Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/25/2013
Publication Date: 8/6/2013
Citation: Janisiewicz, W.J., Conway, W.S., Biggs, A.R., Jurick Ii, W.M., Vico, I. 2013. Biological characterization of Monilinia fructicola isolates from stone fruits in eastern West Virginia. Canadian Journal of Plant Pathology. 35(3):315-327. Interpretive Summary: Despite its economic importance, relatively little is known about fungus, Monilinia fructicola, that causes brown rot of stone fruits in the mid-Atlantic growing region. No other species of this fungus has been reported, but no studies to substantiate this have been conducted. We isolated brown rot causing fungi from decayed fruit collected from peach, nectarine and plum trees in 11 orchards in the eastern West Virginia fruit growing region. These fungi were characterized for their colony appearance on growth media, growth under various temperatures, production of spores that fungus uses to infect other fruit, and susceptibility to a fungicide that has been commonly used in these orchards. We found great diversity with respect to all of these characteristics. Interestingly, some isolates of the fungus were highly resistant to the fungicide, which makes orchard application with this fungicide much less effective. Analysis of DNA isolated from these fungi confirmed that all of them belong to M. fructicola species. This is important because, recently, other species of this fungus were isolated in New York, which may restrict export of stone fruit from this state to countries free of this fungus. Results of this investigation will be used in the selection of the most appropriate isolates for evaluation of the effectiveness of various biological and chemical treatments in controlling brown rot under field and storage conditions.
Technical Abstract: Thirty eight isolates of Monilinia fructicola were isolated from decayed stone fruits (peach, plum, and nectarine) collected from trees growing in eleven eastern West Virginia orchards. The isolates were characterized for colony appearance growth rate under different temperatures, sporulation, and resistance to fenbuconazole, the most commonly used preharvest fungicide in the region. There were five distinct culture phenotypes, ranging from albino to dark, melanized cultures. On PDA, the growth rate per day of the isolates differed greatly at all temperatures tested and ranged from 0.4 to 3.2 mm at 4 deg C, from 2.9 to 7.6 mm at 10 deg C, and from 6.5-15.5 at 24 deg C. Sporulation on peach agar at 24 deg C varied from profuse to no sporulation on three-day-old cultures, with some sporulating only sparsely even on 10-day-old cultures. In spiral dilution tests, the EC50 for fenbuconazole ranged, from 0.003ug/uL to 0.129ug/uL, indicating the possible development of resistance to the fungicide in some orchards. The identity of the isolates at the species level was confirmed using sequences from the ITS region of the nuclear ribosomal RNA gene. Analysis of the Vegetative Compatibility Groups (VCG) of the isolates from individual orchards revealed only a few VCG groups. This, together with the absence of apothecia in orchards heavily infested with M. fructicola, suggests a low prevalence of the sexual stage in eastern West Virginia.