Effects of bolting resistance selection and its influence on other characteristics in sugar beet [Beta vulgaris] multigerm pollen parents

Sugar beet is a biennial cultivar, it is the vegetative growth in the first season of growth and the reproductive growth in the second season of growth. However, unseasonable bolting occurs in some plants when the temperature is low in the seedling stage. Since unseasonable bolting results in a decrease in the sugar content and affects field management, it is very important to breed varieties with high bolting resistance for Hokkaido, Japan. In this study, to develop the varieties with high bolting resistance, multigerm pollen parents were selected to bolting resistance with artificial photothermal treatment. And it was also evaluated selection effectiveness, and influence on yielding ability and disease resistance by bolting resistance selection. As the results, bolting resistance of selected lines, "NK-260BR","NK-269BR","NK-210BR2" and "NK-262BR", were stronger than that of the original lines. Especially bolting resistance of "NK210BR2" was clearly improved by 2nd selection, although original line "NK-210BR" had been already selected for bolting resistance in the past. On the other hand it was different for the effects of bolting resistance selection on sugar yielding ability and disease resistance between materials. In "NK-260BR" and "NK-269BR" the selection was not effective on sugar yielding ability and disease resistance. However root weight of "NK-210BR2" and "NK-262BR" was heavier, and Rhizoctonia root rot resistance of "NK-210BR2" is stronger than that of the original line. It appeared that these differences would be caused by the following reasons. First the reason for increase in root weight of "NK-210BR" and "K-262BR" was considered, because both selected lines were bred from non-bolting plants with heavy crown-root weight, as the result of selection for crown-root shape from non-bolting plants. Moreover, selection pressure caused high because number of selected plants decreased by the storage-rot. Second, the reason for decrease in Rhizoctonia root rot index of "NK-210BR2" was considered that Rhizoctonia root rot resistance of "NK-210BR2" was improved, as the result that some weak plants in root rot diseases were eliminated from non-bolting-plants by the storage-rot.