|Author: ||D.P. Bartholomew|
|Keywords: ||2-hydroxyethylehydrazine, acetylene, aminoethoxyvinylglycine, Ananas comosus, auxin, ethephon, forcing, natural induction, 1-methylcyclopropene|
Pineapple is an ancient Amerindian crop that was spread throughout the tropics by early Spanish and Portuguese explorers.
They were grown in heated green¬houses in Europe and Britain by 1720 and a greenhouse-based commercial pineapple industry began in the Azores in about 1872. It was discovered by accident there in 1874 that plants could be forced into flower (forced) with smoke and growers adopted the practice as a way to schedule fruiting when prices were high.
By the 1920s, growers in Puerto Rico had adapted the practice for in-field use by building smudge fires beneath blocks of pineapple covered with muslin cloth.
It was known that “distillation” of wood produced ethylene and it was shown in 1932 that smoke and ethylene gas were both effective in forcing pineapple.
That discovery led the Hawaiian pineapple industry, then the largest and most technologically advanced in the world, to improve on the new forcing technology.
Hawaiian Pineapple Company patented a method of forcing pineapple with calcium carbide in 1936 and the industry-supported Pineapple Research Institute (PRI) patented a method of forcing pineapple with acetylene or ethylene as a gas or as a water solution.
In 1941, California Packing Corporation patented an apparatus that could mix and apply a water-oil-colloidal earth emulsion containing acetylene or ethylene to field-grown pineapple plants to force them.
In 1942, the PRI reported that pineapple plants could be forced with a low concentration of 1-naphthaleneacetic acid (NAA) while higher concentrations inhibited natural induction (NI) of flowering.
It was shown in 1966 that auxins forced pineapple by stimulating the plant to produce ethylene.
Over a ten year period, the PRI screened thousands of compounds as potential forcing agents and in 1956 reported that 2-hydroxyethylhydrazine (BOH) would force pineapple; in 1967 it was shown that BOH was an ethylene delivery agent.
In 1968, pineapple plants were forced with 2-chloroethylphosphonic acid (ethephon), another ethylene delivery agent.
Currently, pineapples on large plantations typically are forced approximately weekly with ethephon or ethylene.
On smaller farms, forcing pineapples with calcium carbide or acetylene is more common.
Natural induction, which is believed to be an ethylene-driven event, disrupts this orderly process of fruit production and is a serious management problem for growers of ‘MD-2’ (“Gold”) pineapple. ‘MD-2’ is considered “sensitive” to NI in most environments where the winter photoperiod is less than about 11.5 h.
High concentrations of auxins inhibit flowering, but with inconsistent results.
A 1983 study showed that aminoethoxyvinylglycine (AVG), an inhibitor of ethylene biosynthesis, prevented NI of ornamental bromeliads, which like pineapple can be forced with ethephon.
When AVG was commercialized in 1997, field trials were established to explore its potential to control NI of pineapple.
Research over about a 10-year period showed that AVG could consistently control NI with an acceptable cost/benefit in commercial pineapple fields.
AVG is registered for that use in Hawaii and a number of other countries where large commercial pineapple industries are located.
From a historical perspective, when it comes to natural or forced induction of flowering, or its inhibition, all paths eventually lead to ethylene.
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