الفهرس 
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Abstract
Tomato (Lycopersicon esculentum.) belongs to the Solanaceae family is one of the most important vegetable crops grown in Egypt. Significant reduction in fruit yield and quality happens every year in Egypt during winter and early summer seasons since tomato grown under temperatures below 13 °C may inhibit fruit-set. On the other hand, due to the increase of growing tomato area under open field conditions between November to March, there was a persistent need for identification of the genetic factors related to the chilling tolerance as the best strategy for selection of tolerant genotypes and hybrids development. In this investigation we studied the genetic diversity using SCoT marker technique among five varieties and six genotypes of tomato (Floradade, Edkawy , Castle Rock, Super marmande, NC 1 CELBR, KL-45, KL-41, KL- 46, KL- 47, KL-03, KL-52). In addition, investigating The ability of the same genotypes to grow under chilling conditions (the effect of ATP and glycine betaine on the protecting plants and mitigating cold stress effects) as well as selection the most promising Genotypes for further breeding programs. The experiment was carried out at Genetics Department farm, Faculty of Agriculture, Mansoura University, Egypt during winter season of 2017/2018. Seeds were sown in 209-cell trays filled with a commercial substrate. After 35 days, seedlings were transplanted to field at 35 cm apart on one side of ridge 4.5m long and 1m wide. A Randomized Complete Block Design (RCBD) in three replicates was adopted in the current investigation. During this experiment, plants were grown in low temperature condition where level of night temperature drops several times below 10 C. The following chemical agents ATP and glycine betaine were used in concentrations of 100 ppm and 50 ppm, respectively as foliar spray. Plants were sprayed four times with assigned treatments, the first one was at 20 days after transplanting and repeated each 15 days. The major results from this study could be summarized as follows: 1. Eight SCoT primers through PCR were succeeded in targeting the amplification of many DNA sequences in the eleven genotypes of tomato. 2. DNA profiling showed that, SCoT primers generated 14 (3 negative and 11 positive) out of 94 bands with an average of 11.75 bands per primer ranged from seven (SCoT-6 and SCoT-9) to 22 (SCoT-1). 3. The molecular distance (MD) between all studied genotypes based on SCoT ranged from 0.215 to 0.482. The highest molecular distance (MD) was among KL-41 and KL-03 (0.482) followed by Edkawy and KL-52 (0.475), while the lowest MD according to the same data was between Floradade and Edkawy (0.215) followed by KL-46 and KL-47 (0.216). 4. The magnitudes of the mean squares of genotypes were highly significant for all studied traits, except for chlorophyll a, leaf carotenoids content at 60 and 90 days, chlorophyll b and total chlorophyll content at 90 days from transplanting. However, the mean square of treatments were highly significant for all studied traits except for fruit length, fruit diameter, thickness, total soluble solids (TSS), chlorophyll b at 60 days and number of clusters for plant. In addition, the mean squares for genotypes by treatments interaction were not significant for all traits, except for chlorophyll a, b at 60 days from transplanting, lycopene, ascorbic acid , fruit set, average fruit weight, and total yield/plant. 5. The mean values showed that no specific genotype was superior for all studied traits. Where, the variety S. Marmande was the best for fruit weight for treatment (122.30) and total yield at control and treatment with mean values 3.73 and 5.54, respectively. Whereas, the variety NC1 CELBR has the greatest values for fruit length and thickness at control and treatment with mean values 5.37, 5.51, 11.04 and 11.33, respectively. In addition, the Castle Rock had the greatest value for fruit lycopene content at control and treatment with mean values 8.71 and 10.64, respectively. 6. The line KL-46 had the greatest mean value for number of branches and total chlorophyll at control and treatment at 60 days from transplanting with means of 8.33, 10.00, 3.73 and 4.53, respectively. On the other hand, the line KL-45 appeared the highest values for plant height, TSS and firmness at control and treatment with mean values 126.7, 137.7, 6.52, 6.33, 7.50 and 7.67, respectively. 7. The results cleared that the variety Edkawy had the highest relative increase value over untreated plants for plant height, number of branches total yield (26.46, 43.9 and 54%.237 respectively). Also, the variety Floradade have the highest relative increase over control for total chlorophyll content and leaf carotenoids at 60 and 90 days from transplanting (43.47, 86.84, 66.42 and 108.4%, respectively). In addition, the line KL-47 have the highest response comparing to their relative untreated plants for lycopene content (23.36%). 8. The results revealed that the magnitudes of genetic variation were high and positive for all traits and most of the observed variations attributed to genetic cause’s more than environmental factors. This finding is emphasized by the heritability values, which were more than 70% for all studied traits, expect for ascorbic acid which was 43%. The chlorophyll and carotenoids content at 60 and 90 days of transplanting gave the heritability values were less than 30%. 9. from phenotypic data, distances among the eleven tomato genotypes were calculated using Euclidian method. The results of Euclidian distances (ED) matrix. Exhibited that the distances ranged from 12.88 to 58.20. 10. The lines KL-45 and Kl-47 were appeared increasing in peroxidase banding intensity in treatment compared with control in all five peroxidase groups. While, at treatment case the line KL-47 illustrated increasing in banding density in px3 and Px4 with relative motilities of 0.7 and 0.75, respectively. On the other hand, there were no differences in intensity of bands in each of S. marmande and KL-03 between control and treatment. 11. For Polyphenol oxidase (PPO1 and PPo2) increasing in band intensity was recorded in each of S. marmande and Kl-47 cultivars in treatment compared with control with relative motilities (0.45 and 0.60) respectively. While, KL-47 at treatment case was appeared increasing in band intensity of PPO2 compared with control with relative mobility 0.60. 12. Protein analysis resulted nine banding patterns with molecular weights ranging from 13-192 KDa. There were two bands absent in KL-46 at control and present in treatment with molecular weights of 43 and 36 KDa, respectively. While, the line KL-03 represented two bands in control which were absent in treatment with molecular weights of (43 and 66 KDa).In kl-03 variety ,there was one band with MW73,36 KDa absent in control and present in treatment Finally, information on the sensitivity of cultivars to weather conditions is very important for breeders for new cultivars release and also for producers to can select cultivars to grow specifically for both fresh market or for processing. Furthermore, the selection of a suitable cultivar for specific environmental and climatic conditions is of great significance for sustainable production of tomatoes.