bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Anthracnose Fruit Rot Caused by Colletotrichum acutatum on Strawberry in Sweden
Authors: Nilsson U. , Carlson-Nilsson U. , Svedelius G.
Published: May 2007

Strawberries (Fragaria × ananassa) are the most important soft fruit crop in Sweden and most commonly grown as a perennial crop. Colletotrichum acutatum J.H. Simmond was detected on strawberries in Sweden for the first time in the autumn of 2003. Anthracnose caused by C. acutatum has previously been found on rhododendron in Sweden (2). The infected strawberry plants, cv. Kimberly, were found in a field in the northeastern part of Skåne in southern Sweden. The first plant sample was collected during September 2003, and a second sample was collected during the end of June 2004. Symptoms were seen on stolons as elliptical, black, sunken lesions and irregular black leaf spots originating from the tip. No symptoms were seen on immature green fruits. However, the farmer had observed black spots on the fruits the previous year. Immature fruits were collected in the field, surface sterilized with 70% ethanol, dipped for 1 min in 1.25% NaOCl, and thereafter rinsed in distilled water. Fruits were incubated in a moist chamber at 23°C. The first symptoms were seen as black spots after 3 days; later, salmon-colored conidial masses were produced from acervuli in the center of the lesions. The fungus was isolated on potato dextrose agar (PDA) as single-conidia cultures. Colonies were white-to-pale gray with abundant salmon-colored masses of conidia in the center of the culture. Mycelial growth rate on PDA was 7.5 to 7.9 mm per day at 21 ± 1°C. Conidia (11.0 to 16.5 × 3.9 to 5.7 μm) were cylindrical and hyaline with pointed ends, which is consistent with previous reports for C. acutatum (1). Symptoms were reproduced by artificial inoculation on ripe strawberries (cv. Elsanta). A conidia suspension was prepared from single-conidia cultures and each strawberry was sprayed with 0.5 ml of suspension (2.2 × 107 conidia per ml). The strawberries were incubated in a moist chamber at 22°C. The first typical symptoms were seen after 3 days. Single conidia were isolated from infected fruits and plated on PDA. Stolons and leaves of cv. Alice were inoculated with mycelial plugs of C. acutatum, sealed in a plastic bag for 2 days, and then placed in a greenhouse environment at 70% relative humidity and 21°C. Black, sunken lesions were found on stolons after 7 days. A sample of 300 petioles from the infected field was sent to the Central Science Laboratory, York, England that identified the pathogen as C. acutatum using enzyme-linked immunosorbent assay and plating rinse water from petioles onto selective media. With this report, anthracnose caused by C. acutatum on strawberry has now been reported from all the Nordic countries.

References: (1) B. J. Smith. Plant Dis. 74:69, 1990. (2) O. Vinnere et al. Mycol. Res. 106:60, 2002.
First Report of Bipolaris sacchari Causing Leaf Spot on Lygodium japonicum and L. microphyllum in Florida
Authors: Elliott M. L. , Rayamajhi M. B.
Published: May 2007

Lygodium japonicum (Thunb.) Sw. (Japanese climbing fern) and L. microphyllum (Cav.) R.Br. (Old World climbing fern) are invasive, noxious weeds in Florida. During 2001, L. japonicum sporelings were collected from natural sites in Hamilton, Highland, and Madison counties and transported to Broward County (Fort Lauderdale) for research use. During February 2002, leaf spots were observed on pinnules (leaflets) of these containerized plants growing in a shadehouse. A fungus with Bipolaris-like spores was isolated from affected pinnules and purified and stored for future evaluation. In early 2005, the fungus was grown on 1.5% water agar, with sterile, wheat straw pieces embedded in the agar surface, at 26°C and a 12-h photoperiod using cool-white fluorescent and Verilum full-spectrum bulbs. Conidia were 80.5 ± 14.5 μm (range 53.2 to 123.4 μm) × 15.1 ± 1.6 μm (range 12.1 to 19.4 μm), pale brown, slightly curved, narrowly ellipsoid, without a protuberant hilum, distoseptate (8 ± 1, range 6 to 10), and germinated from both polar cells. Conidiophores were septate and smooth. Conidiogenous nodes were smooth. On the basis of these characteristics, the fungus was identified as Bipolaris sacchari (E. Butler) Shoem. (1,2). Pathogenicity toward L. japonicum and L. microphyllum was determined using conidia produced on potato dextrose agar at 26°C and a 12-h photoperiod. A 1 × 106 conidia ml-1 suspension was sprayed until runoff on healthy plants grown in 450-ml containers. Control plants were sprayed with sterile water. There were four replicate plants per treatment. Plants were covered with plastic bags to maintain high humidity and placed in a growth chamber with a 12-h photoperiod at 28°C (light cycle) and 22°C (dark cycle). Bags were removed after 72 h, and small (1 to 2 mm), water-soaked spots were evident throughout the plant canopy on both Lygodium spp. Plants were incubated for three more weeks under the same photoperiod and temperatures with ˜70% relative humidity (light cycle) and ˜45% relative humidity (dark cycle), and then evaluated for disease. At least 50% of L. microphyllum pinnules and 25% of L. japonicum pinnules on each inoculated plant had small (1 to 2 mm), brown leaf spots or larger (approximately 5 mm) necrotic spots. B. sacchari was reisolated from both types of spots from both Lygodium spp.; there was no evidence of fungal sporulation on the plants. No symptoms were apparent on control plants. To our knowledge, this is the first report of B. sacchari on a non-Poaceae host in Florida.

References: (1) J. L. Alcorn. Ann. Rev. Phytopathol. 26:37, 1988. (2) A. Sivanesan. Graminicolous Species of Bipolaris, Curvularia, Dreschslera, Exserohilum and Their Teleomorphs. CAB International, Wallingford, Oxon, UK, 1987.
Two Convenient Methods to Evaluate Soybean for Resistance to Sclerotinia sclerotiorum
Authors: Chen Y. , Wang D.
Published: May 2007

Several greenhouse inoculation methods are available to evaluate soybean (Glycine max (L.) Merr.) for resistance to Sclerotinia sclerotiorum (Lib.) de Bary. Most of these methods are labor intensive and often produce inconsistent results among the tests. The objective of this research was to develop a low-cost and high-efficiency greenhouse inoculation method that can generate a consistent result. We developed a spray-mycelium method in which mycelia were cultured in liquid potato dextrose broth and homogenized before spraying on the soybean leaves. We also developed an inoculation method (the “drop-mycelium” method) in which a drop of homogenized mycelium suspension was dropped on the tips of main stems. Inoculated plants were incubated in a greenhouse chamber with 60 to 80% relative humidity. Plant mortality and area under the wilt progress curve (AUWPC) were used to measure disease severity daily from 3 to 14 days after inoculation (DAI). Eighteen soybean genotypes, including partially resistant line NKS19-90 and susceptible line Resnik, were employed in this study. The spray-mycelium method and the drop-mycelium method were compared with the cut-petiole method in the greenhouse. The three experiments were a randomized complete block design. Twenty-four plants per genotype in each experiment were inoculated at V3 growth stage in the greenhouse. Significant differences (P < 0.05) in disease ratings of plant mortality and AUWPC to Sclerotinia stem rot were found among 18 tested genotypes. The results obtained with the spray-mycelium and drop-mycelium inoculation methods were significantly (R > 0.73, P <0.01) correlated with the results obtained with the cut-petiole inoculation method for both of the plant mortality and AUWPC. Compared with the cut-petiole method, the spray-mycelium and the drop-mycelium methods used less inoculation time and are less expensive in terms of materials. Both of these new methods are low cost, efficient, and reliable and they can be valuable for large-scale evaluation of germ plasm and breeding lines for resistance to Sclerotinia stem rot in a greenhouse or other similar facilities.
Sensitivity of Brazilian Isolates of Phytophthora infestans to Commonly Used Fungicides in Tomato and Potato Crops
Authors: Reis Ailton , Ribeiro Fabiana H. S. , Maffia Luiz A. , Mizubuti Eduardo S. G.
Published: May 2007

Isolates of the US-1 and BR-1 clonal lineages of Phytophthora infestans, collected from tomato and potato fields of two main producing regions of Brazil (south and southeast), were tested for sensitivity to the systemic fungicide metalaxyl, plus the three protectant fungicides mancozeb, chlorothalonil, and cymoxanil. For metalaxyl, one agar test and two leaf-disc tests were carried out. For all tests, metalaxyl insensitive (I), intermediately insensitive (II), and sensitive (S) isolates were detected. There was no association among metalaxyl sensitivity and region, lineage, or host. In the agar test, 35.0% of 210 isolates were classified as I, 36.0% as II, and 29.0% as S. US-1 isolates were classified as 36.1% I, 30.6% II, and 33.3% S. BR-1 isolates were 33.3% I, 23.8% II, and 42.9% S. In leaf-disc test 1 (240 isolates tested), 24.3% were classified as I, 35.0% as II, and 40.7% as S. Isolates of US-1 were 21.0% I, 39.8% II, and 39.2% S, whereas BR-1 isolates were 36.0% I, 20.0% II, and 44.0% S. In leaf-disc test 2 (96 isolates tested), which was based on an effective dose for 50% sporulation inhibition (ED50), most isolates were either I (44.8%) or II (51.0%), and only three (4.2%) were S. The US-1 isolates were 46.0% I, 51.0% II, and 3.0% S. Isolates of the BR-1 lineage were 45.0% I, 52.0% II, and 3.0% S. For mancozeb, the ED50 for 53 of 59 isolates was below 1.0 μg/ml. No isolate grew on medium amended with more than 100 μg of chlorothalonil/ml and the ED50 for 38 of 50 isolates was below 1.0 μg/ml. For cymoxanil, the ED50 for all 47 isolates tested was below 1 μg/ml. There is no evidence of resistance of resistance of P. infestans to protectant fungicides commonly used in Brazil.
Biological Control of Pierce's Disease in the Vineyard with Strains ofXylella fastidiosaBenign to Grapevine
Authors: Hopkins D. L.
Published: May 2007

Naturally occurring strains of Xylella fastidiosa Wells et al. that were weakly virulent or aviru-lent to grapevine were inoculated into the lower internodes of Vitis vinifera L. cv. Carignane plants in the greenhouse and challenge inoculated with pathogenic strains 2 weeks later. Several strains provided some reduction in symptom development. Most effective in preventing or slowing the development of Pierce's disease in the greenhouse tests were a strain from sycamore and two from elderberry. In a 2-year test on ‘Himrod’ grape in the vineyard, strain Syc86-1 (from sycamore), but not strain PD-1 (from grapevine), was effective in limiting the development of Pierce's disease. In tests on new vineyard plantings of ‘Flame Seedless’ and ‘Cabernet Sauvi-gnon’, six strains of X. fastidiosa were evaluated for biological control of the natural progression of Pierce's disease. Only strain EB92-1 (from elderberry) provided good control of the disease in both Flame Seedless and Cabernet Sauvignon. Strain Syc86-1 was ineffective in these vineyard tests. Grape strain PD95-6 did lower disease severity in Flame Seedless when compared with nontreated vines, and grape strain PD91-2 delayed symptoms in Cabernet Sauvignon for 12 to 18 months. Biological control by inoculation of susceptible grapevines with benign strains of X. fastidiosa, especially strain EB92-1, appears to have the potential to control Pierce's disease in commercial vineyards in Florida and other areas where the disease occurs.
First Report of Bougainvillea spectabilis chlorotic vein-banding virus Infecting Bougainvillea Plants in Taiwan
Authors: Tsai C.-H. , Su H.-J. , Liao Y.-C. , Hung T.-H.
Published: May 2007

Bougainvillea (Bougainvillea spectabilis), native to Amazonian rainforests in South America, is an important ornamental and landscaping plant that is widely distributed in tropical and subtropical areas. A new virus disease, Bougainvillea chlorotic vein-banding, caused by a Badnavirus, Bougainvillea spectabilis chlorotic vein-banding virus (BsCVBV), was first reported in Brazil in 2001 (1) and recently discovered in Taiwan. Infected bougainvillea developed symptoms such as mottling, chlorosis, vein-banding, and stunting. Severe leaf-distortion symptoms were observed in the susceptible hybrid Taipei Red, the most popular bougainvillea cultivar in Taiwan. In electron microscopic observations, typical bacilliform virions measuring 28 × 130 to 150 nm were observed in infected bougainvillea cells. In addition, our transmission tests demonstrated that the virus could be easily transmitted among different bougainvillea cultivars by bud grafting but not by mechanical inoculation. Bougainvillea plants showed apparent symptoms 1 month after grafting. For molecular identification, viral DNA was extracted from the test plants (2), and polymerase chain reaction (PCR) was performed using the primers selected from the DNA sequences of ORF III of Sugarcane bacilliform virus (GenBank Accession No. M89923). The sequence of the forward primer was 5′-TCA AAG TTT GAT TTG AAG AGC GGG-3′ and the sequence of the reverse primer was 5′-CTT GCA TAC TGC TCC CCA TCC-3′ The primers amplified a 676-bp PCR product (GenBank Accession No. DQ103759). Nucleotide and deduced amino acid sequences were 82 and 90% identical, respectively, to the corresponding region of the Brazilian strain of BsCVBV (GenBank Accession No. AY532653). These data indicate that the bougainvillea disease occurring in Taiwan is caused by a strain of BsCVBV.

Reference: (1) C. M. Chagas et al. Virus Rev. Res. 6:153, 2001. (2) H.-J. Su et al. J. Phytopathol. 151:290, 2003.
Identification and Characterization of Pestalotiopsis spp. Causing Scab Disease of Guava, Psidium guajava, in Hawaii
Authors: Keith Lisa M. , Velasquez Maile E. , Zee Francis T.
Published: May 2007

Guava is one of the most widely grown plants in the tropics; however, it is affected by many fruit rot diseases. Fruit diseases decrease the marketability of fresh fruit and fruit for processing. A survey of scab disease was conducted at the USDA/ARS Tropical Plant Genetic Resource Management Unit in Hilo, HI, where more than 50 accessions of guava are grown. Symptoms observed were gray/light brown lesions surrounded by dark brown borders on leaves and brown, raised, corky, necrotic lesions on the exocarp of fruit which progressed as the fruits matured. Seventeen isolates from infected fruit, six isolates from lesions on leaves, and nine isolates from additional crops surrounding the guava trees were collected. The main fungi consistently isolated from symptomatic leaves and fruit were Pestalotiopsis spp. Morphology, colony characteristics, and pathogenicity of the isolates were examined and potential sources of host resistance were identified for germplasm characterization studies. Molecular methods were used to identify four Pestalotiopsis taxa (P. clavispora, P. microspora, P. sp. GJ-1, and P. disseminata) on guava in Hawaii. To our knowledge, this is the first report of traditional and molecular methods of identification and characterization being used for fungal pathogens of guava in Hawaii.
Effectiveness of an Attenuated Zucchini yellow mosaic virus Isolate for Cross-Protecting Cucumber
Authors: Kosaka Yoshitaka , Ryang Bo-Song , Kobori Takashi , Shiomi Hiroshi , Yasuhara Hisao , Kataoka Mitsunobu
Published: May 2007

To cross-protect cucumber plants from Zucchini yellow mosaic virus (ZYMV), we used cold treatment to obtain an attenuated isolate of ZYMV, designated ZYMV-2002. ZYMV-2002 was obtained from a virulent ZYMV isolate after repeated low temperature treatment at 12.5 to 15°C followed by five cycles of single-plant transfer. The isolate produced very mild or no symptoms on cucurbit plants. In addition, inoculated cucumber plants had very similar fruit productivity to healthy control plants under field conditions. During field experiments in 2002 and 2003, when other viruses were also present, protected plants significantly suppressed infection with ZYMV, progression of disease severity, and reduction of fruit yield and quality. These results demonstrate that ZYMV-2002 is a potentially useful attenuated ZYMV isolate for reducing the impact of ZYMV.
First Report of Xylella fastidiosa in Oklahoma
Authors: Olson B. R. , Dominiak J. , von Broembsen S. , Berg M. , Bextine B. R.
Published: May 2007

In Oklahoma, during the late summer of 2004, an elm tree (Ulmus americanus L.) located in the Oklahoma Botanical Gardens near Stillwater showed symptoms of marginal leaf scorch bordered by a yellow band between necrotic and green tissues, indicating possible Xylella fastidiosa infection. Three leaves from the symptomatic tree and one leaf from an asymptomatic nearby elm were sampled. DNA was extracted with the Extract-N-Amp kit (Sigma, St. Louis, MO). Samples were tested for X. fastidiosa using real-time polymerase chain reaction (PCR) with Xylella genus specific primers XfF1/XfR2 and dual-labeled TaqMan probe XfP2 (2). Infected oleander from California was used as a positive control. All three samples from symptomatic leaves and the positive control were PCR positive, and the sample from the asymptomatic tree was PCR negative. Attempts to culture an isolate of the bacteria from petioles and branch tissues on PD3 and PW, media selective for X. fastidiosa, failed. For more detailed molecular characterization of the putative pathogen, DNA from additional symptomatic petioles from the same tree was isolated using the cetyltrimethylammoniumbromide (CTAB) extraction. X. fastidiosa specific primers BBXFOUTF1 (5′-AAGCGCCTCCGTGAGTTATC-3′) and BBXFOUTR1 (5′-CCTTCACGCATATCATCACC-3′) were used to PCR amplify the gyrB gene. The amplification product was recovered after gel electrophoresis with QIAquick gel extraction kit (Qiagen, Valencia, CA) and was subjected to automated sequencing (Oklahoma State University Recombinant DNA/Protein Resource Facility). BLASTN alignment (1) of the obtained 381 bp sequence revealed 100% identity with the gyrB gene from elm (GenBank Accession No. AF534966) and mulberry (GenBank Accession No. AF534965) isolates of X. fastidiosa. During 2005, petiole samples from the tree were collected and serological diagnosis was confirmed using enzyme-linked immunosorbent assay (Agdia, Inc., Elkhart, IN). Some strains of X. fastidiosa have very wide host ranges and many of the hosts may be asymptomatic. Therefore, the economic importance and implications of the detection of X. fastidiosa in the state of Oklahoma remain to be determined. To our knowledge, this is the first report of X. fastidiosa in Oklahoma.

References: (1) S. F. Altschul et al. J. Mol. Biol. 215:403, 1990. (2) N. W. Schaad et al. Phytopathology 92:721, 2002.
First Report of Leaf Spot of Smooth Bromegrass Caused by Pithomyces chartarum in Nebraska
Authors: Eken C. , Jochum C. C. , Yuen G. Y.
Published: May 2007

Smooth bromegrass (Bromus inermis Leyss.) is the most common perennial grass species cultivated for forage in North America. During late fall of 2004, smooth bromegrass plants in Lincoln, NE were observed to have brown lesions on leaf midveins that were several centimeters long. Symptomatic leaves were surface disinfested for 1 min in 2% NaOCl and incubated at 25°C on potato dextrose agar (PDA) and water agar. The fungus, Pithomyces chartarum (Berk. & Curt) Ellis, was isolated consistently and identified on the basis of morphological characteristics (1). Colonies were effused and black on PDA. Conidiophores measured 3.5 to 8 × 1.9 to 3.9 μm and were smooth and single. Conidia (7 to 25 × 9.5 to 14 μm) were broadly ellipsoidal, pale brown to dark brown, verrucose with mainly three transverse septa and one to two longitudinal septa. Pathogenicity tests were conducted on 50-day-old plants by spraying with a conidial suspension (2.5 × 105 spores per ml). Control plants were sprayed with sterile water. All plants were kept in a moist chamber (100% relative humidity) for 3 days and then transferred to a greenhouse (25°C, >70% relative humidity, and a 12-h photoperiod). One week after spraying, elongated lesions developed on leaf midveins of inoculated plants from which P. chartarum was consistently reisolated. No symptoms were observed on control plants. While P. chartarum has been described as a saprotroph or a parasite on a wide range of plants primarily in the tropics and subtropics, including the southern United States (2), it was reported previously on B. inermis only in Canada (3). This report expands the distribution and host range of P. chartarum as a pathogen in the United States.

References: (1) M. B. Ellis. Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew, Surrey, England, 1971. (2) D. F. Farr et al. Fungal Databases, Systematic Botany and Mycology Laboratory, On-line publication. ARS, USDA, 2005. (3) J. H. Ginns. Compendium of Plant Disease and Decay Fungi in Canada 1960-1980. Res. Br. Can. Agric. Publ. 1813, 1986.
First Report of Puccinia thaliae on Canna Lily in South Africa
Authors: van Jaarsveld L. C. , Kriel W.-M. , Minnaar A.
Published: May 2007

Canna indica L., known as Indian shot or canna lily, occurs throughout the New World in tropical and subtropical areas. This upright, perennial, rhizomatous herb is a popular garden plant in South Africa because of its spectacular plant habit and growth vigor. During January 2005, canna lily leaves with rust symptoms were collected from Pietermaritzburg in the province of KwaZulu-Natal. Orange-yellow uredinia were observed primarily on the abaxial surfaces, often covering the entire leaf with coalescing pustules. Koch's postulates were completed in repeated tests with spray inoculations of blooming potted plants, urediniospores suspended in water (42 × 104 spores/ml), incubation in a dew chamber for 14 h at 20°C in the dark, and then returned to the greenhouse. Symptoms similar to those of the original collection formed 10 days postinoculation. Only the uredinial stage was observed, which was characterized by hypophyllous, yellow-brown, subepidermal, erumpent, and irregular shaped uredinia. The urediniospores were round to ovoid, orange-yellow, echinulate, and 25 to 35 × 15 to 20 μm. The pathogen was identified as Puccinia thaliae Diet. according to its description on Canna edulis Ker-Gawl. (1). Following the report of P. thaliae on C. indica in Hawaii in 1989 (2), to our knowledge, this is the first description of canna lily rust in South Africa.

References: (1) M. L. Jeeva et al. Plant Pathol. 53:261, 2004. (2) D. E. Gardner and C. S. Hodges. Pac. Sci. 43:4155, 1989.
Cellulase Activity in Isolates of Verticillium dahliae Differing in Aggressiveness
Authors: Novo M. , Pomar F. , Gayoso C. , Merino F.
Published: May 2007

Ten Verticillium dahliae isolates from different Galician locations were classified by degree of aggressiveness. High variability exists independent of locality of origin. Two isolates differing in aggressiveness were evaluated for cellulase production on several carbon sources. V. dahliae is able to degrade crystalline cellulose (Avicel) and, therefore, has the three enzymes necessary for its hydrolysis. The two isolates behaved similarly in the presence of soluble cellulose, but the most aggressive isolate had greater β-1,4-glucosidase (EC. 3.2.1.21) and endo-β-1,4-glucanase (EC. 3.2.1.4) activity. The less aggressive isolate needed more time to degrade crystalline cellulose. Cellulases may not be the determining factor for aggressiveness and symptom expression; however, they may play a role in penetration.
Studies on Maize streak virus and Maize mottle/chlorotic stunt virus in Lagos, Nigeria
Authors: Taiwo M. A. , Hughes J. d'A. , Oke K. E.
Published: May 2007

Despite the development and deployment of maize streak-resistant (SR) germ plasm, virus-induced symptoms are still commonly observed on maize in Lagos, Nigeria. Therefore, surveys were conducted between April 2001 and February 2002 to determine the identity, prevalence, and incidence of maize viruses in 18 local government areas (LGAs) in and around Lagos by visual examination and serodiagnostic screening of symptomatic plants. All 112 fields surveyed during the dry season (September to December) and 18 fields surveyed during the late dry season (December to February) had plants infected by Maize streak virus (MSV), whereas 97.1% of the 170 fields surveyed during the wet season (April to August) had plants infected by MSV. Maize mottle/chlorotic stunt virus (MMCSV) was prevalent in 99.1, 88.9, and 67.4% of the fields surveyed during the dry, late dry, and wet seasons, respectively. The incidence of MSV was higher in 16 of the LGAs. The highest incidence of MSV was 18.9%, whereas that of MMCSV was 7.4%. Serodiagnostic screening of leaf samples showing virus-induced symptoms, using antigen-coated plate enzyme-linked immunosorbent assay, indicated that 1,192/1,475 (80.8%) and 949/1,210 (78.4%) of the samples were positive for MSV and MMCSV, respectively. Vector transmission and host range studies confirmed the identity of the viruses. The results confirm the presence of MSV and MMCSV in Lagos and suggest that the use of MSV-susceptible cultivars is still widespread. Methods of ensuring effective utilization of existing SR germ plasm and controlling maize viruses in general are discussed.
Incidence, Spatial Patterns, and Associations Among Viruses in Snap Bean and Alfalfa in New York
Authors: Shah Denis A. , Dillard Helene R. , Mazumdar-Leighton Sudeshna , Gonsalves Dennis , Nault Brian A.
Published: May 2007

Recent epidemics in snap bean (Phaseolus vulgaris) characterized by virus-like symptoms prompted a survey of commercial fields for Alfalfa mosaic virus (AMV), Cucumber mosaic virus (CMV), and the Bean yellow mosaic virus (BYMV)/Clover yellow vein virus (ClYVV) complex in 2002 and 2003. Snap bean fields were either remote from or adjacent to alfalfa (Medicago sativa), a putative source of these viruses. Bean fields were sampled at the bloom stage in both years. Model-adjusted mean incidences of infection by AMV, BYMV/ClYVV, and CMV were 41.96, 6.56, and 6.69%, respectively, in alfalfa, and 6.66, 6.38, and 17.20% in snap bean. In 2002, 25.9% of snap bean plants were infected by more than one virus; <1% had more than one virus in 2003. Virus incidences did not differ between snap bean adjacent to or remote from alfalfa, but incidence of infection by AMV and BYMV/ClYVV was significantly higher in snap bean planted later in the season rather than earlier. In 2002, there was a positive association between AMV and CMV in the tendency to find both viruses in the same snap bean plant. In some years, infection by aphid-transmitted viruses can become widespread in snap bean in New York.
Southern Blight of Tall Fescue and Bluegrass Caused by Sclerotium rolfsii in Italy
Authors: Polizzi G. , Vitale A. , Castello I.
Published: May 2007

Tall fescue (Festuca arundinacea Schreb.) and Kentucky bluegrass (Poa pratensis L.) are the main turfgrass species cultivated in Sicily (southern Italy) for ready lawn (sod) to ornamental purposes. In July 2004 and May 2005, a widespread disease was noticed in two turf nurseries on the eastern side of Sicily on a ready lawn mixture of F. arundinacea cv. Safari (94%) + P. pratensis cv. Cabaret (6%). Numerous yellow, circular- and crescent-shaped patches as much as 30 to 40 cm in diameter were observed. The turf usually died around the perimeter of the patch, but the grass remained green in the center of the ring with a tuft of green grass in the center (frog eye). Affected turf was initially reddish brown and turned brown as it died. Small, round and off-white or tan seed-like structures were dispersed on mycelial strands at the outer edge of the ring in the mat at the base of grasses. The pathogen was identified as Sclerotium rolfsii Sacc. The fungus was isolated directly as aerial mycelium or sclerotia or following surface disinfection (2 min in 0.5% NaOCl) and plating diseased tissues on potato dextrose agar (PDA). Sclerotia were observed in vitro in 7-day-old cultures. Pathogenicity was tested by inoculating two com-mercial ready lawn strips (80 × 100 cm) of two healthy turfgrass species each with three isolates of the fungus. Thirty sclerotia were placed at the base of stems. Noninoculated ready lawn strips served as control. All plants were covered with plastic bags, exposed to diffused daylight for 5 days, and then maintained in a growth chamber at 25 to 28°C under fluorescent light. Disease symptoms and southern blight signs like the ones observed in the field occurred 2 weeks after inoculation. S. rolfsii was reisolated from affected tissues. Symptoms were not detected on any of the non-inoculated ready lawn strips. The disease was serious enough that chemical treatments were required for its control. Southern blight was previously detected on bermudagrass and other cool-season turfgrass genera (1).To our knowledge, this is the first report of southern blight on tall fescue and bluegrass in Italy.

Reference: (1) R. W. Smiley. Common Names of Plant Diseases. Diseases of Turfgrasses. Online publication. The American Phytopathological Society, St. Paul, MN.
Occurrence of Resistance-Breaking Isolates of Rice yellow mottle virus in West and Central Africa
Authors: Traoré Oumar , Pinel Agnès , Hébrard Eugénie , Dieudonné Gumedzoé Mawena Y. , Fargette Denis , Traoré Alfred S. , Konaté Gnissa
Published: May 2007

Rice yellow mottle virus (RYMV) is the most important rice-infecting virus in Africa. Highly resistant rice (Oryza spp.) cultivars Gigante and Tog5681 were challenged with virus isolates from five countries of the west and central African Sudano-savannah zone in order to investigate the occurrence and prevalence of resistance-breaking (RB) isolates. High resistance was overcome by 38.6% of the isolates. RB isolates could be divided into three main pathogenic groups. Isolates of the first group (17.5%) and of the second group (16.4%) were able to break down the resistance of Gigante only and of Tog5681 only, respectively. Resistance in both cultivars was overcome simultaneously by isolates of the third group (4.7%). In each group, some isolates induced symptoms, whereas plant infection by others was evidenced only by serological tests. RB isolates occurred in all five countries with varying frequencies (19 to 57%). The wide geographical distribution and high frequencies of RB isolates represent a high risk for the durability of resistance to RYMV in the Sudano-savannah zone.
Comparing Disease Forecasters for Timing Fungicide Sprays to Control Foliar Blight on Carrot
Authors: Bounds R. S. , Hausbeck M. K. , Podolsky R. H.
Published: May 2007

Alternaria dauci and Cercospora carotae cause foliar blight on carrot and can reduce yield in severely blighted fields. Historically, fungicides are applied every 7 to 14 days even though applications may be made when environmental conditions do not favor blight development. The purpose of this study was to compare a calendar-based application schedule with three disease forecasting systems for timing fungicide sprays to limit foliar blight, and included (i) an A. dauci disease forecaster, (ii) TOM-CAST, using a threshold of 15 disease severity values, and (iii) a disease forecaster developed to control C. apii on celery. Chlorothalonil was applied weekly or according to the forecasting systems to blight-susceptible ‘Cellobunch’ carrot plants in 2001 and 2002. Overall petiole health was poor ≥8.3; 10 = 100% petiole necrosis) when fungicides were not used. Although all disease forecasters maintained petiole health (≤5.3; 1 = healthy and vigorous), the TOM-CAST program had the best petiole health rating each year (≤2.8). TOM-CAST prompted 38 to 54% fewer applications than the weekly application schedule, resulting in a fungicide savings of $105 and $147/ha in 2001 and 2002, respectively, while providing similar blight control. The number of sprays also was reduced when fungicides were applied according to the A. dauci and C. apii forecasters, but acceptable blight control was not always achieved.
Reduction of Rhizoctonia Bare Patch in Wheat with Barley Rotations
Authors: Schillinger W. F. , Paulitz T. C.
Published: May 2007

Rhizoctonia bare patch caused by Rhizoctonia solani AG-8 is a major fungal root disease in no-till cropping systems. In an 8-year experiment comparing various dryland no-till cropping systems near Ritzville, WA, Rhizoctonia bare patch first appeared in year 3 and continued unabated through year 8. Crop rotation had no effect on bare patch during the first 5 years. However, from years 6 to 8, both soft white and hard white classes of spring wheat (Triticum aestivum L.) grown in a 2-year rotation with spring barley (Hordeum vulgare L.) had an average of only 7% of total land area with bare patches compared with 15% in continuous annual soft white wheat or hard white wheat (i.e., monoculture wheat). In years 6 to 8, average grain yield of both soft white wheat and hard white wheat were greater (P < 0.001) when grown in rotation with barley than in monoculture. Although both classes of wheat had less bare patch area and greater grain yield when grown in rotation with barley, monoculture hard white wheat was more severely affected by Rhizoctonia than soft white wheat. Soil water levels were higher in bare patches, indicating that roots of healthy cereals did not grow into or underneath bare patch areas. This is the first documentation of suppression of Rhizoctonia bare patch disease in low-disturbance no-till systems with rotation of cereal crops.
Quantifying the Feeding Periods Required by Corn Flea Beetles to Acquire and Transmit Pantoea stewartii
Authors: Menelas B. , Block C. C. , Esker P. D. , Nutter F. W.
Published: May 2007

The feeding periods required by corn flea beetles to acquire and transmit Pantoea stewartii were investigated in the Stewart's disease of corn pathosystem. To quantify the effect of acquisition feeding period on percentage of acquisition, field-collected corn beetles were allowed to feed for 6, 12, 24 36, 48, and 72 h on corn seedlings previously inoculated with a rifampicin- and nalidixic acid-restraint strain of P. stewartii. Acquisition of P. stewartii by corn flea beetles was considered positive if the rifampicin- and nalidixic acid-marked strain was recovered on selective media. To quantity the effect of transmission feeding period on percent transmission of P. stewartii by corn flea beetles, P. stewartii- infested corn flea beetles were allowed to feed on healthy corn seedlings for periods of 3, 6, 12, 24, 36, 48, and 72 h. After the appropriate transmission feeding period, leaf tissues surrounding the sites of feeding scars were cultured for the presence of the P. stewartii-marked strain. Transmission of P. stewartii was considered positive if the marked strain was recovered on selective media. Acquisition of P. stewartii occurred within 6 h and the percentage of corn flea beetles that had acquired P. stewartii after 72 h ranged from 68 to 94%. The change in P. stewartii acquisition by corn flea beetles (Y) with respect to acquisition feeding period (X) was best described by the Gompertz model, with R2 values ranging from 91 to 99%. The mean time for acquisition by 50% of the corn flea beetles was 36.5 ± 11.6 h. The minimum transmission feeding time required for corn flea beetles to transmit P. stewartii following a 48-h acquisition feeding period was less than 3 h. The percent transmission of P. stewartii by corn flea beetles was nearly 100% after a 48-h transmission feeding period and was 100% by 72 h. Among population growth models evaluated, the monomolecular model best described the relationship between percent transmission (Y) and transmission feeding periods (X), with R 2 values of up to 84%. However, a nonlinear form of the monomolecular model better quantified the relationship between percent transmission and transmission feeding period, because pseudo-R2 values ranged between 98.1 and 99.5%. The predicted transmission feeding time required for 50% of P. stewartii-infested corn flea beetles to transmit the pathogen was 7.6 ± 0.87 h. These results suggest that the corn flea beetle is a highly efficient vector that can quickly acquire and transmit P. stewartii, thereby requiring insecticide seed treatments and foliar insecticides that act quickly to prevent corn flea beetles from acquiring and transmitting P. stewartii to corn plants.
Identification of a 16SrII-E Phytoplasma in Calendula arvensis, Solanum nigrum, and Chenopodium spp.
Authors: Tolu G. , Botti S. , Garau R. , Prota V. A. , Sechi A. , Prota U. , Bertaccini A.
Published: May 2007

Epidemiological surveys were performed in Northern Sardinia (Italy) in a 10-year-old vineyard affected by “Bois noir” disease. Samples collected between May and October 2003 from chlorotic and stunted weeds belonging to 14 different taxonomic groups were indexed molecularly for detection of phytoplasmas. Nested polymerase chain reaction (PCR) assays using primers specific for the phytoplasma 16SrDNA gene showed three of six Calendula arvensis, one of two Solanum nigrum, and one of seven Chenopodium spp. assayed positive. Restriction fragment length polymorphism analyses and sequencing of amplified 16SrDNA fragments identified a putative phytoplasma in the ribosomal subgroup 16SrII-E. Further characterization of the rps3 gene, coding a ribosomal protein, confirmed the identification. However, the weeds and leafhop-per species collected in the vineyard tested negative by PCR assays for the Stolbur phytoplasma, the causal agent of “Bois noir”. This is the first report of a phytoplasma of the 16SrII-E subgroup infecting C. arvensis, S. nigrum, and Chenopodium spp.
Root-Knot Nematode Resistance in Pearl Millet From West and East Africa
Authors: Timper P. , Wilson J. P.
Published: May 2007

Resistance to Meloidogyne incognita is important to provide stability to pearl millet production and to reduce nematode populations that can damage crops grown in rotation with pearl millet. The objectives of this study were to determine whether resistance to M. incognita exists in pearl millet from West and East Africa, and to determine if heterogeneity for resistance exists within selected cultivars. Resistance was assessed as nematode egg production per gram of root in greenhouse trials. Seventeen pearl millet cultivars of diverse origin were evaluated as bulk (S0) populations. All African cultivars expressed some level of resistance. P3Kollo was among the least resistant of the African cultivars, Zongo and Gwagwa were intermediate, and SoSat-C88 was among the most resistant. Thirty selfed (S1) progeny selections from SoSat-C88, Gwagwa, Zongo, and P3Kollo were evaluated for heterogeneity of resistance within cultivar. Reactions were verified in 13 S2 progeny of each of the four cultivars. In S1 evaluations, each of these cultivars was heterogeneous for resistance. Progeny reaction varied from highly resistant to highly susceptible. Patterns of apparent segregation of resistance varied among the four cultivars. Discreet resistant and susceptible phenotypes were identified in Zongo progeny, and it was estimated that two dominant genes for resistance segregated in this cultivar. Averaged across progenies, egg production on the four cultivars was less (P ≤ 0.001) than on the susceptible hybrid HGM-100, but was not different from resistant hybrid TifGrain 102. Reproduction of M. incognita on the S2 progeny tended to confirm the results from inoculations of S1 progeny. Heritability of nematode reproduction (standardized as the ratio of the value to HGM-100) determined by parent-offspring regression was 0.54. Realized heritability determined by divergent selection was 0.87.
Characterization of Phytophthora capsici Associated with Roots of Weeds on Florida Vegetable Farms
Authors: French-Monar Ronald D. , Jones Jeffrey B. , Roberts Pamela D.
Published: May 2007

Weeds were sampled in commercial vegetable fields in Palm Beach County, FL in August 2001, December 2001, and March 2002 for the presence of Phytophthora capsici. Fields sampled had a recent history of this plant pathogen. P. capsici was successfully isolated from the roots of six of 42 Carolina geranium (Geranium carolinianum) plants, four of 28 American black nightshade (Solanum americanum) plants, and two of 130 common purslane (Portulaca oleracea) plants. All but one of the 12 isolates were of the A1 mating type. All 12 isolates were resistant to mefenoxam, although at different levels. All but one isolate were strongly pathogenic on pepper seedlings. When two or three isolates recovered from each weed were inoculated onto the roots of their weed host of origin, P. capsici was recovered from the roots. Isolates of P. capsici were tested on four other solanaceous weeds of importance or potential importance to agricultural fields in Florida: Solanum nigrum, S. ptycanthum, S. carolinense, and S. capsicoides. Recovery of P. capsici from roots varied with weed species and isolate tested. P. capsici caused disease mortality on S. nigrum, and no reisolation of P. capsici was possible with S. capsicoides. This is the first report of S. americanum and G. carolinianum being alternative hosts for P. capsici under field conditions. This study also validated P. oleracea as an alternative host. In Florida, and perhaps elsewhere, weeds may contribute to pathogen survival in the absence of a host crop or when propagules may not readily survive in soil or plant debris.
First Report of Tomato chlorosis virus in Lebanon
Authors: Abou-Jawdah Y. , El Mohtar C. , Atamian H. , Sobh H.
Published: May 2007

Tomato seedlings showing leaf curl and yellowing symptoms characteristic of Tomato yellow leaf curl virus (TYLCV) were brought to the university laboratory from a commercial tomato greenhouse located in the Damour coastal area, south of Beirut, Lebanon. They were first tested using polymerase chain reaction (PCR) to ascertain their infection by TYLCV and then they were used in a trial to evaluate resistance of three local accessions of tomato to TYLCV, the major limiting factor to tomato production in Lebanon. Whiteflies (Bemisia tabaci), reared on broccoli for several generations, were allowed an acquisition access period of 48 h on tomato seedlings putatively infected with TYLCV and then were transferred to test plants at an average of 40 to 60 whiteflies per tomato seedling at the first-true leaf stage for an inoculation feeding period of 3 days. All treatments were conducted in insect-proof cages. Clear TYLCV symptoms were observed on the three local tomato accessions approximately 3 weeks after inoculation. However, 7 to 8 weeks after inoculation, many plants showed yellowing symptoms on the lower leaves that were not observed in previous experiments. Infections by Tomato chlorosis virus (ToCV) and/or Tomato infectious chlorosis virus (TICV), two criniviruses belonging to the family Closteroviridae, were suspected. Diagnostic tests using PCR for TYLCV detection (1) and reverse transcription (RT)-PCR for detection of ToCV (2) or TICV (3) showed that some tomato plants had a mixed infection with TYLCV and ToCV. None of the tested samples was positive for TICV. The RT-PCR amplicons (434 nt) obtained with the ToCV specific primers were cloned into pGEM-T easy vector. Sequence analysis of one clone revealed more than 99% nucleotide identity with the heat shock protein homologue (HSP70h) of ToCV isolates from the United States (GenBank Accession Nos. AY903448, AF024630, and AY444872) and 100% amino acid identity to ToCV isolates from Italy and Portugal (GenBank Accession Nos. AY048854.1 and AF234029.1). The sequence was submitted to GenBank (Accession No. DQ234079). Twenty-two tomato samples were then collected from plants showing yellowing symptoms on their lower leaves. The samples were taken from two greenhouses at the same farm in the Damour area. Six samples tested positive for ToCV using RT-PCR. To our knowledge, this is the first report of ToCV in Lebanon, but its incidence and distribution was not monitored. However, on the basis of symptoms and preliminary RT-PCR results, the disease does not appear to be widely spread in the country.

References: (1) G. H. Anfoka et al. J. Plant Pathol. 87:65, 2005. (2) D. Louro et al. Eur. J. Plant Pathol. 106:589, 2000. (3) A. M. Vaira et al. Phytoparasitica 30:290, 2002.
First Report of White Rust Caused by Albugo tragopogonis on Sunflower in Belgium
Authors: Crepel C. , Inghelbrecht S. , Bobev S. G.
Published: May 2007

Sunflower (Helianthus annuus) is widely used for cut flowers and decoration in Belgium. A serious outbreak of what was suspected to be white rust on sunflower was observed in an East Flemish nursery near the city of Ghent in August 2004. This disease has previously been reported in Europe (southwest of France) (1) and other parts of the world with losses as much as 70 to 80% (Australia, North and South America, and Africa) (2,3). In the Flemish nursery, only single diseased plants (cv. Sunrich) were found. Blister-like pustules containing sporangia were observed on infected leaves. Initially the blisters were pale green to yellow on the abaxial surface and white on the adaxial surface of the leaves. As the disease progressed, white pustules that formed on the adaxial surface of the leaves slowly turned yellow, and the blisters on the abaxial surface became yellow to orange and necrotic in the center. Finally, the pustules coalesced and the leaves withered. Stem lesions were not observed. Short, cylindrical to spherical-cuboid sporangia, recovered from the pustules on the adaxial surface of leaves, measured between 17.5 and 22.5 μm, with an average of 20.2 μm. Sporangial dimensions were similar to those of Albugo tragopogonis (Pers.) S.F. Gray (1). Inoculations were done by spraying a suspension of 1 × 105 sporangia per ml prepared by scraping pustules from naturally infected leaves. Leaves on three 2-month-old healthy plants were sprayed with this inoculum and three plants sprayed with distilled water served as controls. The plants were kept for 48 h under a humid chamber and subsequently at room temperature (20 to 25°C) on the laboratory bench. Initial symptoms of white rust were observed 12 to 14 days after inoculation. On the basis of symptoms, morphological characteristics, and pathogenicity tests, the pathogen was identified as A. tragopogonis. To our knowledge, this is the first record of A. tragopogonis on H. annuus in Belgium.

References: (1) K. G. Mukerji. Description of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, England, UK, 1976. (2) A. Pernaud and A. Perny, Phytoma 471:43, 1995. (3) P. S. van Wyk et al. Helia 22:83, 1999.