Iron nutrition of fruit tree crops
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Although iron (Fe) needs by fruit trees are relatively low, Fe deficiency represents the main constraint for successful cultivation of fruit tree crops in calcareous and alkaline soils. Kiwifruit, peach and pear, several Citrus and Vaccinium spp. are very susceptible to Fe chlorosis, cherry and grape are relatively susceptible and apple is relatively tolerant. The typical Fe deficiency symptoms, the interveinal leaf yellowing starting from apical leaves which may progress and turn into necrosis, exhibit a temporal and spatial variability, requiring an efficient diagnosis systems. Iron deficiency reduces yields and fruit quality and forces growers to adopt measures for controlling and preventing the development of Fe chlorosis. The most widely adopted Fe fertilizers are the synthetic chelates, that do not represent a sustainable management approach, due to the cost and their potential pollution of the soil and water environments. The genetic approach to prevent chlorosis is based on the choice of tolerant rootstocks, which are known to activate mechanisms for improving Fe uptake under condition of low Fe availability. Unfortunately, for several fruit crops iron tolerant rootstocks have some adverse agronomic characteristics (e.g. excessive vigor) which make their adoption unlikely in modern fruit industry. Alternatives to Fe chelates have been identified and need to be tested and adapted to different conditions: they should aim at the improvement of soil environment for root growth and activity and/or to the enhancement of Fe availability in the soil and in the tree.