The chlorophyll fluorescence parameters response of lentil (Lens culinaris Medik.) genotypes to freezing stress

A factorial experiment in a randomized complete block design with three replications was carried out to evaluate the freezing tolerance of 40 lentil genotypes, at the Research Center for Plant Science, Ferdowsi University of Mashhad, in 2017-2018. The status of chlorophyll fluorescence parameters was studied in eight genotypes (seven tolerant: MLC11, MLC12, MLC17, MLC38, MLC95, MLC409, and MLC410 and one intolerant: MLC9) and five time periods (before stress, 12, 24, 48, and 72 hours) exposed to freezing temperatures (-13, -15 and -18°C) for one hour. The results showed that the value of F'm in MLC409, 72 hours after freezing stress, was slightly different from its value in the early hours. The maximum efficiency of photosystem II (F′v/F′m) was not affected by temperature decline from -13 to -18°C. MLC9 F′v/F′m, however, decreased by 26% when the temperature declined from -13 to -18°C. Furthermore, F′v/F′m decreased by 14% at -18°C 24h after the freezing stress, which was the greatest decrease compared to -13 and -15°C. However, 48 h after freezing stress, the optimal recovery trend was evident at all temperatures. Although the operational efficiency of photosystem II (F′q/F′m) decreased at all three temperatures, 24 h after the freezing stress, this decrease was greater at -18°C than at other temperatures. Except for the MLC9, other genotypes, especially MLC12, could improve freezing stress damage 24 h after stress and gradually return to F′v/F′m before freezing stress. In general, the freezing-tolerant genotypes and in addition to the survival rate of more than 80% at -18°C, showed a high potential to restore the photosystemII performance, which can be considered for further studies for autumn cultivation in cold and highland regions..