Nectria canker, caused by the fungus Neonectria ditissima (formerly Nectria galligena and also commonly known as European canker or apple canker), is one of the most important diseases of apple and pear. The losses resulting from this pathogen are very difficult to quantify as they occur at all stages of production, from the tree nursery to the fruit store. Most of the established apple cultivars are very susceptible to the disease and the more recently introduced cultivars such as Jazz, Braeburn, Reubens, Cameo, Kanzi and Zari are also particularly susceptible. The propagation phase in the nursery presents a high risk period for infection due to the large number of wounds created as part of the production process: these act as entry points for the pathogen which can then persist asymptomatically until planted in the growing site, where plant stress often promotes the expression of the disease. The fungus attacks trees in the orchard, causing cankers and die back of young shoots, resulting in loss of fruiting wood and an increase in pruning costs. Apple canker can be particularly damaging in young orchards in the first few years of orchard establishment, as a result of trunk cankers, particularly following exceptionally wet or cold winters. In some years, up to 10% of trees can be lost annually. N. ditissima also causes a fruit rot that can occur both pre and post-harvest. Infection at flowering or early fruit development may develop into eye rot in orchards, though most infection stays latent and only develops during long-term storage. Post-harvest rot can result in significant losses as high as 10% or more in stored fruit. Nectria rot, which is often found at the fruit stalk end, is also difficult to spot on the grading line, but becomes obvious during marketing and gives rise to rejection of fruit consignments.
The last major review of the literature was in (Swinburne, 1975). Since then, some significant bodies of work have been undertaken and advances in research tools have been made. With the incidence of Nectria canker on the increase due, in part, to increased plantings of susceptible cultivars, it is pertinent that the latest literature is reviewed 40 years on and new research areas identified to mitigate the losses caused by this increasingly significant disease.
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