Development and phenotypic and molecular evaluation of sugar beet hybrids for resistance to rhizomania and root-knot nematode (Meloidogyne spp.)

Rhizomania is the most destructive disease in spring sugar beet along with root-knot nematode and are spreading in some parts of Iran. The best control method against these two diseases is using resistant cultivars. Therefore, the aim of this study was to develop and select a high yield hybrid resistant to rhizomania and root knot nematode. Twenty-seven full-sib families (S1) from SB-34 origin which screened with molecular markers for rhizomania and root knot nematode resistance gene, were used to develop double resistant hybrids. In the spring of 2015, vernalized families were crossed to one single cross (7112*SB-36) in separate isolates. In summer, S1/S2 seeds from the paternal plants and three-way cross hybrid seeds from maternal plants were harvested and cleaned. Out of 27 isolates, only 19 isolates had adequate seeds from both parental lines. In autumn of the same year, selected hybrids were planted in greenhouse in Karaj. Seedlings were analyzed by SCAR and SNP markers linked to rhizomania and root knot nematode resistance genes to determine gene frequencies in hybrids. Based on the results of molecular evaluation, 14 hybrids were selected. In the spring of 2016, selected hybrids along with some controls, overall 20 varieties, were planted in two rhizomania-infected areas in Khorasan Razavi and Fars based on randomized complete block design with six replications. Roots were harvested in autumn and qualitative and quantitative characteristics such as root yield, sugar content, and white sugar yield were measured. Data were analyzed using SAS 9.1.3 software. According to the results of field trials and the frequency of rhizomania resistance gene and root node nematode in the laboratory, hybrid SB36*(7112*930620) with 10.92 t/ha white sugar yield to be used.