First report of brown rot on apple fruit caused by Monilinia fructicola in the United States

Authors: PETER, KARI - Pennsylvania State University; Gaskins, Verneta; LEHMAN, BRIAN - Pennsylvania State University; Jurick, Wayne

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2015
Publication Date: 2/17/2015
Publication URL: https://handle.nal.usda.gov/10113/5156700
Citation: Peter, K.A., Gaskins, V.L., Lehman, B., Jurick II, W.M. 2015. First report of brown rot on apple fruit caused by Monilinia fructicola in the United States. Plant Disease. 99(8):1178. DOI: 10.1094/PDIS-11-14-1099.

Interpretive Summary: Brown rot is a fungal disease that causes decay in the field and during long term cold storage which manifests in significant economic losses. It is an emerging problem for the apple growing, packing and processing industry which makes fruit unmarketable for consumption and processing. A single spore isolate was collected in 2013 from a commercial apple orchard in Pennsylvania and was characterized using standard and nucleic acid-based procedures in the laboratory. The results from this research identified several distinguishing factors that can be used by growers and extension agents to identify the disease and its causal agent. This fungal isolate can also be used by scientists to design rapid detection methods and to screen new compounds for effective disease control.

Technical Abstract: Brown rot, caused by Monilinia fructicola (G. Wint.) Honey, is the most devastating disease of stone fruits in North America resulting in significant economic losses. The fungus has been recently reported to cause pre and postharvest brown rot on apple fruit in Germany, Italy, and Serbia. However, M. fructicola has not been documented to date in the literature for the Mid Atlantic apple growing region of the United States. In September 2013, a ‘Jonamac’ apple with symptoms of brown rot was collected from a commercial apple orchard in Lancaster County, Pennsylvania. The decayed tissue was soft and the surface was covered with a light colored mycelium in concentric rings with tufts of abundant grayish-brown conidia. The infected sample was transported to the lab and a single spore isolate was propagated on Potato Dextrose Agar (PDA). The isolate was cultured on PDA at 25°C with natural light to assess morphological characteristics and was identified to species. The fungus produced a grayish-colored colony with uneven margins and had a dark brown to black colored reverse. Conidia production was sparse on PDA and were formed in branched and unbranched monilioid chains. Lemon shaped conidia were one celled, hyaline and on average 15 x 10 µm (n = 50) which is consistent for M. fructicola (1). Growth rate was analyzed using ½ strength PDA, Richards defined, and V8 agar in triplicate Petri plates and was 3.1 mm/d (+/- 0.30), 3.0 mm/d (+/- 0.17), and 6.4 mm/d (+/- 0.03), respectively which was repeated. Species level identification was verified by obtaining mycelial genomic DNA, amplifying the Internal Transcribed Spacer (ITS) rDNA with ITS4/ITS5 primers via conventional PCR, and sequencing the amplicon directly. MegaBLAST analysis of the 2X consensus amplicon sequence has the highest similarity (100% identical, 0.0 E value) with M. fructicola isolate DL172.04 (Genbank accession # DQ314728.1) and was 99% identical to M. fructicola isolates from Indiana (KJ541032.1), Serbia (JN176564.1) and Chile (JN001480.1). Pathogenicity was verified using 20 ‘Golden Delicious’ apples that were surface sanitized with soap and water, sprayed with 70% ethanol, and wiped dry which was repeated. Fruit were wounded with the head of a sterile finishing nail to a 3 mm depth at the equator and inoculated with water or 25 µl of a 1 x 104 conidial suspension of the fungus. Fruit were placed on cardboard trays in 80-count boxes with plastic liners, and stored at 25°C for 5 days. Water-inoculated and uninoculated control fruit were symptomless, while pathogen inoculated fruit had 100% decay incidence with mean lesion diameters of 36.1 mm (+/-0.39). Inoculated apples had soft, round lesions with even margins and light brown mycelium near the inoculation site. The fungus was reisolated from inoculated, decayed fruit and identified as M. fructicola, thus completing Koch’s postulates. This is the first report of M. fructicola causing brown rot on apple fruit in the United States mid Atlantic apple growing region which may indicate the need for additional management tools to ensure adequate control to prevent local and long distance spread of this pathogen.