A male gametocide is a chemical that kills the pollen cells, but not the female ovules, of a plant. Plants treated with a male gametocide become male-sterile. Male gametocides are normally used on self-pollinating cereals to convert them into open-pollinated plants. Unfortunately, although effective male gametocides are known for some monocotyledons, none are known for dicotyledons.
Beek (1988) was among the first to use male gametocides to achieve a random polycross in wheat. He commented that it was possible to produce millions of crosses with one morning's work. His male gametocide was Ethrel (2-chloroethylphosphonic acid) used at a concentration of 2000 ppm of active ingredient in a water solution sprayed to run-off, at the early boot stage, when the immature inflorescence is about one third the length of the sheath. The solution also contained a wetting agent, and it was followed by a spray of 150 ppm of gibberellic acid (GA3) that reduces the phytotoxic effects of Ethrel (see 7.20.8).
Normally, in wheat breeding, all the crosses are made by hand, every cross is labelled, and every progeny is sown separately.
When using male gametocides, the difference in workload is so huge that the loss of exact knowledge of the parents is immaterial. A heavy workload allows only a small screening population, while a light workload allows to a large screening population.
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