Experimental Research on Frost Indexes for Lycium Barbarum Flowering Phase

Based on researches of frost indexes of Lycium barbarum during 2016-2018, tests of frost index are performed using an artificial frost box in 2019, focusing on flower bud, early flowering and full flowering periods. The temperature of treatment is -8—-1℃, and time duration is 1-6 h, which forms 32 combinations of low temperature and time. Frozen symptoms of Lycium barbarum are divided into 3 degrees (P₁, P₂, P₃) according to observation after freezing. The mild frost is defined as 0≤P₁≤50%, 0≤P₂ < 50% and 0≤P₃ < 10% (P₁, P₂, P₃ not to be zero at the same time). The medium frost is defined as 0≤P₁ < 50%, P₂≥50% and 0≤P₃ < 10%, or 0≤P₁ < 50%, 0≤P₂ < 50% and 10%≤P₃ < 50%. The severe frost is defined as 0≤P₁ < 50%, 0≤P₂ < 50% and P₃≥50%. P₂ and P₃ are decisive for confirming frost levels. The frozen rate of each frozen degree is counted and the judgment standard of frost are formulated. In terms of these studies, frost indexes are established based on low temperature, time of duration, cold level, and rate of cold. Frost indexes are verified by using results of field experiments at 13 sites and investigations into natural frost disaster at 25 Lycium barbarum planting regions. Results indicate that frosts of Lycium barbarum are closely related to the low temperature and its duration. Lower temperature and longer duration lead to more seriously frost disasters. The frost resistance of flower bud period is the strongest, which is significantly stronger than that of early flowering period. The frost resistance of full flowering period is weaker than early flowering to some degree. The result of judgment with frost indexes and the situation of actual disaster have high compliance, coincidence rates are 92.9%, 81.8% and 91.7%, respectively. The indexes have strong practicability which can be used as basics for forecast and assessment of frost damage at different stages of Lycium barbarum flowering phase.