First Report of Neofusicoccum ribis causing postharvest decay of apple fruit from cold storage in Pennsylvania

Authors: Jurick, Wayne; VICO, IVANA - University Of Belgrade; Gaskins, Verneta; Janisiewicz, Wojciech; Peter, Kari

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2013
Publication Date: 3/6/2013
Publication URL: http://handle.nal.usda.gov/10113/58992
Citation: Jurick II, W.M., Vico, I., Gaskins, V.L., Janisiewicz, W.J., Peter, K.A. 2013. First Report of Neofusicoccum ribis causing postharvest decay of apple fruit from cold storage in Pennsylvania. Plant Disease. 97(7):999.

Interpretive Summary: Neofusicoccum ribis is an aggressive fungal plant pathogen that is known to cause stem cankers on a variety of woody plant species. To date, this fungus has not been described on apple fruit causing decay during storage in Pennsylvania and may be an emerging problem for the apple industry. Therefore, the organism was studied in detail to aid in the rapid identification of the fungus, including coloration in culture, growth rate, and the effectiveness of three postharvest fungicides. It was determined that all three fungicides were effective below their labeled rates, and thus are capable of control. This research sheds new light on a previously unknown pathogen of apple fruit in the Pennsylvania area and will benefit multiple audiences. Findings from this research investigation will benefit scientists to develop rapid tools for identification and will also positively impact the apple fruit growing and packing industry by informing them of emerging pathogens and their effective management.

Technical Abstract: Neofusicoccum ribis (Slippers, Crous & M.J. Wingf.), previously known as Botryosphaeria ribis (Grossenb. & Duggar), is an aggressive fungal plant pathogen that is part of the N. ribis/N. parvum species complex that causes stem cankers on a variety of woody plant species. An isolate of N. ribis was obtained from decayed ‘Honeycrisp’ apple fruit from a commercial cold storage facility located in Pennsylvania in October of 2011. The decayed apple fruit sample had a brownish-colored lesion that was soft, dry and leathery on the surface while sporulation was not evident. Three ‘Golden Delicious’ apple fruits were used to conduct Koch’s postulates that were wound-inoculated with a 50 µl mycelial suspension, obtained from aseptically scraping a 7-day-old PDA (Potato Dextrose Agar) culture of the fungus, and was repeated using ‘Fuji apple fruit. The inoculated fruit developed lesions and water inoculated fruit were symptomless after 5 days at 20°C. N. ribis was reisolated from infected tissue and was morphologically identical to the original isolate. Genomic DNA was isolated, a portion of the ß-tubulin gene was amplified with the gene specific primers, the amplicon was sequenced, and analyzed using BLAST. The nucleotide sequence (GenBank Accession KC47853) had 99% identity with N. ribis SEGA8 isolate (GenBank Accession JN607146.1). The N. ribis isolate produced a grayish-white colored mycelium with abundant aerial hyphae on PDA and had an olive-colored reverse. Microscopic investigation revealed septate mycelia with right angle branching and conidiomata were not evident on PDA, V8, Oatmeal Agar (OMA) or Water Agar (WA). Growth on WA was sparse and transparent, and aerial mycelial growth was not produced. Growth rate analyses were conducted on PDA, V8, and OMA and were 10.1 (+/- 1.39), 20.4 (+/- 1.15) and 17.6 (+/-0.70) mm/day at 20°C and the experiment was repeated. The Minimum Inhibitory Concentrations (MIC) for the N. ribis isolate was >1ppm Mertect®, >1 ppm Scholar®, and 50 ppm Penbotec® as the experiment was repeated once. This is the first report of N. ribis causing postharvest decay on apple fruit obtained from a commercial storage facility in Pennsylvania.