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  • Author or Editor: Jason M. Jaworski x
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Cotyledon explants of five watermelon cultivars (`Desert King', `Mickylee', `Sangria', `Sweet Princess', and `Male Sterile') were prepared from 7-day-old in vitro-germinated seedlings. Explants were incubated on shoot regeneration medium for 6 weeks, followed by several 3-week cycles on shoot elongation medium. The five cultivars differed in their ability to form shoots within 9 weeks on the selected media. Shoot regeneration frequency was about 1.5to 2.9-fold greater for `Mickylee' (60%) than `Sangria' (47%), `Sweet Princess' (27%), `Male Sterile' (26%), and `Desert King' (24%). Rooting of elongated shoots (>2 cm) occurred within 2 weeks on medium containing 1 μM IBA and ranged from 25% (`Desert King') to 92% (`Sangria'). Plantlets were transferred to six-pack containers filled with soilless medium (1 Sunshine Mix: 1 coarse perlite) and covered with a transparent plastic lid. Plants were acclimatized to ambient conditions by gradually removing the lid over a period of 3 days after new growth was observed. The percentage of acclimatized plants ranged from 50% (`Sweet Princess' and `Mickylee') to 100% (`Male Sterile'). Acclimatized plants were transferred to the greenhouse and grown for at least 4 weeks before screening for ploidy variants. Ploidy of regenerated plants was estimated by counting the number of chloroplasts per guard cell pair. Plants with an average of 18 or more chloroplasts per guard cell pair were declared tetraploids. Plants with fewer chloroplasts per guard cell pair were declared diploids and discarded. Tetraploid plants were transferred to the field, grown to maturity, and self-pollinated for seed increase.

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