Agronomic means for the control of iron chlorosis in deciduous fruit plants

Iron deficiency induced chlorosis represents the main nutritional disorder in fruit tree orchards grown on calcareous and/or alkaline soils. Until rootstocks tolerant to Fe deficiency chlorosis are available for most susceptible fruit species, the agronomic means of preventing or curing Fe deficiency chlorosis will be considered of utmost importance by fruit growers. Chlorosis of fruit trees has been successfully controlled through foliar or soil applications of Fe chelates, which are expensive and have to be applied annually. In this paper results of research carried out within an EU joint research project are reported, where the effectiveness of alternative, low-input, environmentally friendly management techniques to control Fe deficiency chlorosis has been tested in established kiwifruit, peach and pear orchards located in the Po Valley (Italy), in the Ebro Valley (Spain) and in the area of Imathia (Greece). Iron sulphate supply to the soil proved to be effective only if applied together with high amounts of organic matter such as compost or manure. Promising results in preventing chlorosis were obtained by sowing a mixture of graminaceous species along the tree row and supplying them with Fe sulphate. Laboratory tests indicated that long lasting decreases of pH in calcareous soils are difficult to achieve. We have also followed two approaches using foliar sprays: 1) testing a variety of compounds which may activate the Fe pool likely present in chlorotic leaves (citric, sulphuric, ascorbic and indole-3-acetic acid) and 2) applying Fe sources alternative to synthetic Fe chelates. Sprays aiming to activate the Fe pools in a chlorotic leaf were generally effective, although rarely caused a full recovery. This suggests that inactivation of Fe occurs outside the mesophyll cells. Sprays of Fe sulphate in all the crops tested showed similar or even higher regreening effect than FeDTPA.This study was mainly supported by the AIR3-CT94-1973 project. The >Region Emilia Romagna-C.R.P.V.> grants to B. Marangoni contributed to funding the research carried out in Italy and the grants AGF94-0770 and AGF97-1177 to A. Abadía contributed to funding those carried out in Spain.Peer Reviewe

Using the flower Fe concentration for estimating chlorosis status in fruit tree orchards: A summary report

The mineral analysis of leaves from deciduous fruit trees is not always useful for assessing the Fe nutritional status, because Fe-chlorotic leaves may have considerable concentrations of total Fe (the >Fe-chlorosis paradox>). Another major problem with this approach is that at the recommended time for leaf sampling it is unlikely that any corrective measure could improve crop yield and/or fruit quality. The analysis of flowers, that can be completed in various species before leaves have emerged, has been proposed as a tool to predict the Fe status of the tree later in the year. In this report we summarize the results obtained so far using this technique, in several experiments made in different Mediterranean countries such as Spain, Greece, Italy and Portugal. In peach orchards showing chlorosis the Fe concentration in whole flowers is usually correlated with the chlorophyll concentration later in the year. Preliminary experiments in other crops, such as orange, indicate that the Fe concentration in flowers is also correlated with the leaf chlorophyll content. Furthermore, a peach cultivar grafted on an Fe-efficient rootstock had a higher flower Fe concentration than when grafted on an Fe-inefficient one. This may indicate that the Fe concentration in flowers could be a good estimate of the mobile or active Fe fraction in the tree. Problems for a general application of this technique for diagnosis and prognosis of the Fe nutritional status of trees are discussed.Peer Reviewe