Extended Abstract
1. Introduction: Tomato (Solanum lycopersicum) has great nutritional value and is one of the most important vegetables in the world. The tomato fruits have a large amount of antioxidants, Such as lycopene pigment, vitamins C, and several minerals, which are essential for human health. Salinity stress is one of the plant growths limiting factors globally that causes yield loss in tomato. In addition, in arid and semi-arid regions of the world, such as Iran, soil salinity is one of the major abiotic stresses. Two theories have explained plant growth inhibition under salt stress. First, return to the ion toxicity, and the second is related to the disruption of osmotic functions. Several reports stated that salinity reduces many physiological processes in plants, such as water absorption, nutrient uptake, photosynthetic rate, and yield. tomato is moderately tolerant to salinity, and some tomato cultivars and landraces show greater salt tolerance by demonstrating greater stability in growth with increasing salinity. Moreover, high salt tolerance has been reported for various wild tomatoes. But most of the tomato varieties are salinity susceptible. The genetic variation of tomato landraces could be used to consider salt tolerance improvement in tomato breeding programs. The present study aims to assess the genetic structure of salinity tolerance in tomato during the vegetative growth phase to develop a new breeding population of tomato for salt tolerance.
2. Materials and Methods: An experiment was conducted for the assessment of salt stress response of seven tomato inbred lines originated from Iran, Europe, the US, and Mexico, and their 27 F1 hybrids in a partial diallel design 7×7. A completely randomized factorial design was used with water salinity and tomato genotypes as two factors. Tomato genotypes were subjected to salinity stress at 0 and 10 ds/m. after 20 days, shoot and root dry weights, shoot and root length, root volume, root density, and root/shoot dry weight were measured. To determine leaf sodium and potassium content and sodium/potassium ratio flame Photometer device was used. Also, chlorophyll A, B, and Total chlorophyll content were measured by a spectrophotometer.
3. Results and Discussion: The results revealed significant effects of stress, genotype, and stress×genotype interaction for almost all traits, which indicates that there was a large genetic variation among the tested genotypes in response to the salinity stress. The results of Hyman and Jinks' diallel analysis showed a highly significant epistasis effect governing some traits in both control and salinity conditions. In the control condition, root and shoot length, root density, root dry weight/shoot dry weight, leaf sodium and potassium content, and sodium/potassium ratio were governed by non-epistatic gene action. While in stress conditions, root and shoot length, root density, root dry weight/shoot dry weight, and leaf potassium content showed non-epistatic inheritance. The degree of dominance was higher than one for root and shoot length, root density, root dry weight/shoot dry weight, and leaf potassium, which showed overdominance and dominance effects attributed to the genetic basis of these traits. The proper amount (more than 0.6) of Broadsense heritability for the mentioned traits represented an adequate level of genetic variance in control of the mentioned traits. However, the amount of narrow-sense heritability was low for the traits. Therefore, selection for such traits is likely to be more effective in advanced selfing generations. Regarding the results of the ( ) parameter, the proportion of positive and negative genes for all traits was equal except Root dry weight/shoot dry weight, Root Density, and Shoot length. Hyman’s graphical analysis indicated that some overdominance effects were involved in the control of the traits. According to the results, parent 5 carried superior alleles for the mentioned traits. According to GCA value results, genotype 7 was the best for all shoot traits and also had the highest GCA for root dry weight. Genotype 5 had the highest GCA amount for root length and leaf potassium content. The highest GCA value for chlorophyll A, B, and T was achieved from genotype 3.
4. Conclusion: Heyman and Jinks’ Diallel analysis results showed Epistasis gene action governing traits except root and shoot length, root density, root dry weight/shoot dry weight, and leaf potassium content. For these mentioned traits, High “a” (more than 1) and h²_B (More than 0.6) showed the nonadditive gene effects governing the traits under the salinity condition. Regarding the GCA results, genotypes 7, 5, and 2 were selected for further salt stress tolerance studies.