Psa experts gather in Tauranga
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.”
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.”