EXPLANT ORIGIN AFFECTS THE FREQUENCY OF TETRAPLOID PLANTS FROM TISSUE-CULTURES OF MELON

Adventitious and axillary shoots of melon (Cucumis melo L.) were cultu red from explants on a modified Murashige and Skoog medium containing 10 mum BA. Explants were diversified with regard to genetic source (br eeding lines Miniloup, L-14, and B-line), seed parts (apical and cotyl edon tissue), seed maturity (10-40 days after pollination; DAP), and c otyledon sections with respect to apical-radicle axis (distal and prox imal). Plants were screened for ploidy level by pollen morphometry. Im mature cotyledons produced more tetraploid regenerants than mature cot yledons from seed of breeding line Miniloup; the highest frequency of tetraploid regenerant plants was from cotyledons of embryos harvested 18 and 22 DAP. Explants from the apical meristem of the same seeds pro duced fewer or no tetraploid plants. Proximal sections from immature c otyledons of three genotypes (Miniloup, L- 14, B-line) produced higher frequencies of tetraploids than whole mature cotyledons or whole imma ture cotyledons.