European apple canker: morphophysiological variability and pathogenicity in isolates of Neonectria ditissima in southern Brazil

Abstract

ABSTRACT: European apple canker (EC) is caused by Neonectria ditissima, a pathogen officially registered as a quarantine pest in 2012. Thirty-five isolates of N. ditissima of different geographical regions of southern Brazil from apple branches showing symptoms of EC were identified by the specific pair primers Ch1 and Ch2 and analyzed concerning the virulence on Gala apple cultivar and morphophysiological characteristics. The disease symptoms were characterized and the isolates compared based on average mycelium growth (AMG), mycelium growth index (MGI), colony color, conidia type, dimensions and growth on potato dextrose agar (PDA), malt agar (AM), and synthetic SNAY (SN) culture media. Nineteen isolates showed the greatest AMG on PDA, forming three growth groups of 35.56 (GI), 52.71 (GII), and 62.67mm (GIII). Seven isolates showed MGI greater than 4.0mm diameter on PDA compared with that on AM and SN. The highest conidia production was on SN, and the predominant colony color in all media was white to beige with central pigmentation of brown and borders colored in shades of beige. There were significant differences among the average dimensions of micro- and macroconidia on PDA, AM, and SN. The pathogenicity was confirmed for all isolates despite of different morphophysiological characteristics. There was no correlation among isolates morphophysiological variability, virulence, and geographical origin.