Background: The basic helix–loop–helix (bHLH) is the second largest gene family in the plant, some members play important roles in pistil development and response to drought, waterlogging, cold stress and salt stress. The bHLH gene family has been identified in many species, except forBrassica oleraceaandB. napusthus far.This study aims to identify the bHLH family members inB. oleracea,B. rapaandB. napus, and elucidate the expression, duplication, phylogeny and evolution characters of them.Result: A total of 268 bHLH genes inB. oleracea, 440 genes inB. napus, and 251 genes inB. rapa, including 21 new bHLH members, have been identified.Subsequently, the analyses of the phylogenetic trees, conserved motifs and gene structures showed that the members in the same subfamily were highly conserved. MostKa/Ksvalues of homologous gene were < 1, which indicated that these genes suffered from strong purifying selection for retention. The retention rates ofBrabHLHandBolbHLHgenes were 51.6 and 55.1%, respectively. The comparative expression patterns betweenB. rapaandB. napusshowed that they had similar expression patterns in the root and contrasting patterns in the stems, leaves, and reproductive tissues. In addition, there were 41 and 30 differential expression bHLH genes under the treatments of ABA and JA, respectively, and the number of down regulation genes was significantly more than up regulation genes.Conclusion: In the present study, we identified and performed the comparative genomics analysis of bHLH gene family amongB. oleracea,B. rapaandB. napus, and also investigated their diversity. The expression patterns betweenB. rapaandB. napusshows that they have the similar expression pattern in the root and opposite patterns in the stems, leaves, and reproduction tissues. Further analysis demonstrated that some bHLH gene members may play crucial roles under the abiotic and biotic stress conditions. This is the first to report on the bHLH gene family analysis inB. oleraceaandB. napus,which can offer useful information on the functional analysis of the bHLH gene in plants.

Turnip, one of the oldest groups of cultivated Brassica rapa species, is a traditional crop as well as a form of animal fodder, a vegetable, and a herbal medicine that is widely cultivated in farming and farming-pastoral regions in Tibet. Different regions of the Qinghai–Tibet Plateau (QTP) are home to a rich diversity of turnip owing to their high altitudes and variable climate types. However, information on the morphology and genetic diversity of Tibetan turnip remains limited. Therefore, the genetic diversity of 171 turnip varieties from China and elsewhere (Japan, Korea, and Europe) was analyzed using 58 morphological characteristics and 31 simple sequence repeat (SSR) markers in this study. The varieties showed that the genetic distance ranged from 0.12 to 1.00, and the genetic similarity coefficient ranged between 0.73 and 0.95. Cluster tree showed two distinct clusters. Both morphotype and geography contributed to the group classification. A combination of morphological traits and molecular markers could refine the precision of accurate identification compared to the separate morphological and molecular data analyses. The sampling ratio of 15% to utmost precisely represent the initial population was compared to ratios of 10% and 20%, and the sampling ratio of 15% is recommended for future works when a primary core collection of turnip resources is constructed. These results could furnish a foundation for germplasm conservation and effective turnip breeding in future studies.