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In order to obtain sugar beet families with resistant to major diseases and high sugar content, three F2 populations segregating for the genes resistant to rhizomania and cyst nematode or rhizomania, cyst nematode and rhizoctonia were used. In spring 2020, the seed of the breeding materials were planted in the selection field in Karaj. During the growing season, all necessary activities such as weeding, thinning, irrigation, regular fertilization, and spraying was performed. After two stages of plants thinning in order to maintain 25 cm distance on rows, the leaves were taken and DNA extracted in summer. Using SNP or STS molecular markers, the plants resistant to rhizomania, cyst nematode were identified and kept in the field and other plants were removed. In late autumn, selected roots were transferred to the cold room. In late winter, the sugar content of the selected roots of the was measured and 25 percent of the roots with high sugar content from first and second genotypes were selected and the roots of the third genotype without sugar analysis were selected. In spring 2021, the selected roots were transferred to research field in Ekbatan and Mashad Research Stations and each root was divided longitudinally in to 2-4 pieces and planted in the one cage. In bolting stage, the plants were covered with the cages. In summer of the same year, the seeds of the full sib families were obtained from the 34 cages with double resistance to rhizomania and cyst nematode for genotypes No.1 and No.2 with high sugar content and the 39 cages with triple resistance to rhizomania, cyst nematode, and rhizoctonia for genotype No.3. Key words: Cyst nematode, molecular marker, rhizoctonia, rhizomania, sugar beet.
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