The production of tomato under low-temperature stress in the open fields is a challenge faced by many farmers. The current study compares the use of different ethylene treatments to accelerate the fruit ripening of tomato during two successive seasons under cold stress. The treatments included foliar application of ethrel (2500, 5000, and 7500 ppm) in the open field at the mature green stage, dipping collected fruits in ethrel solution (1000, 1500, and 2000 ppm) right after harvest, and application of gaseous ethylene (100, 200, and 300 ppm) to the harvested fruits. The effects were compared to untreated fruits (control). Characteristics, such as physical properties (ripening, weight loss, firmness, decay, and fruit color), chemical properties (ascorbic acid, acidity, total soluble sugars, and pigments), and enzymatic activities (polygalacturonase and pectin methylesterase), were sampled throughout the storage period. In general, the ethylene gas application was the most effective method in accelerating the fruit ripening process compared to the other methods applied. The highest vitamin C total soluble solid contents and redness parameters were found after applying the highest dose of ethylene gas (300 ppm). This indicates that the ripening of tomato fruits, which are cultivated under cold stress conditions as found during the early summer season in a Mediterranean climate, might be harvested at a mature green stage and exposed to ethylene application.

Gene action and combining ability effects were estimated in forty five hybrids obtained from crossing fifteen lines with three testers using line x tester matting design. These genotypes (fifteen lines, three testers and forty five hybrids) were evaluated for vegetative growth, yield and its quality in late summer season. This study was carried out at Faculty of Agriculture, Kafrelsheikh University, Sidi Salim distrect, North-Delta Region of Egypt. G.C.A and P.C.V. % ranged from 0.88 to 0.98, which was confirmed by the estimated ratio of G.C.V. / P.C.V. Furthermore, broad sense heritability (h 2 bs) values ranged from 76.96 to 95.60 suggesting less effect of environmental and the large portion of σ 2 p was due to the σ 2 g on these traits. The magnitude of variance due to general and specific combining ability was highly significant indicating importance of the additive (σ 2 A) and non-additive (σ 2 D) gene action. However, the ratios of σ 2 GCA / σ 2 SCA (<1) and σ 2 A/ σ 2 D (<1) revealed the preponderance of non-additive variance in the inheritance of all studied traits. The average degree of dominance revealed over-dominance for all studied traits except for ascorbic acid content, which was revealed partial dominance. Highly significant differences were observed among the parents and hybrids for general combining ability (GCA) and specific combining ability (SCA) effects. The parental lines HE-13-2-1, HE-6-5-1, HE-13-1-1 and D-7-3-1 displayed desirable general combiners for most studied traits. The cross combinations HE-13-1-1 x F.M.9, D-4-3-1 x F.M.9, D-2-1-2 x Super Strain B and HE-19-1-1 x Super Strain B are considered the best specific combinations since showed desirable significant SCA effect values for most studied traits.