bluuebunny/crossref_metadata_2025 huggingface dataset:
Epidemic of Potato virus Y and Cucumber mosaic virus in Henan Province Tobacco
Authors: Li X. D. , Li Y. Q. , Wang H. G.
Published: May 2007

Flue-cured tobacco is an important crop in Henan Province, China. During the 2000 growing season, many tobacco plants showed various degrees of mottling, mosaic, vein clearing, or vein necrosis in most of the counties. Some plants even died at an early stage of growth. A survey was conducted in May-June in several tobacco-growing counties, and the incidence of symptomatic plants in individual fields ranged from 10 to 85%. The most widely planted tobacco varieties, NC89, K326, and K346, were highly susceptible. Symptomatic plants were collected from Jiaxian and Xiangcheng counties and samples were tested by enzyme-linked immunosorbent assay for Tobacco mosaic virus (TMV), Cucumber mosaic virus (CMV), Potato virus Y (PVY), and Potato virus X (PVX). Of 65 samples tested, 21 were positive for only PVY, 16 positive for only CMV, one each was positive for only TMV or PVX. Nineteen samples were doubly infected with various combinations of these viruses and six were infected with combinations of three viruses. The causal agent(s) in the remaining sample could not be determined. In total, CMV was detected in 40 samples, PVY in 38, PVX in 10, and TMV in 7 samples. TMV and CMV used to be the most important viruses and PVY occurred only rarely. But PVY has become prevalent in Henan and in neighboring Shandong province (2). CMV and TMV were reported to be the most prevalent viruses in Shanxi (1) and Fujian Provinces (3). Because resistant varieties are not available, and mixed infections are more common, the results presented here explain why huge damage is occurring in tobacco crops in recent years. Some varieties are partially resistant to TMV and CMV but the varieties commonly grown are highly susceptible to PVY. Therefore, breeding for resistance to viruses, especially to PVY, is urgent to control the occurrence of tobacco viral diseases.

References: (1) J. L. Cheng et al. Acta Tabacaria Sin. 4:43, 1998. (2) J. B. Wang et al. Chinese Tobacco Sci. 1:26, 1998. (3) L. H. Xie et al. Acta Tabacaria Sin. 2:25, 1994.
Design of a Polymerase Chain Reaction for Specific Detection of Corn Stunt Spiroplasma
Authors: Barros Thereza S. L. , Davis Robert E. , Resende Renato O. , Dally Ellen L.
Published: May 2007

Corn stunt disease is a major limiting factor in production of corn (Zea mays) in the Americas. To develop a polymerase chain reaction (PCR) assay specific for detection of the causal agent, Spiroplasma kunkelii, PCR primers were designed on the basis of unique regions of the nucleotide sequence of the S. kunkelii spiralin gene. DNA was amplified in PCRs containing template DNAs derived from laboratory strains of S. kunkelii and from naturally diseased corn plants collected in the field. No DNA amplification was observed in PCRs containing template DNAs derived from other Spiroplasma species tested or from healthy corn or corn infected by maize bushy stunt phytoplasma. The availability of a sensitive and specific PCR for detection and identification of S. kunkelii should facilitate studies of the ecology of this pathogen, as well as its influence in the incidence, spread, and severity of corn stunting diseases.
Effect of a Single or Double Soil Solarization to Control Verticillium Wilt in Established Olive Orchards in Spain
Authors: Lopez-Escudero F. J. , Blanco-Lopez M. A.
Published: May 2007

Four soil solarization experiments were completed in three commercial olive orchards infested with Verticillium dahliae in southern Spain. Three of the experiments used lines of trees and one used individual plants. Plantations had different initial inoculum densities of the pathogen. Initial studies indicated that highly virulent (cotton-defoliating) isolates of the pathogen were present in Marinaleda (experiment I), which represents the first record of such isolates affecting olive trees in Europe. Solarization treatments were applied to lines of trees for either one (single) or two consecutive (double) years. Solarization significantly reduced pathogen populations in the top 20 cm of soil for at least 3 years in relation to control plots. Pathogen reduction after the single solarization obscured effects of the second solarization treatment. Decrease of inoculum density in soil by solarization did not correspond to a similar reduction in disease severity. Disease severity was reduced only in orchards with medium or high initial inoculum densities. A second soil solarization treatment did not improve the effect of single solarization on Verticillium wilt control. In orchards with low inoculum densities, soil solarization did not result in significant differences in disease incidence and severity, but improved recovery of trees from the disease. Soil-solarized plots remained free of weeds, but tress in solarized plots did not show significant growth increase measured by trunk perimeter.
Beneficial Effects of Solid Matrix Chemo-priming in Okra
Authors: Conway K. E. , Mereddy R. , Kahn B. A. , Wu Y. , Hallgren S. W. , Wu L.
Published: May 2007

Two field trials at Stillwater and Bixby, OK, evaluated the efficacy of solid matrix priming techniques, alone or in combination with fungicide seed treatment on seedling emergence and reduction of damping-off of okra in field soil naturally infested with Pythium ultimum. The following treatments were evaluated: thiram + carboxin (chemo-primed) (commercially applied), biological seed treatment (bio-primed) (Trichoderma harzianum isolate OK-110, 1 g suspended in 1% carboxymethylcellulose [CMC]), untreated seed (control), and a 1% CMC control. Chemo-primed seeds had a more uniform and faster emergence compared with untreated seeds at both field sites. Within 3 days, 92 and 78% of chemo-primed seeds had emerged at Stillwater and Bixby, respectively, compared with 84 and 71% emergence in the untreated control. Mean emergence of chemo-primed seeds was lower (P ≤ 0.05) than the untreated control. Chemo-primed seeds had greater vigor (P≤ 0.05) at both locations compared with either fungicide-treated or priming alone, at both locations. There were no differences (P ≤ 0.05) in yield among treatments at both locations. P. ultimum was consistently isolated from damped-off seedlings and surrounding soil at both locations. Isolates of P. ultimum were more pathogenic on okra in laboratory tests than isolates of Rhizoctonia spp., Fusarium spp., and other Pythium spp. also isolated from seed or soil.
Outbreak of Potato Late Blight and First Report of Mating Type A2 and Metalaxyl Resistance of Phytophthora infestans in Iceland
Authors: Olafsson S. , Hermansen A.
Published: May 2007

Late blight caused by Phytophthora infestans (Mont.) de Bary was endemic on potato in Iceland from about 1890 until 1961. Probably because of a cooler climate in the 1960s, the disease disappeared and there were no epidemics until 1990 and 1991. Late blight was not found in the period 1992 to 1998 even though the weather conditions were favorable for epidemic development in some of the years. Lack of initial inoculum was probably the limiting factor for an epidemic in Iceland some years. During the summer of 1999, late blight reappeared in Iceland. In August 1999, potato leaves with single lesions of late blight were sampled from two locations and sent to the Norwegian Crop Research Institute. Isolates were trapped by placing infected leaves under tuber slices in petri dishes. Pure cultures were made by picking small pieces of mycelium from the upper side of the potato slice after 7 to 10 days incubation at 15°C and plating them onto modified rye B agar with antibiotics (1). Sixteen isolates maintained on rye B agar were paired with reference isolates of mating types A1and A2 and examined for oospores at the hyphal interfaces between the isolates (1). One isolate was typed as A2 and 15 isolates were A1. Response to metalaxyl was determined for 13 isolates in vitro (1) on rye B agar amended with 5 mg/l metalaxyl-m. One of the A1 isolates was metalaxyl-resistant and 12 isolates, including the A2 isolate, showed intermediate resistance to the fungicide. These data show that the “new” population of P. infestans is now present in Iceland as in the other Nordic countries (1). Iceland imports some seed potatoes each year, mainly from the Netherlands. Imported seed potatoes were probably the source of initial inoculum in 1999 in Iceland. In the future, oospores in the soil might be an additional inoculum source in Iceland since both mating types are now present.

Reference: (1) A. Hermansen et al. Plant Pathol. 49:11, 2000.
Stem Canker of Cabbage Seed Stalks Caused by Botrytis cinerea in Western Washington
Authors: Inglis D. , Derie M. , Hsiang T.
Published: May 2007

Stem cankers were observed during 1998 on bolting stalks of cabbage (Brassica oleracea var. capitata L.) in seed production fields in western Washington. In 1999, approximately 4 ha of cabbage hybrid 'Wk 121, was severely affected. Lesions occurred at the base of seed stalks after they emerged from heads of plants overwintered in the field, or on flower branches and seed-bearing stalks that developed during the growing season. Lesions girdled a branch or stalk, and killed or weakened it so that it broke during pod fill. Isolates of Botrytis cinerea Pers.:Fr. were obtained by plating spores from lesions onto potato dextrose agar. To confirm pathogenicity, stems of 12-day-old seedlings of ‘Wk 121’ were scraped with a razor blade or left intact, atomized with sterile 0.01 % Tween 80 or a suspension of Botrytis cinerea at 1.0 × 106 conidia/ml, and kept at 20°C in a dew chamber in plastic bags. The fungus was reisolated from small lesions on wounded stems inoculated with B. cinerea after 3 days. No lesions developed on non-wounded or wounded control plants. B. cinerea is reported to cause storage rot of cabbage (2) and gray mold on Brassica oleracea L. (cabbage, kale, kohlrabi, wild cabbage) in Washington (1) but not stem canker. This new seed crop disease may be the result of predisposition to infection by freezing injury or mechanical damage on a highly susceptible cultivar grown under cool, wet weather.

References: (1) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society. St. Paul, MN. (2) O. C. Yoder and M. L. Whalen. Can. J. Bot. 53:691, 1975.
Elm Yellows Phytoplasma Lethal to Dutch Elm Disease-Resistant Ulmus americana Cultivars
Authors: Sinclair W. A. , Townsend A. M. , Sherald J. L.
Published: May 2007

Ulmus americana (American elm) clonal cultivars Independence, New Harmony, and Valley Forge, together with the triploid putative hybrid cultivar Jefferson, were tested for reaction to the elm yellows (EY) phytoplasma. These cultivars all possess resistance to the fungal pathogen Ophiostoma novo-ulmi (1,4) but had not been screened for EY resistance or tolerance. Procedures and conditions of the test were similar to those used previously for assessing EY tolerance of Eurasian elm cultivars (3). In brief, 9 to 15 saplings of each cultivar and of U. americana raised from seed (susceptible controls), growing in a field plot at Ithaca, NY, were challenged by grafting their mainstems with bark patches from U. americana naturally affected by EY. Six to nine additional trees of each clone and of the seedling group were left untreated as controls. Inoculations were performed in July 1999, and trees were evaluated for symptoms in early September 2000. Multiple individuals in every inoculated group developed the syndrome typical of EY in U. americana: epinasty, foliar yellowing, yellow discoloration and necrosis of root and stem phloem, odor of methyl salicylate from moist discolored phloem on first exposure to air, defoliation or sudden permanent wilting, and death (2). The numbers of trees with these symptoms, of those inoculated, were: 9 of 9 Independence, 7 of 11 New Harmony, 10 of 14 Valley Forge, 3 of 13 Jefferson, and 12 of 15 trees grown from seed. Untreated controls remained asymptomatic, except for one tree of Valley Forge and two trees grown from seed that became infected naturally and had symptoms like those in the grafted trees. Based on these results, the elm cultivars named above are typical of U. americana in susceptibility to, and intolerance of, EY phytoplasmal infection. Effective EY resistance or tolerance in this species, although once thought to occur in rare individuals (2), remains undocumented.

References: (1) J. L. Sherald et al. Can. J. For. Res. 24:647, 1994. (2) W. A. Sinclair. 2000. Page 121 in: The Elms. C. P. Dunn, ed. Kluwer Academic Publishers, Norwell, MA. (3) W. A. Sinclair et al. Plant Dis. 84:1266–1270, 2000. (4) A. M. Townsend. 2000. Page 271 in: The Elms. C. P. Dunn, ed. Kluwer Academic Publishers, Norwell, MA.
Puccinia sorghi Virulent on Sweet Corn with the Rp1-D Gene in Southern France
Authors: Pataky J. K. , Plaisted D. C. , Scholten D. , de Durand H. F.
Published: May 2007

The Rp1-D gene, which conveys a chlorotic-fleck resistant reaction to Puccinia sorghi, effectively controlled common rust on sweet corn in North America for nearly 15 years. Biotypes of P. sorghi virulent on plants with the Rp1-D gene were widespread in North America for the first time in 1999 and again in 2000 (1,2). Many Rp-resistant sweet corn hybrids that are developed and grown in North America also are grown in Europe, including France where virulence against the Rp1-D gene has not been reported previously. In September 2000, uredinia of common rust were observed on and collected from sweet corn hybrids with the Rp1-D gene in commercial fields and hybrid trials in the Landes and Pyrénées Atlantiques departments of the Aquitaine region of southwestern France. Severity of rust generally was below 5% on these plants except for a few hybrids for which severity was about 20 to 30%. Common rust was not observed on hybrids with the Rp-G gene. Urediniospores were increased as a bulk population on the susceptible sweet corn hybrid Sterling in a greenhouse. Plants with each of 10 single Rp genes (Rp1-A, Rp1-C, Rp1-D, Rp1-E, Rp1-F, Rp1-I, Rp1-K, Rp1-L, Rp1-N, and Rp-G) or each of six compound rust resistance genes (Rp1-D5, Rp1-JC, Rp1-JFC, Rp-GDJ, Rp-GFJ, and Rp-G5JC) were assayed for reactions to this population of P. sorghi. Two to six different sources of seed of each single Rp gene and two different sources of seed of each compound rust resistance gene were replicates with a single pot of 6 to 18 plants grown from a specific seed source. Plants were inoculated three times on successive days by placing 2 or 3 ml of a urediniospore suspension in the whorl of two- to four-leaved seedlings. Reactions were rated 10 days after the last inoculation. Plants without symptoms or with chlorotic-fleck resistant reactions were inoculated again and rated 10 days later. Uredinia did not form on plants with compound rust resistance genes. Plants with the genes Rp1-E, Rp1-I, Rp1-K, and Rp-G also were resistant although a few, very small uredinia (i.e., type-1 uredinia) were observed on a few plants. Plants with the genes Rp1-A, Rp1-C, Rp1-D, Rp1-F, Rp1-L, and Rp1-N were fully susceptible. This pattern of virulence is the same as that observed during the past two years in North American populations of P. sorghi virulent against Rp1-D. Rp-resistance currently available in most sweet corn hybrids will not be effective in France if these virulent biotypes become prevalent.

References: (1) J. K. Pataky et al. Plant Dis. 85:165, 2001. (2) M. C. Pate et al. Plant Dis. 84:1154, 2000.
First Report of Strawberry Fruit Rot Caused by Alternaria tenuissima in Korea
Authors: Lee H. B. , Kim C.-J. , Yu S. H.
Published: May 2007

A strawberry (Fragaria × ananassa Duch.) fruit rot disease has been observed in several vinyl-house fields at Nonsan and Taejon, Chungnam district, Korea, especially following moist and cool conditions in the spring and again in September. Over the past 7 years, incidence of the disease has ranged from 0.2 to 2.0%. Early symptoms on fruits were characterized by small, irregular lesions, which were slightly sunken and appeared light green to black in color as sporulation began. Conidia were 25 to 55 μm long by 10 to 17 μm wide; beaks, when present, were 2 to 3 μm wide and up to 40 μm long; and conidiophores were 20 to 110 μm long by 3 to 5 μm wide. Older lesions were circular, largely sunken, firm, and dark-green to almost black because of abundant sporulation. The fungus isolated from infected fruit tissues was identified as Alternaria tenuissima (Fries) Wiltshire, based on the morphological characteristics of the conidia and conidiophores. Pathogenicity tests were conducted by inoculating slightly wounded, ripe (red) and immature (green) fruits with a conidial suspension (1 × 106 conidia/ml). Twenty-four ripe and immature fruits were inoculated with each of six isolates in duplicate and placed in a moist chamber for 48 h at 25°C and then transferred to vinyl-house field. After 7 to 10 days fruit rot symptoms were visible on the inoculated fruits and appeared nearly identical to lesions observed in the field, although there were differences in aggressiveness among isolates. Control fruits sprayed with distilled water did not develop any symptoms. Green fruits were generally more resistant to infection than ripe ones. The causal fungus was easily reisolated from lesions on inoculated strawberries. Alternaria fruit rot of strawberries has been reported from the USA, UK, and West Germany (2). Howard and Albregts (1) first reported a strawberry fruit rot caused by A. tenuissima in Florida, but the disease is generally not considered important. However, occasionally losses from this disease have been extensive in Korea. To the authors' knowledge, this is the first report of strawberry fruit rot caused by Alternaria tenuissima in Korea.

References: (1) C. M. Howard and E. E. Albregts. Phytopathology 63:638–639, 1973. (2) A. L. Snowdon. Pages 250–252 in: A Color Atlas of Post-Harvest Diseases and Disorders of Fruits and Vegetables. Vol. 1. 1990. Wolfe Scientific, London.
Inheritance of Powdery Mildew Resistance in Sugar Beet Derived from Beta vulgaris subsp. maritima
Authors: Lewellen R. T. , Schrandt J. K.
Published: May 2007

Powdery mildew of sugar beet (Beta vulgaris), caused by Erysiphe polygoni, was introduced into North American in 1974. Since then, chemical control has been needed. Moderate resistance of a slow-mildewing type is known and has been used commercially. High resistance was identified recently in B. vulgaris subsp. maritima accessions WB97 and WB242 and has been backcrossed into sugar beet breeding lines. These enhanced lines were used as sources of powdery mildew resistance to determine the inheritance of resistance. Analyses of segregating testcross families showed that resistance from both sources is inherited as a single, dominant, major gene. The gene symbol Pm is proposed for the resistant allele. The allelism of the resistance from the two wild beet sources was not determined. Pm conditions a high level of resistance, but disease developed on matured leaves late in the season. This late development of mildew on lines and the slow-mildewing trait in susceptible, recurrent lines tended to obfuscate discrete disease ratings.
Isolation and Molecular Characterization of a Chilean Isolate of Zucchini yellow mosaic virus
Authors: Prieto H. , Bruna A. , Hinrichsen P. , Muñoz C.
Published: May 2007

Zucchini yellow mosaic virus (ZYMV) was described in 1981 affecting squash, melon, and other cultivated cucurbits with severe stunting and yellowing symptoms. It was reported to be present in most countries where cucurbits are grown, and in Chile since 1995, from surveys using enzyme-linked immunosorbent assay (ELISA) but without further characterization. A potyvirus was isolated from ELISA-positive symptomatic plants. The results indicate that this virus is ZYMV based on symptoms on herbaceous indicators, immunospecific electron microscopy of the purified particle, and sequencing of 395 bases of the 3′ end of the coat protein gene. The virus was detected in melon, watermelon, and squash plants. In agreement with previous descriptions for ZYMV, the Chilean isolate is a flexuous filamentous particle 740 nm long with one main protein of approximately 36 kDa. Nucleotide sequence comparisons of the 3′ portion of the coat protein gene revealed a high similarity to the Connecticut and California strains.
First Report of Sweet potato sunken vein virus Occurring in Lisianthus
Authors: Cohen J. , Lapidot M. , Loebenstein G. , Gera A.
Published: May 2007

During a survey of Lisianthus (Eustoma grandiflorum) plots in the Northern Negev in Israel, plants infected with Iris yellow spot virus (IYSV) (Genus Tospovirus; 1) were identified. In addition, during electron microscope observations of ultrathin sections through parenchyma phloem cells from some of the IYSV-infected plants, vesicles and virus particles typical of closteroviruses (850 × 12 nm) were observed. As sweet potatoes grown in this area often are infected with Sweet potato sunken vein virus (SPSVV), it was of interest to see if SPSVV also had naturally infected Lisianthus. Using immunosorbent electron microscopy (ISEM) with an antiserum developed against SPSVV (2), trapping and decoration of the suspected chlostero-like particles were observed in some of the field-collected Lisianthus plants. This antiserum did not react with two other closteroviruses, Citrus tristeza virus and Lettuce infectious yellow virus. Inoculation of non-infected Lisianthus plants with SPSVV acquired from sweet potato by whitefly (Bemisia argentifolii), resulted in the presence of vesicles and clostero-like particles in ultrathin sections of parenchyma phloem cells 1 month after inoculation. ISEM tests with SPSVV antiserum were positive. Inoculations of sweet potato from SPSVV-infected Lisianthus plants by whiteflies were not successful. No leaf symptoms of SPSVV were observed in Lisianthus plants, but flower stems were shorter by about one third. These data indicate that Lisianthus is a host for SPSVV. To our knowledge, this is the first report of SPSVV infecting Lisianthus and any species of the Genetianaceae.

References: (1) A. Kritzman, H. Beckelman, S. Alexandrov, J. Cohen, J. Lampel, M. Zeidan, B. Raccah and A. Gera. Plant. Dis. 84:1185, 2000. (2) J. Cohen, A. Franck, H. J. Vetten, D. E. Lesemann and G. Loebenstein. Ann. Appl. Biol. 121:257, 1992.
Use of Quantitative PCR Diagnostics to Identify Tolerance and Resistance to Verticillium dahliae in Potato
Authors: Dan H. , Ali-Khan S. T. , Robb J.
Published: May 2007

A potato breeding population was evaluated for the presence of tolerance and resistance to Verticillium dahliae. Clones were ranked as susceptible or moderately and highly resistant based on symptom expression, and a species-specific polymerase chain reaction (PCR)-based assay was used to determine the Verticillium biomass in the bases of stems. A clone was designated as tolerant if the amount of fungus present in the host tissue was equal to or greater than the collective average amount for all clones in the symptom category above. Tolerant and resistant clones were identified in all trials, but the expression of tolerance was usually unstable across runs. The fungus was detected in some symptomless plants; on the other hand, some symptomatic plants were found to be pathogen-free. These observations emphasize the necessity of accurate quantification of the pathogen biomass in potato during Verticillium resistance breeding programs.
Control of Peach Scab with Reduced Midseason Fungicide Programs
Authors: Scherm H. , Savelle A. T.
Published: May 2007

The effectiveness of reduced fungicide programs, using either extended application intervals or alternate-row middle (ARM) spraying of wettable sulfur or captan, on infection of peach fruit by Cladosporium carpophilum was investigated in a 2-year study in Georgia. Fungicide reductions focused on the midseason cover spray period when scab pressure is typically reduced and when growers would be most likely to adopt reduced spray programs because of the potential for fewer insecticide applications at the same time. In an experimental orchard, sulfur was applied at calyx split and calyx fall, followed by another application of sulfur or captan at first cover. Subsequent midseason applications consisted of sulfur at 12- to 14-day intervals (standard); sulfur at extended 24- to 28-day intervals; or either sulfur or captan applied via ARM spraying at 12- to 14-day intervals at reduced sprayer speed. Plots without midseason sprays after first cover also were included. Fruit scab severity was reduced by all fungicide programs compared with the untreated control. Disease severity with sulfur applied at extended intervals and with ARM spraying of sulfur or captan was not significantly different from that of the standard (P > 0.05) in both years, suggesting that application intensity during midseason can be reduced without compromising scab control. By contrast, plots that did not receive any mid-season sprays after first cover had significantly more disease. Reduced midseason applications of sulfur were further evaluated in two commercial orchards. In one orchard, fruit scab control achieved with extended-interval or ARM spraying during midseason was not significantly different from that of the grower standard. In the second orchard, higher disease severity resulted from midseason ARM applications compared with the standard, presumably because of the longer (14- to 18-day) spray interval used by the cooperating grower for ARM spraying. Reduced midseason fungicide programs did not lead to an increased carryover of inoculum as determined by conidial counts on overwintered twigs at petal fall in the following year.
Integrated Control of Rhizoctonia Crown and Root Rot of Sugar Beet with Fungicides and Antagonistic Bacteria
Authors: Kiewnick Sebastian , Jacobsen Barry J. , Braun-Kiewnick Andrea , Eckhoff Joyce L. A. , Bergman Jerry W.
Published: May 2007

Rhizoctonia crown and root rot, caused by the fungus Rhizoctonia solani AG 2-2, is one of the most damaging sugar beet diseases worldwide and causes significant economic losses in more than 25% of the sugar beet production area in the United States. We report on field trials in the years 1996 to 1999 testing both experimental fungicides and antagonistic Bacillus sp. for their potential to reduce disease severity and increase sugar yield in trials inoculated with R. solani AG 2-2. Fungicides were applied as in-furrow sprays at planting or as band sprays directed at the crown at the four-leaf stage, or four- plus eight-leaf stage, while bacteria were applied at the four-leaf stage only. The fungicides azoxystrobin and tebuconazole reduced crown and root rot disease by 50 to 90% over 3 years when used at rates of 76 to 304 g a.i./ha and 250 g a.i./ha, respectively. The disease index at harvest was reduced and the root and sugar yield increased with azoxystrobin compared with tebuconazole. The combination of azoxystrobin applied at 76 g a.i./ha and the Bacillus isolate MSU-127 resulted in best disease reduction and greatest root and sucrose yield increase.
Characteristics and Frequency of Aphanomyces euteiches Races 1 and 2 Associated with Alfalfa in the Midwestern United States
Authors: Malvick D. K. , Grau C. R.
Published: May 2007

Aphanomyces root rot of alfalfa, caused by Aphanomyces euteiches, kills seedlings and causes decline of established plants in slowly drained soils. Two races of A. euteiches that are pathogenic to alfalfa have been identified. Despite the contribution of race 1 resistance to establishment and yield of alfalfa, race 1-resistant alfalfa cultivars perform poorly in some fields infested with A. euteiches. Many isolates of A. euteiches obtained from the soils of problematic fields are of a race 2 phenotype. The purpose of this study was to determine distribution, frequency, and pathogenic and genotypic characteristics of race 1 (R1) and race 2 (R2) isolates from 21 fields: 13 in Wisconsin, 7 in Minnesota, and 1 in Kentucky. A. euteiches was successfully isolated from the soil of 16 of the 21 fields; 405 isolates were obtained from Wisconsin, 4 from Minnesota, and 48 from Kentucky. Pathogenicity and race phenotype of isolates were characterized on Saranac (susceptible to R1 and R2 isolates) and WAPH-1 (resistant to R1 and susceptible to R2 isolates) alfalfa populations. One Wisconsin field with no recent history of alfalfa production had a high frequency (51%) of R2 isolates, and 43% of all isolates were R2 from fields with a history of alfalfa production. In a location that was planted continuously to pea for 30 years, 27% of the isolates were R2. Random amplified polymorphic DNA (RAPD) analysis of three R1 and three R2 isolates with eight primers generated 43 total polymorphic bands; however, none of the bands were uniquely associated with race phenotype. Cluster analysis based on RAPD bands revealed no consistent genotypic distinctions between R1 and R2 isolates of A. euteiches. Evaluation of eight commercial alfalfa cultivars for resistance to two R1 and two R2 isolates demonstrated that most are susceptible to R2 isolates; however, those selected for R2 resistance express resistance to R2 isolates. The results suggest that R2 isolates represent a widespread risk to alfalfa cultivars having resistance only to R1 isolates in fields with varied cropping histories.
Occurrence of Chilli veinal mottle virus in Solanum aethiopicum in Tanzania
Authors: Nono-Womdim R. , Swai I. S. , Chadha M. L. , Gebre-Selassie K. , Marchoux G.
Published: May 2007

African eggplant, or garden egg (Solanum aethiopicum) is an important vegetable in most sub-Saharan African countries. Since June 1997, viral symptoms, including mosaic, vein clearing, and stunting, have been observed on several crops of African eggplant cv. Tengeru White at a number of sites in the Arusha region of northern Tanzania. Field inspections revealed disease incidence ranging from 50 to 90%. During the same period, high populations of the green peach aphid Myzus persicae were observed in affected crops of African eggplant. These aphids were also found to reproduce in African eggplants. Flexuous, rodshaped virus-like particles, approximately 750 nm long and 12 nm wide, were found in electron microscope leaf dips from field samples of naturally affected African eggplants. The particle size suggested a species of Potyviridae. Thus, 20 field-infected samples of S. aethiopicum (randomly collected from four farms) were assayed in double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) for the presence of Potato virus Y (PVY) and Pepper veinal mottle virus (PVMV), known to infect tomato and other solanaceous crops in the region (2). However, all samples gave negative results. Further DAS-ELISA were performed with the same extracts from naturally infected plants of S. aethiopicum with antisera directed against Tobacco etch virus, Tobacco vein mottling virus, Pepper mottle virus, and Chilli veinal mottle virus (ChiVMV). All 20 samples were positive only for ChiVMV. ChiVMV, a single-stranded RNA virus transmitted in a nonpersistent manner by several aphid species, is one of the most important viruses of pepper in Asia (1). To confirm DAS-ELISA results, an isolate of ChiVMV from African eggplant was transmitted by mechanical inoculations, resulting in disease on tobacco (Nicotiana tobacco cv. Xanthi nc), pepper (Capsicum annuum cv. Yolo Wonder), tomato (Lycopersicon esculentum cv. Tengeru 97), and African eggplant (S. aethiopicum cv. Tengeru White). Extracts from the inoculated plants tested positive for the presence of ChiVMV in DAS-ELISA. This mechanically transmitted isolate did not infect melon (Cucumis melo), cucumber (C. sativus), or cowpea (Vigna unguiculata), which are nonhosts of ChiVMV. To our knowledge, this is the first report of the natural occurrence of ChiVMV in African eggplant.

References: (1) S. K. Green et al. PETRIA 9:332, 1999. (2) R. Nono-Womdim et al. J. S. Afr. Soc. Hort. Sci. 6:41–44, 1996.
First Report of Leaf Spot Caused by Cylindrocladium pauciramosum on Acacia retinodes, Arbutus unedo, Feijoa sellowiana, and Dodonaea viscosa in Southern Italy
Authors: Polizzi G. , Catara V.
Published: May 2007

In October 1997, severe leaf spotting was observed on several ornamental plants growing in different nurseries in southern Italy. These symptoms were detected for the first time on strawberry tree (Arbutus unedo L.) and water wattle (Acacia retinodes Schltdl.). In the latter species, diseased plants showed also stem canker and shoot blight symptoms. Cylindrocladium pauciramosum C.L. Schoch & Crous (teleomorph Calonectria pauciramosa) were found associated with these symptoms (2). More recently, leaf spots were found also on feijoa (Feijoa sellowiana Berg.) and on Florida hopbush (Dodonaea viscosa (L.) Jacq.) in two other nurseries located in Sicily. Infected tissues were surface-sterilized and plated on potato dextrose agar. Plates were incubated at room temperature under fluorescent cool white lights on a 12-h light/dark regime. A Cylindrocladium species was consistently associated with diseased tissues. The isolates of Cylindrocladium collected from feijoa and Florida hopbush were identified on carnation leaf agar as C. pauciramosum on the basis of their obpyriform to broadly ellipsoidal terminal vesicles, conidiophore branching pattern, and conidium morphology, as well as mating type studies with tester strains of C. pauciramosum (1,3). Koch's postulates were fulfilled by inoculating 6-month-old seedlings of the four ornamental plants with a spore suspension of the fungus (104 conidia per ml). Following inoculation, all plants were maintained in a glasshouse where the temperature was 15 to 25° C and relative humidity was 80 to 90%. After 6 to 8 days, symptoms resembling those seen in the nurseries were apparent. The Cylindrocladium species was reisolated from lesions on inoculated plants, thus confirming it to be the causal organism of these diseases. This is apparently the first report of C. pauciramosum leaf spot on these hosts.

References: (1) P. W. Crous and M. J. Wingfield. Mycotaxon 51: 341, 1994. (2) G. Polizzi and P.W. Crous. Eur. J. Plant Pathol. 105:407, 1999. (3) C. L. Schoch et al. Mycologia 91:286, 1999.
Pyricularia grisea Causing Gray Leaf Spot of Perennial Ryegrass Turf: Population Structure and Host Specificity
Authors: Viji G. , Wu B. , Kang S. , Uddin W. , Huff D. R.
Published: May 2007

Gray leaf spot is a serious disease of perennial ryegrass (Lolium perenne) turf in the United States. Isolates of Pyricularia grisea causing the disease in perennial ryegrass were characterized using molecular markers and pathogenicity assays on various gramineous hosts. Genetic relationships among perennial ryegrass isolates were determined using different types of trans-posons as probes. Phylogenetic analysis using Pot2 and MGR586 probes, analyzed with AMOVA (analysis of molecular variance), showed that these isolates from perennial ryegrass consist of three closely related lineages. All the isolates belonged to a single mating type, MAT1-2. Among 20 isolates from 16 host species other than perennial ryegrass, only the isolates from wheat (Triticum aestivum) and triticale (× Triticosecale), showed notable similarity to the perennial ryegrass isolates based on their Pot2 fingerprints. The copy number and fingerprints of Pot2 and MGR586 in isolates of P. grisea from perennial ryegrass indicate that they are genetically distinct from the isolates derived from rice (Oryza sativa) in the United States. The perennial ryegrass isolates also had the same sequence in the internal transcribed spacer (ITS) region of the genes encoding ribosomal RNA as that of the wheat and triticale isolates, and exhibited rice isolate sequence polymorphisms. In pathogenicity assays, all the isolates of P. grisea from Legacy II perennial ryegrass caused characteristic blast symptoms on Marilee soft white winter wheat, Bennett hard red winter wheat, Era soft white spring wheat, and Presto triticale, and they were highly virulent on these hosts. An isolate from wheat and one from triticale (from Brazil) were also highly virulent on perennial ryegrass and Rebel III tall fescue (Festuca arundinacea). None of the isolates from perennial ryegrass caused the disease on Lagrue rice, and vice versa. Understanding the population structure of P. grisea isolates infecting perennial ryegrass and their relatedness to isolates from other gramineous hosts may aid in identifying alternate hosts for this pathogen.
A Rapid Technique for the Evaluation of Potato Germ Plasm for Susceptibility to Pink Rot
Authors: Peters R. D. , Sturz A. V.
Published: May 2007

Disease-free plantlets of 20 potato cultivars commonly grown in Prince Edward Island were inoculated with zoospore suspensions of Phytophthora erythroseptica, the causal agent of pink rot, to determine disease response. All inoculated cultivars developed disease symptoms relative to noninoculated controls, but disease severity differed significantly (P = 0.05) among cultivars. Plantlets of the cultivars Goldrush and Yukon Gold were consistently the most susceptible to the disease, whereas plantlets of cultivars Butte and Russet Burbank were the least susceptible. Most of the cultivars assessed were moderately susceptible to disease. Plantlets of potato cultivars with late-season field maturity were more resistant to disease than those with early or mid-season maturity. Isolates of P. erythroseptica from diverse regions of Prince Edward Island and Maine did not differ significantly (P = 0.05) in pathogenicity. The screening protocol described was a reliable technique to determine the relative resistance of nontuber potato germ plasm to disease, resulting from infection with P. erythroseptica.
Characterization of Fusarium Yellows Resistance in Collard
Authors: Farnham Mark W. , Keinath Anthony P. , Smith J. Powell
Published: May 2007

The yellows disease of cole crops, caused by Fusarium oxysporum f. sp. conglutinans, can be very damaging to collard. Growers in the southeastern United States frequently produce collard in hot, summer months when conditions for yellows development are favorable, and thus, incidence of this disease is increasing. A collection of essentially all U.S. commercial cultivars of collard, various landraces of collard, and other representative cole crops was evaluated for response to artificial inoculation with F. oxysporum f. sp. conglutinans under controlled-temperature conditions. In addition, the same collection was evaluated following transplanting for response to naturally infested soil in the field during summer 1997 and 1998. In all trials, genotype had the most significant effect on percentage of diseased plants, and genotype responses ranged from resistant (0 to 20% diseased) to susceptible (61 to 100% diseased). There was a significant temperature effect on percentage of diseased plants in one growth chamber experiment with five genotypes that resulted primarily from an increase in disease incidence for the cultivar Blue Max at 30°C compared with 25°C. Temperature was not significant in a second experiment with 20 genotypes. In the field, although significant differences were observed among genotypes and between years, a significant genotype × year interaction was not detected for percentage of diseased plants, indicating a similar ranking of genotypes for resistance between years. There was a significant correlation between results from controlled-environment studies and the field. A resistant response to F. oxysporum f. sp. conglutinans was expressed in certain cultivars of collard, including Flash, Heavicrop, and Morris Heading, and also in specific landraces. This resistance was stable in relatively high temperature environments used in evaluations. Results of this research indicate that choice of cultivar is a critical factor in producing collard where conditions favor infection by F. oxysporum f. sp. conglutinans. This information will aid in development of new yellows-resistant cultivars.
First Report of Angular Leaf Spot Caused by Phaeoisariopsis griseola on Bean in Ontario, Canada
Authors: Melzer M. S. , Boland G. J. , Celetti M. J.
Published: May 2007

During the summer of 2000, brown, angular-shaped leaf spots, frequently surrounded by a chlorotic halo, were observed in commercial fields of green bean (Phaseolus vulgaris L.) in Ontario, Canada. Brown synematta (30 to 60 μm × 160 to 330 μm) and brown conidia (2 to 5 septate, usually curved, 5 to 7.3 μm × 35 to 66 μm) from the underside of diseased leaves were plated onto V8 agar. Within 3 to 4 days, dark olive green colonies formed, and after 10 to 14 days, white mycelial growth occurred on the upper surface of colonies, and colonies appeared gray. The causal agent was tentatively identified as Phaeoisariopsis griseola (Sacc.) Ferraris, the cause of angular leaf spot of bean, and this identification was later confirmed by the Centraalbureau voor Schimmelcultures, The Netherlands. New colonies of the fungus were started by streaking conidia across plates of V8 agar and new conidia were produced within 36 h. Conidial suspensions of 1 × 105 conidia/ml were sprayed onto leaves of green bean varieties Goldrush, Strike, Bronco, and Gold Mine. Plants were placed in a mist chamber at 20 ± 2°C for 11 days and then kept at high humidity for four more days. Lesions were observed 8 to 10 days after treatment and synematta developed 12 to 14 days after treatment. Disease symptoms and synematta were observed on all bean varieties tested. P. griseola was reisolated from inoculated plants, fulfilling Koch's postulates. To our knowledge, this is the first report of angular leaf spot occurring on P. vulgaris in Ontario.
First Report of Bacterial Stem Rot Caused by Pectobacterium carotovorum subsp. carotovorum and P. carotovorum subsp. atrosepticum on Grafted Eggplant in Italy
Authors: Catara V. , Bella P. , Polizzi G. , Paratore A.
Published: May 2007

In December 1999, widespread dieback of eggplant (Solanum melongena L., hybrid Mission Bell), grafted onto the interspecific hybrid Beaufort (Lycopersicon esculentum × Lycopersicon hirsutum) and on tomato hybrid Energy, was observed during four rootstock evaluation trials in greenhouses in Sicily, Italy. Dark brown to black, firm but sometimes fissured lesions, 1 to 20 cm long, were observed just above the grafting point. Water-soaked, soft, dark green lesions that turned brown with age were observed on the upper stem. Extensive discoloration of vascular tissues and, in some cases, breakdown of the pith and stem hollowness occurred. Eggplant seedlings, present in the same experimental trials, did not show any symptoms. From symptomatic tissues, numerous bacterial colonies were obtained on nutrient dextrose agar. Bacteria from purified colonies were gram-negative, oxidase-negative, facultatively anaerobic pectolitic on crystal violet pectate agar, which is nonfluorescent on King's B medium. On the basis of biochemical and physiological tests (1), seven of 10 isolates were identified as Pectobacterium carotovorum subsp. carotovorum (Jones 1901) Hauben et al. 1999, comb. nov. (2), and the remaining three were identified as P. carotovorum subsp. atrosepticum (van Hall 1902) Hauben et al. 1999, comb. nov. (2). Four days after prick inoculation of the stems of eggplant and tomato plants, all isolates caused extensive collapse of stems and internal brown discoloration and hollowness, respectively. In a second pathogenicity test, basil leaves of grafted eggplants and eggplant seedlings were either removed or left intact. These plants were then sprayed with bacterial suspensions (108 CFU/ml) of one isolate of each pathogen. Plants were held at 100% relative humidity or in a low-moisture incubator. After 6 days incubation, stem lesions and vascular discoloration, typical of symptoms observed in greenhouses, were observed on plants held at 100% relative humidity. No symptoms were observed in unwounded plants or plants maintained in low relative humidity. Similar symptoms on grafted eggplant have been attributed to physiological disorders (3). To our knowledge, only P. carotovorum subsp. carotovorum has been reported on eggplant as causing fruit rot.

References: (1) N. W. Schaad, ed. 1988. Laboratory Guide for Identification of Plant Pathogenic Bacteria, 2nd ed. American Phytopathological Society, St. Paul, MN. (2) L. Hauben et al. Int. J. Syst. Bacteriol. 41:582, 1999. (3) G. Ginoux and H. Laterrot. Rev. Horticole (Paris) 321:49, 1991.
First Report of Pythium Root Rot on Grain Sorghum in Mississippi
Authors: McLean K. S. , Lawrence G. W.
Published: May 2007

In May 2000, seedling death in grain sorghum (Sorghum bicolor L.) was reported in fields located in the delta region of Mississippi, following a wet planting season when precipitation and relative humidity were 50 and 10.5% greater, respectively, than the 5-year average. Seedlings exhibited various symptoms, including necrosis of the leaf tip and blade, collar rot, root rot, and streaking of the vascular system at the soil line that resulted in plant death. Tissue sections from plants with collar and root rot were plated aseptically on potato dextrose, V8, and cornmeal agars. Pythium ultimum was the only pathogenic fungus isolated and appeared on 63% of tissue sections. Recovered isolates exhibited similar growth and morphology in vitro and were stimulated to produce fruiting structures by the grass leaf-baiting method. Isolates produced primary terminal globose oogonia, 19 μm in diameter. Oospores were aplerotic and approximately 16.4 µm in diameter, with a 2.1-μm-thick wall. Antheridia were monoclinous or diclinous and short-stalked, with 1 to 2 antheridia per oogonium. Zoospores were produced only in sterile water grass blade cultures and were reniform and biciliate, erupting from spherical vesicles in groups of 15 to 30. Pathogenicity tests were conducted in a controlled growth chamber. P. ultimum was increased on sterile common millet seed and incorporated into sterile field soil at an 0.5% (vol/vol) ratio. Noninfested millet seed was incorporated into field soil as a control. Soil was placed in pots, planted with five-grain sorghum seed, and placed in a growth chamber at 5°C, with a 12-h photoperiod. Treatments were replicated five times, and the experiment conducted twice. At 21 days after planting, the inoculated grain sorghum plants developed collar and root rot, with some leaf necrosis, similar to symptoms observed in the field. Symptoms did not develop on the control plants. Reisolations of P. ultimum on corn meal agar and by the grass-baiting method were successful. P. ultimum commonly is in Mississippi soils and is pathogenic to a number of agronomic crops, although it has not been reported previously as a pathogen on grain sorghum in Mississippi.
Resistance to Cucumber mosaic virus in Cowpea and Implications for Control of Cowpea Stunt Disease
Authors: Gillaspie A. G.
Published: May 2007

Cucumber mosaic virus (CMV) and Blackeye cowpea mosaic virus (BlCMV) interact synergistically in dually infected plants of cowpea (Vigna unguiculata subsp. unguiculata) to cause cowpea stunt disease, the most damaging viral disease of this crop in the U.S. Sources of resistance to BlCMV are known and are present in cultivars of cowpea such as Pinkeye Purple Hull-BVR. However, no sources of CMV resistance have been found previously in cowpea. In 1998, PI 441918, a cowpea line growing in regeneration plots, was observed to have few viral symptoms, was not infected with BlCMV, and had a low titer of CMV when tested using direct antigen coating-enzyme-linked immunosorbent assay (DAC-ELISA). In greenhouse tests, infection of PI 441918 with CMV resulted in a lower titer of virus if the inoculated plants were from white seeds of PI 441918 than if the plants were from tan seeds of this PI, and a lower titer of virus than plants of the susceptible cultivar Coronet. In the field, with CMV- and BlCMV-infected plants of Coronet in spreader rows, plants from white seed of PI 441918 had no infection with BlCMV and a low infection rate with CMV. PI 441918 offers a high level of resistance to BlCMV and moderate resistance to CMV, which are important characteristics in a parental line to develop cultivars of cowpea resistant to cowpea stunt disease.