bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of Sources and Inheritance of Resistance to Sphaceloma Scab in Cowpea
Authors: Nakawuka C. K. , Adipala E.
Published: May 2007

Resistance in cowpea to Sphaceloma scab was characterized based on foliar and pod infection. Disease severity on cowpea plants was rated on a scale of 1 to 5, as follows: 1 = no symptoms, 2 = less than 10% infection, 3 = 10 to 20% infection, 4 = 20 to 50% infection, and 5 = more than 50% infection. Mean severity scores were used to calculate areas under the disease progress curve. Of the 75 cowpea lines evaluated, 10 were resistant, 30 were moderately resistant, and 35 were susceptible based on foliar infection. For pod infection, 24 lines were resistant, 40 were either moderately resistant or susceptible, and 11 were very susceptible. Local lines were less infected than plant introductions. In a separate experiment, 25 lines previously considered resistant were evaluated in the field with infested cowpea crop debris and susceptible rows as sources of inocula. Only 3 lines (39, KVu/175, and 46) maintained their high levels of resistance to Sphaceloma scab. Five cowpea lines were subsequently diallel-crossed, and parents and F2 were evaluated in the field to determine the nature of inheritance of resistance to Sphaceloma scab. The majority of the crosses between the resistant and susceptible lines showed intermediate reaction to scab, and high variation was obtained due to genotype and combining abilities. Partitioning of the variance into components due to general and specific combining ability revealed that additive genetic variation constituted the major portion of the total genetic variance for resistance to scab in cowpea.
First Report of Botrytis Blight, Caused by Botrytis cinerea, on Coneflowers
Authors: Chang K. F. , Howard R. J. , Hwang S. F.
Published: May 2007

Coneflowers (Echinacea purpurea (L.) Moench and E. pallida (Nutt.) Nutt. var. angustifolia (DC.) Cronq.) are popular medicinal herbs in North America and Europe. In May 1997, a previously undescribed disease was observed in a commercial field of 3-year-old E. pallida var. angustifolia plants in Vernon, British Columbia, Canada. Diseased plants had small to large, brown or black lesions on leaves and stems. Botrytis cinerea Pers.:Fr. (1,2) was consistently isolated from affected tissues. The pathogen appeared to infect leaves along the margins and tips, and occasionally on other parts of the blade as well. Lesions expanded rapidly under cool, humid conditions. Once the pathogen had invaded the midrib or veins, it advanced rapidly to the petiole and stem, which resulted in collapse of the leaf. The pathogen produced profuse conidia and mycelia on the surface of dead and dying leaves, stems, and blossoms, which resulted in a moldy gray appearance. Under dry conditions, the disease developed slowly or even became quiescent. Large lesions often split and formed holes in leaves. The average size of the conidia produced on naturally infected leaves ranged from 5.5 to 10.5 × 6.8 to 18.3 μm (average 8.1 × 13.0 μm), and on potato dextrose agar (1-month-old culture) ranged from 5.5 to 10.0 × 7.5 to 16.3 μm (average 7.4 × 11.3 μm) based on 100 spore measurements, respectively. Microsclerotia were round, spherical or irregular in shape, and ranged from 1.1 to 3.6 × 1.0 to 3.0 mm. Koch's postulates were verified by spraying potted, 3-month-old, narrow-leaved coneflower (E. pallida var. angustifolia) and 2-year-old purple coneflower (E. purpurea) plants with a spore suspension (4 × 105 conidia/ml). Inoculated plants were enclosed in transparent plastic bags for 7 days at 15/22°C (night/day) with a 12-h photoperiod. Typical symptoms were produced 2 to 7 days after inoculation. Some infected leaves quickly twisted and dried after removal of the plastic bags. Botrytis cinerea was reisolated from the affected tissues. This is the first report of Botrytis blight on Echinacea spp. Although B. cinerea does not usually kill coneflower plants, it often heavily infects disc flowers and young shoots. Therefore, Botrytis blight could have a significant impact on the establishment and productivity of this crop in both the field and greenhouse, especially under cool, wet, growing conditions.

References: (1) J. R. Coley-Smith et al. 1980. The Biology of Botrytis. Academic Press, New York. (2) D. J. Morgan. Trans. Br. Mycol. Soc. 56:319, 1971.
Tolerance to Cucumber Mosaic Virus in Pepper: Development of Advanced Breeding Lines and Evaluation of Virus Level
Authors: Lapidot Moshe , Paran Ilan , Ben-Joseph Rachel , Ben-Harush Serge , Pilowsky Meir , Cohen Shlomo , Shifriss Chen
Published: May 2007

Tolerance to cucumber mosaic virus (CMV) was introduced from an Indian small-fruited hot pepper accession, Perennial, into several bell-type sweet pepper lines by means of pedigree and backcrossing breeding procedures. Tolerance was determined to be incompletely dominant and quantitatively inherited. Breeding lines with variable degrees of tolerance were developed based on inspection of visual symptoms after mechanical inoculation. The breeding lines were subsequently tested for their agronomic performance in the field after mechanical inoculation. Their levels of tolerance in the field closely resembled their previous performances in the greenhouse. There was no association between virus accumulation levels in the upper leaves, as determined by enzyme-linked immunosorbent assay (ELISA), and the degree of tolerance to the virus, as determined by either visual symptoms or field performance. We concluded that the basis for developing tolerant breeding lines from Perennial is primarily their ability to recover from high virus titer and not their restriction of virus multiplication.
Genetic Variability Among Maize Inbred Lines for Resistance to the High Plains Virus-Wheat Streak Mosaic Virus Complex
Authors: Marçon A. , Kaeppler S. M. , Jensen S. G.
Published: May 2007

High plains virus (HPV) is a pathogen that causes a severe disease, especially in susceptible corn genotypes. The virus is transmitted by the eriophyid mite Aceria tosichella, which also transmits wheat streak mosaic virus (WSMV). This often results in a mixed infection by these two viruses. Genetic variability for resistance to the HPV exists among maize inbred lines but has not been characterized. The disease reaction of 30 maize inbred lines to the mixed infection and to WSMV alone was characterized in this study. Evaluation was based on symptom expression and virus titer (HPV and WSMV), as measured by enzyme-linked immunosorbent assay. All lines showed some HPV symptoms, which ranged from a few visible spots to rapid plant death. HPV-resistant inbreds include B73 and B14. Susceptible inbreds include W64A, Wf9, H100, N213, N215, and N194. Five of the six inbreds most severely affected by HPV also had a high WSMV titer, although they displayed few symptoms when inoculated with WSMV alone. Inbred N194 was one of the genotypes most susceptible to HPV, but it showed no detectable WSMV titer. Seedlings of highly susceptible genotypes often died within 2 weeks of infection.
First Report of Powdery Mildew in Greenhouse-Grown Tomatoes in New Jersey
Authors: White J. F. , Johnston S. A. , Wang C.-L. , Chin C.-K.
Published: May 2007

Powdery mildew of tomatoes caused by an Erysiphe sp. has been reported to occur in greenhouses in New York (2). In March and April of 1996, outbreaks of this disease were found in greenhouse-grown tomato plants of cv. PSR55809 at the Cook College campus in New Brunswick, NJ, and in cv. Match in commercial greenhouses in Burlington County, NJ. Identification of an Erysiphe sp. was made by comparative morphology of the conidial state since the perfect stage was not observed. Symptoms included development of patches of white mycelium predominantly on upper surfaces of older leaves followed by chlorosis of tissues colonized by the fungus. Microscopic examination of mycelium revealed the presence of typical Oidium conidiogenous cells and conidia. Conidiogenous cells were short and cylindrical and produce conidia in chains apically. Conidia were hyaline, cylindrical to ellipsoidal, and measured 36 + 4.9 × 16.7 + 2.2 μm (n = 20). Both conidia and symptoms of this powdery mildew are comparable to those previously given for the Erysiphe sp. described in New York (2). Another powdery mildew of tomato, caused by Oidiopsis sicula Scalia, occurs in the western U.S., Mediterranean Basin, Africa, and Asia. However, the conidia of O. sicula are of two types, pyriform and cylindrical, and they are larger than those of an Erysiphe sp. (1). To verify pathogenicity of this Erysiphe sp. to tomatoes, conidia washed from leaves were misted onto uninfected leaves of young tomato plants. After 1 week in a growth chamber (25°C; 80% relative humidity; 12 h of light), typical powdery mildew symptoms were evident on inoculated plants, while unmisted plants remained free of symptoms. Microscopic examination of the fungus on surfaces of leaves confirmed it to be an Erysiphe sp.

References: (1) R. N. Campbell and R. W. Scheuerman. Plant Dis. Rep. 63:1087, 1979. (2) D. M. Karasevicz and T. A. Zitter. Plant Dis. 80:709, 1996.
Races of Puccinia graminis in the United States During 1995
Authors: McVey D. V. , Long D. L. , Roberts J. J.
Published: May 2007

Wheat stem rust overwintered in southern Louisiana, southern Texas, southwestern Georgia, northeastern Arkansas, and southwestern South Carolina in the winter of 1994-95. Wheat stem rust caused negligible yield losses in wheat in the United States. Races Pgt-TPMK and QCCJ made up 39 and 31% of all isolates, respectively. Race TPMK comprised 67% of isolates from farm fields. Race Pgt-QCCJ was most common from barley, making up 93% from 47 collections. Six collections from Hordeum jubatum yielded six isolates each of races QCCJ and QFCS, and one isolate of race TPMK. No virulence was found to wheat lines with genes Sr6, 9b, 13, 22, 24, 25, 26, 27, 29, 30, 31, 32, 33, 37, Gt, or Wdl-1. Oat stem rust overwintered in plots at Beeville and Temple, Texas, in a field near San Antonio, and in southern Louisiana. Yield losses due to oat stem rust in 1995 were negligible. Race NA-27, virulent to Pg-1, -2, -3, -4, and -8, was again the predominant race in the United States, comprising 82% of the 225 isolates from 80 collections. NA-5 and NA-16 were the two other races identified from the United States, comprising 11 and 19% of the isolates. Only race NA-29 was found in four collections from Mexico.
First Report of Stevia as a Host of Sclerotinia sclerotiorum
Authors: Chang K. F. , Howard R. J. , Gaudiel R. G. , Hwang S. F.
Published: May 2007

Stevia (Stevia rebaudiana Bertoni; Asteraceae), an annual plant originating from Paraguay, contains glucosides of a diterpenoid (2), which is used as a low-caloric sweetener in some South American and southeast Asian countries. The main active ingredient, stevioside, is 100 to 300 times as sweet as sucrose. Stevia has been experimentally grown under field conditions in central and western Canada and has the potential to become a commercially viable alternative crop. In August 1996, a previously undescribed stem rot disease was observed on stevia plants at the Crop Diversification Centre South, Brooks, Alberta. The disease was found in research plots where 4-month-old plants were growing in loam soil. Diseased stems showed dark brown lesions above and at soil level when plant height reached approximately 30 cm. Under dry conditions, mild stem lesions caused plant stunting with lower leaves turning black and curling downward. Wilted leaf symptoms gradually spread upward in affected plants. Partial wilting symptoms appeared when girdling was restricted to branches. The entire plant collapsed when girdling of the crown and roots occurred. Superficial white mycelium developed over the basal part of affected stems under moist conditions, especially after rainy periods. Black, round to oblong sclerotia, 3.5 to 10.1 mm in size, formed externally on the crown areas after plant death. Sclerotinia sclerotiorum (Lib.) de Bary (1) was consistently isolated from the diseased plants. To confirm pathogenicity, 4-week-old stevia seedlings were obtained from shoot cuttings and grown in 12-cm pots of soilless mix. Sclerotia produced on potato dextrose agar were inserted into the mix 0.5 cm deep and 0.5 cm from the stems of test plants. Plants were placed in a growth chamber at 22°C with a 12-h photoperiod and 95% relative humidity. Two weeks after soil infestation, plants wilted and S. sclerotiorum was reisolated from the diseased crown tissues. This is the first report on stevia of sclerotinia stem rot, a disease that could significantly reduce foliar growth and stevioside production in field plantings.

References: (1) L. H. Purdy. Phytopathology 69:875, 1979. (2) T. Robinson. 1991. The Organic Constituents of Higher Plants: Their Chemistry and Interrelationships. 6th ed. Cordus Press, North Amherst, MA.
Pathogenicity of Fusarium oxysporum f. sp. phaseoli Isolates from Spain to Phaseolus vulgaris
Authors: Velasquez-Valle R. , Schwartz H. F. , Díaz-Mínguez J. M.
Published: May 2007

Fusarium oxysporum Schechtend.:Fr. f. sp. phaseoli J. B. Kendrick & W. C. Snyder (FOP) is the causal agent of the common bean (Phaseolus vulgaris L.) disease known as Fusarium wilt or Fusarium yellows. FOP has been reported from the Castilla y Leon region in Spain, where it is a serious problem on most commercial bean cultivars (1). Five FOP isolates from Spain (AB-6, AB-111, AB-112, AS-1, and AS-4) obtained from J. M. Díaz-Mínguez and the isolate FOP-CO1 (ATCC 90245) from Colorado were tested for pathogenicity on two American lines: Pinto U.I. 114, considered as a universal susceptible check, and Flor de Mayo, a Mexican landrace. Seedlings were root-clip inoculated and evaluated according to the CIAT 1 to 9 severity scale, in which 1 to 3 = resistant, 3.1 to 6 = intermediate, and 6.1 to 9 = susceptible. Three inoculum concentrations were tested: 104, 105, and 106 conidia/ml. AS-1 and AS-4 produced resistant reactions in both U.I. 114 (1.5 to 2.1 and 1.2 to 1.5) and Flor de Mayo (1.9 to 2.3 and 1.4), respectively, at all inoculum concentrations. Susceptible reactions to AB-6 (7.3 to 8.9), AB-111 (7.6 to 8.9), AB-112 (7.5 to 7.9), and FOP-CO1 (8.1 to 8.6) were observed in Pinto U.I. 114, regardless of inoculum concentration, although severity ratings increased as the inoculum concentration was increased. Flor de Mayo exhibited a susceptible reaction (6.7 to 7.8) to FOP-CO1 at all inoculum concentrations tested, and intermediate reactions to AB-6 (4.9), AB-111 (5.4), and AB-112 (5.0) at the lowest inoculum concentration. Susceptible reactions (7 to 8.2 for AB-6; 6.8 to 7.0 for AB-111, and 7.3 to 7.7 for AB-112) occurred with higher inoculum concentrations, and severity ratings increased as the inoculum concentration increased. Recently, FOP isolates from Greece and Italy were recognized as each belonging to different pathogenic races (2); consequently, more research on the Spanish isolates (AB-6, AB-111, and AB-112) is needed to determine if they are similar to the races reported from the Mediterranean Basin or should be classified as a new FOP race (s).

References: (1) J. M. Díaz-Mínguez et al. Plant Dis. 80:600, 1996. (2) S. L. Woo et al. Phytopathology 86:966, 1996.
Factors Affecting Sporogenic and Myceliogenic Germination of Sclerotia of Colletotrichum coccodes
Authors: Sanogo S. , Pennypacker S. P.
Published: May 2007

Two types of germination were exhibited by Colletotrichum coccodes when sclerotia, placed on moist filter papers in petri plates that were then either not sealed or sealed with Parafilm, were incubated for 5 days at temperatures of 10 to 34°C under a 14-h photoperiod. In sealed plates, germination was primarily myceliogenic; in nonsealed plates, sclerotial germination was only sporogenic. Setose, slightly orange-colored conidial masses were profusely produced on sclerotia at all temperatures greater than 10°C. Hyaline masses of conidia with sparse setae were produced on sclerotia maintained in complete darkness, and no mycelia formed in the sealed plates. In all temperature treatments, the numbers of colony-forming units per 100 sclerotia were greater in nonsealed than in sealed plates and greater under light than in complete darkness.
Chayote Mosaic, a New Disease in Sechium edule Caused by a Tymovirus
Authors: Hord M. , Villalobos W. , Macaya-Lizano A. V. , Rivera C.
Published: May 2007

A sap-transmissible virus was isolated from chayote (Sechium edule) in Costa Rica. Infected plants showed chlorotic spots and rings, and blotchy mosaics, which often coalesced to give a complete mosaic and leaf deformation. By electron microscopy, spherical virus-like particles of approximately 29 nm in diameter were visible, and cytological changes associated with the chloroplasts were observed. The virus particles sedimented in sucrose density gradients as two components, a top component of empty protein shells and a bottom component of electron-dense particles. Electrophoretic analysis showed a single-stranded RNA of approximately 5.7 kb and capsid protein (CP) subunits of ∼22 kDa. The virus was identified as a member of the tymovirus group on the basis of particle morphology, size, sedimentation in sucrose gradients, cytopathological effects, and capsid protein and genome properties, and it was tentatively named chayote mosaic virus (ChMV).
Colonization of Oak Wilt Fungal Mats by Ophiostoma piceae During Spring in Minnesota
Authors: Juzwik Jennifer , Meyer Jason M.
Published: May 2007

The colonization of Ceratocystis fagacearum fungal mats of different ages by Ophiostoma piceae on Quercus spp. was determined in three east-central Minnesota locations during the spring of 1995. The extent of the mat area colonized by O. piceae generally increased with mat age. Subsamples per mat yielding the fungus for the three locations averaged 11 to 27% for immature mats, 65 to 72% for mature mats, and 66 to 96% for aging and declining mats. On a mat-incidence basis, frequencies of O. piceae isolation from at least one subsample of an immature mat ranged from 30 to 53% compared with more than 90% for all other mat ages in the three locations. The average number of colony-forming units of O. piceae per square centimeter ranged from 1 × 103 to 1.2 × 106 and increased with mat age. The extent of C. fagacearum recovery from each mat was lower for aging plus declining mats (P < 0.03) compared with other ages in two locations. On a mat-incidence basis, frequency of C. fagacearum recovery from at least one subsample of a mat averaged 99% for all ages of mats in all locations. The interaction between O. piceae and C. fagacearum on mats, nitidulids, and the oak wound surface is discussed.
First Report of Rhizoctonia solani Causing a Foliar Leaf Spot on Brazilian Pepper-tree (Schinus terebinthifolius) in Florida
Authors: Semer C. R. , Charudattan R.
Published: May 2007

The Brazilian pepper-tree (Schinus terebinthifolius Raddi) native to Brazil, recently has become an aggressive perennial weed in southern Florida. During a survey in December 1995, a foliar disease was observed on several pepper-tree plants in Palm Beach County. Disease symptoms consisted of dark, reddish-purple necrotic lesions, either with or without dry necrotic centers, that were distributed randomly over the leaf surface. Infected leaf samples from two separate sites were plated on potato dextrose agar (PDA; Difco) and water agar and incubated at 25°C in the dark. A fungus resembling a Rhizoctonia sp. was consistently recovered. To prove Koch's postulates, the fungus was grown on PDA for 10 to 14 days, and the cultures blended in a Waring blender. Metamucil (Procter & Gamble) was added to the mixture at the rate of 0.5% wt/vol, and the suspension was used to spray and inoculate 2- and 3-month-old Brazilian pepper-tree seedlings. Seedlings were sprayed until the inoculum dripped off the foliage and after inoculation were maintained at 100% relative humidity. After 48 h in the dew chamber the inoculated seedlings were moved to a greenhouse bench and examined for infection 5 and 10 days later. Inoculation was completed three times with the leaf lesions occurring 94 to 100%. A Rhizoctonia sp. was recovered from the lesions that appeared on the challenged plants. A determination of the anastomosis group was performed by plating it against the tester isolates of R. solani, AG1-1A, AG2-2IV, AG-3, AG-4, and AG-5. In two separate tests anastomosis (imperfect fusion) (1) was observed between the recovered Rhizoctonia sp. and tester strain AG2-2IV of R. solani. The fungus was identified as R. solani, and this is the first report of R. solani causing a leaf lesion of Brazilian pepper-tree in Florida. The potential of this R. solani as a biological control agent of Brazilian pepper-tree remains to be tested.

Reference: (1) B. Sneh et al. Identification of Rhizoctonia Species. American Phytopathological Society, 1991.
Influence of Season and Cropping System on Occurrence of Cowpea Diseases in Uganda
Authors: Edema R. , Adipala E. , Florini D. A.
Published: May 2007

An on-farm survey was conducted for two seasons (first and second rains of 1994) to determine influence of season and cropping systems on occurrence of cowpea (Vigna unguiculata) diseases in Uganda. Viral diseases were widespread in both seasons but were more severe in the intercropped than in the nonintercropped cowpea. In contrast, scab, rust, and powdery mildew were less common and less severe when cowpea was grown in intercrops. High plant populations favored scab and anthracnose, but viral diseases were more severe under low plant populations. Higher incidence and severity of viral diseases, anthracnose, and scab were recorded during the first (wetter) season than during the second (drier) season. Disease level varied considerably among the common cultivars, but these differences may have been influenced by environmental differences.
Improved Detection of Potato Leafroll Luteovirus in Leaves and Tubers with a Digoxigenin-Labeled cRNA Probe
Authors: Loebenstein G. , Akad F. , Filatov V. , Sadvakasova G. , Manadilova A. , Bakelman H. , Teverovsky E. , Lachmann O. , David A.
Published: May 2007

A digoxigenin-labeled cRNA probe of approximately 2,100 bp was more than 2,000 times more sensitive in detecting potato leafroll virus (PLRV) in leaf extracts of Datura stramonium, Physalis floridana, and potatoes than enzyme-linked immunosorbent assay (ELISA). The limit of detecting PLRV with the probe was 1 pg/ml compared with 2 ng/ml by ELISA. The probe detected PLRV easily in dormant tuber tissues at dilutions of up to 1:100. There was no background reaction with healthy extracts. No reactions were observed between the probe and potato X potexvirus or potato Y potyvirus.
Inheritance of Leaf Rust Resistance in Wheat Cultivars Grandin and CDC Teal
Authors: Liu J. Q. , Kolmer J. A.
Published: May 2007

The hard red spring wheat cultivars Grandin and CDC Teal were genetically examined to determine the number and identity of the leaf rust resistance genes present in both wheats. The two cultivars were crossed with the leaf rust susceptible cultivar Thatcher, and the F1 plants were backcrossed to Thatcher. Fifty-four and 80 BC1F1 plants derived respectively from Grandin and CDC Teal were selfed to produce BC1F2 families. The BC1F2 families were tested as seedlings with isolates of Puccinia recondita f. sp. tritici that differed for virulence to specific leaf rust resistance genes. The BC1F2 families were also tested in the adult-plant stage in field rust nursery tests. Segregation of BC1F2 families in the seedling tests indicated that Grandin had resistance genes Lr2a, Lr3, and Lr10, and was heterogeneous for Lr16. CDC Teal was shown to have the seedling leaf rust gene Lr1. In field rust nursery tests, both Grandin and CDC Teal were shown to have adult-plant resistance genes Lr13 and Lr34. Additional leaf rust resistance genes that condition effective field resistance should be incorporated into hard red spring wheat cultivars to diversify the leaf rust resistance in this wheat class.
The Resistance of Mango (Mangifera indica) Cultivars to Tip Dieback Disease in Florida
Authors: Ramos Leandro J. , Davenport Thomas L. , McMillan Robert T. , Lara S. Pablo
Published: May 2007

The resistance of Mangifera indica to tip dieback disease caused by Botryosphaeria ribis, anamorphic state Fusicoccum sp., was determined on 361 trees of 122 mango cultivars and relatives planted in the mango germ plasm collection at the University of Florida, Tropical Research and Education Center, Homestead. Three trees from each cultivar were evaluated on a 1 to 5 scale ranging from those free of tip dieback to those with extensive branch necrosis. Each cultivar was assigned to one of eight major systematic groups based on race or geographic origin. Resistance to tip dieback disease was not associated with any of the groups. No significant differences in mean disease severity were found among the Indian, Southeast Asian, West Indian, Haden, or Sandersha parts of the Haden-Sandersha Complex, Turpentine types, or a group of unclassified cultivars. Two Mangifera species (M. odorata and M. zeylanica) showed the lowest mean disease rating. Cultivars were also grouped into monoembryonic and polyembryonic types. Although several mango cultivars, mainly found in the monoembryonic group, appeared to be free of the disease, resistance to tip dieback was not associated with embryony. This study provides the first indication that field resistance to tip dieback may be present in some mango cultivars.
Comparison of Detection Methods for Citrus Tristeza Virus in Field Trees During Months of Nonoptimal Titer
Authors: Mathews D. M. , Riley K. , Dodds J. A.
Published: May 2007

Enzyme-linked immunosorbent assay (ELISA) can reliably detect citrus tristeza virus (CTV) in samples collected during approximately 6 months of a typical year. Two reverse transcriptase polymerase chain reaction (RT-PCR) methods (total nucleic acid extract and immunocapture based) were evaluated and compared to ELISA in order to develop a more sensitive assay for CTV. From May 1994 to October 1995, 6 sweet orange trees infected with CTV from each of 2 geographic areas (Riverside and the San Joaquin Valley) were tested monthly by each method. In the months of August (San Joaquin Valley samples) and September (Riverside and San Joaquin Valley samples) several of the trees had a significant loss of virus titer such that CTV was not reliably detected by ELISA. By contrast, the 2 PCR methods gave definitive positive results for CTV in samples collected during these months. Different tissue types were analyzed by each of the above assays. Petioles and midribs, both phloem-rich tissues, were each satisfactory for ELISA, while distal leaf tips did not always produce a positive result. All tissue types were equally efficient in producing a positive result in both PCR-based assays. The results of this study provide a basis for CTV testing by PCR in months when virus titer drops to a level generally unacceptable for using ELISA.
Episodic Dynamics of Tar Spot of Annual Lespedeza Within and Among Years
Authors: Mihail J. D. , McGraw R. L. , Verslues P. E. , Taylor S. J.
Published: May 2007

The temporal and spatial dynamics of six tar spot epidemics were examined at two sites in mid-Missouri during 1990 to 1992. The sites, 48 km apart, differed in topography (flat versus slope), soil texture (silt loam versus silty-clay loam), and cropping history (orchard versus row crops). Temporal dynamics of disease incidence differed more among years than between sites. During 1990, temporal dynamics of the two epidemics followed a classic monotonic increase, whereas disease increase was episodic for the four epidemics observed during 1991 and 1992. Disease increase was associated with shading of the plant canopy or with the presence of dodder. Disease increase was related inversely to intercepted photosynthetically active radiation. Taken together, these observations suggest that factors that increase shading in the lespedeza canopy also increase tar spot incidence. For only two of the six epidemics was there a significant relationship between disease incidence (proportion of leaflets diseased) and disease severity (proportion of leaflet area diseased), with disease severity rarely exceeding 10%. These observations suggest that relatively low tar spot incidence may result in significant leaf losses, which would reduce lespedeza hay quality and yield. Further, this study demonstrates the importance of experimental repetition in both space and time to fully appreciate the range of disease dynamics for a single pathosystem.
First Report of Pythium myriotylum on Lemna gibba in Israel
Authors: Flaishman M. A. , Hadar E. , Hallak-Herr E.
Published: May 2007

Much interest has focused on duckweed as an alternative food source. Commercial production of Lemna gibba was initiated in Israel in 1991. During the summers of 1994 and 1995, Lemna gibba was grown commercially in covered ponds. In these two seasons, the plants were found to be infected by Pythium myriotylum, which has previously been reported as a pathogen of duckweed (1). In the ponds where the plants were held at high density, small, wilted, white patches of plants were recognized in early June. By the end of the month over 70% of the plants were infected and died. Microscopic examination of infected plants showed the presence of fungal appressoria and mycelial growth. Fungi were isolated from the plants onto potato dextrose agar (PDA). Ten isolates grown on PDA for 7 days were used to inoculate healthy plants. After 12 days, symptoms developed on plants at 28 or 32°C. Symptoms were similar to those observed on pond-grown plants. Plants maintained at 17 or 22°C did not become infected. The results from the pond and laboratory work showed that high plant density and temperature above 24°C were necessary for infection, and infection takes place by hyphal elements that spread in the water. This is the first report of Pythium myriotylum on Lemna gibba in Israel.

Reference: (1) E. Rejmankova et al. Veröff. Geobot. Inst. Eidg. Tech. Hochsch. Stift. Rübel, Zür. 87:178, 1986.
First Report of Lettuce Chlorosis Virus Naturally Infecting Sugar Beets in California
Authors: Wisler G. C. , Duffus J. E. , Gerik J. S.
Published: May 2007

Sugar beet (Beta vulgaris) plants showing interveinal yellowing and thickened leaves were collected from two fields in Imperial County, CA, for disease assessment in January 1996. Yellowing symptoms were widespread in these fields during the winter of 1995 to 1996. Initial enzyme-linked immunosorbent assays (ELISA) with polyclonal antiserum (ATCC) for beet western yellows virus were consistently negative. Inoculations with Bemisia tabaci “B” biotype (B. argentifolii) whiteflies onto the indicator plants Chenopodium capitatum, C. murale, lettuce (Lactuca sativa), and sugar beet resulted in interveinal yellowing, reddening, and thickened leaves characteristic of whitefly-transmitted closteroviruses (1). Western blot (immunoblot) analyses were performed with antisera to the purified virions of lettuce chlorosis virus (LCV) and lettuce infectious yellows virus (LIYV). Tissue extracts from original beet plants representing two fields and from all subsequent whitefly-inoculated indicator plants consistently showed a single band at ca. 32 kDa, reported to be the molecular mass for LCV capsid protein. Corresponding Western blot analyses for LIYV with the same tissue extracts were negative. No reactions were observed in Western blot assays with tissue extracts from healthy plants. Although sugar beet is a host for LCV as shown by laboratory experiments (1), this is the first report of a natural infection of LCV in sugar beet.

Reference: (1) J. E. Duffus et al. Eur. J. Plant Pathol. 102:591, 1996.
Benefits of Applications of Chlorothalonil for the Control of Black Mold of Tomato
Authors: Davis R. M. , Miyao E. M. , Mullen R. J. , Valencia J. , May D. M. , Gwynne B. J.
Published: May 2007

Chlorothalonil was applied 2, 4, 6, 2 and 4, or 4 and 6 weeks prior to tomato harvest in fields in four counties in California over a 3-year period to assess the economic benefits of chlorothalonil applications, if any, on the reduction of black mold caused by Alternaria alternata. The percentage of visually infected fruit was significantly reduced across all four sites in 2 of the 3 years. At one location, the incidence of black mold was reduced over 50% in all 3 years of the study by a single application of the fungicide. Overall, the mean yield of marketable fruit was 79.8 metric tons per hectare. An average of 5.1% of the fruit harvested in all locations and years had visible symptoms of black mold. Generally, the most effective treatment was a single application of the fungicide 6 weeks before harvest, with no further benefit from a second application of the fungicide. Based on the cost of the fungicide and its application, a single dose of chlorothalonil applied to plots in Solano County, where the highest incidence of disease occurred, would net the grower $160.47 return per hectare. The application of fungicide resulted in significant economic benefits in tests in two of the counties, where the disease is historically a problem.
Influence of Chloride and Nitrogen Form on Rhizoctonia Root and Crown Rot of Table Beets
Authors: Elmer Wade H.
Published: May 2007

The effect of NaCl combined with Ca(NO3)2 or (NH4)2SO4 was examined on table beets (Beta vulgaris) in the presence and absence of Rhizoctonia solani (anastomosis group 2-2), the cause of Rhizoctonia root and crown rot. Transplants of cvs. Detroit Dark Red and Early Wonder grown in the greenhouse in infested soils and fertilized with Ca(NO3)2 (10 mmol of N) were 32% larger in dry weight than plants treated with (NH4)2SO4 (10 mmol of N). In noninfested soils, a 17% increase in dry weights was observed for plants treated with Ca(NO3)2 compared to plants that were fed (NH4)2SO4. When NaCl (0.17 mmol) was applied, the mean dry weight sincreased 40% in noninfested soil and 12% in infested soil compared to plants that received no NaCl. No significant interaction occurred between N fertilizer and NaCl in greenhouse trials. However, in field soils infested with R. solani, NaCl (560 kg/ha) combined with (NH4)2SO4 (112kg of N per ha) produced 26 to 47% more root yield than when (NH4)2SO4 was used alone. Inthe absence of NaCl, Ca(NO3)2 suppressed disease more than (NH4)2SO4, but adding NaCl to Ca(NO3)2 did not increase yield more than Ca(NO3)2 alone. The Cl salts KCl, CaCl2, and MgCl2did not significantly differ from NaCl in their ability to increase the dry weight of beets grownin infested soils. Leaf and root analyses revealed that (NH4)2SO4 applications increased N, P, S, and Mn in tissue more than Ca(NO3)2 applications. Applying NaCl increased tissue levels of Na, Cl, and Mn more than in plants that were not fed NaCl. All of the Cl salts had the effect of increasing concentrations of Cl and Mn in the plant. There was no evidence that the Na ion was disease suppressive. Chloride, however, may be of use in disease management of Rhizoctonia root and crown rot of table beets.
New Races of Phytophthora sojae with Rps1-d Virulence
Authors: Abney T. S. , Melgar J. C. , Richards T. L. , Scott D. H. , Grogan J. , Young J.
Published: May 2007

Hypocotyl inoculations of differential soybean (Glycine max) cultivars were used to identify seven new physiologic races of Phytophthora sojae (syn. P. megasperma f. sp. glycinea). Five of the new races were virulent on soybeans with the Rps1-d allele, while four of the new races were virulent on soybeans with the Rps1-k allele. The Rps1-k and Rps1-d alleles provide resistance to a majority of the previously described races that cause Phytophthora root and stem rot. The seven new races were assigned race numbers 33, 34, 41, 42, 43, 44, and 45 since race numbers 35 through 40 were assigned to other new races recently identified in Ohio, California, Arkansas, and Iowa. The new races identified in this study constituted 14% of the 1993 isolates evaluated from 27 counties in central and northern Indiana. Races 1 and 3 were the most prevalent, representing 31 and 26% of the P. sojae isolates identified in 1993. Races 4, 6, 7, 8, 9, 13, 28, and 29 each constituted 2 to 6% of the 1993 isolates. Other races identified among the 1993 isolates included races 19, 21, 25, and 30.
Infection Efficiency of Venturia inaequalis Ascospores as Affected by Apple Flower Bud Developmental Stage
Authors: Sanogo S. , Aylor D. E.
Published: May 2007

The average infection efficiency of ascospores of Venturia inaequalis deposited on cluster leaves of apple flower buds was 6 to 16%, 3 to 9%, and 0.4 to 0.6% at tight cluster, first pink, and full pink-to-bloom, respectively. No lesions were observed on flower bud cluster leaves at petal fall. However, the leaves on the vegetative shoot emerging from the flower bud were highly susceptible; the average infection efficiency of ascospores on these leaves was 6 to 21%. The infection efficiency was more variable on young cluster and vegetative shoot leaves than on developing and mature cluster leaves. Results from this study indicate that differences in infection efficiency of V. inaequalis ascospores could be identified by apple bud growth stages.
Risk Assessment for Karnal Bunt Occurrence in the Pacific Northwest
Authors: Smiley Richard W.
Published: May 2007

Tilletia indica, the causal agent of Karnal bunt of wheat, was first detected and reported in the United States in 1996. Karnal bunt occurred in the southwestern United States as early as 1992. Wheat contaminated with teliospores of T. indica is likely to have been transported from the Southwest to other regions, including the Pacific Northwest, before presence of the pathogen was discovered. Teliospore and sporidial germination and infection are highly dependent on climatic conditions. The potential for T. indica to infect wheat in the Pacific Northwest has not been reported. The objective of this study was to use published information on environmental factors favorable for infection and historical climate data for the Pacific Northwest to analyze the environmental risk for Karnal bunt to occur if wheat fields in the Pacific Northwest become contaminated by T. indica. Conditions during the past four decades appeared favorable for infection in nonirrigated wheat during 1 of every 3 years at two (Corvallis, OR, and Spokane, WA) of 13 Idaho, Oregon, and Washington locations examined, and every year at all locations where wheat is irrigated. If introduced to the area, it appears possible for T. indica to become established in selected regions of the Pacific Northwest.
First Report of Phomopsis longicolla Infection of Cowpea Pods and Seeds in Mississippi
Authors: Roy K. W. , Ratnayake S.
Published: May 2007

Mature cowpea (Vigna unguiculata (L.) Walp.) pods with scattered, irregular black spots, similar in appearance to those found on mature soybean (Glycine max (L.) Merr.) pods infected with Phomopsis longicolla T. W. Hobbs, were observed in three fields in Oktibbeha County, MS, in September 1994. In a delayed harvest sample of pods and seeds from one field, a fungus identified as P. longicolla (1) was isolated from more than 60% of surface-disinfested, excised pod disks and from 42% of surface-disinfested seeds. Average frequencies of isolation from seeds harvested at the normal time from the other two fields were 27 and 9%. When surface-disinfested soybean seeds (cv. Avery) were placed along the margins of P. longicolla colonies on potato dextrose agar, the radicals from most germinating seeds became necrotic and many seeds did not germinate. Koch's postulates were completed by reisolating the fungus from diseased tissue.

Reference: (1) T. W. Hobbs et al. Mycologia 77:535, 1985.
Occurrence of Vine Decline Diseases of Muskmelon in Guatemala
Authors: Bruton B. D. , Miller M. E.
Published: May 2007

Central American countries have become major production areas of melons (Cucumis melo L.) destined for export to Europe and the United States during the winter months. Double cropping in the same fields year after year has created serious vine decline diseases in melons grown in the Capco area of Guatemala. Vines typically appear healthy until the fruit are approaching maturity, when the crown leaves begin to turn yellow and collapse and the decline gradually radiates outward. There was evidence of slightly water-soaked lesions in the crown of some plants; however, the symptoms were not similar to charcoal rot or gummy stem blight. The roots exhibited some decay, lesions, and discoloration, but were not macerated and rotten. A minimum of 10 affected plants were collected from each of nine fields in the Capco area of Guatemala. Isolations were made from the crown area, primary root, and secondary roots of selected plants by excising 3- to 5-mm pieces and surface sterilizing them for 30 to 60 s with 0.5% sodium hypochlorite. The isolations were made on 2% water agar plus 0.1 g of streptomycin sulfate per liter. Plates were examined for fungal growth daily for 5 days with hyphal tips from all colonies transferred to potato dextrose agar and Synthetischer nährstoffärmer agar (2) and allowed to sporulate. Isolations revealed the presence of several fungi capable of causing vine decline or suspected of being involved in the vine decline complex. Rhizoctonia solani Kühn and Fusarium semitectum Berk. & Ravenel were isolated from more than 50% of plants in some fields. F. semitectum, R. solani, and a Stagonospora-like fungus were isolated from 38, 18, and 17% of the total plants, respectively. R. solani was isolated from the crown more often than from the roots, but its role is not understood. With one exception, F. semitectum was always isolated from the crown area, which may suggest a more significant role in the vine decline complex than suspected previously. The Stagonospora-like fungus, isolated from 30% of the plants from one field, has been reported as a pathogen of cantaloupe that may contribute to the vine decline complex (1). Monosporascus cannonballus Pollack & Uecker and Fusarium oxysporum Schlechtend.:Fr. emend. W. C. Snyder & H. N. Hans. were isolated from 60% of the plants from one field. It was the only field in which M. cannonballus was isolated. Plectosporium tabacinum (van Beyma) M. E. Palm, W. Gams et Nirenberg, a cucurbit pathogen, was isolated infrequently. This is the first report of M. cannonballus, P. tabacinum, and the Stagonospora-like fungus in Guatemala.

References: (1) M. E. Miller et al. Phytopathology 86:S3, 1996. (2) H. I. Nirenberg. Mitt. Biol. Bundesanst. Land Forstwirtsch. Berlin-Dahlem. 169:1, 1976.
First Report of Colletotrichum gloeosporioides f. sp. manihotis, Cause of Cassava Anthracnose Disease, Being Seed-borne and Seed-Transmitted in Cassava
Authors: Fokunang C. N. , Ikotun T. , Dixon A. G. O. , Akem C. N.
Published: May 2007

Cassava anthracnose disease is a major economic disease of cassava in the tropics (2). Infection can lead to a significant loss in planting materials and total field crop failure. The disease has been reported to be transmitted mainly by a bug (Pseudotheraptus devastans Dist) (1). Open pollinated seeds from 13 cassava (Manihot esculenta Crantz) genotypes, stored for 10 months after harvest in 1994, were used to investigate the presence of the cassava anthracnose disease fungus. Seeds, 200 from each genotype, were surface sterilized, cultured on potato dextrose agar (PDA), and incubated for 8 days, at 25 ± 2°C. Microscopic examination indicated that Colletotrichum gloeosporioides was one of the seed-borne fungi, with up to 40% incidence recorded in some genotypes. Seeds from five susceptible genotypes selected for seed transmission studies were planted in fine, steam-sterilized soils in jiffy pots and watered daily for seedling emergence. At a height of 10 to 15 cm, the seedlings were transferred to plastic pots (10.5 cm in diameter) filled with sterilized mixture of soil and sand (2:2, vol/vol). Pots were placed close to each other to obtain a thick plant canopy. Temperature of 25 to 32°C and humidity of 80 to 98% were maintained. After 45 days, some plants had cassava anthracnose symptoms, including defoliation, wilt, and necrotic lesions. Stems, leaves, and roots of infected plants were washed, surface sterilized, and plated on PDA for 5 to 7 days. Microscopic observation of the fungus showed conidia of C. gloeosporioides. The rest of the plants were monitored for 3 months under vector-free conditions for typical anthracnose symptoms. Mean maximum wilt and defoliation of 35 to 38% was recorded in some genotypes. Conidial suspensions of C. gloeosporioides were used in stem-puncture inoculations of young, healthy cassava plants. The typical anthracnose symptoms of stem necrosis were observed 2 weeks after inoculation, confirming isolates as C. gloeosporioides f. sp. manihotis. This is the first report of C. gloeosporioides f. sp. manihotis being seed-borne and seed-transmitted in cassava.

References: (1) B. Boher et al. Agronomie 3:989, 1983. (2) J. C. Lozano. PANS 20:30, 1974.
Occurrence of Squash Mosaic Comovirus Infecting Summer Squash (Cucurbita pepo) in South Dakota and Transmission by Diabroticabarberi
Authors: Langham M. A. C. , Gallenberg D. J. , Gergerich R. C.
Published: May 2007

Summer squash (Cucurbita pepo L.) exhibiting strong mosaic symptoms and leaf deformations were found in Brookings County during the summers of 1994 and 1995. Four isolates were mechanically transmitted to C. pepo cv. Early Prolific Straightneck. Ouchterlony double diffusion tests (conducted both in Arkansas and South Dakota) and protein-A enzyme-linked immunosorbent assays (ELISAs) with squash mosaic virus (SqMV) antisera provided by R. C. Gergerich were positive for SqMV. Pumpkin mosaic virus, a strain of SqMV, was previously reported infecting pumpkin in South Dakota (1). The pumpkin strain was differentiated from other strains of SqMV by its ability to infect lentil (Lens esculenta Moench), garden pea (Pisum sativum L.), and fenugreek (Trigonella foenum-graecum L.). The South Dakota isolates in this study did not infect these hosts, although the Arkansas isolate was found to infect Pisum sativum cvs. Little Marvel and Dwarf Gray Sugar Pod when tested serologically. The presence of adult Diabrotica undecimpunctata howardii Barber and D. barberi (Smith and Lawrence) was noted on infected plants in the area. Transmission tests were conducted with D. barberi provided by the USDA-ARS Northern Grain Insect Research Laboratory, Brookings, SD. The beetles had been previously reared on artificial diet media and germinated corn seed. Individual beetles were given a 48-h acquisition access period on infected or healthy detached squash leaves in petri dishes followed by a 48-h inoculation access period on Early Prolific Straightneck squash plants (1 beetle per plant). Beetles were removed at the end of this period, and the plants were grown under greenhouse conditions for 3 weeks. Plants were assayed for SqMV by protein-A ELISA. Transmission percentages of SqMV were as follows: SqMV (Arkansas isolate), 16.7%; and four South Dakota isolates, 12.5, 11.4, 14.6, and 5.1%. Beetles fed on healthy plants did not transmit virus. The rate of transmission found in this study indicates that D. barbari serves as an efficient vector for the transmission of SqMV in field plantings.

Reference: (1) W. N. Stoner. Proc. S. D. Acad. Sci. 56:178, 1977.