Adventitious regeneration from haploid melon (Cucumis melo L.) leaves as an approach to increase the frequency of diploid plants

Abstract

An efficient process of adventitious regeneration from haploid plant leaves to increase the proportion of diploid plants of six elite melon lines ‘Védrantais’ French cultivar, ‘Piel de Sapo’ Spanish line ‘T111’, and four near isogenic lines (NILs: SC 6–6, SC 7–2, SC 7–4, SC 8–4) has been developed. Several hormone combinations, in vitro culture conditions, and leaf positions on the plant stem were analyzed to improve the regeneration frequency and the percentage of diploid plants in these lines. Flow cytometry showed that diploid plant production was optimized by regeneration from haploid leaves as the percentage of diploid plants increased from 11% with regeneration of diploid cotyledons to 60% in this work. Evaluating the four NILs, only the lines SC 6–6 and SC 8–4 showed a significantly higher percentage of diploidy with 80% and 72.7%, respectively. The leaf position factor had no effect on regeneration and ploidy level, while darkness negatively influenced regeneration but had no effect on ploidy. Furthermore, it was concluded that the hormonal combination (cytokinin plus auxin) induces low endoreduplication activity, which is the phenomenon responsible for the polyploidy. Furthermore, this study provided evidence that in melon polyploidy occurs during the process of organogenesis, and, therefore, one should focus on this phase to avoid polyploidization of cells and, thus, avoid polyploid plants.