Pathogen Profile #18

Hello Robigalia Reader and welcome back to another week of Robigalia, delivering the latest in plant pathology directly to your inbox!

Last month, the South Australian Department of Primary Industries and Regions reported the first detections of tomato brown rugose fruit virus (ToBRFV) in Australia. While authorities aren’t reaching for the panic button just yet, testing of thousands of samples is currently underway to determine the extent of the spread. Scroll down to learn about ToBRFV.

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Tomato brown rugose fruit virus, is an emerging tobamovirus that infects multiple Solanaceae crops, including tomato and chilli/peppers. First identified in Israel in 2014, this RNA virus has since spread globally, now reported in at least 35 countries across four continents. The most recent detection occurred in South Australia in late August, with authorities assessing the outbreak's scale.

ToBRFV enters plants through mechanical wounds or natural openings, invading plant cells to replicate its genome and produce viral proteins. It spreads locally from cell to cell through plasmodesmata, and then systemically through the vascular system, causing symptoms such as leaf mottling and fruit discolouration. Transmission to new hosts happens through mechanical contact, contaminated tools, pollinators in glasshouse settings, and other insects.

ToBRFV thrives in diverse conditions, showing strong temperature tolerance and stability on various surfaces. It can survive in seeds, enabling long-distance spread. The virus's ability to overcome common genetic resistance and persist in plant debris, soil, and water makes it particularly troublesome. These traits have driven its rapid global spread, establishing it as a major threat to tomato production, with yield losses of up to 70% reported.

The economic impact of ToBRFV on the global tomato industry has been substantial. As one of the most consumed fruits globally, tomato production reached around 180 million tonnes in 2019. The virus poses a serious threat to this multi-billion-dollar industry as a result of yield losses. Beyond direct losses, ToBRFV also increases production costs; such as costs associated with disinfecting a greenhouse after an outbreak.

Controlling ToBRFV is challenging, especially due to its ability to overcome the Tm-22 resistance gene in tomatoes. This resistance-breaking trait has led to a multi-faceted control approach, with research is ongoing to develop new resistant cultivars. In the meantime, integrated pest management strategies—such as seed testing, early detection, and rapid removal of infected plants—remain the main defence. In Mexico, these methods are being used alongside experimental treatments with endophytic microorganisms like Beauveria peruviensis, which has shown promise in reducing disease severity.

Regardless of where you’re living, ToBRFV is emerging as a serious threat to tomato cultivation. If you’re interested in learning more about ToBRFV, I’ve summarised a few articles below. Robigalia subscribers can scroll down to access my online database, which includes full summaries of these and all other featured Robigalia articles.

Tomato brown rugose fruit virus papers

Single amino acid change in tomato brown rugose fruit virus breaks virus-specific resistance in new resistant tomato cultivar

• A new study has identified a single amino acid change in the movement protein of ToBRFV that enables it to break resistance in a newly developed resistant tomato cultivar. High-throughput sequencing revealed that an asparagine-to-lysine substitution at position 82 of the movement protein was sufficient to overcome the resistance under commercial greenhouse conditions. These findings highlight the adaptability of ToBRFV and the challenges in developing durable resistance.

The invasive tomato pest Tuta absoluta can transmit the emergent tomato brown rugose fruit virus

• This study revealed that the invasive tomato pest Tuta absoluta can transmit ToBRFV, potentially contributing to the virus's rapid spread in tomato crops. Tuta absoluta adults emerging from larvae reared on infected plants carry infectious ToBRFV inoculum, which they can subsequently transfer to healthy plants. These findings highlight the need to adapt integrated pest management strategies for T. absoluta to mitigate the concurrent threats posed by this insect vector and the emerging viral pathogen in tomato production systems.

Detection of tomato brown rugose fruit virus is influenced by infection at different growth stages and sampling from different plant parts

• A new study sheds light on how the timing of ToBRFV infection and plant age influence virus distribution and detection in tomato plants. Researchers found that early infections lead to predictable systemic spread, while late infections result in random virus distribution, with sepals and fruits often showing earlier detection than leaves in mature plants. These insights have important implications for optimising ToBRFV surveillance strategies based on crop growth stage.

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Until next week,

Alyssa