Crop Load Treatments Research Articles

Canopy management and water use efficiency in vineyards under Mediterranean semiarid conditions

One of the main objectives in Mediterranean vineyards is the water use efficiency due to its scarcity. During the growing season, total available water is significantly lower than the evaporative demand, being this a limiting factor for quality production. Beside other factors, the choice of an adequate training system can help mitigate this negative effect in regard with soil-plant hydric consumption. The use of porous systems can help plants establish a better leaf distribution inside the clusters area, providing more space and enhancing certain physiological processes, both in leaves and berries (de la Fuente et al., 2013), and causing a better utilization of natural resources.Water consumption, dynamics and hydric relations in plants (water potential) and soil (soil water tension and capacity) have been studied on three different systems: sprawl system with 12 shoots m–1 (S1); sprawl system with 18 shoots m–1 (S2) and verti- cal positioned system or VSP with 12 shoots m–1 (VSP1). Yield, dry matter partitioning and berry and must composition have also been obtained at the maturity stage.The main objective of this study was to show the differences in consumption and water use efficiency due to different canopy managements, and to quantify these effects on yield, berry and must composition.The results showed that the vertical system (VSP1) benefited less from total available water at medium level (20; 30 and 50 cm) in the profile soil (0.5–1.5% available water vol.), in comparison with non-positioned and free systems (S1 and S2). On the other hand, S1 and S2 treatments caused more stress to the plant at midday from flowering to veraison (8–10%), but not during ripening. Sprawl system (S1) helps produce more balanced plants compared to VSP1, because it obtains higher number (and weight) of main leaves by shoot, increasing the number of secondary shoots and maximizing the canopy volume. No dif- ferences were observed in the number of clusters, berry size or yield between VSP1 and S1, but higher crop load treatment (S2) showed an evident yield increase (16%) at harvest.Berry and must composition did not change (Brix, pH and total acidity) much, while the composition of anthocyanins improved with low exposure and non-positioned systems (S1 and S2).In addition, both positive effects of sprawl treatments (crop load and training system) resulted in better yield and quality in Mediterranean semiarid conditions under the same inputs (sun, water and soil), causing higher efficiency of natural resources.

Influence of Aminoethoxyvinylglycine on Pecan Fruit Retention

Insufficient fruit retention limits profitability of certain pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivars. The present study examined efficacy of aminoethoxyvinylglycine (formulated as ReTain®; Valent BioSciences, Libertyville, IL), a natural ethylene inhibitor, for increasing crop-load through increased fruit retention in pecan trees grown at three distinct locations within the U.S. pecan belt. Several years of field studies found that timely postpollination ReTain® sprays [132 mg·L−1 a.i. (11.7 oz./acre)] to canopies could increase fruit retention of ‘Desirable’ and increase crop yield by 16% to 38% in trees carrying a “moderate to heavy” crop. ReTain® did not detectably increase fruit retention on trees carrying a “light” crop-load. The ReTain®-associated increase in yield of “heavy” crop-load trees did not necessarily decrease subsequent year yield. ReTain® appears to offer commercial potential as a crop-load management tool for ‘Desirable’ through regulation of Stage II drop (i.e., June-drop), but may not be efficacious for all cultivars.

Effects of crop load and time of thinning on the incidence of split pits, fruit yield, fruit quality, and leaf mineral contents in ‘Andross’ peach

SummaryThe effects of light, moderate, or heavy thinning (5, 10, or 20 cm between fruit, respectively), conducted before (7 d or 15 d), during, or after (7 d or 15 d) pit hardening (PH), on the incidence of split pits, fruit yield, fruit quality characteristics, and leaf mineral contents, were studied in the canning peach (Prunus persica L. Batsch.) cultivar ‘Andross’ over two growing seasons. The percentage of fruit with split pits increased by 58.2% in heavily-thinned trees compared with moderately- or lightly-thinned trees, and by 22.9% for the earliest time of thinning (15 d before PH) compared with thinning during, or after PH. Fruit fresh weight (FW) was greater in moderately- and heavily-thinned trees compared with lightly-thinned trees, but yields were similar among the different crop-load treatments. The latest time of thinning (15 d after PH) also had a negative impact on yield at first harvest and on total yield, fruit FW, and delayed fruit ripening compared to thinning during, and 15 d before PH. Total anti-oxidant capacities and phenolic contents were usually greater in fruit from heavily-thinned compared with lightly- or moderately-thinned trees only when thinning was conducted during, or 15 d after PH. Moreover, anti-oxidant levels were highest in fruit from the earliest-thinned trees. There was no significant effect of crop load, or of time of thinning application treatment on fruit colour, or on the K, P, Fe, Mn, and Cu contents of leaf tissues. In conclusion, light or moderate thinning during PH resulted in minimal split pits during processing, and in optimal yields and fruit quality characteristics in the canning peach cultivar ‘Andross’.

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.

Cuticular Cracking on Nectarine Fruit Surface: Spatial Distribution and Development in Relation to Irrigation and Thinning

Investigations on “natural” cuticular cracks were conducted on nectarine fruit [Prunus persica (L.) Batsch var. nucipersica (Suckow) C.K. Schneid.]. A method for quantifying the cuticular crack surface area on a whole fruit basis was proposed. By using a stratified sampling design, the spatial distribution of the cuticular cracks over three regions (stylar end, peduncle, and cheek), their morphology, and the estimation of the total proportion of cuticular cracks on the fruit were studied. These features were examined during fruit development and in response to several fruit growing conditions corresponding to various crop loads and irrigation regimes. Cuticular cracks on nectarine fruit occurred during the final rapid fruit growth stage. Larger fruit presented higher cuticular crack densities in the apical regions than in the cheek regions. Thin and larger cuticular cracks occurred continuously during fruit development. Cuticular cracks represented 10% to 12.5% of the fruit surface area for well irrigated or low crop load trees, whereas they covered less than 4.5% for the heavy crop load and water deficit treatments. Cheek regions largely contributed to the total cuticular crack surface area (>60%), regardless of the fruit growing conditions. After irrigation was restricted, cuticular crack development was limited. A positive relationship was established between the cuticular crack surface area per fruit surface area and the fruit fresh weight.

Current-year and Subsequent-year Effects of Crop-load Manipulation and Epicormic-shoot Removal on Distribution of Long, Short and Epicormic Shoot Growth in Prunus persica

The distribution of canopy growth among different shoot types such as epicormic, long and short shoots is not well understood in the peach tree. In this experiment, the effects of crop load and early epicormic sprout removal on current and subsequent-year distribution of vegetative growth among epicormic, long and short shoots was investigated in Prunus persica. Field trials were conducted in Winters, California, in 2003-2004. Crop load was manipulated with fruit thinning in 2003 to produce trees that were de-fruited, commercially thinned or full crop, and half of the trees in each cropping treatment had all current year epicormic sprouts removed at the time of fruit thinning. Yield was recorded and trunk and root carbohydrates were sampled to confirm the effect of 2003 crop load differences on tissue carbohydrate concentration. All current-season vegetative-shoot extension growth was harvested from half of the trees in each treatment in the autumn of 2003 and from the other half in the autumn of 2004. Epicormic, long and short shoots were separately evaluated for dry weight, node number and leaf-stem parameters. In 2003, long-shoot dry weight and node number were significantly affected by crop load; however, short-shoot dry weight and node number were not significantly affected. The 2003 crop-load treatments did not affect 2004 vegetative growth of any shoot type. Some re-growth of epicormic shoots followed early epicormic sprout removal: by the end of the 2003 season, trees in the early shoot-removal treatment had approximately one-third of the epicormic-shoot dry weight as unpruned trees. Fruit thinning promoted distribution of growth similar to that of de-fruited trees. While thinning was effective in increasing fruit size, it exacerbated the problem of epicormic sprouting. Early epicormic sprout removal did not stimulate the excessive epicormic re-growth in the same or subsequent year relative to previously studied summer pruning methods.

Effect of late Spring defruiting on net CO2 exchange and leaf area development in apple tree canopies

SummaryThe influence of defruiting on vegetative development and its implications for the time response of canopy net CO2 exchange rate (NCERcanopy), transpiration (Tcanopy) and midday stem water potential ( stem) were analysed during the last 4 months of apple fruit development. Two crop-load treatments were applied 2 months after full bloom: defruited (DF) and fruited (F). The latter did not receive any fruit thinning. Four trees in two groups (with two replications of two trees per crop-load treatment), growing on a dwarfing rootstock (M-9), were monitored diurnally for NCERcanopy and Tcanopy, using a whole canopy gas exchange technique. The effects of defruiting were observed shortly after fruit removal. All parameters measured remained constant or increased over the 4 months until harvest. Canopy gas exchange decreased for all DF trees. Leaf NCER was also lower in DF trees until harvest. In contrast the leaf area of DF trees increased by 20% compared to F trees. Differences in NCERcanopy between treatments were reversed after harvest, when DF trees registered higher NCERcanopy values than F trees because of their larger leaf area. Leaf conductance and transpiration decreased, and stem increased for DF trees compared to F trees during the 4 month period of differential cropping. Daily NCERcanopy values decreased from late May until September, as did incident solar radiation, and temperatures were cooler in September. Inhibition of NCER at the leaf level increased linearly over time, from 10% immediately after thinning, up to 35% before harvest, and exceeded the 20% increase in vegetative growth in DF trees. This down-regulation, which increased proportionally with time, was interpreted as an inadequate replacement of fruit by vegetative sinks in DF trees over the 4 month research period.

Fruit mass, colour and yield of ‘Honeycrisp’™ apples are influenced by manually-adjusted fruit population and tree form

SummaryThe influence of three manually-adjusted crop loads [3, 6 and 9 fruit cm–2 trunk cross-sectional area (TCSA)] on ‘Honeycrisp’™ apple (Malus domestica Borkh) quality and canopy volume were compared with unadjusted control trees. The crop-load treatments were applied at three sites over two consecutive seasons at 50 days after full bloom (DAFB). Sixteen trees at each site were selected annually, with the treatments being applied in a randomisedcomplete-block design. Fruit mass and fruit colour (%) were used to assess quality at harvest, while yield was determined by the mass (kg) of fruit cm–2 TCSA. The canopy volume (CV) for each tree was calculated following harvest and used as a covariate in determining its influence on fruit size and colour. As crop load decreased, harvested fruit mass and % red colour increased. For similar crop-load adjustments, larger tree CVs (in m3) resulted in greater fruit mass. Crop load and fruit-canopy density (fruit m–3 CV) were more highly correlated with fruit mass than with % fruit colour. The highest fruit quality occurred at the three and six fruit cm–2 TCSA. In addition, manually adjusting the crop-load at 50 DAFB did not eliminate the disposition of ‘Honeycrisp’™ towards biennial bearing in Nova Scotia’s climate.

(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.

Production of aroma volatiles in response to deficit irrigation and to crop load in relation to fruit maturity for ‘Braeburn’ apple

Abstract Aroma volatiles are important quality attributes for apples and there is not enough information on how their production is affected by deficit irrigation (DI) or by crop load. We investigated effects of irrigation, crop load, and their interaction on maturity-related quality attributes (aroma volatiles, total soluble solids (TSS), titratable acidity (TA), and firmness) and maturity attributes (internal ethylene concentration, ‘percent ripening fruit’, and starch pattern index) for ‘Braeburn’ apple. Multivariate relationships between these two sets of attributes were also explored. Irrigation treatments were commercially irrigated control (CI) and DI applied throughout the season. Crop load treatments were commercial crop load (CCL) having six fruits per cm 2 of trunk cross-sectional area and light crop load (LCL) having four. There was no interaction between irrigation and crop load on any individual quality attributes. Control and DI fruit had similar maturity at harvest but DI fruit became more advanced in maturity during storage at 20 °C and after cold storage. DI enhanced volatile production during ripening and after cold storage. Firmness and TSS also increased in DI fruit but the increased firmness was lost during subsequent storage. Firmness and TSS increased in LCL in some occasions but crop load had no effect on maturity or aroma volatiles. Fruit TA was not affected by irrigation or crop load. Aroma volatiles poorly correlated with each individual maturity attribute. Canonical correlation analysis showed high multivariate correlation between maturity attributes and maturity-related quality attributes with two underlying dimensions that characterised their relationships. Quality enhancement in DI fruit was related, in part, to the advancement in ripening.

Water use, yield and fruit quality of lysimeter-grown apple trees: responses to deficit irrigation and to crop load

Effective irrigation scheduling for maximum crop yield and quality in a sustainable environment requires a good understanding of crop water use in relation to crop load and soil water availability. This study determined tree water use (TWU), fruit growth, yield, and quality of 'Braeburn' apple grown in lysimeters in response to two irrigation regimes and two crop loads in the growing season of 1997/1998. The irrigation regimes tested were control level of irrigation (CI) and deficit irrigation (DI) and the crop loads were commercial crop load (CCL) and light crop load (LCL) which was equivalent to 60% of the CCL. Tree water use was measured using two methods: soil-water balance through lysimetry and by a heat-pulse technique. There was no significant interaction between irrigation and crop load treatments and therefore only results for the main effects, irrigation and crop load, are presented. DI and LCL reduced TWU. Higher stomatal conductance (gs) was responsible for the higher TWU in CI but not in CCL. Increased mean fruit weight but decreased gross yield was observed in LCL. DI reduced mean fruit weight but had no significant effect on gross yield. Fruit quality, in terms of flesh firmness, total soluble solids, and dry matter concentration, was improved in DI both at harvest and after 12 weeks of cold storage but was, generally, not affected by crop load.

The effect of selective picking on the harvest fruit size distribution of ‘Royal Gala‘ apples

SummaryThe size distribution of fruit on an apple tree on any potential harvest date can be estimated by measuring a sample of fruit early in the season and projecting forward in time using standard growth curves. However, ‘Royal Gala‘ apples grown in New Zealand are picked in multiple harvests spread over about three weeks, so the overall size distribution of harvested fruit can differ significantly from that on any single harvest date. On each havest date, fruit are selected for picking according to background colour, not size. By measuring the sizes at harvest of all fruit on selected limbs of eight ‘Royal Gala‘ trees in Hawkes Bay, New Zealand, we show that the relationship between the size distributions of picked and unpicked fruit can be described by a single-parameter model. Although size is not used directly in fruit selection, we find that larger fruit still tend to be picked first, with the odds of a fruit being selected approximately doubling for each 20.g increase in size. The mean harvest fruit size is largest for the first harvest, and decreases in later harvests, despite ongoing fruit growth. Because the smaller fruit left on the trees continue to grow, the standard deviation of the overall fruit size distribution from multiple harvests can be expected to be significantly smaller than it would have been had all fruit been harvested on the same date. The model is tested using size and background colour measurements collected on tagged fruit at three sites in two years, including a range of shading and crop load treatments. For most combinations of site, year and treatment, the model predicted the size distribution of picked fruit well, but in a few cases a different parameter value was need to obtain a good fit.

Water relations, photosynthesis, growth, yield and fruit size of ‘Braeburn’ apple: Responses to deficit irrigation and to crop load

SummaryInteractions were investigated between irrigation and crop load on photosynthesis, fruit growth and size, and fruit water relations of ‘Braeburn’ apple. The irrigation treatments were a commercially irrigated control (CI) and deficit irrigation (DI) applied throughout the season. The crop load treatments were commercial crop load (CCL) having six fruit per cm2 of trunk cross-sectional area and light crop load (LCL) having four. There were interactions between irrigation and crop load on fruit water potential (Ψfw), fruit turgor potential (Ψfp), and photosynthetic rate (Pn) during mid and late season, and on mean fruit weight at harvest. These parameters were the same for CCL and LCL under CI except for Ψfp which was lower in CCL. Under DI they were lower in CCL than in LCL. For both crop loads DI reduced Ψfw and Ψfp early in the season but from mid-season Ψfp was maintained through osmotic adjustment. Photosynthetic rates were lower in DI than in CI for both crop loads but differences late in the season were significant only for CCL. Mean fruit weight at harvest was similar for CI and DI for LCL, but was lower in DI for CCL. Interactions between irrigation and crop load on fruit size could be due to effects on fruit water relations and photosynthesis.

Fruit growth and mineral element accumulation in pacific rose™ apple in relation to orchard management factors and calyx‐end splitting

The effect of irrigation and crop load of apple (Malus domestica Borkh cv. Pacific Rose) on the fruit growth and mineral element accumulation was investigated. Fruit growth and changes in the concentration and contents of nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg), and potassium (K) in the flesh of Pacific Rose™ apple fruit were recorded over a growing season at the Massey University Fruit Crops Units orchard in the 1998–99 crop season. Fresh mass showed a linear growth while fruit diameter followed a curvilinear growth pattern during the growing season. Low crop load significantly increased fruit size, particularly during the final expansion phase, whereas irrigation had little effect on this attribute. Both low crop load and frequent irrigation treatments increased fruit growth rate, but the effect of the irrigation treatments fluctuated considerably during the season. The incidence of frait splitting was detected at about 20 WAFB when the fruit attained an asymmetrical growth in shape (L/D). The concentrations of N, P, Ca, Mg, and K declined throughout the sampling period. There was however, an increase in concentrations of P and K at the last harvest. The quantity of individual nutrient elements accumulated by the fruit showed an increasing trend during the season. Nitrogen accumulation however, reached maximum at 16 WAFB after which it declined until the last harvest. Fruit mineral element analysis of sound and split fruit revealed that split fruit had higher concentrations and contents of Mg and K and lower contents of Ca and P. As a result, the ratios of Ca: Mg and Ca: K were lower in split fruit as compared with sound fruit.

Changes in primary and secondary growth as influenced by crop load in ‘Fantasmet’® apricot trees

SummaryThe effect of crop load on the growth dynamics of individual shoots was analysed in apricot trees in the third growing season, comparing their development at two initial locations along the bearing branch. Growth dynamics were observed throughout the growing season, from April to August, and took into account both primary growth (i.e..number of expanded leaves) and secondary growth (i.e. basal diameter increment). Crop load influenced primary growth rhythmicity and more precisely growth resumption within the growing season. The length of the growing period and the number of expanded leaves were more signi®cantly reduced on shoots originated from a proximal position along the branch than in a distal position. Thus, crop load enhanced the acrotonic distribution of branching. The allometric relationship between the basal diameter and the number of expanded leaves per shoot was not dependent upon shoot type, location or crop load treatment. Arguments are provided supporting the hypothesis that cambial growth occurring soon after the expansion of the preformed leaves is responsible for cessation of primary growth. This competition was shown to be independent of crop load and to involve only vegetative organs. These results indicate that the sink demand of the secondary growth and the resulting competition with the primary growth should be taken into account in the carbon economy of fruit trees, and that the competition between organs is not equally distributed between the organs of a given type but depends on their relative location.

Calyx-end splitting and physico-chemical properties of ‘Pacific Rose’TM apple as affected by orchard management factors

SummaryCalyx-end splitting (CES) is a preharvest quality defect that affects ‘Pacific Rose’TM apple. This paper reports the results of a study to determine the effects of orchard management factors on fruit physico-chemical properties and the development of CES in ‘Pacific Rose’TM apple. The onset of fruit splitting occurred at about 20 weeks after full bloom (WAFB). Withholding irrigation from 14 WAFB until commercial harvest (26 WAFB) reduced splitting incidence by 46%, whereas low crop load significantly increased splitting by over 61%. There was no consistent significant effect of crop load or irrigation treatment on total soluble solids (TSS), penetrometer or compression measurement of fruit firmness during the season, although withholding irrigation and high crop load generally enhanced fruit firmness.

Towards understanding the role of temperature in apple fruit growth responses in three geographical regions within New Zealand

SummaryThe influence of temperature on growth of ‘Royal Gala’ apples on MM.106 rootstock was studied using trees from one site in each of three regions of New Zealand (Canterbury, Hawkes Bay and Nelson) over three consecutive seasons. Temperatures were recorded as hourly means over each season. Growing degree day accumulation with a base of 10°C (GDD10) and 5°C (GDD5) were calculated, commencing at pollination. Crop loads were established at bloom to a very low level to minimize competition between fruit and provide a clear response of fruit growth to environmental conditions. Some trees were shaded with 70% shadecloth for 7 d beginning either 60 d after pollination (DAP) or 90 DAP. In the third season, other trees were thinned to a medium crop load to compare their fruit growth with that from trees bearing low crop loads. There was a highly significant correlation between GDD10 at 30 DAP and time from pollination to harvest (r2 = 0.96). On the low crop load trees, fruit weight at 50 d was closely correlated with GDD10 accumulated over the 50 DAP (r2 = 0.71). Furthermore fruit weight at 50 DAP was also significantly correlated with fruit weight at harvest (r2 = 0.68). These results support an hypothesis that a potential maximum fruit size is set by about 50 DAP, determined by total fruit cell number, resulting from a temperature-responsive cell division growth phase. Under conditions of no limitations after the cell division phase, all fruit cells would expand to their optimum size to provide the maximum fruit weight achievable for that cell number. Factors which limited carbohydrate availability, such as higher crop loads and shading of trees, reduced final fruit size. In this study, shading for 7 d at 90 DAP did not reduce final fruit size and shading at 60 DAP reduced final fruit size only in some cases. Differences in fruit weight at harvest induced by low and high crop loads were expressed only at the sites that achieved large fruit weight in that season and experienced greatest early season GDD10 accumulation (Hawkes Bay, Nelson). In a cooler region (or season), represented by Canterbury in this example, a fruit weight response to crop load was much less apparent. Ideas towards developing a practical methodology for predicting fruit weight at harvest are discussed.

THE INFLUENCE OF DAMAGE TO PS II ON YIELD AND QUALITY OF APPLES

The object of this experiment has been to determine the effect of simulated biological or enviromental damage at different timies of the growing season on the vegetative and reproductive growth of apple. One method that has been used is to inhibit photosynthesis by applying terbacil a PS II inhibitor at different times during the season to different varieties of apple (Delicous, Empire and Gala) for several years (1993-1996). The degree of inhibition was dose and time dependent. We chose a concentration (50-63 ppm) that inhibited photosynthesis 50-80% within 24 hours of appliction, that recovered fully within 7-10 days. Photosynthesis was measured with an open gas exchange system, or by measuring Fv/Fm with a chlorophyll flourescence system. No differences were found in total terminal shoot growth, cold hardiness, soluble solid concentration, fruit firmness, density of the fruit or fruit color. However, when terbacil was applied at 15 and 30 days after full bloom it induced fruit abscission which was markedly higher for trees with a higher crop load. Yield was reduced in high crop load trees but not low crop load trees. The earlier the simulated stress the greater the effect on the current seasons crop. Yield and size was only affected if the simulated stress occurred early in the season on high crop load trees, or near harvest on high crop load stress. The significance of these findings in relation to pest control will be discussed.

An expolinear model of the growth pattern of the apple fruit

SummaryThe expolinear growth model of Goudriaan and Monteith (1990) is proposed as a new model for the inherent growth pattern of fruit of apple (Malus domestica Borkh.), defined as growth pattern under apparently non–limiting conditions This function has three parameters: maximum relative growth rate, maximum absolute growth rate, and “lost time” (x intercept of the linear growth phase). Apple fruit growth (weight basis) at very low crop loads and apparently optimum environmental conditions, displays an early positive curvilinear growth followed by linear growth to harvest, and is described well by the expolinear function. The model also fits growth patterns of ‘Empire’ and ‘Golden Delicious’ apple fruit differing in the rate of growth in the exponential phase due to differences in the crop load. Estimates of cortical cell numbers in ‘Empire’ fruit from related studies suggest that during the linear phase in mid–season, different growth rates among crop load treatments were apparently controlled by differences in numbers of cells in the fruit, since estimated growth rates per cortical cell were essentially constant over several treatments.

Influence of Crop Load on Photosynthesis and Dry Matter Partitioning of Seyval Grapevines. III. Seasonal Changes in Dry Matter Partitioning, Vine Morphology, Yield, and Fruit Composition

Single leaf photosynthesis, whole vine photosynthesis measured in a whole plant chamber, dry matter partitioning, and several morphological indices were measured at four phenological stages of development on two-year-old, own-rooted Seyval grapevines adjusted to five different crop loads. Crop loads were 0, 1, 2, 4, or 6 clusters/vine with all laterals removed to eliminate intra-vine shading. Leaf area was inversely related to crop load, with differences evident as early as fruit set. Differences in dry weight partitioning did not become evident until mid-season. Leaf and shoot dry weight were inversely correlated, and fruit dry weight positively correlated with crop load, respectively. Root dry weight was inversely related to crop load only at harvest. Leaf area per vine, leaf size, shoot length, node number, and internode length were inversely related to crop load. Berries per cluster and cluster weight were inversely correlated with clusters per vine. Yield and berries per vine were correlated with clusters per vine. Sugar accumulation and shoot maturation were delayed by high crop loads. Implications of the crop load treatments on vine photosynthesis are discussed.