Potato spindle tuber viroid: alternative host reservoirs and strain found in a remote subtropical irrigation area

During 2007–2012, Potato spindle tuber viroid (PSTVd) was detected in volunteer cultivated, wild and native plants during studies to determine whether Pospiviroids occur within the isolated, sub-tropical, Gascoyne Horticultural District (GHD) in central coastal Western Australia (WA). PSTVd was detected infecting volunteer crop plants of tomato, pepper and chilli; introduced weed species Solanum nigrum (blackberry nightshade), Datura leichhardtii (thornapple) and Nicandra physalodes (apple-of-Peru) (Solanaceae), and Conyza bonariensis (flaxleaf fleabane) (Asteraceae); and Australian native species Atriplex semilunaris (annual saltbush), Rhagodia eremaea (thorny saltbush) (Chenopodiaceae), and Streptoglossa sp. (Asteraceae). PSTVd was also detected infecting Physalis angulata (wild gooseberry) in the Ord River Irrigation Area (ORIA), Kimberley region in north-west WA. Comparison of sequences from the three complete and 18 partial RNA nucleotide sequences obtained from 20 GHD and one ORIA isolates with those of published sequences showed that their highest nucleotide sequence identities were to isolate AY962324 belonging to the Chittering strain from south-west WA. On phylogenetic analysis, the three completely sequenced GHD PSTVd isolates grouped within a cluster of isolates from tomato and P. peruviana. These results show that a naturally occurring PSTVd inoculum reservoir is present in the GHD. This reservoir explains the occurrence of repeated PSTVd infections in different years in field crops of tomato, pepper and chilli growing in its market gardens and small farms. These findings have implications concerning PSTVd spread in intensive solanaceous crop field production systems in other subtropical regions of the world

Potato spindle tuber viroid: Stability on common surfaces and inactivation with disinfectants

The length of time Potato spindle tuber viroid (PSTVd) remained infective in extracted tomato leaf sap on common surfaces and the effectiveness of disinfectants against it were investigated.When sap from PSTVd-infected tomato leaves was applied to eight common surfaces (cotton, wood, rubber tire, leather,metal, plastic, human skin, and string) and left for various periods of time (5 min to 24 h) before rehydrating the surface and rubbing onto healthy tomato plants, PSTVd remained infective for 24 h on all surfaces except human skin. It survived best on leather, plastic, and string. It survived less well after 6 h on wood, cotton, and rubber and after 60 min on metal. On human skin, PSTVd remained infective for only 30 min. In general, rubbing surfaces contaminated with dried infective sap directly onto leaves caused less infection than when the sap was rehydrated with distilled water but overall results were similar. The effectiveness of five disinfectant agents at inactivating PSTVd in sap extracts was investigated by adding them to sap from PSTVd-infected leaves before rubbing the treated sap onto leaves of healthy tomato plants. Of the disinfectants tested, 20% nonfat dried skim milk and a 1:4 dilution of household bleach (active ingredient sodium hypochlorite) were the most effective at inactivating PSTVd infectivity in infective sap. When reverse-transcription polymerase chain reaction was used to test the activity of the five disinfectants against PSTVd in infective sap, it detected PSTVd in all instances except in sap treated with 20%nonfat dried skim milk. This study highlights the stability of PSTVd in infective sap and the critical importance of utilizing hygiene practices such as decontamination of clothing, tools, and machinery, along with other control measures, to ensure effective management of PSTVd and, wherever possible, its elimination in solanaceous crops

Iris yellow spot virus found infecting onions in three Australian states

Iris yellow spot virus (IYSV) was detected for the first time in Australia, infecting onions in three and leeks in one state. Identification was confirmed using sap transmission to Nicotiana benthamiana, two IYSV-specific antisera in ELISA, RT–PCR with IYSV-specific primers, and sequence comparison with published 1IYSV sequences. Spring onion, onion seed and onion bulb crops were all infected, with spring onion being the most severely affected. The virus was also detected in nursery-grown onion and leek seedlings

Iris yellow spot virus found infecting onions in three Australian states

Iris yellow spot virus (IYSV) was detected for the first time in Australia, infecting onions in three and leeks in one state. Identification was confirmed using sap transmission to Nicotiana benthamiana, two IYSV-specific antisera in ELISA, RT–PCR with IYSV-specific primers, and sequence comparison with published 1IYSV sequences. Spring onion, onion seed and onion bulb crops were all infected, with spring onion being the most severely affected. The virus was also detected in nursery-grown onion and leek seedlings

High-Throughput sequencing technologies for plant pest diagnosis: challenges and opportunities.

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