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The discovery of tolerance in wild plants will be helpful to tomato growers

tomato plant
Photo by Chad Stembridge on Unsplash

Tomato farms across the world are routinely devastated by canker, a rain-borne bacterial disease that can cause wilt, stem canker and lesions on the fruits, causing them to become unsuitable for consumption and – in combination with the wilting leaves causing sun scald and other issues – resulting in massive economic losses. Clavibacter michiganensis, the bacterium responsible for the disease, spreads throughout affected plants using xylem vessels and readily infects their neighbours, which can cause entire fields of tomato plants to be lost in a short time.

A study carried out by researchers from Cornell University has confirmed for the first time that wild tomato species are susceptible to bacterial canker. However, the researchers also found that wild tomatoes demonstrate some resistance to the disease, which represents a landmark discovery as no tomato species have been previously found to have any form of resistance or tolerance to bacterial canker.

Bacterial canker disease (Clavibacter michiganensis) lesions on unripe tomato
Bacterial canker disease (Clavibacter michiganensis) lesions on unripe tomato

Using laser scanning confocal microscopy and scanning electron microscopy, the researchers were able to monitor the colonization, spread and symptom development of C. michiganensis in wild and cultivated tomato plants. They used a wild type of bacterium and a hypervirulent strain in order to compare their effects, and observed that in both cases the bacteria exhibited preferential colonization of protoxylem vessels in wild tomatoes, and were less able to spread throughout the plant. These results demonstrate that wild tomatoes somehow inhibit the ability of the bacteria to move within the plants, although the exact mechanisms of this process will require further research to identify.

Unfortunately, even with the spread and symptoms of bacterial canker being reduced, the fruits of wild tomatoes have still been observed to develop lesions, and there seems to be no connection between the plant’s ability to resist the spread of the pathogen and the development of fruit lesions. The researchers therefore suggest that these are controlled by different biological mechanisms. Nevertheless, the identification of canker-resistant species will be of significant value to tomato growers and breeders, and may provide a pathway to developing horticultural cultivars that exhibit a similar tolerance.

The full article is available on the APS Journals website:

Peritore-Galve, F. C., Miller, C. & Smart, C. D. (2020) Characterizing Colonization Patterns of Clavibacter michiganensis During Infection of Tolerant Wild Solanum Species. Phytopathology. DOI:

Visit CABI’s Plantwise Knowledge Bank to find species data, factsheets and relevant pest alerts using the following search: (Tomato* OR Solanum) AND Canker

Further reading

Prevalence of (Clavibacter michiganensis subsp. michiganensis) causal organism of bacterial canker in weed species in tomato fields of north west Pakistan.

Potential of Bacillus amyloliquefaciens for biocontrol of bacterial canker of tomato incited by Clavibacter michiganensis ssp. michiganensis.

Bacterial wilt and canker of tomato: fundamentals of a complex biological system.

Bacterial wilt and canker of tomato – Clavibacter michiganensis subsp. michiganensis.

Clavibacter michiganensis ssp. michiganensis: bacterial canker of tomato, molecular interactions and disease management.

Biocontrol rhizobacterium Pseudomonas sp. 23S induces systemic resistance in tomato (Solanum lycopersicum L.) against bacterial canker Clavibacter michiganensis subsp. michiganensis.

Inhibition of alternaria stem canker on tomato by essential oils from Baccharis species.

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