Crop Load Levels Research Articles

Crop load management (CLM) for sustainable apple production in China

Biennial bearing is a common problem encountered in perennial fruit crops. In order to determine a suitable crop load for sustainable development of dryland apple orchards, we defined the concept of “appropriate productivity” and examined five crop load levels in an apple orchard ecosystem on the Loess Plateau, in Changwu, Shaanxi province, China. The orchards were planted with Fuji apple (Malus domestica Borkh.) trees on M. sieversii rootstock since 1996. Crop load was limited to 53–54 (I), 67–68 (II), 80–81 (III), 94–95 (IV), and 107–108 (V) fruit per tree, using flower and fruit thinning by hand. Volumetric soil water content, total nutrient (N, P, and K) contents of branches, and economic benefit were then analyzed under each treatment over a 5-year period. Soil water content was found to be closely related to rainfall, with three seasonal periods recognized annually. Average water content in 2009–2013 ranked treatment II (21.98%)>III (21.57%)>I (20.61%)>IV (20.31%)>V (20.11%), in which treatments II and III were significantly higher than other treatments. With increasing soil depth, the water content showed an “increasing-decreasing-increasing” trend, with the highest value tending to occur within a depth of 40–100cm. The nutrient contents of branches under treatments I–III were good and trees showed strong resistance to apple Valsa canker. From an economic perspective, the percentage of high-quality fruit increased as did the economic benefits in treatments I–III. In conclusion, controlling fruit crop load effectively reduced fluctuations in production, increased the economic benefits, and maintained the health of the orchard ecosystem. The appropriate crop load level for mature apple orchards in the gully region of the Loess Plateau was deemed to be 67–81 fruit per tree.

Response to moderate water stress imposed after pit hardening in mature table olive orchard cv. Azapa

Table olive trees which grow under high evaporative demand with no rainfall in arid zones such as the Azapa Valley, Arica and Parinacota Region, Chile, depend exclusively on irrigation; a common practice recommended in areas with low water availability is regulated deficit irrigation (RDI). The aim of the study was to describe the response of olive to variable water supply after pit hardening to harvest (167–199days) in a mature orchard of cv. Azapa in a biennial cycle. Full replenishment was scheduled until the end of pit hardening (11 weeks after full bloom), then four treatments were compared: T0, 100% of crop evapotranspiration (ETc); T1, 80% ETc; T2, 60% ETc and T3, 40% ETc. The water stress imposed was considered as moderate, according to stomatal conductance data. Water relations were affected more by the level of water supply than by crop load, with a significant reduction of midday water potential in the most restrictive treatment. Vegetative growth occurred mainly during the unstressed period, while shoot growth rate was affected by crop load level. Fruit size distribution in the “on” year (12100kgha−1) were 14 and 20% higher in control and T1 (−2.0MPa), while a reduction in fruit volume was found with −2.7MPa (T3). In the “off” year, yield in RDI treatments were 49 and 67% lower than control, without differences in fruit size distributions. This response could be related to the increase in the rigidity of the cell wall and osmotic adjustment in the most restrictive treatment, as an adaptive response of the trees to arid conditions.

Interaction of Crop Load and Irrigation on Yield, Fruit Size, Color and Stem-end Splitting Ratio of Apple c.v. ‘Gala, Galaxy’

In this study, the interaction between crop load and irrigation level on yield, fruit size, skin color and stem-end splitting fruit ratio in the apple cultivar ‘Gala, Galaxy’ grafted on rootstock M9 were investigated. Six irrigation programs were applied during the whole growth season: deficit irrigation (rates of 0.25 kc, 0.50 kc, 0.75 kc), full irrigation (rate of 1.00 kc), excess irrigation (rate of 1.25 kc) and non-irrigation (rates of 0.00 kc of “Class A” pan evaporation coefficient). Four crop loads in each irrigation application were performed by hand thinning after the June drop as a- a low crop load (3 fruits cm−2 TCA), b- a medium crop load (5 fruits cm−2 TCA), c- a heavy crop load (7 fruits cm−2 TCA), and d- an un-thinned crop load (> 7 fruits cm−2 TCA). The total tree yield increased with crop load and irrigation levels. Fruit size was significantly increased by the low crop load. Irrigation increased the fruit size compared to non-irrigation treatment. Further 0.75 kc, 1.00 kc and 1.25 kc irrigation treatments significantly increased the fruit length. Irrigation reduced the fruit flesh firmness. While the low crop load increased the skin red color, it decreased the fruit skin brightness. The yellowness of skin decreased with increasing in the irrigation amount. Irrigation reduced the skin brightness and yellowness, but it increased red color. Crop load and irrigation significantly affected the stem-end splitting fruit ratio. While the splitting fruit ratio increased with a decrease in the crop load, it decreased with an increase in irrigation amount, relatively. Consequently, the low and medium crop load treatments would be beneficial to increase the ratio of marketable fruits without any significant losses in yield for ‘Gala’ apple, especially under 0.75 kc deficit irrigation treatment.

Leaf carbohydrate metabolism in Malbec grapevines: combined effects of regulated deficit irrigation and crop load

Background and Aims Regulated deficit irrigation and crop load adjustment are viticultural practices used to improve grape and wine composition. Our objective was to evaluate the combined effect of irrigation and crop load levels on leaf photosynthesis, accumulation of non-structural carbohydrates and leaf carbon utilisation during the season. Methods and Results The trial started in 2006 in a Vitis vinifera L. Malbec vineyard in Mendoza. Two irrigation levels (100% and 25% of reference evapotranspiration) and two crop loads (20 and 10 bunches per vine, set at veraison) were studied. During the 2009/10 season, diurnal dynamics of leaf water potential, photosynthesis and carbohydrate concentration were determined at anthesis, veraison and harvest. Deficit irrigation reduced leaf starch concentration at veraison and increased soluble sugars. High-crop load reduced leaf starch concentration at veraison. Starch turnover was correlated with photosynthesis during the previous day. Conclusions Deficit irrigation had a greater effect on carbon allocation between soluble sugars and starch than on total carbohydrate production. Effects of deficit irrigation and crop load operated independently. Significance of the Study This experiment improved our knowledge of carbon assimilation and allocation during the season, which may assist the development of management practices to stabilise yield and fruit composition.

Crop loading studies on ‘Caricia’ and ‘Eva’ apples grown in a mild winter area

The crop load level of an apple (Malus × domestica Borkh.) tree impacts fruit yield and quality parameters, tree vigor and biennial bearing. The optimal crop load is that which allows for consistent annual cropping and fruit quality acceptable to the market. We evaluated the effect of crop load on yield and fruit quality of two low-chill apples cv. ‘Caricia’ and ‘Eva’, growing in a mild winter area. During 2010 and 2011 crop load was manually adjusted from 2 or 3 to 17 fruits cm−2 of trunk cross-sectional area (TCSA). Fruit yield was positively related to crop load in both cultivars but mean fruit weight diminished as the crop load increased. For both cultivars, the production of non-commercial and small-sized fruit increased, whereas production of middle-sized fruit diminished as the fruit load increased. Shoot length was not affected by crop load in ‘Eva’ whereas it was reduced in ‘Caricia’. Red skin color (RSC %) had a quadratic response to crop load in ‘Caricia’. On the other hand, the RSC % of ‘Eva’ fruit was adjusted to a negative logarithmic model as an effect of crop load increment. No biennial bearing was observed in either cultivar. This research study suggests that the maximum limit of crop load for both cultivars is 7 fruits cm−2 of TCSA, and the lower limit of crop load was 3 fruits cm−2 of TCSA for ‘Eva’ and 5 fruits cm−2 of TCSA for ‘Caricia’.

Impact of early cropping on vegetative development, productivity, and fruit quality of Gala and Braeburn apple trees

The effects of 5 crop load levels (all fruit removed and 10, 20, 30, and 40 fruit per tree) in the second growing year on vegetative growth, productivity, and fruit quality were studied in apple cultivars Gala and Braeburn on M9 rootstock in the second and the third leaf. An increase in vegetative growth was observed on the defruited trees in the second growing year. The highest crop load of 40 fruits per tree reduced average fruit weight by 18.7% in Gala compared to those obtained on the trees carrying the lowest crop load (10 fruits per tree). The reduction in average fruit weight was compensated by the increase in yields. Yield per tree in the treatment with the highest crop load was 2.4-fold higher in Gala and 2.7-fold higher in Braeburn than the treatment with the lowest crop load. Yield efficiency (kg cm–2 trunk cross-section area) in both tested cultivars ranked the highest on the trees carrying the heaviest crop. The highest crop load in the second growing year did not have negative consequences on the yield and fruit quality obtained in the third growing year.

Crop load regulation and irrigation strategies to accelerate the recovery of previously water-stressed Japanese plum trees

Regulated deficit irrigation (RDI) has been proven as a useful irrigation strategy in a wide range of fruit crops to deal with water scarcity. However, long-term RDI techniques in developing orchards can reduce tree growth resulting in a loss of tree yield capacity. Strategies that could be used to quickly recover trees from the possible carry-over effects of long-term deficit irrigation are then of physiological and commercial interest. Tree crop load is a determinant factor of the carbohydrates partitioning between fruit and vegetative sinks, being fruit sink strength higher than that of vegetative organs. The working hypothesis of this study was that tree crop load reduction could be employed to alleviate the detrimental effects that long lasting RDI strategies have on tree growth. The recovery of a young plum Japanese orchard (Prunus salicina, cv. ‘Black Gold’) after seven seasons under RDI was studied by testing combinations of two crop load levels (medium and low), two drip irrigation regimes [100 and 133% of crop evapotranspiration (ETc)] and two different number of emitters per tree (six and eight). Results showed that treatments applied led former RDI treatment trees to significantly reduce their differences in tree shaded area and particularly in trunk perimeter with respect to the control treatment trees. After two seasons of treatments, differences in yield, economic return and number of fruit per tree were exclusively due to the crop load levels imposed and not to a smaller size of former RDI treatment trees. Trees watered at 133% ETc and thinned at low crop load, which underwent a very severe RDI strategy previous to this experiment, were the trees that showed the greatest recovery in tree size. In this treatment, the lower competition between fruit and vegetative growth and the increase in the soil wetting area by using a higher number of emitters per tree, probably favored root growth significantly increasing tree growth with respect to the other treatments. Overall, this work shows that crop load regulation is a useful tool to quickly recover plum trees from the detrimental effects of long-term deficit irrigation.

Crop Load Management Does Not Consistently Improve Crop Value of ‘Sweetheart’/‘Mazzard’ Sweet Cherry Trees

The effect of crop load level on vegetative growth, fruit growth, yield, fruit quality, surface pitting, crop value and return bloom was studied over a 2-year period on 9- and 10-year-old ‘Sweetheart’/‘Mazzard’ sweet cherry (Prunus avium) trees. In early spring, whole-tree crop loads were adjusted to two different levels by removal of reproductive buds (either 50% or all but one) from spurs and compared with an unthinned control. In 2009, heavy crop loads of unthinned trees reduced fruit size by 30 days after full bloom (DAFB). At harvest, fruit diameter of thinned treatments was increased 22% and 27% compared with unthinned fruit. Fruit quality attributes [soluble solids concentration (SS), fruit firmness, and total acids (TA)] were significantly greater for thinned treatments. Thinned treatment yields were reduced 40% to 54% relative to unthinned trees, with greater percentages of fruit in large size classes. Despite significantly fewer fruit per tree, moderately thinned trees had a higher estimated crop value ($142 per tree) than unthinned trees ($125 per tree). Crop value was lowest for the heavily thinned treatment ($107 per tree), reflecting overthinning. In 2010, shoot growth was negatively related to crop load level. Fruit growth of unthinned trees was not significantly affected by higher fruit density until 89 DAFB. Yield of 2010 unthinned trees was 87% of 2009, while thinned tree yields were similar between years. Improved fruit quality and greater percentages of large fruit were observed for thinned treatments in 2010; however, crop value was highest for unthinned trees ($190 per tree), even though 18% of the fruit were too small for fresh market sale. Surface pitting was unaffected by crop load level in either year. Return bloom (flowers per reproductive bud and reproductive buds per spur) was significantly, negatively related to the prior season's crop load in 2010 and 2011. In the current sweet cherry pricing structure, higher crop value is associated with large volumes of medium-sized fruit. Thinning to manage crop load of low-medium density, productive ‘Sweetheart’/‘Mazzard’ trees will not be an annual requirement, though in heavy fruit set years crop load management will improve crop value.

Interactive responses to water deficits and crop load in olive (Olea europaea L., cv. Morisca). II: Water use, fruit and oil yield

To understand the relations between water use and yield in response to crop load, two experiments were conducted in olive (cv. Morisca), during six consecutive years (2002–2007) in an experimental orchard located in Badajoz, Southwest Spain. Experiment 1, assessed the responses during the early years of the orchard (2002–2004) using four irrigation treatments that applied fractions of the estimated crop evapotranspiration (ETc) (125%, 100%, 75% and 0%) and three crop load levels (100%, 50% and 0% of fruit removal, termed Off, Medium and On treatments). Experiment 2 assessed the response of more mature trees (2005–2007) to three irrigation treatments (115%, 100%, and 60% of ETc) and the natural crop load which were Off, On, and Medium in 2005, 2006 and 2007, respectively. Yield was reduced by water deficits and so did the estimated tree transpiration which was linearly related to yield (y = 1.2302x − 21.15, R2 = 0.8864), showing the high sensitivity of cultivar Morisca to water deficits. The relations between fruit number and fruit weight showed that high crop loads had lower fruit weights and oil yield, a decrease that was more pronounced as water deficits increased. The yield response to water supply in the control and excess treatments, and the observations on the water relations of these two treatments suggest that the calculations made using the FAO method (Doorenbos and Pruit, 1974) with the crop coefficient proposed by Pastor et al. (1998) and the reduction coefficient (Fereres et al., 1982) to apply 100% of ETc in the control treatment, underestimated the ETc of the orchard. The results indicate that, although the absence of fruits lead to reduced water use as compared to situations of medium and high crop loads, canopy size was much more determinant of orchard water requirements than crop load.

Interactive responses to water deficits and crop load in olive (olea europaea L., cv. Morisca) I. – Growth and water relations

Abstract To characterize the interactions between variable water supply and crop load on vegetative growth and water relations of an olive orchard (cv. Morisca ) planted in 1998 at 417 trees ha −1 , two different experiments were conducted over a six-year period (2002–2007) in Badajoz, Southwest of Spain. Experiment 1, assessed the responses during the early years of the orchard (2002–2004) using four irrigation treatments that applied fractions of the estimated crop evapotranspiration (ET c ) (125%, 100%, 75% and 0%) and three crop load levels (100%, 50% and 0% of fruit removal, termed off, medium and on treatments). Experiment 2, assessed the response of more mature trees (2005–2007) to three irrigation treatments (115%, 100%, and 60% of ET c ) and the natural crop load which were off, on, and medium in 2005, 2006 and 2007, respectively. Although vegetative growth was mainly affected by the level of water supply, crop load also influenced vegetative parameters, especially the interaction between high loads and water deficit. Trunk growth was more sensitive to water deficits than ground cover, and at the branch scale, water deficits reduced branch length and node numbers but only reduced internode length in on trees. Water relations were more affected by the level of water supply than by crop load. Nevertheless, the presence of fruits affected olive tree water status and, particularly, increased the stomatal conductance of on trees during late summer and early fall under all levels of water supply. Interactions between water stress and crop load levels were not very strong, and were more evident in mature than in young olive trees.

Mitigation of severe water stress by fruit thinning in ‘O’Henry’ peach: Implications for fruit quality

Fruit thinning can be used to relieve water stress in peach but it is not known how fruit quality will respond under water limited conditions. To elucidate this, we applied, over the growing seasons of 2003 and 2004, irrigation and fruit thinning treatments to ‘O’Henry’ peach at the onset of Stage III of fruit development. The treatments were full irrigation (FI) and no irrigation (NI) with each receiving three crop load levels: light, commercial and heavy. Fruit size and fruit skin colouration were lower in NI than in FI but the following were higher in NI fruit: firmness, juice titratable acidity and electrical conductivity, and concentrations of dry matter and soluble solids. All the quality parameters were significantly correlated with tree water status, expressed as midday stem water potential. NI fruit matured 5–10 days later than FI fruit. The increased dry matter concentration, juice acidity, and electrical conductivity in NI fruit were indicative of lower quality at harvest. Choosing a light crop load was not effective in improving NI fruit quality except for the size. Since fruit size is the most important fruit quality attribute, its increase might compensate for yield losses resulting from heavy fruit thinning. Nevertheless, when heavy thinning is performed for mitigation of water stress in Stage III, the overall fruit quality will suffer if severe water stress is inevitable because of shortage or lack of irrigation water.

Crop Load Overwhelms Effects of Gibberellic Acid and Ethephon on Floral Initiation in Apple

Potential strategies against biennial bearing in apple [Malus × sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] include promotion of return bloom with an “on”-year application of ethephon or inhibition of return bloom with an “off”-year application of gibberellic acid (GA), but the influence of initial crop load on the efficacy of these bioregulators is poorly understood. In 2004 and 2005, six total trials were initiated in which whole trees were manually adjusted shortly before anthesis to one of three levels of crop load (100%, 50%, 0%) in ‘Cameo’, ‘Honeycrisp’, and ‘Fuji’; GA4 + 7 was overlaid on trees of each crop level in four trials and ethephon in two. In all trials, initial crop load was the primary determinant of return bloom; proportional influence on flower density, fruit density, and yield was generally most pronounced at the 50% crop level. GA4 + 7 consistently reduced floral initiation, whereas ethephon promoted it. Flowering responses from a historically alternating ‘Cameo’ trial site showed greater sensitivity to ethephon and less sensitivity to GA4 + 7 than did responses from parallel trials established in an annually bearing ‘Cameo’ block, suggesting a predilection of nascent buds to a specific fate before the influence of exogenous bioregulators or gibberellins from seeds produced in developing fruit. Light crop loads and GA4 + 7 applications generally promoted shoot extension, whereas heavy crops and ethephon had the opposite effect.

Biological variation in the colour development of Golden Delicious apples in the orchard

AbstractBACKGROUND: In managing apple orchards, crop load and rate of nitrogen (N) fertilisation are two factors with a significant influence on fruit quantity and quality, because they affect all physiological processes in the tree. Both factors are strongly related to external and internal fruit quality, especially to skin colour, sugar and acid contents and mineral composition, and consequently to the keeping quality of fruits. The aim of this study was to assess the effects of both factors (three crop load levels and two N fertilisation levels) on the colour development of Golden Delicious apples during the last month on the tree in two consecutive seasons. Data on skin colour (L*, a*, b* values) were analysed using nonlinear mixed effects modelling to extract information on the variation in biological shift factor for colour and to link this variation to the different strategies used concerning N fertilisation and crop load.RESULTS: The major source of information is contained in the a* value. The behaviour of the a* value could be described by a logistic or an exponential model depending on the season and the experimental set‐up. Nonlinear mixed effects analysis estimating the biological shift factor (maturity) for each individual fruit (random effect) while estimating the rate constant of the decolouration process in common (fixed effect) resulted in explained parts well over 95%.CONCLUSION: The variation in maturity stage between individual fruits is large. Season has the most profound effect on the estimated values, far more important than that of crop load or fertilisation level. The magnitude of variation in colour due to crop load and N fertilisation is not too large. Its effect on the maturity stage of fruits is more profound: the higher the crop load, the higher the variation. The effect of fertilisation seems to be opposite: the higher the fertilisation level, the lower the variation. Copyright © 2009 Society of Chemical Industry

WATER DEFICIT AND CROP LOAD EFFECTS ON YIELD AND FRUIT QUALITY OF APPLE

The goal of this study was to know the effect of late irrigation deficit and crop load on Empire/M.9 apple. Two levels of soil moisture were used: normal irrigation and two drought cycles during the final phase of fruit growth, and three levels of crop load: 1, 3 and 6 fruit·cm -2 of trunk area. The effect of treatments on fruit quality, trunk area, yield and bloom return in four years old potted trees was observed. Results showed that late irrigation deficit do not have any effect on yield, fruit size, and fruit number. With these results it is possible to save water, stopping applying late irrigation in the phase III of fruit growth. Trunk area was affected by late irrigation deficit, but flower density is increased.

Interaction of nutrient supply and crop load of apple trees (Malus domestica Borkh.)

Long term fertilisation trials were combined with storage experiments with 'Jonathan' apple trees and fruits to study influence of tree nutrition on quantity and quality of crop. The site of experiments is a typical Carpathian-basin environment with loamy silt soil, high lime content and arid summers. Conclusions has been drown from six years' set of data. Augmented levels of soil fertilisation increased cropping capacity of apple trees, however, the fruit load has not met with cropping capacity in every year. More the def cit came into view in crop load, less the fruit quality resulted in. The deficit in cropping capacity, however, could not have been determined with simple rates as fruit weight per trunk circumference or similar. Better determination was obtained where foliar nutrient contents were correlated to crop per tree figures. In general terms, the N and Ca content in leaves increased with yields when K and P content formulated reciprocally. When storage quality of 'Jonathan' apple fruits were related to crop load (kg/tree), influence of crop deficit became visible. As the crop load and foliar nutrient levels interacted, the fruit quality (number of disordered apples after 6 month of storage) subjected of both physiological phenomena. Higher determination degree were obtained when crop load was assessed together with single or multiple foliar analysis data.

The Effect of Prohexadione-calcium on Fruit Set and Chemical Thinning of Apple Trees

Prohexadione-calcium (ProCa) has emerged as one of the most important management tools that an orchardist has available to control vegetative growth and to reduce the incidence and severity of fire blight. It has also been implicated in increased fruit set on treated apple trees. This investigation was initiated to confirm the effects of ProCa on fruit set and to evaluate different thinning strategies that might be used to appropriately thin treated trees. ProCa increased fruit set when applied at petal fall at initial rates of 125 or 250 mg·L−1 in three of the four experiments described in this article. Thinners were applied before, at the time of, and after application of ProCa. In all experiments, chemical thinners did not reduce fruit set to the same crop load level on ProCa-treated trees as they did on untreated trees. It was concluded that a different and more aggressive chemical thinning strategy must be used on trees that were treated with ProCa. Fruit size was reduced on ProCa-treated trees. This reduction was usually, but not always, related to increased fruit set. ProCa increased the number of pygmy fruit on ‘Delicious’ apple trees.

Optimal crop load and positioning of fruit in cherimoya ( Annona cherimola Mill.) trees

Dichogamy and the lack of efficient pollinators in most producing countries make hand pollination of cherimoya unavoidable. In contrast to its high-cost, this technique allows growers to fix crop load levels and fruit location within the tree canopy. Over three consecutive years we have studied the optimal fruit load for the cultivar ‘Fino de Jete’ and checked the effects of the vigor of the fruit-bearing shoots and of the fruit position along the shoot on the resulting fruit set and quality. Our results show that yield in well-managed orchards fitted a logarithmic curve with a maximum close to 30 t ha −1 achieved by setting about 400 fruits per adult tree. No significant effects of crop load were detected on fruit size during the first 2 years; in the third year, however, trees with a lower yield produced heavier fruits. An upper limit of 0.22 kg (fresh fruit weight) cm −2 of trunk cross-sectional area is proposed if fruit quality is to be preserved. High yield during three consecutive years did not diminish tree growth. We found no consistent effects of shoot vigor on fruit set and quality. However, a gradient for heavier fruits was observed from the base to the apex of the bearing shoots.

Comparison of two 6-benzyladenine formulations and carbaryl for post-bloom thinning of apples

Abstract Three trials assessed the effects of two 6-benzyladenine (BA) formulations, CyLex® and Accel®, and carbaryl/thiram (C/T) combination sprays as secondary or post-bloom thinners of ‘Fuji’, ‘Delicious’ and ‘Golden Delicious’ apples. Ethephon was applied as a primary thinner at full bloom (FB) on ‘Fuji’ and ‘Delicious’, while NAA was used on ‘Golden Delicious’. CyLex and Accel were applied at different rates at 20 days after full bloom (dAFB) while C/T was applied as a tank mix either once, twice or three times at seven day intervals from 18 dAFB on ‘Fuji’. The ‘Delicious’ and ‘Golden Delicious’ were treated with either Accel or C/T. In ‘Fuji’, all CyLex treatments achieved target crop load levels and resulted in increased fruit weights, but neither Accel nor C/T achieved thinning or fruit weight targets. In ‘Delicious’ Accel showed no thinning effect, while C/T thinned slightly. Accel had no thinning effect on ‘Golden Delicious’. Accel caused development of pygmy fruit in both ‘Fuji’ and ‘Delicious’. All C/T, CyLex and Accel treatments increased fruit soluble solids in ‘Fuji’, while the CyLex and Accel treatments also increased fruit firmness over ethephon alone. Although not achieving target levels of thinning, C/T was more effective than Accel, however neither Accel or C/T improved fruit size. It is concluded that Accel is an ineffective thinner of ‘Fuji’, ‘Delicious’ and ‘Golden Delicious’, while CyLex is an effective and consistent thinner of the difficult to thin cultivar ‘Fuji’.

(100) Effect of Cropload, Irrigation, and Fertilization on Yield and Postharvest Bitter Pit Incidence of `Honeycrisp' Apple

A factorial field experiment was conducted at the New York State Agricultural Experimental Station in Geneva, N.Y., during 2004 and 2005 with `Honeycrisp' apple trees on M.9 rootstock. The main plot factors were three levels of applied nitrogen (0 kg/ha, 50 k/ha, and 100 k/ha); three levels of applied K2O (0 k/ha, 100 kg/ha, and 200 kg/ha); ± foliar nutrient sprays containing N, B, Zn, and Mg, ± foliar sprays of CaCl2 and ± trickle irrigation. The subplot factor was cropload (3, 6, 9, 12, and 15 fruits/cm2 TCA). Trees receiving irrigation or potassium had higher yields and the effect was greater as cropload was increased. There was no effect of nitrogen fertilization, foliar Ca, and foliar N, B, Zn, and Mg on yield. Irrigation and increased potassium fertilization rate reduced fruit soluble solids at harvest. Foliar calcium applications, foliar N, B, Zn, and Mg applications, and nitrogen fertilization rate did not affect fruit soluble solids at harvest. No treatment factor had an effect on fruit firmness at harvest, but, after 4 months on cold storage, fruits from irrigated trees had greater firmness. Bitter pit incidence was lower on apples from trees that did not receive irrigation compared to irrigated trees. The difference was constant under all cropload levels. Foliar calcium applications, foliar N, B, Zn, and Mg applications, nitrogen fertilization rate and potassium fertilization rate did not affect bitter pit incidence.

Effect of Varying Crop Load on Leaf Photosynthesis and Carbon Isotope Discrimination of `Imperial Gala' Apple Tree

Crop load (CL) is a critical regulator of production and quality on apple. It affects leaf photosynthetic rate and usually an increase is detected in leaves close to developing sinks. The objective of this work was to test if 13C discrimination during photosynthesis could be an indicator of carbon sink limitation. The natural plant carbon isotope composition (13C/12C ratio: d13C) is an indicator of water use efficiency and it is an effective tool to study environmental stresses in plants. Seven-year-old trees of Imperial Gala/Bud 9 (n=30), field-grown at the Clarksville Horticultural Research Station in Michigan, were hand-thinned to five levels of CL manipulating the leaf to fruit ratio (LFR: 4, 8, 16, 32, 64) after June drop. Net photosynthetic rate (A) of leaves was monitored daily during the season and elevated rates were observed in low LFR. The A was inhibited in low CL trees (LFR 32 and 64) more in the afternoon (from 20% to 42% in relation to normal CL: LFR 16) than in the morning (from 5% to 20%), and stomatal conductance declined over the afternoon. Shoot and fruit growth were affected (fruit size –11/+11%, shoot length –13/+18% from normal CL; LFR 16). Variations of the stable carbon isotope composition of leaves show a significant reduction of 13C discrimination in low CL trees (–3.2%: d13C –25.82) and an increase of 13C discrimination (+2.7%: d13C –27.38) in relation to normal CL trees (LFR 15.63). The results were similar to those reported in 2004, which imply isotopic discrimination in relation to source limitation. This is the opposite of what you would expect under water stress conditions. Although trees were well-watered during the season, the effect of water stress on apple trees and its interaction with source limitation will be discussed.