Comparative study of root systems in citrus macrophylla seedlings and microcuttings propagated in vitro

Citrus macrophylla is very important as rootstocks for lemons. The in vitro propagation reduces the propagation time, and uses less quantities of seed. Seedlings root system was compared to in vitro rooted microcuttings. MS salt mixtures was used, with 1,5 mg l^-1 IBA, 0,25 g l^-1 activated charcoal, 7,5 g l^-1 agar and 25 g 1^-1 sucrose. After in vitro phase, the plantlets were put in minirhizotron (Riedaker, 1974), under a greenhouse with natural photoperiod. This is a non-destructive system to do direct observations of the roots, in a mixture of peat moss and vermiculite (2:1 v/v). Growth rate was evaluated for 8 weeks. Root system architecture of the seedlings was a typical "pivotant" type. Microcuttings presented a multiplex adventitious pattern (3-4 roots), with one of them taking a major role, assessing a natural seedlings-pattern; in addition, this main root had a gravitropic growth rate, while one of them other presented a plagiotropism and lower growth rate. Main root microcutting, without difference in the others, that presented a fibrous type. In conclusion, the in vitro formed adventitious roots are most efficient that the controls.