The quality of water for use in producing crops can be threatened by different environmental factors, including contamination by plant pathogens. Owing to the limited availability of water and affected by climate change, crop production systems using irrigation has expanded worldwide. Plant pathogens in irrigation water can spread rapidly and cause substantial economic losses. Different water sources can serve as pathways for water-borne plant pathogens, including certain viroids, which are the smallest plant pathogens causing severe diseases in susceptible hosts. In the last decade, a new viroid disease named severe hop stunt disease caused by Cocadviroid rimocitri (citrus bark cracking viroid, CBCVd), has threatened hop (Humulus lupulus L.) production in Slovenia. Like other viroids, CBCVd is a single-stranded pathogenic RNA that primarily spreads through mechanical means, such as contaminated plant sap residue on tools and machines, as well as from the remains of infected plants. Given that hop production relies heavily on irrigation, it is important to assess the risk of CBCVd transmission through contaminated water sources. In our study, we assessed water as a potential pathway for CBCVd transmission through four experiments. CBCVd was detectable in stored contaminated water for at least 16 weeks and remained infective for up to 3 of these weeks. In a dilution experiment, CBCVd was detectable in directly homogenised contaminated plant sap up to a 10−5 dilution, while mechanical inoculations demonstrated infectivity up to a 10−2 dilution. In an experiment in which hop plants were watered with CBCVd-contaminated water once a week for a month, viroid transmission to the plants could not be confirmed. However, in a hydroponic system experiment, examining the release of CBCVd and Cocadviroid latenshumuli (hop latent viroid, HLVd) from the roots of infected plants into the nutrient solution, we confirmed both their release and subsequent transmission to bait plants. Our results indicate that water can serve as a pathway for CBCVd transmission, but this is highly dependent on the plant cultivation system. While no transmission occurred when plants were watered with contaminated water, and infectivity declined rapidly with sap dilution, CBCVd remained detectable in the water solution for at least 16 weeks and infectious for up to 3 weeks. This highlights the importance of preventing CBCVd contamination in hop irrigation systems through infected plants or their remains.

Survival and waterborne transmission of Cocadviroid rimocitri (CBCVd) to hop

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发表日期：

2025年8月28日

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Maja Dobrajc,
Tanja Guček,
Jernej Jakše,
Sebastjan Radišek

摘要

The quality of water for use in producing crops can be threatened by different environmental factors, including contamination by plant pathogens. Owing to the limited availability of water and affected by climate change, crop production systems using irrigation has expanded worldwide. Plant pathogens in irrigation water can spread rapidly and cause substantial economic losses. Different water sources can serve as pathways for water-borne plant pathogens, including certain viroids, which are the smallest plant pathogens causing severe diseases in susceptible hosts. In the last decade, a new viroid disease named severe hop stunt disease caused by Cocadviroid rimocitri (citrus bark cracking viroid, CBCVd), has threatened hop (Humulus lupulus L.) production in Slovenia. Like other viroids, CBCVd is a single-stranded pathogenic RNA that primarily spreads through mechanical means, such as contaminated plant sap residue on tools and machines, as well as from the remains of infected plants. Given that hop production relies heavily on irrigation, it is important to assess the risk of CBCVd transmission through contaminated water sources. In our study, we assessed water as a potential pathway for CBCVd transmission through four experiments. CBCVd was detectable in stored contaminated water for at least 16 weeks and remained infective for up to 3 of these weeks. In a dilution experiment, CBCVd was detectable in directly homogenised contaminated plant sap up to a 10⁻⁵ dilution, while mechanical inoculations demonstrated infectivity up to a 10⁻² dilution. In an experiment in which hop plants were watered with CBCVd-contaminated water once a week for a month, viroid transmission to the plants could not be confirmed. However, in a hydroponic system experiment, examining the release of CBCVd and Cocadviroid latenshumuli (hop latent viroid, HLVd) from the roots of infected plants into the nutrient solution, we confirmed both their release and subsequent transmission to bait plants. Our results indicate that water can serve as a pathway for CBCVd transmission, but this is highly dependent on the plant cultivation system. While no transmission occurred when plants were watered with contaminated water, and infectivity declined rapidly with sap dilution, CBCVd remained detectable in the water solution for at least 16 weeks and infectious for up to 3 weeks. This highlights the importance of preventing CBCVd contamination in hop irrigation systems through infected plants or their remains.