How do media compositions, pretreatments, and genotypes affect haploidization in sweet watermelon (Citrullus lanatus var. lanatus) ovary culture?

Abstract

Currently, consumer demands are rapidly and continuously evolving, which accelerates the development and release of new cultivars. This dynamic process necessitates the integration of biotechnological approaches that can shorten the duration of plant breeding programs. Among these, the doubled haploid (DH) technique, which enables the rapid production of completely homozygous lines in F1 hybrid breeding programs, has been widely and successfully applied in many plant species. Unfertilized ovary culture is one such method and represents a prominent approach for haploid plant production, particularly in the Cucurbitaceae family. However, reports on its successful application in watermelon remain limited. Therefore, the present study aimed to evaluate the effects of culture media composition, pretreatments, and genotype on haploid plant production via ovary culture in watermelon. Although gynogenic embryos and in vitro plantlets were successfully obtained from all tested cultivars, the frequency of haploid induction was influenced by the composition of the culture media, pretreatment conditions, and genotype. The highest haploid induction frequency was achieved using culture media supplemented with a GPT mixture (500 mg L⁻¹ L-glutamine, 250 mg L⁻¹ L-proline, and 0.5 mg L⁻¹ thiamine). Among the tested media, M8 (MS + GPT + 1 mg/l 2,4-D + 1 mg/L BAP + 7 g/L Agar + 30 g/L sucrose + pH:5.8) was identified as the most effective, as it supported haploid plant production across all cultivars. Ploidy analysis of 94 regenerated plants revealed that 82 were haploid (n = 11), 9 were diploid (2n = 22), and 3 were mixoploid (n + 2n). Among the cultivars, Pastel F1 produced the highest number of haploid plants (52), followed by Paskal F1 (14), Crimson Sweet (10), and Crimson Tide F1 (6).