Chlorophyll Fluorescence: A Novel Method to Screen for Herbicide Resistance

The susceptibility to terbacil of six randomly selected strawberry cultivars (‘Aromas’, ‘Chambly’, ‘Harmonie’, ‘Kent’, ‘La clé des Champs’, and ‘Seascape’) was analyzed using chlorophyll florescence (CF) in comparison with visual observation in an attempt to develop a method for use in a breeding program to select herbicide-resistant strawberry lines. Terbacil was applied at one of five rates (0, 0.55, 1.10, 2.20, and 3.30 kg/ha), and CF was measured 1, 3, 7, and 14 d after application. Visible damage was assessed using a scale of 0 to 10 (where 0 is no damage and 10 is the death of the leaf). All cultivars showed a decrease in CF after herbicide application, but this decrease was not the same for all cultivars. ‘Chambly’ and ‘Harmonie’ had the lowest CF changes, and both appeared to be tolerant or resistant to terbacil, in keeping with previously reported results. In contrast, ‘Kent’ and ‘Aromas’ showed a significant decrease in CF on the third day after treatment with terbacil at 2.20 and 3.30 kg/ha, an indication that their chlorophyll system had been damaged by herbicide application without any visible signs of leaf damage. It is concluded that CF can be used as an alternative and more accurate method to evaluate seedlings in a strawberry breeding program aimed at selecting herbicide-resistant lines. This method could be very useful, especially for those lines that do not show any visible leaf damage from herbicide application, even though their chlorophyll system is damaged enough to cease plant growth and development.