| Sumario: | Doubled haploid onion (Allium cepa L.)
plants allow the production of completely
homozygous lines for a later production of hybrids.
The haploid plants are normally produced using in
vitro gynogenesis. The obtained haploid plantlets
must be treated with different agents for doubling
chromosomes. It is necessary to adjust the
concentration and the length of treatment of the
doubling agent. In this case, the effect of 250 and
500 mg.L-1 colchicine and 15.2; 30 and 60 mg.L- 1
amiprophos-methyl during 24 and 48 h was
assessed over the rate of onion haploid plantlets
chromosome doubling. The best duplication
treatment was 250 mg.L-1 colchicine for 48 h,
which yielded 100% of doubled haploid plants. On
the other hand, a positive correlation resulted from
the ploidy level and stomatal size, and a negative
correlation between the level of ploidy and
stomatal density. Significant differences between
the stomatal length, width and density in haploid
and doubled haploid plantlets were observed.
An economical and quick method to test ploidy
level in onion plantlets is proposed through the
measurement of stomatal size and density.
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