Introduction
Phosphite (ALEXCi Phi Series) are Biostimulants based on Phosphite with a dual function on crops: on one side, act as the source of Nutrielements or organic matters, and on the other, act as stimulant of selfdefense mechanisms of plants against fungal pathogens and, also, acts directly on its metabolism to combat it, due to the presence of phosphorous as PHOSPHITE ion.
Phosphites
Phosphorus (P) is one of the essential elements required by all living organisms. It is very reactive and rapidly combining with other elements such as oxygen (O) and hydrogen (H). When it is not fully oxidized, H occupies the place of one O atom and the resulting molecule is called phosphite (or phosphonate), chemically represented as PO3-3.
The phosphite ion can present ionic bonds (sharing electrons) with the hydrogen ions (H+) forming the phosphorous acid (H3PO3) or forming salts through the union with other cations (K, Ca, Mg, etc.).
Characteristics of phosphites
- Phosphite ion is very active in plant particularly because it is unstable and tends to react with everything.
- It is highly water soluble and can be quickly absorbed through plant’s leaves and roots.
- Phosphite has double circulation (systemic) as it moves through the xylem and phloem. Thus, its application can be to any organ of the plant (leaves, stem or root), facilitating the distribution of the nutrient elements to which it is chemically bound.
The phosphite ion is systemic, easily absorbed and translocated through xylem and phloem to all areas of plant.
Its transport by phloem allows it to reach the roots for the control of diseases caused by fungi of the soil in addition to those of foliage.
Functions
The use of Phosphite in agriculture is an important tool due to the remarkable features of phosphite ion, being able to produce a rapid stimulation of important metabolic processes in plants, causing the following effects:
- Double fungal activity
- Vehicle of the important nutrient elements
- Metabolic activator in post-stress states
Double fungal activity (1 and 2)
1) The Oomycetes (Phytophthora, Pythium, Peronospora, Plasmopara, et.) cause two types of diseases:
- The gummosis of crops
- The watering of fruits
The gummosis of crops
The pathogen’s propagules present in soil can directly infect roots and the base of crops.
Symptoms of these diseases are only visible after several months from infection, showing lack of vigour and generalized decay. First symptoms in trunk and main branches are not visible externally, as they consist in a darkening of phloem and cambium. As infection progresses, affected areas begin to crack and emit gummy exudations. In addition, it will make fruits and leaves smaller, and leaves to turn yellow.
The watering of fruits
The splashes caused by rain disseminate the pathogen’s propagules from ground to fruits.
Symptoms of watering can appear after 3-7 days from infection. They are characterized by soft brown rot, which progresses until affecting the whole fruit, that will finally fall to the ground. When the fruits are harvested with still recent infection, it usually develops later in the store.
2) The double fungicidal effect of the ion phosphite is because it has:
- Direct action on fungal metabolism (fungistatic effect)
- Indirect action on pathogens (activator of plant defenses)
Direct action on fungal metabolism (fungistatic effect)
Direct action on fungal metabolism (fungistatic effect)Phosphite ion competes with phosphorus in different metabolic pathways catalyzed by fosforilatives enzymes, for example, in the phosphorylation of AMP and ADP to ATP.
In this way, the processes involved in energy transfer of the fungus suffer a considerable delay and may even be blocked. The effect on fungus could be compared to a state of total absence of available phosphorus in plant to meet the needs of the fungus. The phosphite ion can suspends fungal growth and development, or the germination of their spores (fungistatic action).
Indirect action on pathogens (activator of plant defenses)
Action of the phosphite ion in fungi and plant cell.
- The pathogen is affected by the phosphite ion
- Suppressors decrease or do not occur
- The cell recognizes the condition
- Phosphite acts on the pathogen, leading to the production of external elicitors that stimulate the defense response of plants
- defensive organs send alarm signals to cells that have not yet been attacked
- Structural wall proteins are coded to create structures that reinforce cell walls
- Enzymes are encoded that degrade the wall of the fungus
Vehicle of nutrient elements
So that the plant can assimilate phosphorus, it is necessary that the phosphite can be converted into phosphate. The average time for oxidation of phosphite to phosphate is 3 to 4 months thanks to the microorganisms present in soil and/or in leaves.
Due to this and because the effects explained above are produced by the phosphite ion, the element that accompanies it acts as a nutritional.
Potassium is a primary macronutrient that plays an important role as plant functions regulator.
Metabolic activator in post-stress states
Because the phosphite ion acts on both pathways (phloem and xylem), it enriches the descending sage providing extra energy to overcome stress situations. For example, the leaves close the stomata in situations of stress. When they receive potassium by xylem it causes its opening, resuming the vegetative activity.
Conclusions. Benefits of ALEXCi Phi Series
- Promotes the natural defenses of plants and has fungistatic action
- Strengthens the stem and roots, increasing its resistance to pathogens
- Prevents watering and gummosis diseases in crops
- Activates the metabolism in a post-stress state
- Improves the filling, turgor, homogenization and maturation of fruits
- Increases the quality of fruits
