Phacidiopycnis Washingtonensis Research Articles

Infection conditions for Neofabraea perennans and Phacidiopycnis washingtonensis on developing apple fruit in the orchard

Infection conditions for Neofabraea perennans and Phacidiopycnis washingtonensis on developing apple fruit in the orchard

Genetic and Pathogenic Characterization of Phacidiopycnis washingtonensis from Apple and Pacific Madrone from the Western United States.

Phacidiopycnis washingtonensis is the cause of speck rot of apple and leaf blight of Pacific madrone in Washington State. In total, 314 isolates were collected from apple production areas in eastern Washington and Pacific madrone in western Washington. Using eight microsatellite markers designed in this study, 58 unique multilocus haplotypes were identified. Only one of the haplotypes was shared between the apple and Pacific madrone populations. Analysis of molecular variance showed no genetic differentiation between the apple and Pacific madrone populations. Genetic variation was present within each subpopulation of apple from different geographic locations. The apple population possessed higher genotypic diversity than the Pacific madrone population, suggesting that isolates from apple may represent an older population and could have been introduced into the native habitat of Pacific madrone. P. washingtonensis likely reproduces asexually because populations examined in this study were not in linkage equilibrium. In pathogenicity tests, representative isolates from apple and Pacific madrone all incited leaf blight on Pacific madrone and speck rot on apple fruit regardless of their host of origin. Overall, our findings indicate that the P. washingtonensis population in Washington State is largely asexual, with high genotypic flow and that apple, crabapple, and Pacific madrone could serve as sources of P. washingtonensis inoculum for these hosts.

Identification and characterization of Diplodia mutila, D. seriata, Phacidiopycnis washingtonensis and Phacidium lacerum obtained from apple (Malus x domestica) fruit rot in Maule Region, Chile

Two members of the family Botryosphaeriaceae (Diplodia mutila and D. seriata), one member of the family Bulgariaceae (Phacidiopycnis washingtonensis) and one member of the family Phacidiaceae (Phacidium lacerum) have been described as fungal plant pathogens causing apple rot during preharvest and/or postharvest. During a survey of apple rot in the commercial orchard cvs. Cripps Pink, Fuji and Gala that was conducted in the 2014–2015 and 2015–2016 seasons in the Maule Region, Chile, 820 isolates were obtained from 880 apple rot samples. Phylogenetic analyses of the internal transcribed spacer (ITS) region, portion of the β-tubulin gene (BT), large ribosomal subunit (LSU) region and small ribosomal subunit (SSU) region identified Diplodia mutila, D. seriata, Phacidiopycnis washingtonensis and Phacidium lacerum. Morphological features of isolates of D. mutila, D. seriata, Pha. washingtonensis and P. lacerum were similar to those described in the literature for the respective species. The isolates of D. mutila, D. seriata, Pha. washingtonensis and P. lacerum were sensitive to fludioxonil, pyrimethanil, tebuconazole and thiabendazole fungicides. The significant largest lesion on apple fruits cv. Cripps Pink were developed, when the fruits were inoculated from 15 days before harvest with Pha. washingtonensis while for D. mutila, D. seriata, P. lacerum was the same day of harvest. The fungal species Pha. washingtonensis and P. lacerum were the most important in developing apple rot (lesions) during cold storage. The specie D. seriata was the most predominant fungus obtained from apple fruit rot in the Maule Region, Chile. This study gives a better insight to the fungal species causing apple fruit rot in the Maule Region, Chile.

Pruning of Manchurian Crabapple for Management of Speck Rot and Sphaeropsis Rot in Apple

Phacidiopycnis washingtonensis and Sphaeropsis pyriputrescens are fungal pathogens that cause postharvest speck rot and Sphaeropsis rot, respectively, in apple. Under quarantine regulations established by the Chinese government, export of apple from Washington State to China was banned between 2012 and 2014 because of detection of these pathogens in apple shipments. Previous studies established that pycnidia of P. washingtonensis and S. pyriputrescens survive in twig cankers on manchurian crabapple which serves as a dominant pollinizer in the Washington State apple industry. These pycnidia serve as a primary source of inoculum for infection of apple fruit in the orchard. The objective of this research was to conduct a study at multiple locations in Washington State to determine the efficacy of implementing manchurian crabapple pruning as a method to control speck rot and Sphaeropsis rot in storage. Four commercial orchards at geographically distant locations in Washington State were selected in 2014 and three in 2015. In 2014, two treatments included preharvest pruning of manchurian crabapple and postharvest application of pyrimethanil and untreated control. In 2015, preharvest pruning alone (PO) of manchurian crabapple was included in addition to the two treatments examined in 2014. Pruning conducted in concert with postharvest fungicide treatment significantly reduced the incidence of speck rot and Sphaeropsis rot in storage during the initial experimental field season. During year 2, both the PO and pruning with postharvest fungicide application controlled fruit rot with no significant difference between the two treatments. Findings from this study will be instrumental for the control of these postharvest diseases and maintenance of international market access for fruit from the Pacific Northwest.

Sensitivity of Phacidiopycnis spp. Isolates from Pome Fruit to Six Pre- and Postharvest Fungicides.

Phacidiopycnis washingtonensis and P. pyri cause speck rot and Phacidiopycnis rot on apple and pear, respectively. Infection occurs in the orchard and remains latent, and symptoms appear after months of storage. Decay management relies on orchard sanitation and pre- and postharvest fungicides. In a 2017 survey, speck rot accounted for 6.4% of apple decay in central Washington, whereas Phacidiopycnis rot accounted for 3.9 and 6.7% of total pear decay in Washington and Oregon, respectively. Sensitivities of baseline populations of 110 P. washingtonensis and 76 P. pyri isolates collected between 2003 and 2005 to preharvest fungicides pyraclostrobin (PYRA) and boscalid (BOSC) and to postharvest fungicides thiabendazole (TBZ), fludioxonil (FDL), pyrimethanil (PYRI), and difenoconazole (DFC) were evaluated using a mycelial growth inhibition assay. Mean effective concentrations necessary to inhibit 50% growth (EC50) of P. washingtonensis were 0.1, 0.3, 0.8, 1.8, 2.1, and 4.8 µg/ml for FDL, PYRI, TBZ, DFC, PYRA, and BOSC, respectively. Respective mean EC50 values for P. pyri were 0.2, 0.6, 1.6, 1.1, 0.4, and 1.8 µg/ml. The sensitivity of exposed P. washingtonensis and P. pyri populations collected in 2017 revealed potential shifts toward BOSC and PYRA resistance. The efficacy of the six fungicides to control isolates of each pathogen with different in vitro sensitivity levels was evaluated on apple and pear fruit. FDL, DFC, and PYRI controlled both Phacidiopycnis spp. regardless of their EC50 values after 5 months of storage at 0°C in a regular atmosphere. The consistent occurrence of Phacidiopycnis spp. will require continuous monitoring and development of disease management strategies based on fungicide phenotypes and efficacy of existing fungicides assessed herein.

Occurrence of Phacidiopycnis washingtonensis Causing Speck Rot on Stored Pink Lady Apple Fruit in Chile

Occurrence of <i>Phacidiopycnis washingtonensis</i> Causing Speck Rot on Stored Pink Lady Apple Fruit in Chile

First Report of a New Leaf Blight Caused by Phacidiopycnis washingtonensis on Pacific Madrone in Western Washington and Oregon.

In recent years, a leaf blight disease, consisting of browned, desiccated leaves occurring mainly in the lower parts of the canopy, has been observed during wet springs on Pacific madrone (Arbutus menziesii) in western Washington and Oregon. In May 2009 and 2011, severe outbreaks occurred and symptomatic leaves from madrones growing in the region were sampled to determine the causal agent. Two symptoms, leaf necrosis or blotching along the edges and tips of the leaves, and leaf spot, were observed. Small segments of diseased tissue were cut from the leaves, surface-disinfected, rinsed, and plated on malt extract agar. Fifty percent of the leaf blotch and 30% of leaf spot samples yielded a fungus that was fast-growing (20 mm diameter in 4 days at 25°C) and produced colonies that were a pale gray with dark gray reverse and a felty texture. On potato dextrose agar (PDA), pycnidia formed and exuded conidia in peach-colored droplets after 2 weeks under room temperature and light conditions. Pycnidia were spherical and 12.5 to 39.8 μm, average 24.2 μm in diameter. Conidia were hyaline, ovoid, and 5.8 to 8.5 × 3.1 to 4.7 μm (average 7.0 × 3.7 μm). The fungus was identified as Phacidiopycnis washingtonensis based on its morphology (1). To confirm the identity, the internal transcribed spacer (ITS) region of the rDNA was amplified with ITS1/ITS4 primers (2) and sequenced (GenBank Accession Nos. JQ743784 to 86). BLAST analysis showed 100% nucleotide identity with those of P. washingtonensis in GenBank (AY608648). The fungus was also isolated from lesions on green shoots and the petiole and leaf blade of dead attached leaves. To test pathogenicity, 3-year-old Pacific madrone seedlings (three for each isolate) were inoculated with five isolates of the fungus and maintained in the greenhouse (25°C); the experiment was conducted twice. Five leaves from each tree were cold injured (-50°C) at a marked 5 × 5 mm2 area with a commercial aerosol tissue freezing product prior to inoculation and five leaves were not cold injured. A 5-mm-diameter mycelial plug cut from the margin of 6-day-old PDA culture was applied to the marked areas on the upper leaf surface. The inoculated area was covered with moist cheese cloth and wrapped with Parafilm. Leaves treated with blank PDA plugs served as control. Leaves were enclosed in plastic bags to maintain moisture for the first 15 h post inoculation and cheese cloths were removed after 15 days. All cold-injured inoculated leaves showed symptoms of blight starting at 2 weeks after inoculation, and no symptoms appeared on the controls. On non-cold injured inoculated leaves, only one isolate caused symptoms (80% of all leaves). The fungus was re-isolated from diseased leaves. These results suggest that P. washingtonensis is able to cause foliar blight on Pacific madrone when leaves are subjected to cold stress. Increased disease severity on madrone observed in spring 2011 in Washington and Oregon may have been due to predisposition of foliage to extreme cold in November 2010 and February 2011. This fungus has previously been reported to cause a postharvest fruit rot disease on apple fruit and a canker and twig dieback disease of apple and crabapple trees in WA (1). To our knowledge, this is the first report of P. washingtonensis causing a leaf blight disease on Pacific madrone in North America.

Infection Courts and Timing of Infection of Apple Fruit by Phacidiopycnis washingtonensis in the Orchard in Relation to Speck Rot During Storage.

Phacidiopycnis washingtonensis is the cause of speck rot, a recently reported postharvest fruit rot disease of apple. The pathogen is believed to incite infections in the field, and disease symptoms become evident only during storage. To determine the timing of apple fruit infection in relation to development of speck rot in storage, 'Red Delicious' and 'Fuji' apple fruit were inoculated in the orchard with P. washingtonensis at different times during the growing season, harvested, and monitored for decay development during storage at 0°C. Fruit inoculated in both field and laboratory also were used to identify the infection courts and mode of apple fruit penetration by P. washingtonensis. In all 3 years, stem-end speck rot and calyx-end speck rot developed during cold storage on fruit inoculated during the growing season, regardless of inoculation time; and the incidence of total speck rot in storage increased as the fruit inoculation time approached harvest. On fruit floral parts, the pathogen colonized sepals at higher rates than stamens. Availability of naturally occurring necrotic tissues favored the colonization of the fungus on sepals. Histological studies indicated that infection occurred through micro-cracks on the surfaces of pedicels and sepals of the fruit, and invasion of these tissues was restricted between the cuticle and epidermis. Findings of this study will assist in the development of effective control strategies for speck rot.

Development of PCR Assays for Diagnosis and Detection of the Pathogens Phacidiopycnis washingtonensis and Sphaeropsis pyriputrescens in Apple Fruit.

Speck rot caused by Phacidiopycnis washingtonensis and Sphaeropsis rot caused by Sphaeropsis pyriputrescens are two recently reported postharvest diseases of apple. Infection by these two pathogens occurs in the orchard but remains latent before harvest. Symptoms develop after harvest and are similar to those of gray mold caused by Botrytis cinerea. Accurate diagnosis of these diseases is important during the fruit inspection process, particularly in the instance of fruit destined for export. Early near-harvest detection of latent infections in apple fruit is an important step to implement relevant pre- and postharvest measures for disease control. The aim of this study was to develop polymerase chain reaction (PCR) assays for diagnosis and early detection of latent infections of apple fruit by P. washingtonensis and S. pyriputrescens. Species-specific primers based on the ribosomal DNA internal transcribed spacer region were designed for use in PCR assays. Conventional and real-time PCR assays were developed and validated using fruit inoculated with P. washingtonensis, S. pyriputrescens, or B. cinerea and compared with identifications using traditional isolation-based assays. For wound-inoculated fruit, the PCR assays consistently provided the correct identification of the pathogen used as the inoculant in 6 h of processing time, compared with 5 to 6 days using culture-based methods. Real-time PCR assays effectively detected latent infections in symptomless stem and calyx tissues of fruit that were inoculated with the pathogens in the orchard during the growing season. The PCR assays provide a rapid, accurate method for diagnosis and early detection of these diseases.

Control of a wide range of storage rots in naturally infected apples by hot-water dipping and rinsing

Hot-water rinsing (3 or 4min) and dipping (15, 20 or 25s) at a range of incubation temperatures was applied to apples (cv. ‘Ingrid Marie’ and ‘Pinova’) naturally infected with a range of North West European storage-rot fungi. Significant reductions in the incidence of fruit rot were achieved by incubation periods of 3min at 50–54°C (dipping) and 20 or 25s at 55°C (rinsing), followed by up to 100d cold-storage at 2°C and 14d at 18°C. Pathogens controlled in this way were Neofabraea alba, N. perennans, Monilinia fructigena, Colletotrichum acutatum, Phacidiopycnis washingtonensis and Cladosporium spp. Neonectria galligena was reliably controlled by dipping but not rinsing. No effects of either heat treatment on Gibberella avenacea and Botrytis cinerea were apparent. Following rinsing at 65°C for 20s, the incidence of P. washingtonensis, Penicillium expansum, Mucor spp. and Phoma exigua was higher than in untreated control fruit or in apples rinsed at lower temperatures, and was associated with heat damage. The relative contributions of heat effects on inoculum viability and activation of defence responses of apple fruit are discussed. Hot-water rinsing has several advantages over hot-water dipping related to the efficient processing of fruit either directly after harvest or after long-term storage.

Control of Phacidiopycnis washingtonensis storage rot of apples by hot-water treatments without the ethylene inhibitor 1-MCP

Phacidiopycnis washingtonensis, cause of rubbery rot of apples during long-term storage, was first observed in Denmark in April 2010 on fruits of the 2009 harvest. Hot-water treatments were examined as a possible way to control P. washingtonensis. The effective temperature causing a 50% mortality of infectious spores (conidia) after a 3-min submersion in water was 40.2°C. A significant reduction of rubbery rot was achieved by dipping artificially infected fruit in a water bath at 47–52°C for 3 min. Using naturally infected apples, P. washingtonensis as well as the widespread storage-rot pathogen Neofabraea perennans were effectively controlled by a post-harvest dip at 50°C for 3 min or by a rinse at 55°C for 20 s, followed by cold storage in controlled-atmosphere conditions. In contrast, a treatment of freshly harvested fruits with 1-methylcyclopropene (1-MCP) instead of hot water failed to control P. w a s h i n g t o -nensis.

Phacidiopycnis washingtonensis, Cause of a New Storage Rot of Apples in Northern Europe

Phacidiopycnis washingtonensis was identified by morphology and ITS sequence analysis as the cause of rubbery rot, a new storage disease of apples in northern Germany. Infected fruits had an unusually firm texture and pale appearance after storage in ultra-low oxygen conditions, but turned dark brown to black in ambient atmosphere. Ultimately, the surface of rotted fruits became covered by black pycnidia producing cream-coloured conidial exudates. Rubbery rot affected several apple varieties, including the commercially important ‘Jonagold’ and ‘Elstar’. Losses during storage were commonly below 1% but reached 5–10% in a few cases. Fruits of ‘Golden Hornet’ crab apple trees planted as pollinators in commercial orchards became heavily infected by P. washingtonensis in October. Conidia were released throughout the following season from infected fruit mummies, which remained attached to the crab apple tree.

First Report of Postharvest Fruit Rot in Persimmon Caused by Phacidiopycnis washingtonensis in Italy.

Persimmon (Diospyros kaki L.) is widely grown in Italy, the leading producer in Europe. In the fall of 2009, a previously unknown rot was observed on 3% of fruit stored at temperatures between 5 and 15°C in Torino Province (northern Italy). The decayed area was elliptical, firm, and appeared light brown to dark olive-green. It was surrounded by a soft margin. The internal decayed area appeared rotten, brown, and surrounded by bleached tissue. On the decayed tissue, black pycnidia that were partially immersed and up to 0.5 mm in diameter were observed. Light gray conidia produced in the pycnidia were unicellular, ovoid or lacriform, and measured 3.9 to 6.7 × 2.3 to 3.5 (average 5.0 × 2.9) μm. Fragments (approximately 2 mm) were taken from the margin of the internal diseased tissues, cultured on potato dextrose agar (PDA), and incubated at temperatures between 23 and 26°C under alternating light and darkness. Colonies of the fungus initially appeared ash colored and then turned to dark greenish gray. After 14 days of growth, pycnidia and conidia similar to those described on fruit were produced. The internal transcribed spacer (ITS) region of rDNA was amplified using the primers ITS4/ITS6 and sequenced. BLAST analysis (1) of the 502-bp segment showed a 100% similarity with the sequence of Phacidiopycnis washingtonensis Xiao & J.D. Rogers (GenBank Accession No. AY608648). The nucleotide sequence has been assigned the GenBank Accession No. GU949537. Pathogenicity tests were performed by inoculating three persimmon fruits after surface disinfesting in 1% sodium hypochlorite and wounding. Mycelial disks (10 mm in diameter), obtained from PDA cultures of one strain were placed on wounds. Three control fruits were inoculated with plain PDA. Fruits were incubated at 10 ± 1°C. The first symptoms developed 6 days after the artificial inoculation. After 15 days, the rot was very evident and P. washingtonensis was consistently reisolated. Noninoculated fruit remained healthy. The pathogenicity test was performed twice. Since P. washingtonensis was first identified in the United States on decayed apples (2), 'Fuji', 'Gala', 'Golden Delicious', 'Granny Smith', 'Red Chief', and 'Stark Delicious', apple fruits also were artificially inoculated with a conidial suspension (1 × 106 CFU/ml) of the pathogen obtained from PDA cultures. For each cultivar, three surface-disinfested fruit were wounded and inoculated, while three others served as mock-inoculated (sterile water) controls. Fruits were stored at temperatures ranging from 10 to 15°C. First symptoms appeared after 7 days on all the inoculated apples. After 14 days, rot was evident on all fruit inoculated with the fungus, and P. washingtonensis was consistently reisolated. Controls remained symptomless. To our knowledge, this is the first report of the presence of P. washingtonensis on persimmon in Italy, as well as worldwide. The occurrence of postharvest fruit rot on apple caused by P. washingtonensis was recently described in the United States (3). In Italy, the economic importance of the disease on persimmon fruit is currently limited, although the pathogen could represent a risk for apple.

A New Canker Disease of Crabapple Trees Caused by Phacidiopycnis washingtonensis in Washington State

This is the first report of this fungus causing cankers and twig dieback on crabapple trees. Our findings indicate that canker symptoms on crabapple trees caused by P. washingtonensis are similar to those caused by S. pyriputrescens and that infected crabapple trees may serve as a source of P. washington ensis inoculum for infection of apple. Accepted for publication 23 April 2009. Published 12 June 2009.

Distribution and Incidence of Sphaeropsis Rot in Apple in Washington State.

Sphaeropsis rot, caused by Sphaeropsis pyriputrescens, is a recently recognized postharvest disease of apple in Washington State. To determine the distribution and incidence of this disease as well as other postharvest diseases, decayed fruit were sampled during packing or pre-sizing operations in commercial fruit packinghouses from 26, 72, and 81 grower lots in 2003, 2004, and 2005, respectively. Fungi associated with decayed fruit were isolated and identified. The most common postharvest diseases of apple in the region were blue mold caused by Penicillium spp., primarily P. expansum, gray mold caused by Botrytis cinerea, and Sphaeropsis rot, accounting for 32, 28, and 17% of the decayed fruit, respectively. Percentages of these diseases in the total decayed fruit varied from lot to lot. Bull's eye rot caused by Neofabraea spp. was responsible for 13.4% of the total decay and was most prevalent on Golden Delicious. Other minor diseases included speck rot caused by Phacidiopycnis washingtonensis, Alternaria rot caused by Alternaria spp., Mucor rot caused by Mucor piriformis, and core rot caused by a group of fungi, primarily Alternaria spp. Sphaeropsis stem-end rot was more common than calyx-end rot on Golden Delicious, whereas Sphaeropsis calyx-end rot was more common than stem-end rot on Fuji. On Red Delicious, both stem-end rot and calyx-end rot were common. Sphaeropsis rot resulting from infections through the fruit peel was more commonly seen on Golden Delicious and Fuji than on Red Delicious. The percentage of gray mold was higher on nondrenched fruit than on fruit drenched with thiabendazole (TBZ), whereas blue mold was more prevalent on TBZ-drenched fruit. Our results indicate that Sphaeropsis rot is an important component of storage rots of apples in Washington State.

A Postharvest Fruit Rot in Apple Caused by Phacidiopycnis washingtonensis.

During a survey of postharvest diseases in Red Delicious apples (Malus domestica) conducted in 2003, a previously undescribed postharvest fruit rot was discovered in Washington State. The causal agent has been described as a new species, Phacidiopycnis washingtonensis. In this study, we described the symptomatology of this disease, determined its occurrence and prevalence in Washington State, tested pathogenicity, and determined infection courts on fruit of three apple varieties. Decayed fruit were sampled from 26, 72, and 81 grower lots during March to August in 2003, 2004, and 2005, respectively, during packing operations from commercial packinghouses. Symptoms of decayed fruit were recorded and isolations were made from decayed fruit to correlate causal agents with the disease symptoms observed. Fruit of Red Delicious, Golden Delicious, and Fuji apples were inoculated in the orchards with conidial suspensions of the fungus at 1 and 2 weeks before harvest. All fruit were harvested and stored at 0°C, and decay development on the fruit was monitored monthly for up to 9 months. The symptoms were primarily stem-end rot and calyx-end rot. Infection also occurred at lenticels on fruit skin, particularly on Golden Delicious. The decayed area was spongy to firm and appeared light brown to brown. On Red Delicious, brown to black specks at lenticels often appeared at the decayed area as the disease advanced. This disease occurred in 23, 26, and 17% of the total grower lots, accounting for approximately 1, 4, and 3% of the total decay in 2003, 2004, and 2005, respectively. In 2004 and 2005, severe losses of fruit were observed in three grower lots of Red Delicious, and their losses were as high as 24%. After 9 months in storage, 48, 48, and 24% of Red Delicious, Golden Delicious, and Fuji that were inoculated in the orchards, respectively, developed symptoms of this disease, and the fungus was reisolated from decayed fruit. Stem-end rot was common on Red Delicious and Golden Delicious, whereas calyx-end rot was common on Fuji. We propose "speck rot" as the name of this disease.

Phacidiopycnis washingtonensis--a new species associated with pome fruits from Washington State

A new species of Phacidiopycnis associated with pome fruits is described. The fungus causes fruit rot on apples during storage and is associated with a twig dieback and canker disease of crabapple trees and dead twigs of pear trees. To characterize the biology of the fungus and compare it with Ph. piri, the type species of the genus, effects of nine media and light on mycelial growth and pycnidial production, mycelial growth in response to temperature and mode of conidial germination in response to nutrient were determined. Apple-juice agar, pear-juice agar, prune-juice agar, potato-dextrose agar (PDA) and malt-extract agar, Czapek-Dox agar and oatmeal agar (OMA) favored mycelial growth. Cornmeal agar (CMA) did not favor mycelial growth. Light effect on pycnidial formation was medium dependent. Abundant pycnidia with mature conidia formed in 14 d old PDA and OMA cultures at 20 C, regardless of light, whereas none or very few pycnidia formed on other media in the dark. Fluorescent light stimulated formation of pycnidia except on CMA. The fungus grew at -3-25 C, with optimum growth at 15-20 C. Conidia germinated either by forming germ tubes or less often by budding. Budding of conidia occurred in 1 and 10% pear-juice solutions but not in 100% pear-juice solution. Six isolates of Ph. washingtonensis from different species of pome fruits had identical ITS sequences. The sizes of the ITS region were the same for both Ph. washingtonensis and Ph. piri, and four polymorphic nucleotide sites were found in the ITS region between Ph. washingtonensis and Ph. piri. The similarity in ITS sequences between these two taxa is confirmatory evidence for the erection of the new species of Phacidiopycnis associated with pome fruits we describe here.

Phacidiopycnis washingtonensis—a new species associated with pome fruits from Washington State

A new species of Phacidiopycnis associated with pome fruits is described. The fungus causes fruit rot on apples during storage and is associated with a twig dieback and canker disease of crabapple trees and dead twigs of pear trees. To characterize the biology of the fungus and compare it with Ph. piri, the type species of the genus, effects of nine media and light on mycelial growth and pycnidial production, mycelial growth in response to temperature and mode of conidial germination in response to nutrient were determined. Apple-juice agar, pear-juice agar, prune-juice agar, potato-dextrose agar (PDA) and malt-extract agar, Czapek-Dox agar and oatmeal agar (OMA) favored mycelial growth. Cornmeal agar (CMA) did not favor mycelial growth. Light effect on pycnidial formation was medium dependent. Abundant pycnidia with mature conidia formed in 14 d old PDA and OMA cultures at 20 C, regardless of light, whereas none or very few pycnidia formed on other media in the dark. Fluorescent light stimulated formation of pycnidia except on CMA. The fungus grew at −3–25 C, with optimum growth at 15–20 C. Conidia germinated either by forming germ tubes or less often by budding. Budding of conidia occurred in 1 and 10% pear-juice solutions but not in 100% pear-juice solution. Six isolates of Ph. washingtonensis from different species of pome fruits had identical ITS sequences. The sizes of the ITS region were the same for both Ph. washingtonensis and Ph. piri, and four polymorphic nucleotide sites were found in the ITS region between Ph. washingtonensis and Ph. piri. The similarity in ITS sequences between these two taxa is confirmatory evidence for the erection of the new species of Phacidiopycnis associated with pome fruits we describe here.