Thursday, December 7, 2023

Psa variant under observation 

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Pest management monitoring picks up genetic variation.
A long-term monitoring programme helped identify a new Psa variant in orchards last year.
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Committed follow-up through the national plan on Psa management has paid dividends for growers and scientists in the past year.

The National Pest Management Plan was established after the major outbreak in 2010. It first aimed at delivering more cohesive, collaborative management of the disease in its wake. This included monitoring for any variants or shifts in the disease’s behaviour and characteristics over time.

Ruakura based Plant & Food scientist Stephen Hoyte and Kiwifruit Vine Health (KVH) tech specialist Lina Peacock outlined to delegates at this year’s KVH biosecurity seminar the recent discovery of a Psa variant.

“The industry conducts a survey looking for resistance and every two years looks for any genetic variation. 

“Last year Plant & Food detected a new Psa variant. Sequencing it and checking against plants they found it out-competed existing Psa when put on Hort 16a plants,” Peacock said.

Hort 16a is the earlier Gold kiwifruit variety that was hit so hard in the original Psa outbreak, and later replaced by the more Psa-tolerant SunGold variety.

“We need to know how it would behave on the G3 [SunGold] and Red plants. We had found it on two orchards and then in spring 2022 sampled further and found it in four additional orchards, making it six in total.”
Steve Hoyte said researchers were compelled to quickly develop a PCR test capable of rapidly identifying the new strain, which was achieved.

“What we have found is there is no difference on Gold 3 plants between the two types of Psa [new and existing], but some increase on Red plants – though to a much lesser extent than on Hort16a.

“It is out there in orchards, but it is no more aggressive than the wild type,” Hoyte said.

“But is something that needs to be monitored.”

Peacock said the response highlighted the huge value of collaboration enjoyed across the post-Psa years at a research and personal level. She told growers to get in touch if they see any unusual growth activity, while genetic monitoring of Psa variants will also be continuing.

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