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Influence of Light Availability on Fruit and Oil Characteristics in Olea europea L. P. Proietti1, L. Nasini1, F. Famiani1, P. Guelfi2 and A. Standardi1 1 Dipartimento di Scienze Agrarie e Ambientali, Università degli Studi di Perugia, Italy 2 Agenzia Regionale Umbra per lo Sviluppo e l’Innovazione in Agricoltura, Italy Keywords: light, fruit and oil composition Abstract

The influence of light availability on olive fruit development, oil accumulation and the qualitative characteristics of the oil were studied. The trial was carried out in central Italy, on non-irrigated trees of cultivars ‘Frantoio’ and ‘Leccino’. In October and November, samples of olives grown under conditions of low or high light availability (about 400 and 1100 μmol of photons m-2 s-1) were collected and analysed. Fruit ripening was slightly affected by high availability of light (higher pigmentation and detachment force and lower pulp consistency). Olives grown under well lighted conditions, with respect to those grown at low light intensity, were heavier, had a higher percentage of oil and a lower water content. The pulp/pit ratio was not affected by light intensity. The oils extracted from olives grown under high light conditions had a higher polyphenol content and better sensorial characteristics than those obtained from olives grown at low light intensity. The acidity and peroxide number were not affected by the light conditions. The results highlight the importance of ensuring good, uniform illumination of the entire crown by making optimal choices at the moment of the olive orchard establishment and rationalizing all techniques that affect light availability at the crown level (planting area exposition, training system and spacing, pruning intensity, etc.).

INTRODUCTION

To date, the research, that has been done to determine the effects of shading on olive, has shown that limited light availability reduces floral bud induction, fruit set and growth and oil accumulation of the fruit (Ortega Nieto, 1969; Proietti et al., 1996; Tombesi et al., 1999). Very little information is available about the effect that shading has on the chemical and sensorial characteristics of the oil (Cimato et al., 2001). In addition, the experiments carried out to date often used artificial shading with nets and were limited only to the period of fruit development. These conditions can cause side effects (i.e., reduced transpiration) and differences in the effects related to the period and duration of shading. In addition, the time needed to adapt to the treatment is difficult to estimate. These limitations make it difficult to interpret the results and identify the real effects that natural lightening conditions have on the studied aspects. More knowledge about the effects of natural shading within the canopy on fruit development and oil quantity and quality would be very useful when trying to optimise the choice of the training system, planting distances and pruning. The aim of this study was to evaluate the effects of the availability of different levels of natural light in different portions of the canopy on olive growth and oil accumulation in the fruit and on the main chemical and sensorial characteristics of the oil.

MATERIALS AND METHODS

The trial was carried out in 2006 and 2007, in central Italy, in Deruta (PG) latitude 43° North, in a non-irrigated olive grove (350 m a.s.l.), growing in slightly sloping with a light soil. The 20-year-old trees, cultivars ‘Frantoio’ and ‘Leccino’, were spaced 55 m and trained to the vase system. Ten uniform trees per cultivar having a fruit load at harvest of about 20 kg of olives per tree were selected. In correspondence to the four compass points, for each cultivar 100 fruiting branches (10 per tree) on the external part of the canopy, well exposed to the light, and 100 fruiting branches (10 per tree) in the

Proc. VIth IS on Olive Growing Eds.: E.M. Sampaio and A.C. Pinheiro Acta Hort. 949, ISHS 2012

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internal shaded part of the canopy were selected and labelled. In September, around 11:00 am on a cloudless day, the light intensity was measured in correspondence to the selected fruiting branches using a Licor Quantum/Radiometer/Photometer - 185B; measurements were taken on 100 fruiting branches that were well exposed to light and on 100 fruiting branches located in the shaded portions of the canopy. The sensor for taking the measurements was positioned in the middle part of the branches. At the end of October and November, in both years (2006 and 2007) the following parameters were measured on olive samples from both cultivars (‘Frantoio’ and ‘Leccino’), from well-lighted and shaded branches (8 treatments deriving from the combinations of the considered factors): 1) Detachment force. Fifty olives/treatment were selected at random in correspondence

with the four compass points; a manual dynamometer Carpo, was used to take the measurements.

2) Fresh and dry fruit weight. Samples of 100 olives/treatment were weighed before and after being dried at 95°C, in a ventilated oven, until constant weight.

3) Fruit pigmentation index. 4) Pulp consistency. One hundred drupes/treatment were measured using a hand-held

penetrometer EFFEGI with a 2.0-mm plunger in two opposite positions around the equator of each olive.

5) Oil and water content. The SpectraAlyzer ZEUTEC apparatus was used to carry out the near infra red spectroscopy (NIR, Near Infra Red) measurements.

6) Ratio between the dry weight of the pulp and that of the pit in 20 fruits/treatment. 7) Free acidity, peroxide number, total polyphenol content, fatty acid composition and

chlorophyll content (the latter only in 2007) in the oils extracted from the olives of each treatment, using the Official Methods of Analysis for their determinations.

8) Sensorial characteristics of the olive oils extracted from each treatment. A panel test was conducted according to the EC/Reg. 796/02. The oil used for the

analysis was extracted 1 day after the harvesting of the olive samples (3 samples/ treatment of about 2.5 kg each), using a lab mill and applying the following procedure: crushing with hammers, malaxation for 25 min at room temperature (about 22°C), centrifugation of the mash, without adding water, to separate the oil, filtration of the oil through cotton wool and anhydrous sodium sulphate to eliminate the impurities and residual water. The oils were then stored in dark glass bottles in the fridge (4°C) until used for analysis.

All data, with the only exception of that concerning the fatty acid composition, were statistically analysed by ANOVA and the averages were compared using the Student-Newman-Keuls Test.

RESULTS AND DISCUSSION Light Intensity at Fruit Level

The maximum light availability was, on average, about 1100 µmol of photons m-2

s-1 for the olives on fruiting branches on the external part of the canopy and 400 µmol of photons m-2 s-1 for those on the fruiting branches in the internal (shaded) part of the canopy. No significant differences were recorded between the cultivars. Fruit Ripening Pattern

In October and November of 2006, the olives of the cultivar ‘Leccino’ grown in the well-lighted parts of the canopy had a slightly higher pigmentation and lower pulp consistency than those grown in the shaded portions of the canopy; in 2007, no differences for these parameters were recorded (Table 1). The olives grown in well-lighted parts of the canopy always had a higher detachment force. In October and November of 2006, the olives of the cultivar ‘Frantoio’ grown in the well-lighted parts of the canopy had a lower pulp consistency and a higher detachment force than those grown in the shaded portions of the canopy, whereas no differences in the pigmentation were

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recorded (Table 1). In 2007, no differences were recorded for the considered parameters. In general, the results indicate that the light availability did not affect the

parameters related to fruit ripening (pigmentation, pulp consistency and detachment force) in a constant way. However, even though there were differences related to the cultivar and the year, the high availability of light seems to intensify the olive ripening process (higher pigmentation and lower pulp consistency) and, at the same time, to lengthen the ripening period (higher detachment force). This indicates that olives in well-lighted portions of the canopy can reach a higher ripening level because the ripening process is more intense and lasts for a longer time. The results indicate that the parameters frequently used as ripening indexes, such as pigmentation, pulp consistency and detachment force, evolve in relatively different ways depending on the conditions in which the fruit develops (i.e., less coloured olives can have a lower detachment force than more coloured ones if the latter have developed under good light conditions). This means that to determine the average ripening stage of the fruit, a careful sampling and a specific evaluation of the different indexes must be carried out taking into consideration the above-mentioned effects. Fruit Growth

In both cultivars and years, the dry weight value of fruit grown under good light conditions was higher than that of fruit grown in shaded portions of the canopy; the differences in November were greater than those in October (Table 2). These results are in agreement with data obtained in other studies (Ortega Nieto, 1962; Proietti et al., 1996; Tombesi et al., 1999). Larger fruit that grew in well-lighted parts of the canopy could be the result of the photosynthetic activity of the fruit itself. During the day, part of the CO2 produced by the respiration can be the re-assimilated; moreover, the increased transpiration of the olives growing in good light conditions favours the acquisition of nutrients and hormonal substances contained in the xylem sap and the higher photosynthetic activity of the leaves near the fruits can supply more assimilates (Proietti et al., 1999). In fact, even if there is a certain photosynthetic activity, the fruit is not autotrophic and so its growth depends strongly on the assimilates supplied by the leaves and consequently on the number and efficiency of the leaves available for each fruit (Proietti et al., 1994). The results of a previous study showed that the fruit, even though it is the organ that has the greatest ability to attract assimilates on the shoot, for its growth mainly uses assimilates provided by the leaves inserted on the same shoot. Only under conditions of reduced availability of these substances the fruit attracts assimilates that are available from farther parts but only up to a certain distance (Proietti and Tombesi, 1996). This means that the fruit growing in shaded portions of the canopy cannot reach optimal development even if the overall availability of assimilates is high. Fruit Pulp/Pit Ratio

The pulp/pit ratio did not show differences due to the light availability (Table 2). This result is in contrast to what was observed by Tombesi et al. (1999) in an experiment in which the reduced lighting was obtained artificially during the second phase of fruit growth (from the end of August to harvest). This indicates that the light had a proportional effect on the growth of both the endocarp, which occurs in the first phase of fruit growth, and the mesocarp, which occurs above all in the second phase (Proietti, 2003). In general, the fruit weight and pulp/pit ratio values were higher for the cultivar ‘Leccino’ than ‘Frantoio’. Fruit Water Content

In both cultivars, the water content of fruits grown in the shaded portions of the canopy was higher than that of olives grown in parts that were well exposed to light. From October to November 2006, the water content in the cultivar ‘Leccino’ was much lower than that in ‘Frantoio’ (Table 2). This was probably because ‘Leccino’ was more sensitive to the water shortage that occurred in that period, especially in October (Pannelli

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et al., 2003). In general, the higher water contents in fruits grown in the shaded portions of the canopy are probably due to their reduced transpiration. Fruit Oil Content

In both years and cultivars, the olives grown in the well-lighted portions of the canopy had higher oil content, with greater differences in October (Table 2). This would indicate that the influence of light on the amount of oil produced by the tree is higher when olives are harvested early. The higher oil content in olives grown in the well-lighted portions of the canopy depends on a higher availability of assimilates; it could also be due to a more intense light-induced metabolism which activates enzymes involved in the synthesis of fatty acids, as demonstrated in other species (Picaud et al., 1991). Oil Quality

The free acidity and peroxide number of the oils were not significantly affected by the light availability. All the oils extracted from olives grown in the well-lighted portions of the canopy had higher total polyphenol and chlorophyll contents than those extracted from olives grown in shaded parts of the canopy (Tables 3 and 4). This is very important because the polyphenols have an important positive role in determining the nutritional, health and sensorial characteristics of the oil. As a matter of fact, the antioxidant power of extra virgin olive oils depends largely on the polyphenol content, that together with other antioxidants (i.e., tocopherols and carotenoids), preserve the oil from oxidation alterations. They also help in the prevention of inflammation processes, cancer, cardio-vascular diseases, ageing processes, etc.

The polyphenols also strongly affect the sensorial profile of the oils; they are responsible for the “bitter” and “spicy” tastes, that are considered positive qualitative attributes of the oils, provided that they are not too intense. If the tastes are too strong the acceptability of the oils could decrease. In cultivars, like ‘Leccino’, that constitutionally have a relatively low polyphenol content, it is very important to identify and optimise all the factors that can increase the amount of these substances.

The score (ranging from 1 to 9) for the sensorial analysis (panel test) was not significantly affected by the light; all the oils received a high score (around 8). However, in both years, the oils extracted from olives of the cultivar ‘Frantoio’ grown in well-lighted portions of the canopy were fruitier (in terms of intensity and complexity), more bitter and spicier than those extracted from olives grown in shaded parts of the canopy (Tables 3 and 4).

The fatty acid composition was slightly affected by the light availability. The oils extracted from olives grown in well-lighted portions had slightly higher palmitic, palmitoleic and linoleic acid contents and lower oleic acid content (data not shown). The oleic acid content was always much higher than 72%. The ratios between unsaturated/saturated fatty acids, monounsaturated/saturated fatty acids and oleic/linoleic acids were slightly higher in oils extracted from olives grown in shaded portions of the canopy (data not shown).

CONCLUSIONS

The results of this study provide useful information about the effects of availability of different levels of light on fruit development and oil quality. The light availability slightly affected the ripening process of olives. The results suggest an intensification of fruit ripening (more pigmentation and less pulp consistency) and an extension of the ripening period (greater detachment force). This indicates that the ripening indexes (pigmentation, pulp consistency and detachment force) evolve differently, depending on the conditions in which the fruit develops.

Fruit weight and oil content (% f.w.) increased remarkably when the fruit grew in well-lighted conditions, whereas the pulp/pit ratio was not affected by light availability.

As far as oil quality is concerned, under well-lighted conditions there was a marked increase in the polyphenol content, a slight reduction in the oleic acid content and

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an increase in the palmitic, palmitoleic and linoleic acid contents. In oils obtained from the cultivar ‘Frantoio’ with early harvesting, the fruity, bitter and spicy sensations slightly increased as did the complexity of the sensorial profile.

The results confirm that the availability of high levels of light is essential for a high production (higher fruit weight and oil content), and indicate that well-lighted conditions improve the oil quality in terms of the polyphenol content and complexity of the sensorial profile.

The results of this study highlight the importance of carefully considering all the factors that would provide a good, uniform lighting of the canopy, such as site selection for establishing a new olive grow, planting distances, training system and modality and intensity of pruning, in order to obtain a high yield of high quality oil. The results also provide important information regarding the complex mechanisms involved in fruit development and ripening, particularly the effect that high light availability has on fruit detachment, pigmentation and pulp consistency.

Literature Cited Bongi, G., Di Marco, G. and Soldatini, G. 1988. Fotosintesi e fattori ambientali:

metodologie di studio e prospettive applicative. p.191-214. In: S.M. Cocucci (ed.), La crescita e lo sviluppo della pianta; fattori endogeni ed esogeni, CNR-IPRA, Monografia n.19, Roma.

Cimato, A., Baldini, A. and Moretti, R. 2001. L’olio di oliva, cultivar, ambiente e tecniche agronomiche. Ed. ARSIA, Firenze, p.167.

Farinelli, D., Proietti, P., Famiani, F., Ferranti, F., Pilli, M. and Reale, L. 2003. Intercettazione luminosa e fotosintesi in diverse cultivar di olivo. Atti del Convegno Nazionale “Germoplasma olivicolo e tipicità dell’olio” Perugia, Italy, 5/12/2003:136-141.

Ortega Nieto, J.M. 1969. Estudios y experiencias de la poda del olivo. Ministerio de Agricultura, Madrid.

Pannelli, G., Baldioli, M., Servili, M. and Montedoro, G. 2003. Caratteristiche dei frutti e dell’olio di germoplasma olivicolo in Umbria. Ed. ARUSIA, Perugia, p.205.

Picaud, A., Creach, A. and Tremolières, A. 1991. Studies on the simulation by light of fatty acid synthesis in Chlamydomonas reinhardtii whole cells. Plant Physiological Biochemical 29(5):441-448.

Proietti, P., Preziosi, P. and Tombesi, A. 1988. Influence of shading on olive leaf photosynthesis. Proceedings “2nd International meeting on Mediterranean Tree crops”, Chania, Greece, 2-4/11/1988, p.334-335.

Proietti, P. 1990. Photosynthesis and respiration in olive fruits. Acta Hort. 286:211-214. Proietti, P., Tombesi, A. and Boco, M. 1994. Influence of leaf shading and defoliation on

oil synthesis and growth of olive fruits. Acta Hort. 356:272-279. Proietti, P., Tombesi, A. and Pilli, M. 1995. Differenze nella risposta fotosintetica

all'intensità luminosa tra la pagina superiore ed inferiore di foglie di olivo nel corso della stagione vegetativa. Italus Hortus 1-2:13-18.

Proietti, P. and Tombesi, A. 1996. Translocation of assimilates and source-sink influences on productive characteristics of the olive tree. Advances in Horticultural Science 10:11-14.

Proietti, P. and Palliotti, A. 1997. Contribution of the adaxial and abaxial surfaces of olive leaves to photosynthesis. Photosynthetica 33:63-69.

Proietti, P., Famiani, F. and Tombesi, A. 1999. Gas exchange in olive fruit. Photosynthetica 36:423-432.

Proietti, P. 2003. Changes in photosynthesis and fruit characteristics in olive in response to assimilate availability. Photosynthetica 41(4):559-564.

Proietti, P., Nasini, L. and Famiani, F. 2005. Effect of different leaf-to-fruit ratios on photosynthesis and fruit growth in olive (Olea europaea L.). Photosynthetica 44(2):275-285.

Tombesi, A., Boco, M. and Pilli, M. 1999. Influence of light exposure on olive fruit

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growth and composition. Acta Hort. 474:255-260. Tables Table 1. Characteristics during the ripening period of olives grown in well-lighted (Light)

or shaded (Shade) portions of the canopy in 2006 and 2007.

Cultivar Light avail.

Detach. force (N)

Pigmen. index (0-5)

Pulp consis.

(g)

Detach. force (N)

Pigmen. Index (0-5)

Pulp consis.

(g) October 2006 November 2006

Leccino Shade Light

3.91a 4.25 b

2.33 a 2.43 b

648 b 622 a

4.03 a 4.13 a

2.52 a 2.98 b

374 b 333 a

October 2007 November 2007

Leccino Shade Light

3.39 a 4.35 b

3.78 a 3.76 a

359 a 354 a

3.81 a 4.27 b

2.35 a 2.39 a

326 a 332 a

October 2006 November 2006

Frantoio Shade Light

3.24 a 3.55 b

2.36 a 2.37 a

765 b 597 a

2.66 a 2.92 b

2.56 a 2.57 a

442 b 425 a

October 2007 November 2007

Frantoio Shade Light

3.02 a 3.05 a

3.75 a 3.75 a

329 a 323 a

3.12 a 3.06 a

2.37 a 2.38 a

326 a 325 a

For each column, cultivar and year, means followed by different letters are significantly different at P0.05. Table 2. Growth, oil content and pulp/pit ratio of olives grown in well-lighted (Light) or

shaded (Shade) portions of the canopy in 2006 and 2007.

Cultivar Light avail.

Water content

(%)

Oil content (% f.w.)

Dry weight

(g)

Water content

(%)

Oil content (% f.w.)

Dry weight

(g) October 2006 November 2006

Leccino Shade Light

58.2 b 55.8 a

17.5 a 20.4 b

0.78 a 0.83 b

40.2 b 36.7 a

22.6 a 23.5 b

0.80 a 0.94 b

October 2007 November 2007

Leccino Shade Light

53.1 b 51.3 a

13.7 a 14.2 b

0.58 a 0.63 b

52.1 a 49.2 a

13.1 a 14.6 b

0.60 a 0.73 b

October 2006 November 2006

Frantoio Shade Light

56.5 b 53.1 a

20.6 a 22.7 b

0.74 a 0.83 b

53.8 b 49.9 a

23.9 a 24.3 b

0.81 a 0.88 b

October 2007 November 2007

Frantoio Shade Light

49.5 b 47.2 a

17.6 a 19.1 b

0.52 a 0.58 b

49.7 a 47.5 a

17.4 a 18.3 b

0.57 a 0.66 b

For each column, cultivar and year, means followed by different letters are significantly different at P0.05.

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Table 3. Chemical and sensorial characteristics of oils extracted from olives grown in

well-lighted (Light) or shaded (Shade) portions of the canopy in 2006.

Cultivar Light avail.

Polyphenol content (ppm)

Fruity sensation

(0-5)

Bitter taste (0-5)

Spicy taste (0-5)

Complexity of the fruity sensation

(0-5) October 2006

Leccino Shade Light

309 a 398 b

2.42 a 2.40 a

2.43 a 2.81 a

2.60 a 2.71 a

2.19 a 2.19 a

November 2006

Leccino Shade Light

314 a 397 b

2.90 a 2.89 a

3.00 a 3.15 a

3.10 a 3.15 a

2.75 a 2.76 a

October 2007

Frantoio Shade Light

511 a 546 b

2.10 a 2.45 b

2.25 a 2.47 b

2.65 a 2.85 b

2.00 a 2.15 b

November 2007

Frantoio Shade Light

474 a 550 b

2.86 a 2.80 a

3.23 a 3.30 a

3.20 a 3.32 a

3.00 a 3.00 a

For each column, cultivar and month, means followed by different letters are significantly different at P0.05. Table 4. Chemical and sensorial characteristics of oils extracted from olives grown in

well-lighted (Light) or shaded (Shade) portions of the canopy in 2007.

Cultivar Light avail.

Peroxide number

(meq O2/kg)

Polyphenol content (ppm)

Chlorophyllcontent (ppm)

Fruity sensation

(0-5)

Bitter taste (0-5)

Spicy taste (0-5)

Leccino Shade 3.50 a 551 a - 2.34 a 2.43 a 2.69 a Light 4.80 b 631 b - 2.30 a 2.58 a 2.68 a

Leccino Shade 3.00 a 577 a 1.07 a 2.90 a 3.00 a 3.11 a Light 5.00 b 600 b 1.67 b 2.86 a 2.98 a 2.98 a

Frantoio Shade 4.80 a 450 a - 2.12 a 2.28 a 2.63 a Light 5.90 b 621 b - 2.49 b 2.49 b 2.84 b

Frantoio Shade 3.50 a 503 a 1.10 a 2.86 a 3.23 a 3.21 a Light 5.50 b 636 b 2.10 b 2.84 a 3.21 a 3.20 a

For each column, cultivar and month, means followed by different letters are significantly different at P0.05.

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