Viroid-infected Tomato and Capsicum Seed Shipments to Australia.

Fiona Constable,Mark Gibbs,Joanne Mackie,Grant Chambers,Lindsay Penrose,Andrew Daly,Kevin Davis,Brendan Rodoni

doi:10.3390/v11020098

Abstract

Pospiviroid species are transmitted through capsicum and tomato seeds. Trade in these seeds represents a route for the viroids to invade new regions, but the magnitude of this hazard has not been adequately investigated. Since 2012, tomato seed lots sent to Australia have been tested for pospiviroids before they are released from border quarantine, and capsicum seed lots have been similarly tested in quarantine since 2013. Altogether, more than 2000 seed lots have been tested. Pospiviroids were detected in more than 10% of the seed lots in the first years of mandatory testing, but the proportion of lots that were infected declined in subsequent years to less than 5%. Six pospiviroid species were detected: Citrus exocortis viroid, Columnea latent viroid, Pepper chat fruit viroid, Potato spindle tuber viroid, Tomato chlorotic dwarf viroid and Tomato apical stunt viroid. They were detected in seed lots exported from 18 countries from every production region. In many seed lots, the detectable fraction (prevalence) of infected seeds was estimated to be very small, as low as 6 × 10−5 (~1 in 16,000; CI 5 × 10−6 to 2.5 × 10−4) for some lots. These findings raise questions about seed production practices, and the study indicates the geographic distributions of these pathogens are uncertain, and there is a continuing threat of invasion.

Highlights

Trade in plant materials, especially seeds, tissue cultures and nursery stock, can spread pathogens, changing their epidemiology and geographic distribution
Pospiviroids were on average detected in 6.5% (36/553) of capsicum seed lots tested by Australian laboratories, and over eight years, pospiviroids were on average detected in 5.7%
But not all of it, appeared to be a stochastic effect related to small sample sizes, especially during the period between 2008 and 2012, when only small numbers of tomato seed lots (28 lots) were tested (Figure 2)

Summary

Introduction

Especially seeds, tissue cultures and nursery stock, can spread pathogens, changing their epidemiology and geographic distribution. Pospiviroids are emerging pathogens with several species discovered in solanaceous crop plants in the past 20 years, and more species are spreading to countries and continents where they have not been previously recorded [1,2,3,4,5,6,7,8,9]. Pospiviroids have been detected in cultivated ornamental plants in nurseries, and it was proposed that ornamental plants are the source of the infections in crops [10,11]. Rather than focusing solely on ornamental plants, Australian governments have considered infected tomato, capsicum and chilli seeds as the likely sources of the infections.

Methods

Results

Conclusion