The Effects of Leaf Removal on Adventitious Root Formation and Plant Growth of Grafted Tomatoes

Grafting vegetables is gaining interest among tomato growers throughout the U.S. as a way to manage soilborne diseases and abiotic stress, in addition to increasing crop productivity. One significant barrier for growers is the low availability of grafted plants or the ability to propagate their own. A major challenge during propagation is managing the formation of adventitious roots (AR) from the scion, which if severe enough, can result in loss of rootstock function.  Possible reasons that cause adventitious rooting include a poor graft union, scion water stress, high humidity, and hormone response(s) to wounding. Previous studies have shown that removing leaves increases the success rate, but it is not known how this technique affects the formation of adventitious roots. Our study investigated how leaf removal (LR) affects the formation of adventitious roots on the scion and subsequent plant growth. Three leaf removal treatments, 0% LR, 50% LR and 90% LR, were applied to the scion ‘BHN 589’ and grafted onto rootstock ‘Maxifort’ rootstock. Plants were arranged in a healing chamber using a RCBD (4 reps), and 20 plants in each experimental unit. The experiment was repeated three times using three different healing chamber designs (shade, plastic, humidifier). After 10 days in the chamber, plants were removed and rated weekly on their AR for 3 weeks. For weeks 1-3 in all 3 experiments, plants with 90% LR had significantly lower AR ratings than 0% LR plants (P <0.05).  In the shade chamber, 50% LR plants also had significantly lower ratings than the 0% LR plants (P <0.05). We also performed an experiment to look at how leaf removal affected early plant growth. Four treatments: 0% LR, 50% LR, 90% LR, and nongrafted were applied to the scion ‘BHN 589’ and then grafted onto ‘Maxifort’ rootstock. Plants were grown in a greenhouse using a RCBD with 4 replications and 15 plants in each unit. On day 24 post-grafting, 3 plants samples in each experimental unit were measured for leaf area, shoot biomass root biomass, plant height, stem caliper, and flower count.  Sampling was conducted once every 7 days for 5 weeks. By week seven, all grafted treatments performed similarly for most plant growth parameters and were not statistically different. Our results indicate that leaf removal of the scion can increase high quality plants for growers because of the lower adventitious rooting and does not reduce the early season growth of the transplant.