PHYSIOLOGIA PLANTARUM 91; 339-345. 1994 Copynsht ©pin,whsiaPb,mrun, I994 Primed in Denmark - all rights reserved Light environment, growtli and morphogenesis in a peach tree canopy R. Baraidi, F. Rossi., O. Facini, F. iFasolo, A. Rotondi, M. Magli and F. Nerozzi Baraldi, R., Rossi, F, Facini, O., Fasolo, F, Rotondi, A., Magli, M. and Nerozzi, F. 1994. Light environment, growth and nnorphogenesis in a peach tree canopy. - Physiol. Plant. 91; 339-345. Morphogenic and growth processes were studied in relation to photosynthetically active radiation (PAR), and red, far red and blue spectral bands monitored at three different heights of a peach canopy during the vegeiative season. The P/VR intercepted by the bottom of the tree was significantly lower than that at the top, and blue fluence rate changed with height and season in a manner similar to PAR. Phytochrome photoequilibria indicated spatial and temporal differences in the three layers of the canopy; significantly lower values were detected at the bottom in correspondence with the maximum leaf area index. In this layer, a stimulation of internode elongation and a decrease of flower density were detected. Higher shoot growth rates and about double number of lateral shoots were found at the top ofthe canopy, where a greater number of sun leaves was present. Possible explanations in terms of different growth strategies induced by shade, depletion of blue, and low pbytochi'ome levels at the bottom of the canopy are given. Key words - Light, peach, photomorphogenesis, phytochrome, Prunus persica. R. Baraidi (corresponding author) et ai, Centra Studi Tecnica Frutticola, Consiglio Nazionale deile Ricerche, Via Gohetti 10}. 1-40129 Bologna, Italy. This paper is part of the contributions to the European Symposium Photomoiphogene- sis in Plants, held in Tirrenia, Pisa, Italy, 11-15 July, 1993. tions (Baraidi et al. 1992). Phj'tochrome control of leaf area and leaf shape has also been reported in herbaceotjs Photomorphogenic processes in such complex canopies species (Kasperbauer 1971, Sanchez 1971, McLaren and as those of fruit trees growing in the field are difficult to Smith 1978) and in woody plants (Kwesiga and Grace elucidate becatise of the probletns posed by the ways in 1986, Baraidi et al. 1992). Stimulation of shoot elonga- which light interacts with a variable horizontal and verti- tion and suppression of lateral branching have been found cai leaf area distribtition. Even the specific role of light in many woody plants when grown under shade and low quality in physiological processes is problematic because R/FR ratio (Kwesiga and Grace 1986, Warrington et al. of the scant knowledge of photoreceptors involved in 1988). plant grovi'th and fruit development. Changes in morph- Flower initiation and differentiation in fruit trees ologica] parameters like internode length in herbaceous seems also to be linked to a light-related signal. Light is and woody species are attributed to photoreceptor activ- known to play a significant role in this process; the light ity (Kwesiga and Grace 1986, Child and Smith 1987, inside the canopy generally drops to 30% (or less) of that Kasperbauer 1987, Bain and Attridge 1988, Warrington outside, thereby sharply inhibiting flower bud develop- et al. 1988, Ballare et al. 1991). An involvement of two ment (Cain 1971). Although this phenomenon has repeat- photoreceptors has been found in stem elongation of edly been ascribed to reduced photosynthesis (Jackson Prunus cerasus plantlets grown tinder controlled condi- 1980, Marini and Sower 1990), observations reported in Received II Aagust, 1993; revised 13 December, 1993 23 Physiol. Plani. 9t. 1994 339