Identifying heat tolerant fragaria accessions using chlorophyll fluorescence

Chlorophyll fluorescence (CF) is a rapid, non-destructive technique with the potential to identify photosynthetic tolerance to abiotic stresses in plants. The objectives of this study were to 1) determine the optimum parameters for measuring CF, 2) assess how CF traits such as maximum (Fm) and variable (Fv) fluorescence and their ratio (Fv/Fm) are affected by temperature, and 3) compare the CF traits of a collection of accessions of F. chiloensis and F. virginiana at high temperature. Using 'Tribute' (F. X ananassa) for objectives 1 and 2, the dark adaptation time and light intensity yielded maximum CF values at 20 min and 80% of maximum intensity, respectively. As air temperature increased from 23 to 39 °C, Fv/Fm values declined. This resulted from an increase in background fluorescence and a decrease in Fm. Measurement of CF on a collection of Fragaria accessions planted in the field at temperatures exceeding 32 °C indicated some accessions were more tolerant of the high temperatures than others. Although there were no species-level differences, or differences within provenances of F. chiloensis, F. virginiana accessions from eastern North America were generally more heat tolerant than those from western North America.