Micrographic View of Graft Union Formation Between Watermelon Scion and Squash Rootstock

Abstract

Grafting has become a common practice for watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] production in many parts of the world, due to its efficacy against biotic and abiotic stressors. However, grafting success for watermelon is challenging in part due to the complex anatomy of the cucurbit vascular system. The survival of grafted transplants depends on compatibility between the scion and rootstock, which in turn depends on anatomical, physiological, and genetic variables. A better understanding of cucurbit anatomy and graft union formation would inform grafting approaches and transplant management. An anatomical study was conducted by scanning electron microscopy (SEM) at 11 and 25 days after grafting (DAG) with seedless watermelon cultivar ‘Secretariat’ grafted onto compatible rootstock cultivars ‘Pelop’ (Lagenaria siceraria) and ‘Tetsukabuto’ (Cucurbita maxima × Cucurbita moschata) in comparison to non-grafted watermelon and rootstock seedlings. At 11 DAG, the parenchymatic cells of the central pith of grafted plants were dead and a necrotic layer was observed, representing the beginning of callus formation. New xylem strands were formed in the vascular system, connecting the rootstock with the scion. At 25 DAG, fully developed vascular bundles at the graft interface were observed with both scion-rootstock combinations. Although more studies are necessary to characterize the sequence of physiological events after grafting in Cucurbit species, this is one of the first studies to describe the complex anatomical changes that occur during watermelon graft healing.

Transcriptomic analysis provides an insight into the function of CmGH9B3, a key gene of β‐1, 4‐glucanase, during the graft union healing of oriental melon scion grafted onto squash rootstock

“…Vascular tissue reconnection was essential to grafting success, [ 39 ] and the different combinations of scion and rootstock took a different time to form vascular bundles fully. [ 40 ] In this study, we observed the vascular tissue connectivity of control and TRV‐ CmGH9B3 grafted plants (Figure 3) and found that the TRV‐ CmGH9B3 grafted plants were delayed by one day compared to the control grafted plants. The results suggested that silencing CmGH9B3 could significantly delay the cell adhesion time at the grafted interface of oriental melon scion and squash rootstock.…”

“…Vascular tissue reconnection was essential to grafting success, [39] and the different combinations of scion and rootstock took a different time to form vascular bundles fully. [40] In this study, we observed the vascular tissue connectivity and sucrose metabolism pathways were deeply explored. Some reports suggested that plant hormone signaling was essential for graft union healing.…”