Bruno Marangoni

Agronomic means for the control of iron deficiency chlorosis in deciduous fruit trees

Abstract 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.

Iron source affects iron reduction and re‐greening of kiwifruit (Actinidia deliciosa) leaves

Abstract Among deciduous fruit plants, kiwifruit (Actinidia deliciosa) is one of the most susceptible to iron (Fe) chlorosis. To develop effective means for overcoming Fe chlorosis, it is of upmost importance to gain information about the reduction of Fe by leaf tissues, especially under conditions that lead to chlorosis. In the present study we have characterised the leaf Fe‐chelate reductase (FCR) in Fe sufficient and Fe deficient kiwifruit leaves and for the first time tested the hypothesis that FeIII‐malate is a suitable source of Fe for FCR, in addition to FeIII‐citrate. Under field conditions, we have also tested the re‐greening effects caused by the foliar application of different Fe sources, including FeIII‐malate, FeIII‐citrate, FeIII‐DTPA and an FeII source (FeSO4 + aminoacid‐polypeptide mixture) on chlorotic leaves. The results demonstrated that, similarly to other species, mesophyll tissues of A. deliciosa leaves are able to perform an enzymatic Fe reduction prior to Fe uptake. Plasma membrane enriched material extracted from Fe sufficient leaves reduced FeIII‐malate and FeIII‐citrate. The pH optimum was 6.0–6.2 for FeIII‐malate and 6.5 for FeIII‐citrate. The substrate‐dependence showed higher affinity for malate than for citrate. In contrast to the root level, the activity of the FCR of kiwifruit leaves was not enhanced under Fe deficiency. On the contrary, after two weeks of Fe depletion, the reduction of FeIII‐citrate was 4.5‐fold lower in the Fe deficient plants than in the Fe sufficient ones, while the reduction of FeIII‐malate was not significantly affected. Under field conditions, the Fe solutions caused regreening of chlorotic leaves, whose intensity and duration varied according to Fe source and Fe concentration. Among the treatments, the highest re‐greening effect was caused by FeIII‐DTPA and especially by the FeII source. FeIII‐citrate and FeIII‐malate were less effective in stimulating chlorophyll formation. All treatments increased leaf Fe concentration and content. Although less Fe from malate than from citrate penetrated into the leaves, the re‐greening effect from FeIII‐malate was intermediate between that of FeIII‐DTPA and the one caused by FeIII‐citrate. The results suggest that if FeIII‐malate can reach the plasmamembrane it provides a good source of Fe for leaf Fe uptake.

Nitrogen fertilization management in orchards to reconcile productivity and environmental aspects

Nitrogen fertilization in orchards of Emilia-Romagna Region, (Italy) was based in the past on excessive, not split, applications often supplied late in winter; the NUE (Nitrogen Use Efficiency) was therefore low and the risk of nitrate leaching was high. This paper summarizes the studies conducted in the last 10 years at the Department of Horticulture and Forestry of the University of Bologna aimed to develop a more rational use of nitrogen in orchards and vineyards. Root escavation of mature trees revealed that the use of localized irrigation (drip or microjet) causes a concentration of roots in the area wetted by the emitters. In such a situation, band applications of N to the tree row may allow a reduction of amounts of N fertilizer, while widespread applications, especially if the orchard soil is tilled, lead to an accumulation of nitrates in the alley. Results of several field trials where increasing N rates were applied indicate that the kind of response to N supply depends on the presence in soil of natural sources of nitrogen. This fact clearly stresses the necessity of evaluate the N status of an orchard before N fertilization. Rapid estimation of leaf chlorophyll by portable instruments is a promising index of leaf N concentration, only provided that calibration is made for each cultivar. A method, currently under testing in orchards and vineyards of Emilia-Romagna, is proposed here to adjust N fertilizer rates to the demand of the crop and to the level of available N in soil as determined in soil or soil solution samples.

Response to iron‐deficiency stress of pear and quince genotypes 1

Abstract Roots of iron (Fe)‐efficient dicots react to Fe‐deficiency stress by strongly enhancing the ferric (Fe3+)‐reductase system and by lowering the rhizo‐sphere pH. In this study, we tested whether such adaptation mechanisms characterize pear and quince genotypes known to have differential tolerance to calcareous and alkaline soils. Two trials were performed using micropagated plants of three quince rootstocks (BA29, CTS212, and MC), three Pyrus communis rootstocks (OHxF51 and two selections obtained at the Bologna University: A28 and B21) and of two pear cultivars (Abbe Fetel and Bartlett, own‐rooted). In the first trial, plants were grown in a nutrient solution with [Fe(+)] and without [Fe(‐)] Fe for 50 days. Their root Fe‐reducing capacity was determined colorimetrically using ferrozine and FeEDTA, and Fe uptake of Fe(+) plants was estimated. In the second trial, the rhizosphere pH of plants grown in an alkaline soil was measured by a micro‐electrode. With the only exception of pears OHxF51 and A28...

Iron content in vegetative and reproductive organs of nectarine trees in calcareous soils during the development of chlorosis

Abstract We investigated for 2 years (1995–1996) the time course development of chlorosis and the variation of iron (Fe) content in vegetative and reproductive organs in two nectarine orchards planted with cv Spring Red and cv Stark Redgold on calcareous soils of the Po valley (Italy) with the final aim to evaluate possible tools for the early prognosis of Fe chlorosis and a more efficient fertilization management. Due to the withdrawal of Fe supply, floral Fe concentration significantly decreased in 1996 as compared with 1995 in cv Spring Red, but not in Stark Redgold. Correlation coefficients between Fe and chlorophyll (Chl) from the same leaves were always higher when Fe was considered as amount present per leaf or per unit of leaf area than as leaf dry weight. The fact that chlorotic and green leaves had similar Fe concentration could be explained by an overestimate of Fe in the chlorotic leaf as a consequence of a reduction of its size. However, the decrease of Chl concentration between 60 and 120 days after full bloom (DAFB) occurred while leaf Fe content generally increased, indicating that even during chlorosis development leaves were supplied with some iron. We therefore suggest that the development of chlorosis was associated with an inactivation of Fe in the leaf apoplast. In 1995, regardless the cultivar, floral Fe concentration and leaf Chl were never correlated. In 1996 floral Fe concentration was linearly related to leaf Chl recorded 60 and 120 DAFB in cv Spring Red only. Floral Fe concentration at full bloom 1996, regardless the variety, was linearly related to leaf Chl determined in spring of the previous year, suggesting that flower Fe concentration might be used for assessing the storage of iron during the previous season.

Acid-spray regreening of kiwifruit leaves affected by lime-induced iron chlorosis

Kiwifruit (Actinidia deliciosd) vines suffer iron chlorosis when growing in a calcareous soil and symptoms occur despite the presence of medium-to-high concentrations of leaf iron, suggesting the presence of a mechanism that immobilize Fe in plant tissues. In the present study we found a negative correlation between the leaf pH and the chlorophyll concentration in leaves of kiwi vines showing different degrees of chlorosis in calcareous soil and then investigated the effects of acid sprays on chlorotic leaves of kiwi grown in a markedly calcareous soil. The following solutions were sprayed three times at five- and six-day intervals on separate shoots of the same plant (three plants in total): citric acid (2000 mg L-1 and 6000 mg L-1 ), sulphuric acid (38 mg L-1 ), Fe-DTPA ( 130 mg L-1) and deionized water (control). At the end of the trial (19 days from the beginning of treatment application), Fe-chelate caused the most intensive regreening, followed by citric acid (both rates); sulphuric acid caused only a slight increase of leaf chlorophyll as compared to control. The pH of leaves treated with citric but not with sulphuric acid decreased by about 0.2 units as compared to control. Iron-chelate resulted in the greatest increase of both active (extracted by ferrozine) and total iron. The leaves treated with citric acid at both rates also increased their active iron content by about 50% as compared to control leaves. These findings support that high leaf apoplastic pH of plants in calcareous soil is somehow responsible for Fe immobilization and its physiological deficiency.

Growth and mineral nutrition of pear rootstocks in lime soils

Abstract Little information is available on the tolerance of pear rootstocks to lime-induced iron chlorosis. In a 2-year study, micropropagated plants of the pear rootstocks OH × F 51, OH × F 333, B 21, C 106 and D 50, and Adams quince were grown in low calcareous soil (LC, 1.6% lime) and high calcareous soil (HC, 72.9% lime) as well as in a mixture of HC:LC (50:50, w:w) (M1) at 33.8% lime content and a mixture of HC:LC (75:25, w:w) (M2) at 48.3% lime content. By the end of Year 2, OH × F 51, B 21 and C 106 had reduced dry matter accumulation in stem and roots in HC soil only; the other rootstocks were adversely affected by lower soil-lime contents. Only Adams decreased the shoot-to-root dry weight ratio in relation to increased soil lime. Leaf chlorotic symptoms of plants grown under increasing lime were most severe in OH × F 333, D 50 and Adams. Root Ca concentration increased linearly and root iron and manganese decreased linearly at increasing soil lime rates. Root Cu concentration increased linearly with soil Cu content, the latter being ten-fold higher in HC than LC soil. These findings indicate varying susceptibility of pear rootstocks to lime-induced iron chlorosis. Rootstock tolerance is a necessary condition in order to overcome lime-induced iron chlorosis in pear cultivars. In grafted trees it is, however, possible that mechanisms other than iron uptake are involved in leaf chlorosis.

Prevention of Iron‐Deficiency Induced Chlorosis in Kiwifruit (Actinidia deliciosa) Through Soil Application of Synthetic Vivianite in a Calcareous Soil

Abstract In this study we have tested the hypothesis that lime‐induced Fe deficiency chlorosis of kiwifruit may be prevented by the application of a synthetic iron(II)‐phosphate analogous to the mineral vivianite [(Fe3(PO4)2·8H2O)]. Two experiments, under greenhouse and field conditions, were performed. In the greenhouse, 1‐year old micropropagated plants (Actinidia deliciosa, cv. Hayward), grown in 3‐L pots on a calcareous soil, were treated in early autumn with soil‐applied: (1) synthetic vivianite (1.35 g plant−1) and (2) Fe‐EDDHA (24 mg Fe plant−1). The synthetic vivianite suspension, prepared by dissolving ferrous sulfate and mono‐ammonium phosphate, was injected into the soil as a sole application whereas the Fe‐EDDHA solution was applied four times at weekly intervals. The field experiment was conducted in a mature drip‐irrigated kiwifruit orchard located on a calcareous soil in the Eastern Po Valley (Italy). Treatments were performed in early autumn by injecting synthetic vivianite (1.8 kg tree−1) and Fe‐EDDHA (600 mg Fe tree−1) into four holes in the soil around each tree, at a depth of 25–30 cm. The Fe‐chelate application was repeated at the same rate in the following spring. Untreated (control) plants were used in both experiments. Autumn‐applied Fe fertilisers significantly prevented development of Fe chlorosis under greenhouse conditions whereas in the field only vivianite was effective. In conclusion, these 1‐year results show that vivianite represents an effective alternative to soil‐applied Fe chelates for preventing Fe chlorosis in kiwifruit orchards.

Effects of root-zone temperature on nitrogen accumulation by non-bearing apple trees

SummaryNon-bearing, potted, apple plants were subjected to root temperature of 8.6.1(LRT) or 23.6.18C (HRT) and irrigated with 100 ml of water containing 20 mg of N as NH4NO3, in which both ammonium and nitrate-N fractions were enriched in 15N (10 atom%). The root system of each plant was pressurized (325 kPa) at day 1, 2, 4, and 8 after15 N application to evaluate the transport of nitrogen derived from fertilizer (NDFF) through the xylem. This technique was used to investigate N absorption. LRT reduced the rate of N uptake the day after 15N application relative to HRT. Two, 4 and 8.d after fertilization, the rate of exudation and consequently the uptake rate was similar for LRT and HRT. The total amount of N removed by plants after 8.d was not affected by root treatments. Carbon dioxide assimilation, transpiration rate and stomatal conductance were lower for trees subjected to LRT during the time course of the experiment. We suggest that the delay in N absorption was related mostly to the lower activity ...

Nitrogen absorption and respiration in white and brown peach roots.

The relationship between root age and root physiology is poorly understood, despite its importance for nutrient absorption. In peaches, roots are white when they first appear and then become brown with age, which corresponds to a number of physiological changes. We related root browning to nitrogen (N) absorption and respiration in order to provide a better understanding of how color changes as typically observed using minirhizotrons relate to changes in root physiology. The experiment was conducted on peach seedlings (Prunus persica cv. ‘Guardian’) grown in 30-L pots in a greenhouse. Brown roots showed lower respiration rates than white roots. White roots showed a higher 15N uptake than brown roots and higher concentration of N, potassium (K), magnesium (Mg), manganese (Mn), iron (Fe) and copper (Cu), no significant differences were observed regarding calcium (Ca), and zinc (Zn) concentration.