2017 ASHS Annual Conference

Graft union development involves complex signaling pathways and cell proliferation and differentiation responses, which are regulated by endogenous and exogenous factors. Wounding before grafting may trigger responses that speed graft union development and the resumption of plant growth. However, these wound-activated responses would need to be directed to the graft union, to start more or less immediately, and to result in an uncompromised root-shoot connection at the graft union. We set out to determine if the timing of 50% scion foliar trimming influences grafting success or regrowth rate of newly grafted pepper plants. ‘Aristotle’ (scion) and ‘Foundation’ (rootstock) seedlings were grown from seed in a climate-controlled greenhouse at OARDC. On Day 7 before grafting, non-destructive and destructive measures were taken on representative plants to record plant biomass and other variables. Fifty percent of the leaf area was then removed from another set of identical plants on the same day with before and after measures confirming that treatment targets were met. The process was repeated on Days 2 and 0 before grafting, with untrimmed seedlings. Scion seedlings trimmed on days 7, 2, and 0 before grafting and untrimmed scions were then splice-grafted to untrimmed rootstock seedlings. Grafted plant condition was assessed fifteen days after grafting using four measures describing the change in stem diameter (rootstock, scion), leaf area, and fresh and dry weight (total aboveground tissue, leaf, stem). The experiment was repeated twice in two, 50-day runs concluding on November 13, 2015 and April 28, 2016. Graft success was unaffected by treatment as plant survivorship exceeded 95% in all treatments in both runs. However, interestingly, trimming and trimming timing effects differed between runs. For example, except for leaf fresh and dry weight, grafted plants made with scions trimmed 2 days before grafting were similar to plants made with untrimmed scions. Effects of trimming 7 or 0 days before grafting differed between runs; e.g., absolute values of response variable values for plants made with scions trimmed 7 days before grafting were larger than for control plants (untrimmed scion) in Run 1 but often lower in Run 2. The opposite trend was true for plants made with scions trimmed on Day 0. Still, percent leaf area increase followed the pattern Day 7 > Day 2 > Day 0 > untrimmed. Percent increase in stem diameter followed the opposite pattern.