Efficient Production of a Synthetic Periclinal Chimera of Citrus ‘NF-5’ for Introduction of Disease Resistance

Abstract

An improved method named DHS (Direction-Hormone-Slowlygrowing)-method for efficient introduction of disease resistance to chimera was developed. The connective part of two hypocotyls {‘Kawano-natsudaidai’ (Citrus natsudaidai Hayata) moderately resistant to CTV and ‘Fukuhara orange’ (Citrus sinensis)} grafted together was cut horizontally. Then the hypocotyl of ‘Kawano-natsudaidai’ of the connective part was further cut at an angle of 60° against the stem direction. The cut surface of the hypocotyls was treated with plant hormones. Each treated hypocotyl was covered with paraffin film and grown under light in the laboratory. A slowly-growing adventitious bud produced on the cut surface of ‘Kawano-natsudaidai’ near to the border of the two varieties was selected and grown in a greenhouse. A synthetic periclinal chimera of citrus composed of Germ layer II & III of ‘Kawano-natsudaidai’ (N) covered with Layer I of ‘Fukuhara orange’ (F) was easily obtained by treatment with a mixture of 50μM gibberellin A₃, 1μM 6-benzylaminopurine and 1μM α-naphtaleneacetic acid. The scientific name Citrus natsudaidai+sinensis and the variety name ‘NF-5’ is proposed for the synthetic Periclinal chimera of citrus. The DHS method makes it easy to introduce a tissue resistant to citrus canker and citrus tristeza virus into Layer II & III of citrus. A simple way to identify a variety of a tissue from Layer II & III by HPLC was also established.