ارزیابی و گزینش تست کراس‎های مقاوم به ریزومانیا و پوسیدگی ریشه بر اساس شاخص انتخاب ژنوتیپ ایده‌آل (SIIG)

Extended abstract
Introduction
Sugar beet (Beta vulgaris L.), belonging to the family Chenopodiaceae, is a biennial root crop known for sugar production after sugarcane. Rhizomania and root rot are considered as the most deleterious diseases for sugar beet production and consequently sugar industry. These diseases result in significant yield losses and influence grower profitability. The most efficient way to deal with the disease is to use resistant cultivars. Researchers have introduced various indices to increase selection efficiency. One of these indices is the SIIG index, which was introduced to integrate different methods of stability analysis. For its calculation, a variety of indices and traits with different natures and units can be used, increasing the efficiency of selection. Considering that selecting desirable cultivars with specific and desired characteristics by a single trait alone may not lead to desirable results, in this study, the ideal genotype selection index was used to integrate important traits related to quantitative and qualitative yield for better evaluation of hybrids and identification and selection of ideal hybrids.
Materials and Methods
In order to select the ideal hybrid in terms of all the evaluated traits, 16 hybrids obtained from test cross along with domestic control called Dena and three foreign controls called FD16B3013, Urselina and BTS1930 were evaluated based on randomized complete block design with four replications in five locations of Karaj, Miandoab, Mashhad, Shiraz and Hamedan in 2023. After land preparation including plowing, disking, leveling and plotting, the experiment was planted in late March. The studied materials were evaluated in experimental plots consisting of three rows of 8 m length with 50 cm row space and 18 cm distance between plants in a row. Roots were harvested and weighed in the second half of October, and root yield for each cultivar was converted into t ha^-1. In order to obtain pulp sample, 30 roots were randomly selected from each plot. Roots were washed and weighed, the pulp was prepared in the laboratory, and after freezing, it was sent for qualitative analysis and determination of qualitative related traits including sugar content, white sugar content, root α-amino nitrogen, sodium, and potassium content, alkalinity, extraction sugar coefficient and molasses sugar content. After collecting data from all regions, combined ANOVA, mean comparisons in terms of measured traits and correlation coefficients between traits based on the average data of all regions, as well as the heritability of traits based on the estimated amount of genetic, environmental and phenotypic variances and genotypic and phenotypic coefficients of variation were performed using SAS V. 9.0 software. Finally, in order to evaluate phenotypic diversity and integrate the evaluated traits to determine the ideal hybrid, the ideal genotype selection index (SIIG) was calculated using Microsoft Excel.
Results and Discussion
Bartlett's test confirmed the homogeneity of variance of experimental errors in the studied regions. Therefore, a combined ANOVA was performed to examine the main effects and the interaction between the source of variation. According to the results of the combined ANOVA, the effect of location on all evaluated traits was significant at the (P ≤ 0.01). Also, the difference among cultivars in terms of all evaluated traits (except for potassium content) was significant (P ≤ 0.01), which indicates the existence of genetic diversity among studied cultivars and hybrids, and since the existence of diversity is one of the main pillars of breeding, it contributes the breeder to select desirable plant materials. Since one of the most important stages in breeding program is determining an index for the screening of the plant materials, and the occurrence of different hybrid ranking in terms of each trait, the accurate selection of the best hybrid is not possible. Therefore, in order to screen the best hybrid by considering all the evaluated traits at the first stage, all hybrids and cultivars were ranked separately in terms of each trait. Then, the total ranks were calculated for each of the hybrids and cultivars. The hybrid or cultivar with the lowest and highest total rank values ​​were identified as the best (rank 1) or the weakest (rank 20), respectively. Based on the results obtained, after identifying BTS1930 as the superior cultivar, hybrids No. 12, 9, 8 and 14 were ranked second to fifth, respectively and had a good relative advantage over two other foreign controls Urselina and FD16B3013, which were ranked as sixth and eleventh, respectively. The domestic control cultivar Dena (No. 17) ranked ninetieth and showed a significant difference in terms of rank with the superior hybrids of the new generation, which indicates genetic progress and response to appropriate selection of the new generation hybrids compared with older cultivars that can be registered and introduced as new cultivars. The results of calculating the SIIG index based on the average of traits in all regions in terms of identifying ideal cultivars and hybrids were largely consistent with the results of their ranking as mentioned before. Based on both calculations, hybrids number 12 ((201-9*301-11) * S1 – 980133) and 9 ((201-9*301-11) * S1 – 980126) had a more favorable status than other hybrids. Therefore, these two hybrids and, in the next stage, hybrids number 8 ((201-9*301-11) * S1 – 980119) and 14 ((201-9*301-11) * S1 – 980139) can be introduced as superior and ideal hybrids and can be used for supplementary research. Of course, in this research, in addition to presenting the results of calculating the SIIG index, a two-dimensional diagram of the classification of hybrids and varieties based on SIIG index and sugar yield as the final yield of sugar beet crop based on the average of all regions was also drawn to screen and identify ideal hybrids. Hybrid No. 12 ((201-9*301-11) * S1 – 980133) had a more favorable status than other hybrids, and therefore it can be introduced as a superior hybrid overall.
Conclusion
Overall, results showed that the SIIG index was able to identify ideal cultivars and hybrids and in accordance with the results obtained from the ranking of cultivars and hybrids in terms of all evaluated traits. This index is a selective model and is used to select the most ideal cultivars and hybrids. In other words, using the SIIG index, different traits can be converted into a single index and the selection of superior genotypes can be done more accurately and with less bias in different breeding programs.
Keywords: Dominant diseases, Ideal hybrid, Selection, Sugar beet
References
Hamze H, Mahdi H, Mansouri H. Screening O-type lines of sugar beet in terms of resistance to rhizoctonia root rot. Journal of Sugar Beet. 2021; 37 (2), 153-162 [In Persian]..
Yan W, Kang M.S. GGE biplot analysis: A graphical tool for breeders, geneticists, and agronomists. CRC press. 2002; pp. 288. Doi: https://doi.org/10.1201/9781420040371.