Micrografting of Morus nigra on M. alba

In a previous work, Morus alba ‘Criolla’, ‘Tigrenda’ and ‘Illa Verde’, and M. nigra ‘Bande’, selected for fodder use, were micropropagated and tested in the field. M. alba clones showed significantly higher growth rates than the M. nigra clone after two years. In this work, interspecific micrografting experiments of M. nigra ‘Bande’ scions on M. alba unrooted rootstocks (stenting method) were carried out to evaluate the technique and to provide materials for future studies to test the effect of micrografting on ‘Bande’ performance in the field. In a preliminary experiment, white (4000 °K) LED strips were selected as light source for micropropagation and micrografting, as multiplication rates were similar or higher than using fluorescent lamps. In micrografting experiments, nodal segments of M. nigra ‘Bande’ were micrografted on unrooted nodal segments of the M. alba clones. In the first micrografting experiment, micrografts were established on MS medium + 0.88 µM BAP. At day 60, graft-take was 83.3-91.7% (100% in self-grafts), rooting percentage of the rootstocks was 27.3% in ‘Criolla’, 31.8% in ‘Tigrenda', 35.0% in ‘Illa Verde’ and 0% in ‘Bande’ (self-graft), and 77.3-85.0% of the scions developed new shoots (95.8% in self-grafts). In the second micrografting experiment, the micrografts were established: 1) on MS medium + 0.88 µM BAP; 2) on MS medium; 3) on MS medium, after pretreatment of the micrografts by a 15 s-dipping in 5 mM IBA solution. Graft-take at day 30 ranged between 87.5 and 100%, with no significant differences among scion-rootstock combinations or culture conditions. Percentage rooting of the rootstocks was higher in medium without BAP (79.2% in ‘Illa Verde’; 58.5% for ‘Criolla’). ‘Illa Verde’ rooted significantly better than ‘Criolla’, while rooting of ‘Bande’ was 0%. Dipping in IBA improved the quality of the root system in ‘Illa Verde’.