Screening of apple cultivars for resistance to European canker, Neonectria ditissima

• Published in: Acta horticulturae no. 976; pp. 529 - 536
• Main Authors: Garkava-Gustavsson, L, Zborowska, A, Sehic, J, Rur, M, Nybom, H, Englund, J.E, Lateur, M, Weg, E. van de, Holefors, A
• Format: Journal Article
• Language: English
• Published: International Society for Horticultural Science 01.01.2013
• Subjects: apples; conidia; crop production; cultivars; fungi; fungicides; greenhouses; horticulture; inoculation methods; labor; microbial biomass; orchards; phenotype; plant breeding; screening; shoots; trees
• ISSN: 0567-7572
• DOI: 10.17660/ActaHortic.2013.976.75

European canker, caused by the fungus Neonectria ditissima, is a severe problem in apple production both in Sweden and in many other northern European countries. Even when applying fungicides and good horticultural practices, canker damage occurs almost yearly in nurseries and orchards. Some years, devastating outbreaks destroy numerous trees. To date, complete resistance to N. ditissima is not known in apple. For further research and plant breeding, heritable variation in quantitative resistance should be investigated by phenotyping large sets of cultivars. In the present project, 55 apple cultivars were screened for resistance to N. ditissima. One-year-old shoots from mature trees were inoculated in the greenhouse with a standardized volume and concentration of conidia suspension using different inoculation methods. Two-year-old trees of five cultivars were inoculated in the field. Length of the occurring cankers was measured at regular intervals throughout a period of up to three months. The investigated cultivars showed considerable differences in colonization rate. In cultivars known to be highly resistant, i.e., 'Santana', lesions progressed much slower compared to susceptible cultivars like 'Cox's Orange Pippin' and 'James Grieve'. Since the inoculation-based phenotyping is demanding in labour and time (duration), especially when the test is performed on grafted trees, qPCR-based assessment of fungal biomass at early stages of infection was explored as an alternative or complementary approach for phenotyping.