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.
Highlights
Viroids consist of small (246–401 nucleotides), single-stranded and circular RNA molecules (Flores et al, 2005), and cause severe damage to plants
Low yield of flowers (Horst et al, 1977; Chung et al, 2001; Jeon et al, 2012; Matsushita, 2013; Savitri et al, 2013). Symptoms such as yellow deformed leaves with terminal necrosis, flower distortion, or leaf necrosis were observed on Chrysanthemum stunt viroid (CSVd)-infected Argyranthemum ‘Butterfly’ plants (Marais et al, 2011)
The present study showed that CSVd infection induced obvious symptoms on greenhouse-grown ‘Yellow Empire’ and ‘Border Dark Red’ plants, including stunted growth, irregular shape of plants, flower distortion, and color breaking
Summary
Viroids consist of small (246–401 nucleotides), single-stranded and circular RNA molecules (Flores et al, 2005), and cause severe damage to plants. CSVd infection causes various adverse effects on diseased Chrysanthemum plants including stunted growth, short internodes, poor root development, reduced flower size, and flower color bleaching, resulting in the production of unmarketable plants. Low yield of flowers (Horst et al, 1977; Chung et al, 2001; Jeon et al, 2012; Matsushita, 2013; Savitri et al, 2013). Symptoms such as yellow deformed leaves with terminal necrosis, flower distortion, or leaf necrosis were observed on CSVd-infected Argyranthemum ‘Butterfly’ plants (Marais et al, 2011). CSVd-infected Chrysanthemum plants flowered autonomously whereas CSVd-free plants maintained their normal vegetative growth (Hosokawa et al, 2004a)
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