title: Invasion of shoot apical meristems by Chrysanthemum stunt viroid differs among Argyranthemum cultivars.
abstract: Chrysanthemum stunt viroid (CSVd) is a damaging pathogen attacking Argyranthemum plants. Our study attempted to reveal distribution patterns of CSVd in shoot apical meristems (SAM) and to explore reasons for differential ability of CSVd to invade SAM of selected Argyranthemum cultivars. Symptom development was also observed on greenhouse-grown Argyranthemum plants. Viroid localization using in situ hybridization revealed that the ability of CSVd to invade SAM differed among cultivars. In diseased 'Yellow Empire' and 'Butterfly', CSVd was found in all tissues including the uppermost cell layers in the apical dome (AD) and the youngest leaf primordia 1 and 2. In diseased 'Border Dark Red' and 'Border Pink', CSVd was detected in the lower part of the AD and elder leaf primordia, leaving the upper part of the AD, and leaf primordia 1 and 2 free of viroid. Histological observations and transmission electron microscopy showed similar developmental patterns of vascular tissues and plasmodesmata (PD) in the SAM of 'Yellow Empire' and 'Border Dark Red', while immunolocalization studies revealed a major difference in the number of callose (β-1, 3-glucan) particles deposited at PD in SAM. A lower number of callose particles were found deposited at PD of SAM of 'Yellow Empire' than 'Border Dark Red'. This difference is most likely responsible for the differences in ability of CSVd to invade SAM among Argyranthemum cultivars.
authors.affiliation: State Key Laboratory of Crop Stress Biology for Arid Areas, Key Laboratory of Genetic Improvement of Horticultural Crops of Northwest China, Ministry of Agriculture of China - College of Horticulture, Northwest A&F University, Yangling China ; Bioforsk-Norwegian Institute for Agricultural and Environmental Research, Ås Norway.
authors.forename: Zhibo
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Department of Plant Sciences, Norwegian University of Life Sciences, Ås Norway.
authors.forename: YeonKyeong
authors.initials: Y
authors.lastname: Lee
authors.affiliation: Bioforsk-Norwegian Institute for Agricultural and Environmental Research, Ås Norway.
authors.forename: Carl
authors.initials: C
authors.lastname: Spetz
authors.affiliation: Bioforsk-Norwegian Institute for Agricultural and Environmental Research, Ås Norway.
authors.forename: Jihong Liu
authors.initials: JL
authors.lastname: Clarke
authors.affiliation: State Key Laboratory of Crop Stress Biology for Arid Areas, Key Laboratory of Genetic Improvement of Horticultural Crops of Northwest China, Ministry of Agriculture of China - College of Horticulture, Northwest A&F University, Yangling China.
authors.forename: Qiaochun
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Bioforsk-Norwegian Institute for Agricultural and Environmental Research, Ås Norway.
authors.forename: Dag-Ragnar
authors.initials: DR
authors.lastname: Blystad
keywords: Argyranthemum; Chrysanthemum stunt viroid (CSVd); callose; in situ hybridization; plasmodesmata; shoot apical meristem