Light quality management in fruit Orchards: Physiological and technological aspects

Abstract

Light quality (sunlight spectrum) management promises to provide a new technological alternative to sustainable production in horticultural crops. However, little information exists about physiological and technological aspects on light quality management in fruit crops. Sunlight composition changes widely in orchard canopies, inducing different plant responses in fruit trees mediated by phytochrome (PHY) and cryptochrome (CRY) activity. High proportion of far-red (FR) in relation to red (R) light increases shoot elongation, while blue (B) light induces shoot dwarfng. Red and ultraviolet (UV) light increases fruit skin anthocyanin synthesis, while FR light shows a negative effect. Red and B light can also alter leaf morpho-physiological traits in fruit trees, such palisade thickness, stomatal aperture, and chlorophyll content. Besides improvement of photosynthetically active radiation (PAR) availability, the use of refective flms improves UV and R light proportion, with positive effects on PHY mediated-responses (fruit color, fruit weight, shoot growth), as reported in apple (Malus domestica Borkh.), peach (Prunus persica [L.] Batsch), and sweet cherry (Prunus avium [L.] L.). Colored nets widely alter spectral light composition with effects on plant growth, yield, and quality in apple, kiwifruit (Actinidia deliciosa [A. Chev.] C.F. Liang & A.R. Ferguson), peach, and blueberry (Vaccinium corymbosum L.) orchards. Mechanisms of colored nets seem to be associated to photosynthetic and morphogenetic process regulated by PAR availability, R/B light proportion, and CRY activity. Alteration of light quality affects signifcantly fruit tree plant responses and could be a useful tool for sustainable (e.g. lower use of chemicals and labor-practices) management of yield and quality in modern orchards.

Full text

575574 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012
LIGHT QUALITY MANAGEMENT IN FRUIT ORCHARDS: PHYSIOLOGICAL
AND TECHNOLOGICAL ASPECTS
Richard M. Bastías1, 2*, and Luca Corelli-Grappadelli1
Light quality (sunlight spectrum) management promises to provide a new technological alternative to sustainable production
in horticultural crops. However, little information exists about physiological and technological aspects on light quality
management in fruit crops. Sunlight composition changes widely in orchard canopies, inducing different plant responses in
fruit trees mediated by phytochrome (PHY) and cryptochrome (CRY) activity. High proportion of far-red (FR) in relation
to red (R) light increases shoot elongation, while blue (B) light induces shoot dwarng. Red and ultraviolet (UV) light
increases fruit skin anthocyanin synthesis, while FR light shows a negative effect. Red and B light can also alter leaf
morpho-physiological traits in fruit trees, such palisade thickness, stomatal aperture, and chlorophyll content. Besides
improvement of photosynthetically active radiation (PAR) availability, the use of reective lms improves UV and R
light proportion, with positive effects on PHY mediated-responses (fruit color, fruit weight, shoot growth), as reported in
apple (Malus domestica Borkh.), peach (Prunus persica [L.] Batsch), and sweet cherry (Prunus avium [L.] L.). Colored
nets widely alter spectral light composition with effects on plant growth, yield, and quality in apple, kiwifruit (Actinidia
deliciosa [A. Chev.] C.F. Liang & A.R. Ferguson), peach, and blueberry (Vaccinium corymbosum L.) orchards. Mechanisms
of colored nets seem to be associated to photosynthetic and morphogenetic process regulated by PAR availability, R/B light
proportion, and CRY activity. Alteration of light quality affects signicantly fruit tree plant responses and could be a useful
tool for sustainable (e.g. lower use of chemicals and labor-practices) management of yield and quality in modern orchards.
Key words: Red, far-red and blue light, phytochrome, cryptochrome, photo-morphogenesis, reective lms, colored nets.
1Università di Bologna, Dipartimento di Colture Arboree, Viale
Fanin 46, Bologna, Italy.
2Universidad de Concepción, Facultad de Agronomía, Av. Vicente
Méndez 595, Chillán, Chile.
*Corresponding author (ribastias@udec.cl).
Received: 14 February 2012.
Accepted: 5 July 2012.
he sunlight use efciency (i.e. converting light
energy to dry matter) has long been the main research
focus to obtain sustainable fruit production and quality
in orchard systems. In the recent years, however, more
technological innovation are required for adequate light
management in fruit trees, due to changes of paradigm of
efciency in orchard systems, which must include other
factors, such as climate change, energy cost, and need of
reduction of environmental impact (Palmer, 2011; Blanke,
2011). Optimizing of sunlight use has been achieved
in orchard systems thanks to research development in
cultural practices such as pruning, training system, tree
arrangement, and orchard design, directed toward the
improvement of “quantity of light” (i.e. the amount of
photosynthetically active radiation, PAR) intercepted
and distributed by orchards (Jackson, 1980; Palmer,
1989; Bastías and Widmer, 2002; Corelli-Grappadelli,
2003; Corelli-Grappadelli and Lakso, 2007). However,
alongside the PAR quantity that provide the energy
REVIEW
T
and carbon needed for sustained tree and fruit growth,
plant growth and development also respond to subtle
changes in the light quality (i.e. spectral composition of
sunlight), processes regulated by specic pigment-based
photoreceptors, including red (R) and far-red (FR) light
absorbing phytochromes (PHY) and ultraviolet (UV)
and blue (B) light absorbing cryptochromes (CRY) and
phototropins (PHO) (Fankhauser and Chory, 1997;
Kasperbahuer, 2000; Smith, 2000; Lin, 2002). More
signicant advances in light quality management have
been achieved in vitro plant culture and greenhouse
systems by using supplemental lighting sources (e.g.
light emitting diodes, LEDs), colored soil mulches and
photo-selective lters to manipulate the plant growth,
yield and quality (Muleo et al., 2001; Oren-Shamir
et al., 2001; Hemming, 2011). Nevertheless, due to
the difculty of conditioning the light environment of
orchards, the management of light quality has been much
less developed in fruit trees grown under eld conditions,
consequently more studied have been developed under
controlled conditions (Erez and Kadman-Zahavi, 1972;
Baraldi et al., 1994; 1998; Rapparini et al., 1999). Since in
recent years, manipulation of plant responses by changes
in the light quality composition promises to provide new
technological alternatives for sustainable manipulation of
growth, yield, and quality of harvest in agricultural and

575574 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012
horticultural crops (Devlin et al., 2007; Rajapakse and
Shahak, 2007), the purpose of this article was to review
the current status on light quality management in fruit trees
under eld conditions, with emphasis in physiological
and technological aspects and its potential application for
manipulation of plant growth, productivity, and quality in
orchard systems.
Light quality relations in orchards
Light quality composition. Sunlight reaching the earth
surface changes its spectral and energetic prole in
part due to the normal climate variability and, in recent
years, because of man-induced causes, such as the loss
of stratospheric ozone that affects UV light absorption,
or atmospheric pollutants and CO2 levels that affects
infrared (IR) light absorption. In general the light spectra
that concerns plant physiologists is between 280 and 800
nm, which includes UV-B (280-320 nm), UV-A/B (300-
400 nm), PAR (400-700 nm), and FR (700-800 nm). The
PAR radiation is subdivided into various bands and the
most important for plant physiological processes are B
(400-500 nm), green (G, 500-600 nm) and R (600-700
nm) light (Nobel, 1983; Grant, 1997; Combes et al.,
2000; Corelli-Grappadelli, 2003). In fruit orchards, the
spectral distribution of solar radiation changes widely
as the light penetrates and scatters within the tree
canopy due to the structure and optical properties of the
canopy components, such as leaves, fruits, and branches
(Palmer, 1977; Baldini et al., 1997). In general, the light
environment inside the tree canopy is made up by two
components: the unltered solar radiation (direct and
diffuse) that has passed through gaps in the vegetation,
and the ltered radiation that has been attenuated by the
optical properties of reectance and transmittance of
the leaves, which have a crucial importance in the light
spectrum modication in fruit trees (Grant, 1997; Baldini
et al., 1997).
In walnut (Juglans regia L.) leaves, values of leaf
reectance and transmittance in the FR spectrum are
estimated to be near 50% and in the G spectrum around
20% for both optical properties (Combes et al., 2000),
while in apple (Malus domestica Borkh.) the reectance
and transmittance values in the G spectrum are 10% and
4%, respectively and in the FR spectrum are near 50%
and 30% (Palmer, 1977). Awad et al. (2001) demonstrated
that under sunny conditions, the inner position of apple
tree canopy reduced 40-48% the UV, B, and G light
proportion, while R light was reduced in 58% and FR
light increased in 33%, which affects markedly the R/FR
ratio. Thus, R/FR ratio reached values of 1.6 at different
outside positions of the tree canopy, but near 0.5 in the
inner canopy (Table 1).
Similarly, in peach tree (Prunus persica [L.] Batsch)
canopies the R/FR ratio decreased with height of the tree
and this effect was more marked with time, until full
canopy development. Early in the season the R/FR values
in the top and bottom of the tree canopy were around 1.1
in both parts, while later, near fruit harvest, they reached
values of 0.5 at the top of canopy and 0.3 at bottom,
almost a 50% of difference (Baraldi et al., 1994).
The role of photoreceptors. The reduction of the R/FR
ratio in the inner regions of the tree canopy may produce
different morphological and physiological responses
mediated by the photoreceptors called phytochromes
(PHY) that are responsible for R and FR light signal
transduction (Fankhauser and Chory, 1997; Smith,
2000; Devlin et al., 2007). Phytochrome possesses the
capacity of detecting wavelengths from 300 to 800 nm
with maximum sensitivity in the R (600-700 nm) and
FR (700-800 nm) wavelengths. Phytochrome activity
can be changing continuously through the two inter-
convertible states that naturally occur: R absorbing (Pr)
and FR absorbing (Pfr) forms, which absorb maximally
near 660 and 730 nm, respectively (Sager et al., 1988;
Rajapakse and Kelly, 1994; Smith, 2000). Because the
inner tree canopy has light rich in FR photons (Palmer,
1977; Baraldi et al., 1994; Combes et al., 2000; Awad
et al., 2001), the majority of the PHY pool is converted
to the inactive Pr form, with loss of the active Pfr form.
To estimate the PHY pool mediated responses, the R/
FR ratio has been commonly used. However, most
plant physiologists consider that the R/FR ratio does
not accurately explain PHY-mediated plant responses
and therefore mathematical models using spectral
light information have been proposed to estimate the
PHY photoequilibrium (Φc): the equilibrium state of
biologically active Pfr form in relation to total PHY
(Pfr/Ptotal) (Sager et al., 1988; Rajapakse and Kelly,
1994; Kasperbahuer, 2000; Smith, 2000). Different
reports demonstrate that Φc provides a better indicator
of expected photomorphogenic responses to a specic
spectral light quality in orchard canopies (Baraldi et al.,
1994; 1998; Rapparini et al., 1999; Combes et al., 2000).
In walnut orchards, the curve that relates the R/FR ratio
with Φc have shown a hyperbolic relationship between
both components from the top to the inner canopy, with
marked variations of R/FR ratio (from 0.3-1.2) and less
important variations in Φc (from 0.35-0.68), thus Φc
is especially sensitive to R/FR changes in the range of
0.2-0.7 (shade conditions), but insensitive indeed to R/
Top 5.6 7.9 16.3 18.7 11.6 1.6
2.9 4.1 9.5 7.9 15.4 0.5
Inner (-48%) (-48%) (-41%) (-58%) (+33%) (-68%)
Outer east 5.2 7.4 16.0 19.0 11.7 1.6
Outer west 5.9 8.0 15.9 17.8 11.4 1.6
F-test *** *** ** *** *** ***
Adapted from Awad et al., 2001; **p < 0.01; ***p < 0.001.
UV Blue Green Red
Table 1. Spectral composition of the sunlight at different canopy positions
in apple orchards.
Spectral composition (% of total available light)
Position
of tree
R/FR
ratio
Far-red

577576 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012
FR above about 1.0 (Combes et al., 2000). Although
PHY detects not only R and FR but also B and UV light,
current research indicates the presence in the most plants
of specic photoreceptors for the B and UV regions,
denominated crypthocromes (CRY) and phototropins
(PHO) (Lin, 2002; Devlin et al., 2007). In peach trees,
it has been shown that beside the effect of PHY on plant
growth, the CRY is also involved either independently
or in conjunction with PHY (Erez and Kadman-Zahavi,
1972; Baraldi et al., 1998; Rapparini et al., 1999).
Plant responses to light quality in fruit trees
Growth and development. Under high relative
proportions of FR light the Φc is shifted toward the inactive
Pr form. In these conditions, fruit trees exhibit different
morphological changes, probably associated to “shade-
avoidance” strategies evoked by decreasing Pfr form,
such as shoot elongation, increased apical dominance and
reduced leaf thickness (Baraldi et al., 1994; Combes et
al., 2000). Indeed for many trees the elongation rate of the
shoots has an inverse relationship with the Φc (Pfr/Ptotal)
(Gilbert et al., 2001). In a classic study, Erez and Kadman-
Zahavi (1972) demonstrated that apical growth activity of
peach plants was strongly affected by changes in the Φc
in Pfr form, but also demonstrated that B light are quite
important role in these responses. These observations
were conrmed more later, when, still in peach, was
demonstrated that prolonged irradiation with B photons
induced an inhibitory effect on shoot elongation, and the
morphological responses to B light were widely modied
and enhanced the inhibitory effect on stem elongation
under lower level of Φc, providing the evidence of the
interaction of PHY and CRY in the regulation of shoot
growth in fruit trees (Baraldi et al., 1998; Rapparini et
al., 1999).
The role of light quality conditions, specically
R and FR light, on growth partitioning among fruit
and shoots has been also suggested. In horticultural
crops, long-term FR light exposure initiates events that
result in more carbohydrates being partitioned to stems
and less to leaves and roots as compared to plants that
received R light, affecting the allocation to developing
fruits (Kasperbahuer, 2000; Glenn and Puterka, 2007).
In apple trees, have been underlined the essential role
of light quantity on carbohydrate partitioning patterns
(Tustin et al., 1992; Corelli-Grappadelli et al., 1994;
Corelli-Grappadelli, 2003), but the effects of light quality
conditions in these patterns are not totally studied in fruit
trees.
Dormancy. Different physiological studies indicate that
perception of photoperiod is related to levels of PHY,
which apparently interact with biosynthesis of plant
hormones during control of dormancy-related processes
in fruit trees (Olsen, 2006). However, the role of PHY
and photoperiod on dormancy release has not been totally
understood in fruit trees. In general, it has been postulated
that in a short day FR light is dominant, decreasing the
bud meristematic activity, while in a long day, R light is
dominant and has the opposite effect (Erez and Kadman-
Zahavi, 1972). Previous reports in peach demonstrated that
limitation of illumination affected bursting of vegetative
buds when it occurred shortly before sprouting. In general
R light is more active on bud break and its effects on buds
are reversed by a subsequent FR illumination (Erez et al.,
1968). Baraldi et al. (1994) proposed in apple and peach
that ower bud differentiation can be modulated by R/
FR ratio. However, the spectral light composition has no
effect on ower bud burst or ower bud differentiation, as
was demonstrated by Erez et al. (1966) and Baraldi et al.
(1998). Probably the relationship between PHY system,
photoperiod and dormancy depends also on genetic
factors. For example, photoperiod has no effect on growth
cessation and dormancy induction in apple and pear,
but a partial effect in Prunus species, such as peach and
sweet cherry (Prunus avium [L.] L.), where a pronounced
interaction of photoperiod and temperature exists on the
regulation of growth cessation (Heide and Prestrud, 2005;
Heide, 2008).
Leaf morphology and function. Many authors have
shown the close relationship between orchard light
conditions and morphological and physiological traits.
Thus, in fruit species such as peach (Nii and Kuroiwa,
1988), olive (Olea europaea L.) (Gregoriou et al., 2007),
and apple (Tustin et al., 1992; Corelli-Grappadelli et
al., 1994); sun leaves presented more leaf mass per
area ratio, stoma density and palisade cell thickness
compared to shade leaves. Although anatomical
differences of sun and shade leaves can be attributed to
light intensity changes, the role of light quality has been
also postulated (Kim et al., 2005). Examination of peach
leaf expansion showed that the combination of B + FR
light reduced signicantly leaf area and the thickness
of top and mesophyll palisade layers compared to R +
FR light combination. In addition, leaves exposed to R
+ FR light presented greater thickness of the palisade
mesophyll (Table 2) (Baraldi et al., 1998).
The Φc values demonstrated that, opposite to the
argument that indicates that low Φc generally increases
leaf expansion, in this case leaf expansion was reduced
cm2 %
Transparent 0.57 31.3a 28.8a 67.0a 61b
R/FR 0.49 33.2a 23.5b 46.2b 59b
BL/FR 0.13 24.3b 20.9c 38.5c 67a
Neutral 0.57 33.9a 20.5c 34.0d 67a
Adapted from Baraldi et al., 1998; Φc: phytochrome photoequilibrium.
Table 2. Effect of different light spectrum conditions on leaf peach
morphology.
Thickness (µm)
Light
treatment
Spongy
intercellular
spaces
Calculated
Φc
Leaf
area
Top layer
palisade
Palisade
mesophyll

577576 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012
under lower Φc (Table 2). This behavior was conrmed
in further experiments, concluding that probably the
inhibitory effects of B + FR light on leaf expansion and
thickness are controlled by a specic CRY independent of
the PHY system (Rapparini et al., 1999). Changes in leaf
chlorophyll content were also detected under different
light quality conditions in citrus trees: plants under
nets with more B light proportion had the greatest leaf
chlorophyll a, b and total chlorophyll content, compared
to those with more R light proportion (Li and Syvertsen,
2006). In apple trees, leaf chlorophyll synthesis under
nets with more R and G light transmission was up to
46% highest (Solomakhin and Blanke, 2008). Recent
studies demonstrated prolonged exposition of apple
leaves under nets with more light transmission in the B
spectra increased the leaf stomatal conductance and leaf
transpiration (Bastías et al., 2011), probably by direct
effect of B light on stimulation of stomatal opening has
been previously reported (Farquhar and Sharkey, 1982;
Shimazaki et al., 2007).
Fruit color development. Fruit skin color depends
on the concentration of various pigments, such as
anthocyanins, chlorophylls, and carotenoids, but red
color is due to anthocyanin pigments, mainly cyanidin
3-galactoside (Ju et al., 1999; Awad et al., 2001;
Layne, 2001). Anthocyanin biosynthesis is another
important light-depending process and has been widely
used as a model to study the effect of light quality in
vegetative tissues, while its formation is controlled by
a high-energy photoreaction and has a photo-protective
function to excess light (Mancinelli, 1985; Arakawa et
al., 1985; Arakawa, 1988; Steyn et al., 2002). Different
experiments demonstrated that simultaneous irradiation
with white and UV-B light stimulated anthocyanin
production synergistically in apple fruits. Although the
effectiveness of R light was lower than that of UV-B, it
produces a synergistic effect when given simultaneously
with UV-B. Furthermore, long-term treatment with R and
FR light showed a signicant R-FR reversible response
of photo-regulation of anthocyanin synthesis in apple
skin, indicating a possible role of PHY system and that
FR light could possibly even inhibit color development.
This was conrmed under eld conditions, where at low
light levels and above a critical FR/R ratio (~ 1), there
was no anthocyanin formation in apple fruits (Arakawa
et al., 1985; Arakawa, 1988; Awad et al., 2001).
Manipulation of light quality in orchard systems
Light reection management. The use of reective
ground cover materials such as white woven plastics and
aluminum foil is a good approach for improvement the
light use in orchard systems (Ju et al., 1999; Widmer et al.,
2001; Layne, 2001; Whiting et al., 2008), while have also
become tested with other reective material such as straw,
lime, and biodegradable white paint in organic orchards
(Blanke, 2007). Cover orchard oor with reective
materials produces important effects on improving of fruit
color, fruit size, and return bloom in apple orchard (Ju et
al., 1999; Widmer et al., 2001; Blanke, 2011), as well on
better fruit rmness, sugar content, advanced in maturity
and source:sink relationships in peach and sweet cherry
(Layne, 2001; Whiting et al., 2008).
The main effect of reective lm is the increases
of PAR reection by reecting light incoming to oor
back into the tree canopy, improving widely the light
availability to shading parts of the tree canopy (Widmer
et al., 2001), as well helping to overcome the light
deciency generated in protected fruit orchards under
hail nets or under shade nets (Blanke, 2011). In orchard
with traditional grass ground cover, the PAR reected is
almost 5-10%, while with reective ground covers PAR
reection incoming reached up to 30-40% (Widmer
et al., 2001; Layne, 2001; Glenn and Puterka, 2007;
Blanke, 2007; Figure 1). Although, positive effects
of reective lms on fruit quality and productivity
are attributed to improving the PAR use for net C
assimilation (Whiting et al., 2008), the role of light
quality conditions have been also proposed (Ju et al.,
1999; Layne, 2001). It was demonstrated that reective
lms increases signicantly the UV light component
of sunlight. Indeed different reports have shown that
reection of UV light by reective lms was up to
80% of light incoming to orchard oor (Ju et al., 1999;
Blanke, 2007; Figure 1).
A greater UV light reection was associated
with increased of UDP-galactose:avonoid-3-o-
glucosyltransferase (UFGalT), the most important
enzyme in the anthocyanin synthesis pathway, but
changes in carbohydrate assimilation were not observed
(Ju et al., 1999). Reective lms also increases R light
component to inner parts of canopy, which affects
largely the R/FR ratio (Figures 1). Data taken from
different reports have shown that R/FR calculated in
apple and peach orchards with reective ground lms
was up two fold greater than grass (Layne, 2001; Glenn
and Puterka, 2007). The combined effect of reective
Figure 1. Quantitative values of photosynthetically active radiation (PAR),
ultraviolet (UV) and red/far-red (R/FR) light proportion in fruit orchards
with grass (A) and reective ground covers (B) (data taken from Ju et al.,
1999; Widmer et al., 2001; Layne, 2001; Glenn and Puterka, 2007; and
Blanke, 2007).

579578 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012
lms on increases of UV and R light proportion should
be stimulating by synergistic effect the anthocyanin
synthesis (Arakawa et al., 1985; Arakawa, 1988) and
can explain the better color development in fruits grown
with reective lms (Layne, 2001; Widmer et al., 2001;
Blanke, 2007), whereas the large R/FR ratio can explain
the enhanced the fruit weight, associated probably
to the PHY mediated process affecting the dry matter
partitioning to developing fruit (Glenn and Puterka,
2007).
Light spectrum management. Recently a new approach
has been developed for manipulation of light quality in
orchard systems, based on plastic photo-selective colored
nets with special optical properties (Shahak et al., 2004).
Depending on type of color, photo-selective nets alter
widely the spectral light composition (Figure 2). In
general white and/or black nets are wavelength neutral and
reduced by the same amount full sunlight over the entire
range. In contrast, the red and blue nets altered widely
the spectral light distribution. Red net increased the light
transmission in R and FR spectra (600-800 nm), while the
blue net enhanced the proportion of B light (400-500 nm)
and reduced the R light proportion (600-700 nm) (Oren-
Shamir et al., 2001; Shahak et al., 2004; Solomakhin and
Blanke, 2008; Bastías et al., 2011; Lobos et al., 2012).
Horticultural effects of colored nets have been recently
evaluated in fruit orchards. In apple orchards, red net
improved fruit size compared to black net (Shahak et
al., 2008). Solomakhin and Blanke (2008) also reported
increased apple fruit size under colored nets, but without
effect on yield. In peach, fruit grown under red nets were
rmer, sweeter and fruit size was also improved (Shahak
et al., 2008), while in highbush blueberries (Vaccinium
corymbosum L.), red and white nets increased the number
of fruits and yield per plant in comparison with traditional
black net (Retamales et al., 2008; Lobos et al., 2012).
Although the use of colored nets is already taking hold
among fruit growers, physiological mechanisms involved
in this technology are still not totally understood. Possible
explanations have been attributed to the effect of light
conditions on leaf gas exchange process (Shahak et al.,
2004). The most important effect of colored nets is on
reduction of PAR availability. Moderate shading, as was
demonstrated in citrus and apple trees, would reduce plant
radiation, heat and water stress, increase gas exchange
and availability of carbohydrates for fruit and tree growth
(Jifon and Syvertsen, 2003; Corelli-Grappadelli and
Lakso, 2007).
The question is: Why does color of nets affect
differentially vegetative and fruit growth? Colored nets
altered gas exchange and morphological aspects in
blueberries, but the effect was more linked to reduction
of radiation load (PAR quantity), while light quality
conditions under colored nets had a weaker effect on leaf
gas exchange and morphological characteristics (Lobos et
al., 2012). However, changes in leaf chlorophyll content
were detected by effect of spectral light composition
under colored nets in citrus trees: plants under blue nets
had the greatest leaf chlorophyll a, b, and total chlorophyll
content, whereas leaves under red nets had the lowest (Li
and Syvertsen, 2006). Solomakhin and Blanke (2008)
also demonstrated that apple leaf chlorophyll synthesis
under red and green nets was increased, but this did not
affect leaf photosynthesis capacity.
Later, also in apple, was demonstrated that irrespective
of PAR intensity, blue net was more effective than red net
to increase leaf net CO2 assimilation and transpiration
(Bastías et al., 2011). From the photo-morphogenetic point
of view, the PHY and CRY action could be also involved
(Rajapakse and Shahak, 2007). Solomakhin and Blanke
(2008) underlined the possible role PHY on vegetative
growth and development of apple trees grown under
colored nets, but the R/FR ratio (principal component
of PHY activity) does not change widely among colored
nets. More clear differences have been found in the R/B
ratio among blue and other net colors (Oren-Shamir et al.,
2001; Shahak et al., 2004; Bastías et al., 2011).
In kiwifruit (Actinidia deliciosa [A. Chev.] C.F. Liang
& A.R. Ferguson), blue nets reduced signicantly the
vigor of vines, whereas the red net appeared to stimulate
vigor (Basile et al., 2008), while apple trees grown under
red net presented greater shoot length in comparison to
those grown under full sunlight and neutral white net
(Figure 3). Intensity of PAR and R/FR ratio did not
differ among red and white nets (Figures 3A and 3B);
however, the B/R ratio under red net was 5-10% lower
than white and full sunlight conditions, respectively
(Figures 3C). Since changes in B/R ratio are associated
to CRY photoreceptor regulating shoot dwarng and/or
elongation (Baraldi et al., 1998; Rapparini et al., 1999;
Cummings et al., 2008), management of B and R light
proportions by colored nets could be an interesting tool
to manipulate the vegetative growth and development in
fruit orchards.
Figure 2. Spectral irradiance (visible plus near-infrared) pattern of full
sunlight and different colored nets (Adapted from Bastías et al., 2011).

579578 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012
CONCLUSIONS
Orchard canopies present marked changes on light
quality conditions and mainly in the R/FR ratio and PHY
mediated plant responses.
Shoot growth and fruit color development are the most
clearly plant response regulated by light quality conditions
in fruit trees. Changes in the proportion in B, R, and FR
light alter the pattern of shoot growth and anthocyanin
synthesis, mediated by the interaction of PHY and CRY
photoreceptors. However, the effect of light quality on
leaf morphological and functional characteristics should
be studied with more attention in further research.
Light quality manipulation could be achieved by
reective lms and colored nets in orchard systems.
Although the positive effects of this technology are
normally associated to improving the PAR use for net
C assimilation, different reports demonstrated that,
irrespective PAR availability, reective lms and colored
nets alter widely the light quality composition in the UV,
B, and R light with ensuing effects on PHY and CRY
plant mediated responses such as shoot growth, color
development, and fruit growth.
On summary, alteration of light quality makes signicant
differences in fruit trees and could be a useful tool for
sustainable (e.g. lower use of chemicals and labor-practices)
manipulation of yield and quality in orchards. Since novel
technologies such as reective lms and colored nets, which
are already taking hold among fruit growers, alters widely the
light quality conditions; more research and knowledge will
be necessary in the future about interactions of plant and light
quality under orchard systems.
ACKNOWLEDGEMENTS
We thank to colleagues from the Department of Fruit Tree
and Woody Plant Science (University of Bologna) and
the National Research Council (CNR, Bologna, Italy),
including Drs. Pasquale Losciale, Federica Rossi and
Osvaldo Facini for the helpful contributions during the
elaboration of the present manuscript.
Manejo de la calidad de la luz en huertos frutales:
Aspectos siológicos y tecnológicos. El manejo de la
calidad de la luz (espectro de la luz solar) promete proveer
una nueva alternativa tecnológica para la producción
sostenible de cultivos hortícolas. Sin embargo, existe poca
información acerca de aspectos siológicos y tecnológicos
sobre el manejo de la calidad de la luz en cultivos frutales.
La composición de luz solar cambia ampliamente en la
canopia de los huertos, induciendo diferentes respuestas en
la planta mediadas por la actividad del tocromo (PHY) y
criptocromo (CRY). Una alta proporción de luz roja-lejana
(FR) en relación a la roja (R), incrementa la elongación de
brotes, mientras que la luz azul (B) induce un acortamiento
de brotes. La luz R y ultravioleta (UV) incrementan la
síntesis de antocianinas en la piel de los frutos, mientras que
la luz FR muestra un efecto negativo. La luz R y B también
pueden alterar caracteres morfo-siológicos de la hoja en
árboles frutales, tales como grosor de la palizada, apertura
estomática y contenido de clorola. Además de mejorar la
disponibilidad de la luz fotosintéticamente activa (PAR), el
uso de lm reectantes mejora la proporción de luz UV y R,
con efectos positivos sobre respuestas mediadas por el PHY
(color de fruto, peso de fruto y crecimiento de brotes), como
se reportó en manzano (Malus domestica Borkh.), duraznero
(Prunus persica [L.] Batsch) y cerezo (Prunus avium [L.]
L.). Las mallas de color alteran ampliamente la composición
espectral de la luz con efectos sobre el crecimiento de planta,
rendimiento y calidad en huertos de manzano, duraznero,
kiwi (Actinidia deliciosa [A. Chev.] C.F. Liang & A.R.
Ferguson) y arándano (Vaccinium corymbosum L.). Los
mecanismos de las mallas de color parecen estar asociados
a procesos fotosintéticos y morfogenéticos regulados
por la disponibilidad de PAR, la proporción de luz B/R,
y actividad del CRY. La alteración de la calidad de la luz
afecta signicantemente respuestas de la planta en árboles
frutales y podría ser una herramienta útil para el manejo
sostenible (ej. bajo uso de químicos y prácticas laboriosas)
del rendimiento y calidad en huertos modernos.
Palabras clave: luz roja, roja lejana y azul, tocromo,
criptocromo, foto-morfogénesis, lm reectantes, mallas
de color.
Figure 3. Mean shoot length (A); photosynthetic photon ux density, PPFD (B); and red/far-red (R/FR), and blue/red (B/R) light proportions (C); estimated
in ‘Fuji’ apple trees grown under full sunlight and red and white nets (Bastías et al., unpublished data).

581580 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 72(4) OCTOBER-DECEMBER 2012
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