Detection of Apple Hammerhead Viroid, Apple Luteovirus 1 and Citrus Concave Gum-Associated Virus in Apple Propagation Materials and Orchards in the Czech Republic and Hungary

Abstract

Grafting cultivars onto rootstocks is a widely used practice by the apple industry predominantly aimed at faster fruit bearing. Using high-throughput sequencing, we revealed the presence of recently described viral agents, namely apple hammerhead viroid (AHVd), apple luteovirus 1 (ALV-1), and citrus concave gum-associated virus (CCGaV), in germplasm collections and production orchards in the Czech Republic and Hungary. The HTS results were validated with RT‒(q)PCR, and Northern blotting techniques. To obtain further insight about the presence of these agents, RT-PCR based surveys were carried out and showed their widespread presence alone or in mixed infections. The pathogens were present both in production areas and in feral samples. In addition, rootstock-to-scion transmission of ALV-1 and CCGaV was confirmed using commercial rootstock materials. Phylogenetic relationships based on partial sequences of distinct variants were also investigated. Furthermore, the rosy apple aphid was found to be ALV-1-positive, suggesting that it might be a potential vector of the virus.

Elimination of Solanum nigrum ilarvirus 1 and Apple Hammerhead Viroid from Apple Cultivars Using Antivirals Ribavirin, Rimantadine, and Zidovudine

“…Apple hammerhead viroid (AHVd, Pelamoviroid; family Avsunviroidae [11]) has been identified in apple trees and is associated with symptoms such as trunk splitting, mosaic, necrosis, shoot decline, and dieback in China [28]. This problem has also been reported in various apple cultivars in Canada [13], the United States, Japan, Italy, Spain, New Zealand [29,30], Republic of Korea [31], India [32], Tunisia [33], the Czech Republic, and Hungary [10]. These data indicate that AHVd is widespread worldwide, and further research is needed to test methods for its elimination from apple propagation material.…”

“…The virus statuses of selected initial mother plants of the apple cultivars ‘Šampion’, ‘Jonagored Supra’, and ‘Selena’ maintained in technical isolation at the RBIP were evaluated before the beginning of chemotherapy by HTS [ 10 ]. The HTS results were validated with RT-(q)PCR.…”

“…Its use in practice represents the possibility of obtaining a completely new quality of propagation material of apple varieties and rootstocks. One of the objectives of our previous study [ 10 ] was to determine by HTS testing whether it is possible to find plants completely free of virus-like sequences among apple cultivars maintained as elite plant material in the insect -proof screenhouse of the Research and Breeding Institute of Pomology Holovousy Ltd. (RBIP). During this study, we detected apple hammerhead viroid (AHVd) [ 11 ] in the cultivar ‘Šampion’, and AHVd in mixed infection with Solanum nigrum ilarvirus 1 (SnIV-1) [ 12 ] in ‘Selena’ and ‘Jonagored Supra’ cultivars.…”

What Can Be Learnt by a Synoptic Review of Plant Disease Epidemics and Outbreaks Published in 2021

“…It has subsequently been reported worldwide, including countries in Africa, Asia, Europe and North and South America (CABI, 2023). However, it is invariably found in samples from plants infected with other viruses, making the correlation between viroid infection and any specific symptoms impossible to determine (Várallyay et al, 2022). We therefore assess the new reports in 2021 -in Tunisia, India (two different states) and Brazil -as not necessarily reflecting new spread of a potentially damaging pathogen to a new location, but instead more likely reflecting the increasing availability of increasingly sophisticated bioinformatic methods to detect a long-standing and perhaps even benign association, and so do not discuss this species further.…”