Prebreeding for Future Challenges in Nordic Apples;

1. Prebreeding for Future Challenges in Nordic Apples; Susceptibility to Fruit Tree Canker and Storage Diseases Nybom H1, Røen D2, Karhu S3, Garkava-Gustavsson L4, Tahir I4, Haikonen T3, Røen K2, Ahmadi-Afzadi M1,4, Ghasemkhani M1,4, Hjeltnes SH2 1Swedish University of Agricultural Sciences – Balsgård, Kristianstad, Sweden, 2Graminor AS,Leikanger, Norway 3MTT Agrifood Research Finland, Piikkiö, Finland 4Swedish University of Agricultural Sciences, Alnarp, Sweden

2. Apples are very popular in the Nordic countries, but production costs are high, access to pre-harvest chemicals is restricted and post-harvest application is banned BUT the market for locally produced, organic fruit is growing. Consequently, climate adaptation and disease resistance/tolerance are major issues for the apple breeding programs in Norway, Sweden and Finland. A Public Private Partnership was initiated in 2012 to evaluate susceptibility against some of the most devastating apple diseases in the Nordic countries, in local and international cultivars of interest for breeding. The targeted diseases are caused by different fungi; fruit tree canker (Neonectria ditissima) and storage rots (Neofabraea spp., Colletotrichum acutatum and Penicillium expansum).

3. Fruit tree canker In Sweden, two sets of 30–40, partially overlapping cultivars were tested at Balsgård and Alnarp, respectively, during two years, while another set of 30 cultivars was analysed in Norway during two years. A set of 8 shared control cultivars were analysed in all experiments. Complete resistance to fruit tree canker is not known in apple. Instead, apple cultivars display a continuous variation for partial resistance to the disease. We evaluated damage caused by conidia inoculation of manually inflicted ‘leaf scars’ on cut shoots, in water bottles in a greenhouse. Resulting lesions were measured every 5 days during 6–8 weeks, and the data used for comparisons of infection severity. Conidiospores of Neonectria ditissima Lesions caused by inoculation 6 shoots with 1–3 inoculation points each, are scored per cultivar

4. Fruit tree canker Significant differences between cultivars were found. Data for the two years were correlated, as also data for those cultivars that were evaluated at more than one site. Least susceptible cultivar so far encountered in our experiments is the ornamental Prairifire with a pedigree including M. atrosanguinea, M. zumi calocarpa and M. niedzwetskyana. At SLU (Balsgård and Alnarp) high level of tolerance was noted also for Aroma, Frösåker, Golden Delicious, Liberty, Maigold, Pirja and Santana. In addition, SSR- and AFLP-based evaluation of diversity among single-spore isolates of Neonectria ditissima has been initiated at SLU, as well as a transcriptomics study. See also presentations on: Approaches to evaluation of resistance to European canker (Neonectria ditissima) in apple by Garkava-Gustavsson L. & co-authors and Development of a qPCR detection procedure to quantify fruit tree canker caused by Neonectria ditissima in apple trees by Ghasemkhani M. & co-authors Results for trial at Njøs in Norway 2013; Elise and William’s Prideare significantly more susceptible than the remainder.

5. Storage rots In the Nordic countries, infections by fungal diseases is the main cause of decay during apple storage. Regulations for use of fungicides are very strict! Storage rots are especially serious in organic orchards, causing losses of 20% or more. Data are now available from two years of inoculating freshly harvested fruit with Penicillium expansum (blue mould), and evaluating the damage after 6 or 12 weeks of cold storage. Lesion diameter = decay severity varied significantly among cultivars. 80 cultivars have been screened, including 10 shared control cultivars. Fu Shuai showing no symptoms of infection High tolerance was noted in Fu Shuai, Sampion, Gloster, Gala Must, Pilot and Retina at Njøs, and in Servernij Sinap, Pepin Schafranovij, Kolinowskaya, Arona, Ausma and Olga at Balsgård. Zonga showing average symptoms of infection Negative correlations were found between decay severity and date of harvest as well as between decay severity and fruit firmness at harvest. A positive correlation was found between decay severity and firmness decline (softening) during storage. Content of soluble solids had little influence on the decay.

6. Storage rots Spontaneous storage rots were evaluated in 2013 for 26 local cultivars in Finland, based on symptoms and spore morphology. The majority of storage rots were associated with Neofabraea spp., with large difference in susceptibility between the cultivars. Inoculations will be carried out in 2014. Inoculations have been made also with Neofabraea (bull’s eye rot) and Colletotrichum acutatum (bitter rot). Some of the inoculated fruit was sprayed 5–6 hours later with solutions containing alkylresorcinols extracted from rye bran. This compound decreased disease symptoms substantially, and is now tested in an orchard trial. At the end of 2014, we will have Penicillium and SNP data (conducted within FruitBreedomics) for at least 200 apple cultivars. This will be used for a genome-wide association study. See also the presentation on: Genetics of resistance to fungal storage disease in apple; inoculation-based screening, transcriptomics and biochemistry by Ahmadi-Afzadi M. & co-authors Proportions of identified storage rot pathogens in the Finnish set of organically grown local cultivars. Fruit of Aroma inoculated with Neofabraea, and 12 weeks of cold storage. Control: unsprayed fruit, 11: fruit sprayed with AR11, 1: fruit sprayed with AR1.

7. Literature Ahmadi-Afzadi M., Tahir I., Nybom H. 2013. Impact of harvesting time and fruit firmness on the tolerance to fungal storage diseases in an apple germplasm collection. Postharvest Biol. Technol. 82: 51–58 Dey E.S., Ahmadi-Afzadi M., Nybom H., Tahir I. 2013. Alkylresorcinols isolated from rye bran by supercritical fluid of carbon dioxide and suspended in a food-grade emulsion show activity against Penicillium expansum on apples. Arch. Phytopathol. Plant Protect. 46: 105–119 Garkava-Gustavsson L., Zborowska A., Sehic J., Rur M., Nybom H., Englund J.-E., Lateur M., van de Weg E., Holefors A. 2013. Screening of apple cultivars for resistance to European canker, Neonectria ditissima. Acta Horticult. 976: 529–536 Ghasemkhani M., Sehic J., Ahmadi-Afzadi M., Nybom H. and Garkava-Gustavsson L. Screening for partial resistance to fruit tree canker in apple cultivars. Acta Horticult., in press. Tahir I., Ahmadi-Afzadi M., Nybom H., Dey E.S. Rye bran alkylresorcinols inhibit growth of Penicillium expansum and Neofabraea perennans in vitro and in vivo on different apple cultivars. Eur. J. Hortic. Sci., in press. Tahir I., Nybom H., Ahmadi-Afzadi M., Røen K., Sehic J., Røen D. Susceptibility to blue mould caused by Penicillium expansum in apple cultivars adapted to a cool climate. Manuscript submitted. Acknowledgements Financial and administrative support was received from the Nordic Council of Ministers and NordGen