Cellulose nanocrystal dispersions improve cold tolerance in developing apple flowers

Cold damage to reproductive buds or flowers is a perennial concern to tree fruit producers. In fact, cold damage has caused more economic losses to crops in the US than any other weather hazard. The potential losses (yield reductions to complete crop failure) from cold damage are predicted to increase with variable weather patterns resulting from climate change. Cellulose nanocrystals (CNC) represent a new generation of renewable nano-biomaterials with many unique physical and chemical properties, including their low thermal conductivity, that can be produced in abundance from a wide variety of plant-based materials. Our team has developed a process for creating CNC dispersions that can be sprayed onto trees, forming an insulating film, and increasing the cold tolerance of reproductive buds. This work was conducted to test the efficacy of the dispersions on apple 'WA 38' (Malus x domestica Borkh. 'WA 38') flowers open cluster stage. Trees were treated with 3% CNC dispersion using a single nozzle, air-assisted, electrostatic sprayer. Flowers were tested for cold tolerance using a controlled freezing test 24 h post application. Treated trees were also analyzed for possible deleterious effects on rate of floral development as well as fruit set. CNC Treated flowers had a 1.9 degrees C decrease in lethal temperature resulting in 10 percent flower death (LT10) and no significant effect on floral development nor fruit set. These results further expand on the utility of CNC dispersions to decrease cold damage in tree fruits, demonstrating its transferability across species and at later stages of bud development, when threat of cold damage is most severe. These characteristics further implicate CNC dispersions as an effective sprayable frost protectant to be utilized in future cold damage prevention strategies.