Valdensia leaf spot, caused by Valdensia heterodoxa, is a serious disease of lowbush blueberry. The disease may develop rapidly, resulting in extensive defoliation of fields. The purpose of this study was to examine the effects of temperature and wetness duration on various components of the infection cycle to gain a better understanding of epidemic development that might lead to improved management practices. Lesions on leaves appeared 6 h after inoculation at 20°C and were larger on young 3-week-old leaves compared with 8-week-old leaves. Incidence of infection on 3-week-old leaves was lowest at 5°C, highest at 15 and 20°C, and failed to occur at 30°C. Defoliation began 48 h after inoculation at 20 and 25°C but was slower at higher and lower temperatures. Conidia production and release from colonized leaves began 48 h after inoculation at 15 and 19°C. Total conidia production was lowest at 7°C, highest at 15°C, and progressively declined at 19 and 23°C. Production of conidia lasted 2 to 3 days. Sclerotia formed mainly along the midveins and were similar in size at 5 to 15°C, largest at 20°C, and smallest at 25°C. Conidia formed directly on sclerotia that were overwintered outdoors and then incubated on moist filter paper. Conidia production began after 48 h at 10, 15, and 20°C. Total production was lowest at 5°C, highest at 20°C, failed to occur at 25°C, and ceased after 10 days at all temperatures. These data show that at optimal temperatures, relatively short wet periods are required for conidia production on overwintered sclerotia, infection of leaves, and subsequent conidia production on diseased leaves that may account for the sudden and rapid spread of disease in fields. The data will be useful for helping growers identify weather conditions favorable for disease development.

Septoria leaf spot and stem canker is an important disease of lowbush blueberry, but the causal pathogen has not been accurately identified. Based on sequence analysis of the internal transcribed spacer, translation elongation factor 1 alpha, RNA polymerase II second largest subunit, 28S nuclear ribosomal DNA gene, and β-tubulin genes, the pathogen aligns closely with the genus Sphaerulina. The phylogenetic analyses based on these loci demonstrate that while the pathogen is closely related to the species Sphaerulina amelanchier, it is sufficiently distinct to warrant a new species designation. No ascomata of the teleomorph were found; however, ascospores recovered from leaves fit, morphologically, with the genus Mycosphaerella. The morphological data also support a new species designation. Based on the host that this pathogen infects, we propose the name as Sphaerulina vaccinii and the disease as Sphaerulina leaf spot and stem canker. Under field conditions, it appears that initial inoculum originates from pycnidia on overwintered leaves and stem lesions (cankers) on fruiting stems. More than 90% of the initial inoculum was released during the flowering period from late May through June. Leaf spots began to appear in early June and disease severity increased in a linear manner over time. Secondary inoculum production from diseased foliage was minimal and not considered important epidemiologically. Defoliation resulting from disease began in early July and increased in a nonlinear manner thereafter. Manual defoliation of blueberry stems at various times prior to harvest showed the substantial extent to which premature defoliation by this disease can affect yield. Stem lesions were also shown to have an impact on yield, even though stems were not killed.

Leaf spot and stem canker caused by Sphaerulina vaccinii is associated with premature defoliation in lowbush blueberry resulting in reduced yields. In this study, we investigated the impact of free water, RH, temperature, light, and plant age on leaf infection under controlled conditions. On potato dextrose agar, germination of conidia was usually polar. Growth was minimal at 5 and 10°C, increased at 15 and 20°C, was maximal at 25°C and decreased at 30°C. Percentage of germinated conidia on inoculated blueberry leaves incubated in dark controlled-humidity chambers for 3 days (25°C) was 86.0, 90.5, 81.3, and 28.3 in free water, 100, 97.5 or 95% RH, respectively. Germination did not occur at 90 or 85% RH. Infection of inoculated plants, however, was not favored by free water, but rather by high RH (>95%) and a 14-h photoperiod (180 μmol/m2 per second). Infection failed in continuous darkness, continuous light, or continuous darkness followed by 4, 8, or 12 h of light. Light and scanning electron microscopy showed that hyphal penetration into stomata on abaxial leaf surfaces was strongly tropic. When germ tubes grew in close proximity to a stomate, a penetration hypha formed at ∼90° angles to the germ tube and took the closest path to the stomate. Stomatal penetration was usually direct, but occasionally appressorium-like hyphal swellings formed over stomatal openings. When inoculated plants were exposed to high RH (>95%) at various temperatures, infection occurred after 4 days at 10°C, after 3 days at 15°C and after 1 day at 20 and 25°C. Infection failed to occur at 30°C. Disease severity also increased with duration of the humid period. When leaves were examined microscopically, those that had been incubated for 6 days showed a substantially greater network of epiphytic growth with more stomatal penetrations compared with those incubated for 3 days. Infection was substantially reduced when the humid period was interrupted by alternating days of low RH (60%). Two-week-old leaves were 2.7 times more susceptible than 8-week-old leaves.

In the spring of 2018, necrotic and canker symptoms were observed on stems of young apple trees that were bench-grafted by growers on four rootstocks (EMLA 9, Supporter 4, M9-T337 and Pajam 2) in Annapolis Valley, Nova Scotia. The objective of this study was to isolate and identify the causal organism of the disease on apple rootstocks. The diseased tissue obtained from eight infected plants of the four rootstocks showing visible necrotic and canker symptoms was used for microorganism isolation on potato dextrose agar (PDA). More than 90% of the isolates on PDA yielded a similar type of fungal colony. Based on the colony and spore morphology and presence of both alpha and beta spores, Diaporthe was proposed as a major pathogen from the symptomatic tissue. Analysis of partial sequences of four unlinked loci DNA-lyase (APN2), histone-3 (HIS), translation elongation factor 1 alpha (TEF1-alpha) and the internal transcribed spacer (ITS) 5.8S region of rDNA of the representative fungal isolates from young apple trees confirmed its identity as D. eres (Phomopsis fukushii). The pathogenicity of the representative D. eres isolate was confirmed on 1-year-old young apple trees bench-grafted on four different rootstocks in greenhouse tests. Necrotic and sunken canker symptoms like those observed on the nursery-grown young apple trees appeared on stems of all inoculated plants. The necrotic and canker lesions were observed 3 days after inoculation; they spread both directions from the inoculation point and led to the death of the young plants after 4 weeks. To our knowledge, this is the first report of D. eres causing stem canker and death of young apple rootstock in Canada.

Buckwheat is a rapidly growing cover crop with the potential to improve soil quality and health. In this study, the impact of buckwheat plant material (BPM) as a soil amendment on seedling emergence and suppression of damping-off and root rot of radish (Rhizoctonia solani) and cucumber (Pythium ultimum) was investigated in pot assays. Fresh BPM grown in a greenhouse potting mix for 4 weeks was chopped in small 1-2 cm long pieces and incorporated into field soil containing 0-10% of R. solani or P. ultimum inoculum produced on sterilized rye seed. The infested soil was then incubated for 0-8 weeks prior to planting radish or cucumber seed. The effects of BPM on plant growth and disease development were determined 2 weeks after planting. There was no disease protection if radish and cucumber seeds were planted within 1-2 weeks after soil incorporation of BPM. Disease protection was evident when planting was delayed for 3 weeks after BPM amendment to soil. BPM soil amendment provided protection of radish plants from Rhizoctonia damping-off and protection of cucumber plants from Pythium damping-off and root rot. BPM amendments had no effect on promoting plant growth but slightly increased soil pH. In amended soil receiving 4% and 10% of BPM planted with radish or cucumber seeds 0, 3 and 8 weeks later, total populations of indigenous fungi were 0.66-2.01 log units higher and bacteria were 0.53-0.92 log units higher compared with the populations in the non-amended soils. Buckwheat soil amendment offers a potential option to improve plant and soil health.

Severe blight and necrotic symptoms were observed on a 3-year-old alfalfa crop cultivar Blue Jay' at Indian Head, Saskatchewan during the summer of 2017. Symptoms appeared on blossoms, leaves and stems, and most of the infected plants were severely defoliated. The objective of this study was to isolate and identify the causal agent of the disease. Isolations from diseased alfalfa plants showing visible blight and necrotic symptoms collected from the infected field were made on potato dextrose agar (PDA). Morphological observations of the developing fungal colonies on PDA showed the presence of dark grey to dark green mycelium and conidia borne in chains with vertical and transverse septa, indicating the presence of the fungus Alternaria alternata. Molecular analysis of the ITS-5.8S region of rDNA (541 bp) and the TEF-1 gene region (606 bp) of the fungal isolates from alfalfa confirmed their identity as A. alternata. The pathogenicity of representative isolates was confirmed on alfalfa Blue Jay' and Spredor 4' plants in growth chamber tests. Necrotic and blight symptoms like those observed in the field appeared on leaves and stems followed by defoliation. To our knowledge, this is the first report of A. alternata causing a foliar disease on alfalfa in Canada.

The bacterium Xanthomonas fragariae (Xf) causes the economically important angular leafspot disease to which a high level of resistance has not been found within the cultivated strawberry Fragaria xananassa. The 2002 introduction of resistance donors 'US 4808' and 'US 4809' by the Fruit Laboratory at the Beltsville Agricultural Research Centre, provided sources of resistance at the octoploid level derived from F. virginiana. Moving this resistance through three generations of back crossing to different recurrent F. xananassa parents along with screening progeny (12-week-old seedlings) for resistance with a spray inoculation method, followed by selection based on horticultural traits, has created improved resistant genotypes. Selection from mature plants of seedling populations that had not been screened for Xf resistance gave 50% resistant selections - much higher than expected. Therefore, an experiment was designed to determine if some plants develop resistance after 12 weeks of age. Seven controlled crosses were performed in the greenhouse including three resistant (R) x resistant, three resistant x susceptible (S), and one SxS. The SxS cross was included to provide susceptible seedlings, to ensure that the inoculation procedure was effective. Four replicates of seedling sets of 10 to 12 plants per cross were inoculated at 12 or 17 weeks and rated for disease 3 weeks later.The RxR seedlings inoculated at 12 weeks had a mean disease rating of 1.19 compared to 2.28 for seedlings inoculated at 17 weeks. The RxS seedlings inoculated at 12 weeks had a mean disease rating of 2.75 compared to 3.56 for seedlings inoculated at 17 weeks. When seedlings were classified as resistant or susceptible, data analysis showed no significant differences in percent resistant between the inoculation times. These results argue against our hypothesis that older plants show resistance not identified in young seedlings and validate our procedure of screening young seedlings grown to the four to five trifoliate leaf stage. Resistant to susceptible segregation ratios of approximately 3: 1 and 1: 1 were found in RxR and RxS progeny, respectively, indicating that resistance shows a measure of dominance over susceptibility.

The bacterium Xanthomonas fragariae causes the economically important angular leafspot disease to which a high level of resistance has not been found within the cultivated strawberry Fragaria × ananassa. The 2002 introduction of resistance donors ‘US 4808’ and ‘US 4809’ by the Fruit Laboratory at the Beltsville Agricultural Research Centre provided sources of resistance at the octoploid level derived from F. virginiana. Moving this resistance through three generations of back crossing to different recurrent F. × ananassa parents along with screening progeny for resistance with a spray inoculation method, followed by selection based on horticultural traits, has created improved resistant genotypes. Resistant × susceptible crosses have produced from zero to 21% resistant progeny with a mean of 4.8% for 25 crosses. The presence of undesirable traits, such as small and soft fruit, variegation, pistillate flowers, and susceptibility to powdery mildew, has slowed progress, but this linkage drag can be overcome by increasing screened population size and additional backcross generations. Two resistant × resistant crosses were made in 2009, yielding 32.2 and 32.7% resistant seedlings.

Preserving the structural arrangement of the components of a bacterial infection process within a plant for microscopy study is a technical challenge because of the different requirements of each component for optimal preservation and visualization. We used low temperature scanning electron microscopy (cryo-SEM), anhydrous fixation at ambient temperature and freeze-substitution for transmission electron microscopy to examine fractured and sectioned strawberry leaves infected with Xanthomonas fragariae. Cryo-SEM images of fractured samples showed the bacterial colonization of mesophyll air spaces in the leaf, limited by the vascular bundles and the orientation and packing of bacteria in extracellular polysaccharide. Transmission electron microscopy of samples fixed using osmium tetroxide dissolved in FC-72 solvent at ambient temperature showed that the entire plant/bacteria/extracellular polysaccharide system was preserved in situ, and showed plasmolysis of mesophyll cells and disruption of organelles. In freeze-substitution samples, osmium tetroxide in FC-72 solvent gave superior preservation of the extracellular polysaccharide as compared to a conventional cocktail. In addition, strands believed to be xanthan were preferentially contrasted to show their density and orientation around the bacterial cells. We conclude that anhydrous fixation using osmium tetroxide in FC-72 at ambient temperature gave the best preservation of the entire system, and freeze-substitution using this same fixative enhanced the visualization of strands in the biofilm.

The effect of the natural volatile hexanal was studied as an antifungal agent on the major postharvest fungal pathogens Botrytis cinerea, Monilinia fructicola, Sclerotinia sclerotiorum, Alternaria alternata, and Colletotrichum gloeosporioides. The antifungal effect of hexanal vapor was dependent on concentration and treatment duration, but sensitivity of the pathogens varied. All spores of B. cinerea and M. fructicola were killed after exposure to 900 microL/L for 12 h at 20 degrees C, and almost all were killed after a 24-h exposure to 450 microL/L. Only moderate numbers of spores were killed at a concentration of 200 microL/L. Mycelial growth of S. sclerotiorum on agar was completely inhibited after a 12-h exposure to 900 microL/L, but only slight inhibition occurred at 450 microL/L and none at 200 microL/L. Mycelium of A. alternata and C. gloeosporioides appeared more sensitive, with strong inhibition occurring after a 12-h exposure at 450 microL/L. Similar trends in spore viability and mycelial growth were observed at 7 degrees C. The antifungal effect of hexanal vapor was further tested on raspberry fruit naturally infected with B. cinerea and on peach fruit inoculated with spores of M. fructicola. Decay was markedly reduced in raspberry and almost completely controlled in peach after exposure to 900 microL/L hexanal vapor for 24 h. The potential of hexanal for postharvest decay control is discussed.

Volatile compounds contribute to carrot ( Daucus carota ) flavor. However, effects of postharvest treatments on these compounds are not defined. To characterize treatment effects, fresh carrots (cv. Sunrise) were treated with 0 or 1.0 μL/L 1-methylcyclopropene (1-MCP) at 10 °C for 16 h, then exposed to 0, 0.3, or 1.0 μL/L ozone (O 3 ) at 10 °C for 1, 2, or 4 days, and subsequently stored at 0 °C for up to 24 weeks. Twelve terpenes were identified in the headspace over whole carrots, including dimethylstyrene (22.5%), alpha-pinene (19.1%), caryophyllene (15.8%), beta-pinene (9.1%), p-cymene (8.3%), limonene (7.7%), gamma-terpinene (6.7%), myrcene (4.7%), gamma-terpinolene (4.5%) camphene (1.0%), alpha-phellandrene (0.52%), and sabinene (0.03%). Most terpenes responded similarly to treatments and storage. Immediately after treatment with 1.0 μL/L O 3 for 1, 2, or 4 days, total terpene concentrations were 45%, 85%, and 87% greater than concentrations in non-treated controls. Caryophyllene, beta-pinene, and sabinene did not increase in response to the O 3 treatment unlike the other terpenes. 1-MCP reduced terpene concentrations by an average of 18%. O 3 treatments also stimulated stress volatile production. Ethanol headspace concentrations were 8-, 21-, and 43-times greater than the nontreated controls immediately following treatments with 0.3 nL/L O 3 for 4 days or 1.0 μL/L O 3 for 2 or 4 days, respectively. However, after 8 weeks, no differences among treatments were observed. Hexanal production also was stimulated by all O 3 treatments, being 2- to 11-times greater than controls immediately following treatment. 1-MCP reduced O 3 -stimulated ethanol and hexanal production by 23% and 8%, respectively.

To investigate the effect of ozone and 1-MCP treatments on quality of carrot, fresh carrots were treated with or without 1.0 mul(.)L(-1) 1-methylcyclopropene (1-MCP) for 16 h before storage or after 12 weeks of storage at 0 degreesC, and then exposed to 0, 300, or 1,000 nl(.)L(-1) ozone at 10 degreesC for 0, 1, 2, or 4 days. The carrots were then stored at 0 degreesC for up to 24 weeks. Decay and mold incidence, electrolyte leakage, surface discoloration and 6-methyoxymellein (6-MM, also known as isocoumarin) content in the peel tissue of carrots were evaluated. While no decay of the roots was observed, the incidence of saprophytic mold on the crowns was reduced during the first 8 weeks of the study, following the 300 nl(.)L(-1) ozone treatments of 1, 2, or 4 days. A similar effect was found on the carrots treated after 12 weeks. The 1,000 nl(.)L(-1) ozone treatments for 2 or 4 days caused severe tissue injury resulting in the highest mold incidence of 65% after 24 weeks of storage. The 1,000 nl(.)L(-1) ozone also induced a greater rate of electrolyte leakage in the peel and caused surface discoloration. The discoloration index, using a scale of 0-2, was 1.55 compared with 0.3 for those treated with 300 nl(.)L(-1) ozone. 6-MM, which causes bitterness, was affected by the concentration of ozone and the treatment time. Treatments of 300 and 1,000 nl(.)L(-1) ozone for 4 days induced 6-MM production in carrot peels reaching concentrations as high as 167 and 365 mug(.)g(-1), respectively, and the accumulation of 6-MM increased during storage. Treatment with 1-MCP effectively reduced 6-MM accumulation induced by the ozone treatments. The concentration of 6-MM remained below 150 mug(.)g(-1) in carrots treated with 1-MCP and 1,000 nl(.)L(-1) ozone for 4 days.

IntroductionCorona discharge has been reported to reduce the decay andextend the storage life of fruits and vegetables. Potentialmechanisms by which the corona could affect produce qualityinclude the destruction of ethylene and volatiles, removal of airbornefungal spores, and the production of ozone, negative air ions(NAI) and other reactive species. Ozone and/or NAI have beenreported to inhibit or kill pathogenic microbes and reduce decay offresh produce (Tanimura 1997, 1998). This...