2019 ASHS Annual Conference

Currently most Oregon olive growers purchase stock plants from California nurseries. As Oregon’s olive industry grows, producers are looking to on-farm propagation to reduce costs. Determining best practices for olive propagation in Oregon is needed. The objectives of this study were 1) to evaluate four rooting hormone rates during three seasons to determine their impact on average primary root number and average root length, and 2) to determine which season is associated with the most successful rooting. On May 25, July 24, and Oct. 15, 2018, 96 8-cm cuttings were taken from mature Arbequina olive trees in Dayton, OR. Cuttings were dipped in one of four hormone treatments (3000ppm IBA, 8000ppm IBA, 2000IBA + 1000NAA, and 4000IBA+2000NAA), and planted in 32-cell, 6.67 cm trays filled with 2:1 peat:perlite. Cells were organized in a completely randomized design in trays, and kept in a temperature-controlled greenhouse on benches with bottom heat and automated mist irrigation, at the North Willamette Research and Extension Center in Aurora, OR. Data was collected three months after each propagation date by counting total primary roots per cutting and measuring total root length for all roots 0.5cm or greater. Data was analyzed using ANOVA on SAS version 9.4. Season was significant (p < 0.0001) for root number and length, with spring having the greatest root number and length, followed by summer and fall (not statistically different). For spring propagation, hormone rate had a significant effect on root number (p = 0.0004) and length (p = 0.0007), with the highest rate, 8000ppm IBA, having the greatest average number of roots (12.5), and the highest average root length (65 cm). There were no significant effects from hormone rate treatments during summer or fall. In a sub-trial using covered trays with hand watering instead of mist during fall propagation, hormone rate treatments had a significant effect on root number (p = 0.0384) and length (p = 0.0347). In this instance, 3000ppm IBA was associated with the highest average root number (6) and length (27 cm). Comparing rooting success across seasons, the interaction of season and hormone rate was significant (p < 0.0004) for root number, but not length. Initial results suggest that propagation season may have more influence on rooting success than specific hormone-rates, and that the interaction between season and hormone may have a greater effect than any treatment alone. This study will be replicated in 2019.