News February 2021, North America, Pests and Diseases, Pressreleases, Production/Agronomy

Does the aerial stem rot bacterium cause blackleg?

Aerial stem rot is caused by the same bacterium that causes tuber soft rot, Pectobacterium carotovorum subsp. Carotovorum, writes Dr Eugenia Banks, potato specialist at the Ontario Potato Board in Canada in the latest issue of her regular email newsletter, issued yesterday. She provides a few essential pointers to growers regarding the bacterium – in response to a question she received from a potato grower in Ontario.

Dr Banks writes: “This is the same bacterium that your grandparents had to deal with, but under another name – Erwinia carotovora. The bacterium survives in the soil and can be found infecting potato stems because rain splashes the bacterium onto the stems.” 

Dr Banks says bacteria penetrate stems wherever there are wounds, which can be caused by hail, high winds, torrential rains or farm equipment.  Once into the stem, the bacteria move up towards the tip of the stem. Rain also washes bacteria off infected stems and into the soil where the bacteria can enter the daughter tubers through open lenticels if soil moisture is high. 

Those daughter tubers can then rot when injured or washed and put away or bagged wet. If planted, and the weather is wet and warm the tubers can rot rapidly.  If the rot is slow, then bacteria can move up the stem causing blackleg, either pre- or post- emergence.

“In short,” Dr Banks says, “the answer to the question whether the aerial stem rot bacterium can cause blackleg, is YESThe bacterium can cause blackleg in a potato crop grown from infected seed, under the specific circumstances described above.”

Source: Dr Eugenia Banks
Email: [email protected]
Cover photo: Aerial stem rot moves up the stems | Eugenia Banks

Initial lesions on stems first appear as a clear rot | Photo: Eugenia Banks
Eventually, the rotten tissue turns black and acquires a fishy smell
when invaded by secondary bacteria
| Photo: Eugenia Banks

Lukie Pieterse, Editor and Publisher of Potato News Today

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