EFFECT OF SHADE SCREEN ON PRODUCTION, FRUIT QUALITY AND GROWTH PARAMETERS OF 'FINO 49' LEMON TREES GRAFTED ON CITRUS MACROPHYLLA AND SOUR ORANGE

Spain is the second largest lemon fruit producer in the world and one of the largest exporters. About 80% of the production is located in the arid southeast regions. In these areas, shade screens reduce leaf temperature and light intensity at midday in summer and spring periods, resulting in increased photosynthetic leaf water use efficiency (WUE_phy = A_CO2/E_leaf). In this work we analyzed the effect of shading with Aluminet-50 screen (which reduces about 50% the incident photosynthetically active radiation) on the production, fruit quality, leaf mineral composition, and growth parameters of ‘Fino 49’ lemon trees grafted on two rootstocks, Citrus macrophylla (CM) and sour orange (SO) over a four-year period (2008-2011), using six-year old trees at the beginning of the experiment. Shade screen had similar effect on trees grafted on either rootstock. Shading increased tree height and canopy perimeter producing trees with about 60% larger canopy volume than control trees grown under full sunlight. However, while trees on Citrus macrophylla and sour orange under full sunlight produced 81 and 45 kg/tree, similar trees under shade produced 70 and 33 kg/tree, respectively. Shading affected the physical characteristics of the fruits from trees on Citrus macrophylla with fruits under shade being smaller than fruits from trees under full sunlight. Leaf water potential (Ѱ_w) was greater in trees under shade screen. Leaf mineral concentration was affected by shading that decreased B and Cu on either rootstock.