Studies on apple physiology by managing light quality with photoselective nets

The objectives of this thesis were to seek possible improvements of physiological performances in apple, when affecting the light quality of the orchard. During fruit developmental stage, a yellow net seems more prone to give the higher growth rates. On the other hand, red and blue nets slowed growth. The reasons may be found in the different scattered light and in the transmission of PAR, which impacted on photomorphogenic responses. It is possible that spur leaves of those fruit were in a less suitable condition to be photosynthetically efficient. Water transport, i.e. sap flow, was influenced by light spectrum modification. Based on the obtained results, the daily patters of sap transport indicated a red photoselective net less suitable and a white net more apt, for commercial purposes, at the orchard level. When considering fruit growth, a blue photoselective net appeared more convenient, as fruit weight gain during the summer was higher, despite slightly higher water flows compared to a white net. As for carbohydrate dynamics during dormancy and before bud break, the soil effect was too strong to generate distinctions among different light environments. However, canopy air temperature was influenced, being warmer under a white net and colder under a blue one. The dynamics of carbohydrate translocation was more evident when completely isolating apple cuttings, under the effect of different spectrum. A blue net will delay flowering, compared to a white one, while consuming more starch, for metabolic processes, leaving a red net with an intermediate behaviour. In this specific case, the results could be due to the influence of spectrum on photoreceptors activity. Future studies could take into account these differences and endeavour to modify soil temperature and test photoselective netting during dormancy, to evaluate how spectrum can influence carbohydrate translocation in the field and repercussions on bloom quality.