Evaluation of the cold tolerance with some biochemicals analyses in the genotypes obtained from mutation breeding in some citrus species and cultivars

ABSTRACT EVALUATION OF THE COLD TOLERANCE WITH SOME BIOCHEMICALS ANALYSES IN THE GENOTYPES OBTAINED FROM MUTATION BREEDING IN SOME CITRUS SPECIES AND CULTIVARS Many Citrus species have come into existence as a result of natural mutations, and new varieties have been developed by vegetative propagation of these mutants. Due to cross pollination, high heterozygosity and infertility, the development of new varieties of Citrus species with classical hybridization breeding is a costly and labour intensive process, which is sometimes impossible to accomplish. In recent years, the artificial mutation breeding method has been used in development of citrus varieties. This method makes it possible to improve one or more characteristics of a variety (which is accepted by the market, farmer or consumer) while preserving the positive characteristics. In the light of this hypothesis, in this study, identification of Effective Dosage of The Mutagen (EMD) in the Moro orange, Interdonato lemon, and Mexican lime and determination of new genotypes that are tolerant to cold in the mutant populations created with the identified aimed dosages. As a biological material, Moro orange, Interdonato lemon and Mexican lime were used in this study. Shoots, including buds, were irradiated with gamma ray from a Cobalt 60 (60Co) source, in order to develop new varieties by creating variation in all varieties of the chosen species. Then the irradiated buds were grafted onto a local sour orange (Citrus aurantium (L.) Yerli) rootstock using the T budding technique. In the first phase of the study, the EMD was identified for each citrus cultivar and the M1V1 populations were formed up by applying gamma ray with the identified EMD to buds of the cultivars. In the second phase, M1V2, M1V3 populations were created from clonal propagation of the M1V1 population. Afterwards, ten mutant individuals were identified in each Citrus species based on pre-selection criteria. In the third phase, the ratio of leaf water content, chlorophyll content, total soluble protein amount, and membrane permeability were determined in the selected mutant and control individuals from each of the Citrus cultivars. In addition, the mutant candidates were evaluated in three different periods for proline concentration and the artificial freezing test, based on the Ion leakage method. As a result of this study; the EMD was determined to be 68 Gy, 50 Gy, and 45 Gy in Moro Blood orange, Interdonato lemon, and Mexican lime respectively. In terms of physiological properties examined in the study, it was observed that gamma ray application resulted in the reduction of grafting success, shortened shoots and internode length. When mutant candidates were analyzed in terms of biochemical properties, it was found that the rational leaf water content, in general, increased in the citrus species, Moro orange M-5 and Mexican lime L-9 genotypes and decreased in all of Interdonato genotypes. While Moro orange genotypes in general showed a decrease in chlorophyll content, an increase was recorded for Interdonato lemon I-3 genotype and Mexican lime L-7, L-8, and L-9 genotypes compared to plants. Regarding total soluble protein concentrationin in plants, an increase has been identified in M-10, M-3, M-1 genotypes from Moro orange, I-3 genotype from Interdonato lemon and L-2 genotype from Mexican limes. Proline accumulation in the plants was shown to vary depending on species. The lowest level was found in M-5, I-5, and L-9 genotypes. In the freezing test, the low temperature tolerance was found to be -4.11C for I-4, -3.51C for L-8, and -2.91C for L-9. In conclusion, we could conclude that EMD, Biochemical properties, and tolerance to low temperatures vary depending on citrus species. KEYWORDS: Citrus, Chlorophyll content, Freezing test, GR (EMD), Interdonato lemon, Membrane damage, Mexican lime, Moro blonde orange, Induced mutation, Leaves water content, Proline, Protein.