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Article: Silicon and plant's resistance to pathogenic fungus attacks

Article by agronomist Oscar Fontão Lima Filho (Embrapa) talks about the importance of silicon to combat pathogenic fungi.
3342010-03-03T12:34:00-03:00America/Sao_PauloMarch2010Wed, 03 Mar 2010 12:34:00 -030003pm31
Source: Embrapa

The benefits of adding plant ashes and animal manure to the soil to increase productivity has been known by farmers for thousands of years. This and a number of other products processed by men – in the form of fertilizers and soil acidity corrective – are sources of the plant nutrients, that is, mineral elements considered essential for plants to grow and to complete their life circle, playing several vital roles in plant metabolism.

The lack or excess of one or more of this minerals affects not only growth and productivity, but may also have an impact on plants resistance or tolerance to diseases and plagues. Resistance is basically determined by the ability the host has to limit penetration, development and/or reproduction of the invading agent. Tolerance, on the other hand, is characterized by the plant's ability to keep growing in a satisfactory way, while being infected or attacked by plague. Even being genetically controlled, resistance and tolerance are highly influenced by environmental factors. Among these, we highlight the mineral nutrition of the plant, whose soil fertility can be manipulated by means of fertilization and acidity correction.

Science has already demonstrated the involvement of silicon in several structural, physiologic and biochemical aspects of plants' lives, with very diverse roles. Silicon plays an important role in plant-environment relations, as it can provide culture with better conditions to resist climatic, edaphic and biological adversities, leading to an increase in production volume and quality. Stresses caused by extreme temperatures, short summers and heavy or toxic metals, for instance, can have its effects reduced by the use of silicon. One of the most important beneficial effects is silicon ability to reduce plants susceptibility to diseases caused by fungus.

Plants resistance to diseases can be increased by forming mechanical barriers and/or by changing the plant's chemical responses to the parasite attack, thus increasing the synthesis of toxins that can act inhibiting or repelling substances. Mechanical barriers include changes in anatomy, such as thicker epidermic cells and a higher degree of lignification and/or silicification (silicon impregnation). The amorphous silica located in the cell wall has a marked effect on the cellular wall physical properties. When it is accumulated in the cells of the epidermal layer, silicon can be a stable physical barrier to the penetration of some fungus, specially in grass. In this aspect, the role of silicon incorporated to the cellular wall is similar to that of the lignin – which is a structural component resistant to compression.

Besides the physical barrier, due to the accumulation in the epidermis of leaves, silicon also activates genes involved in the production of secondary compounds of metabolism, such as Polyphenols, and enzymes related to plants' defense mechanisms. This way, the increase of silicon in plant tissues increases plant's resistance to pathogenic fungus attack, due to the supplemental production of toxins that can act as substances inhibiting the pathogenic. Some examples of diseases which find resistance of the host with silicon supplementation include rice blast fungus, diaporthe sojae  in soy, Powdery mildew  in wheat, soy, barley, cucumber and tomato, Rhizoctoniose in rice and sorghum , cercospora beticola  in coffee trees, among others.

The technology based on the use of silicon is clean and sustainable, with a great potential to reduce the use of agrochemical and increase productivity through a more balanced and physiologically more efficient nutrition, which means more productive and vigorous plants, with less diseases.

Oscar Fontão de Lima Filho

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