Application Note: PGRs in Agriculture

PGR	Application	Mechanism	Crop
2,4-D (Synthetic Auxin)	Selective herbicide	Kills dicot weeds; monocots resistant	Wheat, Rice fields
NAA	Prevent fruit drop	Maintains auxin in abscission zone	Apple, Pear
IBA/NAA	Rooting of cuttings	Promotes adventitious root formation	Ornamentals, cuttings
Auxin spray	Parthenocarpy (seedless tomatoes)	Substitutes seed-produced hormone	Tomato
$GA_{3}$	Grape elongation	Extends stalk internodes; larger bunches	Grape
$GA_{3}$	Bolting induction	Rapid internode elongation	Sugarcane (sucrose dilution)
$GA_{3}$	Malting acceleration	Induces alpha-amylase in aleurone	Barley (brewing)
$GA_{3}$	Break seed dormancy	Replaces cold/light requirement	Various crops
Cytokinin	Delay leaf yellowing	Richmond-Lang effect	Post-harvest greens
Cytokinin	Tissue culture propagation	Promotes shoot formation	Banana, Orchid, Potato
Ethylene / Ethephon	Uniform fruit ripening	Activates ripening cascade	Banana, Mango
Ethephon	Feminization	Increases female flowers	Cucumber
Ethephon	Pineapple flowering	Triggers meristem transition	Pineapple
ABA	Antitranspirant	Stomatal closure	Transplanting, drought
ABA	Weed control	Stimulates abscission	Selective defoliation

Problem	Solution	PGR Used
Bananas ripen too fast	Store in low $O_{2}$ + $KMnO_{4}$ sachets	Remove ethylene
Spinach yellows in storage	Cytokinin spray	Cytokinin
Grapes too crowded	$GA_{3}$ spray at fruit set	$GA_{3}$
Seedless grape/tomato wanted	Auxin or GA spray on flowers	Auxin/GA