LIGHT ENVIRONMENT WITHIN MATURE RABBITEYE BLUEBERRY CANOPIES INFLUENCES FLOWER BUD FORMATION
2009; International Society for Horticultural Science; Issue: 810 Linguagem: Inglês
10.17660/actahortic.2009.810.61
ISSN2406-6168
AutoresPaola Yañez, J.B. Retamales, Gustavo A. Lobos, Alejandro del Pozo,
Tópico(s)Greenhouse Technology and Climate Control
ResumoBlueberries are an understory species. Light interception and distribution within the canopy impact on fruit quantity and quality. The aim of this experiment was to characterize light distribution in rabbiteye blueberries cv. Choice and determine its impact on flower bud formation. Fourteen-year-old plants growing in a commercial planting in Coihueco, Chile (36o21 S; 71o50 W) were used. Photosynthetically active radiation (PAR) was measured on sunny days (December 2006 to March 2007), with a ceptometer at 7 levels separated every 20 cm from the top edge of the canopy. In July 2007, four canes from each plant were removed from the center (interior) of four plants (reps) and the number of flower buds present in each 20 cm section was measured. Full sun PAR was 1,200-1,693 μmol m s. Data, expressed relative to light levels on top of the canopy as percent full sun (% FS), show a strong reduction in PAR towards the canopy center; thus light at 20 cm from the top was 51-80% FS, 39-58% FS at 40 cm, 17-37% FS at 60 cm, and only 9-18% FS at 80 cm. The first 60 cm from the canopy top contained 63.7% of total flower buds, while the first 80 cm accumulated 83% of this total. Only 13.4% of flower buds were formed in the basal 120 cm when light was less than 66 and 96 μmol m s in December and January, respectively. Light is reduced as distance from canopy edge increases. On each position there is a clear relationship between light availability and flower bud numbers, which implies that growers should maintain certain light levels to allow flower bud formation within the canopy of rabbiteye blueberries. INTRODUCTION Although blueberries are understory plants, the light environment in which the plant develops has an important impact on production levels. Light interception and its distribution within the canopy impact strongly on fruit yield and quality (Johnson and Lakso, 1991). There is a direct relationship between the amount of light intercepted by an orchard and its yield potential (Maib et al., 1996). Furthermore, light has an important role in plant development, especially in bud differentiation. In blueberries, the vegetative growth and flower bud development are reduced under low light intensity (Gough, 1994). The aim of this experiment was to characterize light distribution in rabbiteye blueberries cv. Choice and determine its impact on flower bud formation. MATERIALS AND METHODS The experiment was conducted in a commercial planting of rabbiteye blueberries in the Coihueco area (36o21 S; 71o50 W), Chile. Fourteen-year-old plants of cultivar Choice planted at 3 x 1.2 m were used. Plants were drip irrigated according to environmental demand established through a Class A evaporimeter. Each year winter pruning removed weak, sick and the oldest 3-5 canes (>5 year-old). Since plants formed an edge within the row, five experimental units of similar vigor and condition were chosen; each unit consisted of the growth developed 0.6 m on each side of the plant center. Photosynthetically active radiation (PAR) was measured on sunny days between December 2006 and March 2007, with a ceptometer (Sunfleck, Decagon, USA) at 7 levels separated every 20 cm from the top edge of the canopy. Plant rows were NorthSouth oriented and PAR measurements with the ceptometer were taken on both sides of Proc. IX IS on Vaccinium Eds.: K.E. Hummer et al. Acta Hort. 810, ISHS 2009 472 the row (East and West) in two positions for each level: canopy edge and canopy interior. Finally, PAR values from West and East side for each position in a given level were averaged. In July 2007 four canes from each plant were cut and removed from the center of five plants (reps), and the number of flower buds present within each 20 cm section was recorded. RESULTS AND DISCUSSION PAR values ranged from 1,200 to 1,693 μmol m s (full sunlight) and from 1,322 to 1,559 μmol m s (top of canopy). There was a strong reduction in PAR closer to the base of the canopy (Table 1). When data are expressed relative to light levels on top of the canopy (percent full sun or % FS), the reduction in PAR is clearly seen; thus light was 51-80% FS at 20 cm from the top, 39-58% FS at 40 cm, 17-37% FS at 60 cm, and only 918% FS at 80 cm. This pattern of light distribution was similar for the three measurements (December, January and March). The number of flower buds in the different portions of the canopy showed a close relationship with the light conditions (Fig.1). The first 60 cm from the canopy top contained 63.7 % of total flower buds, while the first 80 cm accumulated 83% of this total. Only 13.4 % of the flower buds were formed in the basal 120 cm when light was less than 66 and 96 μmol m s in December and January, respectively. Thus, reduction in light intensity has an important effect on flower bud formation, as was demonstrated in experiments where outdoor light intensity was reduced by 50% and a marked reduction in blueberry growth and fruit production was observed (Eck et al., 1990). The situation can be improved with horticultural practices as has been demonstrated with the use of growth inhibitors in pears (Elfving et al., 2003) CONCLUSIONS Our data shows that light availability within blueberry plants is reduced as distance from canopy top is increased. Moreover, these data evidence a clear relationship between light availability and flower bud formation, and stresses the need to maintain certain light levels during the growing season to allow flower bud formation in blueberries. The light distribution characterized in this experiment is representative of adult rabbiteye blueberry orchards in central Chile. Under these conditions, blueberry growers would need to modify the architecture of the canopy in order to improve light distribution and develop a greater productive volume of the plants under our environmental and management conditions. ACKNOWLEDGEMENTS We express our gratitude to Programa Bicentenario de Ciencia y Tecnologia (PBCT-Conicyt, Chile) and Universidad de Talca for funding this work, and to Juan Esteban Costa (Berries Cato S.A.), for allowing us the use of the orchard for the experiment. Literature Cited Eck, P., Gough, R.E., Hall, I.V. and Spiers, J.M. 1990. Blueberry management. p.273333. In: G. J. Galletta and D. G. Himelrick (eds.), Small Fruit Crop Management. Prentice-Hall, New Jersey. Elfving, D.C., Lombardini, L., McFerson, J.R., Drake, S.R., Faubion, D.F., Auvil, T.D., Van Ee, G. and Visser, D.B. 2003. Effects of directed applications of prohexadione Ca to tops of mature pear trees on shoot growth, light penetration, pruning and fruit quality. J. Am. Pom. Soc. 57: 45-57. Gough, R.E.1994. The Highbush blueberry and its management. Food Products Press, New York. Johnson, R.S. and Lakso, A.N. 1991. Approaches to modelling light interception in orchards. HortScience 26: 1002-1004.
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