bluuebunny/crossref_metadata_2025 huggingface dataset:
Discharge and Dissemination of Ascospores by Venturia inaequalis During Dew
Authors: Stensvand Arne , Amundsen Terje , Semb Lars , Gadoury David M. , Seem Robert C.
Published: May 2007

Abundant airborne ascospores of the apple scab pathogen (Venturia inaequalis) have never before been observed during periods of dew. We studied ascospore release in V. inaequalis in two orchards in southeastern Norway using Burkard 7-day volumetric spore traps. At Ås in 1990, 1992, and 1997, and at Svelvik in 1992, a total of 14.8, 1.4, 0.27, and 26.9%, respectively, of the season's total spore release was trapped during periods of dew. Dew followed by spore release was observed 22 days at the two locations. During one night with dew at Ås in 1990 and two nights with dew at Svelvik in 1992, approximately 13 and 20%, respectively, of the season's total spore numbers were observed. High numbers of spores were trapped prior to sunrise, and on an average, 48.4% of the spores were trapped prior to 0400 in the morning. Episodes in which more than 1% of the season's inoculum was released during dew occurred around bloom of apple, which is the peak period for ascospore discharge, and followed more than 2 days of fair weather (clear, warm days and cool, humid nights). The ordinary suppression of ascospore release in V. inaequalis during darkness has been overcome in previous studies under laboratory conditions when protracted periods favorable for ascospore maturity occur without opportunity for ascospore discharge. This is the first confirmed report of relatively large (>10% of the season's total inoculum) numbers of airborne ascospores in orchards during dew. The sequential occurrence of specific weather conditions, for example (i) fair-weather days, (ii) cool nights with abundant dew formation, (iii) significant release and dispersal of airborne ascospores, and (iv) poor drying conditions or additional hours of leaf wetness due to fog or rain, would be required for dew-released ascospores to constitute a threat of infection. Absent the foregoing, release during dew is more likely to deplete the ascospore supply with no consequent increase in the overall risk of disease.
Eucalyptus Rust: A Disease with the Potential for Serious International Implications
Authors: Coutinho T. A. , Wingfield M. J. , Alfenas A. C. , Crous P. W.
Published: May 2007

Eucalyptus spp. are propagated extensively as non-natives in plantations in many parts of the tropics and sub-tropics. A number of diseases result in serious losses to this economically important forest resource. Eucalyptus rust, caused by Puccinia psidii, is one such example. The economic losses due to this disease are the result of infections of seedlings, young trees, and coppice. P. psidii occurs predominately in Central and South America, but reports of a similar rust are known from other areas. Eucalyptus rust is a remarkable disease in that the pathogen is not known on eucalypts in their centers of origin. It has apparently originated on native Myrtaceae in South America and is highly infective on some Eucalyptus spp. planted there. P. psidii causes one of the most serious forestry diseases in Brazil and is considered to be the most serious threat to eucalypt plantations worldwide. Advances in eucalyptus rust research are reviewed here, with a focus on topics such as distribution, host range, pathogen specialization, symptomatology, etiology, epidemiology, and control.
First Report of Natural Infection of Pisum sativum subsp. elatius by Mycosphaerella pinodes in Bulgaria
Authors: Kaiser W. J. , Muehlbauer F. J. , Hannan R. M. , Mihov M.
Published: May 2007

Pisum sativum L. subsp. elatius (Steven ex M. Bieb.) Asch. & Graebn. is a wild pea species that is native to Bulgaria. It readily crosses to the cultivated pea species P. sativum subsp. sativum. Field pea is an important component in the crop rotation system of the northeast region of Bulgaria. Little is known or published on the diseases of wild Pisum subspecies. In June 1997, brown to reddish brown, irregularly shaped lesions 5 to 10 mm in diameter were found on the leaves and stems of P. sativum subsp. elatius growing under native conditions in the low growing vegetation in a mixed forest habitat on the Black Sea coast at Albena, Bulgaria (43°22′26″N; 28°05′02″E) at an elevation of about 50 m. Black pycnidia were observed within lesions and contained hyaline, primarily two-celled conidia that measured 7 to 17 × 3 to 5 μm. On artificially inoculated pea stem pieces incubated on 2% water agar (WA) at 22 to 24°C for 28 days, pseudothecia developed with hyaline, two-celled ascospores constricted at the septum and measuring 12 to 17 × 4 to 7 μm. Black chlamydospores produced singly or in chains also formed in infected foliar tissues and on potato dextrose agar (PDA) and WA. Isolations were made from the lesions on pea tissue onto WA and PDA after disinfesting in 0.25% NaOCl for 5 min. Koch's postulates were fulfilled by inoculating the foliage of P. sativum subsp. sativum cvs. Dark Skin Perfection and Sounder and P. sativum subsp. elatius (W6-20047), and reisolating the fungus from lesions that developed on the inoculated leaves and stems. The wild Pisum fungus was identified as Mycosphaerella pinodes (Berk. & Blox.) Vestergr. based on cultural and morphological characteristics (2), pathogenicity tests, and by comparing random amplified polymorphic DNA (RAPD) markers with those of American Type Culture Collection (ATCC) isolates 201628 to 201633 of M. pinodes. The fungus was identified as a pathogen of cultivated peas in Bulgaria by Kovachevsky and Hristov (1) in 1949. This is the first report of M. pinodes infecting P. sativum subsp. elatius in Bulgaria and other countries where P. sativum subsp. elatius is a native plant species.

References: (1) I. H. Kovachevsky and A. Hristov. 1949. Bulgarian Acad. Sci., Scientific-Popular Ser. 10. (2) E. Punithalingam and P. Holliday. 1972. CMI Descript. of Pathog. Fungi and Bacteria, no. 340. Commonwealth Mycol. Institute, Kew, England.
Widespread Occurrence of Tomato Geminiviruses in Brazil, Associated with the New Biotype of the Whitefly Vector
Authors: Ribeiro S. G. , de Ávila A. C. , Bezerra I. C. , Fernandes J. J. , Faria J. C. , Lima M. F. , Gilbertson R. L. , Maciel-Zambolim E. , Zerbini F. M.
Published: May 2007

Although tomato golden mosaic virus (TGMV) was reported in Brazil more than 20 years ago (3), tomato-infecting geminiviruses have not been of economic significance in the country until recently. However, a sharp increase in the incidence of geminivirus-like symptoms in tomatoes has been reported in several areas of Brazil since 1994. This has coincided with the appearance of the B biotype of Bemisia tabaci, which, as opposed to the A biotype, readily colonizes solanaceous plants (2). We have isolated geminiviruses from symptomatic tomato plants in the Federal District, in two different areas of the state of Minas Gerais, and in the state of Pernambuco. Tomato plants in these areas showed a variety of symptoms, including yellow mosaic, severe leaf distortion, down-cupping, and epinasty. Whitefly infestation was high in all fields sampled, and in some fields, particularly in Pernambuco, incidence of virus-like symptoms was close to 100%, and no tomatoes of commercial value were harvested (1). Using primer pairs PAL1v1978/PAR1c496 and PCRc1/PBL1v2040 (4), DNA-A and -B fragments were polymerase chain reaction (PCR)-amplified from total DNA extracted from diseased plants, cloned, and sequenced. Sequence comparisons of the PCR fragments indicated the existence of at least six different geminiviruses. The nucleotide sequence homologies for DNA-A fragments ranged from 67 to 80% for the 5′ end of the cp gene, and from 44 to 80% for the 5′ end of the rep gene. Data base comparisons indicated the viruses are most closely related to TGMV, bean golden mosaic virus from Brazil (BGMV-Br), and tomato yellow vein streak virus (ToYVSV), although homologies were less than 80% for the fragments compared. A similar lack of a close relationship with each other and other geminiviruses was obtained with two DNA-B component PCR products compared, corresponding to the 5′ end of the BC1 open reading frame. Infectious, full-length genomic clones from the tomato viruses are being generated for biological and molecular characterization.

References: (1) I. C. Bezerra et al. Fitopatol. Bras. 22:331, 1997. (2) F. H. França et al., Ann. Soc. Entomol. Bras. 25:369, 1996. (3) J. C. Matyis et al. Summa Phytopathol. 1:267, 1975. (4) M. R. Rojas et al. Plant Dis. 77:340, 1993.
Phototropism of Conidial Germ Tubes of Botrytis cinerea and Its Implication in Plant Infection Processes
Authors: Islam S. Z. , Honda Y. , Sonhaji M.
Published: May 2007

The germ tubes of Botrytis cinerea showed negative phototropism to near ultraviolet (NUV) and blue (300 to 520 nm) light followed by far-red (700 to 810 nm), whereas red light (600 to 700 nm) induced positive phototropism significantly. Minimum germ tube growth occurred during exposure to negative phototropism-inducing wavelengths, whereas it was maximum under positive phototropism-inducing wavelengths. NUV radiation and blue light that induced negative phototropism of B. cinerea promoted infection-hypha formation on both onion scale and broad bean (Vicia faba) leaf epidermal strips, whereas positive phototropism-inducing red light suppressed it, resulting in a high proportion of germ tubes without infection hyphae. In broad bean leaf infection, the number of infection points and area of necrosis per drop of conidial suspension were higher under NUV radiation and blue light than that of a dark control or leaflets pretreated with NUV radiation and blue light. In contrast, lower numbers of infection points and very small necrotic lesions developed under red light. In the case of red-light-pretreated leaflets, the number of infection points developed were higher, but areas of necrosis did not increase significantly compared with leaflets kept under red light without pretreatment. These results show the importance of phototropism of conidium germ tubes in plant infection.
Purification and Characterization of Peach Mosaic Virus
Authors: Gispert Carmen , Perring Thomas M. , Creamer Rebecca
Published: May 2007

Virus particles were observed by transmission electron microscopy in preparations extracted from symptomatic leaves of Chenopodium amaranticolor that had been mechanically inoculated with peach mosaic virus. The particles were long, flexuous, filamentous rods with an average length of 888 nm. Purified preparations had an A 260/280 nm ratio of 1.25. RNA extracted from purified virus was approximately 8.1 kilobases, and a capsid protein of approximately 27 kDa was found. Polyclonal rabbit antiserum, produced against purified virus, reacted with samples from peach mosaic and cherry mottle leaf-infected plants when used in Western blot analysis.
Changes in Cell Ultrastructure and Zeatin Riboside Concentrations in Hedera helix, Pelargonium zonale, Prunus avium, and Rubus ulmifolius Leaves Infected by Fungi
Authors: López-Carbonell M. , Moret A. , Nadal M.
Published: May 2007

Ultrastructural alterations in epidermal and mesophyll cells and variations in endogenous zeatin riboside (ZR) concentrations were studied in leaves of Hedera helix, Pelargonium zonale, Pru-nus avium, and Rubus ulmifolius infected by Colletotrichum trichellum, Puccinia pelargonii-zonalis, Cercospora circumscissa, and Phragmidium violaceum, respectively. Infected tissues showed a marked increase in vesicles, myelin-like structures, and electron-dense bodies associated with plasma membranes. The main changes to the chloroplast included thylakoid swelling and disruption of the chloroplast envelope. The ZR content of the green islands was always higher than that of the yellow, senescent parts of the same leaves; the highest levels of ZR were observed in the green areas of infected Prunus avium (462.2 pmol g-1 fresh weight [FW]) and Rubus ulmifolius (441.6 pmol g-1 FW), followed by Pelargonium zonale (263.8 pmol g-1 FW) and Hedera helix (219.8 pmol g-1 FW); the yellow zones of the same leaves had lower ZR contents (78.3, 73.9, 73.6, and 18.1 pmol g-1 FW, respectively). The green islands had almost the same ZR content as the controls (green healthy leaves). These results suggest a relationship between ultrastructural alterations and ZR content of these plant species (blackberry, cherry, English ivy, geranium) in reacting to this type of biotic stress and could confirm the role of cytokinins as senescence-delaying hormones.
Reactions of Open-Pollinated Sweet Corn Cultivars to Stewart's Wilt, Common Rust, Northern Leaf Blight, and Southern Leaf Blight
Authors: Pataky J. K. , du Toit L. J. , Revilla P. , Tracy W. F.
Published: May 2007

Over 800 open-pollinated (OP) varieties of sweet corn were grown and named in the century prior to the development of hybrids, but only a few of the historically important OP cultivars exist today. Alleles that could improve disease resistance of modern sweet corn may be present in the OP cultivars still in existence. The objectives of this research were to compare 36 OP sweet corn cultivars to modern commercial hybrids for reactions to Stewart's wilt, common rust, northern leaf blight (NLB), and southern leaf blight (SLB), and to classify the OP cultivars based on phenotypic reactions to these four diseases. Plants were inoculated in 1994, 1995, and 1996 with Erwinia stewartii, Puccinia sorghi, Exserohilum turcicum, or Bipolaris maydis. Symptoms were rated on a whole-plot basis, and ratings were analyzed by analysis of variance (ANOVA). Means were separated by Bayesian least significant difference values. Some of the OP cultivars had phenotypes that were intermediate to moderately resistant to Stewart's wilt, common rust, NLB, or SLB, but none of the cultivars were more resistant than the best commercial hybrids. Distributions of ratings for rust, NLB, and SLB were less disperse for the OP cultivars than for commercial hybrids. Hence, the resistance of modern sweet corn germ plasm to Stewart's wilt, rust, and NLB appears to be greater than that of the OP cultivars. OP cultivars and four standard hybrids were placed into groups based on a hierarchical cluster analysis of disease reactions. The seven groups formed from the cluster analysis of disease ratings were considerably different than those formed from isozyme variation and morphological characteristics. The partial resistance of some cultivars, e.g., Golden Sunshine, Country Gentleman, Stowell's Evergreen, and Red, may be relatively diverse since these cultivars were placed in different groups based on isozyme and morphological variation. OP cultivars with moderate levels of resistance may be sources of resistance alleles not present in commercial hybrids.
Management of Meloidogyne hapla on Lettuce in Organic Soil with Sudangrass as a Cover Crop
Authors: Viaene Nicole M. , Abawi George S.
Published: May 2007

Host suitability for Meloidogyne hapla of six cover crops was tested in the greenhouse. Sudan-grass cv. Trudan 8 and rye (mixture of cultivars) were nonhosts; oat cv. Porter was a poor host; and phacelia cv. Angelia, oilseed radish cv. Renova, and yellow mustard cv. Martigena were maintenance hosts. When incorporated as a green manure before planting of lettuce cv. Mon-tello, sudangrass was the most effective of the cover crops in reducing egg production of M. hapla. Soil amendment with all parts of sudangrass resulted in lower reproduction of M. hapla on lettuce than soil amendment with only roots of sudangrass. Soil incorporation of 2-month-old (or younger) tissues of sudangrass was more effective in reducing nematode reproduction on subsequent lettuce plants than incorporation of 3-month-old tissues. Sudangrass was grown as a cover crop after lettuce for three growing seasons in field microplots and incorporated as a green manure before the first fall frost. Weight of lettuce heads was significantly higher and reproduction of M. hapla was significantly lower in sudangrass-amended microplots compared with those left fallow between lettuce crops, but results varied with year and nematode infestation level.
First Report of Colletotrichum coccodes on Soybean in the United States
Authors: Riccioni L. , Conca G. , Hartman G. L.
Published: May 2007

Anthracnose symptoms were observed on soybean (Glycine max (L.) Merr.) cv. Yale in Illinois in September 1996. Lower stems were girdled by lesions that contained black fungal stroma. Colletotrichum coccodes (Wallr.) S. J. Hughes was isolated from surface-sterilized portions of diseased stems incubated on potato dextrose agar (PDA). Cultures produced abundant black sclerotia and acervuli with setae. Acervuli produced straight and fusiform conidia (15 to 23 × 3 to 4 μm) in honey-colored masses. Ovate or long clavate appressoria were formed on slide microcultures. Pathogenicity tests were carried out in the greenhouse on soybean plants, cvs. Panda and Pony at the V4 growth stage, by (i) spraying a conidial suspension (2 ×106 conidia per ml) on seedlings and (ii) placing a mycelial PDA plug above the first two nodes of the stem, previously wounded with a sterile needle. Plain sterile water and plugs without mycelia were used as controls. Six plants per cultivar and per treatment were used. Plants were covered with polyethylene bags for 3 days. Anthracnose symptoms gradually appeared near maturity and plants senesced prematurely with both inoculation methods. Averaged over both cultivars, 100 and 50% of the plants showed symptoms when inoculated with a conidial suspension and mycelial plugs, respectively. Control plants did not have any symptoms. C. coccodes was consistently reisolated from stems, leaves, petioles, and pod peduncles with symptoms, and was not reisolated from noninoculated plants. Seeds collected from plants inoculated with either method showed infection rates up to 14 and 8% on cvs. Panda and Pony, respectively, while seeds collected from control plants showed 0% infection rate. The most common pathogen associated with soybean anthracnose is C. truncatum (Schwein.) Andrus and W. D. Moore, but other species have been reported to cause anthracnose. C. coccodes was reported on soybean in Italy (1). This pathogen has a wide host range and causes serious damage, mostly on solanaceous crops. This is the first report of the presence of the pathogen on soybean in the United States.

Reference: (1) G. Conca et al. Petria 4:193, 1994.
Root Rot by Rhizoctonia solani on Ambrosia grayi in Texas
Authors: Wheeler T. A. , Dotray P. , Winchester J.
Published: May 2007

Ambrosia grayi (A. Nelson) Shinners is a pernicious perennial weed that infests over 200,000 ha of cotton in Texas and New Mexico. It reproduces primarily by rhizomes, which are found up to 3 m deep in the soil. With the exception of Roundup Ultra on Roundup-ready cotton, no herbicides can be applied in-season to control this weed without injuring cotton. A search was conducted for soilborne pathogens as potential biocontrol agents by surveying cotton fields and small lakes for A. grayi plants with root lesions. Roots were washed with running water for 2 min and segments of root lesions were placed on water agar (1.5%) with hyphae of emerging fungi transferred to potato dextrose agar (PDA). Eighty isolates of fungi were collected; most were Fusarium spp. or Rhizoctonia solani. Replicated experiments with isolates were conducted. Each isolate was grown on PDA and then 1/4 of the media in a petri plate (12.6 cm2) was mixed with 450 cm3 autoclaved soil and placed in a styrofoam cup. A piece of rhizome (3 to 5 cm in length) was placed 5 cm below the soil surface in the infested cup. Roots with necrosis were plated on PDA to recover fungi, which were grown in pure culture and used to reinfest soil. Significant disease (in repeated tests) was caused by two isolates of R. solani, compared with the noninfested check, as indicated by a reduction in number of emerging plants per pot, increase in root necrosis, and decrease in fresh and dried leaf weight. Roots growing from the infected rhizomes were discolored and rotted without distinct lesions. Both of these isolates were identified as AG4 by anastomosis with tester ATCC #46134 by the cellophane technique (1).

Reference: (1) D. E. Carling et al. Phytopathology 77:1609, 1987.
Thlaspi arvense, a New Host for Alternaria brassicicola
Authors: Cobb A. C. , Dillard H. R.
Published: May 2007

A leaf spot was observed on cruciferous weeds growing in a cabbage field located in Geneva, NY, on 1 August 1996. The leaf spots on the weeds were dark gray to black in color and varied in size from pinpoints to 1 mm in diameter. The cabbage (Brassica oleracea L. var. capitata L.) was infected with Alternaria brassicicola (Schwein.) Wiltshire, the cause of Alternaria leaf spot. The weeds were identified as Thlaspi arvense L., a winter annual commonly referred to as field pennycress, stinkweed, or fanweed depending on geographic location. Isolations from the diseased weed tissue yielded A. brassicicola (2). The numerous conidia occurred in chains of 10 or more, ranged in size from 14 to 53 μm in length, were 5 to 18 μm wide, contained from 1 to 6 transverse septa with rare longitudinal septa, and were olivaceous in color. An apical beak was absent. On potato dextrose agar (PDA) the colony was dark olive-green to black in color and velvety. Seed was collected from the T. arvense plannts in the spring of 1997. One hundred seeds were placed in petri plates containing PDA amended with 0.01% of chloramphenicol and streptomycin sulfate. A. brassicicola was not isolated from the seeds. A different area of the field was planted to cabbage in 1997 and the cruciferous weeds were allowed to grow. The 1997 population of T. arvense consisted of plants from the previous season that flowered early and plants from seeds that germinated late in the season but did not flower. A. brassicicola was isolated from nonflowering weeds in September and from flowering weeds in October. Nonflowering plants were removed from the field in November, planted in pots, and placed in the greenhouse to induce flowering. Identity of both plant populations was confirmed as T. arvense (Warren Lamboy, Cornell University, Geneva, NY). Pathogencity of A. brassicicola isolates from T. arvense was demonstrated on cabbage and T. arvense by following Koch's postulates. Conidia (105) from a 5-day-old culture isolated from T. arvense grown on PDA were atomized onto field pennycress and cabbage plants with a Preval sprayer. The plants were enclosed in plastic bags and put under lathe shading in the greenhouse. The pathogen was reisolated from symptomatic tissue of both plants after 5 days. This weed could serve as a potential source of A. brassicicola inoculum because it is not controlled by herbicides used in crucifer production systems. Alternaria raphani has been reported on T. arvense in Canada (1). This is believed to be the first report of A. brassicicola on T. arvense.

References: (1) K. Mortensen et al. Can. Plant Dis. Surv. 73:129, 1993. (2) P. Neergaard. 1945. Danish Species of Alternaria and Stemphylium. Oxford University Press, London. pp. 137–138.
Pathogenicity and Formulation of Typhula phacorrhiza, a Biocontrol Agent of Gray Snow Mold
Authors: Wu C. , Hsiang T.
Published: May 2007

In previous testing, we found that gray snow mold, caused by Typhula ishikariensis or T. incarnata, could be controlled by applying T. phacorrhiza onto turf grass prior to snowfall. To test for phytopathogenicity of this biocontrol agent, the five most disease-suppressive isolates were cultured on mixed grains and applied to 12 turfgrass cultivars and 2 winter wheat cultivars in December 1995 and 1996. After snow melt in April 1996 and 1997, significantly greater winter injury was visible on plots treated with the pathogens compared to T. phacorrhiza-treated plots or untreated plots. Except for one cultivar in 1996, there were no significant differences between T. phacorrhiza-treated plots and untreated plots. Pelletized alginate formulations of T. phacorrhiza containing kaolin clay with various nutritional amendments were tested for viability and efficacy. After 64 weeks of storage, viability remained >85% at -15°C and >70% at 4°C, but <30% at 10°C and 25°C. Significant control of gray snow mold by T. phacorrhiza using small numbers of pellets (20 g/m2) was equivalent to using larger amounts of mixed grain inoculum (200 g/m2) or wheat bran inoculum (100 g/m2) in 2 years of field testing.
A Leaf Inoculation Method for Detection of Xanthomonas oryzae pv. oryzicola from Rice Seed
Authors: Xie G. L. , Mew T. W.
Published: May 2007

A leaf-inoculation method for detecting Xanthomonas oryzae pv. oryzicola in rice seed was developed and tested. The method is based on inoculating leaf segments on agar with seed washings in a moist chamber. Freshness of inoculated leaf segments is maintained by addition of 75 to 100 ppm benzimidazole to the 1% water agar after sterilization. Using cells from pure cultures, the minimum inoculum concentration to initiate leaf streak lesions on the segments was found to be 103 CFU/ml. Inoculum prepared from seeds harvested from severely infected mother plants induced lesions typical of leaf streak, followed by bacterial ooze. With 4 g of seed, the incubation period was 3.5 days and bacterial ooze appeared within 5 days. The minimum amount of seed needed to detect the bacterium based on seed washings varied according to disease severity of the mother plants. The bacteria isolated from lesions on the leaf segments were confirmed as X. oryzae pv. oryzicola after bacteriological, serological, and Biolog tests were conducted. The results confirm that the detached-leaf method is as simple and reliable as the immuno-radiometric assay and inoculation on intact pot-grown rice plants in the greenhouse.
Performance of Frogeye Leaf Spot-Resistant and -Susceptible Near-Isolines of Soybean
Authors: Mian M. A. R. , Boerma H. R. , Phillips D. V. , Kenty M. M. , Shannon G. , Shipe E. R. , Blount A. R. Soffes , Weaver D. B.
Published: May 2007

Frogeye leaf spot (FLS) caused by Cercospora sojina Hara is a disease of soybean (Glycine max (L.) Merr.) that causes significant seed yield losses in warm, humid environments of southeastern United States. The Rcs3 gene in soybean has been reported to condition resistance to all known races of C. sojina. The objectives of this study were to determine the effectiveness of Rcs3 in limiting seed yield loss due to FLS and to compare the seed yield of the resistant and susceptible near-isolines (NILs) in the absence of significant FLS disease. Four pairs of NILs—Colquitt/Colquitt-Rcs3, Gordon/Gordon-Rcs3, Thomas/Thomas-Rcs3, and Wright/Wright-Rcs 3—were evaluated in 23 field experiments in Alabama, Florida, Georgia, Louisiana, Mississippi, and South Carolina during 1992 to 1994. The amount of damage to susceptible soybean caused by FLS was dependent on the specific environment. All four of the Rcs3 NILs were resistant to the prevalent races of FLS in all environments. In the absence of significant FLS disease, each of the Rcs3 NILs was at least equal to the respective susceptible line in its seed yield. In the presence of FLS infestation, the susceptible lines suffered significant seed yield loss (up to 31%) compared to their Rcs3 NILs. The effect of FLS on seed yield was dependent on cumulative disease severity over the growing season. Thus, the area under disease progress curve was more useful than percent of leaf area infected at the end of the growing season (R7 stage of development) in explaining the seed yield loss due to FLS.
A Sensitive ELISA for Pythium ultimum Using Polyclonal and Species-Specific Monoclonal Antibodies
Authors: Yuen G. Y. , Xia J. Q. , Sutula C. L.
Published: May 2007

A double-antibody sandwich indirect enzyme-linked immunosorbent assay (ELISA) was developed for the detection and quantification of Pythium ultimum. A polyclonal antibody produced to cell walls of P. ultimum was used as the capture antibody, while a P. ultimum-specific mono-clonal antibody (MAb E5) was used for recognition of the fungus. In the ELISA, culture extracts of 7 isolates of P. ultimum exhibited strong positive reactions, whereas none of the 37 isolates of other Pythium spp. and fungal genera had positive reactions. P. ultimum was detected by ELISA in roots of bean, cabbage, and sugar beet seedlings grown in pathogen-infested soil. ELISA optical density readings for infected bean and sugar beet root samples were highly correlated (r > 0.9) with infection levels determined by culturing the samples on water agar. The correlation between the two methods of testing cabbage roots was low, but all cabbage roots in which P. ultimum was detected by culturing were strongly positive in the ELISA. Samples of roots infected with P. irregulare and those with no Pythium infection did not react in the ELISA. The ELISA was highly sensitive; the fungus was detected in culture extracts diluted 1:5,000,000 and in roots with less than 1 infection per 100 cm root.
Leafroll Virus Is Common in Cultivated American Grapevines in Western New York
Authors: Wilcox W. F. , Jiang Z.-Y. , Gonsalves D.
Published: May 2007

American grapevines (Vitis labrusca L. ‘Niagara’; Vitis × labruscana L. H. Bailey ‘Concord’ and ‘Catawba’; V. labrusca × V. riparia Michx. ‘Elvira’) from 24 vineyards in the New York portion of the Lake Erie production region (>13,000 ha cultivated) were tested to explore a possible relationship between virus infection and an unexplained fruit set malady in the district. One-year-old cane segments were collected 4 to 6 weeks before budbreak from 65 individual vines, which previously had been identified as malady positive or negative. Preparations from bark scrapings were tested for the presence of double-stranded (ds) RNA and for fan leaf degeneration virus, tobacco streak virus, and grapevine leafroll associated closterovirus-3 (GLRaV-3) by enzyme-linked immunosorbent assay (ELISA). Mechanical transmission of other potential viruses to Chenopodium quinoa was attempted with sap extracted from young shoots forced from intact segments of sampled canes. GLRaV-3 was detected in 17 (26%) of the sampled vines from eight (33%) of the vineyards, but there was no apparent relationship between infected vines and the fruit set malady. Vines of all four cultivars were infected. dsRNA was detected in all 17 samples positive for GLRaV-3 plus four additional samples. No other viruses were detected. Near harvest, nine vines (from two vineyards) previously testing positive for GLRaV-3 were examined and retested; all nine tested positive again, although none showed any overt symptoms of viral infection. This is believed to be the first report of GLRaV-3 from American grape vineyards in New York. The source of these infections is unknown: all vines were self rooted, the individual vineyards had been planted independently at different times, and V. vinifera and its hybrids are rare in the district. Wild grapevines (primarily V. riparia) are abundant in the region, although it has been reported that leafroll disease does not occur naturally in wild North American grapes (1). Nevertheless, our results indicate that cultivated American grapevines can be common reservoirs of GLRaV-3, and furthermore suggest the need to reassess the possibility that wild grapes also may serve as reservoirs of the virus. Trials are currently underway to determine possible effects of GLRaV-3 on cv. Concord, the most widely planted variety in the region.

Reference: (1) A. C. Goheen. 1988. Leafroll. Page 52 in: Compendium of Grape Diseases. R. C. Pearson and A. C. Goheen, eds. American Phytopathological Society, St. Paul, MN.
Downy Mildew of Arugula, Caused by Peronospora parasitica, in California
Authors: Koike S. T.
Published: May 2007

Over the past 5 years, commercial acreage of the leafy crucifer arugula (Eruca sativa) has increased greatly in the Salinas Valley (Monterey County), California, and the crop is an important component in packaged salad products. A foliar disease has affected this crop and at times reduced its quality to the extent that it could not be harvested. Symptoms consisted of small (1 to 4 mm in diameter), irregular, dark brown to black speckling on adaxial leaf surfaces. Speckling sometimes expanded into tan spots 3 to 8 mm in diameter. Corresponding abaxial surfaces usually supported white fungal growth typical of a downy mildew. Conidiophores had main trunks with dichotomous branches ending in slender curved tips. Conidia were ovoid in shape, measuring 22 to 25 μm long and 19 μm wide. The fungus was identified as Peronospora parasitica. Pathogenicity was established by gently pressing diseased leaves onto arugula test plants and incubating plants in a humidity chamber for 48 h. Downy mildew developed after 6 days and the same fungus was observed. Although this disease has occurred on this crop for several years, this is the first documentation of P. parasitica on arugula in California. A previously described foliar bacterial disease caused by Pseudomonas syringae (1) has similar symptoms, making field diagnoses difficult if fungal signs of the downy mildew are not present on the leaf.

Reference: (1) S. T. Koike et al. Plant Dis. 80:464. 1996.
Models of Early Spring Survival of Wheat Leaf Rust in the Central Great Plains
Authors: Eversmeyer M. G. , Kramer C. L.
Published: May 2007

Severe leaf rust epidemics, which result in economic yield reductions in the Great Plains wheat-producing region of the United States, are usually initiated by Puccinia recondita f. sp. tritici inoculum that has survived in the local field from the previous wheat crop until early spring. Models were developed for an epidemic year beginning at physiological maturity of one wheat crop to maturity of the following wheat crop. Meteorological variables for periods prior to final tiller development of the wheat crop during 1980 to 1992 at several sites in the central Great Plains winter-wheat-production area were used to model inoculum survival from one wheat crop until early spring of the next crop. Stepwise multiple regression was used to identify weather variables that explained the most variation in inoculum survival at the final tiller development wheat growth stage. Inoculum survival was recorded on a 0 to 9 scale with 0 indicating no survival and 9 indicating inoculum on all wheat plants in the field. Independent variables used in development of models were daily deviations from the 10-year average of maximum and minimum temperature, fungal temperature equivalence function, cumulative fungal temperature function, precipitation, cumulative precipitation, and snow cover averaged for 10-day periods prior to dates inoculum forecasts were desired. Models were constructed to forecast inoculum survival from data collected prior to fall wheat planting, the beginning of winter dormancy of the wheat, and the final tiller development wheat growth stage. Of the observed occurrences of leaf rust overwintering, 70% were forecast by models constructed using weather data prior to wheat planting decision time. Overwintering could be forecast by models constructed with data prior to the wheat entering winter dormancy 80% of the time. Models constructed with data collected prior to final tiller development in the spring forecast overwintering of leaf rust inoculum 95% of the time. Results from these models will be used to develop forecasts of leaf rust epidemics and resulting yield reductions.
Tomato Yellow Leaf Curl Virus-Is Causes a Novel Disease of Common Bean and Severe Epidemics in Tomato in Spain
Authors: Navas-Castillo Jesús , Sánchez-Campos Sonia , Díaz Juan Antonio , Sáez-Alonso Elisa , Moriones Enrique
Published: May 2007

Field surveys were conducted in the autumn of 1997 in the main tomato (Lycopersicon esculentum)-growing regions of southern Spain following a severe tomato yellow leaf curl epidemic in tomato. Tomato yellow leaf curl virus (TYLCV)-Is was found to have spread to all regions and to coexist with TYLCV-Sr, which has been present since 1992. TYLCV-Is was also shown to be the causal agent of bean leaf crumple, a novel disease that has caused severe economic losses in fresh-market common bean (Phaseolus vulgaris) crops of southern Spain since September 1997. The disease was reproduced by infecting beans with cloned TYLCV-Is obtained from infected tomato plants collected in Almería. This is the first report of bean leaf crumple disease and the first report of a geminivirus in bean from Spain.
Root Diseases and Nematodes in Bahiagrass-Vegetable Rotations
Authors: Sumner D. R. , Minton N. A. , Brenneman T. B. , Burton G. W. , Johnson A. W.
Published: May 2007

A double-crop of cucumber-snap bean was grown continuously for 4 years and compared with rotations of 1, 2, or 3 years of bahiagrass followed by vegetables. No nematicides or soil fungicides were applied. Root and hypocotyl disease severity in snap bean from Rhizoctonia solani AG-4 and Pythium spp. was decreased after 2 years of bahiagrass compared with 1 year of bahiagrass and 1 year of vegetables or continuous vegetables. Root galling caused by Meloidogyne incognita was less following 2 or 3 years, but not 1 year, of bahiagrass than following continuous vegetables. The beneficial effect of the rotation with bahiagrass lasted only 1 year. Then root injury from soilborne pathogenic fungi and root-knot nematodes was similar to that in continuous vegetables. Plant populations and yield of vegetables were greater following 3 years of bahiagrass than following 1 year of bahiagrass and 3 years of vegetables or continuous vegetables. Two years of bahiagrass followed by 1 or 2 years of vegetables did not increase yield of vegetables consistently.
Spatial Distribution of Green Mold Foci in 30 Commercial Mushroom Crops
Authors: Royse D. J. , Boomer K. , Du Y. , Handcock M. , Coles P. S. , Romaine C. P.
Published: May 2007

Statistical analyses were performed on spatial distributions of mushroom green mold foci caused by Trichoderma spp. in 30 standard Pennsylvania doubles (743 m2production surface) selected at random from over 900 total crops mapped. Mapped production houses were divided into four tiers of six beds each with 16 sections per bed (total = 384 sections per double). Each section contained approximately 2 m2. Green mold foci were mapped according to presence or absence in each section as they became visible during the course of the mushroom production. There was a trend toward higher disease incidence at the ends of the doubles, although this was not consistent from level to level. Spatial analysis revealed that green mold foci were more likely to occur in neighboring sections along the beds rather than above, below, or across from each other. Cultural practices that were associated with movement along the beds, i.e., nutrient supplementation, spawning, bed tamping, surface covering, etc., were considered the most likely factors influencing the incidence of green mold in spawned compost. Airborne contamination was considered a less likely source of inocula contributing to epidemic development. Sanitation practices that reduce spore loads along the beds are expected to provide the greatest degree of green mold control.
Corn Stunt Complex Mollicutes in Belize
Authors: Henríquez N. P. , Kenyon L. , Quiroz L.
Published: May 2007

Successive plantings of sweet corn in Orange Walk District, Belize (<200 m ASL) were observed to be performing poorly. Plants were stunted with shortened upper internodes, over-production (proliferation) of ears, and chlorosis of ears and leaf bases. Plants of hybrid white corn in Cayo District (<200 m ASL) had leaf-base chlorosis, mid-vein reddening, chlorotic bands on the leaves, and die-back of leaf tips: symptoms attributed to infection by the corn stunt complex (CSC) pathogens. Spiroplasma kunkelii was detected in symptom-bearing leaf-base samples of white corn but not sweet corn, using a specific F(ab')2 protein-A enzyme-linked immunosorbent assay (ELISA; D. Gordon, Ohio). Polymerase chain reactions with maize bushy stunt (MBS) phytoplasma-specific primers (1) resulted in amplification products of the expected size (740 bp) when DNA extracts from either sample type were used as template. DNAs from apparently healthy sweet or white corn from the field, or from glasshouse-grown sweet corn, did not yield this product. MBS and S. kunkelii are transmitted by leafhoppers of the genus Dalbulus, often simultaneously with maize rayado fino virus, the other CSC component (not tested for in this study). All the sweet corn varieties examined had a high incidence of the symptoms, suggesting that they are highly susceptible to one or both of the CSC mollicutes. With the increase in area dedicated to maize production and successive year-round plantings, the potential for spread and increased incidence of MBS or CSC in Belize is considerable.

Reference: (1) N. A. Harrison et al. Plant Dis. 80:263, 1996.
First Observation of the Breakdown of High Resistance in Yangambi km 5 (Musa sp.) to the Black Leaf Streak Disease in Cameroon
Authors: Mouliom-Pefoura A.
Published: May 2007

The most important diseases of Musa spp. in Cameroon, as in many other banana-producing areas, are those caused by Mycosphaerella musicola and M. fijiensis. Investigations during 1988 and 1989 in Cameroon in areas under high disease pressure revealed that Yangambi was highly resistant to M. fijiensis. During field observations between September 1992 and September 1994, necrotic symptoms were recorded on Yangambi from October to February in 1992-93 and 1993-94 and from June to September in 1994 at elevations of 700 to 1,100 m. In 1995, perithecia were recorded from necrotic tissues between May and November at 80 m, between September and October at 700 and 900 m, and between October and November at 1,100 m; mean number of perithecia per mm2 of samples was 8.6, 10.6, 17.6, and 17.9 at 80, 700, 900, and 1100 m, respectively. No viable ascospores was isolated from them. In 1997, this variation in the behavior of Yangambi was confirmed at 1,250 m elevation with necrosis between late August and early December, and ascospores of M. fijiensis were isolated from samples collected during October. Appearance of necrosis occurs when optimal climatic conditions for the development of M. fijiensis are obtained. This first and complete shift in pathogenicity of M. fijiensis to overcome the resistance of Yangambi is the end of a process that started 5 years ago after almost 8 years' exposure of the cultivar in the same locality.
Claviceps africana Discovered in India
Authors: Bogo A. , Mantle P. G.
Published: May 2007

The African ergot pathogen (Claviceps africana Frederickson, Mantle, & de Milliano) of sorghum (Sorghum bicolor (L.) Moench) was recently discovered in the Americas (4) and Australia, having previously only been recognized outside Africa in Thailand and Japan (3). The fungus provides a striking example of intercontinental epiphytotics of uncertain origins. Another fungus (C. sorghi Kulkarni, Seshadri & Hegde), the anamorph of which (Sphacelia sorghi McRae) is morphologically similar to that of C. africana and also causes ergot disease of sorghum, is considered to be the pathogen endemic to the Indian subcontinent (1,2). Five isolates of endemic ergot pathogen of sorghum from different locations in Southern India were provided as C. sorghi by ICRISAT, Hyderabad. The isolates were morphologically indistinguishable when cultivated on an asparagine-sucrose-salts agar, producing a white mycelium but no spores. Suspensions of hyphal fragments of each isolate were inoculated into gaping florets of a male-sterile sorghum grown at the Chelsea Physic Garden, London, in 1998. Infection of a few florets occurred with difficulty (<0.1% efficiency) by two of the isolates (from Andhra Pradesh and Madhya Pradesh states) to give a pathology typical of C. africana (2), especially with respect to the prominent young sphacelium forcing the glumes apart before first exudation of honeydew, the low concentration of honeydew oligosaccharides, and the white cascade of secondary sporulation on honeydew. This sphacelial fructification functioned as highly infective inoculum in other inflorescences, readily producing similar pathology leading to the formation of persistently small, roughly spherical “sclerotia” that were typical of C. africana in the recent American epiphytotics, but bearing none of the sclerotial characteristics of C. sorghi. Analysis of ergot tissue from near-mature inflorescences revealed dihydroergosine, an alkaloid that differentiates C. africana from C. sorghi, together with festuclavine, the identity of which was shown by GCMS (gas chromatography-mass spectrometry) (2). This evidence from pathogen isolates was complemented by analysis of a sample of small, spherical “sclerotia” from ICRISAT that also had a similar alkaloid composition. It is therefore clear that C. africana is now in India and this influences not only the interpretation of data on sorghum ergot disease published in recent years from that region, where the identity of the pathogen may not have been rigorously monitored, but also future phytopathological strategies for sorghum more widely in Asia.

References: (1) R. Bandyopadhyay et al. Plant Dis. 82:356, 1998. (2) D. E. Frederickson et al. Mycol. Res. 95:1101, 1991. (3) P. G. Mantle and H. A.-G. Hassan. Int. Sorghum Millets Newsl. 35:97, 1994. (4) E. M. Reis et al. Plant Dis. 80:463, 1996.
The Complex Viral Etiology of St. Augustine Decline
Authors: Cabrera Over , Scholthof Karen-Beth G.
Published: May 2007

St. Augustine decline is a viral disease of St. Augustinegrass, a turfgrass grown in the Gulf Coast region of the United States. Analyses of 204 plants in two locations in southeast Texas indicate that the disease is caused by an infection with panicum mosaic virus (PMV), alone or in any combination with satellite panicum mosaic virus (SPMV) and/or its satellite RNAs (satRNAs). This is the first report of the incidence of PMV satRNAs in field samples of St. Augustinegrass. Leaf symptoms of plants collected from the field ranged from severe bleaching to a mild chlorotic mottle, but after 5 months in the greenhouse, the plants had a relatively homogeneous chlorotic mottle phenotype, suggesting that environmental conditions have a significant influence on the development of this disease.
Electron Microscopic Detection of Novel, Coiled Viruslike Particles Associated with Graft-Inoculation of Prunus Species
Authors: James D. , Godkin S. E. , Rickson F. R. , Thompson D. A. , Eastwell K. C. , Hansen A. J.
Published: May 2007

Coiled, viruslike particles (spirions) were detected by electron microscopic examination of crude extracts from flowers, leaves, and/or roots of infected Prunus avium, P. mume, and P. serrulata. The particles were observed in ultrathin sections of lower epidermis, palisade, and spongy mesophyll cells of leaves of P. avium and P. mume. Spring (March and April) appears to be optimal for detection of the particles in both screenhouse and field-grown plants. The particles were successfully graft-transmitted to P. armeniaca (cvs. Luizet and Tilton), P. avium (cvs. Bing, F12/1, Mazzard, and Sam), P. mahaleb, and P. persica (cv. Elberta). Individual spirions measured 132 × 34 nm. The particles appear to be coiled forms of a filamentous virus. Filaments extending from some coiled particles were approximately 13 nm wide, with striations at a pitch of 3.24 nm. No disease symptoms or cytopathological abnormalities were associated with the presence of the particles in the Prunus species studied. The particles were not detected in virus-free control plants.