با همکاری انجمن علمی منظر ایران
نوع مقاله : مقالات پژوهشی
نویسندگان
1 گروه مهندسی تولید و ژنتیک گیاهی، دانشکده کشاورزی، دانشگاه زنجان، زنجان، ایران
2 گروه خاکشناسی، دانشکده کشاورزی، دانشگاه زنجان، زنجان، ایران
کلیدواژه‌ها
عنوان مقاله English
نویسندگان English
Introduction
Despite a large number of studies on tomato, there is still limited information on how inbreeding depression affects seedling morphological traits under greenhouse conditions. These traits are important because they influence early plant establishment in the field and, consequently, the expression of yield-related characteristics. In tomato, hybrids are preferred because of their superiority in yield and fruit quality compared to their parents. The productive capacity of the F1 hybrid is broken in the F2 and subsequent generations due to segregation of favorable genes. Inbreeding depression, which occurs due to increased homozygosity and the expression of deleterious recessive alleles, can lead to reduced vegetative vigor and weakened morphological traits in segregating generations such as F2. Therefore, the present study was conducted to evaluate seedling morphological traits in F1 and F2 generations and to calculate the percentage of inbreeding depression in some common tomato hybrids.
Materials and Methods
The experiment was carried out during 2023 and 2024 in the research field and greenhouse of the University of Zanjan, Iran. In the first year, 22 cultivars were evaluated using a split block design (based on randomized complete blocks) with two replications. Eight superior F1 hybrids (SUPESET, JENNIFER, KAKI, MARVEL, FERGUSON, 8320, BASSIMO, and BRIVIO) were selected based on yield and growth indices, and their F2 seeds were produced. Due to the self-pollinating nature of tomato and the very low outcrossing rate (0.0–5.2%), individual flower isolation was not performed in the first year. However, plots were spaced 2 meters apart in the field to reduce any possibility of cross-pollination. In the second year, the F1 and F2 generations of these hybrids were grown in the research greenhouse under a randomized complete block design with two replications. Seedling traits including stem diameter (using digital caliper with 0.01 mm accuracy), plant height, leaf length, leaf width, petiole length, root length, shoot fresh weight, and root fresh weight were measured. Inbreeding depression percentage was calculated using the formula: [(F1 mean - F2 mean) / F1 mean] × 100. Statistical analysis was performed using SPSS v26, and mean comparisons were done using Tukey's test. Independent t-test was used to compare F1 and F2 means.
Results and Discussion
The genotype effect was significant for most of the traits, indicating significant genetic diversity among the studied materials. A comparison of F1 and F2 revealed a considerable difference, indicating a decline in trait values from F1 to F2. The highest inbreeding depression was observed for plant height (21.28%), root fresh weight (21.08%), stem diameter (13.82%), and root length (13.56%), while the lowest was recorded for leaf length (5.90%) and petiole length (6.89%). A greater degree of inbreeding depression may point to higher heterosis as well as a greater contribution of dominance effects. The extent of inbreeding depression for stem diameter, plant height, and leaf length varied among the eight hybrids examined. For example, in stem diameter, the highest inbreeding depression was observed in Ferguson and Kaki hybrids (20.57% and 19.90%), while the lowest was in Marvel hybrid (0.98%). In plant height, Jennifer hybrid showed the highest inbreeding depression (32.80%), followed by Superset (27.87%). In root length, genotype 8320 showed the highest inbreeding depression (21.09%), while Marvel and Superset showed the lowest (1.48% and 3.60%, respectively). In shoot fresh weight, the highest inbreeding depression was observed in Bassimo (17.76%), while Marvel showed the lowest (0.33%). Some hybrids showed negative inbreeding depression, indicating the superiority of F2 over F1 for that trait, such as leaf length in Bassimo (-10.93%) and petiole length in Brivio (-6.10%). Independent t-test results showed that differences between F1 and F2 means were significant for all seedling morphological traits at the 5% probability level. The highest t-values were observed for stem diameter (5.822), root length (5.628), and leaf width (5.060).
Conclusion
These results can be applied in tomato breeding programs in advanced generations obtained from self-pollination of these cultivars. For cultivars with low inbreeding depression, the best derived inbred lines can be introduced as new varieties. When inbreeding depression is high, it is necessary to exploit heterosis through reciprocal crosses and selection of the best hybrid. The amount of inbreeding depression can be a practical indicator for evaluating the stability of seedling morphological traits and selecting the appropriate breeding strategy for improving tomato traits at the seedling stage. The findings of this study also highlight the importance of considering both shoot and root traits when evaluating inbreeding depression in tomato seedlings.
Acknowledgement
The authors thank the University of Zanjan for providing research facilities. Also, the supervisor and advisor are thanked for their valuable guidance.
کلیدواژه‌ها English
