Fig. 4.

Tissue distributions of Citrus exocortis viroid (CEVd) and Hop stunt viroid (HSVd) revealed by digoxigenin-labeled in situ hybridization (DIG-ISH) under a transmitted light microscope. a-d) Viroid-negative citrus tissues hybridized with viroid DIG-labeled probes as controls. e-h) Co-infected citrus tissues hybridized with CEVd DIG-labeled probes. i-l) Co-infected citrus tissues hybridized with HSVd DIG-labeled probes. a, e and i Transverse sections of viroid-negative (a) and co-infected (e and i) citrus roots. b, f and j Transverse sections of viroid-negative (b) and co-infected (f and j) citrus rootstock bark. c, g and k) Transverse sections of viroid-negative (c) and co-infected (g and k) citrus twig bark. d, h and l) Transverse sections of viroid-negative (d) and co-infected (h and l) citrus leaves. Bars in original photographs (a-l) = 5 μM; bars in small photographs (e-l) = 15 μM. PT = pith; P = phloem; X = xylem; E = endodermis; C = cortex; CC = cork cambium; PF = phloem fiber; OG = oil gland; PST = palisade tissue