Gibberellin-mediated internode elongation for grafting and early flowering induction in Brassicaceae crops.

In Brassicaceae crops such as cabbage and turnip, which are harvested for their vegetative organs, floral induction can reduce the eating quality of these organs. Therefore, developing late-flowering varieties that are insensitive to vernalization is a key breeding objective. However, a major challenge in breeding these cultivars lies in the contradiction between the late-flowering trait and the need to induce flowering for crossing. To address this, we developed a flowering induction technique using grafting, in which gibberellin-induced elongated internodes are used as scions and grafted onto the flower stalk of Brassica rapa cv. 'CHOY SUM EX CHINA 3', which constitutively expresses FLOWERING LOCUS T (FT), as the rootstock. This method is applicable even to rosette-type Brassicaceae plants with short internodes. Histological and radioisotope analyses confirmed the reconnection of vascular bundles and the functionality of component transport across the graft junction. Additionally, gibberellin treatment was found to promote flowering in the presence of FT, most likely through an activation of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 3, a gene known to promote floral meristem development. This rapid flowering system offers a practical strategy for accelerating the breeding of late-flowering Brassicaceae crops.