The possibility in maize for chromosome doubling from maternal haploid derived dry seeds was examined. Dry seeds were plated on germination medium with different colchicine concentrations and were stored for different durations. Seeds were rinsed with sterile water after treatment and transferred onto medium without colchicine to promote germination. Colchicine (Ferak, Art., No 535122) from 250 mg/l to 600 mg/l was used for chromosome doubling. A filter-sterilized aqueous colchicine solution was added to the colchicine supplemented induction medium. In Experiment 1, colchicine (250 mg/l) treatment lasted for 168 h, in Experiment 2 (600 mg/l) it lasted for 8 and 16 h. Genotypes A (Ig1IRL-93-18/8-6 h) and B (Ig1IRL-93-18/8-6 x A654) were used. The ploidy status of the obtained plants was determined by chromosome counting of germinated root tip cells. Compared to Exp. 1, Exp. 2 treatment induced a greater response. The maternal plants obtained showed diploid, tetraploid and hexaploid cells at root meristem level. Considering the total number of cells produced, high levels of colchicine (Exp. 2) were very effective. A suitable combination was: for genotype A - 600 mg/l, 16 h, 100 % doubled haploids; for genotype B - 600 mg/l, 8 h, 87.8 % doubled haploids and different variants of chimeras. It was surprising that a decrease in colchicine (Exp. 1) significantly affected the aptitude for obtaining cells with different ploidy levels - tetraploid, hexaploid and chimeras for genotype A to totally depressed development of seeds for genotype B.
In summary, the results from this study suggest that optimum colchicine treatment of maternal haploid dry seeds appeared to be genotype dependent.
This work was supported by grant B-602 from the National Fund of Scientific
Investigations of the Bulgarian Ministry of Education and Science.
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