Goat horns: Platforms for viroid transmission to fruit trees?

Abstract

Mechanical inoculations with contaminating tools and propagation of infected budwood were considered the main causes for the omnipresence of multiple viroid species among citrus and other Middle Eastern and Mediterranean fruit trees and grapevines. However, neither means could explain viroid infections of wild trees -scattered on terrains inaccessible to humansnor the finding of similar viroids among graft-incompatible plants. Northern hybridization of RNA extracts made of scrapings from the surfaces of goat (Capra hircus) horns that were rubbed against etrog (Citrus medica) stems infected with a citrus viroids complex, revealed accumulation of considerable amounts of Citrus exocortis viroids (CEVd) and Hop stunt viroids (HSVd). Experimental transmission of both CEVd and HSVd was obtained by rubbing healthy citrus plants with goat horns that had been rubbed 24 h earlier on infected etrog stems. These results implicate goats as possible vectors of viroids. Transmission via goats could have facilitated the long-range spread of viroids among cultivated and wild plants and vice versa and also among graft-incompatible plants.

Modes of Viroid Transmission

“…Mistletoe comes directly into contact with apple trees through haustoria, during which it may become systemically infected with ACFSVd and transmit the viroid from infected to uninfected trees [ 10 ]. Domesticated goats have been reported to transmit viroids when their horns were rubbed against viroid-infected trees [ 80 , 81 ]. Transmission via goats could have facilitated the long-range spread of viroids among cultivated and wild plants and vice versa, as well as among graft-incompatible plants.…”

Xyloporosis: A history of the emergence and eradication of a citrus viroid disease

“…The fact that HSVd was found among different non-graft-compatible fruit trees in the Mediterranean region and Near East, including wild saplings in remote areas (Kaponi et al 2009; PE Kyriakopoulou, personal communication), and the apparent absence of any flying insect vector suggested the possibility of mechanical transmission (Garnsey and Jones 1967). One possible mechanical vector over long distances is the goat, as demonstrated by Cohen et al (2005). Sano (1988) was the first to report the presence of an HSVd-like molecule in citrus upon examining citron plants from Japan.…”

Analysis of immunogenicity of minor envelope protein GP3 of porcine reproductive and respiratory syndrome virus in mice

“…Viroid detection mainly depends either on time-consuming biological assays or on molecular techniques aimed to detect the presence of their RNA genomes [3]. Commonly applied techniques are the direct visualization of viroid RNAs after gel electrophoresis [10,11], molecular hybridization [12][13][14][15][16][17][18][19] and PCR amplification [20][21][22][23][24][25][26][27][28]. The choice and applicability of these methods for different viroids depends on the diagnostic purposes, the availability of trained personnel and viroid titer in infected tissues.…”