Location: Food Quality LaboratoryTitle: First report of Botryosphearia dothidea causing white rot on apple fruit in Maryland Author
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2013
Publication Date: 2/13/2013
Publication URL: http://handle.nal.usda.gov/10113/56562
Citation: Jurick II, W.M., Vico, I., Gaskins, V.L., Janisiewicz, W.J., Peter, K.A. 2013. First report of Botryosphearia dothidea causing white rot on apple fruit in Maryland. Plant Disease. DOI: 10.1094/PDIS-01-13-0053-PDN. Interpretive Summary: Botryosphaeria dothidea is a fungus that infects woody plants causing decay on grapevine, apple, pear, and almond trees and also causes decay on apple fruit in the field and during storage. To date, this fungus has not been described on apple fruit causing decay during storage in Maryland 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 growth characteristics in culture and the effectiveness of 3 postharvest fungicides. It was determined that all 3 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 Maryland 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: Botryosphaeria dothidea [Fr. : Moug.] Ces. & De Not. infects over 80 genera of woody plants causing stem cankers on grapevine, apple, pear, and almond trees and also causes white rot on apple fruit in the field and during storage. A B. dothidea isolate was obtained from decayed ‘Fuji’ apple fruit exhibiting white rot symptoms from a local farm market in Beltsville, Maryland in May 2010. The fruit had characteristic large dark brown lesions with irregular margins. Decay expanded unevenly towards the core and the tissue was soft. Koch's postulates were conducted using three ‘Golden Delicious’ apple fruit that were wound-inoculated with a mycelial suspension of the fungus, obtained from aseptically scraping a 7-day-old PDA (Potato Dextrose Agar) culture, and was also repeated using ‘Fuji’ apple fruit. Large, brown, slightly sunken, soft lesions with undefined edges developed 5 days after inoculation at 20°C and water-only inoculated fruit were symptomless. The fungus was reisolated from infected tissue and was morphologically identical to the original isolate from decayed apple fruit. Genomic DNA was isolated from the fungus and amplified with gene specific primers for the ribosomal DNA internal transcribed spacer region ITSI-5.8S-ITS2. Both forward and reverse strands of the 542 bp amplicon were sequenced and assembled into a contig. The nucleotide sequence (GenBank Accession KC473852) indicated 99% identity to B. dothidea isolate CMM3938 (GenBank Accession JX513645.1). The B. dothidea isolate produced, black-colored aerial mycelium with a white margin on PDA and had a black reverse. Conidiomata were evident after 10-14 days at 20°C only on Oatmeal Agar (OMA). Conidia were hyaline, smooth and straight, fusiform with an subobtuse apex and a truncate base (20 -) 24.33 (-26) X (4 -)5 (- 7) µm (n=50). The Minimum Inhibitory Concentration (MIC) for the isolate was >1 ppm for Mertect® and Scholar® and 50 ppm for Penbotec® which are well below the labeled rates for these postharvest fungicides and the experiment was repeated one time. This is the first report of B. dothidea causing white rot on apple fruit in Maryland.