Abstract
Melon (Cucumis melo) is one of the top 10 fruits in the world, and its production often suffers due to soil-borne diseases. Grafting is an effective way to solve this problem. However, graft incompatibility between scion and rootstock limits the application of melon grafting. In this study, the melon was grafted onto eight Cucurbitaceae species (cucumber, pumpkin, melon, luffa, wax gourd, bottle gourd, bitter gourd, and watermelon), and graft compatibility evaluation and anatomical observation were conducted. Taking melon homo-grafted plants as control, melon grafted onto cucumber and pumpkin rootstocks was compatible, while melon grafted onto luffa, wax gourd, bottle gourd, bitter gourd, and watermelon rootstocks was incompatible based on the scion dry weight on day 42 after grafting. Meanwhile, we found that starch–iodine staining of scion stem base is an index to predict graft compatibility earlier, on day 14 after grafting. Further, microsection observations showed that there was more cell proliferation at graft junction of melon hetero-grafted combinations; vascular reconnection occurred in all graft combinations. However, excess callose deposited at graft junction resulted in the blockage of photosynthate transport, thus, leading to starch accumulation in scion stem base, and finally graft incompatibility. In addition, undegraded necrotic layer fragments were observed at graft junctions of melon grafted onto incompatible bitter gourd and watermelon rootstocks. The above results provide clues for the selection and breeding of compatible Cucurbitaceae rootstocks of melon and demonstrate that starch accumulation in scion base and callose deposition at graft junction is associated with melon graft compatibility.
Highlights
Grafting, as an asexual plant propagation technology, has been applied for about 3000 years (Melnyk and Meyerowitz, 2015)
Luffa, wax gourd, bottle gourd, bitter gourd, and watermelon rootstocks were graft incompatible with melon, and scion dry weight of all tested cultivars was significantly lower than melon homo-grafted plants (Figure 1B)
There was a significant difference in scion height of melon grafted onto different pumpkin rootstocks, but no heterografted combination showed a significantly lower height as compared with melon homo-grafted plants (Figure 2)
Summary
As an asexual plant propagation technology, has been applied for about 3000 years (Melnyk and Meyerowitz, 2015). It is widely used in agriculture as it enhances abiotic/biotic stress resistance, extends the harvesting period, improves fruit yield and quality, adjusts flowering time, and improves fruit tree architecture When watermelon was grafted onto different pumpkin rootstocks, the survival rate of graft incompatible combinations was significantly reduced (Yetisir and Sari, 2003; Yetisir et al, 2007). Tomato/pepper healing junction showed the asynchronous stem bulging 30 days after grafting (Masayuki et al, 2000; Thomas et al, 2021), which was observed in graft incompatible melon (Cohen et al, 2007; Zhou et al, 2018)
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