bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Red Clover Vein Mosaic Carlavirus Naturally Infecting Lentil
Authors: Larsen R. C. , Myers J. R.
Published: May 2007

Lentil (Lens culinaris Medik.) is an important legume crop grown in the dryland Pacific Northwest areas of eastern Washington and Oregon, and northern Idaho. Lentil is highly susceptible to pea enation mosaic enamovirus (PEMV) and bean leafroll luteovirus (BLRV), and infection may result in severe yield losses. Recently, lentil was also found to be infected experimentally with red clover vein mosaic carlavirus (RCVMV) (1). The virus is most commonly transmitted in the Pacific Northwest by the pea aphid (Acyrthosiphon pisum Harris) in a nonpersistent manner. In 1997, cv. Brewer lentil bait plants were planted at the Vegetable Research Farm at Oregon State University to monitor incidence of PEMV and BLRV. Many of the plants developed symptoms typical of PEMV. However, other plants exhibited severe stunting, proliferation of axillary branches, and general chlorosis or death. Bait plants were harvested in August, and 204 random samples were tested for PEMV, RCVMV, BLRV, alfalfa mosaic alfamovirus (AMV), and pea streak carlavirus (PeSV) by standard enzyme-linked immunosorbent assay (ELISA) protocols. Antiserum for RCVMV was made in the Prosser lab against an isolate from chickpea collected in Washington State (1). RCVMV was detected in 76 (34%) of the 204 samples. PEMV, AMV, BLRV, and PeSV were detected in 197 (89.5%), 23 (11.3%), 2 (0.9%), and 0 (0%) of samples, respectively. Results showed that 75/76 of the samples positive for RCVMV were also coinfected with PEMV. Plants infected with RCVMV in the greenhouse also produced mild systemic mosaic symptoms in selected hosts inoculated mechanically, including pea (Pisum sativum L.), chickpea (Cicer arietinum L.), faba bean (Vicia faba L.), and lentil. Lentil and chickpea also showed moderate to severe stunting. Chlorotic local lesions were formed on Chenopodium amaranticolor Coste & Reyn. and C. quinoa Willd. Oligonucleotide primers were designed with sequence data obtained from the Washington isolate of RCVMV (1), and identification of the virus was verified in pea and lentil by polymerase chain reaction (PCR). Primer design of RCV34V and RCV653C targeted a 619-bp fragment located in the viral coat protein gene. Plants testing positive by ELISA yielded PCR products of the expected size when visualized on agarose gels. This is the first report of natural infection of lentil by RCVMV.

Reference: (1) R. C. Larsen et al. Phytopathology 87:S56, 1997.
First Report of Cylindrocladium Black Rot (C. parasiticum) on Partridgepea and Sicklepod
Authors: Brenneman T. B. , Padgett G. B. , McDaniel R. G.
Published: May 2007

Partridgepea (Cassia fasciculata Michx.) is grown in the southeastern U.S. in food plots for game birds. In 1997, numerous dead plants were observed in a commercial planting for seed production. Perithecia of Calonectria ilicicola Boedijin & Reitsma (imperfect stage: Cylindrocladium parasiticum Crous, Wingfield & Alfenas), a serious pathogen of peanut (Arachis hypogaea L.), were found on the crown of diseased plants. Two isolates each from partridgepea and peanut were grown on potato dextrose agar for 5 weeks. Microsclerotia produced were added to a 2:1 mixture of pasteurized field soil and Pro-mix potting medium (25 microsclerotia per g of mix). Both infested and noninfested potting mixes were put in Super Cell Cone-Tainers (Stuewe & Sons, Corvallis, OR) in the greenhouse and planted to one pre-germinated seed each of either peanut or partridgepea (10 replications). Soil moisture was kept at field capacity and after 7 weeks root rot severity (0 to 4 scale with 4 = dead plant) and fresh weight of whole plants and roots were determined. Mean disease ratings for peanut were 2.1 and 2.5 with the peanut and partridgepea isolates, respectively, and 0.1 for the controls. Mean disease ratings for partridgepea were 3.2 and 3.2 with the peanut and partridgepea isolates, respectively, and 1.0 for the controls. Peanut and partridgepea plant weights were reduced by 50 and 68%, respectively, compared with controls. Reductions in root weights were similar to those for whole plants. The pathogen was consistently recovered from diseased roots. In summary, all four isolates were pathogenic to both hosts, but partridgepea was more susceptible (P ≤ 0.05) than peanut to C. parasiticum. Sicklepod (Senna obtusifolia (L.) H. Irwin & Barneby), one of the most troublesome weeds in the southeastern U.S., was previously observed to have black rot symptoms and perithecia of C. ilicicola on the crowns of diseased plants. Plants grown in soil infested with an isolate of the fungus from sicklepod exhibited typical symptoms and the pathogen was reisolated from diseased tissue. Rotation with soybean (Glycine max L.) traditionally has been the major concern for peanut production in fields with a history of Cylindrocladium black rot; however, these additional hosts also should be considered.
Influence of pH and Matric Potential on Germination of Cephalosporium gramineum Conidia
Authors: Blank Cynthia A. , Murray Timothy D.
Published: May 2007

Germination of Cephalosporium gramineum conidia in soil was up to twofold greater at -0.064 MPa than at -0.037 and -0.007 MPa when incubated at 5°C for 2 days. Soil pH from 4.7 to 7.5 did not have a significant influence on germination of conidia and the interaction between soil pH and matric potential on germination was not significant. Soil fungistasis, which was previously observed for conidia of C. gramineum, was not observed in these studies. Germination of conidia on mineral salts agar containing phosphate buffer was significantly less at pH 4.5 than at 5.5, 6.5, or 7.5 at 5°C in one of two experiments; however, pH had no influence on germination at 10 or 20°C in two experiments. Although Cephalosporium stripe is more severe under conditions of high soil moisture and low soil pH, increased germination of conidia in response to these factors does not explain the observed increase in disease.
Occurrence, Distribution, and Relative Incidence of Mosaic Viruses Infecting Field-Grown Melon in Spain
Authors: Luis-Arteaga Marisol , Alvarez José María , Alonso-Prados José Luis , Bernal Juan J. , García-Arenal Fernando , Laviña Amparo , Batlle Assumpció , Moriones Enrique
Published: May 2007

The main areas for field-grown melon (Cucumis melo) production in Spain were surveyed for the occurrence and relative incidence of cucumber mosaic virus (CMV), papaya ringspot virus-watermelon strain (PRSV-W), watermelon mosaic virus-2 (WMV-2), and zucchini yellow mosaic virus (ZYMV) during the growing seasons of 1995 and 1996. Samples from 1,152 plants showing symptoms of virus infection were collected from commercial melon fields and analyzed by enzyme-linked immunosorbent assay (ELISA). CMV and WMV-2 were the most frequently found viruses, both by the number of locations and by their incidence in each location. In contrast, PRSV-W and ZYMV were detected in fewer sites and at lower incidences. PRSV-W was not found in 1996. In 79% of the samples, only one virus was detected; 15% of the samples were doubly infected. Both the incidence of plants showing symptoms of viral infection and the relative incidence of each of the four viruses varied according to the region, while the main trends of virus distribution were similar for 1995 and 1996.
Evidence for a Third Taxonomic Subgroup of Peanut Stunt Virus from China
Authors: Zeyong Xu , Higgins Colleen M. , Kunrong Chen , Dietzgen Ralf G. , Zhongyi Zhang , Liying Yang , Xiaoping Fang
Published: May 2007

On the basis of host reactions and serology, six Chinese peanut stunt virus (PSV) strains were found to be distinct from PSV-E and PSV-W, two type strains representing distinct serological subgroups. Chinese PSV strains were characterized by infecting Chenopodium amaranticolor and C. quinoa systemically. All Chinese strains were serologically closely related to each other, but distinct from PSV-E and more distant from PSV-W. Using two PSV-specific primers designed from conserved regions of the PSV RNA3 nucleotide sequence, cDNA transcribed from RNA3 of two Chinese PSV strains, Mi and S, was amplified by PCR and cloned. The sequenced cDNA of the two PSV strains included 654 nt of the coat protein (CP) gene. The identity of the CP gene nucleotide sequence between PSV-Mi and PSV-S was 99.0%, with 99.5% amino acid identity. Identity of the CP gene nucleotide sequence was 75.6 to 77.8% between PSV-Mi and -S (the two Chinese strains) and PSV-ER and -J in PSV subgroup I; and 74.1 to 74.4% between PSV-Mi and -S, and PSV-W in subgroup II. Based on these results, we propose placing PSV Chinese strains into a new PSV subgroup III.
Plectosporium tabacinum, a Pathogen of the Invasive Aquatic Weed Hydrilla verticillata in Florida
Authors: Smither-Kopperl M. L. , Charudattan R. , Berger R. D.
Published: May 2007

Plectosporium tabacinum, the anamorph of Plectosphaerella cucumerina, was isolated in 1996 from Hydrilla verticillata (hydrilla), an invasive aquatic weed in Florida. P. tabacinum, applied as a suspension of conidia, was pathogenic to hydrilla shoots maintained in aqueous solutions in test tubes. Koch's postulates were fulfilled in several repeated experiments. Infected shoots became slightly chlorotic within 24 h after inoculation. Infected leaves remained intact and were supported by water pressure but collapsed upon removal from water. Histological studies of leaves stained with malachite green and acid fuchsin revealed fungal hyphae within plant cells. The disease developed over a range of temperatures from 15 to 30°C. At 25°C, symptoms were most severe in 5% Hoagland's solution, followed by river water, deionized water, 0.5% Hoagland's, tap water, and spring water. Disease severity increased as inoculum concentration was increased from 105 to 107 conidia ml-1. This is the first report of P. tabacinum as a pathogen of hydrilla, a fully submerged aquatic plant species.
Detection and Differentiation of Phaeoisariopsis griseola Isolates with the Polymerase Chain Reaction and Group-Specific Primers
Authors: Guzmán P. , Gepts P. , Temple S. , Mkandawire A. B. C. , Gilbertson R. L.
Published: May 2007

Specific detection of the two major groups of Phaeoisariopsis griseola(Andean and Mesoamerican) from infected common bean (Phaseolus vulgaris) leaves was achieved by amplification of different-sized DNA fragments with polymerase chain reaction (PCR) using group-specific primer pairs. These primer pairs were designed based on DNA sequences of cloned random amplified polymorphic DNA (RAPD) fragments. Using this method, P. griseola isolates from diverse geographical regions (five countries) were differentiated into the two previously established groups. Various sources of fungal tissue and DNA extraction methods were tested in order to develop a rapid PCR-based method to detect and differentiate P. griseola isolates. A simple and rapid sonication method was developed that allowed for PCR detection of P. griseola from mycelia or synnemata and conidia collected from angular leaf spot lesions on bean leaves.
Identification of Pisum sativum Germ Plasm with Resistance to Root Rot Caused by Multiple Strains of Aphanomyces euteiches
Authors: Malvick D. K. , Percich J. A.
Published: May 2007

Aphanomyces root rot is a serious disease of pea (Pisum sativum), and additional sources of resistance are needed for development of disease-resistant cultivars. Accessions (n = 123) from the P. sativum Plant Introduction (PI) collection with the highest relative levels of resistance to one strain of Aphanomyces euteiches were previously identified from among approximately 2,500 accessions evaluated. The chosen 123 accessions were evaluated in this study for resistance to root rot caused by multiple strains of this pathogen. Five strains representing different US geographical locations and pathogenicity characteristics were used to evaluate pea seedlings in a greenhouse. Disease severity (DS) and percent loss of fresh biomass (inoculated vs. non-inoculated plants) were determined 15 days after inoculation. Significant differences (P = 0.05) in levels of DS and biomass loss (BL) occurred among the accessions after inoculation individually with the five strains. The relative rank of accessions based on DS and BL varied with the strain of A. euteiches used for inoculations. The 20 accessions with the lowest DS after inoculation with each strain were identified. Based on lowest DS, two accessions were among the 20 identified with all five individual strains, and four other accessions were among the 20 identified with four of the five strains. The results suggest that the P. sativum PI collection contains useful accessions for breeding programs aimed at developing pea varieties with resistance to A. euteiches.
Cucumber Mosaic Virus on Asiatic Hybrid Lilies in India
Authors: Ram Raja , Sharma Anupama , Singh R. K. , Chauhan Daizy , Zaidi A. A.
Published: May 2007

Asiatic hybrid lilies are popular cut flowers with a range of bright colors. Of the several viruses reported from lily (2,3), cucumber mosaic virus (CMV) reduces flower quality and yield (1). Classical symptoms of CMV were observed in recently introduced plants of Asiatic hybrid lilies in Kangra Valley, Himachal Pradesh. The symptoms were mild leaf mosaic, ring spot, transient vein yellowing, occasionally with growth deformation, and flower breaking. Leaf samples from cvs. MonteNegro, Yellow Present, Apeldoorn, Toscana, Connecticut King, and Adelina were collected randomly on the basis of symptom expression. Viral-associated double-stranded RNA (dsRNA) analysis was used to analyze tissue from symptomatic and asymptomatic plants for evidence of a possible cucumovirus. dsRNA analysis resulted in a banding profile typical of that seen with cucumoviruses. There was no evidence of dsRNA in the asymptomatic tissue. Presence of CMV in the symptomatic plants was also confirmed by enzyme-linked immunosorbent assay with antiserum from Agdia (Elkhart, IN). Virus from symptomatic tissues was purified and 30 nm polyhedral, viruslike particles were observed that were subsequently tested for CMV with counter immunoelectrophoresis with antibodies of CMV-C and CMV-D (antibodies obtained from H. A. Scott, University of Arkansas) and ATCC CMV antisera PVAS 242-A. Our isolate differs from other prevalent CMV isolates of Kangra Valley, having a narrow host range and not being readily sap transmissible. However, this isolate is normally transmitted to progeny bulblets. Lack of fallow periods, continuous cropping of other CMV-susceptible bulbous crops, and occasional sprouting of uncollected lily bulblets enhance inoculum build-up. Planting of CMV-tested lilies is recommended to avoid disease losses and to reduce viral inoculum floriculture fields. This is the first report of CMV in Asiatic hybrid lilies in India.

References: (1) M. P. Benettii and L. Tomassoli. Acta Hortic. 234:465, 1988. (2) P. Brierley. Phytopathology 30:250, 1940. (3) L. Tomassoli and M. P. Benettii. Adv. Hortic. Sci. 2:117, 1988.
A Serious Outbreak of Race 6 of Xanthomonas campestris pv. vesicatoria on Pepper in Southern Florida
Authors: Pernezny K. , Collins J. , Stall R. E. , Shuler K. , Datnoff L. E.
Published: May 2007

In the 1997-1998 winter vegetable season, a widespread and serious outbreak of bacterial spot occurred on pepper in commercial fields throughout southern Florida. This was the first serious epidemic of bacterial spot on pepper in southern Florida since the 1993-1994 season. Cultivars affected included those with resistance to races 1–3 of X. campestris pv. vesicatoria, commonly found in previous Florida surveys (1). Field sampling designs, isolation methods, and pathogen identification were carried out as previously described (1). Twenty-seven fields were sampled in Palm Beach, St. Lucie, Martin, Broward, and Collier counties. The race of each strain was determined by infiltration of 3.0 × 108 CFU per ml of sterile tap water suspension into Early Calwonder and three near-isogenic lines of Early Calwonder with genes for vertical resistance to specific races of the pathogen. Test plants were maintained in the greenhouse and observed for hypersensitive and disease reactions over several days. Of a total of 244 X. campestris pv. vesicatoria strains collected, 73.4% were identified as race 6 and 10.2% as race 4. Irrespective of the presence of resistance genes in cultivars sampled, race 6 (eastern Florida) and race 4 (southwestern Florida) predominated in this study. Copper tolerance was widespread among X. campestris pv. vesicatoria strains of all races, with 91% of the strains showing tolerance to 250 g per ml of CuSO4 · 5H2O incorporated into 0.5% (wt/vol) glucose-nutrient agar. Selection pressure resulting from widespread planting of race 1, 2, 3-resistant cultivars may have contributed to this outbreak. High disease pressure also may be related to the unusually wet winter. Rainfall accumulation from December 1997 through March 1998 was 25.6 cm above normal.

Reference: (1) K. Pohronezny et al. Plant Dis. 76:118, 1992.
Use of Partial Host Resistance in the Management of Bacterial Blight of Rice
Authors: Adhikari Tika B. , Shrestha Anil , Basnyat Ram Chandra , Mew T. W.
Published: May 2007

The progress of bacterial blight epidemics, caused by Xanthomonas oryzae pv. oryzae, varies with environment. The irrigated lowland rice production environment in central Terai (plain) is less conducive to the disease than the irrigated lowland rice production environment in eastern Terai in Nepal. The effect of partial resistance on bacterial blight was studied in central Terai during the wet seasons of 1994, 1995, and 1996. Three partially resistant rice cultivars, Sabitri, Laxmi, and IR54 (possessing the Xa4 gene), and susceptible check IR24 were included in this study. Analysis of pooled data from the 3 years of experiments indicated that rice cultivars differed in resistance based on three epidemiological parameters: disease severity (DS), area under the disease progress curve (AUDPC), and rate of disease increase (r). Estimates of DS, AUDPC, and r were reduced and yield loss was negligible in the partially resistant cultivar Laxmi compared with the susceptible check IR24. IR54, which has partial resistance to X. oryzae pv. oryzae, also showed low DS, AUDPC, and r, which prevented yield loss due to bacterial blight. The locally adapted cultivar Sabitri showed intermediate estimates of DS, AUDPC, r, and yield loss. Earlier and more severe disease developed in the susceptible check IR24, resulting in a yield loss of 22%. Yield losses were mainly due to reductions in number of tillers, number of grains per panicle, and 1,000-grain weight. These data indicate that the use of rice cultivars with high levels of partial resistance will be an effective tool for the management of bacterial blight in central Terai and similar environments in Nepal.
Natural Infection of Sorghum by Foxtail Mosaic Virus in Kansas
Authors: Seifers Dallas L. , Harvey Tom L. , Haber Steve , She Y. M. , Chernushevich Igor , Ens Werner , Standing Kenneth G.
Published: May 2007

Sorghum (Sorghum bicolor) was infected by a mechanically transmissible, flexuous, rod-shaped virus. Antiserum made against the purified virus reacted specifically in enzyme-linked immunosorbent assay to the virus and to the potexvirus foxtail mosaic virus (FoMV), indicating that the sorghum virus was an isolate of FoMV. Comparison of the sorghum isolate (H93) to FoMV PV 139 showed that H93 differed biologically by causing severe symptoms in sorghum, not readily infecting certain barley lines, and causing only faint symptoms in barley. At the molecular level, the capsid of H93 had a mass of 23.9 kDa and 217 amino acid residues compared with 23.7 kDa and 215 residues previously reported for the nucleic acid sequence of FoMV. The amino acid sequences of the two viruses were greater than 96% identical. They varied by having four substitutions, one deletion, and three insertions between residues 66 and 67. This is the first report of natural infection of sorghum by FoMV, thus extending its host range among cereal crops.
Sexually Fertile Magnaporthe grisea Rice Pathogens in Thailand
Authors: Mekwatanakarn Poonsak , Kositratana Wichai , Phromraksa Tawatchai , Zeigler R. S.
Published: May 2007

Sexual fertility and mating type distribution of Magnaporthe grisea field isolates collected in Thailand were analyzed from sites previously found to harbor diverse populations of the pathogen. Three hundred forty-one single conidium isolates of M. grisea collected from five sites in north, northeast, and central Thailand were evaluated for in vitro sexual fertility and mating type by pairing with strains of known mating type. Most isolates (67%) were infertile when crossed with the hermaphrodite tester strains; but fertile isolates of each mating type that yielded viable ascospores were detected in all sites from the northeastern and northern regions. MAT1-2 predominated over MAT1-1 in bioassay mating type. Male fertility (female sterility) predominated in fertile MAT1-1 (50 to 75%) and MAT1-2 (50 to 85%) isolates from all locations in Thailand; however, hermaphroditic and/or female fertile isolates were also detected in all but one site. Fertility, as determined by perithecia density, was low (<10 perithecia cm-2) for most isolates, although a few produced in excess of 20 perithecia cm-2.
Identification of Resistance to Rhizoctonia Limb Rot in a Core Collection of Peanut Germ Plasm
Authors: Franke M. D. , Brenneman T. B. , Holbrook C. C.
Published: May 2007

Diseases caused by Rhizoctonia solani lead to significant reductions in peanut yields and quality throughout the world. A subset of accessions from the peanut germ plasm core collection plus the commercial cultivars Florunner, Southern Runner, Georgia Browne, and Georgia Green were evaluated for resistance to limb and seedling hypocotyl infections caused by R. solani. Georgia Green and core accessions 95 (PI 497351), 197 (PI 331326), 208 (PI 274193), 244 (PI 343361), 246 (PI 343398), and 524 (PI 288178) had levels of resistance comparable to Georgia Browne, the only commercial cultivar reported to have partial resistance to Rhizoctonia limb rot. Eleven core accessions, representing the full range of disease expression, and the commercial cultivars were evaluated in growth chambers to quantify their susceptibility to seedling hypocotyl infections and to determine if evaluating seedlings could serve as a primary screening method to identify potential sources of limb rot resistance. The most resistant core accessions to seedling hypocotyl infections were 234 (PI 159664) and 366 (PI 268968), and the most resistant commercial cultivar was Georgia Green. There was not a significant correlation between resistance to limb rot in the field and the severity of hypocotyl infections in growth chambers, indicating that resistance to hypocotyl infections is not a good indicator of resistance to Rhizoctonia limb rot.
First Report of Black Rot of Cauliflower and Kale Caused by Xanthomonas campestris pv. campestris in Yugoslavia
Authors: Obradović A. , Arsenijević M.
Published: May 2007

In Yugoslavia, Xanthomonas campestris pv. campestris was isolated from forage kale in 1964 and cabbage in 1997 (1). Recently, the incidence and severity of black rot symptoms on cabbage, cauliflower, and kale have increased. Gram-negative, rod-shaped, motile bacteria were isolated from the diseased leaf and vascular tissues of cauliflower and kale plants collected from 1995 to 1998. The isolates formed yellow, convex, mucoid colonies on yeast dextrose chalk medium, metabolized glucose oxidatively, grew at 37°C, hydrolyzed gelatin and esculin, produced acids from d-arabinose, glucose, sucrose, and trehalose, and did not reduce nitrates. They were nonfluorescent, amylolytic and pectolytic, oxidase negative and catalase positive, and tolerant to 5% NaCl but not to 0.1% triphenyl tetrazolium chloride. Koch's postulates were completed by injecting bacterial suspensions (108 CFU/ml) into leaf petioles of cabbage, cauliflower, and kale seedlings (2- to 3-leaf stage). Dark green watersoaking of petioles and leaf veins followed by yellowing and collapse of inoculated plants was observed after 3 to 5 days. When compared with published information (2), the isolates were identified as X. campestris pv. campestris. This is the first occurrence of this bacterium in cauliflower and kale in Yugoslavia.

References: (1) O. Jovanovic et al. Plant Prot. Belgrade 221:175, 1997. (2) N. W. Schaad. 1988. Laboratory Guide for Identification of Plant Pathogenic Bacteria. 2nd ed. The American Phytopathological Society, St. Paul, MN.
Factors Influencing Biological Control of Sphenoclea zeylanica with Alternaria alternata f. sp. sphenocleae
Authors: Masangkay Rhomela F. , Paulitz Timothy C. , Hallett Steven G. , Watson Alan K.
Published: May 2007

Alternaria alternata f. sp. sphenocleae is an endemic disease causing a few small necrotic foliar lesions and occasionally a foliar blight on Sphenoclea zeylanica, a problem weed in paddy rice. The effects of inoculum concentration, dew period, and plant age on the biocontrol of S. zeylanica with A. alternata f. sp. sphenocleae were studied under controlled environmental conditions. S. zeylanica plants are susceptible from seedling to maturity. When higher inoculum concentrations (106 conidia ml-1, 108 conidia m-2) were applied to plants of different ages with a long dew period, 100% leaf area damage occurred earlier than when lower inoculum concentrations (104 conidia ml-1, 106 conidia m-2) were used. At the higher inoculum concentrations, a significantly (α < 0.01) higher percent reduction in plant height was obtained, and all plants were killed. A dew period of 8 h was sufficient to cause 100% mortality when plants were inoculated with 106 conidia ml-1, whereas a dew period of 16 h was required with 104 conidia ml-1 to achieve the same effect. At all dew periods, a significantly (α < 0.01) higher percent dry weight reduction was obtained with higher inoculum concentrations. Field performance of this bioherbicide candidate relies on the primary infection established by inoculum application, as secondary infections have not been observed. Effective use rates can be reduced during the rainy season, while higher rates are required during the dry season.
Variability in Postharvest Decay Among Apple Cultivars
Authors: Spotts R. A. , Cervantes L. A. , Mielke E. A.
Published: May 2007

The level of resistance to decay caused by four fungal pathogens, the force required to break the epidermis, and the extent of open sinuses as measures of potential decay resistance were determined for the fruit of several apple cultivars. No single cultivar was the most resistant to each of the four pathogens in this study. In addition, each cultivar that was the most resistant to one pathogen also was the most susceptible to one of the other pathogens. However, Royal Gala was the most resistant to the wound pathogens Botrytis cinerea, Penicillium expansum, and Mucor piriformis. Fuji and Oregon Spur II were more resistant than other cultivars to Pezicula malicorticis. The epidermis (skin) of Fuji and Granny Smith were the most resistant to puncture, requiring an average of 81.5 and 87.0 Newtons, respectively, to break the epidermal layer. Fuji had the highest percentage of fruits with open sinuses, with a mean of 38%, whereas Braeburn had 0% of fruit with open sinuses. The cultivar information presented herein may be a valuable measure of decay resistance and may be of use to the apple industry.
Leaf Blight of Endive and Escarole, Caused by Rhizoctonia solani, in California
Authors: Koike S. T. , Subbarao K. V.
Published: May 2007

Endive (Cichorium endivia) and escarole (broad-leaf type of C. endivia) are two of the many leafy vegetables produced commercially in coastal California. For several years, both crops have been affected by a disease that causes soft, watery, brown leaf decay. In the tightly appressed heads of endive and escarole plants, decay generally spreads in a concentric circle, resulting in circular whorls of brown, rotted leaves within diseased heads. Such symptoms make the heads unmarketable. In the Salinas Valley (Monterey County), the disease was much more prevalent during 1998, when weather was affected by “El Niño.” Rhizoctonia solani was isolated consistently from symptomatic leaves of both endive and escarole. Pathogenicity was tested by placing two agar plugs of representative isolates inside the leaf whorls of 15 potted plants each of endive (cv. Tres Fine Maraicchere) and escarole (cv. Full Heart). Watery, brown leaf decay, similar to symptoms observed in the field, occurred on all plants within 7 days after inoculation, and R. solani was reisolated. Control plants, treated with sterile agar plugs, did not develop disease. Tests were repeated, and results were similar. Anastomosis-group testing revealed that four endive isolates belonged to AG2-2 (1). This appears to be the first report of leaf blight of endive and escarole caused by R. solani in California.

Reference: (1) Sneh et al. 1991. Identification of Rhizoctonia Species. The American Phytopathological Society, St. Paul, MN.
First Report of a Bean-Infecting Begomovirus from Macroptilium lathyroides in Puerto Rico That Is Distinct from Bean Golden Mosaic Virus
Authors: Idris A. M. , Bird J. , Brown J. K.
Published: May 2007

Bean golden mosaic begomovirus (BGMV) was long suspected to cause bright yellow mosaic symptoms in Macroptilium lathyroides (L.), a weed common to Puerto Rico. M. lathyroides plants exhibiting bright yellow mosaic symptoms were collected from Puerto Rico during 1994 to 1999, and the biotic and molecular characteristics of the suspect begomovirus were determined. Symptoms in M. lathyroides, indistinguishable from those observed in field-infected plants, were reproducible by whitefly transmission (Bemisia tabaci type B) and biolistic inoculation of leaf extracts (1). In bean, Phaseolus vulgaris (L.) ‘Topcrop,’ the M. lathyroides virus caused green-yellow mosaic foliar symptoms and stunting, reminiscent of symptoms caused by BGMV from Puerto Rico (BGMV-PR). However, biolistic- or whitefly-mediated inoculation of M. lathyroides with BGMV-PR resulted in no discernible infection. Sequence analysis (2) of the coat protein (CP) gene (AF176092) and common region of the A (CR-A) (AF176093) and B (CR-B) (AF176094) components of the virus from M. lathyroides indicated that these sequences shared only 77.3 to 79.3% and 62.4 to 68.8% identity, respectively, with BGMV from the Dominican Republic, Honduras, Guatemala, Jamaica (JAM), and PR. Alignment of the M. lathyroides virus CP sequence with other well-studied begomoviruses indicate its closest relative is BGMV-PR (82%) and that it shares less than 73% identity with partial CP sequences of Macroptilium golden mosaic virus-JAM (AF089839, AF089840). The directly repeated CR sequences of the M. lathyroides virus, putatively involved in AC1 binding, are TGGTGACTGGTG and are distinct from TGGAGACTGGAG, the analogous direct repeat in BGMV-PR. We provisionally designate the new, previously undescribed begomovirus species from M. lathyroides, Macroptilium mosaic virus (MaMV). Results indicate MaMV-PR and BGMV are distinct, bean-infecting begomoviruses from the Caribbean and that MaMV-PR may pose a new threat to bean production, particularly where the type B vector is established.

References: (1) J. K. Brown and R. Ryan. Phytopathology 81:1217, 1991; (2) A. M. Idris and J. K. Brown. Phytopathology 88:648, 1998.
Race 1,2y of Fusarium oxysporum f. sp. melonis on Muskmelon in Sicily
Authors: Magnano di San Lio G. , Cacciola S. O. , Pane A.
Published: May 2007

Muskmelon (Cucumis melo L.) is very important economically to agriculture in Italy. The Sicily area accounts for ≈40% of the total muskmelon production. Fusarium wilt caused by Fusarium oxysporum f. sp. melonis (Leach & Currence) W.C. Snyder & H.N. Hans. is the most prevalent and damaging disease of muskmelon in Sicily. Use of cultivars with major resistance genes, Fom 1 and Fom 2, is the most effective control measure for combating the disease. During March 1999, severe infections of Fusarium wilt were noted in a commercial muskmelon crop, cv. Firmo F1, grown in plastic tunnels in Syracuse Province (eastern Sicily). The muskmelon seedlings had been transplanted into the tunnels during January 20 days after soil fumigation with methyl bromide. Firmo F1 possesses both Fom 1 and Fom 2 genes. Of 18,000 Firmo F1 plants, ≈6,500 showed symptoms consisting of stunting, vein clearing; leaf yellowing, wilting, and dying; brown necrotic streak; and gummy exudates on the basal portion of vines. A pinkish white mold developed on dead tissues when infected plants were kept at high relative humidity. The pathogenicity of both a single-conidium isolate of F. oxysporum f. sp. melonis from a symptomatic Firmo F1 plant and two isolates of races 0 and 1, recovered previously from other cultivars in Sicily and used as references, was tested with three differential muskmelon cultivars, Charentais T, Doublon, and CM 17187 (1), as well as three commercial cultivars, Ramon, Cassella, and Geamar (possessing Fom 1, Fom 2, and both Fom 1 and Fom 2 resistance genes, respectively). Muskmelon seedlings were inoculated by the root-dip method (3), using a suspension of 5 × 105 conidia per ml. Inoculated seedlings were transplanted to plastic pots filled with sterilized soil and placed in a greenhouse (25 to 30°C). Symptoms were scored 7 to 10 days after inoculation. The isolate from Firmo F1 was pathogenic to all cultivars tested, the race 0 isolate was pathogenic only to cv. Charentais T, and the race 1 isolate was pathogenic only to cvs. Charentais T, Doublon, and Ramon. F. oxysporum was reisolated from symptomatic plants. Based on its pathogenicity and symptomology, the isolate from Firmo F1 was classified as race 1,2y (yellows), according to the nomenclature proposed by Risser et al. (1). Race 1,2 poses a serious threat to muskmelon production in Sicily, because all currently used cultivars are susceptible to the race, and other control measures, such as preplant soil fumigation with methyl bromide and solarization, are not as effective as use of resistant cultivars. Further study is needed to establish which is the prevalent race of F. oxysporum f. sp. melonis in Sicily. This report confirms that race 1,2 occurs in all major muskmelon-production areas in Italy (2).

References: (1) G. Risser et al. Phytopathology 66:1105, 1976. (2) G. Tamietti et al. Petria 4:103, 1994. (3) F. L. Wellman. Phytopathology 29:945, 1939.
Spatial Pattern Analysis and Sequential Sampling for the Incidence of Leaf Spot on Strawberry in Ohio
Authors: Turechek W. W. , Madden L. V.
Published: May 2007

Spatial pattern of the incidence of strawberry leaf spot, caused by Mycosphaerella fragariae (Ramularia brunnea), was quantified on commercial strawberry farms in Ohio. For each planting of strawberry, one or two transects were randomly chosen, and the proportion of leaflets (out of 15) with leaf spot was determined from N = 29 to 87 evenly spaced sampling units. Based on a likelihood ratio test, the beta-binomial distribution described the frequency of diseased leaflets better than the binomial in 93% of the 59 data sets over 3 years. Estimates of mean incidence ranged from 0.0009 to 0.82, with a median of 0.05. Estimates of the beta-binomial aggregation parameter, θ, ranged from 0 to 1.06, with a median of 0.20. Moreover, the estimate of the slope of the binary power law, fitted to the variance data for the 59 data sets, was significantly (P < 0.01) greater than one, indicating that heterogeneity, and hence the pattern of disease incidence at the spatial scale of the sampling units or smaller, was dependent on mean incidence. Spatial autocorrelation and Spatial Analysis by Distance IndicEs (SADIE) analyses detected significant positive association of disease incidence among sampling units in approximately 40% of the data sets, indicating that disease clusters extended beyond the borders of the sampling units in these fields. Collectively, the results show that strawberry leaf spot was characterized by relatively tight clusters of disease (based on θ) that extended beyond the borders of the sampling units in a little under half of the data sets (based on correlations). The information on heterogeneity was used to develop fixed and sequential sampling curves to precisely estimate disease incidence. The sequential-estimation procedure was evaluated using statistical bootstrap methods and performed well over the range of disease incidences encountered.
Characterization of Botrytis cinerea from Table Grapes in Chile Using RAPD-PCR
Authors: Thompson J. R. , Latorre B. A.
Published: May 2007

Random amplified polymorphic DNA (RAPD) analysis was performed on 29 isolates of Botrytis cinerea Pers. ex Fr. isolated from table grapes (Vitis vinifera L.) and other crops in Chile with 29 decaprimers. No single primer was found to differentiate either the host or the geographical origin of each of the B. cinerea isolates tested. The DNA profiles obtained, particularly with primers OPA4 and OPA11, distinguished isolates of B. cinerea from other epiphyte fungi found on table grapes, including Alternaria alternata, Aspergillus niger, Cladosporium herbarum, Epiccocum nigrum, Rhizopus stolonifer, a Penicillium sp., and yeasts (Cryptococcus laurentii, Rhodotorula glutinis, and Saccharomyces cerevisiae). Regardless of host origin, primers OPA4 and OPA11 amplified a strong fragment of 1.2 kilobases (kb) and two fragments of 1.10 and 0.7 kb, respectively. These DNA fragments were obtained even when only one conidium of B. cinerea was in the test sample. Three main groups were clearly defined based on the genetic similarities found in additional RAPD analysis with 19 arbitrary decaprimers and 15 selected isolates of B. cinerea. The overall similarity coefficients (SC) between the groups obtained ranged from 0.326 to 0.891. Interestingly, all isolates from table grapes were included in group I (SC: 0.761 to 0.826), isolates from apple and tomato were in group II (SC: 0.739 to 0.848), while isolates from blueberry were either in group I (SC: 0.804) or III (SC: 0.673). Consequently, the genetic variability determined by RAPD analysis among these B. cinerea isolates suggested a possible host:pathogen relationship. However, further research is needed to clarify its pathological significance.
Monogenic Dominant Resistance to Gummy Stem Blight in Two Melon (Cucumis melo) Accessions
Authors: Zuniga T. L. , Jantz J. P. , Zitter T. A. , Jahn M. K.
Published: May 2007

Two melon (Cucumis melo L.) accessions, plant introduction (PI) 157082 and PI 511890, reported to be resistant to gummy stem blight, a disease incited by the fungus Didymella bryoniae, were crossed with a susceptible parent to determine the inheritance of resistance. Resistance in both accessions is due to a single dominant gene, based on analysis of F1, F2, and backcross populations. Additionally, PI 157082 was crossed with PI 140471, the other source of resistance identified to date, to examine the genetic relationship of resistance found in these two sources. The frequency of susceptible individuals from the (PI 157082 × 140471) F2population was consistent with a 15:1 resistant:susceptible ratio, indicating that PIs 140471 and 157082 possess different resistance genes.
Detecting Multiple Species of Phytophthora in Container Mixes from Ornamental Crop Nurseries
Authors: Ferguson A. J. , Jeffers S. N.
Published: May 2007

A baiting bioassay was developed to detect species of Phytophthora, i.e., those typically associated with ornamental crops, in container mixes that are used routinely in producing container-grown landscape plants. Both fresh and air-dried subsamples of container mixes were baited to improve detection of species that persist as dormant propagules. Leaf disks of Camellia japonica detected Phytophthora spp. most frequently and consistently, but intact needles of shore juniper also were effective baits and less likely to become contaminated. Phytophthora spp. were detected at baiting durations of 24, 48, and 72 h; both detection and contamination were greatest at 72 h. To minimize problems from contamination and maximize detection, camellia leaf disks and shore juniper needles were used simultaneously; half of the baits were removed at 24 h and the other half were removed at 72 h. Baiting at temperatures of 15, 20, and 25°C did not have a dramatic effect on detection; however, Phytophthora spp. occasionally were detected more frequently at 20 and 25°C than at 15°C. Both camellia leaf disks and shore juniper needles were colonized readily by zoospores of P. cinnamomi, P. nicotianae (= P. parasitica), P. cryptogea, and P. citricola but were not colonized as readily by zoospores of P. cactorum. Disks from leaves of C. sasanqua and six cultivars of C. japonica were effective as baits; however, some differences among camellia types occurred. P. cinnamomi, P. nicotianae, P. citricola, P. citrophthora, P. cryptogea, and P. cactorum have been detected in naturally infested container mixes using this baiting bioassay.
Influence of Aspergillus flavus Strains on Aflatoxin and Bright Greenish Yellow Fluorescence of Corn Kernels
Authors: Wicklow Donald T.
Published: May 2007

The objective of this study was to relate the diversity of a naturally occurring population of Aspergillus flavus to their ability to contaminate grain with aflatoxin and produce bright greenish yellow fluorescent (BGYF) kernels. A total of 19 strains of A. flavus isolated from a corn field near Kilbourne, Illinois were used as inoculum, including 16 genotypes (DNA fingerprinting), and representing both aflatoxin producers and non-producers. A commercial corn hybrid (Pioneer 3394) was grown in this field in 1996 and 1998. A total of 20 ears in the late-milk to early-dough stage of maturity were inoculated with each A. flavus strain using a toothpick-wound procedure. At harvest, 20 to 24 of the kernels nearest to each wounded site were separated into three categories: wound-inoculated kernels, intact BGYF kernels, and all other intact kernels. Sample weights of intact BGYF kernels in 1996 and 1998 grain samples averaged 5.0 and 9.5% of the total sample weight, respectively. Aflatoxin-producing strains were associated with a higher frequency (P < 0.05) of BGYF kernels for grain samples harvested in 1998. Removal of the individual wound-inoculated kernels and the intact BGYF kernels from corn ears inoculated with 13 aflatoxin-producing strains of A. flavus lowered mean aflatoxin values from 115 ng/g (range = <1 to 387 ng/g) to 2 ng/g for 1996 grain samples and from 744 ng/g (range = 20 to 1,416 ng/g) to 33 ng/g for 1998 grain samples. Results indicated substantial variation among A. flavus genotypes in their ability to produce aflatoxin in the germ and endosperm of infected BGYF kernels. The naturally occurring A. flavus population may include a majority of strains that produce no aflatoxin but exhibit BGYF and are thus aflatoxin “false positives” when corn grain is examined with an ultraviolet light at 365 nm. Intraspecific competition between aflatoxin-producing and non-producing strains would be expected to naturally suppress the severity of aflatoxin outbreaks within the Midwestern corn belt.
Stem and Crown Rot of Chervil, Caused by Sclerotinia sclerotiorum, in California
Authors: Koike S. T.
Published: May 2007

Chervil (Anthriscus cerefolium) is a culinary herb grown commercially in California. In 1999, chervil plantings in shade houses in coastal California exhibited symptoms of a previously undescribed disease. Tan to gray lesions, surrounded by pinkish tissue, developed on crowns and lower sections of stems. Affected stems wilted, and plants eventually collapsed and rotted. More than 50% of the plants in the early spring planting were diseased. White mycelium and large, irregular, black sclerotia (3 to 6 mm diameter) were observed on infected stems and crowns. Isolations from symptomatic stems, mycelium, and sclerotia produced colonies of Sclerotinia sclerotiorum. Following previously described methods (2), pathogenicity was confirmed by culturing isolates on potato dextrose agar and allowing the fungus to colonize sterilized toothpicks placed on the surface of the agar. The pointed toothpick tips were inserted ≈3 mm deep in stems of potted chervil. Sterile toothpicks were inserted in control chervil plants. All plants were incubated in a mist chamber for 48 h and then kept in a greenhouse. Two other hosts of S. sclerotiorum, cauliflower (Brassica oleracea var. botrytis cv. White Rock) and celery (Apium graveolens cv. Conquistador)were inoculated in the same way. After 7 to 10 days, symptoms and mycelium similar to those originally observed developed on inoculated chervil plants, and S. sclerotiorum was reisolated. Plants left for 14 or more days supported sclerotia. Chervil inoculated with sterile, uncolonized toothpicks did not develop symptoms. Results were similar for cauliflower and celery plants. Pathogenicity tests were repeated, and the results were similar. A separate set of chervil was inoculated by placing sclerotia at the base of plants; these plants also developed disease but at a much lower incidence (<50%). This is the first report of Anthriscus cerefolium as a host of S. sclerotiorum. The related plant cow parsley (A. sylvestris) has been reported as a host of S. sclerotiorum in England (1).

References: (1) M. J. Hims. Plant Pathol. 28:197, 1979. (2) S. T. Koike. Plant Dis. 81:1334, 1997.
First Report of Virus and Phytoplasma Pathogens Associated with Yellow Leaf Syndrome of Sugarcane in Cuba
Authors: Arocha Y. , Gonzalez L. , Peralta E. L. , Jones P.
Published: May 2007

Yellow leaf syndrome (YLS) has been seen recently in sugarcane (Saccharum sp.) in Cuba. The primary symptom is a yellow discoloration of the midrib that may spread from the midrib to the lamina in cane 6 months and older. In certain cultivars, such as CP 5243, EPC 17-395, and F31-156, a reddish coloration has been observed. In severe cases, plants are stunted and can be pulled easily. YLS was first reported from Hawaii, followed by Brazil, Florida, and Australia, where it is associated with a luteovirus: sugarcane yellow leaf virus (ScYLV). However, in South Africa, YLS is associated with a phytoplasma: sugarcane yellow leaf phytoplasma (ScYLP) (1). A survey performed in Jovellanos, Matanzas, Cuba, for ScYLV, using enzyme-linked immunosorbent assay with antiserum provided by B. E. L. Lockhart, showed that only a small percentage of canes with YLS carried the virus. A nested polymerase chain reaction (PCR) (1) was used to amplify phytoplasma 16S/23S rDNA from sugarcane leaves with YLS symptoms, also collected from Jovellanos. Restriction fragment length polymorphism analysis with HaeIII, RsaI, and AluI produced patterns similar to those of members of the aster yellows group for 260 of 277 samples tested. Sequencing of the 16S/23S intergenic rDNA PCR products, followed by BLAST (basic local alignment search tool) analysis, confirmed the high homology (97%) of these amplimers to the DNA of phytoplasmas belonging to the aster yellows I-A subgroup. This is the first report of ScYLV and ScYLP from Cuba, and it demonstrates the difficulty of determining the identity of the YLS pathogen based on symptoms alone.

Reference: (1) C. P. R. Cronjé et al. Ann. Appl. Biol. 133:177, 1998.