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PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND

Searching for red needle cast disease resistance

From Forest Health News 283, August 2018.

One of the long term goals in the fight against red needle cast (RNC) of radiata pine, caused by Phytophthora pluvialis, is breeding for disease resistance. Minimising dependence on chemical control for needle diseases is important in ensuring the continued success and resilience of radiata plantation forests. With a much shorter history of RNC in New Zealand compared with other foliar diseases, such as dothistroma needle blight and cyclaneusma needle cast, opportunities to measure and understand the genetic resistance to this disease have so far been limited to a handful of genetic trials.

Using a screening technique where detached needles are exposed to the pathogen (Fig. 1), the Healthy Trees, Healthy Future programme has screened around representatives of a Radiata Pine Breeding Company (RPBC) elite population. Development of greater numbers of larger needle lesions indicated susceptibility, while development of no, or few lesions of small size, indicated greater resistance to RNC.

We observed a broad range in the response of this population to infection, with some clones that were clearly susceptible and others that were clearly more resistant. These differences also appeared to be heritable, which supports what we have seen to date in genetic field trials, and tells us that improving resistance through breeding is possible.

There are limitations with lab-based assays, and development of some sophisticated statistical models was required to analyse the data generated using this screening tool. Continued work is required to better understand the sources of variation observed in these experiments. We look forward to opportunities to validate these results against field data from the RPBC’s regional trials. Using such lab-based screening methods remains a viable option to assess resistance to RNC when no information is available for a population.

Natalie Graham, Scion.

Graham NJ, Suontama M, Pleasants T, Li Y, Bader MKF, Klápšte J, Dungey HS, Williams NM, 2018. Assessing the genetic variation of tolerance to red needle cast on a Pinus radiatabreeding population. Tree Genetics & Genomes 14:55. https://doi.org/10.1007/s11295-018-1266-9

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