Application of Multigerm Restorer Lines for Improving Monogerm Maintainer Lines in Sugar Beet

In China, the annual formulation of hybrid combinations in sugar beets is significantly lower than that in foreign countries, primarily due to the limited availability of monogerm sterile and maintainer line pairs. This limitation constrains the production of three-line matching hybrids, resulting in considerably fewer hybrid combinations compared with those developed by foreign breeding companies. Increasing the number of monogerm maintainer lines in sugar beets, as a way to address this limitation, can be achieved by improving these lines with sugar beet multigerm restorer lines. The more the monogerm maintainer lines in sugar beet, the more monogerm sterile lines can be created through backcrossing. Hence, a large number of pairs of monogerm sterile and maintainer lines with excellent multigerm traits can be obtained in sugar beet. This study aimed to pollinate monogerm maintainer lines using multigerm restorer lines in sugar beets. Seeds obtained from these monogerm maintainer lines were collected, and mother roots were obtained through southern propagation. After vernalization and self-pollination in the second year, nonhybrid monogerm plants were eliminated. Molecular marker-assisted selection was used to evaluate the fertility gene composition of 697 sugar beet lines. The monogerm maintainer lines were quickly selected based on the results of molecular marker fertility identification combined with field investigation of morphological and embryological characteristics. The experimental results revealed that out of 697 sugar beet breeding lines, 600 were multigerm lines, accounting for 86.08%, and 97 were monogerm lines, accounting for 13.92%. The fertility identification results of the nuclear Rf1 locus showed that 36 out of 97 monogerm lines contained recessive genes. Therefore, 36 sugar beet monogerm maintainer lines were obtained. The approach of using multigerm restorer lines to improve monogerm maintainer lines, coupled with molecular marker technology and the field investigation of morphological and embryological characteristics, contributed to an increased number of sugar beet monogerm maintainer lines. This method enabled the acquisition of more pairs of sugar beet monogerm sterile lines and maintainer lines, enriching the sugar beet germplasm resource bank and promoting the development of the sugar beet breeding industry.