Document Type : original paper
Authors
1
Assistant Professor, Crop Physiology, Department of Legume, Research Center for Plant Sciences, Ferdowsi University of Mashhad,
2
Professor, Crop Physiology, Faculty of Agriculture, Ferdowsi University of Mashhad
3
Assistant Professor, Khorasan-e-razavi Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization (AREEO), Mashhad, Iran,
4
Department of Agrotechnology, Ferdowsi University of Mashhad, Mashhad, Iran
5
PhD. in Horticulture Science, Department of Horticulture Science, Faculty of Agriculture, Ferdowsi University of Mashhad, Iran
Abstract
Introduction: One of the reasons for the low seed yield of lentils is the use of landraces, the lack of mechanized harvesting, and spring cultivation. Despite the advantages of fall planting, freezing stress is one of the most important abiotic factors influencing the growth and yield of lentils. Freezing stress increases photoinhibition and the loss of maximum efficiency of PSII photochemistry. Chlorophyll fluorescence is a non-destructive and rapid technique used to screen for abiotic stress tolerance plants. Considering the advantages of fall planting of lentils, this study was conducted to identify lentil genotypes to freezing stress-tolerant by chlorophyll fluorescence technique.
Materials and methods: The experiment was conducted under controlled conditions in the fall and winter of 2018 at Ferdowsi University of Mashhad. The investigated factors included 18 lentil genotypes and four freezing temperatures (0, -15, -18, and -20°C). Freezing temperatures were applied in the middle of February in the thermogradian freezer. The chlorophyll fluorescence trends in time points include before stress, 24, 48, 72, 120, and 144 hours after freezing by using a fluorometer were determined. The survival was evaluated visually three weeks after rewarming. The lethal temperature of 50% of plants according to survival percentage (LT50su), the reduced temperature of 50% of plants according to dry matter (RDMT50), and the reduced temperature of 50% of plants according to plant height (RHT50) were determined by fitting the graph of the mentioned traits against the freezing temperatures.
Results: Between zero and -18°C, the decreasing trend of the maximum efficiency of PSII photochemistry in the light if all reaction centers were open (F′v/F′m) was very low, but with decreasing temperature from -18 to -20°C, the decreasing trend of F′v/F′m it became intense. At temperatures of zero, -15, and -18°C, 24 hours after applying the freezing stress, the recovery of F′v/F′m was observed. MLC407 has the highest ability to recover freezing stress damage to PSII at -18°C. Among the studied genotypes, MLC103 had the lowest, and MLC286 and MLC454 had the highest PSII operating efficiency in the light (F′q/F′m). Improvement in F'q/F'm was observed during the recovery period at zero, -15, and -18°C. As the temperature decreased from -18 to -20°C, a downward and irreversible process was observed in the value of F'q/F'm. Freezing stress decreases the photochemical quenching (F'q/F'v) at the end of the recovery period in MLC13, MLC33, MLC38, MLC84, MLC103, MLC334, MLC407 and MLC409. Decreasing the temperature from zero to -15°C decreased the estimates of the fraction of open PSII reaction centers (qL) in MLC334 and MLC407. MLC8, MLC11, MLC13, MLC17, MLC33, MLC47, MLC70, MLC286, MLC303, MLC334, MLC407, MLC409, MLC454 and MLC472 at -15°C and MLC11 and MLC47 at -18 °C had a survival rate over 50%. The lowest RDMT50 was observed in the MLC47 genotype(-18.9°C), and MLC47 and MLC11 had the highest ability to maintain dry weight. The cluster analysis results showed the relative superiority of the third group of genotypes, including MLC8, MLC11, MLC47, MLC70, MLC334, MLC407, MLC409, and MLC454 in the studied traits. Standardized canonical coefficient of traits RHT50, RDMT50, F′0, F′m, F′v, F′v/F′m, F′q/F′m, F′q/F′v and qL in the first canonical functions was significant.
Conclusion: In general, there was a significant variation between genotypes regarding the ability of the photosynthetic apparatus during the recovery after freezing stress. The lowest changes in chlorophyll fluorescence were observed at zero, -15, and -18°C, and the greatest at -20°C. In most of the genotypes, 24 hours after freezing stress, a suitable recovery was observed, which indicates the high freezing stress tolerance of these genotypes. The results showed the relative superiority of the third group of genotypes in the studied traits.
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