The Effect of Cutting Position Relative to Cotyledon on Survival Rate, Axillary Sprouts, Adventitious Root Formation, and Regrowth of Grafted Pepper Seedlings

Producing grafted vegetable plants is complicated or made untenable by adventitious roots erupting from the scion axillary sprouts developing on the rootstock. Removing both unwanted organs is labor intensive but necessary in fruit production because their presence has several undesirable effects. Still, chemical-mediated removal of axillary sprouts is challenging because offsite movement of the chemical (e.g., to roots via stem flow) may damage the root system. The goal of this experiment was to document the effects of rootstock and scion seedling cutting position -- above or below the cotyledon -- on plant survival and regrowth, and axillary sprout and adventitious root formation. Seedlings of “Early Sunsation” were used as the scion and rootstock when grafted to four other varieties (“Jalapeño M”, “Cayenne Large Thick”, “Hungarian Hot Wax” and “Thai Hot”) using the splice-tube method. Seedlings were cut either immediately above or below the cotyledons and plants representing three combinations of cut position were prepared 1) scion epicotyl/rootstock hypocotyl, 2) scion epicotyl/rootstock epicotyl and 3) scion hypocotyl/rootstock hypocotyl. Twenty newly-grafted plants representing each of the eight variety and three cut-position combinations (24 treatments; 480 plants total) were arranged in a completely randomized design within a standard healing chamber in a climate-controlled greenhouse room at the OSU-OARDC in Wooster, OH. Plant survival rate and regrowth rates were recorded 15 days after grafting using destructive and non-destructive measures; adventitious root and axillary sprout development were also scored. The experiment was repeated twice June-September 2015. Survival and plant data were unaffected by variety combination and interactions involving variety combination and cut position were not significant. Percent survival (79%) was significantly lower among plants prepared with the scion hypo-/rootstock hypocotyl combination but it did not differ between the two other combinations, averaging 93%. Axillary sprouts developed in nearly 76% of plants with the scion epi-/rootstock epicotyl combination but not in any other combination. Similarly, adventitious roots developed in plants with the scion hypo-rootstock hypocotyl combination but not in any other combination. Plant fresh and dry weights were greater when both the scion and rootstock were cut at the epicotyl and similar in the other cut position combinations. Grafted plant leaf area calculated by WinCam from digital images was unaffected by cut position treatment. Additional related research is underway and involves seedlings representing the scion hypocotyl/rootstock epicotyl cut position combination.