2018 ASHS Annual Conference

Golden kiwifruit (Actinidia chinensis Planch) has recently emerged as a new potential fruit crop for the Southeastern United States. Successful trials in Alabama, along with initial success at Stephen F. Austin State University, Nacogdoches, TX, has led to more extensive trialing of this crop in Texas. Both A. chinensis and A. deliciosa require winter chilling for overcoming dormancy and for flowering. Texas is subject to both inconsistent chilling and erratic winter temperatures. Warm temperature exposure during winter has resulted in the apparent negation of chilling in other fruit species. This study was conducted to investigate the floral and vegetative response of two pistillate kiwifruit cultivars to warm temperature interruption during chilling accumulation. Dormant one-year-old canes of A. chinensis ‘AU Golden Dragon’ and A. deliciosa ‘AU Fitzgerald’ were collected in December 2018 (335 C.U.), shortly after leaf abscission. Canes were cut to ten nodes after removing the first six basal nodes, placed in jars filled with distilled water, and transferred to respective chilling treatments. Treatments included continuous chilling (in addition to base chilling) at one-week (168 C.U.) increments (0 to 5 weeks) and chilling exposure at the same increments with intermittent warm temperature. For the warm temperature treatments, each week of chilling was followed by three days of exposure to warm conditions. Chilling and warm temperature exposure were simulated by 7°C / 4°C and 25°C / 17.2°C (day / night) temperatures, respectively, using separate climate-controlled growth chambers. Following chilling treatments, canes were forced in a third chamber at 22.8°C to 26.0°C with LED lighting. Vegetative bud break, along with floral bud number and development stage, were recorded for each cane and with respect to nodal position at two-day intervals. Maximum flower bud number was highly dependent on chilling exposure (R² = 0.99 for ‘AU Fitzgerald’) for the consistent chilling treatments. A strong node-position influence was also observed, with distal nodes producing more vegetative shoots and floral buds. While warm temperature interruption resulted in an insignificant reduction in average flower bud number (per-cane) for ‘AU Fitzgerald’, a significant increase was observed for the ‘AU Golden Dragon’ at higher chilling treatments. At 4- and 5-week chilling treatments, 634% and 449% more flower buds, respectively, were recorded as compared to treatments with the same amounts of consistent chilling. These results suggest that the two species may respond differently to intermittent warm winter temperatures, and perhaps even favorably in the case of A. chinensis.