Chemical changes in ultra-low nicotine tobacco produced by grafting with Solanum melongena L.
Ultra-low nicotine tobacco production has been given broad attention due to the possible regulation of nicotine content in cigarette tobacco. A pot experiment was carried out in Xiangcheng County, Henan Province, in 2017, to study the feasibility of producing very low nicotine tobacco leaves and to investigate the changes in chemical composition of low nicotine tobacco obtained by grafting with eggplant (eggplant as rootstock, flue-cured variety Yunyan 87 as scion). Three treatments were set up as follows: (1) both scion and rootstock with flue-cured tobacco as control, represented by “tobacco/tobacco”; (2) tobacco as scion, eggplant as rootstock without soil covering the bottom of the scion, represented by “tobacco/eggplant without soil covering”; (3) tobacco as scion, eggplant as rootstock with soil covering the bottom of scion to stimulate root production, represented by “tobacco/eggplant with soil covering”. The results showed that the tobacco-eggplant grafting did not cause significant morphological, botanical and agronomic changes to the tobacco plant and tobacco leaf. Nicotine level in grafted tobacco leaves decreased dramatically with average nicotine content in fresh tobacco leaves being lowered to 0.06 %, and in flue-cured leaves lowered to 0.8 %, which represented a 94 % and 95 % decrease compared with tobacco/tobacco control. The contents of nornicotine and anabasine were also decreased, although the percentage decrease was less for anabasine, indicating that the anabasine may have a certain degree of biosynthesis capacity in leaves in addition to roots. Anatabine contents were not detectable in both fresh leaves and cured leaves of tobacco/eggplant without soil covering. Covering soil at the bottom of scion stimulated adventitious root emergence and growth which was able to undergo alkaloid biosynthesis, resulting in a significant increase of nicotine content in the grafted tobacco leaves compared with no soil covering grafted tobacco. The content of chlorophyll in tobacco/eggplant tobacco leaves was significantly higher and matured slower than the control plants. The contents of amino acids, the precursors of alkaloids, increased significantly in grafted tobacco, and higher levels of protein, starch, total nitrogen and lower levels of sugar contents were also observed. This study provided technical support for selectively and dramatically reducing and regulating nicotine content in cured tobacco through agricultural approaches.