With a view to integrating a physiological approach into the durum wheat breeding program some chlorophyll florescence parameters of light-adapted leaves were investigated. The variability for these parameters in a collection of large numbers of durum wheat genotypes – breeding lines, old and modern Bulgarian and foreign cultivars, was studied. The genotypes were cultivated under field conditions during 2010/2011 at the Field Crops Institute in Chirpan. The chlorophyll fluorescence was measured on flag leaves during the grain filling stage with a portable chlorophyll Fluorometer – MINI-PAM – WALZ-GmbH – Germany. Significant differences were found between durum wheat genotypes for both parameters – momentary fluorescence yield (F) and maximal fluorescence yield (F’m ). The quantum yield (Y) varied less between the genotypes in comparison with other studied fluorescence parameters and ranged between 0.289 for cultivar Dejana to 0.493 for cultivar Gergana. The established differences in the fluorescence parameters of durum wheat genotypes revealed the significant differences in the capacity for absorption and use of light of the studied genotypes and indicated that chlorophyll
fluorescence might be a useful tool for characterising genetic polymorphism.