Non-vernalization Flowering and Seed Set of Cabbage Induced by Grafting Onto Radish Rootstocks

Abstract

Cabbage (Brassica oleracea var. capitata) requires a long-term low-temperature exposure for floral induction, causing a delay in the breeding cycle. The objective of this study is to develop a method to induce flowering in cabbage without low-temperature treatment, using a grafting method. We conducted grafting experiments using two flower-induced Chinese kale cultivars (B. oleracea var. alboglabra) and seven radish cultivars/accessions as rootstocks and investigated the flowering response of grafted cabbage scions without low-temperature treatment. “Watanabe-seiko No.1” cabbage, when grafted onto the two Chinese kale cultivars, did not formed flower buds. Flowering was successfully induced in “Watanabe-seiko No.1” by grafting onto three out of the seven tested radish cultivars, and in “Kinkei No.201” and “Red cabbage” by grafting onto one tested radish cultivar. In “Watanabe-seiko No.1,” the earliest flower bud appearance was observed at 29 days after grafting. Seeds were also obtained from the three cabbage cultivars that flowered by grafting. Gene expression analysis of “Watanabe-seiko No.1” cabbage scions which formed flower buds by grafting, revealed high expression of the homolog of the floral integrator, SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (BoSOC1), at the time of flower bud appearance. However, in the same leaf samples, we observed low expression of two homologs of florigen, FLOWERING LOCUS T (BoFT.C2 and BoFT.C6). In addition, two homologs of the floral repressor FLOWERING LOCUS C (BoFLC3 and BoFLC4), which are known to be down-regulated before flower bud differentiation in the vernalization pathway, were highly expressed, indicating that grafting onto radish induces cabbage flowering independently of the vernalization pathway. The expression level of the radish FT homolog (RsFT) in “Rat’s tail-G2,” which had highly induced flowering in the grafted cabbage scion, was higher than in the other radish cultivars. However, although “Rat’s tail-CH” effectively induced flowering in the cabbage scion, the expression of RsFT was low in this cultivar. In this study, floral induction of non-vernalized cabbage cannot be explained by the expression levels of RsFT in rootstock plants, alone. The flowering of non-vernalized cabbage would be induced by transmissible agents from rootstocks and not by the expression of cabbage FT, BoFT, from the scion itself.

Effect of Self- and Inter-Cultivar Grafting on Growth and Nutrient Content in Sweet Basil (Ocimum basilicum L.)

“…capitata ) vernalization requirement was removed with radish ( Raphanus sativus var. caudatus ) rootstocks allowing for more efficient breeding ( Motoki et al, 2019 ). Chen et al (2019) reported cabbage grafted to Chinese kale ( Brassica oleracea var.…”

From Emergence to Flowering: Four Beet (Beta vulgaris ssp.) Cultivars’ Phenological Response to Seed Priming

“…First, plants need to fulfil the photothermal induction requirement prior to the reproduction stage, which leads to a long seed production process and a delayed breeding cycle. Furthermore, photothermal induction requirements limit the geographical distribution of seed production [19]. Since breeding efforts have focused mostly on the vegetative production of beets, they have centered on the suppression of bolting, due to the negative effect of bolters on yield [3,[13][14][15]18].…”

Investigation of the Field Performance of Progenies Obtained by a Non-vernalization-grafting Floral Induction Method in Terms of Application to Cabbage Breeding and Seed Production

“…However, his findings were overlooked for more than 50 years, probably due to the low reproducibility of this phenomenon. We investigated the grafting-induced flowering of cabbage in detail under a controlled environment and found that a high success rate for floral induction could be achieved by using specific accessions of radish as a rootstock (Motoki et al, 2019(Motoki et al, , 2022. Expression analysis of flowering-related genes was conducted to deduce the mechanism of floral induction by grafting, and it was revealed that FLC homologs were highly expressed and FT homologs were lowly expressed in cabbages which were induced to flower by grafting (Motoki et al, 2019).…”

“…We investigated the grafting-induced flowering of cabbage in detail under a controlled environment and found that a high success rate for floral induction could be achieved by using specific accessions of radish as a rootstock (Motoki et al, 2019(Motoki et al, , 2022. Expression analysis of flowering-related genes was conducted to deduce the mechanism of floral induction by grafting, and it was revealed that FLC homologs were highly expressed and FT homologs were lowly expressed in cabbages which were induced to flower by grafting (Motoki et al, 2019). FLC acts as a repressor of FT in A. thaliana (Helliwell et al, 2006;Michaels et al, 2005); therefore, it was assumed that the grafted cabbage scions were induced to flower by exogeneous FT protein from the rootstock (Motoki et al, 2019).…”