Horticulture Techniques for Profit

Study Notes

PGRs (Plant Growth Regulators) are endogenous and exogenous substances that affect plant growth and development in many ways, having direct economic implications.

Rising global demand for food production and the need for improvement in agricultural productivity have led to the use of chemicals to improve crop plant growth and development.
The use of PGRs to improve crop growth and development dates back to the 1930s with the discovery of auxins.

Increasing yield:
Chlormequat chloride to shorten and stiffen wheat straw, allowing increased use of nitrogen fertilizers
GA (Gibberellins) to increase fruit set of mandarin, clementines, and tangerines, with a benefit/cost ratio of 9:1
GA to overcome losses of apple yield due to frost damage
GA to increase berry size of seedless grapes, with a benefit/cost ratio of 40:1
GA to overcome low-temperature constraints to sugarcane growth
Ethapon to stimulate latex flow in rubber
Glyphosine to ripen sugarcane, resulting in a 10-15% increase in sucrose
Improving quality:
GA + mechanical thinning to increase berry size of seedless grapes
Ethylene to de-green citrus fruit
Daminozide or chlorphonium chloride to dwarf pot-plants, making them more acceptable to the consumer market
Gibberellins to delay ripening and improve storage life of bananas
Increasing value:
GA to advance or retard maturity of artichoke to capture higher prices
GA to retard ripening of grapefruit to spread harvesting and capture higher prices
Extending season and increasing continuity of supply:
Maleic hydrazide and other sprouting inhibitors to extend storage of bulbs and root crops
GA to force rhubarb for early production

Direct labor replacement:
Maleic hydrazide and fatty alcohol contact bud killers to control growth of suckers in tobacco
NAA (Naphthaleneacetic acid) to thin overset fruit
Dikegulac-sodium to control growth of hedges
Facilitating mechanization:
Fruit looseners (e.g., Ethapon) to aid synchronized ripening and loosening of fruit for mechanical harvesting
Retardants (e.g., daminozide) to reduce length of peanut runners and facilitate harvesting
Defoliants to remove excessive vegetation on crops
Simplifying plant breeding:
Sex change in Cucurbits: a mixture of Gibberellins A4 and A7 to increase staminate flowers
Extending season and increasing continuity of supply:
Maleic hydrazide to extend storage of bulbs and root crops

The success of PGR use depends on:
- Clear understanding of the need of agriculture
- Scope for growth modifications
- Various plant physiological processes