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Gibberellic acid and flower bud development in loquat (Eriobotrya japonica Lindl.)
Scientia Horticulturae 129 (2011) 27–31
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Gibberellic acid and flower bud development in loquat (Eriobotrya japonica Lindl.) Carmina Reig a , Vittorio Farina b , Giorgio Volpe b , Carlos Mesejo a , Amparo Martínez-Fuentes a , Francesca Barone b , Francesco Calabrese b , Manuel Agustí a,∗ a b
Instituto Agroforestal Mediterráneo, Universidad Politécnica de Valencia, Camino de Vera s/n, Valencia 46022, Spain Dipartimento DEMETRA, Facoltá di Agraria, Università degli Studi di Palermo, Viale delle Scienze, Ed. 4, Palermo 90128, Italy
a r t i c l e
i n f o
Article history: Received 1 September 2010 Accepted 23 February 2011 Keywords: Flowering Gibberellic acid Loquat Premature shoots Sprouting
a b s t r a c t The application of gibberellic acid (GA3 ) to the whole loquat tree from mid-May to early June and from early August to the onset of flowering, significantly reduced the number of premature flowering shoots per current shoot and per m3 of canopy, and so reduced the total number of panicles per m3 of canopy. The number of vegetative shoots per m3 of canopy was also significantly reduced by applying GA3 . The response depended on the concentration applied and produced optimal results at 50 mg l−1 . Differences in the number of flowers per panicle and leaves per shoot were not significantly modified by the treatment. Nevertheless, GA3 applied directly to the developing apex near to flower differentiation reduced the number of flowers per panicle by 25–35% and without modifying the morphological characteristics of the panicle. Results suggest that less sprouting of lateral buds was largely responsible for the reduction in flowering intensity caused by GA3 . Best treatments reduced thinning costs (60%, approximately) of premature flowering shoots, slightly increased fruit diameter and significantly improved fruit colour and juice quality, thus advancing harvest date. © 2011 Elsevier B.V. All rights reserved.
1. Introduction By 2006 world loquat fruit production was about 550 × 103 t, with a crop area exceeding 130 × 103 ha, China (450 × 103 t) and Spain (36 × 103 t) being the main producing countries, followed by Turkey (12 × 103 t), Japan and Pakistan (10 × 103 t) and others (Lin, 2007). Nowadays, Spain is the most important exporting country for fresh consumption. Loquat tree (Eriobotrya japonica Lindl.) belongs to the family Rosaceae, sub-family Maloideae. It is a subtropical evergreen fruit tree species native to southern China that, under Mediterranean climatic conditions, the tree flowers profusely in panicles, with many premature flowering shoots, in autumn and early winter, sets in a lower proportion in late winter, and ripens in spring. Polar gibberellins are known to inhibit flower bud initiation in many angiosperm species, including temperate fruit crops (Sedgley and Griffin, 1989). Luckwill (1970) in pome fruits hypothesized that gibberellins produced in seeds inhibit flower formation since they coincide with embryo growth in developing fruitlets. Accordingly, for many polycarpic plants, the application of gibberellic acid (GA3 ) during flower induction interrupts the floral process and partially reduces the intensity of flowering. This technique has been used efficiently in pome fruits
∗ Corresponding author. Tel.: +34 963879330; fax: +34 963877331. E-mail address: [email protected] (M. Agustí). 0304-4238/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2011.02.017
(Tromp, 2000), mangoes (Turnbull et al., 1996), avocados (SalazarGarcía and Lovatt, 2000), apricots (Southwick et al., 1997), citrus (Monselise and Halevy, 1964), peaches and nectarines (Painter and Stembridge, 1972) and plums (González-Rossia et al., 2006). The response has been related to the date of treatment, concentration applied, and the total amount of active material applied per tree (Painter and Stembridge, 1972; González-Rossia et al., 2007). Although abscisic acid (ABA) has been reported to play a dominant role in flower induction and differentiation in loquat, lower levels of gibberellins are needed for inflorescence primordium formation (Liu et al., 2007). Yang et al. (2007) reported that GA3 applied at an early stage of flower induction significantly reduced flowering rates in loquat trees, but the authors did not determine the appropriate concentration and date of treatment, thus more studies are needed to make the best use of GA3 . Fruit size is often too small for loquat market demand, and so producers increase size by severely thinning fruits and removing premature flowering shoots, which are vigorous and weak shoots, that produce fruits of limited quality. Moreover, although loquat trees flower profusely they are not subject to alternate bearing, and so it can be worthwhile reducing vigor and flowering to an appropriate level in order to cut thinning and pruning costs. The aims of this study were to determine the optimal GA3 concentration and the appropriate date(s) of treatment to reduce flowering in loquat trees and the effects on yield and fruit quality.
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C. Reig et al. / Scientia Horticulturae 129 (2011) 27–31
2. Materials and methods
20 18
Panicles m -3
16 14 12 10 8 6 4
b
b
a
a
b
b
b
a
a
a
a
2 0
Date of treatment Fig. 1. Influence of gibberellic acid (150 mg l−1 ) on flowering intensity of cv. ‘Algerie’ loquat tree. Effect of treatment date. Standard errors are given as vertical bars. Values expressed per m3 of canopy. Each value is the average of six trees. Means with different letters differ significantly (P ≤ 0.05). Values are for the Callosa orchard (Spain) and for 2007.
3. Results Gibberellic acid significantly reduced the number of panicles per loquat tree, and the magnitude of the response depended on the date of treatment and the concentration applied. The application of 150 mg l−1 of GA3 from mid-May to early June and from early August to the onset of flowering (mid-September) significantly reduced the number of panicles per m3 of canopy of treated trees by 40–65% in comparison with the control trees (Fig. 1). Treatments applied in early May and from mid-June to mid-July did not significantly reduce the number of panicles per m3 of canopy in comparison with the control trees (Fig. 1). Fifty milligrams per litre of GA3 applied in early September also significantly reduced the number of panicles per m3 of canopy by 45% in comparison with the controls (Fig. 2). Increasing concentrations up to 200 mg l−1 did not significantly improve the response. Similar results were obtained when applying GA3 in early June (data not shown). An average reduction of between 40% and 60% of panicles per m3 of canopy, i.e. between 30% and 70% of flowers per m3 of canopy, was obtained in all the experiments that applied 50 mg l−1 of GA3 16 14 12
Panicles·m -3
Experiments were carried out using 20–25 year-old ‘Algerie’ and ‘San Filipparo’ loquat trees (E. japonica Lindl.), grafted onto loquat seedling and grown in commercial orchards in Callosa, Alicante, Spain (38◦ 39 N; 00◦ 07 W) and Palermo, Sicily, Italy (38◦ 04 N; 13◦ 25 E). Trees were pruned to vase shape, planted at 4 m × 3 m and 4 m × 5 m spacing, depending on the orchard, on a loamy clay soils, with drip irrigation. Fertilization, pest management, thinning, and pruning were in accordance with normal commercial practices. To determine the appropriate date of treatment, on different dates from early May to the onset of flowering (middle of September), 150 mg l−1 of GA3 (Arabelex-L; 1.6%, w/v; Aragro; Madrid, Spain) was sprayed fortnightly to whole trees of cv. ‘Algerie’ (Callosa). In early June and early September increasing concentrations of 0, 50,100,150 and 200 mg l−1 of GA3 were sprayed to whole trees of cvs. ‘Algerie’ (Callosa and Palermo) and ‘San Filipparo’ (Palermo) to determine the optimum concentration. In both experiments GA3 was sprayed by hand-gun at a pressure of 25–30 atm, wetting the trees to the point of run-off. In a separate experiment, 0, 50, 100, 150, 200 and 250 mg l−1 of GA3 were hand sprayed directly on the developing apex of 25 randomly selected shoots per tree of cv. ‘Algerie’ (Callosa) (5 ml of the GA3 solution per apex). In all cases, a non-ionic wetting agent (alkyl polyglycol ether) was added at a rate of 0.01%. In all the experiments, a randomized complete-block design with single tree plots of six replications each was performed. Experiments were run for four years (2005–2008) using different trees each year. Total vegetative shoots and total reproductive shoots per tree, including current shoots (shoots developing into principal panicles) and premature reproductive shoots were measured at 317 and 507 growth stages of the BBCH-scale (Martínez-Calvo et al., 1999), respectively. Results are expressed per m3 of canopy to standardize orchard and year values. Premature reproductive shoots are also expressed per current reproductive shoot. The numbers of leaves per shoot, racemes per panicle, and flowers per raceme were also recorded from 25 randomly selected main reproductive shoots per tree. The total number of flowers per m3 of canopy was calculated by multiplying the average number of flowers per panicle by the total number of panicles per m3 of canopy, thus determining the percentage of GA3 flowering inhibition with regard to the control trees. At the 701–702 growth stages of the BBCH-scale, the percentage of fruit set was evaluated by counting the number of fruits per panicle. At harvest, crop load and fruit characteristics were evaluated for the most effective treatments. Fruits were harvested according to appropriate commercial colour and size standards. The yield and number of fruits per tree were recorded on each harvest date, results being expressed per m3 of canopy. Number of fruits per panicle and average fruit weight were also recorded. At first picking date, 25-fruit samples were randomly picked from each treatment and each replication. Fruit firmness was assessed using a fruit pressure tester FT-011 (Fachini, Italy) with a 1.5-mm diameter flat cylinder probe. Total soluble solids (TSS) concentration of juice (◦ Brix) was assessed with a digital refractometer (Atago, Japan) and acid concentration analyzed by titration with 0.1 N NaOH. Fruit colour was established by determining the a and b Hunter co-ordinates. Three measurements were made per fruit at the equatorial area using a Minolta Chroma Meter CR-300. At flowering, all premature flowering shoots were manually thinned by removing the panicle. The time spent for thinning was measured per tree and per worker. Analysis of regression, or variance, was performed on the data (P ≤ 0.05) using the Student–Newman–Keuls’ multiple range test for means separation. Percentages were transformed to arcsin to homogenize the variance.
10 8 6 4
b
a
0
50
a
a
a
2 0
100
150
200
GA3 (mg l -1) Fig. 2. Effect of gibberellic acid concentration on flowering intensity of ‘Algerie’ loquat tree. Treatments were applied four months after shoot sprout (early September). Standard errors are given as vertical bars. Values expressed per m3 of canopy. Each value is the average of six trees. Means with different letters differ significantly (P ≤ 0.05). Values are for the Callosa orchard (Spain) for 2007.
C. Reig et al. / Scientia Horticulturae 129 (2011) 27–31
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Table 1 Effects of gibberellic acid (50 mg l−1 ) applied during the two periods of sensitivity on the total number of panicles developed per m3 , number of flowers and leaves per panicle, and the percentage of flowering inhibition in loquat trees cvs. ‘Algerie’ and ‘San Filipparo’ grown in Callosa d’En Sarrià (Spain) and Palermo (Italy). Values corresponding to years 2007 and 2008. Each value is the average of six replica of one tree each. Cv
Growing area
Date of treatment
Treatment (mg l−1 )
Panicles per m3
Algerie
Callosa
– 2007 Early June 2007 Early September – 2007 Early June 2007 Early September – 2008 Early June 2008 Early September
0 50 50 0 50 50 0 50 50
13.8 8.4 7.3 8.4 3.8 3.7 7.8 4.7 5.7
– 2008 Early June 2008 Early September
0 50 50
Palermo
Callosa
San Filipparo
Palermo
± ± ± ± ± ± ± ± ±
0,7 a 1.0 b 0.2 b 0.1 a 0.1 b 0.4 b 0.5 a 0.4 b 0.3 b
Flowers per panicle 113.4 114.7 116.6 81.4 75.8 60.1 126.4 116.5 111.0
6.1 ± 0.3 a 3.6 ± 0.2 b 3.2 ± 0.1 b
± ± ± ± ± ± ± ± ±
3.1 1.1 7.3 5.2 3.2 3.6 9.5 9.2 6.3
Leaves per panicle 8,4 7.9 9.9 8.2 6.2 6.6 8.3 8.6 9.2
70.5 ± 3.8 78.6 ± 3.2 82.1 ± 3.0
± ± ± ± ± ± ± ± ±
Inhibition (%)a
1.0 0.3 1.0 0.3 0.4 0.4 3.5 3.1 4.1
– 39.1 40.8 – 70.2 68.6 – 29.4 31.9
7.0 ± 0.5 8.3 ± 3.5 7.9 ± 0.4
– 33.9 36.3
Means followed by different letters in the same orchard are significantly different at P ≤ 0.05. a Percent of inhibition of total flowers per m3 . Table 2 Effect of gibberellic acid concentration locally applied to the apex in early September on the number of flowers per panicle in loquat tree cv. ‘Algerie’. Values correspond to three years of treatment at Callosa (Spain). Each value is the average of, at least, 15 panicles per tree and six trees. Concentration
2005
2006
2008
0 50 100 150 200 250
100.2 ± 9.2 a
133.9 ± 12.6 a
129.6 100.3 86.9 82.0 80.6 68.6
98.4 ± 10.2 b 66.4 ± 3.8 b
± ± ± ± ± ±
15.2 a 11.1 b 3.5 bc 5.0 bc 4.6 bc 4.0 c
Means followed by different letters in the same year are significantly different at P ≤ 0.05.
in either early June or early September (Table 1). The response was irrespective of the growing area, cultivar, and year. Nevertheless, differences in the number of flowers per panicle and leaves per shoot were not significantly modified by GA3 (Table 1). The morphological characteristics of the panicle, i.e. size, shape, and number of racemes, were not modified by GA3 either (data not shown). When 100–200 mg l−1 of GA3 was applied directly to the developing apex, instead of the whole tree, at a date close to flower differentiation (early September), all treated apexes developed into panicles, but the number of flowers per panicle was significantly reduced on average by 25–35% in cv. ‘Algerie’ (Table 2). This response was irrespective of the year of treatment. Fifty milligrams per litre of GA3 also significantly reduced the number of flowers per panicle, the response being between the control and higher concentrations. There was a greater reduction in the number of flowers per panicle (≈50%) when 250 mg l−1 of GA3 was applied (Table 2). Similar results were obtained when applied in early June (data not shown). Fifty milligrams per litre of GA3 applied to the whole tree also significantly reduced the number of premature shoots, both per current shoot and per m3 of canopy, irrespective of the date of
treatment (early June and early September), growing area, and cultivar (Table 3). Since premature shoots almost always develop into panicles, a reduction in their number by applying GA3 influences the reduction of total panicles per m3 of canopy. Higher concentrations of up to 200 mg l−1 gave rise to similar results (data not shown). This reduction of total panicles per m3 of canopy explains the reduction of flowering presented in Table 1. This drop in the number of flowers correlated significantly and negatively with the significant increase in the percent of fruit set (r = −0.566, P ≤ 0.01). This increase in fruit set compensated for the reduction in the number of flowers, and crop load (kg tree−1 ) (r = +0.157) and fruit weight (g) (r = +0.290) increased slightly but not significantly (Table 4). Time spent on hand thinning premature shoots was reduced from 17.3 min per worker in control trees to 6.5 and 6.1 min per worker in trees treated with GA3 of 50 mg l−1 at early June and early September, respectively. The number of vegetative shoots per m3 of canopy also reduced after applying 50 or 150 mg l−1 of GA3 in early June and early September (Fig. 3). A reduction of between 30 and 40% was recorded irrespective of the concentration applied and the date of treatment. Fruit characteristics were slightly altered by treatments (Table 5). The diameter of fruit at harvest increased up to 4% (45.6 mm) with regard to control (43.9 mm) for the best treatment. Flesh resistance to puncturing and TSS concentration were not significantly different at harvest; however, acid concentration of juice was significantly reduced; fruit colour was increased by treatments (Table 5). Since fruit size, colour and flesh ripeness are the factors that determine the appropriate harvesting date, their increase advanced commercial harvest (Table 4). 4. Discussion Gibberellins have been reported to inhibit flower bud initiation in many fruit tree species (Faust, 1989). Thus, gibberellins are apparently positioned in the flowering plant program to interfere
Table 3 Effects of 50 mg l−1 gibberellic acid applied during the two periods of sensitivity on the number of premature panicles (PP) and current panicles (P) in ‘Algerie’ and ‘San Filipparo’ loquat trees. Values for 2008. Each value is the average of six replica of one tree each. Palermo
Callosa
‘Algerie’
PP shoot−1 PP m−3 P m−3
‘San Filipparo’
‘Algerie’
Control
Early June
Early September
Control
Early June
Early September
Control
1.40 ± 0.23 a 4.89 ± 0.05 a 3.46 ± 0.02
0.85 ± 0.18 b 1.71 ± 0.04 b 2.03 ± 0.05
0.87 ± 0.16 b 1.69 ± 0.05 b 2.02 ± 0.05
1.31 ± 0.23 a 3.43 ± 0.17 a 2.60 ± 0.13
0.72 ± 0.12 b 1.50 ± 0.08 b 2.07 ± 0.12
0.85 ± 0.21 b 1.09 ± 0.01 b 2.15 ± 0.07
1.65 ± 0.08 a 0.43 ± 0.12 b 20.99 ± 1.67a 7.63 ± 1.93 b 12.66 ± 0.80a 19.08 ± 2.42
Means followed by different letters in the same line of the same variety are significantly different at P ≤ 0.05.
Early June
Early September 0.51 ± 0.14 b 7.60 ± 1.67 b 19.31 ± 3.73
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C. Reig et al. / Scientia Horticulturae 129 (2011) 27–31
Table 4 Effect of gibberellic acid (50 mg l−1 ) applied at early June or early September on the number of fruits per panicle and per m3 of canopy, yield, fruit weight and the percentage of fruits harvested at the first picking date in loquat tree cv. ‘Algerie’. Values are for the Callosa orchard (Spain) for 2008. Each value is the average of six replica of one tree each. Treatment date
Fruits per panicle
Fruits per m3
Yield (kg m−3 )
Fruit weight (g)
1st picking date Fruits (%)
Control Early June Early September
6.7 7.1 7.5
17.9 18.0 18.6
0.88 0.90 0.93
49.0 49.8 50.1
24.5 a 39.6 b 47.3 b
Means followed by different letters in the same column are significantly different at P ≤ 0.05. Table 5 Effect of gibberellic acid (50 mg l−1 ) applied at early June or early September on ‘Algerie’ loquat fruit characteristics at maturity. Values are for the Callosa orchard (Spain) for 2008. Each value is the average of 25 fruits and six trees. Treatment date
Diameter (mm)
Ø/ha
Resistance (N)
TSS (◦ Brix)
Acidity (%)
Control Early June Early September
43.9 a 45.0 ab 45.6 b
0.82 0.84 0.82
11.7 n.d. 11.7
9.9 n.d. 9.8
0.92 a n.d. 0.81 b
Colourb a
a/b
8.10 a 9.60 b 9.82 b
0.27 a 0.35 b 0.34 b
Means followed by different letters in the same column are significantly different at P ≤ 0.05. n.d.: not determined. a Diameter/height ratio. b Hunter co-ordinates.
with flower formation (Goldschmidt et al., 1997). Accordingly, the use of GA3 is a common practice for reducing flowering in citrus (El-Otmani et al., 2000), avocado (Salazar-García and Lovatt, 2000), apricot (Southwick et al., 1997), mango (Turnbull et al., 1996), pomes (McArtney and Li, 1998), and even in stone fruit trees (Painter and Stembridge, 1972; Southwick and Glozer, 2000; González-Rossia et al., 2006, 2007). Our results for loquat also show a reduction in flowering by means of GA3 . Two dates of sensitivity have been observed, from mid-May to early June, and from early August to the onset of flowering. The period in between has been identified as a summer rest period, as reported by Hueso et al. (2007). The first date of sensitivity coincides with that observed by Fatta del Bosco (1961) by means of defoliation and also under Mediterranean climatic conditions. The period also coincides with that reported by Luckwill (1970) in pome fruit trees when linking embryo growth and flowering intensity. The second date of sensitivity had not been identified until now. Yang et al. (2007) reduced
Vegetative shoots m -3
2
1,5
1
0,5
0
bb
a a
aa
0
50
150
Early June
aa
aa
50
150
Early September
GA3 (mg·l -1) and date of treatment Fig. 3. Effect of gibberellic acid concentration and date of treatment on vegetative shoots developed in ‘Algerie’ loquat tree. Standard errors are given as vertical bars. Values expressed per m3 of canopy. Each value is the average of six trees. Means with different letters differ significantly (P ≤ 0.05). Values are for the Callosa orchard (Spain) for 2008.
flowering intensity in loquat by applying GA3 in summer, but differences in climatic conditions, cultivars, treatment and, above all, tree age (two-year-old trees), make comparison difficult between their results and ours. According to loquat phenological growth stages, the first date of sensitivity can be associated with flower bud induction and the second date with flower bud differentiation. In our experiments, and for a given concentration, the number of flowers per panicle reduced significantly only when GA3 was applied directly to the apex, indicating that response depends on the total amount of active material applied per apex rather than the concentration. This effect is similar to that obtained for peaches and nectarines (González-Rossia et al., 2006). It is important to note that GA3 applied to whole trees significantly reduced flowering intensity because of a reduction in the number of panicles per m3 of canopy instead of the flowers per panicle. It has been reported that the inhibitory effect of GA3 on flowering takes place by interfering with induction and differentiation processes, thus reducing the number of floral buds per node, and the number of flowers per bud, respectively (Luckwill, 1970; Bradley and Crane, 1960; Monselise and Halevy, 1964; Guardiola et al., 1982) and by reducing bud sprouting (García-Luís et al., 1986). A combination of the reduction in the number of shoots per tree, the number of floral buds per node, and the number of flowers per bud explains the reduction in the number of flowers per tree in fruit tree species (Reig et al., 2006), including loquat. Nevertheless, how to explain GA3 reduces the total number of panicles per m3 of canopy when the apexes directly treated always develop a panicle? The major effect of GA3 observed in our experiments was caused by a significant reduction in the number of premature flowering shoots, rather than a reduction in the number of current panicles which remained unchanged. This effect of GA3 in reducing the number of sprouting lateral buds explains the reduction in the total number of panicles per m3 of canopy, as the same time as the development of current shoots into panicles remains unaffected. This effect also demonstrates that GA3 diminishes the proportion of buds that are able to sprout, thus reducing the number of buds ready to flower. The effect also affects vegetative shoots. Premature shoots are vigorous shoots and almost always develop into panicles bearing fruit of limited quality and no commercial interest. Accordingly, the use of GA3 in a loquat orchard seems a useful technique for reducing the number of this type of
C. Reig et al. / Scientia Horticulturae 129 (2011) 27–31
panicle per tree and so reducing their thinning costs (60%, approximately) and the number of limited quality fruit. In addition, an early reduction in the number of premature shoots enables the tree to maximize its capacity to increase fruit size (Weinberg, 1941). Our results also demonstrated that reduction of flowering increased the percentage of fruit set; however, both factors compensated and treatments did not increase the yield significantly. Nevertheless, it lacks commercial importance since fruit needs to be thinned to 2–4 fruit per panicle to reach enough quality (Agustí et al., 2000). Treatments, however, slightly increased fruit diameter and significantly improved skin colour and reduced juice acidity, even under no-thinning conditions of our experiments, allowing advancing harvesting date. In conclusion, our results show a new period of sensitivity to GA3 for reducing flowering in loquat trees after the summer rest period that has not previously reported. We also detected a period of sensitivity before the summer rest period that has been previously reported by other authors by means of defoliation. In both cases, flowering intensity is reduced because 50 mg l−1 or higher concentrations of GA3 prevent partially premature shoots from sprouting; this effect reduces thinning costs. Improved fruit quality allowed advancing date of harvest. Acknowledgements The authors would like to thank Mr. E. Soler and Mr. V. Martínez for technical assistance, to Cooperativa de Callosa d’En Sarrià for the orchard facilities provided, and to Centro de Lenguas (UPV) for revising the English. References Agustí, M., Juan, M., Almela, V., Gariglio, N., 2000. Loquat fruit size is increased through the thinning effect of naphthaleneacetic acid. Plant Growth Regul. 31, 167–171. Bradley, M.V., Crane, J.C., 1960. Gibberellin-induced inhibition of bud development in some species of Prunus. Science 131, 825–826. El-Otmani, M., Coggins Jr., C.W., Agustí, M., Lovatt, C., 2000. Plant growth regulators in citriculture: world current uses. Crit. Rev. Plant Sci. 19, 395–447. Fatta del Bosco, G., 1961. Indagini sull’epoca di differenziazione delle gemme nel nespolo del giappone. Riv. Ortoflorofrut. It. 86, 104–118. Faust, M., 1989. Physiology of Temperature Zone Fruit Trees. John Wiley & Sons, New York, USA.
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Gibberellic acid and flower bud development in loquat (Eriobotrya japonica Lindl.) Carmina Reig a , Vittorio Farina b , Giorgio Volpe b , Carlos Mesejo a , Amparo Martínez-Fuentes a , Francesca Barone b , Francesco Calabrese b , Manuel Agustí a,∗ a b
Instituto Agroforestal Mediterráneo, Universidad Politécnica de Valencia, Camino de Vera s/n, Valencia 46022, Spain Dipartimento DEMETRA, Facoltá di Agraria, Università degli Studi di Palermo, Viale delle Scienze, Ed. 4, Palermo 90128, Italy
a r t i c l e
i n f o
Article history: Received 1 September 2010 Accepted 23 February 2011 Keywords: Flowering Gibberellic acid Loquat Premature shoots Sprouting
a b s t r a c t The application of gibberellic acid (GA3 ) to the whole loquat tree from mid-May to early June and from early August to the onset of flowering, significantly reduced the number of premature flowering shoots per current shoot and per m3 of canopy, and so reduced the total number of panicles per m3 of canopy. The number of vegetative shoots per m3 of canopy was also significantly reduced by applying GA3 . The response depended on the concentration applied and produced optimal results at 50 mg l−1 . Differences in the number of flowers per panicle and leaves per shoot were not significantly modified by the treatment. Nevertheless, GA3 applied directly to the developing apex near to flower differentiation reduced the number of flowers per panicle by 25–35% and without modifying the morphological characteristics of the panicle. Results suggest that less sprouting of lateral buds was largely responsible for the reduction in flowering intensity caused by GA3 . Best treatments reduced thinning costs (60%, approximately) of premature flowering shoots, slightly increased fruit diameter and significantly improved fruit colour and juice quality, thus advancing harvest date. © 2011 Elsevier B.V. All rights reserved.
1. Introduction By 2006 world loquat fruit production was about 550 × 103 t, with a crop area exceeding 130 × 103 ha, China (450 × 103 t) and Spain (36 × 103 t) being the main producing countries, followed by Turkey (12 × 103 t), Japan and Pakistan (10 × 103 t) and others (Lin, 2007). Nowadays, Spain is the most important exporting country for fresh consumption. Loquat tree (Eriobotrya japonica Lindl.) belongs to the family Rosaceae, sub-family Maloideae. It is a subtropical evergreen fruit tree species native to southern China that, under Mediterranean climatic conditions, the tree flowers profusely in panicles, with many premature flowering shoots, in autumn and early winter, sets in a lower proportion in late winter, and ripens in spring. Polar gibberellins are known to inhibit flower bud initiation in many angiosperm species, including temperate fruit crops (Sedgley and Griffin, 1989). Luckwill (1970) in pome fruits hypothesized that gibberellins produced in seeds inhibit flower formation since they coincide with embryo growth in developing fruitlets. Accordingly, for many polycarpic plants, the application of gibberellic acid (GA3 ) during flower induction interrupts the floral process and partially reduces the intensity of flowering. This technique has been used efficiently in pome fruits
∗ Corresponding author. Tel.: +34 963879330; fax: +34 963877331. E-mail address: [email protected] (M. Agustí). 0304-4238/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2011.02.017
(Tromp, 2000), mangoes (Turnbull et al., 1996), avocados (SalazarGarcía and Lovatt, 2000), apricots (Southwick et al., 1997), citrus (Monselise and Halevy, 1964), peaches and nectarines (Painter and Stembridge, 1972) and plums (González-Rossia et al., 2006). The response has been related to the date of treatment, concentration applied, and the total amount of active material applied per tree (Painter and Stembridge, 1972; González-Rossia et al., 2007). Although abscisic acid (ABA) has been reported to play a dominant role in flower induction and differentiation in loquat, lower levels of gibberellins are needed for inflorescence primordium formation (Liu et al., 2007). Yang et al. (2007) reported that GA3 applied at an early stage of flower induction significantly reduced flowering rates in loquat trees, but the authors did not determine the appropriate concentration and date of treatment, thus more studies are needed to make the best use of GA3 . Fruit size is often too small for loquat market demand, and so producers increase size by severely thinning fruits and removing premature flowering shoots, which are vigorous and weak shoots, that produce fruits of limited quality. Moreover, although loquat trees flower profusely they are not subject to alternate bearing, and so it can be worthwhile reducing vigor and flowering to an appropriate level in order to cut thinning and pruning costs. The aims of this study were to determine the optimal GA3 concentration and the appropriate date(s) of treatment to reduce flowering in loquat trees and the effects on yield and fruit quality.
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2. Materials and methods
20 18
Panicles m -3
16 14 12 10 8 6 4
b
b
a
a
b
b
b
a
a
a
a
2 0
Date of treatment Fig. 1. Influence of gibberellic acid (150 mg l−1 ) on flowering intensity of cv. ‘Algerie’ loquat tree. Effect of treatment date. Standard errors are given as vertical bars. Values expressed per m3 of canopy. Each value is the average of six trees. Means with different letters differ significantly (P ≤ 0.05). Values are for the Callosa orchard (Spain) and for 2007.
3. Results Gibberellic acid significantly reduced the number of panicles per loquat tree, and the magnitude of the response depended on the date of treatment and the concentration applied. The application of 150 mg l−1 of GA3 from mid-May to early June and from early August to the onset of flowering (mid-September) significantly reduced the number of panicles per m3 of canopy of treated trees by 40–65% in comparison with the control trees (Fig. 1). Treatments applied in early May and from mid-June to mid-July did not significantly reduce the number of panicles per m3 of canopy in comparison with the control trees (Fig. 1). Fifty milligrams per litre of GA3 applied in early September also significantly reduced the number of panicles per m3 of canopy by 45% in comparison with the controls (Fig. 2). Increasing concentrations up to 200 mg l−1 did not significantly improve the response. Similar results were obtained when applying GA3 in early June (data not shown). An average reduction of between 40% and 60% of panicles per m3 of canopy, i.e. between 30% and 70% of flowers per m3 of canopy, was obtained in all the experiments that applied 50 mg l−1 of GA3 16 14 12
Panicles·m -3
Experiments were carried out using 20–25 year-old ‘Algerie’ and ‘San Filipparo’ loquat trees (E. japonica Lindl.), grafted onto loquat seedling and grown in commercial orchards in Callosa, Alicante, Spain (38◦ 39 N; 00◦ 07 W) and Palermo, Sicily, Italy (38◦ 04 N; 13◦ 25 E). Trees were pruned to vase shape, planted at 4 m × 3 m and 4 m × 5 m spacing, depending on the orchard, on a loamy clay soils, with drip irrigation. Fertilization, pest management, thinning, and pruning were in accordance with normal commercial practices. To determine the appropriate date of treatment, on different dates from early May to the onset of flowering (middle of September), 150 mg l−1 of GA3 (Arabelex-L; 1.6%, w/v; Aragro; Madrid, Spain) was sprayed fortnightly to whole trees of cv. ‘Algerie’ (Callosa). In early June and early September increasing concentrations of 0, 50,100,150 and 200 mg l−1 of GA3 were sprayed to whole trees of cvs. ‘Algerie’ (Callosa and Palermo) and ‘San Filipparo’ (Palermo) to determine the optimum concentration. In both experiments GA3 was sprayed by hand-gun at a pressure of 25–30 atm, wetting the trees to the point of run-off. In a separate experiment, 0, 50, 100, 150, 200 and 250 mg l−1 of GA3 were hand sprayed directly on the developing apex of 25 randomly selected shoots per tree of cv. ‘Algerie’ (Callosa) (5 ml of the GA3 solution per apex). In all cases, a non-ionic wetting agent (alkyl polyglycol ether) was added at a rate of 0.01%. In all the experiments, a randomized complete-block design with single tree plots of six replications each was performed. Experiments were run for four years (2005–2008) using different trees each year. Total vegetative shoots and total reproductive shoots per tree, including current shoots (shoots developing into principal panicles) and premature reproductive shoots were measured at 317 and 507 growth stages of the BBCH-scale (Martínez-Calvo et al., 1999), respectively. Results are expressed per m3 of canopy to standardize orchard and year values. Premature reproductive shoots are also expressed per current reproductive shoot. The numbers of leaves per shoot, racemes per panicle, and flowers per raceme were also recorded from 25 randomly selected main reproductive shoots per tree. The total number of flowers per m3 of canopy was calculated by multiplying the average number of flowers per panicle by the total number of panicles per m3 of canopy, thus determining the percentage of GA3 flowering inhibition with regard to the control trees. At the 701–702 growth stages of the BBCH-scale, the percentage of fruit set was evaluated by counting the number of fruits per panicle. At harvest, crop load and fruit characteristics were evaluated for the most effective treatments. Fruits were harvested according to appropriate commercial colour and size standards. The yield and number of fruits per tree were recorded on each harvest date, results being expressed per m3 of canopy. Number of fruits per panicle and average fruit weight were also recorded. At first picking date, 25-fruit samples were randomly picked from each treatment and each replication. Fruit firmness was assessed using a fruit pressure tester FT-011 (Fachini, Italy) with a 1.5-mm diameter flat cylinder probe. Total soluble solids (TSS) concentration of juice (◦ Brix) was assessed with a digital refractometer (Atago, Japan) and acid concentration analyzed by titration with 0.1 N NaOH. Fruit colour was established by determining the a and b Hunter co-ordinates. Three measurements were made per fruit at the equatorial area using a Minolta Chroma Meter CR-300. At flowering, all premature flowering shoots were manually thinned by removing the panicle. The time spent for thinning was measured per tree and per worker. Analysis of regression, or variance, was performed on the data (P ≤ 0.05) using the Student–Newman–Keuls’ multiple range test for means separation. Percentages were transformed to arcsin to homogenize the variance.
10 8 6 4
b
a
0
50
a
a
a
2 0
100
150
200
GA3 (mg l -1) Fig. 2. Effect of gibberellic acid concentration on flowering intensity of ‘Algerie’ loquat tree. Treatments were applied four months after shoot sprout (early September). Standard errors are given as vertical bars. Values expressed per m3 of canopy. Each value is the average of six trees. Means with different letters differ significantly (P ≤ 0.05). Values are for the Callosa orchard (Spain) for 2007.
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Table 1 Effects of gibberellic acid (50 mg l−1 ) applied during the two periods of sensitivity on the total number of panicles developed per m3 , number of flowers and leaves per panicle, and the percentage of flowering inhibition in loquat trees cvs. ‘Algerie’ and ‘San Filipparo’ grown in Callosa d’En Sarrià (Spain) and Palermo (Italy). Values corresponding to years 2007 and 2008. Each value is the average of six replica of one tree each. Cv
Growing area
Date of treatment
Treatment (mg l−1 )
Panicles per m3
Algerie
Callosa
– 2007 Early June 2007 Early September – 2007 Early June 2007 Early September – 2008 Early June 2008 Early September
0 50 50 0 50 50 0 50 50
13.8 8.4 7.3 8.4 3.8 3.7 7.8 4.7 5.7
– 2008 Early June 2008 Early September
0 50 50
Palermo
Callosa
San Filipparo
Palermo
± ± ± ± ± ± ± ± ±
0,7 a 1.0 b 0.2 b 0.1 a 0.1 b 0.4 b 0.5 a 0.4 b 0.3 b
Flowers per panicle 113.4 114.7 116.6 81.4 75.8 60.1 126.4 116.5 111.0
6.1 ± 0.3 a 3.6 ± 0.2 b 3.2 ± 0.1 b
± ± ± ± ± ± ± ± ±
3.1 1.1 7.3 5.2 3.2 3.6 9.5 9.2 6.3
Leaves per panicle 8,4 7.9 9.9 8.2 6.2 6.6 8.3 8.6 9.2
70.5 ± 3.8 78.6 ± 3.2 82.1 ± 3.0
± ± ± ± ± ± ± ± ±
Inhibition (%)a
1.0 0.3 1.0 0.3 0.4 0.4 3.5 3.1 4.1
– 39.1 40.8 – 70.2 68.6 – 29.4 31.9
7.0 ± 0.5 8.3 ± 3.5 7.9 ± 0.4
– 33.9 36.3
Means followed by different letters in the same orchard are significantly different at P ≤ 0.05. a Percent of inhibition of total flowers per m3 . Table 2 Effect of gibberellic acid concentration locally applied to the apex in early September on the number of flowers per panicle in loquat tree cv. ‘Algerie’. Values correspond to three years of treatment at Callosa (Spain). Each value is the average of, at least, 15 panicles per tree and six trees. Concentration
2005
2006
2008
0 50 100 150 200 250
100.2 ± 9.2 a
133.9 ± 12.6 a
129.6 100.3 86.9 82.0 80.6 68.6
98.4 ± 10.2 b 66.4 ± 3.8 b
± ± ± ± ± ±
15.2 a 11.1 b 3.5 bc 5.0 bc 4.6 bc 4.0 c
Means followed by different letters in the same year are significantly different at P ≤ 0.05.
in either early June or early September (Table 1). The response was irrespective of the growing area, cultivar, and year. Nevertheless, differences in the number of flowers per panicle and leaves per shoot were not significantly modified by GA3 (Table 1). The morphological characteristics of the panicle, i.e. size, shape, and number of racemes, were not modified by GA3 either (data not shown). When 100–200 mg l−1 of GA3 was applied directly to the developing apex, instead of the whole tree, at a date close to flower differentiation (early September), all treated apexes developed into panicles, but the number of flowers per panicle was significantly reduced on average by 25–35% in cv. ‘Algerie’ (Table 2). This response was irrespective of the year of treatment. Fifty milligrams per litre of GA3 also significantly reduced the number of flowers per panicle, the response being between the control and higher concentrations. There was a greater reduction in the number of flowers per panicle (≈50%) when 250 mg l−1 of GA3 was applied (Table 2). Similar results were obtained when applied in early June (data not shown). Fifty milligrams per litre of GA3 applied to the whole tree also significantly reduced the number of premature shoots, both per current shoot and per m3 of canopy, irrespective of the date of
treatment (early June and early September), growing area, and cultivar (Table 3). Since premature shoots almost always develop into panicles, a reduction in their number by applying GA3 influences the reduction of total panicles per m3 of canopy. Higher concentrations of up to 200 mg l−1 gave rise to similar results (data not shown). This reduction of total panicles per m3 of canopy explains the reduction of flowering presented in Table 1. This drop in the number of flowers correlated significantly and negatively with the significant increase in the percent of fruit set (r = −0.566, P ≤ 0.01). This increase in fruit set compensated for the reduction in the number of flowers, and crop load (kg tree−1 ) (r = +0.157) and fruit weight (g) (r = +0.290) increased slightly but not significantly (Table 4). Time spent on hand thinning premature shoots was reduced from 17.3 min per worker in control trees to 6.5 and 6.1 min per worker in trees treated with GA3 of 50 mg l−1 at early June and early September, respectively. The number of vegetative shoots per m3 of canopy also reduced after applying 50 or 150 mg l−1 of GA3 in early June and early September (Fig. 3). A reduction of between 30 and 40% was recorded irrespective of the concentration applied and the date of treatment. Fruit characteristics were slightly altered by treatments (Table 5). The diameter of fruit at harvest increased up to 4% (45.6 mm) with regard to control (43.9 mm) for the best treatment. Flesh resistance to puncturing and TSS concentration were not significantly different at harvest; however, acid concentration of juice was significantly reduced; fruit colour was increased by treatments (Table 5). Since fruit size, colour and flesh ripeness are the factors that determine the appropriate harvesting date, their increase advanced commercial harvest (Table 4). 4. Discussion Gibberellins have been reported to inhibit flower bud initiation in many fruit tree species (Faust, 1989). Thus, gibberellins are apparently positioned in the flowering plant program to interfere
Table 3 Effects of 50 mg l−1 gibberellic acid applied during the two periods of sensitivity on the number of premature panicles (PP) and current panicles (P) in ‘Algerie’ and ‘San Filipparo’ loquat trees. Values for 2008. Each value is the average of six replica of one tree each. Palermo
Callosa
‘Algerie’
PP shoot−1 PP m−3 P m−3
‘San Filipparo’
‘Algerie’
Control
Early June
Early September
Control
Early June
Early September
Control
1.40 ± 0.23 a 4.89 ± 0.05 a 3.46 ± 0.02
0.85 ± 0.18 b 1.71 ± 0.04 b 2.03 ± 0.05
0.87 ± 0.16 b 1.69 ± 0.05 b 2.02 ± 0.05
1.31 ± 0.23 a 3.43 ± 0.17 a 2.60 ± 0.13
0.72 ± 0.12 b 1.50 ± 0.08 b 2.07 ± 0.12
0.85 ± 0.21 b 1.09 ± 0.01 b 2.15 ± 0.07
1.65 ± 0.08 a 0.43 ± 0.12 b 20.99 ± 1.67a 7.63 ± 1.93 b 12.66 ± 0.80a 19.08 ± 2.42
Means followed by different letters in the same line of the same variety are significantly different at P ≤ 0.05.
Early June
Early September 0.51 ± 0.14 b 7.60 ± 1.67 b 19.31 ± 3.73
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Table 4 Effect of gibberellic acid (50 mg l−1 ) applied at early June or early September on the number of fruits per panicle and per m3 of canopy, yield, fruit weight and the percentage of fruits harvested at the first picking date in loquat tree cv. ‘Algerie’. Values are for the Callosa orchard (Spain) for 2008. Each value is the average of six replica of one tree each. Treatment date
Fruits per panicle
Fruits per m3
Yield (kg m−3 )
Fruit weight (g)
1st picking date Fruits (%)
Control Early June Early September
6.7 7.1 7.5
17.9 18.0 18.6
0.88 0.90 0.93
49.0 49.8 50.1
24.5 a 39.6 b 47.3 b
Means followed by different letters in the same column are significantly different at P ≤ 0.05. Table 5 Effect of gibberellic acid (50 mg l−1 ) applied at early June or early September on ‘Algerie’ loquat fruit characteristics at maturity. Values are for the Callosa orchard (Spain) for 2008. Each value is the average of 25 fruits and six trees. Treatment date
Diameter (mm)
Ø/ha
Resistance (N)
TSS (◦ Brix)
Acidity (%)
Control Early June Early September
43.9 a 45.0 ab 45.6 b
0.82 0.84 0.82
11.7 n.d. 11.7
9.9 n.d. 9.8
0.92 a n.d. 0.81 b
Colourb a
a/b
8.10 a 9.60 b 9.82 b
0.27 a 0.35 b 0.34 b
Means followed by different letters in the same column are significantly different at P ≤ 0.05. n.d.: not determined. a Diameter/height ratio. b Hunter co-ordinates.
with flower formation (Goldschmidt et al., 1997). Accordingly, the use of GA3 is a common practice for reducing flowering in citrus (El-Otmani et al., 2000), avocado (Salazar-García and Lovatt, 2000), apricot (Southwick et al., 1997), mango (Turnbull et al., 1996), pomes (McArtney and Li, 1998), and even in stone fruit trees (Painter and Stembridge, 1972; Southwick and Glozer, 2000; González-Rossia et al., 2006, 2007). Our results for loquat also show a reduction in flowering by means of GA3 . Two dates of sensitivity have been observed, from mid-May to early June, and from early August to the onset of flowering. The period in between has been identified as a summer rest period, as reported by Hueso et al. (2007). The first date of sensitivity coincides with that observed by Fatta del Bosco (1961) by means of defoliation and also under Mediterranean climatic conditions. The period also coincides with that reported by Luckwill (1970) in pome fruit trees when linking embryo growth and flowering intensity. The second date of sensitivity had not been identified until now. Yang et al. (2007) reduced
Vegetative shoots m -3
2
1,5
1
0,5
0
bb
a a
aa
0
50
150
Early June
aa
aa
50
150
Early September
GA3 (mg·l -1) and date of treatment Fig. 3. Effect of gibberellic acid concentration and date of treatment on vegetative shoots developed in ‘Algerie’ loquat tree. Standard errors are given as vertical bars. Values expressed per m3 of canopy. Each value is the average of six trees. Means with different letters differ significantly (P ≤ 0.05). Values are for the Callosa orchard (Spain) for 2008.
flowering intensity in loquat by applying GA3 in summer, but differences in climatic conditions, cultivars, treatment and, above all, tree age (two-year-old trees), make comparison difficult between their results and ours. According to loquat phenological growth stages, the first date of sensitivity can be associated with flower bud induction and the second date with flower bud differentiation. In our experiments, and for a given concentration, the number of flowers per panicle reduced significantly only when GA3 was applied directly to the apex, indicating that response depends on the total amount of active material applied per apex rather than the concentration. This effect is similar to that obtained for peaches and nectarines (González-Rossia et al., 2006). It is important to note that GA3 applied to whole trees significantly reduced flowering intensity because of a reduction in the number of panicles per m3 of canopy instead of the flowers per panicle. It has been reported that the inhibitory effect of GA3 on flowering takes place by interfering with induction and differentiation processes, thus reducing the number of floral buds per node, and the number of flowers per bud, respectively (Luckwill, 1970; Bradley and Crane, 1960; Monselise and Halevy, 1964; Guardiola et al., 1982) and by reducing bud sprouting (García-Luís et al., 1986). A combination of the reduction in the number of shoots per tree, the number of floral buds per node, and the number of flowers per bud explains the reduction in the number of flowers per tree in fruit tree species (Reig et al., 2006), including loquat. Nevertheless, how to explain GA3 reduces the total number of panicles per m3 of canopy when the apexes directly treated always develop a panicle? The major effect of GA3 observed in our experiments was caused by a significant reduction in the number of premature flowering shoots, rather than a reduction in the number of current panicles which remained unchanged. This effect of GA3 in reducing the number of sprouting lateral buds explains the reduction in the total number of panicles per m3 of canopy, as the same time as the development of current shoots into panicles remains unaffected. This effect also demonstrates that GA3 diminishes the proportion of buds that are able to sprout, thus reducing the number of buds ready to flower. The effect also affects vegetative shoots. Premature shoots are vigorous shoots and almost always develop into panicles bearing fruit of limited quality and no commercial interest. Accordingly, the use of GA3 in a loquat orchard seems a useful technique for reducing the number of this type of
C. Reig et al. / Scientia Horticulturae 129 (2011) 27–31
panicle per tree and so reducing their thinning costs (60%, approximately) and the number of limited quality fruit. In addition, an early reduction in the number of premature shoots enables the tree to maximize its capacity to increase fruit size (Weinberg, 1941). Our results also demonstrated that reduction of flowering increased the percentage of fruit set; however, both factors compensated and treatments did not increase the yield significantly. Nevertheless, it lacks commercial importance since fruit needs to be thinned to 2–4 fruit per panicle to reach enough quality (Agustí et al., 2000). Treatments, however, slightly increased fruit diameter and significantly improved skin colour and reduced juice acidity, even under no-thinning conditions of our experiments, allowing advancing harvesting date. In conclusion, our results show a new period of sensitivity to GA3 for reducing flowering in loquat trees after the summer rest period that has not previously reported. We also detected a period of sensitivity before the summer rest period that has been previously reported by other authors by means of defoliation. In both cases, flowering intensity is reduced because 50 mg l−1 or higher concentrations of GA3 prevent partially premature shoots from sprouting; this effect reduces thinning costs. Improved fruit quality allowed advancing date of harvest. Acknowledgements The authors would like to thank Mr. E. Soler and Mr. V. Martínez for technical assistance, to Cooperativa de Callosa d’En Sarrià for the orchard facilities provided, and to Centro de Lenguas (UPV) for revising the English. References Agustí, M., Juan, M., Almela, V., Gariglio, N., 2000. Loquat fruit size is increased through the thinning effect of naphthaleneacetic acid. Plant Growth Regul. 31, 167–171. Bradley, M.V., Crane, J.C., 1960. Gibberellin-induced inhibition of bud development in some species of Prunus. Science 131, 825–826. El-Otmani, M., Coggins Jr., C.W., Agustí, M., Lovatt, C., 2000. Plant growth regulators in citriculture: world current uses. Crit. Rev. Plant Sci. 19, 395–447. Fatta del Bosco, G., 1961. Indagini sull’epoca di differenziazione delle gemme nel nespolo del giappone. Riv. Ortoflorofrut. It. 86, 104–118. Faust, M., 1989. Physiology of Temperature Zone Fruit Trees. John Wiley & Sons, New York, USA.
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