Psa ex­perts gather in Tau­ranga

The Orchardist - - Contents - By Les­ley Board

New Zealand re­searchers and our ki­wifruit in­dus­try in gen­eral are lead­ers in­ter­na­tion­ally in the fight against the bac­te­rial disease Psa. That was the con­sen­sus among many of the 160 del­e­gates to the first ever in­ter­na­tional sym­po­sium on Psa, held in Tau­ranga last month. It was jointly con­vened by Dr David Tan­ner, Ze­spri's gen­eral man­ager – sci­ence & in­no­va­tion and Dr Joel Vanneste, plant bac­te­ri­ol­o­gist with the New Zealand In­sti­tute of Plant & Food Re­search (NZIPFR). David said he was greatly en­cour­aged by re­marks from em­i­nent sci­en­tists at­tend­ing. They were im­pressed by the speed at which the New Zealand in­dus­try had tack­led the prob­lem head-on and by what had been achieved in terms of con­trol in just three years.

This Bac­te­ria will adapt

“If peo­ple were ex­pect­ing some WOW fac­tor or magic so­lu­tion to come out of this gath­er­ing it was never go­ing to hap­pen,” David said. “If and when we can breed a fully re­sis­tant ki­wifruit va­ri­ety that will cer­tainly be a WOW fac­tor for us, but we al­ready know that the bac­te­ria will then adapt. Psa is here to stay.This meet­ing is about shar­ing our knowl­edge and our re­sources so that re­search is not du­pli­cated and so that col­lec­tively we can go for­ward. That's why the theme of the gath­er­ing was Learn­ing To­gether is Learn­ing Faster.” Sci­en­tists came from Italy, China, France, Spain, Ja­pan, Canada, USA, South Korea, Nor­way, Aus­tralia and New Zealand for an in­ten­sive three-day gath­er­ing which in­cluded a visit to Plant & Food Re­search at Te Puke, some G3 or­chards and a spe­cial ses­sion for New Zealand grow­ers. David said the French and Ital­ian del­e­gates in par­tic­u­lar were im­pressed at the way grow­ers at Te Puke had been able to turn heav­ily in­fected G3 vines around in a rel­a­tively short time.

We need each other

“I was equally im­pressed by the will­ing­ness of del­e­gates to share their knowl­edge and re­sources.A sci­en­tist from Nor­way, where they don't even grow ki­wifruit, said he was here to un­der­stand more of the prob­lem and to look at op­por­tu­ni­ties to as­sist. We have thrown a lot of re­sources at the prob­lem but oth­ers are adding to our bank of knowl­edge – they need our re­search as much as we need theirs. Gath­er­ings like this help us avoid du­pli­ca­tion and to wisely spend the lim­ited funds we have for R&D.”

The idea to hold the sym­po­sium orig­i­nated at a meet­ing in Brus­sels 18 months ago and was taken up by the In­ter­na­tional So­ci­ety for Hor­ti­cul­tural Sci­ence (ISHS).

“This is a topic that is not only sci­en­tif­i­cally ex­cit­ing but more im­por­tantly, com­mer­cially and eco­nom­i­cally im­por­tant for us all. I learned a lot from the speak­ers and through talk­ing to oth­ers at the sym­po­sium – it was like gath­er­ing to­gether pieces of the puz­zle.”

Out­stand­ing re­search ef­fort

Dr Vanneste said no­body could have pre­dicted there would be a ma­jor in­ter­na­tional con­fer­ence about what was un­til re­cently a mi­nor pathogen of a mi­nor crop – ki­wifruit be­ing just 0.2% of the global fruit bas­ket.That changed in 2008 with the dis­cov­ery of Psa in Latina, Italy, fol­lowed by out­breaks in all ma­jor ki­wifruit pro­duc­ing coun­tries with the pos­si­ble ex­cep­tion of Iran and the USA.

“As a plant bac­te­ri­ol­o­gist I have seen this sce­nario played out many times on crops which glob­ally might be more im­por­tant than ki­wifruit – for in­stance pears in Morocco are be­ing dev­as­tated and pa­paya are un­der threat in Tonga.” Other out­breaks how­ever, for eco­nomic or po­lit­i­cal rea­sons were not met by any con­certed ef­fort to un­der­stand the pathogen or con­trol it.

“In the case of Psa we had just the op­po­site. The in­dus­try, producers, the gov­ern­ment and the sci­en­tific com­mu­nity came to­gether and started the most im­por­tant re­search ef­fort on a plant bac­te­rial pathogen I have ever seen in my life.” One rea­son for it hap­pen­ing in New Zealand was the fact that ki­wifruit is our most im­por­tant hor­ti­cul­ture crop, earn­ing over $1 bil­lion in ex­ports in 2009. In Europe, Psa had been in­cluded as one of the ma­jor tar­gets of the re­search pro­posal (Dropsa) val­ued at 6 mil­lion Eu­ros. One rea­son was the im­por­tance of the in­dus­try to Latina where more than 10,000ha are in ki­wifruit.

Psa al­most a model pathogen

Dr Vanneste said there were al­ready some sig­nif­i­cant re­sults emerg­ing but much more needed to be done. “This re­search ef­fort has el­e­vated Psa from an un­known pathogen to one of the most stud­ied plant pathogen bac­te­ria. This makes it al­most a model pathogen – there are very few from which we would have as many strains fully sequenced as we have for Psa.”

Bring­ing to­gether a team of ex­perts in dif­fer­ent fields was crit­i­cal to suc­cess. “My hope is that this sym­po­sium will be the place where col­lab­o­ra­tions will start.”

What about ge­netic mod­i­fi­ca­tion?

Pro­fes­sor Costa from the Univer­sity of Bologna, Italy, said the Latina re­gion had suf­fered se­verely when their Hort16A was in­fected and 2,000ha of ki­wifruit had been de­stroyed or cut out be­tween 2010 and 2012. In his own re­gion of Emilio-Ro­magna, five va­ri­eties of ki­wifruit were grown and all were in­fected.

“We have used he­li­copters to do wind pol­li­na­tion and we now won­der if pollen is ac­tu­ally spread­ing the disease. Can it mul­ti­ply in the flower and go on to in­fect the plant? We are also look­ing at the take-up of el­e­ments such as ni­tro­gen and whether growth reg­u­la­tors and our prun­ing and crop­ping sys­tems con­trib­ute to its spread.”

He also raised the ques­tion of ge­netic mod­i­fi­ca­tion. “We know that we can ge­net­i­cally mod­ify the plant to make it disease re­sis­tant but would that be ac­cept­able? There are a lot of peo­ple around the world eat­ing ge­net­i­cally mod­i­fied food and they are still alive – even Olympic cham­pi­ons!”

No ssmp­toms in AC­TINI­DIA ARGUTA

Dr Li Li of China said Psa was first re­ported there in 1985 and since then had spread to most pro­duc­ing ar­eas. It was first listed and iden­ti­fied as Psa in 1992 but com­mer­cial pro­duc­tion of ki­wifruit had de­vel­oped much later there than in other coun­tries.

“It varies be­tween prov­inces but at present less than 1.5% of vines are in­fected over our to­tal grow­ing ar­eas. We have iso­lated 207 strains of Psa across China. There are a large num­ber of vir­u­lent types and great diver­sity but so far no symp­toms in A.arguta plants. We are breed­ing for the fu­ture and do not be­lieve that Psa will cause us se­vere eco­nomic loss in the short term.”

Bi­o­log­i­cal con­trols

Dr Francesco Spinelli, a plant pathol­o­gist at Bologna Univer­sity, said there ap­peared to be more bac­te­ria where zinc was lack­ing in the grow­ing medium. Field tri­als also showed that while cop­per was quite ef­fec­tive as a pro­tec­tant, a com­bi­na­tion of cop­per and Bion ap­peared to work best and had shown a disease re­duc­tion of 85 to 95%.

“We have found the bac­te­ria colonises the stigma of flow­ers and in­vades the host tis­sues, which can lead to sec­ondary symp­toms. Even asymp­to­matic flow­ers can have in­fected pollen. We are look­ing for bi­o­log­i­cal con­trols to pro­tect our flow­ers and at least one bac­terium seems quite ef­fec­tive at this stage.”

Lift in or­chard val­ues

Del­e­gates to the sym­po­sium paid their own costs, in­clud­ing a reg­is­tra­tion fee of $700, while spon­sors paid the air­fares and reg­is­tra­tion for two of the key speak­ers.

David Tan­ner said there was no doubt that Psa has changed the New Zealand ki­wifruit in­dus­try for­ever. “As grow­ers we now have to give more at­ten­tion to de­tail and that is both time con­sum­ing and costly. Grow­ers who were ready to re­tire have had to go back into their or­chards over the last three years. Look­ing ahead we need to make it pos­si­ble for younger peo­ple to come through and grow ki­wifruit suc­cess­fully – if the com­mu­nity can come up with some mod­els to make that hap­pen, then I see good prospects for in­dus­try longevity. One of the signs of a pos­i­tive out­come in New Zealand for all the con­certed ef­fort to beat Psa, has been the re­cent lift in or­chard sales val­ues.”

Key peo­ple at the sym­po­sium were ( from left) Dr Joel Vanneste – Plant & Food Re­search; Dr Li Li – Wuhan Botan­i­cal Gar­den, Chi­nese Academy of Sciences; Dr Francesco Spinelli – Univer­sity of Bologna; Prof. Guglielmo Costa – Univer­sity of Bologna; Dr Dave T

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