Bay of Plenty Times

Psa re­search of­fers hope

KI­WIFRUIT: Cul­ti­vars from nat­u­rally re­sis­tant wild va­ri­eties could well be the key to re­silience, Donna Rus­sell re­ports

- Science · Oceania News · Ecology · New Zealand · Beijing · Royal Society · New Zealand Government · Plant & Food Research

Anew re­search project that may help fu­ture-proof the ki­wifruit in­dus­try has re­ceived a Fast Start Mars­den grant. The three-year project, led by Dr Jay Ja­yara­man at Plant & Food Re­search, is in­ves­ti­gat­ing how the Psa plant pathogen evolves dur­ing in­fec­tion of the ki­wifruit plant.

Psa (Pseu­domonas sy­ringae pv ac­tini­diae) has been the most se­ri­ous chal­lenge to the ki­wifruit in­dus­try in re­cent years, forc­ing grow­ers to re­place thou­sands of sus­cep­ti­ble plants with more re­sis­tant cul­ti­vars at a huge cost to the in­dus­try.

“The in­dus­try is re­cov­er­ing a lot bet­ter than ex­pected. The new va­ri­eties are per­form­ing well but still re­quire reg­u­lar cop­per sprays to keep the plants healthy and re­sis­tant to the bac­te­ria,” he said.

“We want to ex­plore al­ter­na­tive ways to man­age the disease in fu­ture, par­tic­u­larly if the Psa pathogen man­ages to adapt to the new cul­ti­vars. As much as pos­si­ble, we want to fu­ture-proof the in­dus­try to cre­ate more se­cu­rity for grow­ers.”

Ja­yara­man and his team of re­searchers plan to draw on the early va­ri­eties of wild ki­wifruit that have been kept at Plant & Food Re­search since they were col­lected by early botanists.

He has al­ready no­ticed that some of these early wild va­ri­eties are nat­u­rally re­sis­tant to Psa.

“These va­ri­eties are closer to the wild ki­wifruit. Some­have small ed­i­ble fruit and some are not tasty at all.”

Decades of breed­ing work went into cre­at­ing the first com­mer­cial cul­ti­var, which turned out to be par­tic­u­larly sus­cep­ti­ble to Psa.

Ki­wifruit grow­ers now largely rely on the Ze­spri Sun­gold G3 va­ri­ety, which has a vi­brant yel­low colour and trop­i­cal flavour, and the tra­di­tional Hay­ward Ze­spri Green va­ri­ety.

The new Red19 cul­ti­var, called Ze­spri Red Ki­wifruit, was launched this year as a com­mer­cial crop af­ter more than a decade of de­vel­op­ment in a part­ner­ship be­tween

Ze­spri and Plant & Food Re­search.

The Red va­ri­ety adds a sweet, juicy, rasp­ber­ryflavour to the Sun­gold flavour and is now avail­able to com­mer­cial grow­ers.

Ja­yara­man said de­vel­op­ing new cul­ti­vars took many years, so re­searchers are in a race against time to en­sure any new cul­ti­vars are more re­sis­tant to Psa.

“We are all re­ally fo­cused and there are hun­dreds of sci­en­tists who are in­volved and want New Zealand grow­ers to do well.”

Psa was dis­cov­ered in New Zealand’s ki­wifruit crops in 2010 and ge­nomic se­quenc­ing had es­tab­lished that the strain had most likely ar­rived from China. There is only one strain in New Zealand although there are many oth­ers around the world.

Psa causes disease by se­cret­ing pro­teins that sup­press the ki­wifruit plant’s im­mune re­sponse. Much like in the hu­man im­mune sys­tem, the ki­wifruit plant iden­ti­fies and re­sponds to the pathogen re­sult­ing in leaf spot­ting, canker and cane dieback and vine death.

“The disease is al­most ev­ery­where in New Zealand and spreads eas­ily through water and air, and through foot traf­fic and ve­hi­cles. It in­fects the en­tire plant and can kill the ear­lier va­ri­eties within a few weeks,” Dr Ja­yara­man said.

Grow­ers have adopted care­ful or­chard man­age­ment tech­niques to try and con­tain the disease, in­clud­ing re­strict­ing vis­i­tors to or­chards and de­vel­op­ing biose­cu­rity plans.

Dr Ja­yara­man said he hopes fu­ture cul­ti­vars will be so re­sis­tant to Psa that they can be spray-free. “That would be a dream re­sult if that is pos­si­ble.

“We would like fu­ture or­chardists to have a min­i­mal im­pact on the en­vi­ron­ment.”

There are hun­dreds of sci­en­tists who are in­volved and­want New Zealand grow­ers to do well.

■ The Mars­den Fund, man­aged by the Royal So­ci­ety Te Ap rangi on be­half of the New Zealand gov­ern­ment, sup­ports New Zealand’s best in­ves­ti­ga­torini­ti­ated re­search in the ar­eas of science, en­gi­neer­ing, maths, so­cial sci­ences and the hu­man­i­ties. This project is one of two Plant & Food Re­search Mars­den grants awarded for this round.

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 ?? Photo / Plant & Food Re­search ?? Ki­wifruit re­searcher Dr Jay Ja­yara­man of Plant & Food Re­search.
The new red ki­wifruit va­ri­ety has been re­leased for com­mer­cial use this year.
Photo / Plant & Food Re­search Ki­wifruit re­searcher Dr Jay Ja­yara­man of Plant & Food Re­search. The new red ki­wifruit va­ri­ety has been re­leased for com­mer­cial use this year.

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