Low-toxicity herbicide dicamba promotes microspore embryogenesis and plant regeneration for doubled haploid production in purple cauliflower

Cauliflower (Brassica oleracea var. botrytis L.) is an important vegetable grown worldwide. Colored cauliflower is highly desirable because of its aesthetic appearance and nutritional benefits. The use of isolated microspore culture technology to obtain doubled haploid (DH) lines could expedite breeding. However, the low frequency of microspore embryogenesis, particularly in colored cauliflowers, remains a major hurdle for the practical application of this technique. In this study, nine genotypes of cauliflower microspores were successfully induced among the 15 differently colored genotypes. The addition of 0.5 µmol·L−1 dicamba to NLN-13 medium increased the number of embryos per bud in purple cauliflower genotypes 20WY06, 20WY08, and 20WY10. The number of embryos was 4.64-, 5.45-, and 4.03-folds higher than that of the control, respectively. Meanwhile, 0.5 µmol·L−1 dicamba effectively promoted plantlet regeneration. The spontaneous diploidization rates of the purple cauliflower ranged from 52.63% to 54.76%, suggesting potential applicability in breeding without artificial doubling. A total of 76 purple cauliflower DH lines were generated. One DH line identified, DHP03, with high vitamin C and anthocyanin could be further applied to purple cauliflower breeding. This is the first study to utilize dicamba in improving the rate of microspore embryogenesis and plantlet regeneration, supply the DH lines in hybrid seeds, and shorten the breeding cycle of purple cauliflower.