) fruit with high acidity.

Effect of Crop Load on Diurnal Leaf Photosynthesis, Stomatal Conductance, and Annual Carbon Isotope Composition of `Imperial Gala' Apple Tree

The naturally occurring carbon isotope composition (or 13C: 12C ratio, expressed with the notation d13C) of plant tissue may be used as an indicator of water use efficiency during plant growth. d13C has been shown to be an effective tool to study physiological response of plant to environmental conditions, especially water stress. The objective of this work was to test if d13C could be an indicator of carbon limitations or a low source: sink ratio. Trees of `Imperial Gala'/Bud 9 (n = 12), 6-years-old, field grown at the Clarksville Horticultural Research Station (Clarksville, Miss.), were assessed with different crop load (LCL = Low Crop Load, 0.76 ± 0.44 fruit per trunk sectional area (TCA); NCL = Normal Crop Load, 7.25 ± 1.83 fruit/TCA; HCL = High Crop Load, 15.83 ± 1.76 fruit/TCA) and leaf: fruit ratio (LCL: 52.78 ± 8.55, NCL: 13.33 ± 3.06, HCL; 4.31 ± 0.68) immediately following June drop. Net photosynthetic rate of leaves were monitored during the season and elevated rates were observed in NCL and HCL and correlated with the fruiting process. Photosynthesis was inhibited in LCL more in the afternoon (from 20% to 42% in relation to NCL) than in the morning (from 5% to 20%) and this was positively correlated with crop sink strength. Variations of the stable carbon isotope composition of roots (fine and coarse), fruit, leaves, and current-year stems were examined. The d13C varied by tissue (fruit &gt; shoot and leaf &gt; root) and in relation to the level of crop load (d13C‰ in fruit: LCL –23.513 ± 0.248, NCL –24.891 ± 0.594; and HCL –24.935 ± 0.375). These results may have implications for analysis of isotopic signals in carbohydrate stress and fractionation steps will be discussed.

Cropload Affects Fruit Quality of Honeycrisp Apple

In 2001 and 2002, we imposed a wide range of croploads (0-15 fruits/cm2 of TCA) on 4- and 5-year-old Honeycrisp/M.9 trees by manual hand thinning soon after bloom to define appropriate croploads that give adequate repeat bloom and also the best fruit quality. At harvest each year we evaluated fruit ripening and quality. Samples were stored for 5 months in air at 38 °F and 33 °F and evaluated for fruit firmness and storage disorders. Cropload was negatively correlated with tree growth, return bloom, fruit size, fruit red color, fruit sugar content, fruit starch content, fruit firmness, fruit acidity, fruit bitter pit, fruit senescent breakdown, fruit rot and fruit superficial scald, but was positively correlated with leaf blotch symptoms, fruit internal ethylene concentration at harvest, and fruit soggy breakdown. There was a strong effect of cropload on fruit size up to a cropload 7, beyond which there was only a small additional effect. Although there was considerable variation in return bloom, a relatively low cropload was required to obtain adequate return bloom. Fruit red color was reduced only slightly up to a cropload of 8 beyond which it was reduced dramatically. The reduced fruit color and sugar content at high croploads could indicate a delay in maturity of but, fruits from high croploads were also softer, had less starch and greater internal ethylene. It that excessive croploads advance maturity. Overall, croploads greater than 10 resulted in no bloom the next year, and poor fruit size, color and flavor, but these fruits tended to have the least storage disorders. Moderate croploads (7-8) resulted in disappointing return bloom and mediocre fruit quality. For optimum quality and annual cropping, relatively low croploads of 4-5 were necessary.

Crop Load Effects on Subsequent Peach Floral Development, Pistil Size at Anthesis and Fruit Size at Maturity

The effects of low and high crop loads in 2002 on floral development (Summer 2002), pistil size at anthesis (Spring 2003), and subsequent season fruit size at maturity (Summer 2003) were studied. Trees were all thinned to the same crop load in 2003. Three peach cultivars (Elegant Lady, O'Henry and Fairtime) with different ripening times (mid-July, mid-August, and early-September, respectively) were used to assess the effects of current season crop on floral development for the subsequent season. Based on previous literature, we reasoned that the maximum competition for carbohydrates between maturing fruit and developing buds is likely to occur at fruit maturity, especially under heavy crop loads. In 2003, individual fruit were harvested and weighed at maturity. In all three cultivars, a heavy crop load reduced the percentage of floral buds initiated and delayed floral differentiation. A heavy crop load also reduced pistil size at anthesis and fruit size at maturity in the subsequent season. These data support the practice of vigorous pruning to annually renew fruiting wood in peach to minimize the influence of crop in the previous season on the subsequent season's fruit and maintain large fruit sizes.

Influence of crop load on yield and grape quality of cv. `Chardonnay`

In the research we tried to define proper crop load for cv. `Chardonnay` (Vitis vinifera L. cv. `Chardonnay`) trained on the 1.7 m high cordon trellis in the Vipava Valley. The experiment was designed as a block trial. Three levels of crop load were employed and inspected for their influence on yield and grape quality: normal crop load with 20-30 buds per vine, lower crop load with 20 buds and higher crop load than normal with 40 buds per vine. Bearing wood at the normal and higher than normal crop load was canes with 8-10 buds per cane and at the lower crop load longer spurs with 4-5 buds per spur. The lower crop load resulted in lower yield/vine together with higher must sugar content, its lower acids content and higher pruning weight. The extent of differences was strictly dependent on the climatic conditions in each year of the experiment. The normal crop load showed its great variability in the research results. The grape quality was quite high in all three treatments. Satisfactory must sugar content was obtained with the normal or even higher crop load. The proposed number of buds at winter pruning is approximately 40-45 buds/kg of pruning weight. Normal Ravaz index for defined conditions is between 7-10. In spite of the fact that the weather conditions in each year of the experiment appear to have had the strongest impact on the must acids content, the problem of its additional decrease should be taken into consideration when the lower crop load is applied.

Impact of Training System and Vine Spacing on Vine Performance, Berry Composition, and Wine Sensory Attributes of Riesling

Own-rooted Riesling vines were subjected over a four-year-period to five training treatments (alternate double crossarm, ADC; Lenz Moser, LM; low cordon, LC; low-V, LV; and pendelbogen, PB) and three vine spacings (1.4, 1.8, and 2.4 m). Divided canopies led to weights of cane prunings (vine size) and mean cane weights that were optimal (0.32 to 0.65 kg/m canopy; 15.4 to 34.5 g/cane). Yields were consistently highest for divided canopies as well. Crop loads (ratio of yield: weight of cane prunings) of divided canopies exceeded the presently accepted level (10 to 12) beyond which wine quality could be compromised, but berry, must, and wine composition (Brix, titratable acidity, and pH) were not strongly impacted by training system. Increasing vine spacing led to lower vine size (per m row), cane weights, and occasionally reduced Brix. Riesling wines were also not strongly influenced by training system, except for higher vegetative aroma in the ADC wines. These data strongly suggest that high wine quality may be obtained from divided canopies despite large crop size and high crop loads.

Impact of Training System and Vine Spacing on Vine Performance, Berry Composition, and Wine Sensory Attributes of Seyval and Chancellor

Own-rooted Seyval and Chancellor vines were subjected over a four-year period to five training treatments (Geneva Double Curtain, GDC; Hudson River Umbrella, HRU; 6-arm Kniffin, 6AK; midwire cordon, MWC; and Y-trellis, YT) and three vine spacings (1.4, 1.8, and 2.4 m). Divided canopies led to weights of cane prunings (vine size) and mean cane weights that were optimal (0.32 to 0.65 kg/m canopy; 15.4 to 34.5 g/cane) for Chancellor but below optimum (0.19 to 0.27 kg/m canopy; 9.4 to 13.9 g/cane) for Seyval. Yields were consistently highest for divided canopies as well as 6-AK. Crop loads (ratio of yield:weight of cane prunings) of divided canopies exceeded the presently accepted level (10 to 12) beyond which wine quality could be compromised, but berry, must, and wine composition (Brix, titratable acidity, and pH) were not strongly impacted by training system. Increased vine spacing led to smaller vine size (per m row), lower cane weights and yield (Seyval only), and occasionally reduced Brix. GDC wines produced from Seyval were characterized by highest melon flavor, lowest earthy and vegetative flavors, and lowest astringency. Chancellor GDC wines had highest berry flavor. These data strongly suggest that high wine quality may be obtained from divided canopies despite large crop size and high crop loads.

Leaf light-saturated photosynthesis for wild and cultivated peach genotypes and their hybrids: A simple mathematical modelling analysis

SummaryWe measured leaf photosynthetic activity, stomatal conductance and leaf carbohydrate reserves (soluble sugars and starch) for seven peach genotypes of different introgression level, i.e. commercial varieties, Prunus davidiana and genotypes derived from Prunus davidiana. In early May, branches of each genotype were girdled and leaf to fruit ratio treatments were applied to obtain contrasting source-sink ratios. Photosynthetic activity was significantly different between treatments. We adjusted an asymptotic curve (monomolecular) to the strong relationship between light-saturated photosynthesis (Asat) and stomatal conductance (gs). This monomolecular curve appeared to be independent of genotype and year. Thus, one unique value for the maximum of Asat (Amax) and one unique value for the initial increase rate of Asat per unit of gs (q) were estimated (Amax=20.68 µmol m–2 s–1 and q=83.73). Leaf reserves (soluble sugars and starch) became significantly larger for low crop loads than for high crop loads, whatever the genotype. Genotype effect on soluble sugars and starch concentrations was limited. Low Asat appeared to be correlated with a high accumulation of leaf reserves. A three-parameter curve was used to describe the relationship between photosynthesis activity and leaf reserves. Values of the parameters of this relation appeared to be independent of genotype and year. Practical considerations on source-sink conditions and experimental treatments are recommended.

Effects of crop load on tree water use in apple (Malus x domestica Borkh.)

Sap flow rate measurements were carried out during two consecutive ('on' and 'off') years in an apple orchard cv. 'Florina' M.26 to analyse the effects of various crop load on tree water use. Sap flow rate was measured by thermal dissipation method in trunks of nine trees from June to the harvest. Crop load was between 0.2-9.0 fruits • cm -2 of trunk cross section area (equal to 0.5-35.0 fruits•m-2 of leaf area), trunk diameter varied between 4.7-8.7 cm.&#x0D; Total leaf area was estimated by leaf counting or using shoot girth and leaf area relationship. In both years, fruit growth rate was determined by measuring diameter of 280 marked fruits with 7 days frequency. Fruit volume calculated as a function of fruit diameter based on a previously determined relationship.&#x0D; Total leaf area of trees ranged from 4.4 to 19.5 m2 and it was closely related to trunk cross section area. At high crop load the fruit growth rate peaked in August with 0.51.tree-l.day-1 and the leaf area specific total fruit volume reached 61 m2 before the harvest.&#x0D; There was a linear relationship between total leaf area and daily water use, while the leaf area specific water use was influenced by crop load rate. The relationship was described by piecewise linear regression with the breakpoint at crop load rate of 12 fruits•m2 of leaf area. At low crop load the slope of the fitted regression line was less than at high crop load rate.

Nutrient demand of stone fruits

Effects of nitrogen, phosphorus and potassium fertilization were investigated on the change of nutrient content, vegetative and generative production of apricot, peach and sour cherry trees, as well as on frost hardiness in long term experiments. Nitrogen and phosphorus fertilization increased only the concentration of these elements in cherry leaves without effect on growth and yield. Consequent potassium effect was proved on these stone fruit species. Effect on yield appeared following the first higher crop load.&#x0D; Potassium supply has positive effect on frost hardiness of apricot and sour cherry flowers and peach flower buds.&#x0D; In peach, the lime content of soil decreased the yield but it could be compensated by potassium dressing to some extent. Favourable nutrient boundary values were determined for soil and foliage.