A SIMPLE PROTOCOL FOR MICROPROPAGATING DIPLOID AND TETRAPLOID WATERMELON USING SHOOT-TIP EXPLANTS

Shoot-tip explants from 21-day-old aseptically-germinated watermelon s eedlings were incubated on solidified MS medium containing test concen trations of benzyladenine (BA) and kinetin (each at 0, 1, 5 or 10 muM) , and thidiazuron (TDZ; 0, 0. 1, 1 or 5 muM) for 8 weeks. Approximatel y 1.5x-2.8x more axillary shoots formed at the optimum BA level (1 muM ) compared to the best TDZ (0.1 muM) or kinetin (10 muM) concentration . The ability of various diploid and tetraploid genotypes to undergo p rolonged axillary shoot proliferation on medium with 1 muM BA was exam ined. Among the genotypes tested, the number of axillary shoots per ex plant was greater for 'Bush Jubilee' and 'Jubilee II' than for 'Minile e', 'Dixielee', and the tetraploid genotypes. For a majority of the ge notypes tested, the number of shoots per explant was low (2.7-4.0) dur ing the first month of culture, peaked (5.3-12.5) at 2 to 3 months, an d then declined (3.7-7.7) at 6 months. In contrast, the number of shoo ts per explant was greatest (11.7) for 'Bush Jubilee' during the first month of culture and declined to 7.7 by the sixth subculture. The per centage of rooted shoots varied from 60% to 100% and the percentage of acclimatized plants ranged from 21% to 96% depending on the genotype and the length of time in culture. Using this procedure, 13,200 finish ed plants could be produced in 3 months from 250 seedlings.