IDENTIFICATION OF TETRAPLOID REGENERANTS FROM COTYLEDONS OF DIPLOID WATERMELON CULTURED IN-VITRO

Adventitious shoots were obtained from the diploid watermelon [Citrull us lanatus (Thunb.) Matsum. & Nakai] cultivars Dixielee, Jubilee II, M ickylee, Minilee, and Royal Sweet by culturing excised cotyledons on s hoot regeneration medium for six weeks. Tetraploid and diploid regener ants were identified by counting the number of chloroplasts per guard cell pair from leaves of regenerated plants. Cross fertilization of pu tative tetraploids with diploid pollinators and the production of trip loid seed confirmed the efficacy of this approach. The mean number of chloroplasts for tetraploid regenerants was 19.1 whereas diploids aver aged 11.2. These values were similar to tetraploid and diploid plants from seed. Ovary diameter, petal, and anther diameter of male flowers, and leaf length by width ratio were also good indicators of plant plo idy. Progeny obtained from self-fertile tetraploids of 'Mickylee' were crossed with various diploid pollinators to produce triploid hybrid s eed. All triploid plants from tissue culture-derived tetraploids produ ced fruit comparable in quality to fruit produced by currently-availab le triploid hybrids, demonstrating that in vitro tetraploid induction can be used to produce high quality tetraploid plants for use in tripl oid hybrid seed production.