Current Opinion in Agriculture Curr. Opin. Agric. 2013 2(1), 28–31. Evaluation of heterosis and combining ability using diallel cross in tomato lines for salinity tolerance during seedling stage H Kaveh 1* , H Nemati 1 , M Farsi 1 , S Vatandoost 1 , T Jalali 2 1 Department of Horticulture, Faculty of Agriculture, Ferdowsi University of Mashhad, Iran. 2 Technical-Vocational University of Iran, Al-Zahra institute of Mashhad, Iran. * Corresponding author's E-mail: hamed.kaveh@yahoo.com Abstract Great numbers of studies on tomato breeding have been performed for resistance to environmental stresses as well as pests. In genetic investigation and breeding of tomato, it is tried to use tomato lines with the most variance on morphological and agronomical traits to obtain better results. In this survey combining ability and heterosis of 7 inbred lines of tomato and their F1 hybrids were investigated for salinity tolerance during seedling stage using diallel cross. So seed germination percentage and seedling emergence percent and rate under salt stress examined in a complete randomized design with 4 replications. Results of analysis showed that the reciprocal effects and special combing ability (SCA) were significant for all traits on probability of 1 %. Analysis of Wr-Vr regression also showed that seed germination percentage and seedling emergence percentage and rate under salt stress controlled by over dominance effects. Best line for resistance to salt stress in juvenility was R205 which has the most general combing ability (GCA) for all three traits connected to salt resistance. Keywords: Cytoplasm effect, Dominance, Reciprocal cross, Seedling growth, Trait control Abbreviations: GCA, general combing ability; SCA, special combing ability Introduction Tomato (Solanum lycopersicon) (2n=2x=24) is one of the most important solanaceous vegetable crop of Peru-Eucador origin (Peralta, Knapp et al. 2005). It is a moderate nutritional crop and is considered an important source of vitamin A, vitamin C and minerals. To meet ever increasing demand for tomato, use of F1 hybrids is one of the means to meet the demand (Nuez 2008). As F1 hybrids in tomato offer several advantages such as earliness, higher productivity, improved quality, resistance to biotic and abiotic stresses and also provide a quick and convenient way of combining desirable characters (Omholt 2000). The phenomenon of hybrid vigour or heterosis in tomato was first discovered by Hedrick and Booth in 1908(Kurian, Peter et al. 2001). It has been realized that hybrids perform better than self pollinated cultivars in respect of uniformity of product, yield, quality, resistance to pest and diseases. Adoption to different environmental condition and long storage life (Titok 1994). The heterosis in tomato has been exploited for developing hybrids through hand emasculation and hand pollination (Omholt 2000). It is well documented that the amount and quality of irrigation water available in many of the arid and semiarid regions of the world are the main limiting factors to the extension of agriculture" (Munns 2002; Al-Busaidi 2009). High Soil salinity level can be a major environmental constraint to crop productivity. Most crops are susceptible to salt stress and either die or have a yield or growth reduction (Kaveh 2011). In tomato (Solanum lycopersicum), high concentrations of salt (150 mM NaCl and 15 mM CaCl2) in the germination media significantly delays onset and reduces the rate of germination (Foolad 1997; Foolad 1999; Foolad 2004; Kaveh 2011). The tomato response to salt stress is differently regulated in different development stages. Salinity slows down tomato shoot growth and the growth of younger seedlings; the higher the saline concentration the larger the reduction in shoot growth (Foolad 2004; Li, Liu et al. 2011). Material and methods Plant material In this study, seven Lines ME, KaLN3, Fla, CT6, LA3770, R2- 05 and DB selected from 133 tomato lines of the Ferdowsi University of Mashhad collection, based on variation in morphological biological and agronomical traits. Crossing method After choosing the parental lines, six plants of each line cultivated in separate rows with a distance of 80 cm between rows and 50 cm between the plants in greenhouse condition. Hand emasculation and hand pollination of different tomato lines were done after flowering. Pollinated flowers covered with cover sheets to prevent unwanted pollinations. Seed extraction Full ripe tomato fruits were collected and seed extraction was done using fermentation method (Nemati, 2010).