Cellulose nanocrystals reduce cold damage to reproductive buds in fruit crops

Every year tree fruit and grape growers suffer significant economic losses from cold damage to reproductive buds. A combination of pre-planned passive and active frost protection methods has been prevalently used to achieve some level of protection. Herein, we describe a new effective approach to protecting reproductive fruit buds from cold damage. Electrostatic application of cellulose nanocrystals (CNC) dispersion to fruit buds forms a thermal insulation layer with low thermal conductivity (0.061 W m−1 K−1). The dispersion was applied to dormant grapevine (Vitis vinifera) buds, and hardiness was evaluated by differential thermal analysis (DTA). CNC-treated buds were more resistant to freezing temperatures than untreated buds. Cold hardiness was improved by 2-4 °C with CNC treatment. The hardiness of sweet cherry (Prunus avium L.) reproductive buds at the 'first white' stage of development was also tested comparing CNC-treated (2% mass) and non-treated clusters. Pistil mortality was evaluated 24 h after treatment. Untreated pistils were killed at ca. −1 °C while the CNC-treated buds were hardy to ca. −4 °C. The temperature at which ca. 10%, 50%, or 90% of untreated pistils were killed was ca. −1.5 °C, −2.8 °C and −5.5 °C, the temperature at which ca. 10%, 50%, or 90% of treated pistils were killed was ca. −4.4 °C, −6.5 °C and −7.7 °C. In general, CNC treatment improved cold-hardiness of grape and sweet cherry buds by about 2-4 °C. These results demonstrate great potential for field applications of CNC to improve speciality crop yield security by protecting reproductive buds from cold damage.