bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Infection of Hop Cones by Alternaria alternata in Australia
Authors: Pethybridge S. J. , Hay F. S. , Wilson C. R. , Sherriff L. J. , Leggett G. W.
Published: May 2007

The hop (Humulus lupulus L.) is a dioecious climbing plant, cultivated for its resins, which are produced in the cone, used primarily for the bittering of beer. In Australia, hops are grown in the states of Victoria and Tasmania. In late summer 2001, necrotic lesions were observed on the tips of bracts and bracteoles of developing cones at three hop farms in Tasmania. The necrotic area varied between 1 and 25% of the bracts and bracteoles, and in some cases progressed throughout the entire hop cone. Pieces of infected hop cones were surface sterilized for one minute in 2% sodium hypochlorite, plated on 2% water agar, and incubated at 22 ± 2°C. The most frequently isolated fungi (total number of isolations = 60) were transferred to 2% water agar and potato dextrose agar. In 90% of cases, the isolated fungus was Alternaria alternata (Fr.:Fr.) Keissl, as identified by M. Priest, NSW Agriculture, Australia. The pathogenicity of A. alternata was determined on detached, freshly picked cones of hop cultivar “Nugget.” Cones (n = 25) were inoculated with a conidial suspension of the fungus (1,000 spores per ml) and incubated at room temperature in a sealed container on plastic mesh over tissue wetted with sterile distilled water. Symptoms first appeared three days after inoculation as necrotic tips of bracts and bracteoles, and within 10 days the entire cone had become necrotic. Symptoms were more severe in vitro compared to in the field. This was probably due to the maintenance of detached cones under constant high relative humidity. Disease symptoms did not appear on cones inoculated with sterile distilled water. The pathogen was reisolated from inoculated cones, completing Koch's postulates. The pathogenicity of A. alternata to hop cones was reported in the United Kingdom in 1988. To our knowledge, this is the first report of A. alternata on hop cones in Australia.

References: (1) P. Darby. Trans. Br. Mycol. Soc. 90:650–653, 1988.
Pathotypes of Pyricularia grisea in Rice Fields of Central and Southern China
Authors: Chen H. L. , Chen B. T. , Zhang D. P. , Xie Y. F. , Zhang Qifa
Published: May 2007

Blast, caused by the fungal pathogen Pyricularia grisea, is the most devastating disease of rice worldwide. Knowledge of the pathotype composition of the pathogen in rice fields is essential for rational deployment of resistance genes in rice breeding programs. In this study, we assayed the pathotypes of the pathogen populations using samples recently collected from 13 major rice-growing provinces of central and southern China. In all, 792 single spore isolates were tested for pathogenicity reactions using 13 host differentials consisting of six indica and seven japonica near-isogenic lines (NILs). The compositions of the pathogen populations were complex; 48 pathotypes were identified with the indica NILs, 82 pathotypes were detected with the japonica NILs, and a total of 344 pathotypes were identified with both indica and japonica NILs. There were large differences in distribution of the pathotypes among the different rice-growing areas. Even neighbor provinces seemed to differ sharply in types and frequencies of the most prevalent pathotypes. There was also a large difference in the frequencies of the isolates producing compatible reactions on the NILs, indicating the difference in frequencies of avirulence genes in the pathogen populations. The data provided very useful information for formulating strategies for improving blast resistance in rice breeding programs.
Comparison of Epidemics of Botrytis Fruit Rot and Powdery Mildew of Strawberry in Large Plastic Tunnel and Field Production Systems
Authors: Xiao C. L. , Chandler C. K. , Price J. F. , Duval J. R. , Mertely J. C. , Legard D. E.
Published: May 2007

Epidemics of Botrytis fruit rot (Botrytis cinerea) and powdery mildew (Sphaerotheca macularis f. sp. fragariae) in annual strawberry were compared in large plastic tunnel and field production systems during the 1998-99 and 1999-2000 seasons. Treatments were factorial combinations of two main plots (field and tunnel) and four subplots, including combinations of two cultivars (Camarosa and Sweet Charlie) and two captan schedules arranged in a split-plot design with three replications. The mean incidence of Botrytis fruit rot was 88 to 94% lower in tunnels than in the field. The incidence of Botrytis fruit rot for the untreated control in tunnels was less than 2%, which was 89% lower than that of the 7-day captan schedule in the field. This indicates that Botrytis fruit rot can be controlled effectively without fungicides in a tunnel cultural system. Powdery mildew was severe on susceptible cultivar Camarosa in tunnels. Early season yields of cultivar Sweet Charlie were significantly higher in tunnels than in the field. Shorter periods of leaf wetness and higher temperatures in tunnels may have contributed to a lower incidence of Botrytis fruit rot and a higher incidence of powdery mildew on fruit in tunnels compared with open field plots.
First Report of Colletotrichum acutatum on Strawberry in Finland
Authors: Parikka P. , Kokkola M.
Published: May 2007

Strawberry (Fragaria × ananassa) is the most important small fruit crop in Finland. The quarantined pest Colletotrichum acutatum was detected for the first time on strawberry in August 2000, in Eastern Finland. Waiting-bed plants of cultivar Elsanta had symptoms typical of anthracnose rot (black spot) on the fruit, and small black lesions were seen on stolons. The rainy, warm, and humid weather of the summer favored the development and spread of the disease. C. acutatum was isolated from lesions on the fruit. Abundant sporulation was observed on lesions, and the fungus was readily isolated on potato dextrose agar (PDA) from surface-sterilized fruit pieces. Spores (11.5 to 19.8 × 3.3 to 4.0 μm) were acute at both ends, and acervuli with salmon pink spore masses matched the descriptions of C. acutatum (1). At first, the colonies were white and later became ash gray. The growth rate of the fungus was 8.0 to 8.8 mm per day, at 27°C. The identification was confirmed with enzyme-linked immunosorbent assay at the Central Science Laboratory, York, U.K. In order to fulfill Koch's postulates, young potted strawberry plants were inoculated by misting with a suspension of 10.4 × 106 conidia per ml of C. acutatum. Healthy runner plants of micropropagated cultivars Bounty, Cudaruska, Jonsok, Korona, and Oka (10 plants of each cultivar) were inoculated and incubated for 3 days, at 100% relative humidity. After 3 weeks at 20 to 21°C and 16 h of light per day, dark, elongated lesions measuring 2 to 15 mm were observed on the stolons. All tested cultivars developed symptoms on stolons and petioles, but no crown infections were detected. Flowering and fruit-bearing plants of cultivars Honeoye, Sara, and Senga Sengana were similarly inoculated and incubated. The first symptoms of fruit rot were detected 5 days after inoculation on the ripening fruit of Honeoye. Less severe fruit rot was seen on the fruit of Senga Sengana and the Fragaria vescana cultivar Sara. Salmon pink sporodochia developed on infected fruit, stolons, and leaves, within 5 days on moist filter paper, and C. acutatum was isolated on PDA. No other pathogens were present. Because C. acutatum is a quarantined pest in Finland, all strawberry plants of the infected lot on this particular farm were destroyed and future use of the field will be restricted.

Reference: (1) C. M. Howard et al. 1992. Plant Dis. 76:976–981.
First Report of Occurrence of Verticillium Wilt on Some Ornamental Trees in Sicily
Authors: Polizzi G. , Vitale A. , Catara V.
Published: May 2007

In July 1998, a widespread lethal collapse of butterfly tree (Bauhinia purpurea L.), puka tree (Meryta sinclairii Hook.), Indian laurel (Ficus microcarpa L.), golden rain tree (Koelreuteria paniculata Laxm.), and Brazilian pepper tree (Schinus terebinthifolius Raddi.) has been observed in an ornamental growing area near Catania in eastern Sicily. The diseased plants showed yellowing of the leaves and twig dieback. In cross sections of infected trunks, roots, twigs or shoots, characteristic discoloration of xylem vessels was observed, resembling a vascular wilt disease. The disease was chronic with a lingering decline progressing for years. The isolate that was consistently recovered from diseased tissues on PDA was identified as Verticillium dahliae Kleb., based on verticillate conidiophores with phialides and conidia and melanized microsclerotia. Pathogenicity tests were performed on 4- to 6-month-old seedlings of all five ornamental plants by inoculating a suspension of the fungus (1). Symptoms were observed after 5 to 7 months, and V. dahliae was reisolated, confirming Koch's postulates. To our knowledge this is the first report of V. dahliae on Indian laurel, golden rain tree, and Brazilian pepper tree in Italy, and the first report of the disease on butterfly tree and puka tree.

Reference: H. A. Melouk and C. E. Horner. Phytopathology 65:767, 1975.
First Report of Columbia Root-Knot Nematode (Meloidogyne chitwoodi) in Potato in New Mexico
Authors: Thomas S. H. , Sanderson S. A. , Handoo Z. A.
Published: May 2007

Following a report of Columbia root-knot nematode in potatoes (Solanum tuberosum L.) imported by Mexico from the United States in spring 2000, six fields in San Juan County, NM, were surveyed in August 2000. Soil samples from two fields in which the exported potatoes had been produced contained second-stage juveniles that were tentatively identified as Columbia root-knot nematode. During the 2000 potato harvest, state inspectors detected tubers from four additional fields that exhibited symptoms of Columbia root-knot nematode, including warty exteriors and discrete small brown lesions that were apparent to a depth of 1 cm below the tuber surface. Meloidogyne chitwoodi Golden et al. (1) was confirmed from a subsample of tubers sent to the USDA Nematology Laboratory in Beltsville, MD, in October 2000. Identification was based on morphological examination of the nematodes recovered from tubers. To our knowledge, this is the first report of M. chitwoodi from New Mexico. No Columbia root-knot nematodes were recovered from soil samples collected at 26 locations throughout San Juan County in 1988 and 1989, nor had symptomatic tubers or plants been observed in this area previously. Columbia root-knot nematode most likely represents a recent introduction into northwestern New Mexico. Additional information regarding distribution of this nematode within the region is needed.

References: (1) A. M. Golden et al. J. Nematol. 12:319–327, 1980.
Association of a Monopartite Begomovirus with Yellow Mosaic Disease of Pumpkin (Cucurbita maxima) in India
Authors: Singh R. , Raj S. K. , Chandra G.
Published: May 2007

Pumpkin (Cucurbita maxima) is an economically important vegetable crop of the family Cucurbitaceae. Yellow mosaic in C. maxima was observed in and around Lucknow, India, during the winter season of 1999-2000. High populations of whiteflies (Bemisia tabaci) were associated with diseased plants. Whiteflies were allowed to feed on diseased C. maxima plants and placed on healthy C. maxima seedlings. Symptoms of yellow mosaic disease were successfully reproduced in the seedlings. These results suggested a possible involvement of a geminivirus with the disease. Total DNA was extracted from infected and uninfected C. maxima seedlings by the CTAB method. DNA samples were used as templates in polymerase chain reaction (PCR) using degenerate primers A (5′-TAATATTACCKGWKGVCCSC-3′) and B (5′-TGGACYTTRCAWGGBCCT TCACA-3′), which have been designed to amplify a region of about 500 to 600 nt from DNA-A of a majority of begomoviruses (1). The PCR products obtained were analyzed on a 1.5% agarose gel. The major amplicon obtained from the DNA of infected plants was about 550 bp as expected from these primers. However, no such amplicon was observed in DNA samples from uninfected plants. The amplicon obtained from PCR was cloned in a suitable cloning vector. Three separate clones were sequenced and the corrected sequence data (GenBank Accession No. AF381977) was compared with the corresponding sequences of other known geminiviruses. The highest identity (88%) was with a strain of monopartite Tomato leaf curl virus (TLCV) from southern India (GenBank Accession No. U38239). The first 34 nucleotides showed significant identity (91% and 97%, respectively) with Althea rosea enation mosaic virus (GenBank Accession No. AF014881) and TLCV strain D2 reported from Australia (GenBank Accession No. AF084006), both of which are monopartite begomoviruses. These results establish the provisional identity of the pathogen causing yellow mosaic disease on pumpkin in India as a closely related strain of the monopartite TLCV. The yellow leaf disease of muskmelon in Thailand and watermelon leaf curl disease in Pakistan also were recently reported to be caused by an Indian strain of TLCV (2,3). However, to our knowledge this is the first report of detection of a monopartite geminvirus causing yellow mosaic disease on pumpkin in India.

References: (1) D. Deng et al. Ann. Appl. Biol. 125:327, 1994. (2) S. H. Khan et al. Plant Dis. 84: 102, 2000. (3) K. Sarmretwanich, Plant. Dis. 84:707, 2000.
First Report of Tan Spot on Wheat in Pakistan
Authors: Ali S. , Francl L. J. , Iram S. , Ahmad I.
Published: May 2007

Tan spot is caused by Pyrenophora tritici-repentis and is an economically important foliar disease of wheat worldwide. The fungus produces two types of symptoms, necrosis and chlorosis, on susceptible wheat cultivars. Isolates have been grouped into five races based on their ability to induce necrosis (nec+) and chlorosis (chl+) on appropriate wheat differentials (1,2). During March 2000, foliar diseases of wheat were surveyed in major wheat-growing areas of the Punjab Province of Pakistan. Tan spot was observed at 13 locations in the province. Diseased leaf samples were collected from all 13 locations to satisfy Koch's postulates. Isolations were made by placing 2-cm-long diseased leaf pieces in petri dishes with three layers of dampened Whatman No. 1 filter paper. The leaf pieces were incubated under an alternating cycle of 24 h of light at 21°C and 24 h of dark at 16°C. A fungus that produced erect, single dark yellow-brown conidiophores with single light yellow-brown conidia was recovered from all the samples and identified as Drechslera tritici-repentis, the anamorph of Pyrenophora tritici-repentis. Single spores were transferred on V8 potato dextrose agar for further study. Seven single spore isolates recovered from the samples were imported through APHIS and tested for pathogenicity and race structure in a growth chamber at North Dakota State University. Two-week-old seedlings of wheat differentials were inoculated individually with a spore suspension of each isolate, and consistent results were found in four replicated experiments. Four of seven isolates were identified as race 1 (nec+chl+), whereas, three isolates did not correspond to any of the currently identified five races. For all these isolates, one of the differentials (Katepwa), which exhibits necrosis, chlorosis, or neither symptom to the five described races, showed both necrosis and chlorosis. This is the first report of the occurrence of tan spot of wheat in Pakistan. The widespread presence of tan spot in the region is a potential threat to wheat production.

References: (1) De Wolf et al. Can. J. Plant Pathol. 20:349, 1998. (2). Lamari et al. Can. J. Plant Pathol. 17:312, 1995.
Ecology of Armillaria spp. in Mixed-Hardwood Forests of California
Authors: Baumgartner Kendra , Rizzo David M.
Published: May 2007

Incidence of Armillaria root disease and the population structure of associated Armillaria spp. was studied in California mixed-hardwood forests. Four 3,000-m2 plots, consisting of Quercus kelloggii, Q. agrifolia, Lithocarpus densiflorus, Arbutus menziesii, Umbellularia californica, and Pseudotsuga menziesii, were intensively sampled. Root collars were examined for mycelial fans, decayed wood, and rhizomorphs. From 404 trees (333 living, 71 dead), Armillaria mellea and A. gallica were recovered and identified from 148 isolates. The most abundant tree species in each plot was the tree species most frequently infected by A. mellea or A. gallica. The majority of A. mellea isolates were recovered from mycelial fans on living trees. Recent mortality due to A. mellea was found only in one plot. A. gallica was mainly identified from epiphytic rhizomorphs. Only one to three somatic incompatibility groups (SIGs) for each species were found in each plot. Estimated sizes of SIGs varied from the extent of a single root system to the entire width of the plot. Based on our results, both A. mellea and A. gallica are common in mixedhardwood forests, yet A. mellea appears to be a more aggressive pathogen. A. gallica is capable of attacking live hosts, but occurs on living roots more frequently as epiphytic rhizomorphs.
Soil Sampling Techniques for Determining the Effect of Cultural Practices on Rhizoctonia oryzae-sativae Inoculum in Rice Field Soils
Authors: Miller Thomas C. , Webster Robert K.
Published: May 2007

Methods were evaluated to quantify sclerotia in rice fields affected with aggregate sheath spot disease. Recovered sclerotia were compared with disease ratings at harvest for paddies subjected to various postharvest cultural straw management practices. Sclerotial inoculum level was not always correlated with subsequent disease incidence in rice aggregate sheath spot disease, suggesting alternative sources of inoculum and other factors influencing disease development. Straw management practices affected the inoculum load of Rhizoctonia oryzae-sativae, as determined by methods recovering sclerotia from California rice field soil samples. Traditional wet sieving of soil samples was improved using a potassium carbonate solution to float heavier sclerotia that normally remained in the sediment. The relationship of inoculum in the soil from seedbeds and the incidence of resulting disease measured just before harvest was investigated over 3 years at three sites. A linear dose-response was found at only one site where the number of floating sclerotia was more strongly correlated with disease incidence than total number of sclerotia (floating plus nonfloating sclerotia). Floating sclerotia were more easily counted using a water floatation extraction (WFE) than were total sclerotia by using a potassium carbonate floatation extraction (PCFE) or a combination of the two assays (WFE + PCFE), and the WFE more accurately predicted disease incidence than did either PCFE or WFE + PCFE. All assays detected significant differences between inoculum levels as influenced by various straw residue management practices, with removal of straw residue significantly reducing number of soil-borne sclerotia.
Incidence and Distribution of Raspberry bushy dwarf virus in Commercial Red Raspberry (Rubus idaeus) Crops in Scotland
Authors: Chard Jane , Irvine Susan , Roberts Adrian M. I. , Nevison Ian M. , McGavin Wendy J. , Jones A. Teifion
Published: May 2007

A survey was done in 1998 to determine whether Raspberry bushy dwarf virus (RBDV) was established in raspberry fruiting plantations in Scotland. Raspberry-producing holdings were selected according to geographical area and size. Samples (201), each comprising 60 shoots per stock, were obtained from 77 holdings and tested by enzyme-linked immunosorbent assay (ELISA). ELISA-positive shoots from each infected stock were grafted onto cultivar Glen Clova, which is resistant to the Scottish-type isolate of RBDV (RBDV-S), to establish whether the virus is a resistance-breaking (RB) isolate. RBDV was detected in 22% of the stocks sampled, with 2 to 80% incidence of infection. No RBDV was in any of the 40 plantations containing cultivars resistant to RBDV-S or in Glen Clova plants, which were grafted successfully with samples from 15 infected plantations, indicating that no RB isolates were detected. The percentage of infected plantations increased with time from the planting date. In order to investigate possible sources of infection, ELISA for RBDV was made in 1999 on samples of stocks of raspberry cultivars entered for the lowest certified grade (Standard Grade) in Scotland and, in 1994 to 1997, on certified stocks planted with material originating from outside Scotland. No RBDV was detected in any of the samples. RBDV was found only rarely in samples of wild raspberry in Angus and Perthshire.
Molecular Detection of Strain L47 of Aureobasidium pullulans, a Biocontrol Agent of Postharvest Diseases
Authors: Schena Leonardo , Sialer Mariella Finetti , Gallitelli Donato
Published: May 2007

The strain L47 of Aureobasidium pullulans is an effective biocontrol agent of postharvest diseases. When applied in the field before harvesting it requires a specific monitoring method to evaluate colonization and dispersal in the environment. The randomly amplified polymorphic DNA technique (RAPD) was used for a preliminary screening of A. pullulans genetic variability among 205 isolates. This approach allowed the selection of a 1.3-kb fragment (L4) present solely in isolates L47 and 633. In Southern blots, a digoxigenin (DIG)-labeled L4 amplicon specifically recognized the corresponding fragment present in the polymorphic pattern of L47 and 633. The L4 fragment was cloned, sequenced, and used to design two sequence-characterized amplification region (SCAR) primers and a 242-bp riboprobe. Both the SCAR primers and the 242-bp DIG-labeled riboprobe were highly specific for L47. In classical polymerase chain reaction (PCR), with a series of 10-fold dilutions of L47 DNA, the limit of detection was 20 pg/μl. The Ap13 primer was also modified to obtain a Scorpion primer for detecting a 150-bp amplicon by fluorescence emitted from a fluorophore through a self-probing PCR assay. This assay specifically recognized the target sequence of L47 strain over a number of other A. pullulans isolates in field-treated grape berry washings. The limit of detection was 105 cells per ml, i.e. 10 times higher than the limit of the CFU method. The method is also proposed as a way to demonstrate the ability of L47 strain to penetrate the epidermis of sweet cherry fruits and to track it in the mesocarp.
First Report of Tomato yellow leaf curl virus Infecting Pepper Plants in Cuba
Authors: Quiñones M. , Fonseca D. , Martinez Y. , Accotto G. P.
Published: May 2007

The begomovirus Tomato yellow leaf curl virus (TYLCV) is one of the major threats to tomato production in tropical and subtropical regions worldwide. TYLCV was found in Cuba in 1994 and later became the most serious constraint to tomato production (2). During a field survey in 2001, pepper plants (Capsicum annuum) were observed in a greenhouse in Camagüey Province, showing mild interveinal yellowing and curling of leaves. Total nucleic acids were extracted from these plants and from pepper samples collected in previous years that showed similar symptoms. Polymerase chain reaction (PCR) was performed on extracts using a primer pair (TY-1/TY-2) (1) specific for the capsid protein (CP) gene of begomoviruses and a second primer pair (IR2353+: CTGAATGTTTGGATGGAAATGTGC; IR255-:GCTCGTAAGTTTCCT CAACGGAC) designed to amplify the part of the genome encompassing the intergenic region (IR) of the Cuban isolate of TYLCV-IS (2). With these primer pairs, amplicons of the expected size were obtained from five samples (one collected in 1995 in Havana Province, two in 1999 in Sancti Spiritus, and two in 2001 in Camagüey.) The CP fragment was digested with RsaI, while the IR amplicon was digested with AvaII and EcoRI. In all cases the patterns obtained corresponded to digestion patterns for identical PCR fragments obtained from TYLCV-infected tomatoes. The IR amplicon sequence from one sample showed ≈99% identity with the corresponding region of the TYLCV-IS isolated from tomato in Cuba. To our knowledge, this is the first report of TYLCV-IS infection in peppers in Cuba.

References: (1) G. P. Accotto et al. Eur. J. Plant. Pathol. 106:179, 2000. (2) Y. Martínez et al. J. Phytopathol.144:277, 1996.
First Report of Tobacco Bushy Top Disease in China
Authors: Mo X.-H. , Qin X.-Y. , Tan Z.-X. , Li T.-F. , Wu J.-Y. , Chen H.-R.
Published: May 2007

In 1993, a severe epidemic of a new disease of flue-cured tobacco (Nicotiana tabacum) occurred in western Yunnan Province, People's Republic of China. Since then, over 40,000 ha of tobacco have been affected, with an average incidence of ≈15%. Infected plants were stunted, and leaves showed symptoms of vein distortion, vein clearing, mottling, and rounding. Axillary buds sprouted from the main stem of infected plants early and formed lateral shoots, on which other shoots were produced. As a result, the infected plants presented the characteristic “bushy” appearance. Aphid- (Myzus persicae (Sulzer)) and sap-transmission experiments were conducted. In aphid-transmission tests, after an acquisition feeding period of 24 h on diseased tobacco, the shortest test feeding that resulted in infection was 5 min. The causal agent(s) was readily sap-transmissible, but it could not be transmitted from sap-inoculated plants to healthy plants by aphids. Thirty-two species of plants in eleven families were tested by sap-inoculation for infectivity to alternative hosts by the casual agent(s). All the species of Nicotiana tested were infected. All the hosts were restricted to the solanaceae. The symptoms, transmission, and host range of this disease were identical to those of tobacco bushy top disease in Zimbabwe (1). Using umbravirus-specific primers (3), a 550-bp DNA fragment was amplified by reverse transcription-polymerase chain reaction (RT-PCR) from diseased tobacco, whose sequence (GenBank Accession No. AF402620) indicated the occurrence of an umbravirus. The results coincided with the taxonomic status of Tobacco bushy top virus, one of the causal agents of tobacco bushy top disease (1), a tentative species of the genus Umbravirus (2). To our knowledge, this is the first report of tobacco bushy top disease in China and the first report of a large outbreak of the disease outside sub-Saharan Africa.

References: (1) L. F. Gates. Ann. Appl. Biol. 50:169, 1962. (2) F. A. Murphy. et al. Page 388 in: Virus Taxonomy: Sixth Report of the International Committee on Taxonomy of Viruses, Page 388, 1995. (3) P. Vercruysse et al. J. Virol. Methods 88:153, 2000.
First Report of Dieback Caused by Verticillium dahliae on Blighia sapida in the United States
Authors: McMillan R. T. , Graves W. R. , Wood T. F. , Leahy R. M.
Published: May 2007

Mature akee trees, Blighia sapida K. Koenig, in a local south Florida commercial orchard had wilt and dieback symptoms during spring 1999. A fungus isolated from the gray xylem root tissue on V8 agar was identified as Verticillium dahliae Klebahn at the Division of Plant Industry of the Florida Department of Agriculture and Consumer Services. Twenty akee seedlings were transplanted into 3.85-liter plastic pots and grown in a greenhouse at a daytime temperature of 28°C and nighttime temperature of 23°C. When plants were approximately 25 cm high, a 15-cm knife was used to sever roots in the four quadrants of each pot. Inoculum was made from a 2-week-old culture of V. dahliae on V8 agar and blended with 160 ml of sterile water, and 15 ml of this slurry was poured into the disturbed soil of each of 10 treated plants. A plate of uninoculated V8 agar was applied, as above, to 10 control plants. Plants were kept in the greenhouse. After 6 weeks, inoculated plants showed symptoms of leaf wilt, dieback and plant death. No symptoms were seen on control plants. V. dahliae was isolated directly from the gray vascular tissue of inoculated plants. The inoculation experiment was repeated three times, fulfilling Koch's postulates. To our knowledge, this is the first report of Verticillium dieback on B. sapida in the United States.
Variation in Aggressiveness Among Isolates of Cercospora from Maize as a Potential Cause of Genotype-Environment Interaction in Gray Leaf Spot Trials
Authors: Carson M. L. , Goodman M. M. , Williamson S. M.
Published: May 2007

The use of genetically resistant maize hybrids is the preferred means of control of gray leaf spot, caused by Cercospora zeae-maydis. One problem faced by maize breeders attempting to breed for resistance to gray leaf spot is the high degree of genotype-environment interactions observed in disease trials. In North Carolina gray leaf spot trials conducted at four locations in the western part of the state, we found consistent hybrid-location interactions over the 1995 and 1996 growing seasons. Isolates of C. zeae-maydis from those test locations were evaluated on the same hybrids used in the multilocation testing at a location in central North Carolina that does not have a history of gray leaf spot. The hybrid-isolate interactions observed in the isolate trial mirrored the hybrid-location effects seen in the multilocation testing. Most of the interactions arose from changes in the magnitude of differences between hybrids when inoculated with the isolates rather than from any change in hybrid ranking. Analysis of internal transcribed spacer-restriction fragment length polymorphisms (RFLPs) and mitochondrial rDNA RFLPs of those isolates and others revealed that both type I and type II sibling species of C. zeae-maydis, as well as C. sorghi var. maydis, are isolated from typical gray leaf spot lesions. Breeders should use the most aggressive isolates of C. zeae-maydis to maximize discrimination between genotypes in gray leaf spot trials.
Serological Studies Using Polyclonal Antisera Prepared Against the Viral Coat Protein of Four Begomoviruses Expressed in Escherichia coli
Authors: Abouzid A. M. , Freitas-Astua J. , Purcifull D. E. , Polston J. E. , Beckham K. A. , Crawford W. E. , Petersen M. A. , Peyser B. , Patte C. , Hiebert E.
Published: May 2007

Polyclonal rabbit antisera were produced to the coat protein of Bean golden mosaic virus Brazil isolate (BGMV), Cabbage leaf curl virus (CabLCV), Tomato yellow leaf curl virus (TYLCV), and Tomato mottle virus (ToMoV), all expressed in Escherichia coli by the pETh expression vector. The expressed coat protein of each virus was purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis for use as an immunogen. The antisera to BGMV, CabLCV, TYLCV, and ToMoV reacted in indirect (plate-trapping) enzyme-linked immunosorbent assay (ELISA) with extracts from begomovirus-infected tissue. The antisera to BGMV, CabLCV, TYLCV, and ToMoV also reacted specifically with the test begomovirus antigens in leaf imprint blots and Western blots. The CabLCV and TYLCV antisera were used to detect Bean golden yellow mosaic virus antigens by immunogold labeling of thin sections of infected bean tissues. In tissue blot immunoassays, the TYLCV antiserum reacted well with TYLCV antigens but not with ToMoV antigens, while CabLCV antiserum reacted well with ToMoV antigens and weakly with TYLCV antigens. The results indicate that polyclonal antisera prepared to expressed begomovirus coat proteins were useful for the detection of begomoviruses in an array of assays.
Effect of Bt-Corn Hybrids on Deoxynivalenol Content in Grain at Harvest
Authors: Schaafsma A. W. , Hooker D. C. , Baute T. S. , Illincic-Tamburic L.
Published: May 2007

Concentrations of the mycotoxins deoxynivalenol (DON) and fumonisin B1 in grain were compared among Bt-transformed corn hybrids and their non-Bt isolines on 102 commercial corn fields across Ontario from 1996 to 1999. Intensities of naturally occurring populations of Ostrinia nubilalis were assessed from tunneling measurements in the stalks of non-Bt isolines in 1996 and 1997. Mean concentrations of fumonisin B1 across hybrids were <0.25 μg g-1 in every year of the study. Relationships between the concentration of fumonisin B1 and intensity of O. nubilalis or with the use of Bt corn hybrids could not be determined because the concentrations of fumonisin B1 were below the lower limit of detection in most fields (<0.1 μg g-1). However, DON was more prevalent with mean concentrations across fields from 0.42 μg g-1 in 1997 to 1.12 μg g-1 in 1999. The effect of Bt hybrids on reducing concentrations of DON was mainly dependent on the intensity of O. nubilalis in each field. Where a high intensity (stalk injury) of O. nubilalis was observed (>4 cm of tunnel per stalk in the non-Bt), the use of Bt hybrids reduced concentrations of DON by an average of 59% from concentrations in the non-Bt isoline. Where the intensity of O. nubilalis was low (<4 cm of tunneling per stalk), concentrations of DON were not different among Bt and non-Bt hybrids. Concentrations of DON were low and not different between events Bt11 and 176 among Bt hybrids. A quadratic relationship was developed showing that the concentration of DON increased with intensity of O. nubilalis feeding. This study cautiously supports the use of Bt corn to reduce the risk of high concentrations of DON at harvest in Ontario.
Erigeron Witches'-Broom Phytoplasma in Brazil Represents New Subgroup VII-B in 16S rRNA Gene Group VII, the Ash Yellows Phytoplasma Group
Authors: Barros Thereza S. L. , Davis Robert E. , Resende Renato O. , Dally Ellen L.
Published: May 2007

A previously undescribed phytoplasma, Erigeron witches'-broom phytoplasma, was detected in diseased plants of Erigeron sp. and Catharanthus roseus exhibiting symptoms of witches'-broom and chlorosis in the state of São Paulo, Brazil. On the basis of restriction fragment length polymorphism (RFLP) analysis of 16S rDNA amplified in the polymerase chain reaction (PCR), Erigeron witches'-broom phytoplasma was classified in group 16SrVII (ash yellows phytoplasma group), new subgroup VII-B. Phylogenetic analysis of 16S rDNA sequences indicated that this phytoplasma represents a new lineage that is distinct from that of described strains of ash yellows phytoplasma. Erigeron witches'-broom phytoplasma is the first member of the ash yellows phytoplasma group to be recorded in Brazil.
Fungal Species Composition in Maize Stalks in Relation to European Corn Borer Injury and Transgenic Insect Protection
Authors: Gatch E. W. , Munkvold G. P.
Published: May 2007

The maize stalk rot complex is comprised of several fungal pathogens, including Gibberella zeae, Colletotrichum graminicola, Stenocarpella maydis, and several members of the genus Fusarium. The European corn borer (ECB) (Ostrinia nubilalis) can contribute to stalk rot development by creating entry wounds and by serving as a vector of some stalk rot pathogens, particularly Fusarium verticillioides. Transgenic insect protection of maize hybrids with insecticidal proteins derived from Bacillus thuringiensis greatly reduces ECB injury and may therefore alter the species composition and diversity of the stalk rot complex. Field experiments were conducted in 1998, 1999, and 2000 to compare the species composition and diversity of fungi infecting stalks of Bt and non-Bt maize hybrids. Hybrids representing five Bt types (or “events”) and their near-isogenic non-Bt counterparts were subjected to manual and natural infestations with ECB larvae. Stalk tissue samples were cultured to determine fungal species composition. At least one species was isolated from nearly every stalk and from both diseased and symptomless tissues. G. zeae was the most common species in 1998 and 1999, but C. graminicola was most common in 2000. The mean proportions of stalks infected with F. verticillioides, F. proliferatum, and F. subglutinans were significantly lower in Bt hybrids than in non-Bt hybrids in 2 of the 3 years. Conversely, the mean proportion of stalks infected with G. zeae was higher in some Bt hybrids than their non-Bt counterparts in two of the three years. F. verticillioides was more likely to be isolated from ECB-injured tissue, whereas G. zeae and C. graminicola were more likely to be isolated from tissue not associated with ECB injury. The overall species diversity of the stalk rot complex was lower in some Bt hybrids compared with their non-Bt counterparts in 1998 and 1999. ECB activity appeared to alter fungal species composition in stalks, reflecting the association between ECB injury and specific stalk rot pathogens, particularly F. verticillioides. The species composition of fungi infecting stalks of Bt hybrids differed from that of non-Bt hybrids, but the implications of this result are not yet clear.
Histology of Sweet Orange Stem Pitting Caused by an Australian Isolate of Citrus tristeza virus
Authors: Brlansky R. H. , Howd D. S. , Broadbent P. , Damsteegt V. D.
Published: May 2007

Some strains of the Citrus tristeza virus (CTV) cause stem pitting in sweet orange (Citrus sinensis (L.) Osbeck). This abnormality causes tree decline and reduction in fruit size and yield of affected citrus trees. Stem-pitting symptoms can occur on trunks, on all sizes of limbs, and on the twigs where fruit are produced. Variously sized pits or grooves in the wood often contain a yellow gum. Irregular growth of the phloem occurs in the area of these xylem pits. The histology of stem pitting caused by an Australian CTV isolate was studied in sweet orange using light and electron microscopy. Using scanning electron microscopy, details of the wood pits containing the gumming material were revealed. In thin sections of bark tissue, outgrowths of the phloem tissue were found at various intervals that corresponded to the pits in the wood. Higher numbers of viral inclusions were detected in the phloem outgrowths than were present in the other sieve elements.
Pythium spp. Infecting Hydroponically Grown Lettuce in South Africa
Authors: Labuschagne N. , Gull C. , Wehner F. C. , Botha W. J.
Published: May 2007

Root rot and wilting of lettuce (Lactuca sativa L. var. capitata L.) commonly occur in hydroponic systems in South Africa. Plants showing stunted growth, wilt, and root rot were collected at two commercial hydroponic systems in Gauteng Province, and root segments were plated on a Pythium selective medium (1). P. irregulare and three species groups without oogonia (F, HS, and T) were identified (2). Pythium groups F, HS, and T, and P. irregulare were represented by 63, 6, 5, and 26% of the isolates, repectively. Koch's postulates were confirmed in two greenhouse experiments by inoculating 4-week-old lettuce cv. Lutetia seedlings grown in aerated nutrient solution at 21°C. Two V8 juice agar cultures of an isolate of each species or species group were blended in 500 ml of sterile water, and 166 ml of suspension was added to the nutrient solution in each of three 5-liter receptacles containing four lettuce seedlings. Control plants received sterile V8 juice agar suspension. After 4 weeks, all Pythium isolates caused root rot and reduced fresh plant weight significantly, although no wilting occurred. Symptoms were more severe with P. irregulare and Pythium group HS than with groups F and T. Compared to the control, P. irregulare reduced fresh root and shoot weight of plants by 51 and 38%, Pythium group HS by 41 and 33%, Pythium group T by 29 and 26%, and Pythium group F by 30 and 24%, respectively.

References: (1) W. J. Botha and R. L. J. Coetzer. S. Afr. J. Bot. 62:196, 1996. (2) M. W. Dick. Keys to Pythium. University of Reading Press, Reading UK, 1990.
First Report of Leaf Rust of Southern High-Bush Blueberry Caused by Pucciniastrum vaccinii in Southwestern Spain
Authors: Barrau C. , de los Santos B. , Romero F.
Published: May 2007

Leaf rust was first observed in 1997 on southern high-bush blueberry (Vaccinium corymbosum L.) cvs. Sharpblue, Gulfcoast, and Misty, in two production fields in Huelva Province of Andalucía, in southwestern Spain. Depending on environmental conditions, these cultivars may remain evergreen in this region. In early spring, when the temperature reaches 20°C, typical yellowish-orange pustules first appear on the abaxial side of older leaves and later on new leaves. Leaf lesions began as chlorotic dots and developed into necrotic spots. As much as 85% of the fruits on symptomatic bushes showed pustules on the scar area. Multiple infection cycles were possible during the growing season as urediniospores reinfect leaves at the end of summer. Disease was considered of minor importance, but defoliation occurred when spotting was severe. Urediniospores were yellowish-orange, abovoid to elliptical (15 to 26 × 10 to 20 μm), with a thick, slightly roughened wall and a central pore. Telia formed in the lower epidermis and were smooth and brown. Teliospores (7 to 10 × 12 to 15 μm) were sessile, oblong to columnar, with two or more cross walls. Urediniospore and teliospore dimensions and morphology agree with the description of P. vaccinii, (G. Wint.) (1). A pathogenicity test was carried out with 2-year-old ‘Sharpblue’ and ‘Star’ plants. Expanded leaves were sprayed with freshly collected urediniospores suspended in a 0.05% solution of Tween 20 in water; plants were covered with plastic bags for 48 h and held in a chamber at 20 to 25°C in the shade. After 10 days, yellowish-orange pustules, similar to the original symptoms, developed on 80% of inoculated leaves of ‘Sharpblue’, while ‘Star’ plants remained symptomless. Leaf rust has not been reported on Ericaceae in Spain. The evergreen state of some southern high-bush cultivars in this area could allow the pathogen to overwinter as urediniospores. To our knowledge, this is the first report of P. vaccinii on blueberry plants in Spain.

Reference: (1) P. R. Bristow and A. W. Stretch. Pages 20–22 in: Compendium of Blueberry and Cranberry Diseases. F. L. Caruso and D. C. Ramsdell, eds. American Phytopathological Society, St. Paul, MN, 1995.
Botrytis porri in Onion Seed Crops and Onion Seed
Authors: du Toit L. J. , Derie M. L. , Hsiang T. , Pelter G. Q.
Published: May 2007

Nine fields direct-seeded with onion (Allium cepa L.) were surveyed in central Washington in the spring and summer of 2001 for Botrytis species associated with onion seed crops produced in this semiarid region. Forty plants were sampled from each field in a ‘W’ pattern in April, and 20 plants were similarly sampled from each field in June and July. Each plant was placed in a separate plastic bag, stored at 4 ± 2°C for 3 to 5 weeks, sliced lengthwise using a knife sterilized with 70% ethyl alcohol, incubated in a moist chamber for 5 days, and examined under a dissecting microscope. Fungal growth resembling Botrytis spp. was transferred to acidified potato dextrose agar (PDA) for species identification based on colony morphology, rate of growth, and spore and sclerotium characteristics (3). Cultures were incubated on a laboratory bench at 24 ± 4°C with 8 to 16 h of daylight. A species resembling B. porri (3) was detected in 3 fields in April at an incidence ranging from 3 to 28%, and in 2 of the same 3 fields in each of June and July at incidences ranging from 5 to 10%. Infected plants were asymptomatic at the time of sampling. The isolates formed brown, cerebriform sclerotia and sporulated sparsely. Subsamples of seed harvested from each field were assayed for Botrytis spp. To detect internal infection, 400 seeds from each of the nine fields were soaked in 0.525% NaOCl for 60 s, triple-rinsed in sterile deionized water, air dried, placed on a selective agar medium (2) with 20 seed per 9-cm-diameter petri plate, and incubated at 24°C (12 h day/night) for 14 days. Seeds were examined 5, 10, and 14 days after plating, and fungi resembling Botrytis spp. were transferred to acidified PDA for species determination. Isolates resembling B. porri were detected in 0.75% of seed from two of the three fields in which this species was isolated from plant samples. The internal transcribed spacer 1 region of ribosomal DNA of four isolates of the putative B. porri (two from plant samples and two from seed) were sequenced, and all four sequences matched that of B. porri registered in GenBank (Accession No. Z99666) most closely. Botrytis porri is a pathogen of garlic (A. sativum L.), leek (A. porrum L.), and wild garlic (A. vineale L.), but can infect onion and shallot (A. ascalonicum L.) when inoculated on these hosts (1). To our knowledge, this is the first report of natural infection of onion by B. porri, and the first report of seedborne B. porri on onion.

References: (1) W. R. Jarvis. Pathology. Page 62 in: Botryotinia and Botrytis Species: Taxonomy, Physiology, and Pathogenicity. Canada Department of Agriculture, Monograph No. 15, 1977. (2) G. Kritzman and D. Netzer. Phytoparasitica 6:3, 1978. (3) A. H. Presly. Plant Pathol. 34:422, 1985.
Puccinia hemerocallidis, Cause of Daylily Rust, a Newly Introduced Disease in the Americas
Authors: Hernández José R. , Palm Mary E. , Castlebury Lisa A.
Published: May 2007

A rust of daylilies was introduced recently into North and Central America. In order to confirm the identity of this rust as Puccinia hemerocallidis, numerous specimens from Costa Rica and the United States were examined morphologically and compared with specimens from China, Japan, Russia, and Taiwan. In addition, the internal transcribed spacer (ITS) region of the ribosomal DNA was sequenced from six representative fresh specimens from the Americas and Asia. We conclude that the rust introduced into the Americas is P. hemerocallidis, for which a modern description is provided with illustrations of the uredinial and telial stages.
Marker-Assisted Selection for Resistance to Black Shank Disease in Tobacco
Authors: Johnson E. S. , Wolff M. F. , Wernsman E. A. , Rufty R. C.
Published: May 2007

Bulked segregant (BSA) and random amplified polymorphic DNA (RAPD) analyses were used to identify markers linked to the dominant black shank resistance gene, Ph, from flue-cured tobacco (Nicotiana tabacum) cv. Coker 371-Gold. Sixty RAPD markers, 54 in coupling and 6 in repulsion phase linkage to Ph, were identified in a K 326-derived BC1F1 (K 326-BC1F1) doubled haploid (DH) population. Thirty RAPD markers, 26 in coupling and 4 in repulsion phase linkage to Ph, were used to screen 149 K 326-BC2F1 haploid plants. Complete linkage between the 26 coupling phase markers and Ph was confirmed by screening 149 K 326-BC2F1 DH lines produced from the haploid plants in black shank nurseries. RAPD markers OPZ-5770 in coupling and OPZ-7370 in repulsion phase linkage were used to select plants homozygous for the Ph gene for further backcrossing to the widely grown flue-cured cultivar K 326. Black shank disease nursery evaluation of 11 K 326-BC4S1 lines and their testcross hybrids to a susceptible tester confirmed linkage between Ph and OPZ-5770. The results demonstrated the efficiency of marker-assisted selection for Ph using a RAPD marker linked in coupling and repulsion. Complete linkage between 26 RAPD markers and the Ph gene was confirmed in the K 326-BC5 generation, and RAPD phenotypes were stable across generations and ploidy levels. These RAPD markers are useful in marker-assisted selection for Ph, an important black shank resistance gene in tobacco.