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New Zealand Plant Protection 63 (2010): 280

Pathogenicity of field and laboratory-grown inoculum of Neonectria galligena on potted apple trees

R.W.A. Scheper, B.M. Fisher and P.N. Wood


European canker, caused by Neonectria galligena, is an important disease of apple trees worldwide. In this study, methods were developed for conidium production in culture and for testing the pathogenicity of N. galligena. Conidia produced in culture were one- or two-celled, while conidia collected from cankers were multi-celled. Isolate ICMP9472 produced enough conidia in culture to produce inoculum (210 5 conidia/ml) to test the pathogenicity in comparison with that of conidia harvested from apple cankers from Motueka (field inoculum) and a two-day-old suspension of conidia from Motueka apple cankers, on potted 'Royal Gala' trees in a glasshouse under continual misting. The germination rates of the three inocula were similar (50-79%). Two months after inoculation, all inoculated wounds were infected, regardless of inoculum source. However, cankers caused by field inoculum (fresh and two- day-old) were significantly larger (average 10.8 mm and 10.6 mm, respectively) than those caused by isolate ICMP9472 (5.1 mm). Six months after inoculation, cankers caused by fresh field inoculum were significantly larger than those caused by 2-day-old inoculum, which were significantly larger than those caused by isolate ICMP9472. In addition, cankers caused by fresh field inoculum were significantly more active than those caused by older field inoculum or isolate ICMP9472.

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