These fluctuations are unlikely to have been associated with soil moisture since irrigation does not alter the overall pattern of growth, although it may affect the rates of shoot growth Mota et al.
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Such a periodicity is also apparently independent of reproductive growth, although fruitless trees may outgrow those bearing fruit Mota et al. They also found a parallelism between stomatal conductance and shoot growth accompanying the onset of the declining growth phase, and thus hypothesized that photo-synthesis might to some extent modulate the growth of the coffee tree.
However, according to Silva et al. The growth periodicity, however, fluctuates similarly in both species cf. Figures 1 and 2. Thus, water availability rather than temperature would play a decisive role on the growth resumption following the period of restrained growth. The delayed growth resumption in unirrigated trees was accompanied by a compensatory growth in October Figure 2. Similar responses have been observed in arabica coffee Browning and Fisher, Node production on lateral branches and leaf formation parallel the oscillations in growth of plagiotropic branches in conilon coffee Ronchi and DaMatta, Both leaf growth rate and final area vary seasonally, with leaves reaching larger sizes, and faster, if expansion is initiated at the beginning of the rainy, hot season Silveira, , a phenomenon also observed in arabica coffee Rena and Maestri, Regardless of the timing of formation, leaf shedding in both arabica and conilon coffee plants increase by the end of the dry season, which coincides with the harvesting and post-harvesting periods.
In the main Brazilian area of conilon cultivation, strong winds are common in these periods, thereby exacerbating leaf shedding. Moreover, leaf longevity was high in the former group of trees. Larger leaf retention and longevity might partially be associated with improved growth in irrigated plants at the end of the dry season, as discussed above. Despite these considerations, little is known about how conilon growth seasonality is physiologically controlled. Flowering: Although flowering is one of the most important physiological processes of the coffee tree Barros et al.
Coffee flowering embraces a complex sequence of biochemical, physiological and morphological events which are affected by several factors such as temperature, light, soil and air water availability, carbon-to-nitrogen ratio, crop load and genotype Rena and Barros, Little effort has been undertaken to advance our understanding of the physiological mechanisms associated with flowering processes in coffee, and the principal, science-based available information has been summarized in reviews published over the last 30 years focusing on arabica Barros et al.
The following discussion is centred on the examination of both the practical and theoretical basis of coffee blossoming concentration, one of the most controversial issues currently debated by the Brazilian coffee growers and researchers. Unequal fruit ripening is practically inevitable under natural conditions because coffee blossoming in non-equatorial regions as in south-central Brazil occurs at different times e. In addition to the temporal and physiological hierarchy of flower bud initiation and differentiation within each branch, and also among different nodes of the same plagiotropic branch which are strongly affected by environment-genotype interactions , the occurrence of sporadic and sometimes low-intensity rains during the latter phases of flower bud development is believed to be the one of the uncontrolled factors responsible for several blossom periods in arabica coffee Rena et al.
As a consequence, fruit ripening is remarkably unsynchronised, with serious consequences for coffee management and production. The large variation in the percentages of ripe, green and dry cherries often observed at fruit harvesting time leads to i an increasing cost of coffee production since more than one harvesting operation will be necessary, which may also cause mechanical damage to the coffee trees; and ii an impaired beverage quality due to a low percentage of ripe cherries as compared to that of green and dry cherries, and a greater number of bean defects and ineffective control of pathogen and insect attacks on coffee fruits Rena and Barros, ; Guerra et al.
Under natural conditions, dormancy of flower buds is often broken by the first rains in the season following a dry period Barros et al. Recent field investigations on coffee blossom concentration through a controlled water deficit, imposed on irrigated crops at the latter stages of flower bud development, has been undertaken in Brazil Guerra et al. The theoretical and physiological basis underlying the implementation of an internal water deficit to concentrate coffee blossoming seem, at a first glance, simple as described below: i when flower buds have passed the dormancy or quiescent period and have reached the ripe-to-flower stage, they become sensitive to the stimulus for regrowth, often provided by the so-called blossom showers or by treatments simulating rainfall after a dry period Barros et al.
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This means that branch nodes of coffee trees subjected to controlled water deficit will show, after resuming irrigation, a higher percentage of opened flowers compared to those of continuously irrigated plants. It should be stressed that secondary and other minor blossomings may also occur possibly because buds had not reached the critical ready-to-open stage during the main blossoming Schuch et al. Unfortunately, implementation of an adequate, controlled water deficit under farm conditions is a difficult task. The establishment of the timing of water deficit imposition is one of the most controversial aspects concerning blossoming concentration in Brazil.
The moment when watering should be suspended until the trees reach a threshold water potential of approximately Of course, fixing a calendar time to suspend and resume irrigation, as has been recommended for the Brazilian savannahs Cerrado Guerra et al.
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Although this proposed procedure makes irrigation management easy for growers, it is well known that even for coffee-producing regions showing an absolute dry season, several factors soil characteristics, mean air temperature and temperature drops, relative humidity, leaf area index, planting spacing and orientation, plant age and crown architecture, cultivar will affect the rate of water deficit progress and hence the time required to reach an adequate water deficit.
Probably, the developmental stage of flower buds, which can be circumstantially affected by endogenous and environmental factors, seems to be the most suitable parameter to be considered when irrigation must be resumed, perhaps more so than water deficit severity per se, for successful blossom concentration Rena et al. Although there are several practical advantages associated with blossoming concentration, the coffee tree does not seem to have evolved in this direction.
For most coffee cultivars, even in unshaded plantations in non-equatorial regions, up to four blossoming periods are commonly observed under field conditions Rena and Barros, Hence, the development of all coffee fruits within a single tree is temporally fractionated over several sequential but not simultaneous growth periods.
Moreover, fruits within a particular blossoming exhibit different growth rates Barros et al. This assures that coffee beans seed endosperm , which act as priority sinks for assimilates and minerals Cannell, , will be filled in an unsynchronized way, so reducing exhaustion of coffee tree reserves. In fact, this may explain the performance of the cv. Fruiting: While arabica coffee is self-compatible, most, if not all other coffee species are self-sterile Mendes, Raw and Free observed nonetheless little effect on the initial fruit set in arabica coffee bushes caged with honey bee colonies, though the yield of mature berries increased by a half.
These results are suggestive of a pollen grain population effect, as a large number of pollen grains germinate on the stigma and usually several pollen tubes grow within the style Mendes, It is thus conceivable that fertilisation and initial fruit set are not affected by the degree of pollination, but further retention of the fruits has some relation with the number of germinated pollen grains. Flowers in arabica coffee open in the first hours of morning and pollination is known to occur in the forenoon Alvim, , which may explain the adverse effect of rain in the morning Awatramani and Satyanarayana, The low fruit set found by Nacif was probably the result of a heavy crop load occurring in the previous year.
Several factors affect fruit set in coffee including both leaf Rao and Setly, ; Phillips, and flower Raju et al. Apart from any effect of floral atrophy, fruits will not develop if a viable embryo sac is not formed, pollination does not occur or, after pollination, if the normal process of fertilisation is affected in any way Huxley and Ismail, Fruit set is also affected by environmental factors such as heavy rains both during flower expansion Huxley and Ismail, and at anthesis Awatramani and Satyanarayana, , mineral nutrition Meza, ; Reis and Arruda, , and sudden temperature drops Meza, In addition to varying with species and cultivars Srinivasan, , fruit set also depends on the flower position on the plant Reis and Arruda, : the higher the branch position the greater the percentage of fruit set.
Five developmental stages for coffee fruit have been recognised Cannell, ; Barros et al. Fruits at this stage cannot be regarded as dormant, since they have a high respiration rate. Growth of the pericarp and seeds is mostly by cell division instead of by cell expansion.
The expansion of the integument sets the maximum size of the bean. Cell expansion predominates by the end of this stage. Dry matter is deposited mainly in the beans seeds , which reach their final dry mass when the fruit is still green. Maturity of the beans becomes complete when not only their maximum dry matter content is reached, but maximum germination capacity as well. Ripening may spread over a period of about l0 weeks, from the 24th to the 34th week from blossoming.
It must be added that while the whole fruit may still accumulate dry mass if it remains attached for a longer time to the mother plant, the seed may lose dry mass once matured. Loss of seed dry mass may be due to interruption of the translocation of photoassimilates from the fruit to the seed, seed deterioration and substrate consumption by respiration. In fact, respiration of the pulp increases during ripening, as does markedly the sugar content Eira et al.
Three well defined periods of fruit drop have been described in arabica coffee see Barros et al. Fruit drop takes place mostly in the first three months after blossoming, however. The first wave of fruit drop results from fertilisation failure and seems to be unavoidable.
Pinhead drop seems to be unrelated to the level of fruit set and therefore to insufficient assimilate supply. Severe defoliation can cause some shedding, especially of younger fruits, but later on fruit set appears to be highly unrelated to defoliation. The second wave appears to be linked to the beginning of endosperm formation, which has been associated, at least partially, with low carbohydrate supply and water deficit. The third period of fruit loss seems less important and more erratic, and probably results from competition, since it is affected by leaf and shoot diseases.
In any case, the growth pattern may vary with a number of factors including environmental conditions, characteristics used to measure fruit growth e. For example, within C. However, a sigmoidal type curve for the rise in fresh mass has also been recorded in fruits of robusta coffee Dancer, ; Oyebade, For conilon, the increase in fruit dry mass followed a sigmoidal pattern in irrigated trees, and a bi-sigmoidal pattern in unirrigated individuals Silveira, Nevertheless, appropriate statistical tools must be used to accurately and precisely decide about the models that best fit fruit growth; unfortunately in almost all the above cases such an approach was seldom considered.
In any case, it seems that fruits of conilon coffee gain mass on both a fresh and a dry basis which follows a bi-sigmoidal pattern Ronchi et al. Water shortage, particularly during the rapid fruit expansion stage a critical period , often reduces the growth of the berries Dancer, ; Cannell, b, ; Miguel et al.
In fact, fruits that expand during the wet weather become larger, with larger locules, which are subsequently filled with larger beans than fruits which expand during the hot, dry weather Cannell, The rains during the season are a key ecological factor in determining the interval between flowering and seed maturation.
In many Coffea species adapted to dry regions this interval is very short, only about three months for some species from eastern Africa such as C.
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For most coffee species, the interval between flowering and complete fruit ripening is about eight to 12 months. For conilon trees, such an interval is also highly dependent on the clone studied, varying from 36 Ronchi and DaMatta, to 55 Felmer, weeks. This greatly facilitates harvesting management. Furthermore, the rate of fruit development is also strongly affected by air temperature.
Fruiting ripening and cup quality: In addition to genetic background Carvalho, and harvesting and post-harvesting procedures Clarke, ; Vincent, , production of coffee berries with superior beverage quality appears to be highly dependent on the climate conditions Guyot et al. The search for good quality beverage has spread the cultivation of coffee to higher altitudes, as observed in southeastern Brazil, and in countries such as Costa Rica, Guatemala and Honduras, where beans are graded by site elevation. The slowed-down ripening process of coffee berries at higher elevations lower air temperatures , or under shading, allows more time for complete bean filling Vaast et al.
The slower maturation process should therefore play a central role in determining high cup quality, possibly by guaranteeing the full manifestation of all biochemical steps required for the development of the beverage quality Silva et al. Indeed, elevation, but not soil water availability Silva et al. Besides the beneficial effect of longer duration of the bean-filling period, a larger leaf area-to-fruit ratio better bean-filling capacity may also be linked to superior cup quality Vaast et al.
Although Ethephon hastens ripening of the pulp, it does not seem to affect the development of the bean, the marketable part of the crop.
As a consequence, poor beverage quality is obtained if beans have not reached full development at the time of Ethephon spray. Whatever the case, undesirable effects of Ethephon, such as leaf and fruit fall, have also been observed Clowes, b; Gopal, ; Opile, ; Oyebade, ; Winston et al. Rapid vegetative growth and fruit development appear to occur at different times, suggesting incompatibility or competition between the two processes.
Climatic factors may modulate the vegetative growth and fruit production in such way that usually they do not coincide Maestri and Barros, ; Barros et al. In its native lands, and also in most non-equatorial regions, coffee flower and fruit development are phased to maximise the likelihood that the fruits will expand during the rainy period and after a flush of new leaves Cannell, This would allow the development of an adequate leaf area to support the subsequent fruit expansion. However, particularly in unshaded plantations the coffee tree tends to flower heavily, thus producing a high crop load without a concomitant balance in leaf area formation.
In fact, coffee berries act as priority sinks so that dry matter allocation to them may be more than four times that allocated to branch growth over the annual production cycle Vaast et al. Therefore, reduced shoot growth and high branch die-back see below are commonly observed. This response has been traditionally associated with carbohydrate deficiency Cannell, , and references therein , although in more recent investigations no consistent pattern between shoot growth depression and exhaustion of stored carbohydrate was observed Carvalho et al.
Recently, Costa et al. They also showed that leaf rust Hemileia vastatrix increased with increasing fruit load, which certainly leads to extensive defoliation, particularly following harvesting. Fruits, in addition to inhibiting the outgrowth of branch buds, may also restrict the supply of assimilates to the roots. In a year of high fruit burden 12, kg dry beans ha -1 , dry matter of the root system five-year-old plants dropped from 3.
Root growth recovered afterwards reaching 2. These results indicate that heavy crops may dramatically jeopardise the function of the root system, which ultimately could exacerbate the occurrence of die-back and tree degeneracy. Die-back or descending branch death is a phenomenon of a complex nature; it refers to the death of twigs starting from the apex and progressing downwards. Usually, leaves turn prematurely yellow and fall, leading to extensive defoliation of the trees. The affected branches dry out and are ultimately shed. The syndrome has been registered in practically all coffee growing countries, resulting in severe loss of both yield and quality of coffee Clowes, Although the descending death of plagiotropic branches has been often associated with pathogens like Colletotrichum , Phoma and other microorganisms Thorold, ; Chokkanna, , a growing body of evidence suggests that the pathological infections are merely consequences of the debility of the tissues rather than its primary cause.
In fact, no pathogen was found in tissues exhibiting the first signs of degeneracy, and attempts to reproduce the dieback symptoms through the inoculation of the pathogens in healthy branches proved unsuccessful Barros et al. The occurrence of die-back has been associated with environmental stresses such as soil and atmospheric water deficits, high temperatures, high insolation or to the combined effects of these stresses Barros et al.