In studying source-sink relationships, the development of both the vegetative and reproductive parts of the plant is subject to a functional interdependence between the two, where they both benefit from and compete with each other. This direct relationship between the two parts is more clearly understood when the leaf is called the source, because it produces and exports photoassimilates, while the fruit is called a sink, because it imports and consumes the photoassimilates Wubs et al.
In this study, it was considered that the competition between the reproductive fruit and vegetative sinks stem and branches was not fully established, as it was verified that the fruit load essentially did not alter the plant height, stem and skirt diameter and length of branches Figure 2. Contrary to expectations, the presence of fruit did not inhibit vegetative growth. Many authors have reported strong competition between the two types of growth in coffee plants Cannel, ; Amaral et al. Some have even pointed out that the biennial production of the crop is the most profound expression of this competitiveness Cannel, ; Rena; Maestri, ; Laviola et al.
For them, if there is no significant increase in leaf area by the end of the rapid fruit growth stage, there may be a depletion of the plants during the period of greatest demand grain filling and, thus intensifying the biennial production phenomenon Pezzopane et al. Prior to the reproductive stage, proper cultural practices such as control of pests, diseases and weeds; irrigation and balanced fertilization provide a rapid increase in leaf area and improves the chances of a good grain formation Livramento et al.
These authors argued that trees in these conditions synthesize sufficient amounts of carbohydrates to ensure high fruit loads, whilst at the same time maintaining its vegetative state. However, in crops with high yields that do not receive appropriate cultural practices, reserves are exhausted.
This study confirmed the observations made by Livramento et al. In general, trees with fruit had higher levels of soluble sugar and the same level of starch in leaves and roots, compared to those that had their fruit removed Figure 3. The lowest level of reducing sugars RS in the roots of plants with fruit is probably due the mobilization of glucose to the synthesis of starch. This may explain the same level of starch in plants with and without fruit. Alternatively we can not discard the hypothesis that the lowest level of RS is probably due to mobilization of glucose and fructose, derived from the conversion of sucrose to the root growth.
This behavior, as previously mentioned, probably happened because of the excellent health and nutritional status of the trees and because of the low fruit production of the four year old trees. Several studies show that an increase in the source-sink ratio through the removal of fruit can cause a decrease in the net assimilation rate of carbon due to retro-inhibition derived from the accumulation of carbohydrates in leaves Stitt, This possibility does not apply in this case, since there was no accumulation of soluble carbohydrates in the leaves of the trees that had all fruits removed.
On the other hand, higher levels of carbohydrates in leaves and roots of trees with fruit shows indirectly that they were operating at much higher rates of carbon assimilation than those without fruit. This observation is confirmed when one considers that the size of the fruit and the weight of the seeds were not deficient.
As the fruits and seed were well developed, and the plants did not have any dry branches, it is considered that the strength of these sinks had not been diminished. These results suggest that coffee plants adjust their photosynthetic capacity to the fruit load.
Higher values of photosynthesis, to the extent that the fruit load increases, have been reported for coffee Franck et al. This gain in photosynthesis was credited to the greater availability of internal CO 2 associated with higher stomatal conductance Damatta et al. This work also discusses the source-sink relationship, considering the behavior of shoot and root system.
In the topmost layer of soil ranging from cm, the density of root length DRL of plants with and without fruit essentially did not change Figure 4. However in the cm layer there was greater DRL in plants that had their fruits removed. Our data shows that the presence of fruit on the plants limited the mobilization of assimilates to the root system since, in this organ, the levels of soluble sugars were lower than those plants without fruit Figure 3. As mentioned earlier the lowest level of RS in the roots of plants with fruit is probably due to mobilization of glucose and fructose, derived from the conversion of sucrose in root growth.
It should be noted here that the plants with fruit were possibly operating with high rates of net carbon assimilation. This remark comes with the observation that there was a great mobilization of sucrose to the roots and yet its level in the leaves, here represented by AST, still remained high 34 mg g -1 FM in plants without fruit.
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Once in the roots, much of the sucrose may have remained as such and the rest may have been cleaved, generating glucose and fructose. Finally, these simple sugars may have been directed towards the growth of roots, and part of the glucose mobilized into starch. From the above it is concluded, similar to what was reported by Livramento et al. The mobilization of sugars from the shoot stimulating the growth of roots was also observed in peach by Borba et al. Finally, we did observe that plants without fruit showed greater vegetative vigor than the fruit loaded plants Figure 2. Thus it is possible to suggest that this vigor was due to other factors not related to carbohydrate reserves.
In addition, these results suggest that the positive relationship between levels of fruit and carbohydrate content cannot be generalized, since it does not benefit all growth parameters. In fact, it reflects a particular condition in which the plants were still young, had low fruit load and were strong, due to proper management of the crop. The greater amount of foliage on plants without fruit, here represented by the greatest vegetative vigor Figure 2 , may have been responsible for further developing root systems Figure 4.
These results reveal, for plants with high vegetative vigor, the existence of a compensatory growth between roots and shoots in order to benefit each other without leading to the depletion of its carbohydrate reserves. This compensatory distribution of the size of carbohydrates sinks fruit and shoot associated with the quality of sources leaves , allows root system growth to benefit from changes in shoot growth. So it can be stated that the final root system conformation depends, among other factors, on physiology, plant health and crop management.
In this case, the majority of the explanations refer to the accumulation of high proportions of the total assimilates in the fruit, limiting the mobilization of these metabolites to the roots with negative effects on their growth. In addition, previous studies show intense death of radical roots soon after harvest Rena; Maestri, This death has been attributed to the competition for carbohydrates established between the shoot and root systems, especially in plants with high production. During the fruiting process, fruit filling occurs primarily through the use of photosynthates produced directly from current photosynthesis.
As the photosynthesis of coffee trees compared to other C3 plants is low Ceulemans; Saugier, and insufficient to meet the demand for assimilates by the fruit, trees with large yields uses carbohydrate reserves stored in different plant organs, including the root system. Such behavior was reported by Hidalgo in grapes and Borba et al. By acting as a source of photosynthates, the radical roots have their carbohydrates stocks depleted and respiration paralyzed, resulting in death Borba et al. In our case, this sequence of events culminating in the death of radical roots was not observed, probably due to the high vigor of the crop throughout the growing season and high levels of carbohydrates in the roots of plants with fruit.
Additionally, chemical and physical conditions and soil moisture are also determining factors Alves; Livramento, The spatial distribution of roots horizontally into three soil depths showed that the roots grew preferentially in a zone laterally located to the planting row, corresponding to the area of fertilizer deposition under the canopy of tree. It also revealed, as example of the quantitative data, a higher density of roots at , which decreased in the and increased again in the cm deep layer. A greater presence of the roots in the surface layers of the soil has been reported in several studies Huxley et al.
Studies made by Matiello et al.
According to these authors, the presence of nutrients at depth was responsible for the wider distribution of the root system in the deep soil. This fact helps to explain a greater concentration of roots in the layer of compared to cm. The results of our paper clearly contrast with what has been published by some authors in the literature about source-sink relationships for coffee plants. The joint data analysis shows that young trees, with moderate fruit load, and with good nutritional and health status produce carbohydrates in quantities sufficient to maintain the vegetative and reproductive growth, without harming the growth of the root system.
In the most superficial layer of soil ranging from cm, the density of root length DRL of plant with and without fruit essentially did not change. However in the layer of cm, plants without fruit had higher DRL than plants with full fruit load. Our data show that the presence of fruit on the plants limited the mobilization of assimilates to the root system, since in this organ, the levels of soluble sugars was lower than those plants without fruit.
The joint data analysis shows that young trees, with moderate fruit load, and with good nutritional and health status produce carbohydrates in quantities sufficient to maintain vegetative and reproductive growth, without harming root system growth. Alves, J. Morfologia do cafeeiro. In: Carvalho, C. Morfologia e fisiologia do cafeeiro. Lavras: UFLA, Amaral, J. Borba, M. Teores de carboidratos em pessegueiros submetidos a diferentes intensidades de poda verde em clima tropical. Revista Brasileira de Fruticultura , Jaboticabal, v. Cannel, M.
Crop physiological aspects of coffee bean yield: a review. Kenya Coffee , Nairobi, v. Effects of fruiting, defoliation and ringbarking on the accumulation and distribution of dry matter in branches of Coffea arabica L. Experimental Agriculture, Melbourne, v. Carvalho, C. Carvalho, G. Ceulemans, R. In: Raghavendra, A. Physiology of trees. New York: J. Wiley, DaMatta, F. In field grown coffee trees source-sink manipulation alters photosynthetic rates, independently of carbon metabolism, via alterations in stomatal function.
New Phytologist , Cambridge, v. Franck, N. Soluble sugars mediate sink feedback down-regulation of leaf photosynthesis in field-grown Coffea arabica. Tree Physiology, Victoria, v. Guerra, A.
The manipulation of fruiting
Salvador: UFBA, Hidalgo, L. Tratado de viticultura general. Madrid: Mundi, Huxley, P. Tracer studies with P on the distribution of functional roots of Arabica coffee in Kenya. Annals of Applied Biology , Warwick, v. Kinney, K. Effects of CO 2 and NO 3 availability on deciduous trees: phytochemistry and insect performance. Ecology , Durham, v. In the same study, covering blueberry and raspberry fruit with various edible coatings reduced oviposition by D.
Applications of foliar calcium fertilizers targeting blueberry fruit increased skin penetration force in some cases Ochmian but not others Hanson ; investigation of their potential to reduce D. In addition to potential reduction of D. Preharvest applications of calcium sulfate delayed postharvest softening of blueberry kept in storage Angeletti et al.
Gibberellic acid GA 3 is usually applied during bloom to enhance fruit set NeSmith Anti-cracking biofilms are applied to improve elasticity of the skin and accelerate maturity Kaiser et al. Given the potential of various fruit coatings to improve fruit quality as well as reduce infestation, our third objective was to evaluate the effects of spraying blueberry fruit with various compounds on D. To summarize, this study was designed to 1 determine the probability of oviposition by D.
Oviposition by D. Field-collected blueberry fruits for laboratory bioassays were verified by microscope to be free from damage and infestation prior to use. In Oregon, flies used in all laboratory and field experiments were from a laboratory colony that originated from locally collected flies in November , to which wild flies were added each year. In North Carolina, flies used in field experiments were from a laboratory colony that originated from locally collected flies in October Flies used in experiments were 5—day old.
Five female and four male D. Ten cages were set up on 15 July For further analyses, each fruit was individually tracked and stored frozen. For this trial and others, TSS could not be measured on some small green fruit because they did not contain sufficient liquid for the refractometer. Three female and two male D. Each cage contained at least five fruit of each ripeness stage with no more than 10 fruit per stage. Ten cages were set up per day 40 total on 8, 12, 14, and 19 August at an experimental blueberry farm in Linn County, Oregon. Each cage contained a 1.
A water-soaked sponge was also placed at the bottom of the cage. Immediately after egg-counting, flesh firmness and diameter were measured using the deflect test option in a FirmTech2 BioWorks, Wamego, KS. For this trial and others, firmness readings could not be taken on some smaller green and hard fruit. Immediately after flesh firmness testing, the penetration force of the fruit epidermis was measured with a penetrometer consisting of a gram-force gauge Wagner Instruments, Greenwich, CT with a No. The ball of the pin was removed, and the blunt end was used to poke fruit.
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Three readings were taken per fruit on the girth and averaged. Fruit were then immediately frozen and later macerated for measuring TSS and pH as described above. In NC-field 1, five females were exposed to five hanging fruit on a lateral enclosed in a mesh sleeve cage Fruit clusters initially had one ripeness stage present. Nine cages were set up for this experiment on 10 July In NC-field 2, five females were exposed to 10 fruit of mixed ripeness stages.
Nine cages were set up on 18 July In both trials, each cage provided flies with a yeast-sugar solution in a tube as described earlier. First, the effect of multiple variables firmness, penetration force, TSS and pH on the probability of oviposition of a given fruit was evaluated using a generalized linear model with a binomial distribution and logit link function.
Each fruit was an observational unit and scored for the binary outcome for the presence or absence of oviposition to estimate oviposition probability. Analyses were conducted separately for each trial, with fruits from cages pooled for analysis. Second, key variables identified in the first analyses were then tested individually as single independent variables using a logistic regression i.
Third, to explore how attack density affects oviposition probability, logistic regressions were conducted for subsets of data within the OR-field trial by attack density. Low-density attack was defined as cages where an average of less than one egg was laid per fruit, and high-density attack included cages averaging one or more eggs laid per fruit. Analyses were done in JMP Field infestation of fruit by naturally occurring D.
On 20 September , raspberries were collected from an experimental mixed-cultivar plot in Linn County, Oregon. Eight sample sets were collected across the farm per date. For each sample set, 25 green, 25 pink, and 25 fully blue fruit were collected concurrently in a location consisting of 2—4 bushes. For raspberry infestation, counts of D. Each sample of 15 raspberries or 25 blueberries was an observational unit. Separate tests were conducted for the red, black, and yellow-fruited cultivars.
For blueberry infestation, counts were compared for the effects of ripeness stage, date, and interactions with a generalized linear model with a Poisson distribution. Five sprayable compounds were tested with the aim to reduce D. Fruit treated with these five compounds were compared to control fruit that were not sprayed with compounds. Four sets of blueberry bushes were assigned one of the six treatments in a randomized block design within one row. Treatments were applied to three consecutive bushes, comprising a set, and the middle bush was designated as the sample bush.
Fruiting laterals were uncovered once pesticide sprays had dried. In the oviposition bioassay, each treatment was replicated in ten cages, with 15 fruit of varying ripeness stages, five females and four males in each cage as described in the fruit characteristics trial. Cages were set up from 10 July to 6 August using fruit collected from the field the previous day. Additional ripe blue fruit were collected from the same plants and directly measured for firmness, diameter, and calcium Ca concentration; these fruit were not exposed to D.
On 10, 15, 23, and 31 July, and 6 and 14 August , fruit were collected and directly measured for firmness and diameter at the farm site using FirmTech2. The number of eggs laid per fruit, with cage as the observational unit, was compared among spray treatments using a generalized linear mixed model with a Poisson distribution, and date as a random effect. Next, the firmness, penetration force, TSS, pH, diameter, and arc-sin transformed Ca concentration of fruits were compared among treatments using a generalized linear mixed model with a normal distribution and date as a random effect and each fruit as the observational unit.
Analyses are only shown for a subset of the data, blue-colored fruit, as this is the stage that is harvested, and any physiological changes may affect storage and marketability of fruit. The probability of oviposition by D. Probability of oviposition by D. Bars show the observed proportions while curves describe the fitted relationship by logistic regression. Numbers inside the boxes refer to the number of fruit within each subset, and subsets in a are as low as 34 because fewer fruits at the lower cN values were available.
Mean number of D. Letters denote significant difference within each date. Color figure online.
Coatings sprayed on blueberry plants during fruit development from immediately after fruit set through early blue stage in a mature field near Salem, Oregon, US. Fruit were used in a laboratory assay for oviposition by D. For growers, the risk of infestation is more important than the amount of infestation per berry, and a predictive model and threshold would be a helpful decision-making tool for timing of insecticide application.
This result is consistent with a Pearson correlation analysis and categorical grouping of winegrapes by infestation status showing that oviposition is highly dependent on penetration force Ioriatti et al. In our trials, the probability of oviposition also increased as pH increased and sometimes increased as TSS increased fruit became sweeter and less acidic , also consistent with Ioriatti et al. Notably, significant trends were found in datasets with a range of 20— observations, and with a range of attack rates of 1.
These models help us to understand the behavior of D. Natural attack rates in the field are expected to be lower than in the caged arenas, and therefore, the probability values should also be lower. For comparison, in the field study, fruit collected from an unsprayed field were naturally infested at 0.
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The trials presented here did not clearly delineate a threshold of when oviposition would not occur for the metrics of firmness, epidermal penetration force, TSS, or pH. In contrast, a threshold penetration force of 52 cN has been found on an artificial diet Burrack et al. The lack of thresholds in our trials might suggest that prediction of susceptibility on fruit versus artificial media is more complicated than relying on a single characteristic, or alternatively, our experimental design was not adequate for determining a threshold.
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Within a cage, D. In the field, infestation by naturally occurring D. While this confirms previous laboratory assays, the magnitude of difference was more pronounced in the field. In this field study, infestation on raspberry was 5—6-fold higher among ripe raspberry fruit, and 7—fold higher among ripe blueberry fruit compared to ripening fruit. In a prior laboratory choice study, infestation was 1.
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Stronger preference for ripe fruit may be expected in the field because D. One explanation for this reduction could be that females do not prefer the tactile cues of sprayed fruit, or alternately it could be due to a mechanism mediated through physiological changes in the fruit. In general, the calcium-based treatments increased fruit firmness, penetration force, and Ca concentration, while some treatments slightly reduced fruit diameter by 3. However, in previous studies Ochmian , fruit may also have been firmer as a result of a small average berry size.
The small reduction in size associated with fruit treated with chelated calcium or calcium borate may be a response to plant stress or osmotic or turgor changes in treated fruit. In our trial, application of GA 3 in mid-June when fruit were first showing color increased the size of blue-colored blueberry fruit relative to the control.
Application of GA 3 at early bloom has been shown to increase fruit set and reduce berry size in rabbiteye blueberry NeSmith ; NeSmith and Krewer , but this growth regulator is not typically used during fruit development. The anti-cracking biofilm had no impact on fruit characteristics or oviposition behavior relative to the control.
None of the coatings prevented D. Some calcium-based coatings did improve fruit quality suggesting additional horticultural benefit separate from pest control. The measurement of host potential consists of locating the host, success of oviposition, and larval development, and the studies presented here address various phases.