Abstract: The aim of this study was to investigate the in vitro rooting technique of Malus Zumi micro-shoots in outdoor environment. In middle ten days of April the culture bottles in which the micro-shoots were inoculated were respectively located under three shading conditions in outdoor environment for rooting culture, and many times experiments on rooting in vitro of Malus Zumi micro-shoots under shading in outdoor environment in 2016, 2017 and 2018. The result showed that under climate condition in Tianjin agricultural university courtyard the temperature in culture bottle was controlled below 35 ℃ and the light intensity on the bottle top was above 2 000 lx using shading methods of tree shading, two course sunshade net shading or three course sunshade net shading from middle ten days of April to last ten days of May. There was no significant difference among the rooting and growth index of Malus Zumi plantlets under the three shading methods which could be all used for culturing the micro-shoots in this period. Using tree shading in outdoor the suitable time for rooting in vitro of Malus Zumi micro-shoots were the periods from last ten days of April to early July and from early September to middle ten days of October, and the most suitable period was from last ten days of April to first ten day of June, and in these periods the rooting rate of the micro-shoots reached 87.3%-97.8%. These results can be used as reference for reducing the cost of Malus Zumi plantlet in vitro and promoting applying the rapid technique of Malus Zumi to production.

Key words: Malus Zumi, outdoor environment, in vitro rooting, shading, cultural period