bluuebunny/crossref_metadata_2025 huggingface dataset:
A Model Defining the Relationship Between Temperature and Leaf Wetness Duration, and Infection of Watermelon by Colletotrichum orbiculare
Authors: Monroe J. S. , Santini J. B. , Latin R.
Published: May 2007

Controlled environment experiments were conducted to determine the relationship between temperature, leaf wetness duration, and infection of watermelon by Colletotrichum orbiculare. Flats of watermelon seedlings were inoculated and exposed to various combinations of temperature (12, 15, 18, 21, 24, 27, and 30°C) and leaf wetness duration (2, 4, 8, 12, 16, and 24 h). The experimental design was a split-plot, with whole units represented by temperature and subunits represented by leaf wetness duration. Anthracnose incidence, defined as the percentage of symptomatic seedlings in each flat 10 days after inoculation, increased with increasing leaf wetness duration at all levels of temperature. The optimum temperature for infection ranged from 21 to 24°C. At most temperatures, as little as 2 h of leaf wetness was required for infection. Analysis of variance with orthogonal polynomial contrasts and multiple regression procedures was used to define the relationship of anthracnose incidence to temperature and leaf wetness duration.
Increased Organic Matter in the Growing Medium Decreases Benlate DF Phytotoxicity
Authors: van Iersel M. W. , Bugbee B.
Published: May 2007

Some benzimidazole fungicides are phytotoxic to bedding plants. Organic pesticides are bound to the organic matter fraction in the root zone and their availability to plants depends on the composition of the growing medium. Thus, pesticide phytotoxicity may be affected by the fraction of organic matter in the growing medium. We conducted two studies to examine the relationship between benzimidazole phytotoxicity and organic matter content of the growing medium. In the first study, plants were grown in diatomaceous earth, containing no organic matter, and drenched with different fungicides. Benlate DF reduced carbon accumulation (growth) of the plants by 32 and 73% at the 0.5× and 1× label rate, respectively. Carbon gain of plants drenched with either Derosal or 3336 WP was similar to that of the control plants. Both Benlate DF and 3336 WP significantly decreased the number of flowers on the plants. The second study quantified the phytotoxicity of Benlate DF in media containing different amounts of organic matter. The growth of Benlate DF-treated plants was strongly affected by the amount of peat. Net photosynthesis decreased and the severity of visual symptoms (chlorosis) of Benlate DF phytotoxicity increased in media containing less peat. Benlate DF phytotoxicity strongly depends on the amount of organic matter in the growing medium, probably due to sorption of the active ingredient of Benlate DF and/or its breakdown products to the organic matter.
Benefits of Cotton Seed Treatments for the Control of Seedling Diseases in Relation to Inoculum Densities of Pythium Species and Rhizoctonia solani
Authors: Davis R. M. , Nunez J. J. , Subbarao K. V.
Published: May 2007

Twenty-five field trials conducted over a 3-year period in five San Joaquin Valley counties included the following treatments: nontreated cotton seed; seed treated with myclobutanil for the control of Rhizoctonia solani-induced damping-off; seed treated with metalaxyl for the control of Pythium-induced damping-off; and seed treated with a combination of the two fungicides. The following parameters were measured: soil populations of Pythium spp. and R. solani at planting, soil temperature at planting, air temperatures for 5 days after planting, soil particle analysis, EC, calcium, pH, organic matter, and plant stands from each treatment. In 1993 and 1994, myclobutanil and the combination of the two fungicides resulted in improved stands in 15 of 18 fields. Metalaxyl did not increase stands in any field in 1993 to 1994. In 1995, the combination of fungicides increased stands relative to the nontreated seeds and was more effective in increasing stands than myclobutanil or metalaxyl alone. Pythium populations were much greater in 1995 than in 1993 to 1994 and may explain the increase in plant stands with the combination of fungicides and metalaxyl alone. Covariate analysis of the data indicated no relationship between stand increases from fungicide seed treatment and any of the soil parameters measured. Heat units following planting were not limiting and had no effect on stands. Populations of pathogens were not related to benefits of fungicides, with the exception of a negative correlation between stand increases from seed treatment with myclobutanil and Pythium populations. Apparently, seed protected with a fungicide active against R. solani were more susceptible to infection by Pythium spp. In general, the fungicide seed treatment active against R. solani increased stands of the cultivar Maxxa regardless of soil type and pathogen populations. Increased stands from the metalaxyl treatment occurred in 1 of the 3 years of the study.
Integration of Biological and Chemical Controls for Rhizoctonia Aerial Blight and Root Rot of Rosemary
Authors: Conway K. E. , Maness N. E. , Motes J. E.
Published: May 2007

Aerial blight, caused by Rhizoctonia solani AG-4, was identified as a major disease of greenhouse mist-produced rosemary cuttings. An isolate of the biocontrol fungus Laetisaria arvalis, selected for tolerance to the experimental fungicide CGA 173506, was used as an amendment to potting soil. Combined treatment of rosemary with L. arvalis and a foliar spray of the fungicide at one-half the recommended rate reduced disease more than treatment with either the fungus or fungicide alone. Similar synergism was not observed for combinations of Trichoderma harzianum as a soil amendment and a foliar spray of the fungicide iprodione applied at the labeled rate.
First Report of Grapevine Virus A in Spain
Authors: Zabalgogeazcoa I. , de Blas C. , Cabaleiro C. , Segura A. , Ponz F.
Published: May 2007

Grapevine trichovirus A (GVA), a flexuous, filamentous, phloem-limited virus with an approximately 7.3-kbp RNA genome, is widespread in grapevines showing symptoms of leafroll and/or rugose wood. The virus can be mechanically inoculated to Nicotiana benthamiana and N. clevelandii. A field survey of diseased Vitis vinifera white and red cultivars was carried out in Pontevedra (northwest Spain) during the autumn of 1993. We detected the presence of GVA in vines showing leafroll symptoms by an immunocapture-reverse transcription-polymerase chain reaction (PCR) method (2) with GVA-specific primers (1). Bands of the expected size of 430 bp were obtained with extracts from petioles and stem bark as reaction substrates. To verify these results, Northern (RNA) blots with double-stranded (ds) RNAs isolated from grapevines were prepared. Hybridization was positive in two out of 10 samples analyzed. The probe was a 32P-labeled 430-bp PCR product amplified from extracts of N. benthamiana plants infected with GVA strain Is151 (gift of A. Mina-fra). The specificity of this probe was confirmed in dot blot hybridization, as a positive signal was obtained with extracts from GVA-inoculated N. benthamiana, but not with extracts of phosphate buffer-inoculated N. benthamiana, turnip mosaic potyvirus-inoculated Arabidopsis thaliana, or potato potyvirus Y-inoculated N. xanthi plants. The probe did not hybridize to dsRNAs extracted from enzyme-linked immunosorbent assay-positive GLRaV-III-infected grapevines. GVA has been identified in other Mediterranean countries, but to our knowledge this is the first report of the detection of GVA in Spain.

References: (1) A. Minafra and A. Hadidi. J. Virol. Methods 47:175, 1994. (2) G. Nolasco et al. J. Virol. Methods 45:201, 1993.
First Report of Sirococcus clavigignenti-juglandacearum on Black Walnut
Authors: Ostry M. E. , Katovich S. , Anderson R. L.
Published: May 2007

Sirococcus clavigignenti-juglandacearum is killing butternut (Juglans cinerea) throughout North America. Although black walnut (J. nigra) and other Juglans spp. can be infected with artificial inoculations (2), butternut previously was thought to be the only known natural host. In May 1985, a black walnut, 48 cm in diameter with multiple elliptical cankers on the main stem and lower branches, was found by R. L. Anderson in North Carolina. No fruit bodies were present but isolation from cankers characteristic of those found on butternut produced sporulating pure cultures identical to those described for S. clavigignenti-jugland-acearum (1). A large butternut with coalescing, elliptical cankers was located about 45 m from the infected walnut. In spring 1996, in a plantation in southeastern Minnesota, examination of two 20-year-old black walnuts exhibiting branch dieback revealed hyphal pegs and hyaline, two-celled, fusiform conidia identical to those described for S. clavi-gignenti-juglandacearum (1) on 1994 and 1995 branch wood. Isolations from symptomatic twigs resulted in recovery of the fungus in pure culture. Scattered, naturally occurring, infected, mature butternut and butternut saplings with multiple branch and stem cankers were growing throughout the plantation. Severe winter injury of black walnut in southeastern Minnesota the preceding 3 years may have predisposed trees to infection.

References: (1) V. M. G. Nair et al. Mycologia 71:641, 1979. (2) M. E. Ostry et al. Gen. Tech. Rep. NC-165, St. Paul, MN: USDA, Forest Service, North Central For. Exp. Stn., 1994.
Natural Epiphytotic of the Rust Puccinia psidii on Melaleuca quin-quenervia in Florida
Authors: Rayachhetry M. B. , Elliott M. L. , Van T. K.
Published: May 2007

Melaleuca quinquenervia (Cav.) S. T. Blake (melaleuca), a tree of Australian origin, is an invasive weed of natural areas in southern Florida and has been listed as a federal noxious weed. During January 1997, severe incidence of a rust disease was detected on new growth of about 70% of the melaleuca trees over a 2-km strip in Broward and Dade counties. These top-pruned trees were 3 to 5 m tall with bushy appearance and had many new shoots. The rust was observed on melaleuca saplings and trees in a 20-km radius in January through March 1997. Leaf lesions began as chlorotic flecks that expanded, produced spores, and developed into necrotic spots. Infected leaves were severely distorted. Branches were severely defoliated and succulent twigs were often girdled by lesions, causing dieback of the new growth. Yellow uredinia were observed on all young leaves and some petioles and twigs. Urediniospore morphology and dimensions (17 to 27 × 15 to 24 µm) are consistent with the description of Puccinia psidii G. Wint. (1) and the University of Florida's herbarium material of P. psidii on Pimenta dioica (L.) Merr. (allspice) (2). An inoculation test was conducted with 40-cm-tall melaleuca seedlings. Fully expanded leaves and terminals of these seedlings were brushed or sprayed with freshly collected urediniospores, covered with plastic bags, and placed in a growth chamber maintained at 16°C (night) and 26°C (day) with a corresponding 12-h light cycle for 72 h. The plastic bags were then removed and the seedlings maintained in high humidity and ambient temperatures in a shadehouse. Typical symptoms and sporulation occurred after 10 and 12 days, respectively, following inoculation. Although P. psidii has been recorded on 11 genera in Myrtaceae in the Americas (1,2), including melaleuca, an epiphytotic of this magnitude on melaleuca has not been reported. A different race of P. psidii has been suspected to cause sudden epiphytotics on Pimenta officinalis Lindl. in Jamaica (1). Further research related to host range is warranted to determine the specificity of P. psidii, as this rust may have potential as a microbial biological control agent of melaleuca.

References: (1) G. F. Laundon and J. M. Waterson. C.M.I. Descriptions of Pathogenic Fungi and Bacteria No. 56, 1965. (2) R. B. Marlatt and J. W. Kimbrough. Plant Dis. Rep. 63:510, 1979.
First Report and Pathogenicity of Myrothecium roridum, Curvularia eragrostidis, and C. lunata on seeds of Striga hermonthica in Nigeria
Authors: Czerwenka-Wenkstetten I. M. , Berner D. K. , Schilder A. , Gretzmacher R.
Published: May 2007

Striga is a weed known to be devastating to crops in the tropics. Yield reductions in maize of up to 90% have been observed in West Africa. In September 1994, a seed lot of Striga hermonthica (harvested in 1993 in sorghum fields in Abuja, Nigeria) was observed to have a very low germination rate (20 to 40%). Single-spore isolates from fungal colonies growing on the striga seeds were identified as Myrothecium roridum, Curvularia eragrostidis, and C. lunata. Pathogenicity to striga was tested. Striga seeds were preconditioned for 10 days at 28°C in darkness to break dormancy, then surface sterilized in 1% NaOCl for 7 min, rinsed in sterile, distilled water, and placed in eight central wells of a 24-well plate with up to 300 seeds per well. Seeds were covered with water and inoculated with fungi by placing in each well a 4-mm-diameter hyphal plug taken from a 4-day-old potato dextrose agar culture of one of the isolates. Seeds without fungi served as controls. After 24 h, striga seeds were surface sterilized as above and dispersed evenly in petri dishes with two layers of filter paper soaked in 10 ppm of 1,000 ml of GR-24 (3 [2,5-Dihydro-3-methyl-2-oxo-5-furanyl) oxymethylene]-3, 3a, 4, 8b-tetra-hydroindeno-[1, 2-b] furan-2-one) to induce germination. Seed germination was evaluated after 24 h of incubation in darkness at 33°C. Striga germination was reduced by 100% by M. roridum and 48% by C. era-grostidis and C. lunata.
New Disease on Ornamental Asparagus Caused by Xanthomonas campestris in Florida
Authors: Norman D. J. , Yuen J. M. F. , Hodge N. C.
Published: May 2007

From dark, water-soaked lesions on stems of asparagus tree fern (Asparagus virgatus) in commercial nurseries in Florida, 33 xanthomonad strains were isolated. Strains formed large, round, butyrus, bright yellow colonies on yeast dextrose calcium carbonate medium, and were gram negative, oxidase negative, catalase positive, motile, strictly aerobic, and did not hydrolyze starch. Strains were further characterized by carbon substrate utilization patterns (Biolog), and by fatty acid methyl esters (FAME) analyses. The metabolic fingerprints of most strains were similar to Xanthomonas campestris pv. vitians, and X. campestris pv. dieffenbachiae from Xanthosoma or Syngonium. Representative strains from A. virgatus were not pathogenic on Dieffenbachia. X. campestris pv. dieffenbachiae strains that did not hydrolyze starch produced scattered lesions on A. virgatus stems. However, starch-hydrolyzing strains of X. campestris pv. dieffenbachiae did not produce symptoms when inoculated onto A. virgatus. FAME analysis indicated the strains were X. campestris pv. vitians or X. campestris pv. translucens; however, low similarity indices ( x = 0.461) indicated that the asparagus strains were not represented in the MIDI library database. FAME analysis profiles were also compared to the University of Florida database, which contains 1,048 X. campestris strains of which 200 are X. campestris pv. dieffenbachiae. Similarity indices were again low with 15 strains matched to X. campestris pv. secalis (x = 0.412), seven strains to X. fragariae (x = 0.224), six strains to X. campestris pv. translucens ( x = 0.437), and five strains matched < 0.20 to other pathovars. Five representative strains were tested on six Asparagus species or cultivars: A. virgatus, A. setaceus, A. macowanii, A. densiflorus ‘Sprengeri’ , A. densiflorus ‘Myers’, and A. officinalis. All five strains were pathogenic on A. virgatus but were less virulent on A. setaceus and A. densiflorus ‘Sprengeri’.
Rind Stippling on Valencia Oranges by Copper Fungicides Used for Control of Citrus Black Spot in South Africa
Authors: Schutte G. C. , Beeton K. V. , Kotzé J. M.
Published: May 2007

Four copper sprays and copper mixtures with dithiocarbamates aggravated stippling of the fruit rind of Valencia oranges if sprayed in succession at registered rates during the recommended protection period from October to January for control of citrus black spot in South Africa. Copper stippling was more severe on treatments in which copper oxychloride was sprayed in succession, individually, or in combination with mancozeb or maneb/ZnO. On the other hand, less copper stippling was observed on treatments in which three mancozeb applications were altered with a single copper oxychloride as tank mixtures with or without mancozeb, which was sprayed during midsummer (December and January). Cupric hydroxide resulted in more general copper stippling lesions than any other copper oxychloride spray program. Four successive applications of the wettable powder copper oxychloride formulation resulted in more copper stippling when compared with the suspension concentrate formulation. Stippling was calculated to be more severe with late applications of copper fungicides during December and January. In another experiment, all contact fungicides tested were effective in controlling citrus black spot.
Control of Soilborne Pathogenic Fungi in Fields of Sweet Onion
Authors: Sumner Donald R. , Gitaitis Ronald D. , Gay J. Danny , Smittle Doyle A. , Maw Bryan W. , Tollner Ernest W. , Hung Yen Con
Published: May 2007

Populations of soil fungi from fields planted to sweet onion were assayed on selective media. In pathogenicity tests, Rhizoctonia solani AG-4, Pythium irregulare, and Phoma terrestris were the fungi most virulent on onion seedlings. Plots were fumigated with methyl bromide (MBR), chloropicrin (CP), MBR + CP (67% + 33%), metam sodium, 1,3,-dichloropropene (1,3-D), or 1,3-D + 17% CP in four field experiments in 2 years. Sweet onion was transplanted or direct seeded in October or November and harvested in April or May. MBR + CP and CP were effective in reducing populations of Phoma terrestris, Pythium spp., Fusarium spp., and R. solani AG-4 in soil. Metam-sodium and 1,3-D + 17% CP were less efficacious, and MBR and 1,3-D were ineffective. There were no differences in the percentage of bulbs with decay at harvest or after curing among treatments. Increased yield of marketable bulbs was associated with control of soilborne pathogenic fungi. In fields continuously cropped to onion, decreased yield was primarily associated with control of pink-root induced by Phoma terrestris, and P. terrestris was identified in soil from 74% of the fields assayed.
Bacterial Leaf Spot of Celery in California: Etiology, Epidemiology, and Role of Contaminated Seed
Authors: Little E. L. , Koike S. T. , Gilbertson R. L.
Published: May 2007

Pseudomonas syringae pv. apii, causal agent of bacterial leaf spot (BLS) of celery, was first identified in California in 1989. By 1991, BLS was apparent in all celery-growing areas of the state. Greenhouse-produced transplants were affected most severely, and disease incidence approached 100% in some greenhouses. In this study, sources of inoculum and factors contributing to disease development were investigated in three Salinas Valley greenhouse operations during the 1991, 1992, and 1993 celery transplant seasons (January to August). Epiphytic P. syringae pv. apii was not detected on celery transplants until April or May of each year. Increased epiphytic populations preceded BLS outbreaks, and high-pressure, overhead irrigation favored bacterial infiltration and disease development. In seed-wash assays, P. syringae pv. apii was recovered from 5 of 24 commercial celery seed lots. In field tests, epiphytic P. syringae pv. apii was found on umbels of inoculated celery plants, and seeds from these plants were heavily contaminated with P. syringae pv. apii. Contaminated seed produced seedlings with large epiphytic P. syringae pv. apii populations. Hot-water treatment (50°C for 25 min) eliminated >99.9% of seed contamination. Based on these results, disease management techniques are proposed.
Disease Progress, Yield Loss, and Control of Xanthomonas fragariae on Strawberry Plants
Authors: Roberts P. D. , Berger R. D. , Jones J. B. , Chandler C. K. , Stall R. E.
Published: May 2007

The progress of angular leaf spot, caused by the bacterium Xanthomonas fragariae, was examined in field plots of strawberry in the 1994 and 1995 seasons. Disease severity increased intermittently to maxima of circa 25% in 1994 and 15% in 1995. Angular leaf spot reduced marketable yield 8.6% in 1994 and 7.7% in 1995, despite differences in disease severity and base marketable yields for the two seasons. Minimal spread of the pathogen occurred from field plots with inoculated plants to plots with non-inoculated plants. A mixture of cupric hydroxide plus mancozeb was applied at the label rate (1×) at 7- to 14-day intervals and at a reduced rate (0.1×) at 2- to 4-day intervals. The bactericidal mixture at the 1× rate significantly decreased disease, but this mixture was phytotoxic; both plant size and yield were reduced. The 0.1× rate was nonphytotoxic and it reduced disease severity in both years and increased yield in 1994. Lesions of angular leaf spot were detected on strawberry transplants imported from nurseries in Canada and northern United States in both 1993 and 1994. X. fragariae was isolated from those lesions.
Net Blotch and Necrotic Warts Caused by Streptomyces scabies on Pods of Peanut (Arachis hypogaea)
Authors: de Klerk A. , McLeod A. , Faurie R. , van Wyk P. S.
Published: May 2007

Peanut (Arachis hypogaea L.) grown in rotation with potato (Solanum tuberosum L.) in the Northern Cape Province and at one locality in the Free State Province, South Africa, have developed unusual pod symptoms since the 1994 to 1995 season. Symptoms ranged from a net blotch with scattered lesions to dark brown, necrotic, wartlike lesions on the cv. Sellie. Streptomyces scabies (2) was consistently isolated from both types of lesions. Pathogenicity was confirmed in greenhouse tests. Inoculum was prepared by growing colonies on yeast malt extract agar for 21 days. Ten milliliters of sterile, distilled water was poured over the colonies of two different isolates and lightly scraped with a sterile needle. Separate sets of sterile soil were amended with spore suspensions of different isolates at a rate of 10 ml/kg and thoroughly mixed. Seeds of cv. Sellie and minitubers of potato cv. BP1 were planted in infested soil in 3-kg plastic bags. Uninfested soil served as controls. Each set of pots for both peanut and potato had three replications. Pots were kept in a glasshouse at 27°C for 12 weeks. Plants were lifted, disease development recorded, and infected plant parts prepared for reisolation on antibiotic-amended water/ agar according to the protocols of Loria and Davis (3). Both lesion types recorded under field conditions developed on peanut pods in the glasshouse upon reinoculation. Incidence ranged between 2 and 3 pods out of 8 to 10 pods per plant while minitubers were nearly 100% infected. Streptomyces scabies was isolated from lesions on both peanut and potato. Net blotch caused by an unknown Streptomyces sp. is a significant problem on peanut pods in Israel (1). However, the species found in Israel was not identified and could be different from the one reported here, according to Y. Barash (Tel Aviv University, personal communication). This is a first report of S. scabies being pathogenic on peanut in South Africa.

References: (1) Y. Barash et al. (In Hebrew.) Hassadeh 72:688, 1992. (2) D. H. Lambert and R. Loria. Int. J. Syst. Bacteriol. 39:387, 1989. (3) R. Loria and J. R. Davis. Streptomyces scabies. Pages 114-119 in: Laboratory Guide for Identification of Plant Pathogenic Bacteria. 2nd ed. N. W. Schaad, ed. American Phytopathological Society, St. Paul. MN, 1988.
First Report of Cowpea Aphid-Borne Mosaic Potyvirus from Cowpeas Grown Commercially in the U.S.
Authors: Kline A. S. , Anderson E. J.
Published: May 2007

Cowpea aphid-borne mosaic potyvirus (CABMV) is one of several seed-borne viruses known to limit cowpea (Vigna unguiculata (L.) Walp. subsp. unguiculata) production in Africa, Europe, and Asia, but CABMV has not been reported on commercially grown cowpeas in the United States (1). However, a sesame (Sesamum indicum L.)-infecting isolate of CABMV was recently characterized from plants growing near cowpea introduction plots in Georgia (2). In February 1997, we received samples of three seed lots of cowpea cv. Chinese Red that had been harvested in southern Texas during 1996. Approximately 28% of the plants grown from these seed lots expressed strong mosaic symptoms on primary and trifoliate leaves. Viruslike symptoms were reproduced following mechanical transmission to plants of Chinese Red cowpea, Nicotiana benthamiana, and soybean (Glycine max L.) cv. Lee. When Coronet and Pinkeye Purple Hull-BVR cowpeas were inoculated with sap extracts from symptomatic Chinese Red plants, chlorotic lesions developed on inoculated leaves, but only Coronet plants supported symptomless systemic infections. Similarly inoculated plants of Chenopodium quinoa (L.) and common bean (Phaseolus vulgaris L.) cvs. Pinto and Black Valentine developed localized chlorotic lesions. In Ouchterlony gel diffusion assays, extracts from symptomatic cowpea plants did not react with antisera to blackeye cowpea mosaic potyvirus (BlCMV), cucumber mosaic cucu-movirus (CMV), southern bean mosaic sobemovirus, cowpea mosaic comovirus, cowpea severe mosaic comovirus, or cowpea chlorotic mottle bromovirus. In the indirect enzyme-linked immunosorbent assay, sap extracts from symptomatic plants reacted with antiserum to CABMV, giving OD values at A405 of 0.10 to 0.25, and reacted weakly with antiserum to BlCMV, with OD values at A405 less than 0.035. Extracts from healthy control plants gave OD values at A405 less than 0.010. No positive reactions were obtained with antisera to bean yellow mosaic potyvirus, peanut mottle potyvirus, soybean mosaic potyvirus, or CMV. To our knowledge, this is the first report of CABMV in commercially grown cowpea from the U.S.

References: (1) A. G. Gillaspie et al. Plant Dis. 79:388, 1995. (2) H. R. Pappu et al. Arch. Virol. 142:1, 1997.
Annual Spread Rate of Tomentosus Root Disease
Authors: Hunt R. S. , Peet F. G.
Published: May 2007

The spread rate of tomentosus root disease, caused by Inonotus tomentosus, was investigated by a new technique employing temporal differences in the initiation of the reduced annual radial increment between pairs of diseased trees. Pairs of infected trees (stumps) located on the periphery of disease centers were selected in each of six widely separated spruce (Picea spp.) stands in British Columbia. Distances between 12 pairs of stumps were measured, and disks were collected from each stump. Similarly, disks from four additional pairs were collected from trees in a younger stand. Uninfected control disks were collected for all sites. Tree-ring measurements were determined for all disk samples and the year in which the reduction of the annual increment attributable to I. tomentosus began was determined for infected trees. The difference between initiation years for pairs of infected trees divided into the distance between them produced an average annual spread rate of 20 cm/yr. This rate will be used in developing a model for the disease.
Characteristics of Beet Soilborne Mosaic Virus, a Furo-like Virus Infecting Sugar Beet
Authors: Heidel G. B. , Rush C. M. , Kendall T. L. , Lommel S. A. , French R. C.
Published: May 2007

Beet soilborne mosaic virus (BSBMV) is a rigid rod-shaped virus transmitted by Polymyxa betae. Particles were 19 nm wide and ranged from 50 to over 400 nm, but no consistent modal lengths could be determined. Nucleic acids extracted from virions were polyadenylated and typically separated into three or four discrete bands of variable size by agarose-formaldehyde gel electrophoresis. RNA 1 and 2, the largest of the RNAs, consistently averaged 6.7 and 4.6 kb, respectively. The sizes and number of smaller RNA species were variable. The molecular mass of the capsid protein of BSBMV was estimated to be 22.5 kDa. In Northern blots, probes specific to the 3′ end of individual beet necrotic yellow vein virus (BNYVV) RNAs 1–4 hybridized strongly with the corresponding BNYVV RNA species and weakly with BSBMV RNAs 1, 2, and 4. Probes specific to the 5′ end of BNYVV RNAs 1–4 hybridized with BNYVV but not with BSBMV. No cross-reaction between BNYVV and BSBMV was detected in Western blots. In greenhouse studies, root weights of BSBMV-infected plants were significantly lower than mock-inoculated controls but greater than root weights from plants infected with BNYVV. Results of serological, hybridization, and virulence experiments indicate that BSBMV is distinct from BNYVV. However, host range, capsid size, and the number, size, and polyadenylation of its RNAs indicate that BSBMV more closely resembles BNYVV than it does other members of the genus Furovirus.
Seed Transmission of Hibiscus Latent Ringspot Virus (HLRSV)
Authors: Rubies-Autonell C. , Turina M.
Published: May 2007

Commercial seed lots of various cultivars of kenaf (Hibiscus cannabinus) were shown to transmit hibiscus latent ringspot virus (HLRSV) to progeny seedlings in different percentages up to a maximum of 26%. In these greenhouse tests, no symptoms were observed in the infected seedlings. Enzyme-linked immunosorbent assays (ELISA) of dissected kenaf seeds suggested that seed infection occurs through the embryo. HLRSV was also shown to be seed transmitted in Chenopodium amaranticolor and C. quinoa, in 11% and in less than 1%, respectively, of the seed collected from mechanically inoculated plants. However, transmission of HLRSV through seed was not detected in Abutilon theophrasti. C. quinoa and C. amaranticolor plants infected through seed transmission were invariably symptomless as opposed to mechanically inoculated plants that exhibited systemic symptoms of yellow flecking.
Susceptibility of Selected Cotton Cultivars to Seedling Disease Pathogens and Benefits of Chemical Seed Treatments
Authors: Wang Heping , Davis R. Michael
Published: May 2007

The susceptibility of 12 Upland cotton cultivars to three soilborne fungi, Pythium ultimum, Rhizoctonia solani, and Thielaviopsis basicola, was evaluated in greenhouse experiments. Based on symptom development and seedling survival, cultivars highly resistant to P. ultimum included Delta Pine (DP) 6166, Prema, DP 6100, and Maxxa. A relatively low incidence of pre-emergence damping-off caused by R. solani occurred in ChemBred 7, DP 6100, and Royale, although all cultivars subsequently suffered significant post-emergence damping-off. All cultivars were equally susceptible to T. basicola. In both greenhouse and field evaluations, there were no benefits of metalaxyl seed treatment in Pythium-resistant cultivars. Seed treatment with carboxin-pentachloronitrobenzene for the control of Rhizoctonia-induced damping-off resulted in stand increases in all 12 cultivars in greenhouse tests and in 3 of 6 cultivars in field trials.
Daikon (Raphanus sativus cv. longipinnatus) as a Host of Alternaria brassicae in California
Authors: Koike S. T. , Molinar R. H.
Published: May 2007

In the spring of 1997, commercial plantings of daikon or Chinese radish (Raphanus sativus L. cv. longipinnatus) in the San Joaquin Valley, Fresno County, were damaged by a disease previously undocumented in California. Symptoms consisted of small (2 to 5 mm diameter), circular to oblong, brown to light tan leaf spots that contained concentric rings. Following rains in January, leaf spots proliferated, coalesced, and resulted in significant necrosis of foliage. An Alternaria species with conidia with prominent beaks and spores produced singly or in chains of two was consistently observed on and isolated from the host. Conidia from naturally infected daikon leaves had mean dimensions of 190.1 × 23.1 μm, with a mean beak length of 60.0 μm. The isolates were identified as Alternaria brassicae (2). Pathogenicity was confirmed by culturing six representative isolates on sterilized 20% V8 juice solution for 14 days under a 12 h light/12 h dark cycle, filtering the suspensions through cheesecloth, adjusting spore concentrations to 25,000 conidia per ml, and spraying suspensions onto 4-week-old seedlings of daikon cvs. April and Summer. Plants were incubated in a humid chamber for 48 h and then maintained in a greenhouse. After 5 days, leaf spots similar to the original symptoms developed on all inoculated plants. The pathogen was reisolated and identified as A. brassicae. Control plants sprayed with distilled water remained symptomless. The inoculation test was repeated and results were the same. With the method described above, daikon isolates were also inoculated onto the following A. brassicae hosts (1): radish (Raphanus sativus L. cv. EXCO 517), broccoli (Brassica oleracea L. subsp. botrytis cv. Greenbelt), Chinese cabbage (Brassica campestris L. subsp. pekinensis cv. Cha-Cha), and broccoli raab (Brassica rapa L. subsp. rapa cv. Spring Raab). After 5 (radish) to 12 (other hosts) days, similar leaf spots developed on all inoculated plants and A. brassicae was reisolated and identified. Control plants sprayed with distilled water remained symptomless. These inoculations were repeated and results were the same. For California, this is the first report of black spot caused by A. brassicae on commercially grown daikon.

References: (1) S. T. Koike. Plant Dis. 81:552, 1997. (2) E. G. Simmons. Mycotaxon 55:55, 1995.
Effect of Crop Pruning on Sclerotinia Blight of Peanut
Authors: Bailey J. E. , Brune P. D.
Published: May 2007

Sclerotinia blight of peanut, incited by Sclerotinia minor, causes serious losses when cool, moist conditions prevail in the plant canopy. The effects of altering canopy structure by pruning were investigated in this study. Disease incidence was used to calculate area under the disease progress curve (AUDPC) for field plots receiving various shoot-pruning treatments. In 1990, pruned plots and iprodione-sprayed plots did not differ in AUDPC, but pruned plots produced higher yields. Disease levels and yield of July top-pruned plants did not differ from those of August top-pruned plants. Pruning tops and sides in August reduced yields compared to pruning tops and sides in July, even though August pruning produced lower AUDPC. Without fungicide treatment, the 1991 pruned plots had less disease than nonpruned plots, although yields did not differ significantly. Pruned plots treated with fungicides for control of Sclerotinia blight had less disease than nonpruned plots treated with these fungicides, but there were no differences in yield. Pruning peanut canopies to alter microclimate or enhance fungicide penetration may reduce disease and increase yield when S. minor damage is yield limiting.
Inheritance of Anthracnose Resistance in Common Bean Differential Cultivar AB 136
Authors: Alzate-Marin Ana Lilia , Baía Gilson Soares , de Paula Trazilbo José , de Carvalho Geraldo Assis , de Barros Everaldo Gonçalves , Moreira Maurilio Alves
Published: May 2007

Inheritance of anthracnose resistance of the common bean (Phaseolus vulgaris L.) differential cultivar AB 136 to races 89, 64, and 73 (binary system designation) was studied in crosses with the susceptible differential cultivars Michelite (race 89), Mexico 222 (race 64), and Cornell 49-242 (race 73). In each cross two progenitors, the F1, F2, and backcross-derived plants were inoculated with the respective race under environmentally controlled greenhouse conditions. The results indicate that single dominant gene(s) control resistance to races 89 and 64, giving a segregation ratio of 3:1 in the F2, 1:0 in the backcrosses to AB 136, and 1:1 in the backcross to Michelite (race 89), and to Mexico 222 (race 64). For race 73, the following segregation ratios between resistant and susceptible plants were observed: 13:3 in the F2, 1:0 in the backcross to AB 136, and 1:1 in the backcross to Cornell 49-242. Such results suggest that two independent genes may determine resistance of AB 136 to race 73, one dominant (Co-6) and one recessive that is proposed to be assigned co-8. Genotypes Co-6_ or co-8 co-8 would condition resistance, whereas susceptibility would be present in genotypes co-6 co-6 Co-8_. Given the dominant nature of anthracnose resistance genes present in line AB 136 and its resistance to 25 races of Colletotrichum lindemuthianum identified in Brazil by other researchers, we included this cultivar as one of the donor parents in our molecular marker-assisted backcross breeding program, to develop common bean cultivars resistant to anthracnose and adapted to Central Brazil.
Control of Downy Mildew in Greenhouse-Grown Cucumbers Using Blue Photoselective Polyethylene Sheets
Authors: Reuveni Reuven , Raviv Michael
Published: May 2007

Six types of polyethylene sheets with or without a blue pigment, having an absorption peak at the yellow part of the spectrum (580 nm), in combination with three levels of UV-B (280 to 320 nm) absorbance, were investigated for their effects on sporangial production and colonization of Pseudoperonospora cubensis on cucumbers in growth chambers. The effect of these photoselective sheets on the epidemiology of downy mildew in greenhouse-grown cucumbers has been investigated in several locations. The addition of the blue pigment to the films resulted in a significant inhibition of colonization and sporangial production of P. cubensis, whereas filtration of the UV spectrum enhanced the colonization but had no effect on the sporangial production. The appearance of the first symptom-bearing plants was delayed under the blue covers, and consequently, a significant reduction in the disease incidence of downy mildew was recorded under all blue sheets at each corresponding level of UV-B transmittance in five different field experiments through four seasons. Regardless of the differences in disease incidence, there were no significant differences among the yields that were obtained under the various sheets, probably due to the lower photosynthetically active radiation transmissivity of the blue films. The optimal features required for a desirable commercial sheet are discussed.
First Report of Powdery Mildew, Caused by an Oidium sp., on Poinsettia in California
Authors: Koike S. T. , Saenz G. S.
Published: May 2007

In December 1996 and January 1997, powdery mildew was observed on potted poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) plants in Monterey County, CA. Mycelia were observed on stems, petioles, mature and immature leaves, and bracts. Severely diseased leaves became twisted and bent and senesced prematurely. The white mycelia were conspicuous, epiphytic, and amphigenous; hyphae measured 4.6 to 6.9 μm in diameter. Growth initially was in patches but eventually became effused. Appressoria were slightly lobed to lobed and sometimes opposite. Conidiophore foot cells were cylindrical, sometimes bent at the base, and slightly flexuous to flexuous. Foot cells measured 30.0 to 46.2 μm × 5.8 to 6.9 μm and were followed by one to two shorter cells. Conidia were cylindrical to slightly doliform and measured 25.4 to 32.3 μm × 11.6 to 18.5 μm. The length-to-width ratios of conidia generally were greater than 2.0. Conidia were produced singly, placing the fungus in the Pseudoidium-type powdery mildew group. Conidia germinated at the ends, and no fibrosin bodies were observed. Cleistothecia were not found. The fungus was identified as an Oidium species. Pathogenicity was demonstrated by gently pressing infected leaves having abundant sporulation onto leaves of potted poinsettia plants (cvs. Freedom Red, Peter Star Marble, and Nutcracker White), incubating the plants in a moist chamber for 48 h, and then maintaining plants in a greenhouse. After 12 to 14 days, powdery mildew colonies developed on the inoculated plants, and the pathogen was morphologically identical to the original isolates. Uninoculated control plants did not develop powdery mildew. This is the first report of powdery mildew on poinsettia in California. This fungus appears similar to Microsphaera euphorbiae but has longer, slightly flexuous foot cells that do not match the description for M. euphorbiae (1,2). An alternative identification would be Erysiphe euphorbiae; however, there are no available mitosporic descriptions for morphological comparisons (1,2). In the United States, powdery mildew of poinsettia previously has been reported in various states in the Pacific Northwest, Midwest, and Northeast.

References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN.
First Report of Plasmodiophora brassicae on Cabbage in Eastern North Carolina
Authors: Cubeta M. A. , Cody B. R. , Williams P. H.
Published: May 2007

Clubroot, caused by Plasmodiophora brassicae Woronin, has occurred for at least 50 years in three counties in northwestern North Carolina, but has not been reported previously from eastern North Carolina, where most commercial cabbage is produced. In the fall of 1995, clubroot was observed in a direct seeded, commercial cabbage field in Plymouth, NC. Diseased cabbage plants were stunted and roots exhibited clublike swellings. Clubs were randomly harvested from roots of five plants to obtain a composite isolate to determine which race(s) of P. brassicae are infecting cabbage in eastern North Carolina. Three experiments were conducted, using the procedure of Williams (2). Four replicates of 10, 1-week-old seedlings of eight different crucifer cultivars were inoculated by dipping in a spore suspension (1 × 108 cysts/ml) of P. brassicae and planted in pasteurized potting mix. Seedlings dipped in sterile water served as controls. Inoculated seedlings were incubated in a greenhouse at 18 to 28°C for 6 to 8 weeks and assessed for clubroot incidence and severity. The isolate of P. brassicae from eastern North Carolina was most virulent on cabbage (Brassica oleracea var. capitata cv. Jersey Queen), collard (B. oleracea var. acephala cv. Vates), and wild mustard (B. nigra); moderately virulent on canola (B. napus cv. Brutor) and rutabaga (B. napus cvs. Laurentian and Wilhelmsburger); and least virulent on cabbage (cv. Badger Shipper). Canola (B. napus cv. Nevin) and control seedlings were not infected and exhibited no symptoms. Similar results were obtained for all experiments. Based on these results, the isolate of P. brassicae from eastern North Carolina was designated as race 6 and pathotype 5 according to Williams (2) and Some (1), respectively. However, further experiments with single-cyst-derived isolates from individual clubs obtained from different geographic locations are needed to accurately characterize field populations of P. brassicae on cabbage in eastern North Carolina.

References: (1) A. Some et al. Plant Pathol. 45:432, 1996. (2) P. H. Williams. Phytopathology 56:624, 1966.
Epiphytic Pseudomonas syringae on Dry Beans Treated with Copper-Based Bactericides
Authors: Garrett K. A. , Schwartz H. F.
Published: May 2007

The response of epiphytic populations of Pseudomonas syringae and other bacteria on dry bean plants to four copper-based bactericides was evaluated. The bactericides showed little difference in efficacy, but epiphytic populations on pinto bean leaflets, flowers, and pods were occasionally reduced when compared to populations on non-treated control plants, especially after repeated bactericide applications. Although there was a trend toward a relationship between epiphytic leaflet and flower populations, there were cases where P. syringae was undetected on one organ but abundant in samples from the other organ. P. syringae pv. syringae strains recovered from epiphytic populations demonstrated much greater copper resistance than did strains of P. syringae pv. phaseolicola, as measured by growth on media amended with cupric hydroxide. This difference between the pathovars may have implications for integrated pest management strategies.
Evaluation of Maize Germ Plasm for Resistance to Maize Rayado Fino Virus
Authors: Bustamante Pedro I. , Hammond Rosemarie , Ramirez Pilar
Published: May 2007

Maize rayado fino virus (MRFV) causes severe yield losses in maize (Zea mays) in Latin America with reductions of 40–50% on indigenous genotypes and 100% in some new cultivars. A collection of 20 different maize genotypes were obtained from the Center for the Improvement of Maize and Wheat (CIMMYT, México), Estación Experimental Fabio Baudrit (EEFB-Alajuela), and the Consejo Nacional de la Producción (CNP-Costa Rica). Enzyme-linked immunosorbent assay (ELISA) and symptom severity were used to evaluate the responses of the maize genotypes to MRFV infection under screenhouse conditions. Two genotypes from the CIMMYT germ plasm collection (accession nos. 2980-93 and 3974) showed mild and delayed symptoms and low MRFV concentrations as determined by ELISA.
Disease Severity and Yield of Sweet Corn Hybrids with Resistance to Northern Leaf Blight
Authors: Pataky J. K. , Raid R. N. , du Toit L. J. , Schueneman T. J.
Published: May 2007

Reactions of supersweet (sh2) sweet corn to northern leaf blight (NLB) and associated yields were evaluated in Belle Glade, Florida and Urbana, Illinois in yield-loss trials, hybrid evaluations, and evaluations of breeding materials. Hybrids differed significantly for NLB in all trials. Severity of NLB ranged from 0 to 66% on 35 sh2 hybrids in yield-loss trials, and from 0 to 60% on 80 sh2 hybrids in hybrid evaluations. NLB ratings ranged from 1 to 9 (approximately 0 to 80% severity) on 375 hybrids and 186 inbred lines in evaluations of breeding materials. Various methods of rating NLB and ratings from multiple dates were highly correlated, with correlation coefficients ranging from 0.76 to 0.98. Yield, measured as weight of ears and number of marketable ears from inoculated plots as a percentage of that from control plots, decreased as disease severity increased. Linear or quadratic regression models explained 31 to 70% of the variation in percent yield as a function of disease severity at harvest. The effects of NLB on yield were limited by NLB-resistance in several hybrids, including CCO 3268, Chieftain, Crisp N Sweet 710A, Day Star, Envy, Forever, GSS 1526, Jupiter, Midship, Prime Plus, Sch 5005, and SummerSweet 7630. Although high levels of partial resistance to NLB were prevalent among 375 new experimental sh2 hybrids and 186 sh2 inbred lines evaluated in 1995, use of the gene HtN may increase in the near future as breeders are incorporating this resistance into new inbreds and hybrids. Breeders and plant pathologists would be wise to continue improving partial resistance to NLB without using the gene HtN in genotypes with adequate levels of partial resistance, because the widespread use of the gene HtN will select for virulent races of Exserohilum turcicum which occur in Florida, or for races with new combinations of virulence.
A Hydroponic Seedling Assay for Resistance to Cephalosporium Stripe of Wheat
Authors: Cowger Christina , Mundt Christopher C.
Published: May 2007

A procedure was developed to rate winter wheat seedlings approximately 20 days old for resistance to Cephalosporium stripe, a vascular wilt caused by the soilborne fungus Cephalosporium gramineum. Seedlings were inoculated after 12 to 15 days of growth in liquid culture in controlled-environment chambers, then assessed for disease symptoms at 7 to 8 days post-inoculation. Disease severity was assayed by measuring chlorophyll in the youngest fully expanded leaf, using a chlorophyll meter. Four replicated trials tested a total of 12 winter wheat cultivars, including both hard red cultivars from the U.S. Southern Plains and soft white winter cultivars from the U.S. Pacific Northwest. With one exception, the procedure consistently ranked cultivars correctly, according to field performance, as moderately resistant or susceptible. Jagger, a moderately resistant, hard red Kansas wheat, was ranked with susceptible cultivars in one of three trials.