Identifying the gene which makes some kiwifruit more resistant to Pas-V is just one of the Plant & Food research projects underway in the battle against the disease.

Dr Stuart Kay, Plant & Food's kiwifruit business manager, says many of the vines in the Te Puke research orchard are surviving well despite being in an environment with high inoculum levels of Psa.

'We have yet to find a specific resistance gene but we are rapidly screening the existing kiwifruit material for tolerance.”

Important as that and other research into ways to control the bacteria is, Stuart says the development of a range of Psa resistant cultivars is pivotal to the future of the kiwifruit industry.

'Having plants which can survive Psa-V is just part of the answer. If we find them, we then need to breed plants which are not only tolerant of Psa but also have fruit which looks good, tastes good and stores well.”
To find those varieties the Plant & Food Research and Zespri kiwifruit breeding programme has increased the number of new seedlings being screened from 20,000 to 50,000 and, is looking to increase it further as new technologies and methodologies are developed.
New technologies are being developed to speed up the rate at which cultivars with tolerance to Psa can be identified. This includes research into the molecular basis of Psa resistance to support the development of genetic tools to identify plants in the breeding programme with intrinsic resistance to the disease.

However, these plants will be bred using conventional breeding, not genetic engineering practices, and it will be several years before the breeders and Zespri can be sure which plants have the potential to become commercial varieties. Green, gold and red varieties are all included in the trial.

Additional to the development of new cultivars research is looking at systems that can potentially induce resistance in the existing kiwifruit cultivars. The outcomes of this research would be complementary and could augment use of plant protection products and new cultivars.

Stuart says how orchards are managed and potentially where the vines grow are also factors in whether or not the vines can cope with the disease.

'With biology, nothing is black and white. There are so many variables, but it does appear New Zealand has the climatic conditions which suit Psa.”

Research is also underway at Plant & Food and a number of other agencies to find protectant sprays and orchard management techniques which will help limit the impact of Psa.

'We have found that Psa doesn't survive well in compost and soil but it is unclear if there is something in the compost or soil which attacks the bacteria or if it is simply the case that Psa has not evolved to live in these environments.”