Effects of Grafting and Vernalization on the Flowering and Head Quality of Cabbage

Cabbage (Brassica oleracea L. var. capitate) is plant-vernalization-responsive type plant which requires vernalization to induce flowering in tropical and subtropical lowland areas where lack sufficient low temperature. Grafting is widely used in commercial production of cucurbits and solanaceous vegetables, so as to, e.g., improve resistance to soil-borne diseases and tolerance to abiotic stresses, promote plant vigor, increase yield, and induce or promote flowering. This research aims to set up the healing conditions for cabbage grafting, and investigate effects of grafting and vernalization on flowering, gene expression levels of flowering related genes and leaf head qualities, though four experiments. In experiment I, the best healing conditions for grafted cabbage seedlings were developed. The highest survival rate of grafted seedlings was found under healing conditions of 15℃, relative humidity (RH) 85%, and dark or high light intensity (79~107 μmol∙m-2∙s-1). On the growth of grafted cabbage seedlings after grafted 35 days, the highest seedling index was shown under healing conditions of 20℃, RH 75% or 95%, and high light intensity (79~107 μmol∙m-2∙s-1). Experiment II investigated the effects of different species and cultivars of rootstock on flowering and leaf head qualities in grafted cabbage plants. Cabbage ‘K-Y cross’ grafted onto different rootstocks did not promote flowering. Cabbage ‘K-Y cross’ grafted onto Chinese kale rootstocks ‘Jie Lan’ had significant higher content of ascorbic acid and total soluble solids in leaf head than cabbage ‘K-Y cross’ self-grafted or ungrafted plants, but only when grown in containers. Experiment III investigated the effects of vernalization on flowering and gene expression levels of flowering related genes in grafted cabbage plants. Cabbage ‘K-Y cross’ grafted onto Chinese kale cv. ‘Cuei Jin’ rootstock (C/K), treated with 5℃ or 10℃ artificial vernalization for 6 weeks, and then transplanted to 25/20℃ environment did not flower. Although expression level of BoFLC4-1 reduced, while BoVIN3 and BoFT increased as the vernalization time extented. However, the expression levels of BoFLC4-1, BoVIN3 and BoFT in C/K were not changed much faster than that of self-grafted or ungrafted cabbage plants. Grafted cabbage plants with different rootstocks grown in highland for natural vernalization flowered earlier than that grown in sea level, but days to flowering in grafted cabbage with different rootstocks were not earlier than that of self-grafted or ungrafted cabbage plants. In experiment IV, we try to grafted cabbage ‘K-Y cross’ on the flowering stalk of Chinese kale ‘Cuei Jin’, but it still cannot induce or promote flowering. In conclusion, even though grafted cabbage on rootstocks of different Chinese kale cultivars or cabbage cv. ‘He Fong’ could not promote flowering, but the research developed the best healing conditions for grafted cabbage seedlings which could be used to test the possibility of flowering promotion when combination with different rootstock species or be applied in other grafting purposes in the future.