Fig. 1

Survival and shoot regeneration of cryopreserved shoot tips of ASGV-infected shoots and histological studies on micrograft developments of shoots regenerated from cryopreservation for virus transmission in apple ‘Gala’. A surviving shoot tip (a), elongated shoot (b) and well-developed shoot (c) after 1, 8 and 16 weeks of post-culture following cryopreservation by droplet-vitrification. Shoot regenerated after 16 weeks of post-culture following cryopreservation by encapsulation-dehydration (d) and shoot tip culture (e). Preparations of scion and rootstock, and micrografting of the virus-infected shoots regenerated from cryopreserved shoot tips on the healthy rootstock (f). A longitudinal section of micrografts at day 0 of micrografting (g). A longitudinal section of micrografts at day 3 of micrografting (h). A closer view (i) showing callus formation, as indicated by arrows, in micrograft conjunction of scion and rootstock in black square in h. A longitudinal section of micrografts at day 7 of micrografting (j). A closer view (k) showing new cambial cells, as indicated by arrows, initiated from the callus formed in the micrograft conjunctions in black square in j. A longitudinal section of micrografts at day 10 of micrografting (l). A closer view (m) showing primary vascular bundle development, as indicated by arrows, in the micrograft conjunctions in black square in l. A longitudinal section of micrografts showing complete developments of vascular bundles between scion and rootstock at day 21 of micrografting (n). N. benthamiana leaves inoculated with sodium phosphate buffer without virus (o), with virus preserved by shoot tip culture (p) and with virus cryopreserved by droplet-vitrification (q). Typical ASGV symptoms are indicated by the black arrows. Bars in a, c–f and o–q = 1 cm; b, g, h, j, l, n = 1 mm