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

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.

Viability and release of Neonectria ditissima ascospores on apple fruit in Brazil

“…The characteristics of N . ditissima spores detected in mummified fruit were consistent with those reported in the literature (Campos et al, 2017; Chaverri et al, 2011; Dillon Weston, 1927; Ogawa & English, 1991; Weber, 2014). The identification of N .…”

“…The characteristics of N. ditissima spores detected in mummified fruit were consistent with those reported in the literature (Campos et al, 2017;Chaverri et al, 2011;Dillon Weston, 1927;Ogawa & English, 1991;Weber, 2014). The identification of N. ditissima was also confirmed using quantitative PCR amplification of DNA extracted from the tissue of apple plants with symptoms inoculated with a fungal isolate from mummified fruit.…”

“…ditissima isolates ( n = 35) tested were pathogenic to 3‐year‐old Gala apple plants maintained in a greenhouse. Young cankers produced small sporodochial fruiting bodies at 14 dai (Campos et al, 2017). Inoculation with N .…”

“…Incubation and latent periods in apple plants and fruit inoculated with N . ditissima isolates have also been investigated in Brazil (Alves & Nunes, 2017; Campos et al, 2017; Gelain et al, 2020). Within 8–12 dai with mycelium plugs (5 mm diameter), all N .…”

“…In November of the same year, canker lesions were evident, but the growth of the fungus was not detected in the branch (Dillon Weston, 1927). Incubation and latent periods in apple plants and fruit inoculated with N. ditissima isolates have also been investigated in Brazil (Alves & Nunes, 2017;Campos et al, 2017;Gelain et al, 2020). Within 8-12 dai with mycelium plugs (5 mm diameter), all N. ditissima isolates (n = 35) tested were pathogenic to 3-year-old Gala apple plants maintained in a greenhouse.…”