Chlorosis is a physiopathology caused by Iron deficiencies attacking many plants more or less sensitive to the lack of this microelement. The lack of iron intake, even at low levels, slows down the process of photosynthesis and respiratory systems of the plant, with negative consequences on agricultural production, both in terms of quality and quantity.
Biological role: iron is the constituent of the protein molecule of cytochromes, involved in the biosynthesis of chlorophyll and chloroplasts, it regulates the mechanisms of vegetative growth and participates in several oxidation-reduction of photosynthetic and respiratory processes.
Symptoms: The deficiency shows as a typical chlorosis (yellowing) starting from the youngest leaves of the plant.
If the iron-deficiency continues over time, the youngest leaves tend to die (photo 3), while the oldest ones also begin to turn Yellow with the following consequences: arrest of vegetative growth, leaf fall and often death of the plant itself.
Causes: in most cases they are not to be traced in the scarce presence of iron in the soil, but they are essentially linked to the nature of the ground limestone: it favors the presence of high concentrations of bicarbonate ions which cause an increase of the soil pH, making the iron insoluble and not usable by plants. But the high pH of the soil is not the only factor responsible for the chlorosis: even the excesses of nitric fertilizers, soils rich in phosphorus, aluminum and heavy metals, low temperature of the soil and the frequent tillage operations that favor the oxidation ferrous ion Fe2 + (absorbable from by plants) in ferric ion Fe3 + (insoluble) can aggravate the symptoms of iron deficiency.
Therapy: basically based on the use and administration of iron chelates. The chelates are organic-metallic compounds, with a molecular structure ring that fail to capture and incorporate within them the ferrous ion (Fe2 +) making it available to the plants, even under conditions of alkaline pH. Such compounds are water soluble and directly absorbed by the roots and the leaves. There are both organic and synthetic chelates, such as lignosulfonates or fertilizers based on iron chelated with amino acids and peptides.
Like the plants, some microorganisms present in nature secrete siderophores (Neilands 1995), water soluble pigments of low molecular weight, which can bind in a specific manner the trivalent iron (Fe3 +) (Faraldo-Gomez and Sanson, 2003) facilitating the intracellular transport and assimilation of iron in plants (Weller, 1988; Meldrum, 1999). Experiments with microorganisms producing siderophores, especially those belonging to the genus Pseudomonas, Bacillus and with mycorrhizae, have shown a significant reduction of iron chlorosis compared to plants not treated with beneficial microorganisms (Bavaresco et al., 2002).
In conclusion, we can say that the application of microorganisms improves iron absorption by the plant: the use of microorganisms, combined with a good organic fertilizer and foliar fertilizers containing iron chelate with peptides and/or amino acids, is a natural remedy to prevent chlorosis.
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– AA.VV. Manuale di viticoltura, a cura di Matteo Marenghi (Edagricole, 2005).
– Bavaresco L., Amodio G., Fogher C (2002). Interazione tra portainnesto e infezione radicale con microrganismi sul controllo della clorosi ferrica e sulla produttività e la qualità dello Chardonnay. Vignevini, 5: 83-88.
– Faraldo-Gòmez J.D., Sansom M.S.P. (2003). Acquisitino of siderophores in Gram nagative Bacteria. Molecular Cell Biology, 4:105-116
– Meldrum A.J. (1999). Regulation of Pyover-1. Dine Biosynthesis in Pseudomonas aeru-ginosa. Tesi: Queen’s University Kingston, Ontario, Canada.
– Neilands J.B. (1995). Siderophores: Structure and Function of Microbial Iron Transport Compounds. Journal Biological Chemestry. 270, 26723-26726
– Weller D.M., (1988). Biological control of soilborne plant pathogens in the rhizosphere with bacteria. Ann. Rev. Phytopathol. 26, 379-407