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

Adventitious and axillary shoots of melon (Cucumis melo L.) were cultured from explants on a modified Murashige and Skoog medium containing 10 mum BA. Explants were diversified with regard to genetic source (breeding lines Miniloup, L-14, and B-line), seed parts (apical and cotyledon tissue), seed maturity (10-40 days after pollination; DAP), and cotyledon sections with respect to apical-radicle axis (distal and proximal). Plants were screened for ploidy level by pollen morphometry. Immature cotyledons produced more tetraploid regenerants than mature cotyledons 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 produced fewer or no tetraploid plants. Proximal sections from immature cotyledons of three genotypes (Miniloup, L- 14, B-line) produced higher frequencies of tetraploids than whole mature cotyledons or whole immature cotyledons.