Synseed germination, conversion, and acclimatization of seedless watermelon ‘Quality’

Seedless watermelons are triploid hybrids (3n) that have been growing in popularity since the 1990s. However, the high production cost and low germination rate of the hybrid seeds pose a major problem in their production. The synseed technology could make a promising alternative for seedless watermelon propagation; however, this alternative has not yet been explored. This study aimed at producing synseeds of seedless watermelon ‘Quality’ using shoot tips as the propagules after which their germination and conversion were evaluated under in vitro and ex vitro conditions. In vitro shoot multiplication with different concentrations of 6-benzylaminopurine (BAP), synseed production from BAP-multiplied shoot tips, synseed sowing in vitro using several substrates and medium supplements, and synseed sowing ex vitro using different antimicrobial agents were investigated. Results indicated that 1.0 mg L⁻¹ BAP resulted in the highest number of shoots per shoot tip explant. Synseeds produced from BAP-multiplied shoot tips achieved faster germination compared to synseeds from non-BAP-derived shoot tips, but there was no difference in terms of conversion and acclimatization survival rates. Agar showed greater conversion and acclimatization survival rates as well as root number, root length, and shoot length than the other substrates especially when indole-3-butyric acid (IBA) at 1.0 mg L⁻¹ was added to the medium. However, this study demonstrated the possibility of using vermiculite as an alternative substrate to agar. PPM at 0.5% was a better microbial agent than 100.0 mg L⁻¹ mancozeb for ex vitro synseed sowing as it achieved zero contamination and maintained the growing potential of synseeds with 65% germination, 85% survival, and 25% rooting rates.