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Ciencia e investigación agraria

versión On-line ISSN 0718-1620

Cienc. Inv. Agr. v.37 n.1 Santiago abr. 2010 

Cien. Inv. Agr. 37(1):133-141. 2010



Boron dynamics related to fruit growth and seed production in kiwifruit (Actinidia deliciosa, cv. Hayward)

Dinámica del boro en relación con el crecimiento del fruto y la producción de semillas en kiwi (Actinidia deliciosa, cv. Hayward)


Carlos Sotomayor1, Paulina Norambuena1, and Rafael Ruiz2

1Pontifcia Universidad Católica de Chile, Facultad de Agronomía e Ingeniería Forestal. Casilla 306-22. Santiago, Chile. 2Instituto de Investigaciones Agropecuarias. CRI La Platina. Casilla 439-3. Santiago, Chile.


The effect of foliar boron treatments on fruit growth and seed development in Actinidia deliciosa, cv. Hayward, was studied. The distal leaves (BH) or fowers (BF) of a shoot were sprayed with 500 mg L-1 boric acid during the fowering period. The mobility of boron from the leaves to the fowers through the phloem was determined by spraying only the leaves. From 0 to 96 h after treatment, leaves and fowers were sampled and total boron was assessed. At harvest time, fruit weight and diameter plus seed weight and number were measured for the different treatments. The weight of fruits growing from shoots with boron-treated leaves were 14.1% higher than the control, while the weight of fruits derived from boron-treated fowers was 17% higher than that of fruits from untreated fowers. Regarding fruit length, signifcant differences between boron treatments and the control were observed, with an 8.2% and 8.5% increase for BH and BF treatments, respectively. No signifcant differences were found in fruit diameter. Fruits grown from shoots with boron-treated leaves had 43% more seeds than fruit grown from untreated control shoots, while fruits resulting from boron-treated fowers had 44% more seeds. This demonstrates the positive effect of boron treatment in seed production. No differences were observed in seed weight between treatments. The correlation coeffcient between seed number and fruit weight was r2 = 0.1294 for BF, r2 = 0.1298 for BH and r2 =0.0002 for the control. There was no variation in non-treated leaves and fowers with respect to boron concentration for a 96 h time period. On the contrary, in sprayed leaves boron levels reached up to 16 mg kg-1 between 24 and 48 h and slightly decreased after 96 h, demonstrating the boron absorption capacity of leaves. In the fowers from the shoots with boron-treated leaves, there was a signifcant 14 mg kg-1 increase in boron concentration from 24 to 96 h, showing boron mobility from leaves to fowers.

Key words: Boric acid, boron, fruit weight, kiwifruit, seed number, seed weight.


Se estudió el efecto de aplicaciones foliares de ácido bórico 0.5 g L-1 sobre el crecimiento del fruto de kiwi (Actinidia deliciosa), cv. Hayward y el desarrollo de semillas. Las aplicaciones fueron realizadas sobre hojas distales de brotes (BH) o sobre fores (BF). Se buscó también establecer la movilidad del boro desde hojas a fores con aplicaciones realizadas solamente sobre hojas distales de brotes forales. entre 0 y 96 hs post-aplicación se realizaron análisis químicos tanto en hojas como fores, con y sin tratamiento foliar, para determinar boro total. en la cosecha se midió peso y diámetro de frutos y número y peso de semillas según tratamiento. el peso de frutos del tratamiento BH superó signifcativamente al testigo en 14,1 %, en tanto los del tratamiento BF alcanzaron un 17,3 % más. Los tratamientos BF y BH aumentaron signifcativamente el diámetro de frutos en un 8,2 y 8,5%, respecto del testigo. No se encontraron diferencias estadísticas entre tratamientos respecto a diámetro ecuatorial. Los frutos del tratamiento BH produjeron 43% más semillas que el testigo, mientras que los del tratamiento BF las incrementaron en 44%, ambos aumentos signifcativos. esto indicaría el efecto favorable del boro aplicado en la producción de semillas. No hubo diferencias entre tratamientos en peso individual de semillas. La correlación entre número de semillas y peso del fruto respectivo fue de r2 = 0,1294 para BF, r2 = 0,1298 para BH y r2 = 0,0002 para el testigo. en las hojas sin aplicación de boro (testigos), durante 96 horas, no hubo variaciones en la concentración de boro total, tanto en hojas como en fores. en las hojas tratadas, el nivel de boro subió signifcativamente en 16 mg kg-1 después de 24 h, manteniéndose así hasta 48 horas. en cuanto al boro aplicado en hojas distales, y medido en las fores del mismo brote, el nivel subió signifcativamente en 14 mg kg-1 a las 24 h y hasta las 96 h. esto demostraría la eventual movilidad foemática del boro entre hojas y fores.

Palabras clave: Acido bórico, boro, kiwi, número de semillas, peso de semillas, peso de frutos.



Kiwifruit (Actinidia deliciosa var. deliciosa (A.Chev) C.F.Liang et A.R. Ferguson) is a functionally dioecious plant which requires a cultivar with pistillate fowers (e.g., Hayward) and another cultivar with staminate fowers (e.g., Matua) to produce fruit. Optimal production can only be achieved if the conditions for pollination and fruit development are favorable (Tromp et al., 2005).

The staminate fowers of kiwifruit produce numerous pollen grains which insects transport to the stigmas of pistillate fowers. Pistillate fow-ers have numerous ovules (> 1,000 ovules per fower), each one corresponding to a potential seed. vasilakakis et al. (1997) found that the presence of a high number of seeds is required to sustain the large kiwifruit cv. Hayward and determined a correlation (r = 0.816) between the number of seeds and fruit weight. Other authors, as Bellini et al. (1989), Hopping (1990), Intoppa and Piazza (1990), Lawes and Woolley (1990), Testolin et al. (1991) and valenzuela and Konig (1991), have also found a high correlation between fruit weight and the number and weight of seeds, demonstrating that the Hayward ki-wifruit needs more than 1,000 seeds to reach a weight greater than 100 g.

For about 80 years, boron has been known to be an essential element for the growth of higher plants; however, its biochemical function is still unknown (Bolanos et al., 2004). A series of physiological processes have been studied where boron is essential, such as processes associated with plant reproduction and basic fowering and fruiting (Blevins and Lukaszewski, 1998). The most recent studies attribute the essential processes of structural conservation of cell walls, functional conservation of cell membranes and the support of metabolic activities specifc to boron (Bolanos et al., 2004).

Flower tissues have relatively higher boron content than vegetative tissues. Although the pollen grains of most species are naturally low in boron, the styles, stigmas and ovaries generally have higher concentrations, according to Blevins and Lukaszewski (1998). According to Dell and Huang (1997), low boron levels in fowers reduce fertility by damaging pollen formation and affecting the growth of the pollen tube. Low boron levels can also have post-insemination effects that affect embryogenesis, leading to seed abortion and fruit malformation.

In vascular plants, boron moves passively from the roots to the leaves and shoots via transpiration (Husa and McIlrath, 1965). Once in the leaves, boron is, in general, restricted to the apoplast (Sattelmacher, 2001). Therefore, boron is considered to be relatively immobile in the dicotyledonous phloem, and a continuous supply is required to achieve normal plant growth (Brown and Hu, 1998). However, in plants where a portion of the photoassimilates is translocated in the phloem as sugars-alcohols, boron is transported freely from mature organs to growing tissues (Liakopoulos et al., 2005). In the Malus, Pyrus and P r u n u s species, it has been found that boron mobility is due to the formation of stable complexes with sorbitol. In species that do not produce large amounts of polyols (e.g., walnut), once boron has entered the leaves via transpiration, it does not undergo secondary transportation to the phloem but remains immobilized and accrues in the leaves (Brown and Hu, 1998; Brown and Shelp, 1997).

A few authors (Nyomora et al., 2000; Wojcik and Wojcik, 2003) have found an improvement in productivity from fruit trees treated with foliar applications of boron. According to Hanson et al. (1985), in 'Italian' plum trees and in 'D'Anjou' pear trees, the increase in foliar concentration of boron by pre-anthesis applications have led to a signifcant improvement of fruiting or fruit setting. In addition, fruiting and productivity in almond trees have been signifcantly increased with foliar applications of boron (Ny-omora et al., 2000; Nyomora and Brown, 1999; Sotomayor and Castro, 1997; Nyomora and Brown, 1997; Hanson, 1991).

The mobility of boron has not been determined in Actinidia. Papadakis et al. (2004), in a study of boron toxicity in fruit plants, mentioned that orange trees and kiwifruit are species where boron may have restricted phloematic mobility. On the other hand, Sotiropoulos et al. (2004) stated that the presence of high concentrations of boron in mature leaves in comparison to young leaves is evidence of boron immobility in the phloem of kiwifruit. In this context, Sotiro-poulos et al. (2006) studied boron distribution in kiwifruit, and found that the decrease of this element from the basal part to the apical part could be attributed to low boron mobility in the plant, although they also found that the boron content is not uniform in kiwifruit.

Although sucrose is the main sugar that is translocated in A. deliciosa, Bieleski et al. (1997) determined that this plant genus contains an unusually high inositol level, reaching 20% of the total soluble carbohydrates in the leaves. In addition, Klages et al. (2004) found that mio-inositol represents between 10 and 20% of the soluble carbohydrates in the mature leaves of A. deliciosa, cv. Hayward. Together, this data points to the possibility that mio-inositol may permit boron mobility via a simplistic route, where sugar alcohols form complexes with boric acid. Thus, boron accrues in the meristemat-ic zones in A. deliciosa fruits.

Currently, the growth of Hayward kiwifruit requires the development of technology to increase productivity and, specifcally, fruit size, an important quality factor that is fundamental for its commercialization (Calvanese, 2008; So-tomayor, 1996).

Therefore, the objective of this work was to study boron mobility in kiwifruits, cv. Hayward. We determined whether boron is displaced from leaves to fruits and determined the effect of foliar and fower boron applications on fruit weight and their capacity to produce seeds.

Materials and methods

During the 2006-2007 season, two parallel experiments were carried out in a 20-year-old kiwi-fruit, cv. Hayward, orchard located in Nogales, v Region of Chile (32º44'06'' S, 71º14'12'' W). The planting used pollinating plants of the cvs. Matua and Tomuri, at a proportion of 5% each. Pollination was carried out with 20 beehives per hectare during the fowering season. The productivity of the orchard was 20 t ha-1, which is near the average for Hayward kiwifruit production in Chile. The soil is of alluvial origin, loam, deep and with good drainage. The irrigation was carried out by micro-spraying with well water.

In January, foliar boron concentration in this orchard was 30 to 40 mg kg-1 of total boron, and soil boron concentration was 1 mg kg-1. Both values are considered appropriate, according to international standards (Clark et al., 1986; Beutel et al., 1994). The experimental unit was composed of specifc mixed shoots, with four fowers (further fruits) in the basal portion and four to six leaves in the distal or apical portion of the shoot, separated by 20 to 40 cm from the fowers (distal leaves).

Effect of boron on kiwifruit fruiting (Experiment 1)

The effect of 0.5 g L-1 boric acid (H3BO3) was studied. Boric acid was sprayed on leaves or fowers from the same shoot during kiwifruit fruiting. The applications were made during the period of fower opening (November 1, 2006). An experimental design of random blocks was used, with nine replications. Three specifc mixed shoots from each plant were selected (experimental units), with four fowers and at least four distal leaves each. The following treatments were considered: a) BF: Spraying of 0.5 g L-1 boric acid on individual fowers of the mixed shoot; b) BH: Spraying of 0.5 g L-1 boric acid on distal leaves of the mixed shoot; and c) T: control, without boron application (only water).

The fruits were harvested on March 6, 2007, and the individual weight and diameter of fruits (polar and equatorial), number of seeds and seed weight were measured. The data obtained for each parameter were processed by an analysis of variance, using the program SAS 2008 (SAS Institute Inc., Cary, NC, USA). In cases where signifcant differences appeared, the treatments were compared by their means, by Tukey Kramer's procedure (p ≤ 0.05). The correlation between the number of seeds (as an independent variable) and the respective weight of the fruit (as a dependent variable) was estimated separately, according to the treatments.

Boron dynamics on kiwifruit (Experiment 2)

Boron mobility between distal leaves sprayed with 500 mg L-1 boric acid and the fowers of the same shoot was studied. According to a randomized block design with six replications, fve homogeneous and healthy kiwifruit plants, cv. Hayward, were selected. Four specifc mixed shoots were marked in each plant, with four fowers and at least four distal leaves. On November 5, 2006, the distal leaves were sprayed with boric acid, when they were at 50% of opening. Leaves were sprayed only with water in the control group.

A sampling of treated leaves and fowers at 0, 24, 48 and 96 h after the application was taken. Analyses of these samples were made in the Laboratory of Foliar and Soil Analysis, Pontif-cia Universidad Católica de Chile. The samples were washed, ground and dried, with a further calcination at 500ºC in presence of calcium oxide and further digestion with hydrochloric acid. The measurement of total boron was done using a colorimetric method based on azome-thine (Walinga et al., 1995).

An analysis of variance and the Tukey Kramer test were performed with the data obtained. Then, orthogonal contrasts between treatments. Then, orthogonal contrasts between treatments and control were carried out.

Results and discussion

Effect of boron on kiwifruit fruiting (Experiment 1)

Weight. The highest weights corresponded to fruits whose distal leaves or fowers had been sprayed with boric acid during the anthesis period, while the control fruits (without boron application) reached a signifcantly lower weight. Signifcant differences were not observed in fruit weight between the treatment with boron to the fowers (BF) and boron to the leaves (BH), but both were different in comparison to the control, with an increase of 17.3 and 14.1%, respectively (Table 1).

This result indicates that the exogenous application of boron may improve kiwifruit fruiting, which agrees with the data on plum trees (Hanson et al., 1985), almond trees (Nyomora et al., 2000), pear trees (Wojcik and Wojcik, 2003) and avocados (Jaganath and Lovatt, 1995).

Fruit diameter. With respect to the longitudinal diameter of fruits, signifcant differences were observed between the treatments and the control, with an increase in diameter of 8.2 and 8.5% in relation to the control, for the BF and BH treatments, respectively. On the other hand, the equatorial diameter did not reveal a statistical difference between treatments and control (Table 1).

Sotomayor (1996) stated that the equatorial diameter should not increase beyond a certain limit, because the 'Hayward' kiwifruit fruit must maintain a certain length/width ratio. Thus, fruits with a 1.28 ratio are considered appropriate or normal, while a ratio lower than 1.20 represents a fruit that is too wide. From a commercial point of view, a ratio of 1.24 is considered optimal. Therefore, the values obtained in this experiment can be considered appropriate for the fruits from all treatments (Table 1).

Number of seeds. The fruits subjected to boron treatment produced a higher number of seeds in comparison to the control, and the BF treatment obtained the highest fgure (p ≤ 0.05). The BF and BH treatments did not show a signifcant difference compared to each other, and led to an increase in the number of seeds, in relation to the control group, of 44 and 43%, respectively.

The results obtained confrm the positive correlation between the number of seeds and ki-wifruit weight, as mentioned in previous works (Hopping, 1990; Lawes and Woolley, 1990). The higher the number of seeds, the higher the fruit weight will be. The results obtained agree with studies by Lovatt and Dugger (1984), Nyo-mora et al. (2000), Loomis and Durst (1992) and Lovatt (1999), which showed that boron plays a role in pollen germination and the further development of the pollen tube, allowing for an increased amount of fertilized ovules and more seeds per fruit.

Seed weight. Signifcant differences were not observed in the individual weight of seeds between the treatments with boron in comparison to the control (Table 1). From these results, it can be deduced that boron application did not have an effect on seed size; thus, this parameter does not infuence the fnal weight of the fruits.

Fruit weight /Number of seeds ratio. The correlation between variables was r2 = 0.1294 for BF, r2 = 0.1298 for BH and r2 = 0.0002 for the control. While the correlation is relatively weak in the treatments with boron, it is positive and differs

from the control which is practically null. The results obtained confrm the positive correlation existing between the number of seeds and the kiwi-fruit fruit weight, as mentioned in previous works (Hopping, 1990; Lawes and Woolley, 1990).

Boron dynamics in kiwifruit (Experiment 2)

The results of the chemical analysis of leaves with and without application of boric acid are shown in Table 2, before the application and after 24, 48 and 96 h.

In leaves without boron application or in the control (Table 2), there were no signifcant differences in the concentration of total boron between 24 and 96 h. On the contrary, in leaves where boron was applied, the boron concentration increased signifcantly 24 h after the application and was still increased at 96 h.

This result shows that boric acid was absorbed to growing organs in species where the element by the leaves and rapidly increased in concen- is mobile. The main factor conferring mobil-tration, and that this concentration was main- ity to boron in the phloem is the synthesis of tained for at least 96 h. Foliar boron may then sugar-alcohols and the subsequent transporta-begin to be exported mainly to the fruits and tion of B-poliol complexes. On the other hand, the shoot, normalizing the foliar boron level. In Bieleski et al. (1997) mentioned that Actinidia addition, this agrees with Klages et al. (1998), plants contain unusually high levels of inositol, who indicated the possibility that mio-inositol is and Klages et al. (2004) indicated the possibil-transported through the phloem from the leaves ity that this sugar might be transported by the to the fruits. phloem from the leaves to the fruits, forming B-inositol complexes that may allow boron mo-In shoot fowers whose leaves did not receive bility. Therefore, boron may accrue in the mer-boron application (control), the concentration istematic zones in fruits of A. deliciosa. of boron did not vary at 96 h (Table 3). On the contrary, in fowers with leaves subject to boron When the average number of seeds in fruits application, the level of boron increased signif- from boron treatment applied on distal leaves cantly to 14 mg kg-1 at 24 h and maintained this of the shoots (BH) was analyzed, it was ob-accumulation during the 4 days of the test. This served that the treatment increased the number shows that boron applied on distal leaves from of seeds by 43%. This may be interpreted as the same shoot was able to translocate rapidly an effect of boron translocation from the distal (24 h) to the fowers (sinks) and be maintained leaves to the fowers, leading to a subsequent at a concentration higher than normal for 96 h. higher number of seeds. This would demon-Thus, it can be deduced that the favorable effect strate that boron presents a certain phloematic of boron application may occur in the leaves and mobility in kiwifruit, according to the condi-result in the production of a higher number of tions of this experiment. This result contrasts seeds. with studies by Papadakis et al. (2004) and by Sotiropoulos et al. (2004), which found an im-Brown and Hu demonstrated in 1998 that bo- mobility of boron in the phloem of kiwifruit ron applied by the foliar route may translocate shoots.


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Received 14 May 2009. Accepted14 July 2009.

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