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The effect of yield, harvest time and fruit size on the oil content in fruits of irrigated olive trees (Olea europaea), cvs. Barnea and Manzanillo
Scientia Horticulturae 99 (2004) 267–277
The effect of yield, harvest time and fruit size on the oil content in fruits of irrigated olive trees (Olea europaea), cvs. Barnea and Manzanillo Shimon Lavee a,b,∗ , Maria Wodner a b
a Institute of Horticulture, Volcani Center, Bet-Dagan 50-250, Israel Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel
Accepted 12 June 2003
Abstract The oil content in olive fruits of different sizes from irrigated high (‘on’) and low (‘off’) yielding olive trees of cvs. Barnea and Manzanillo were determined at different stages of fruit maturation. The fruit size range at all stages of maturation is significantly higher on low yielding ‘off’ trees than on high yielding ‘on’ trees. The oil content in the mesocarp of olive fruits is not yield or fruit size dependent. Only in young fruit at early stages of green maturation is the oil content in the fruit’s mesocarp higher in the low yielding ‘off’ trees than in the high yielding ‘on’ ones. At full black maturation, the relative oil content in the mesocarp is uniform in all fruits regardless of size and level of yield. The final oil content in the fruits is dependent on the interaction between the growing conditions and the genetic potential of the variety. The amount of oil produced by an olive tree seems to be regulated mainly by the amount of mesocarp available for oil biosynthesis. The ratio of mesocarp/endocarp (flesh/pit) within each cultivar is strongly related to fruit size, and thus affected by high and low yields. © 2003 Elsevier B.V. All rights reserved. Keywords: Irrigated olive; Fruit load; Fruit size and oil accumulation interactions
1. Introduction Oil accumulation in olive fruits starts towards the end of the pit (endocarp) hardening period. Under irrigated conditions it continues linearly until the change of external color in most varieties (Lavee and Wodner, 1991). These data were based on representative fruit samples taken from the trees at each point during the developmental period. As fruit set ∗ Corresponding author. Present address: Institute of Horticulture, Volcani Center, Bet-Dagan 50-250, Israel. Tel.: +972-3-968-3360; fax: +972-3-966-9583. E-mail address: [email protected] (S. Lavee).
0304-4238/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0304-4238(03)00100-6
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on the tree is an on going process which lasts between 1 and 3 weeks, fruits of different sizes and stages of development are present at any given time on the trees. The level of contribution of the different fruit types on the tree to the linearity of oil accumulation in the fruit is not clear. Generally, cultivars with smaller fruit have at maturation a higher oil content than cultivars with large fruit (Morettini, 1972). However, we could not find any information regarding the oil content in small and large fruit developing on the same tree. Furthermore, during ‘on’ years with heavy yields the fruits of all olive varieties are considerably smaller than those in ‘off’ years with a low yield (Hartmann, 1949; Shulman and Lavee, 1979). On the other hand, it is generally accepted, although not proven, that in all olive varieties the oil content in the larger ‘off’ year fruits is higher than that in the ‘on’ year fruits in spite of their smaller size. Whether oil accumulation in the small and large fruits present on the same tree has a similar rate and pattern is still questionable. Different amounts and sizes of fruits were also described at different places in and around the canopy of mature olive trees (Ortega Nieto, 1969). It was shown that the fruits on the inner part of the canopy were smaller and produced at the same harvest date less oil than the fruit on the more illuminated exterior parts of the canopy. Defining these patterns is of particular importance for developing criteria for optimizing the harvest time. Harvest time optimization is becoming a major issue due to the rapid adoption of both old and new harvest mechanization systems. In the present study we tried to determine, over a period of 7 years, the distribution, developmental pattern and oil accumulation of the different fruit types under ‘on’ and ‘off’ year conditions. Two significantly different cultivars, Barnea and Manzanillo were chosen for this study.
2. Materials and methods Nine-year-old cvs. Barnea and Manzanillo trees in an intensive, irrigated olive orchard at the Volcani Center in Bet-Dagan were chosen for this study. Both the cvs. Barnea and Manzanillo trees were planted at a density of 300 trees per hectare in that orchard. Five ‘on’ trees with a heavy fruit load of about 70 kg per tree and five ‘off’ trees with a low fruit load of about 10 kg per tree were chosen annually over a period of 7 years. Starting at the beginning of green maturation, fruits were sampled from every one of the chosen trees on each of four consecutive dates with intervals of 35 days between the samplings. Five-hundred fruits were harvested separately from each experimental tree at each of the four sampling dates over the initial 4-year period. The average fruit size on high and low fruiting trees was determined at each sampling date. Thereafter, the distribution of fruit size was established by grouping the fruits in each sample on basis of 500 mg weight differences for cv. Manzanillo and 250 mg weight differences for cv. Barnea. The relative number of fruits in each size group was established separately for high and low yielding trees at each sampling date. The data reported are mean values of four independent experiments conducted consecutively during the four initial years of the study. The oil content in the fruits was determined by a refractometric method based on a quantitative reduction of the refraction index (RI) of chloronaphthalene (1-Cl-N) by oil
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(Lavee et al., 1988). Five grams of fresh mesocarp dried at 80 ◦ C was homogenized and extracted in 10 ml 1-Cl-N for 30 min. The RI was determined by a table refractometer at a constant temperature of 25 ◦ C and the oil content deducted from a calibration curve prepared using olive oils of the same cultivars studied. The oil content was determined in fruits of each size group of every individual sample from the high and low yielding trees of both cultivars at each sampling date during 4 years. The oil content of a representative fruit sample at each date was also determined. A 4-year verification study of the results was conducted. During the fourth experimental year and the three following ones fruit samples from early green and late black maturation were collected. Five replications of equal size (weight) small and large fruits from the low and high yielding trees were chosen and their oil content were analyzed. Most of the results obtained during the main study are presented as mean values of four independent experiments performed in four consecutive years. Standard errors (S.E.) were calculated using the yearly experiments as four independent blocks.
3. Results The fruit size, on ‘on’ and ‘off’ trees of cvs. Barnea and Manzanillo was determined over a period of 105 days starting around 1 September (with a 2–3 days variation during the different years of the study). The mean size of the fruit on the high yielding ‘on’ trees was as expected, significantly smaller than on the low yielding ‘off’ trees (Figs. 1 and 2).
Fig. 1. The change in fruit size and oil content in olive fruits of cv. Barnea on high (‘on’) and low (‘off’) yielding trees, from early green maturation to full black ripeness. (Mean of four independent experiments during 4 years each based on five repetitions of 500 fruits. The oil content in the fruits is expressed both on dry (dw) and fresh (fw) weight basis. Error bars indicate the S.E.)
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Fig. 2. As Fig. 1 for cv. Manzanillo.
The increase of fruit size during the studied maturation period was about linear in all cases although the rate of increase was higher in fruits on the ‘off’ trees than on the ‘on’ trees. Thus, the difference in mean fruit size between fruits on low and high yielding trees was larger in December after the 105 days of growth, than in September. This was considerably more pronounced with the fruit of cv. Barnea due to the higher growth rate of the fruits on the low yielding ‘off’ trees than in cv. Manzanillo. The fruit growth rate on the ‘on’ trees was about the same in both cultivars. The comparable mean oil content in the various samples showed an opposite pattern. The oil content in fruits of ‘off’ trees was already relatively high in September and significantly higher than in the fruits on ‘on’ trees. However, the increase in the oil content during the late stages of the 105 days growth period was relatively small in the fruit on ‘off’ trees while it increased most significantly in the fruit on ‘on’ trees. The initial difference (on 1 September) in the mean oil content in fruit on high and low fruiting trees was more pronounced in the relatively high oil producer cv. Barnea (Fig. 1) than in the table olive cv. Manzanillo (Fig. 2). However unexpectedly, in both cultivars, at the end of the late 105 day of the final growing period the relative oil content in the fruits on trees being in the ‘on’ and ‘off’ cycle was the same. This was true both on fresh and dry weight basis of the fruits. The distribution of fruits of different sizes on high and low fruiting trees was determined at each of the four sampling dates during the 105 days of the late growth period studied. In both cultivars the size range of the fruits on the ‘off’ year trees was larger than on the high yielding ones (Figs. 3 and 4). This was particularly the case for cv. Manzanillo in which the fruit size distribution curve was considerably flatter on the low yielding trees, indicating a more uniform distribution of the different sized fruits than on the high yielding
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Fig. 3. The relative distribution of fruits of different sizes on high (‘on’) and low (‘off’) yielding cv. Manzanillo trees at four developmental stages of the fruits starting at early green maturation (1 September) every 35 days until 14 December. (Mean of four independent experiments during four consecutive years. S.E. did not exceed 5% of the value in any of the fruit size groups.)
ones (Fig. 3). On high yielding trees, a clear characteristic fruit size peak was apparent on all four sampling dates in both cultivars. On the low yielding trees of cv. Barnea the distribution of fruits was more similar to that on the ‘on’ trees showing a more distinct peak than in the case of the cv. Manzanillo (Fig. 4). Still, the distribution of fruit sizes was larger on ‘off’ than on ‘on’ trees also in cv. Barnea. As the final mean relative oil content in the fruits on ‘off’ and ‘on’ trees, in December, was about the same while the mean fruit size was considerably different, the relationship
Fig. 4. As Fig. 3 for cv. Barnea (S.E. did not exceed 3.5% of the value in any of the fruit size groups).
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Fig. 5. The relation between the relative (%) oil content and fruit size (g) on high (‘on’) and low (‘off’) yielding cv. Barnea trees at four maturation stages (A: 1 September, B: 5 October, C: 9 November, and D: 14 December. T − 0, T + 35, T + 70, and T + 105 days, respectively).
between fruit size and oil content on the high and low yielding trees was determined. The oil content in fruits of different sizes on ‘on’ and ‘off’ trees was plotted together at each sampling date (Figs. 5 and 6). At the initial sampling date of cv. Barnea on 1 September the oil content of the fruits was directly correlated with their size. The oil content in the fruits of both ‘on’ and ‘off’ trees increased rather linearly in accordance with the increase in fruit size. Still the oil content in the small fruits on ‘off’ trees was significantly higher than in fruits with a comparable size on ‘on’ trees (Fig. 5A). A similar relationship between fruit size and oil content was also apparent in the fruit of the second sampling 35 days later (Fig. 5B). However, the gradient of the oil content in relation to fruit size in the samples from ‘off’ trees was more moderate and the higher oil content in small fruits to those of similar size from ‘on’ trees was less pronounced. In the November sample after further growth of the fruit, the relationship between oil content and fruit size on ‘off’ trees was apparent only for the smaller fruits. In fruits from ‘on’ trees the relationship prevailed but fruits of similar sizes from ‘on’ and ‘off’ trees had the same relative oil content (Fig. 5C). A month later, in December, the oil content of all fruits on the ‘off’ trees had about the same oil content regardless of their size. The larger fruits on the ‘on’ trees had the same oil content as those on ‘off’ trees. The smaller fruits, however, still had a lower oil content and retained the positive correlation between oil content and fruit size (Fig. 5D).
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Fig. 6. As Fig. 5 for cv. Manzanillo.
The relationship of oil content to fruit size during the late development of fruit on high and low yielding cv. Manzanillo trees was generally similar to that obtained with the cv. Barnea (Fig. 6). However, already at the first sampling date in September, the differences in the relative oil content between fruits of various sizes were significantly smaller than in cv. Barnea, particularly on the ‘off’ trees. The oil content increased and reached a uniform level in all fruits regardless of size on the ‘off’ trees early, during September, and on the ‘on’ trees during the following 35 days. Thus, the relative oil content of cv. Manzanillo reached a uniform level regardless of fruit size and yield load at the beginning of November (Fig. 6C). The overall lower oil content in the fruits of cv. Manzanillo than in those of cv. Barnea is not related to the fruit load but to the genetic nature of each of the two cultivars. The results in each of the four consecutive years studied, were similar thus; the data presented are mean values of the four independent experiments. For verification of these somewhat unexpected results, a limited but highly precise comparison was undertaken during the fourth year of the study and three consecutive additional ones. Groups of small and large fruits, of equal weight per size, were collected from ‘on’ and ‘off’ cv. Barnea trees during 4 years and similarly from cv. Manzanillo for 2 years. Such fruit samples were collected twice a year, early at the beginning of green maturation
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Fig. 7. The relation between the oil content in equal sized large and small fruits from high (‘on’) and low (‘off’) yielding cv. Barnea trees at the beginning and end of the maturation season over a 4-year period. Error bars indicate S.E.
and late at full black ripening. The relative oil content in each fruit sample was determined and is reported separately for each of the 4 years. During all 4 years the oil content in both the small and large cv. Barnea fruits harvested early in the season was higher in the fruits from the low yielding trees than in those from the high yielding ones (Fig. 7). On the other hand, in all late samples regardless of fruit size the oil content was either the same in fruits from high and low yielding trees or even somewhat higher in those from the ‘on’ trees. Still, in three of the years the small fruits regardless of their origin had a somewhat lower oil content than the large ones at black maturation (Fig. 7). Both the large and small fruits chosen were either the smallest or the largest with equal size to be found on both the high and low yielding trees. With cv. Manzanillo this comparison was made only during 2 years but a third intermediate fruit size was added at each sampling date. Generally, the results with cv. Manzanillo were of a similar nature than those with cv. Barnea, however, the pattern during the 2 years was slightly different (Fig. 8). During the first year the oil content in the fruits from high yielding trees reached the same level or even higher at the early sampling date, except in the smallest fruit size group. At the late harvesting date fruit size had no effect on the oil content and fruit load did not reduce and even slightly increased it. In the second year, in which maturation of this cultivar was somewhat later, the oil content in all three fruit sizes at the early sampling date was higher in the fruits from the ‘off’ trees. This was still noted with the smallest fruit even at the late sampling. However, the oil content in the
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Fig. 8. As Fig. 7 but during 2 years and three defined fruit sizes for cv. Manzanillo.
larger fruits was not affected by the fruit load of the trees and generally also not by fruit size.
4. Discussion The olive is naturally an alternate fruit-bearing tree. The degree of alternation is highly affected by the environmental conditions and horticultural techniques applied (Hackett and Hartmann, 1967; Lavee, 1989). The general fruit mass as well as the individual fruit size varies strongly between ‘on’ and ‘off’ trees (Drobish, 1930; Lavee and Spiegel, 1958). A significant reduction in the individual fruit size is typical for high yielding ‘on’ trees. In smaller fruits the flesh/pit (mesocarp/endocarp) ratio is in most cases reduced. Morettini (1972) indicated that fruit growth till pit hardening and thus pit size, are less effected by the number of fruits developing on the tree than the fruit growth thereafter. Fruit growth after pit hardening is mainly due to the development of the mesocarp and partly to the expansion of the exocarp. As oil accumulation in the fruit occurs in the mesocarp, the growth of which is reduced on high yielding trees, it was assumed that the oil accumulation in such fruits is reduced as well and thus, negatively correlated to yield. This, however, was not scientifically verified to the best of our knowledge. The smaller mean fruit size on the high yielding olive trees within each cultivar was apparent also in this study for cvs. Barnea and Manzanillo. The oil content, however, while significantly lower in the fruit of high yielding trees at the beginning of green maturation, reaches at full maturation, later in the season, the same level as that in the fruits on low yielding trees. Similar results were obtained for each of the two cultivars tested and were apparent both on a fresh and dry weight basis.
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This indicates that in fruit of ‘off’ trees oil accumulation is more rapid and reaches its genetic-environmental maximum considerably earlier than in fruits of ‘on’ trees. These results indicate that the ability of the fruit mesocarp cells to synthesize and accumulate oil is not limited by the amount of fruit developing on the trees within each variety. Still, as in previous studies (Lavee and Wodner, 1991) these results were based on mean fruit size and oil content values. Thus, a more accurate comparison on individual fruit sizes basis was performed. This fruit size and oil accumulation interaction was recorded at different stages of fruit development and maturation. In both cultivars the nature of fruit size distribution was significantly different for the high yielding ‘on’ and low yielding ‘off’ trees. Fruit size distribution on ‘on’ trees was, at all sampling dates, narrower with a large percent of the fruit having a characteristic size at each date. For the cv. Manzanillo ‘on’ trees fruit size distribution was somewhat wider than on cv. Barnea ‘on’ trees. At all sampling dates fruit size distribution on the ‘off’ trees of cv. Manzanillo was even wider showing a flat fruit size distribution curve with no clear peak. Generally, at any time, a population of different fruit sizes could be found on all trees with overlapping sizes between ‘off’ and ‘on’ trees in both cultivars. The extensive oil analysis performed on all fruit sizes at each sampling date simultaneously on the ‘on’ and ‘off’ trees indicates that, except in the small fruit during the early stages of maturation, fruit of similar size on high and low yielding trees have the same metabolic ability to synthesize and accumulate oil. It also showed in each of the two cultivars that the relative amount of oil in the fruit once reaching an annual maximum is not fruit size dependent. The relatively lower oil content in the small fruit present only on the high yielding trees of cv. Barnea prevailed also at the later stages of maturation. This was not the case with the small fruits of the earlier maturing cv. Manzanillo. It could be assumed that the less developed probably younger small fruits would also reach the annual maximal relative oil content as did the larger further developed fruits at a later date. Generally, from the oil accumulation data of both cultivars it could be concluded that the metabolic potential of the olive tree is not a limiting factor for synthesizing and accumulating the maximal genetic-environmentally determined amount of oil even at high fruit yields. Due to the unique and unexpected nature of these results, a careful and precise verification study was performed starting in the fourth year of the study and continued for an additional 3 years. Pairs of small and large fruits of cv. Barnea, with equal weight, were collected from ‘on’ and ‘off’ trees at the beginning of green and at full black maturation for four consecutive years and their oil content was analyzed. With cv. Manzanillo three fruit size pairs from ‘on’ and ‘off’ trees, early and late in the season were analyzed for their oil content for two independent years only. The results with cv. Barnea fully confirmed the previous findings showing in each of the years a somewhat higher oil content in the early samples of small fruits from the ‘off’ trees than in those from the ‘on’ years. This was also found in the earliest samples of the large fruits as well. At full maturation the oil content in fruit pairs from ‘on’ and ‘off’ trees was about the same though the pairs of small fruits had a slightly lower oil content than the pairs of the large ones. Similar results were obtained with the cv. Manzanillo in which, however, as discussed earlier at full black maturation, the small and large fruits from both fruit loads had about the same oil content. This slight difference between the two cultivars seems to be due to a better balance between tree growth and
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fruit development. This is supported by the slightly different behavior of the cv. Manzanillo fruits in 1991 and 1993. In the first year with a somewhat earlier maturation the large fruit from ‘on’ trees at the early harvest already had the same or even higher oil content than the parallel sized fruits from the ‘off’ year trees. In 1993, however, the relative maturation of fruit on the trees with a high fruit load was later. In that case the small fruit on the ‘on’ trees still contained a slightly (non-significant) lower oil content than the ‘off’ trees even at the black mature late harvest time. These small differences in the rate of oil accumulation are probably due to an interaction between the amount of fruit yield and the variation in climatic conditions. Generally, it could be concluded that even in ‘on’ years with a high fruit production oil biosynthesis in the fruit’s mesocarp is not limited. It seems that in olive the overall production control based on the metabolic potential, is regulated via fruit size, limiting the general mass of oil producing mesocarp on the trees. Thus, the relative oil content in the mesocarp at full maturation will reach a uniform level, based on the genetic-environmental conditions regardless of fruit size and tree load.
References Drobish, H.E., 1930. Olive thinning and other means of increasing size of olives, Bulletin 490. University of California, Berkley. Hackett, W.P., Hartmann, H.T., 1967. The influence of temperature on floral initiation of olive. Physiol. Plant. 20, 430–436. Hartmann, H.T., 1949. Growth of the olive fruit. Proc. Am. Soc. Hort. Sci. 54, 86–94. Lavee, S., 1989. Involvement of plant growth regulators and endogenous growth substances in control of alternate bearing. Acta Hortic. 239, 311–322. Lavee, S., Spiegel, P., 1958. Spray thinning of olives with growth regulators. Ktavim 9, 129–138. Lavee, S., Wodner, M., 1991. Factors affecting the nature of oil accumulation in fruit of olive. J. Hort. Sci. 66, 583–591. Lavee, S., Wodner, M., Avidan, B., 1988. A rapid refractometric method for determination of the oil content in olive (Olea europaea) fruit. Adv. Hort. Sci. 2, 33–37. Morettini, A., 1972. Olivicoltura, Ramo Editoriale degli Agricoltori. Rome, 522 pp. Ortega Nieto, J.M., 1969. La poda del olivo. In: M. Pastor Muñoz (Ed.), Olive Pruning. IOOC, Madrid, 1989, 111 pp. Shulman, Y., Lavee, S., 1979. Fruit development and maturation as effected by treatments of auxin. Riv. Ortoforofrutti. Ital. 63, 31–40.
The effect of yield, harvest time and fruit size on the oil content in fruits of irrigated olive trees (Olea europaea), cvs. Barnea and Manzanillo Shimon Lavee a,b,∗ , Maria Wodner a b
a Institute of Horticulture, Volcani Center, Bet-Dagan 50-250, Israel Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel
Accepted 12 June 2003
Abstract The oil content in olive fruits of different sizes from irrigated high (‘on’) and low (‘off’) yielding olive trees of cvs. Barnea and Manzanillo were determined at different stages of fruit maturation. The fruit size range at all stages of maturation is significantly higher on low yielding ‘off’ trees than on high yielding ‘on’ trees. The oil content in the mesocarp of olive fruits is not yield or fruit size dependent. Only in young fruit at early stages of green maturation is the oil content in the fruit’s mesocarp higher in the low yielding ‘off’ trees than in the high yielding ‘on’ ones. At full black maturation, the relative oil content in the mesocarp is uniform in all fruits regardless of size and level of yield. The final oil content in the fruits is dependent on the interaction between the growing conditions and the genetic potential of the variety. The amount of oil produced by an olive tree seems to be regulated mainly by the amount of mesocarp available for oil biosynthesis. The ratio of mesocarp/endocarp (flesh/pit) within each cultivar is strongly related to fruit size, and thus affected by high and low yields. © 2003 Elsevier B.V. All rights reserved. Keywords: Irrigated olive; Fruit load; Fruit size and oil accumulation interactions
1. Introduction Oil accumulation in olive fruits starts towards the end of the pit (endocarp) hardening period. Under irrigated conditions it continues linearly until the change of external color in most varieties (Lavee and Wodner, 1991). These data were based on representative fruit samples taken from the trees at each point during the developmental period. As fruit set ∗ Corresponding author. Present address: Institute of Horticulture, Volcani Center, Bet-Dagan 50-250, Israel. Tel.: +972-3-968-3360; fax: +972-3-966-9583. E-mail address: [email protected] (S. Lavee).
0304-4238/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0304-4238(03)00100-6
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on the tree is an on going process which lasts between 1 and 3 weeks, fruits of different sizes and stages of development are present at any given time on the trees. The level of contribution of the different fruit types on the tree to the linearity of oil accumulation in the fruit is not clear. Generally, cultivars with smaller fruit have at maturation a higher oil content than cultivars with large fruit (Morettini, 1972). However, we could not find any information regarding the oil content in small and large fruit developing on the same tree. Furthermore, during ‘on’ years with heavy yields the fruits of all olive varieties are considerably smaller than those in ‘off’ years with a low yield (Hartmann, 1949; Shulman and Lavee, 1979). On the other hand, it is generally accepted, although not proven, that in all olive varieties the oil content in the larger ‘off’ year fruits is higher than that in the ‘on’ year fruits in spite of their smaller size. Whether oil accumulation in the small and large fruits present on the same tree has a similar rate and pattern is still questionable. Different amounts and sizes of fruits were also described at different places in and around the canopy of mature olive trees (Ortega Nieto, 1969). It was shown that the fruits on the inner part of the canopy were smaller and produced at the same harvest date less oil than the fruit on the more illuminated exterior parts of the canopy. Defining these patterns is of particular importance for developing criteria for optimizing the harvest time. Harvest time optimization is becoming a major issue due to the rapid adoption of both old and new harvest mechanization systems. In the present study we tried to determine, over a period of 7 years, the distribution, developmental pattern and oil accumulation of the different fruit types under ‘on’ and ‘off’ year conditions. Two significantly different cultivars, Barnea and Manzanillo were chosen for this study.
2. Materials and methods Nine-year-old cvs. Barnea and Manzanillo trees in an intensive, irrigated olive orchard at the Volcani Center in Bet-Dagan were chosen for this study. Both the cvs. Barnea and Manzanillo trees were planted at a density of 300 trees per hectare in that orchard. Five ‘on’ trees with a heavy fruit load of about 70 kg per tree and five ‘off’ trees with a low fruit load of about 10 kg per tree were chosen annually over a period of 7 years. Starting at the beginning of green maturation, fruits were sampled from every one of the chosen trees on each of four consecutive dates with intervals of 35 days between the samplings. Five-hundred fruits were harvested separately from each experimental tree at each of the four sampling dates over the initial 4-year period. The average fruit size on high and low fruiting trees was determined at each sampling date. Thereafter, the distribution of fruit size was established by grouping the fruits in each sample on basis of 500 mg weight differences for cv. Manzanillo and 250 mg weight differences for cv. Barnea. The relative number of fruits in each size group was established separately for high and low yielding trees at each sampling date. The data reported are mean values of four independent experiments conducted consecutively during the four initial years of the study. The oil content in the fruits was determined by a refractometric method based on a quantitative reduction of the refraction index (RI) of chloronaphthalene (1-Cl-N) by oil
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(Lavee et al., 1988). Five grams of fresh mesocarp dried at 80 ◦ C was homogenized and extracted in 10 ml 1-Cl-N for 30 min. The RI was determined by a table refractometer at a constant temperature of 25 ◦ C and the oil content deducted from a calibration curve prepared using olive oils of the same cultivars studied. The oil content was determined in fruits of each size group of every individual sample from the high and low yielding trees of both cultivars at each sampling date during 4 years. The oil content of a representative fruit sample at each date was also determined. A 4-year verification study of the results was conducted. During the fourth experimental year and the three following ones fruit samples from early green and late black maturation were collected. Five replications of equal size (weight) small and large fruits from the low and high yielding trees were chosen and their oil content were analyzed. Most of the results obtained during the main study are presented as mean values of four independent experiments performed in four consecutive years. Standard errors (S.E.) were calculated using the yearly experiments as four independent blocks.
3. Results The fruit size, on ‘on’ and ‘off’ trees of cvs. Barnea and Manzanillo was determined over a period of 105 days starting around 1 September (with a 2–3 days variation during the different years of the study). The mean size of the fruit on the high yielding ‘on’ trees was as expected, significantly smaller than on the low yielding ‘off’ trees (Figs. 1 and 2).
Fig. 1. The change in fruit size and oil content in olive fruits of cv. Barnea on high (‘on’) and low (‘off’) yielding trees, from early green maturation to full black ripeness. (Mean of four independent experiments during 4 years each based on five repetitions of 500 fruits. The oil content in the fruits is expressed both on dry (dw) and fresh (fw) weight basis. Error bars indicate the S.E.)
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Fig. 2. As Fig. 1 for cv. Manzanillo.
The increase of fruit size during the studied maturation period was about linear in all cases although the rate of increase was higher in fruits on the ‘off’ trees than on the ‘on’ trees. Thus, the difference in mean fruit size between fruits on low and high yielding trees was larger in December after the 105 days of growth, than in September. This was considerably more pronounced with the fruit of cv. Barnea due to the higher growth rate of the fruits on the low yielding ‘off’ trees than in cv. Manzanillo. The fruit growth rate on the ‘on’ trees was about the same in both cultivars. The comparable mean oil content in the various samples showed an opposite pattern. The oil content in fruits of ‘off’ trees was already relatively high in September and significantly higher than in the fruits on ‘on’ trees. However, the increase in the oil content during the late stages of the 105 days growth period was relatively small in the fruit on ‘off’ trees while it increased most significantly in the fruit on ‘on’ trees. The initial difference (on 1 September) in the mean oil content in fruit on high and low fruiting trees was more pronounced in the relatively high oil producer cv. Barnea (Fig. 1) than in the table olive cv. Manzanillo (Fig. 2). However unexpectedly, in both cultivars, at the end of the late 105 day of the final growing period the relative oil content in the fruits on trees being in the ‘on’ and ‘off’ cycle was the same. This was true both on fresh and dry weight basis of the fruits. The distribution of fruits of different sizes on high and low fruiting trees was determined at each of the four sampling dates during the 105 days of the late growth period studied. In both cultivars the size range of the fruits on the ‘off’ year trees was larger than on the high yielding ones (Figs. 3 and 4). This was particularly the case for cv. Manzanillo in which the fruit size distribution curve was considerably flatter on the low yielding trees, indicating a more uniform distribution of the different sized fruits than on the high yielding
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Fig. 3. The relative distribution of fruits of different sizes on high (‘on’) and low (‘off’) yielding cv. Manzanillo trees at four developmental stages of the fruits starting at early green maturation (1 September) every 35 days until 14 December. (Mean of four independent experiments during four consecutive years. S.E. did not exceed 5% of the value in any of the fruit size groups.)
ones (Fig. 3). On high yielding trees, a clear characteristic fruit size peak was apparent on all four sampling dates in both cultivars. On the low yielding trees of cv. Barnea the distribution of fruits was more similar to that on the ‘on’ trees showing a more distinct peak than in the case of the cv. Manzanillo (Fig. 4). Still, the distribution of fruit sizes was larger on ‘off’ than on ‘on’ trees also in cv. Barnea. As the final mean relative oil content in the fruits on ‘off’ and ‘on’ trees, in December, was about the same while the mean fruit size was considerably different, the relationship
Fig. 4. As Fig. 3 for cv. Barnea (S.E. did not exceed 3.5% of the value in any of the fruit size groups).
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Fig. 5. The relation between the relative (%) oil content and fruit size (g) on high (‘on’) and low (‘off’) yielding cv. Barnea trees at four maturation stages (A: 1 September, B: 5 October, C: 9 November, and D: 14 December. T − 0, T + 35, T + 70, and T + 105 days, respectively).
between fruit size and oil content on the high and low yielding trees was determined. The oil content in fruits of different sizes on ‘on’ and ‘off’ trees was plotted together at each sampling date (Figs. 5 and 6). At the initial sampling date of cv. Barnea on 1 September the oil content of the fruits was directly correlated with their size. The oil content in the fruits of both ‘on’ and ‘off’ trees increased rather linearly in accordance with the increase in fruit size. Still the oil content in the small fruits on ‘off’ trees was significantly higher than in fruits with a comparable size on ‘on’ trees (Fig. 5A). A similar relationship between fruit size and oil content was also apparent in the fruit of the second sampling 35 days later (Fig. 5B). However, the gradient of the oil content in relation to fruit size in the samples from ‘off’ trees was more moderate and the higher oil content in small fruits to those of similar size from ‘on’ trees was less pronounced. In the November sample after further growth of the fruit, the relationship between oil content and fruit size on ‘off’ trees was apparent only for the smaller fruits. In fruits from ‘on’ trees the relationship prevailed but fruits of similar sizes from ‘on’ and ‘off’ trees had the same relative oil content (Fig. 5C). A month later, in December, the oil content of all fruits on the ‘off’ trees had about the same oil content regardless of their size. The larger fruits on the ‘on’ trees had the same oil content as those on ‘off’ trees. The smaller fruits, however, still had a lower oil content and retained the positive correlation between oil content and fruit size (Fig. 5D).
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Fig. 6. As Fig. 5 for cv. Manzanillo.
The relationship of oil content to fruit size during the late development of fruit on high and low yielding cv. Manzanillo trees was generally similar to that obtained with the cv. Barnea (Fig. 6). However, already at the first sampling date in September, the differences in the relative oil content between fruits of various sizes were significantly smaller than in cv. Barnea, particularly on the ‘off’ trees. The oil content increased and reached a uniform level in all fruits regardless of size on the ‘off’ trees early, during September, and on the ‘on’ trees during the following 35 days. Thus, the relative oil content of cv. Manzanillo reached a uniform level regardless of fruit size and yield load at the beginning of November (Fig. 6C). The overall lower oil content in the fruits of cv. Manzanillo than in those of cv. Barnea is not related to the fruit load but to the genetic nature of each of the two cultivars. The results in each of the four consecutive years studied, were similar thus; the data presented are mean values of the four independent experiments. For verification of these somewhat unexpected results, a limited but highly precise comparison was undertaken during the fourth year of the study and three consecutive additional ones. Groups of small and large fruits, of equal weight per size, were collected from ‘on’ and ‘off’ cv. Barnea trees during 4 years and similarly from cv. Manzanillo for 2 years. Such fruit samples were collected twice a year, early at the beginning of green maturation
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Fig. 7. The relation between the oil content in equal sized large and small fruits from high (‘on’) and low (‘off’) yielding cv. Barnea trees at the beginning and end of the maturation season over a 4-year period. Error bars indicate S.E.
and late at full black ripening. The relative oil content in each fruit sample was determined and is reported separately for each of the 4 years. During all 4 years the oil content in both the small and large cv. Barnea fruits harvested early in the season was higher in the fruits from the low yielding trees than in those from the high yielding ones (Fig. 7). On the other hand, in all late samples regardless of fruit size the oil content was either the same in fruits from high and low yielding trees or even somewhat higher in those from the ‘on’ trees. Still, in three of the years the small fruits regardless of their origin had a somewhat lower oil content than the large ones at black maturation (Fig. 7). Both the large and small fruits chosen were either the smallest or the largest with equal size to be found on both the high and low yielding trees. With cv. Manzanillo this comparison was made only during 2 years but a third intermediate fruit size was added at each sampling date. Generally, the results with cv. Manzanillo were of a similar nature than those with cv. Barnea, however, the pattern during the 2 years was slightly different (Fig. 8). During the first year the oil content in the fruits from high yielding trees reached the same level or even higher at the early sampling date, except in the smallest fruit size group. At the late harvesting date fruit size had no effect on the oil content and fruit load did not reduce and even slightly increased it. In the second year, in which maturation of this cultivar was somewhat later, the oil content in all three fruit sizes at the early sampling date was higher in the fruits from the ‘off’ trees. This was still noted with the smallest fruit even at the late sampling. However, the oil content in the
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Fig. 8. As Fig. 7 but during 2 years and three defined fruit sizes for cv. Manzanillo.
larger fruits was not affected by the fruit load of the trees and generally also not by fruit size.
4. Discussion The olive is naturally an alternate fruit-bearing tree. The degree of alternation is highly affected by the environmental conditions and horticultural techniques applied (Hackett and Hartmann, 1967; Lavee, 1989). The general fruit mass as well as the individual fruit size varies strongly between ‘on’ and ‘off’ trees (Drobish, 1930; Lavee and Spiegel, 1958). A significant reduction in the individual fruit size is typical for high yielding ‘on’ trees. In smaller fruits the flesh/pit (mesocarp/endocarp) ratio is in most cases reduced. Morettini (1972) indicated that fruit growth till pit hardening and thus pit size, are less effected by the number of fruits developing on the tree than the fruit growth thereafter. Fruit growth after pit hardening is mainly due to the development of the mesocarp and partly to the expansion of the exocarp. As oil accumulation in the fruit occurs in the mesocarp, the growth of which is reduced on high yielding trees, it was assumed that the oil accumulation in such fruits is reduced as well and thus, negatively correlated to yield. This, however, was not scientifically verified to the best of our knowledge. The smaller mean fruit size on the high yielding olive trees within each cultivar was apparent also in this study for cvs. Barnea and Manzanillo. The oil content, however, while significantly lower in the fruit of high yielding trees at the beginning of green maturation, reaches at full maturation, later in the season, the same level as that in the fruits on low yielding trees. Similar results were obtained for each of the two cultivars tested and were apparent both on a fresh and dry weight basis.
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This indicates that in fruit of ‘off’ trees oil accumulation is more rapid and reaches its genetic-environmental maximum considerably earlier than in fruits of ‘on’ trees. These results indicate that the ability of the fruit mesocarp cells to synthesize and accumulate oil is not limited by the amount of fruit developing on the trees within each variety. Still, as in previous studies (Lavee and Wodner, 1991) these results were based on mean fruit size and oil content values. Thus, a more accurate comparison on individual fruit sizes basis was performed. This fruit size and oil accumulation interaction was recorded at different stages of fruit development and maturation. In both cultivars the nature of fruit size distribution was significantly different for the high yielding ‘on’ and low yielding ‘off’ trees. Fruit size distribution on ‘on’ trees was, at all sampling dates, narrower with a large percent of the fruit having a characteristic size at each date. For the cv. Manzanillo ‘on’ trees fruit size distribution was somewhat wider than on cv. Barnea ‘on’ trees. At all sampling dates fruit size distribution on the ‘off’ trees of cv. Manzanillo was even wider showing a flat fruit size distribution curve with no clear peak. Generally, at any time, a population of different fruit sizes could be found on all trees with overlapping sizes between ‘off’ and ‘on’ trees in both cultivars. The extensive oil analysis performed on all fruit sizes at each sampling date simultaneously on the ‘on’ and ‘off’ trees indicates that, except in the small fruit during the early stages of maturation, fruit of similar size on high and low yielding trees have the same metabolic ability to synthesize and accumulate oil. It also showed in each of the two cultivars that the relative amount of oil in the fruit once reaching an annual maximum is not fruit size dependent. The relatively lower oil content in the small fruit present only on the high yielding trees of cv. Barnea prevailed also at the later stages of maturation. This was not the case with the small fruits of the earlier maturing cv. Manzanillo. It could be assumed that the less developed probably younger small fruits would also reach the annual maximal relative oil content as did the larger further developed fruits at a later date. Generally, from the oil accumulation data of both cultivars it could be concluded that the metabolic potential of the olive tree is not a limiting factor for synthesizing and accumulating the maximal genetic-environmentally determined amount of oil even at high fruit yields. Due to the unique and unexpected nature of these results, a careful and precise verification study was performed starting in the fourth year of the study and continued for an additional 3 years. Pairs of small and large fruits of cv. Barnea, with equal weight, were collected from ‘on’ and ‘off’ trees at the beginning of green and at full black maturation for four consecutive years and their oil content was analyzed. With cv. Manzanillo three fruit size pairs from ‘on’ and ‘off’ trees, early and late in the season were analyzed for their oil content for two independent years only. The results with cv. Barnea fully confirmed the previous findings showing in each of the years a somewhat higher oil content in the early samples of small fruits from the ‘off’ trees than in those from the ‘on’ years. This was also found in the earliest samples of the large fruits as well. At full maturation the oil content in fruit pairs from ‘on’ and ‘off’ trees was about the same though the pairs of small fruits had a slightly lower oil content than the pairs of the large ones. Similar results were obtained with the cv. Manzanillo in which, however, as discussed earlier at full black maturation, the small and large fruits from both fruit loads had about the same oil content. This slight difference between the two cultivars seems to be due to a better balance between tree growth and
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fruit development. This is supported by the slightly different behavior of the cv. Manzanillo fruits in 1991 and 1993. In the first year with a somewhat earlier maturation the large fruit from ‘on’ trees at the early harvest already had the same or even higher oil content than the parallel sized fruits from the ‘off’ year trees. In 1993, however, the relative maturation of fruit on the trees with a high fruit load was later. In that case the small fruit on the ‘on’ trees still contained a slightly (non-significant) lower oil content than the ‘off’ trees even at the black mature late harvest time. These small differences in the rate of oil accumulation are probably due to an interaction between the amount of fruit yield and the variation in climatic conditions. Generally, it could be concluded that even in ‘on’ years with a high fruit production oil biosynthesis in the fruit’s mesocarp is not limited. It seems that in olive the overall production control based on the metabolic potential, is regulated via fruit size, limiting the general mass of oil producing mesocarp on the trees. Thus, the relative oil content in the mesocarp at full maturation will reach a uniform level, based on the genetic-environmental conditions regardless of fruit size and tree load.
References Drobish, H.E., 1930. Olive thinning and other means of increasing size of olives, Bulletin 490. University of California, Berkley. Hackett, W.P., Hartmann, H.T., 1967. The influence of temperature on floral initiation of olive. Physiol. Plant. 20, 430–436. Hartmann, H.T., 1949. Growth of the olive fruit. Proc. Am. Soc. Hort. Sci. 54, 86–94. Lavee, S., 1989. Involvement of plant growth regulators and endogenous growth substances in control of alternate bearing. Acta Hortic. 239, 311–322. Lavee, S., Spiegel, P., 1958. Spray thinning of olives with growth regulators. Ktavim 9, 129–138. Lavee, S., Wodner, M., 1991. Factors affecting the nature of oil accumulation in fruit of olive. J. Hort. Sci. 66, 583–591. Lavee, S., Wodner, M., Avidan, B., 1988. A rapid refractometric method for determination of the oil content in olive (Olea europaea) fruit. Adv. Hort. Sci. 2, 33–37. Morettini, A., 1972. Olivicoltura, Ramo Editoriale degli Agricoltori. Rome, 522 pp. Ortega Nieto, J.M., 1969. La poda del olivo. In: M. Pastor Muñoz (Ed.), Olive Pruning. IOOC, Madrid, 1989, 111 pp. Shulman, Y., Lavee, S., 1979. Fruit development and maturation as effected by treatments of auxin. Riv. Ortoforofrutti. Ital. 63, 31–40.