Abstract
Most strawberry cultivars have flowers that are sensitive to temperatures below 0°C. The development of early or very early cultivars with frost resistant flowers is essential in climates with a danger of spring frosts. Traditionally, breeding programs have used visual screening methods to evaluate the damage to pistils and anthers caused by frost. These methods rely on natural seasonal conditions, are time consuming, and do not provide accurate information on the exact temperature that caused the damage. The objective of this study was to evaluate the use of chlorophyll fluorescence (CF) to estimate the low temperature susceptibility of 64 strawberry cultivars. Strawberry flowers were exposed to continuous low temperatures (0°C for 24 h, 1°C for 24 h, -2°C for 24 h, and finally -3°C for 24 h) and CF was measured following the treatments. Variable fluorescence (Fv) decreased somewhat with time in all genotypes when the flowers were held at -3°C, however, the reduction varied with cultivar. The slight reduction of Fv in the more chilling-tolerant cultivars was not significant, while significant linear or quadratic declines were observed in the more chilling susceptible cultivars. Overall, chlorophyll fluorescence appears to be an effective, simple method for evaluating the low temperature susceptibility of strawberry genotypes.