The Plant Hormone Gibberellin

Gibberellin (GA) was first identified in the pathogenic fungus Gibberella fujikuroi, which causes a disease in rice called ‘foolish-seedling’.

By producing large quantities of GA, the plants become long and slender, are incapable of supporting their own weight, and are chlorotic and partially infertile .

Further research established GA as a hormone that is essential for many developmental processes in plants, among them are seed germination; organ elongation and expansion through cell growth; trichome development; transition from vegetative to reproductive growth; and flower, seed, and fruit development .

GA manipulation in agriculture is common practice; the best-known contribution of GA manipulations to agriculture is the introduction of dwarfing alleles into staple crops. This manipulation resulted in one of the cornerstones of the so-called ‘green revolution’ and led to a massive increase in global wheat and rice yields. Identification of the genes responsible for these traits showed that the encoded proteins interfere with the action or production of GA .

Among more than 130 GAs identified in plants, fungi, and bacteria to date, only a subset, namely GA1, GA3, GA4, and GA7 are thought to function as bioactive hormones .

Additional forms of GA that exist in plants are precursors of the bioactive forms or deactivated metabolites .

Effects of gibberellin A3 and cytokinins on natural and post‐harvest, ethylene‐induced pigmentation of Satsuma mandarin peel

Natural and post-harvest ethylene-induced pigment changes in the rind of Satsuma mandarin (Citrus unshiu Marc.) fruits respond differently to the exogenous application of growth regulators.

Both gibberellin A3 and the synthetic cytokinins N6-benzyladenine and kinetin opposed the ethylene-induced chlorophyll destruction, while the loss of chlorophyll during natural maturation was retarded by the gibberellin but not by the cytokinins.

This different behaviour suggests that ethylene may not be playing a central role in the endogenous control of ripening.

Carotenoid accumulation during natural maturation is apparently controlled through a different mechanism than chlorophyll loss since it is reduced both by the cytokinins and gibberellin A3.

Kinetin and gibberellin A3 increased to a similar extent the accumulation of reducing sugars and free amino acids, and reduced that of non-reducing sugars in the peel during natural maturation.

Their differential effect on chlorophyll loss may not be explained through their effects on sugar accumulation.

Gibberellic acid

Gibberelin Gibberellic acid (also called Gibberellin A3, GA, and GA3) is a hormonefound in plants and fungi .

Its chemical formula is C19H22O6. When purified, it is a white to pale-yellow solid. Plants in their normal state produce large amounts of GA3.

It is possible to produce the hormone industrially using microorganisms. Nowadays, it is produced by submerse fermentation, but this process presented low yield with high production costs and hence higher prices.

One alternative process to reduce costs of the GA3 production is Solid-State Fermentation (SSF) that allows the use of agro-industrial residues.

Gibberellic acid is a simple gibberellin, a pentacyclic diterpene acid promoting growth and elongation of cells. It affects decomposition of plants and helps plants grow if used in small amounts, but eventually plants develop tolerance to it. GA stimulates the cells of germinating seeds to produce mRNA molecules that code for hydrolytic enzymes.

Gibberellic acid is a very potent hormone whose natural occurrence in plants controls their development. Since GA regulates growth, applications of very low concentrations can have a profound effect while too much will have the opposite effect. It is usually used in concentrations between 0.01 and 10 mg/L.

GA was first identified in Japan in 1926, as a metabolic by-product of the plant pathogen Gibberella fujikuroi (thus the name), which afflicts rice plants; fujikuroi-infected plants develop bakanae (“foolish seedling”), which causes them to grow so much taller than normal that they die from no longer being sturdy enough to support their own weight.Gibberellins have a number of effects on plant development.

They can stimulate rapid stem and root growth, induce mitotic division in the leaves of some plants, and increase seed germination rate.Gibberellic acid is sometimes used in laboratory and greenhouse settings to trigger germination in seeds that would otherwise remain dormant.

It is also widely used in the grape-growing industry as a hormone to induce the production of larger bundles and bigger grapes, especially Thompson seedless grapes.

In the Okanagan and Creston valleys, it is also used as a growth replicator in the cherry industry.

It is used on Clementine Mandarin oranges, which may otherwise cross-pollinate with other citrus and grow undesirable seeds.

Applied directly on the blossoms as a spray, it allows for Clementines to produce a full crop of fruit without seeds.

Silicone Surfactants

Silicone surfactants have the intriguing and commercially viable ability to reduce the surface tension of polar and non-polar liquids to values 15–20 mN/m lower than commonly achieved with organic-based surfactants.

The latest developments on understanding and commercially exploiting the phenomenon of superwetting are reviewed.

Silicone surfactants demonstrate a marked tendency to form aggregate structures featuring surfactant bilayers including vesicles and lamellar liquid crystals.

Adjuvants’ role in combatting herbicide resistance  

Tank mix compatibility rule

Growers use tank mixes all the time to apply all of the required ag inputs in an efficient manner. Every one of these mixes is different and while many will not cause any problems, some formulations are not compatible with each other and cause a big mess and a bigger headache. Ag professionals can use a couple of techniques to avoid tank mix compatibility issues in their sprayer.

Tank mix compatibility issuesMixing Order

When mixing products, growers should add products to the spray tank in a specific order to avoid mixing problems. While growers need to consult the labels on the products they are using for specific mixing instructions, generally products should be added to the tank using the W-A-L-E-S method

Jar Test

If growers have a specific tank mix that they are concerned with, a small “jar test can save a lot of hard work and money. In this test, we mix the products that would be in the tank mix in a small, clear, pesticide-safe container at the same concentrations as the tank mix. We can then evaluate the jar test and examine the compatibility of the products in the mix. It is much easier to dispose of a small container of incompatible mix rather than clean out a large sprayer tank full of the same mix.