Two scientists are disputing the significance of Italian research into the Psa bacteria that is infecting kiwifruit vines in Italy, Korea and New Zealand.

The research paper in question is called Pseudomonas syringae pv. actinidiae Draft Genomes Comparison Reveal Strain-Specific Features Involved in Adaptation and Virulence to Actinidia Species.

Psa in spring is shown with a red ooze.

It is authored by Simone Marcelletti, Patrizia Ferrante, Milena Petriccione, Giuseppe Firrao, and Marco Scortichini.

The paper's abstract suggests the current destructive Psa strain is a recent independent evolution that didn't evolve from the Psa population that caused the epidemics in 1984-1992 in Japan and Italy.

All Psa strains share the genetic potential for copper resistance, antibiotic detoxification, high affinity iron acquisition and detoxification of nitric oxide of plant origin.

Similar to other sequenced phytopathogenic pseudomonads associated with woody plant species, the Psa strains isolated from leaves also display a set of genes involved in the catabolism of plant derived aromatic compounds.

Pukekohe based scientist Nathan Balasingham says the paper shows the kiwifruit industry's PSA management strategy is on the wrong track.

The Italian research supports the claim that plant material with no symptoms of the disease can, in fact, be carrying the bacteria and introduce it into orchards, says Nathan. He says the strain's genetic resistance to copper and streptomycin illustrates why orchard experience is showing that spraying antibiotics on vines has not produced good results.

'Orchardists have reported phytotoxic or plant poisoning problems from antibiotic sprays but their reports have been ignored or blamed on poor spray application technique,” says Nathan.

Zespri scientist Greg Clark challenges Nathan's interpretation.

'There are bits in there about the copper resistance and the antibiotic resistance, but it also points out in the paper that the key genes associated with copper resistance are absent from the Psa strains that were looked at,” says Greg.

'They have a base resistance that is required for any organism living in a natural environment where you encounter copper.

'It's got broad spectrum antibiotic resistance, which all bacteria have that live as an epiphyte.

'They require it to protect themselves from other bacteria that want to occupy the same niche.

'Bacteria just produce antibiotics – that's where things like streptomycin come from, it's a natural thing that bacteria produce to protect their space, their environment from the hundreds of other bacteria species that are wanting to occupy the same space.

'So there's no specific streptomycin resistance there at all and it's not even mentioned in the paper.”

Nathan says the Italian findings are very timely for New Zealand kiwifruit orchardists and encourage the practice of fighting the organism within the vine.

He's advocating using Thermomax and Agrizest together with Humic Acid to develop healthier and more resilient plants. Nathan manufactures and sells Agrizest.

Nathan says another important result from the Italian scientists' investigation has been to show the ability of the current virulent Psa form to breakdown essential oils that the plant produces, stores and uses as a natural chemical defence.

This means the practice of removing vine foliage is a bad strategy as it removes the ‘factory' that produces these essential, protective oils.

An integrated pest management process gives the industry the opportunity to manage the disease and still produce quality fruit that delivers higher returns, says Nathan.

At the same time, residue risks are abated and fertiliser and girdling cost are saved.

Greg says Nathan's news release on the Italian research reeks of pushing products that haven't been proven.

Zespri has set up a meeting with Nathan next week.

'Mr Balasingham is familiar to Zespri and to Kiwifruit Vine Health, and we understand that he is a promoter of the two products that he has identified in his media release as part of his answer to Psa,” says a Zespri spokesman.

He went on to say that Zespri, in partnership with KVH, is running an extensive global research and development programme involving multiple leading research partners – working with some of the most reputable biological scientists in the world, with a view to identifying the best, long term viable options for kiwifruit growers.

'By necessity this research has to be independent and thorough.

'Zespri and KVH must consider all the Psa research and develpment work being done and its enormous potential for delivering a range of viable and long-term answers to Psa.”