2017 ASHS Annual Conference

Grafting cucurbits onto disease resistant and vigorous rootstock improves plant performance and yield under conditions of biological and abiotic stress. Single cotyledon grafting is a widely used grafting method for cucurbits, but success can be affected by differences between scion and rootstock of stem diameter, genetic compatibility and also of graft healing conditions. Cucumber typically have smaller hypocotyl (stem) diameters than other cucurbit scions and large differences between stem diameter of cucurbit scion and rootstock are typical, especially when using large stemmed hybrid squash rootstocks. During healing, as the interfacing tissue layer develops between scion and rootstock, scion cut end typically enlarges, covering the rootstock cut surface at the union. This typically happens during the first few days of healing under optimum healing conditions and is presumably critical to high grafting success. Scion genotype can also affect graft compatibility. In this test, scion material of slicer-type cucumber Cucumis sativus ‘Dasher II’ and long, seedless type ‘Rembrandt’ were grafted onto squash Cucurbita maxima x C. moschata hybrid rootstock ‘StrongTosa’. Plants were grafted at the appropriate developmental stage using the single cotyledon method. Three different grafting/healing conditions were tested: 1-2) plants grafted without cutting off rootstock roots and either roots in substrate saturated with water (uncut/wet) or with roots in moist substrate not saturated with water (uncut/dry) and 3) plants grafted after cutting off rootstock roots and the cutting stuck into moist substrate not saturated with water (cut/dry). All three conditions were in each of two separate healing chambers for each cultivar maintained at 28 °C. Relative humidity was ~100% RH for the first 5 days and then gradually reduced to ambient for remaining 2 days. Percent of live scions, and number of aerial roots at the graft union were measured; degree of union strength and internal rooting were evaluated eight days after grafting. Based on Pearson Chi-square test, graft union strength was significantly greater for cut/dry than uncut/dry but uncut/dry vs. uncut/wet and cultivar were similar. ‘Rembrandt’ and uncut/dry treatment had more aerial roots than ‘Dasher II’ and cut/dry, respectively, but uncut/wet vs. uncut/dry were similar. This may indicate that hormonal balance between scion and rootstock altered by genotype or grafting method (with or without roots) was more influential on grafting success than rootstock water status (e.g., root pressure) in cucumber grafting. Specific grafting and healing methodology may improve graft union strength potentially resulting in consistently high grafting success.