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The frequency of strains of Monilinia fructicola that are resistant to the demethylation inhibiting fungicide tebuconazole in Brazil was determined by three methods. The first involved testing 295 isolates for relative growth under a discriminatory dose of 0.3 µg mL−1. The second and the third methods involved testing 120 isolates for the effective concentration for 50% population inhibition (EC50); one method employed the discriminatory dose of 0.3 µg mL−1 and the other method utilized the baseline dose of 0.046 µg mL−1 to separate the strains based on sensitivity. The frequencies of resistance among the isolates based on the three methods were determined by measuring mycelial growth in fungicide-amended media. The shifts in M. fructicola sensitivities were determined by comparing the EC50 density distributions of the baseline (2000–2004, n=31), intermediate (2005–2008, n=88), and current (2009–2011, n=120) isolate populations. The frequency of resistance to tebuconazole varied according to the a...

This study assessed the efficacy of phosphites, Trichothecium roseum (TR) and a combination of phosphites and TR compared with lime sulphur (LS) to control brown rot, caused by Monilinia fructicola, in an organic orchard with high inoculum pressure under subtropical conditions in Brazil. The treatments were applied from blossom to harvest on two peach cultivars (‘Granada’ and ‘Chimarrita’) during 2005 and 2006. Disease incidence was assessed from full bloom to post-harvest. Two other experiments were performed under post-harvest conditions using mature fruit harvested from organic and conventional orchards and inoculated with 106 conidia mL−1 of TR followed by M. fructicola. The incidence of blossom blight ranged from 25% to 64% on flowers collected from untreated controls, whereas all treatments reduced blight over both cultivars and years. For ‘Chimarrita’, disease incidence reached 8% in mature fruit on the tree and 43% on fruit post-harvest. In both years, TR treatment reduced fruit infection ...

Monilinia fructicola, the causal agent of brown rot, was recovered from decayed stone fruits (peach, plum and nectarine) in 11 West Virginia orchards. There was significant variation among these isolates with respect to colony morphology, growth rate, sporulation level, sensitivity to fenbuconazole, vegetative compatibility and virulence. Species identification was confirmed using ITS sequences from the nuclear ribosomal RNA gene. The cultural phenotypes on potato dextrose agar (PDA) ranged from white to dark, melanized colonies. The growth rate of the isolates on PDA ranged from 0.3 to 3.2 mm day−1 at 4 °C, from 2.9 to 7.6 mm day−1 at 10 °C, and from 4.8 to 19 mm day−1 at 24 °C. There was a statistically significant relationship between the growth of the isolates on PDA and their aggressiveness on nectarines at 24 °C, especially at higher inoculum concentrations. Sporulation of 3-day-old cultures on peach agar at 24 °C varied from profuse to no sporulation, with some isolates sporulating only sp...

Rhizopus rot caused by Rhizopus stolonifer is a potentially serious postharvest disease of Canadian-grown peaches. Several new fungicides are effective against brown rot (Monilinia fructicola) of peaches, but little is known of their postharvest efficacies against R. stolonifer. Harvested peaches were arranged in trays, individually punctured once and co-treated with a suspension of both R. stolonifer sporangiospores and cells of an isolate of Pseudomonas syringae or one of 13 fungicides at 0.5–1.0 times the dilute concentration used to control brown rot in orchard programs. In subsequent experiments, the peaches were inoculated with R. stolonifer, incubated for 6 h, chilled, and a day later the inoculated sites were brushed with a suspension of fludioxonil, tebuconazole, or P. syringae. In the co-treatment studies, azoxystrobin, fenhexamid, fenbuconazole, myclobutanil, benomyl, and sulfur reduced rhizopus rot by 0–22%. Cyprodinil and propiconazole gave 20–60% reduction, while fludioxonil, tebuconazole, a...

Commercially ripe peaches were wounded and co-inoculated with phylloplane isolates of Pseudomonas syringae (MA-4 and NSA-6), Pseudomonas fluorescens (BAP-3), or an isolate of Candida sp. (NSD-4) in combination with either conidia of Monilinia fructicola (cause of brown rot) or sporangiospores of Rhizopus stolonifer (cause of rhizopus rot). Isolates NSA-6 and MA-4 at a concentration of 1 x 107 CFU/mL reduced brown rot to 28% and 73%, respectively, from 98% in the inoculated check after 5 days incubation at 22°C. Both isolates reduced rhizopus rot to 5% and 8% from 53% in the inoculated check after 5 days incubation. The P. syringae isolates when used in 2-min soak treatments were less effective against natural, preharvest M. fructicola infections of late-harvested peaches. Isolates MA-4 and NSA-6 suppressed brown rot from 63% to 30% and from 95% to 71-81%, respectively, after 3 and 4 days incubation at 22°C. The use of 0.5% CaCl2 in the soak suspension significantly improved the activity of P. syringae but...

Polymerase chain reaction (PCR)-mediated analysis of rDNA from isolates of Monilinia fructicola and Monilinia laxa from Michigan cheny orchards revealed interspecies restriction site variation in the internal transcribed spacer 1 (ITSI) region and length variation in the small subunit (SSU) rRNA gene. 1TS1 sequences from both species were 146 by long; however, the ITSI of M. laxa differed at three positions from the ITSI of M. fructicola. Although the sequences of the ITS1 regions from both species were nearly identical, the enzyme tilrel cuts the PCR-amplified ITSI region of the two species differentially. PCR amplification of the 3′ end of the SSU rRNA gene yielded products of approximately 940 and 520 by from M. fructicola and M. laxa, respectively. A 421-bp group I intron was detected by PCR within the SSU rDNA of 32 isolates of M. fructicola but not in the eight isolates of M. laxa. Intron sequences from each of four isolates of M. fructicola were identical, and the SSU rDNA flanking sequenc...

European plums (Prunus domestica “Stanley”) with a high incidence of symptomless latent infections of Monilinia fructicola, were harvested soft-ripe or firm-ripe, surface disinfested in NaOCl, soaked for 4 min in fungicide suspensions at 20°C and incubated for 7-11 days at >95% RH at 20°C. Using soft-ripe fruits, all 12 fungicides reduced brown rot relative to the water check after 7 days incubation, with tebuconazole and flusilazole being numerically superior. Using firm-ripe fruits, five sterol-inhibiting fungicides and iprodione reduced brown rot infections after 7 days incubation, with tebuconazole, flusilazole and myclobutanil being numerically superior. Fruits were soaked for 4 min in suspensions of tebuconazole and flusilazole at 33, 67, and 100 mg a.i./L, and incubated for 7-8 days. Treatments were moderately effective with no rate response except for soft-ripe plums soaked in flusilazole. Five sterol-inhibiting fungicides were applied twice at mid-season to Stanley trees having fruits with a high...