bluuebunny/crossref_metadata_2025 huggingface dataset:
Soybean Seedcoat Mottling: Association with Soybean mosaic virus and Phomopsis spp. Seed Infection
Authors: Koning G. , TeKrony D. M. , Ghabrial S. A.
Published: May 2007

Soybean mosaic virus (SMV) infection predisposes soybean (Glycine max) seed to Phomopsis spp. seed infection and may induce seedcoat mottling. The extent of seedcoat mottling associated with the accumulation of SMV or Phomopsis spp. infection of the seedcoat was investigated in 1996 and 1997. Plants of two SMV-susceptible cultivars, ‘Clark’ and ‘Williams’, were sap inoculated with the G2 strain of SMV at growth stage R2. Control plants (SMV-resistant isolines L78-434 and L78-379, respectively) were not inoculated. Harvested seed were evaluated visually for seedcoat mottling and sorted into four categories (severe, banded, blemish, and none) according to the degree of seedcoat pigmentation. Seed infection with Phomopsis spp. was determined and SMV accumulation was assessed by enzyme-linked immunosorbent assay and nucleic acid hybridization analysis. Phomopsis spp. were isolated from seed of all mottling categories, with the incidence of infection increasing as the degree of seedcoat mottling increased. SMV was detected in both mottled and nonmottled seedcoats, with generally higher levels of SMV in mottled seedcoats. However, the relationship of SMV titer to seedcoat mottling was inconsistent across cultivars and years. Thus, the extent of seedcoat mottling was not directly related to the accumulation of SMV in the seedcoat.
Sensitivity of Watermelon Cultigens to Ambient Ozone in North Carolina
Authors: Holmes Gerald J. , Schultheis Jonathan R.
Published: May 2007

Foliar ozone (O3) injury is common on watermelon grown in eastern North Carolina. During the 2000 and 2001 growing seasons, 93 cultivars and breeding lines (i.e., cultigens) were evaluated for foliar injury caused by ambient levels of O3. One tetraploid, 42 diploid, and 50 triploid cultigens were evaluated. Injury developed on all cultigens in both years, but severity of injury varied among cultigens and between years. Visible foliar injury (percent surface area necrotic or chlorotic) was rated 1 week after the first harvest in both years. Mean injury for all cultigens was 39% in 2000 (range = 16 to 66%) and 20% in 2001 (range = 2.5 to 60%). This corresponded to greater mean seasonal O3levels (12-h [0900 to 2100 h EST] mean daily O3concentration between early May and mid-June) in 2000 (58 ppb) than in 2001 (52 ppb). Triploid cultigens were less sensitive to injury than diploid cultigens. Mean injury for all triploids was 31% in 2000 and 16% in 2001, whereas injury for diploids was 47% in 2000 and 25% in 2001. Injury level was consistently negatively correlated with average number of days between transplanting and harvest. Correlations between injury level and yield, fruit size, fruit shape, and fruit sweetness were inconsistent between years and/or insignificant. O3tolerance in watermelon cultivars should receive increased attention in watermelon breeding programs and in cultivar selection in areas of high O3pollution.
First Report of Koch's Postulates Completion of Sudden Death Syndrome of Soybean in Argentina
Authors: Scandiani M. , Ruberti D. , Pioli R. , Luque A. , Giorda L.
Published: May 2007

Foliage symptoms on soybean resembling those of sudden death syndrome were detected in Argentina during 1991 and 1992 in the Pampas Region and during 1992 and 1993 in the Northwest Region. Isolations were made in 1999, 2000, and 2001 from soybean plants (Glycine max (L.) Merr.) showing these symptoms. Five isolates of fungi obtained from taproot tissue and blue sporulation on taproot exteriors were selected for further evaluation. These isolates were plated on potato dextrose agar supplemented with streptomycin (PDAS). Based on the spore morphology, colony growth rate, morphology and pigmentation on PDAS, and lack of microconidia (1) five isolates were identified as Fusarium solani f. sp. glycines. Soybean cvs. Ripley, Spencer, Pioneer 9492RR, and A6445 RG were inoculated in greenhouse tests with each of the isolates using toothpick and soil infestation methods for a total of six experiments. Isolate 171 provided by J. Rupe (University of Arkansas, Fayetteville) was tested as a positive control. Foliar symptoms typical of sudden death syndrome and similar to those in the field were observed 14 and 25 days, respectively, after inoculations using the toothpick and soil infestation methods. Lesions produced on leaves averaged 3.6 for all five isolates and 4 for the reference strain using a disease severity scale where: 1 = no symptoms; 2 = slight symptom development with mottling and mosaic on leaves (1 to 20% foliage affected); 3 = moderate symptom development with interveinal chlorosis and necrosis on foliage (21 to 50% foliage affected); 4 = heavy symptom development with interveinal chlorosis and necrosis (51 to 80% foliage affected); and 5 = severe interveinal chlorosis and necrosis (81 to 100% foliage affected). Noninoculated controls were symptomless. Differences in virulence were observed among the isolates. Based on disease symptoms in the greenhouse and cultural morphology on PDAS, the isolates were classified as Fusarium solani f. sp. glycines. Isolates recovered from symptomatic plants resembled Fusarium solani f. sp. glycines on PDAS and peptone/p-chloro-nitrobenzene agar amended with streptomycin, confirming Koch's postulates. Fusarium solani f. sp. glycines was recovered from 60% of inoculated plants.

Reference: (1) K. W. Roy et al. Plant Dis. 81:1100,1997.
Influence of Age of Apple Flowers on Growth of Erwinia amylovora and Biological Control Agents
Authors: Thomson S. V. , Gouk S. C.
Published: May 2007

The influence of flower age on growth of Erwinia amylovora, the causal pathogen of fire blight of apples and pears, was investigated under humid and arid conditions in Hamilton, New Zealand (NZ), and Logan, UT, USA, respectively. ‘Royal Gala’ apple flowers ranging from 1 to 8 days old were atomized with E. amylovora. Pistils were dissected and washed separately from the remaining floral parts (flowers ex pistils) for estimation of bacterial numbers. Pistils, 1 to 3 days old (USA) and 1 to 4 days old (NZ), supported exponential growth of E. amylovora, but bacterial populations did not increase when older flowers were inoculated. Scanning electron microscopy showed round and turgid papillae on stigmas of 1-day-old flowers. Papillae on 4- to 6-day-old stigmas were completely collapsed and covered in mucilage. Populations of E. amy-lovora on the flowers ex pistils were characteristically lower than pistil populations. High populations of saprophytic bacteria were found on both floral parts of all ages, but there was no difference in their numbers on 3- to 6-day-old pistils. This suggests their presence did not inhibit the growth of E. amylovora on older stigmas. The results demonstrate that stigmas on 1- to 3-day-old flowers often support rapid growth of E. amylovora, but flowers inoculated when more than 4 to 5 days old do not support growth or only limited growth. The same location and pattern of bacterial growth occurred with the biological control agents Pseudomonas fluorescens PfA506n and Pantoea agglomerans (Erwinia herbicola) Eh318nr. The distinct effect of flower age on growth of antagonistic bacteria and E. amylovora may be important in deciding when to treat with biological control organisms or bactericides.
First Report of Charcoal Rot on Soybean Caused by Macrophomina phaseolina in North Dakota
Authors: Bradley C. A. , Río L. E. del
Published: May 2007

In late August 2002, patches of soybean (Glycine max) plants in a field in Richland County, ND exhibited symptoms and signs of charcoal rot and died prematurely. Dead plants had a silvery-gray appearance, and black microsclerotia (76 ± 28 μm in diameter) were present in the vascular tissue of the lower stems and roots. Stem tissue was placed in petri dishes containing potato dextrose agar (PDA). Gray hyphae grew from the stem tissue and subsequently turned black and formed microsclerotia (188 × 139 ± 48 μm). The fungus was identified as Macrophomina phaseolina (Tassi) Goid. based on colony color and morphology and size of the microsclerotia (1). To confirm pathogenicity, soybean plants (cv. Garst D 041 RR) were grown in the greenhouse and inoculated with the previously obtained isolate of M. phaseolina. Stems of soybean plants at the V2 stage were excised just below the third node. Mycelia plugs of a 1-week-old culture of M. phaseolina were placed into the large end of disposable micropipette tips (200 μl). The micropipette tips containing the M. phaseolina culture were subsequently placed over 10 excised soybean stems. To serve as a control, 10 excised soybean stems were inoculated with micropipette tips containing plugs of noninfested PDA. Thirty days after inoculation, micropipette tips were removed, and lesions that had developed on the stem were measured. The mean lesion length of M. phaseolina inoculated stems was 7 mm; no lesions developed on the control plants. M. phaseolina was reisolated from infected tissue of inoculated plants that were placed on PDA. Charcoal rot was only observed in the Richland County field; however, no surveys were conducted to determine the prevalence of the disease throughout the soybean production area of North Dakota. Because it is now known that this disease occurs in North Dakota, growers, extension personnel, and crop consultants must scout for the disease and practice recommended management strategies.

Reference: (1) G. S. Smith and T. D. Wyllie. Charcoal rot. Pages 29–31 in: Compendium of Soybean Diseases, 4th ed. G. L. Hartman, J. B. Sinclair, and J. C. Rupe, eds. The American Phytopathological Society, St. Paul, MN, 1999.
First Report of White Rust Caused by Albugo bliti on Seabeach Amaranth in the United States
Authors: Keinath A. P. , Strand A. E. , Hamilton R. D.
Published: May 2007

Seabeach amaranth (Amaranthus pumilus Raf.), a threatened annual marine plant, is a primary colonizer of the windward side of Atlantic coastal dunes. It serves an important ecological role in dune accumulation and stabilization. Because Hurricane Floyd eliminated all native seabeach amaranth in South Carolina in 1999, experimental reestablishment plantings have been attempted. In August 2000, seabeach amaranth on Dewees and Cape Island in Charleston County, Huntington Beach in Georgetown County, and Otter Island in Colleton County, South Carolina were stunted and senesced prematurely. Leaves on affected plants were only one-half of the normal size and internodes were shortened. Most plants (>90%) at each location were affected. Diseased leaves had small, pale green-to-tan spots above hypophyllous pustules that contained numerous, dry, hyaline, subglobose conidia. Conidia measured 13.5 (10 to 17) × 15.0 (11 to 18) μm. Based on morphological characters and the host, the pathogen was identified as Albugo bliti (Biv.-Bern.) Kuntze (1,2). No oospores were observed. Diseased plants were collected from Dewees and Otter Islands and kept frozen for use as a source of inoculum. Six A. pumilus plants each of six Plant Introductions (PI), 553080 through 553085, that had been grown from seed were sprayed with a suspension of 4.7 × 105 conidia per ml. One plant of each PI was sprayed with sterile distilled water as a noninoculated control. All plants were placed in a humidity chamber for 48 h and then moved to a greenhouse bench. Thirteen days after inoculation, all inoculated plants had pustules of white rust. Diseased plants had a mean of 42 pustules per plant and PI's did not differ in susceptibility. Five of six noninoculated plants also had white rust pustules, but only a mean of 2.3 (range 1 to 5) pustules each. White rust likely appeared on noninoculated plants because plants were spaced closely together in the chamber. Pustules and conidia on inoculated plants were identical to those on plants collected originally. Albugo bliti has been reported on 19 other Amaranthus species (1), but to our knowledge, this is the first report of white rust on seabeach amaranth in the United States. White rust reduced the biomass of infected plants and, hence, their ability to trap sand. White rust was not observed on subsequent plantings in 2001 and 2002 at any location.

References: (1) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory, On-line publication. ARS USDA, 2002. (2) G. W. Wilson. Bull. Torrey Bot. Club 34:61, 1907.
Soybean Cyst Nematode Reduces Soybean Yield Without Causing Obvious Aboveground Symptoms
Authors: Wang J. , Niblack T. L. , Tremain J. A. , Wiebold W. J. , Tylka G. L. , Marett C. C. , Noel G. R. , Myers O. , Schmidt M. E.
Published: May 2007

Field experiments were conducted at locations in northern and southern Illinois, central Iowa, and central Missouri from 1997 to 1999 to investigate the effects of Heterodera glycines on soybean growth, development, and yield. A wide range of infestation levels was present at all locations. Two locally adapted cultivars, one resistant to H. glycines, were grown at each location. Cultivars were planted in alternating four-row strips with 76 cm between rows. For each cultivar, 20 1-m-long single-row plots were sampled every 2 weeks starting 4 weeks after planting. Infection by H. glycines reduced plant height and leaf and stem weight on the resistant cultivars in the first 12 weeks after planting, and delayed pod and seed development 12 to 14 weeks after planting. Biomass accumulation was not reduced on the susceptible cultivars until 10 weeks after planting; reduction in pod and seed development occurred throughout the reproductive stages. Susceptible cultivars produced significantly lower yields than resistant cultivars, but the yield reductions were not accompanied by visually detectable symptoms.
Evaluation of Components of Partial Resistance to Oat Crown Rust Using Digital Image Analysis
Authors: Díaz-Lago J. E. , Stuthman D. D. , Leonard K. J.
Published: May 2007

Digital image analysis is an objective and nondestructive method potentially capable of providing accurate and precise estimates of disease resistance components. This study was conducted to quantify components of partial resistance to crown rust through the analysis of sequential digital images of inoculated leaves of adult oat plants, and to compare components found in two sources of resistance unrelated genetically. Uredinium density, relative infection frequency, latent period, days to first pustule appearance, uredinium size, and disease progress rates were assessed on three oat lines (RS-line 3W-C2R-9-3b, MN-841801, Starter) in two greenhouse experiments. Resistant lines had fewer and smaller uredinia, and these appeared later than in the susceptible check. Relative infection frequency, latent period, and uredinium size were equally important components in the expression of the partial resistance to crown rust, and the two sources of resistance could not be differentiated by any of the variables studied. The analysis of sequential digital images of diseased leaves produced precise estimates of partial resistance components and disease progress rates.
Reduced Midseason Pesticide Program for Control of Scab and Plum Curculio in Peach
Authors: Lan Z. , Scherm H. , Horton D. L.
Published: May 2007

Risks to peach production from scab (caused by Cladosporium carpophilum) and plum curculio (Conotrachelus nenuphar), two key pests in the southeastern United States, are high until 2 months past petal fall and then decreases during midseason. This suggests that reduced-input pesticide strategies may effectively control both pests during the latter period. In this study, we evaluated midseason pesticide applications according to an alternate-row middle (ARM) spray program in which sprays were applied only to every other tree row while reducing tractor speed and keeping application intervals unchanged relative to conventional spraying of both sides of the trees. In a 2-year trial in a research orchard, conventional sprays of fungicide (primarily sulfur) and insecticide (primarily phosmet) were applied at 10- to 14-day intervals until first cover, followed by continued conventional sprays of fungicide and insecticide (standard), conventional sprays of one pesticide together with ARM sprays of the other pesticide, or combined ARM sprays of both pesticides. Schedules with midseason ARM sprays of both pesticides also were evaluated in two commercial orchards in 2 years. In all experiments, plots receiving combined ARM sprays were equivalent to the standard in fruit quality and control of scab and plum curculio. Combined ARM spraying resulted in lower environmental nontarget effects (as estimated by the Environmental Impact Quotient) and reduced application time by 25 to 33% for each midseason spray and 12.5 to 18.5% for the entire period from petal fall to the preharvest interval.
First Report of Phytophthora cactorum on American Ginseng (Panax quinquefolius) in Bulgaria
Authors: Bobev S. G. , Baeyen S. , Crepel C. , Maes M.
Published: May 2007

American ginseng (Panax quinquefolius) is a recently introduced crop in Bulgaria. In autumn 2001, several 2-year-old plants from Stara Zagora County exhibited symptoms of wilting and dying. Laboratory analysis also revealed some browning of the ginseng root surface and discoloration of the vascular tissues. During later stages of the disease, roots became soft, rubbery, and disintegrated. After storage in a humid chamber for 3 to 5 days, roots were covered with a white, cottony mycelium. Following the transfer onto potato dextrose agar, this fungus formed rounded colonies of white, aerial mycelium. Pathogenicity of the isolate was demonstrated by inoculation of roots that were surface-disinfected with alcohol (70%) for 30 s and rinsed with sterile water. Roots were wounded with a scalpel, and agar pieces from a 1-week-old culture were placed under the cortical tissue. Five inoculated root pieces were kept in a humid chamber at 24 to 25°C, and the pathogen was reisolated subsequently from necrotic lesions that developed from wounds. No symptoms were found in the five wounded but noninoculated control roots. The pathogen was reisolated from the diseased tissue to fulfill Koch's postulates. Microscopic examination showed that the pathogen had an aseptate mycelium (mean diameter of 5.3 μm), did not form hyphal swellings or chlamydospores, and had simple sympodial branching of the sporangiophores. Sporangia had a caducous nature with a pedicel length of 4.7 μm (1.7 to 6.7 μm). Sporangia were ovoid to obpyriform in shape, papillate, and nonproliferating measuring 30.6 (26.6 to 40.0) μm × 24.3 (23.3 to 30.0) μm. The length/width ratio varied between 1.25 and 1.3. The fungus was homothallic and produced paragynous antheridia and spherical oogonia with a diameter of 30.6 μm (26.6 to 33.3 μm) on V8 agar and in petri solution. Oospores were aplerotic and spherical (25 to 30 μm in diameter). Based on symptoms and pathogen characteristics (2), the disease was identified as Phytophthora root rot caused by Phytophthora cactorum. Additionally, the identity of the isolate was verified by sequence determination of the ribosomal internal transcribed spacer I region and alignment to the GenBank-EMBL DNA database (1), which revealed 100% sequence similarity with P. cactorum. To our knowledge, this is the first report of P. cactorum on American ginseng in Bulgaria.

References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389,1997. (2) D. C. Erwin and O. K. Ribeiro. Morphology and identification of Phytophthora species. Pages 96–125 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996.
Rice yellow mottle virus Is Transmitted by Cows, Donkeys, and Grass Rats in Irrigated Rice Crops
Authors: Sarra Soungalo , Peters Dick
Published: May 2007

Rice yellow mottle virus (RYMV), endemic in Africa, is believed to be spread by chrysomelid beetles, although the infections in a field often cannot be explained by the prevailing number of beetles. We show that the grass rat Arvicanthis niloticus, domestic cows (Bos spp.), and donkeys (Asinus spp.) are potent and efficient transmitters of RYMV. Spread of RYMV by rats was demonstrated in cage experiments wherein individual rats transmitted the virus from healthy to infected rice plants and confirmed in a field experiment. Experiments with cows and donkeys showed that they could transmit the virus in plots with healthy and infected plants and to plots with healthy plants. A high percentage of seedlings became infected when a cow grazed in a seedbed after being fed with infected rice plants. Transmission also was observed when cows were allowed to graze on the stubble of infected fields. The disease incidence increased at least fourfold over time to approximately 36% of the plants infected in the experimental plots of two stubble fields. The results obtained in these stubble fields suggest that cattle-mediated spread will enhance the size of the virus load in the contraseason and the infection potential to infect the next crop.
First Report of Potato mop-top virus on Potato from the United States
Authors: Lambert D. H. , Levy L. , Mavrodieva V. A. , Johnson S. B. , Babcock M. J. , Vayda M. E.
Published: May 2007

Potato mop-top virus (PMTV) is a tripartite pomovirus vectored by the powdery scab plasmodiophoromycete Spongospora subterranea pv. subterranea (1). PMTV occurs on potato (Solanum tuberosum) in Europe, the Andes, Asia, and Canada. Internal necrotic arc and fleck tuber symptoms (“spraing”) may reduce commercial acceptance of some cultivars (3). PMTV symptoms were discovered in ‘Shepody’ tubers at the Aroostook Research Farm, Presque Isle, ME in May 2002 and subsequently in ‘Russet Burbank’ tubers in commercial storage from the 2001 Maine crop. Symptomatic tubers exhibited single or multiple concentric necrotic arcs that were partial or complete, but exhibited no distinct external symptoms. The presence of PMTV in eight ‘Shepody’ tubers was indicated by positive enzyme-linked immunosorbent assay (ELISA; Adgen, Ltd., Auchincruive, Ayr, Scotland) and confirmed by reverse transcription polymerase chain reaction (RT-PCR). ‘Russet Burbank’ potatoes were visually diagnosed, and the corresponding halves of 128 symptomatic tubers were forwarded to the University of Maine and APHIS (Beltsville, MD). Of these, ELISA readings in Maine were strongly positive (>3 × background) for 88, ambiguous (1.5-3 × background) for 13, and negative for 27. Subsamples from these three categories were positive by PCR in 17 of 17, 9 of 9, and 12 of 14 cases, respectively. A similar rating, positive or ambiguous, in ELISA testing was identical for all but one case at Beltsville. Confirmation of PMTV required PCR testing, resulting in a characteristic PCR product of 401 bp that was generated from the coat protein coding region on RNA 2 (2) using the primer pair PMTV 1 5′-GCAGCCGTCGAGAATAGATA-3′ (RNA nucleotides 316–335) and PMTV 4 5′-GCGAGTTGATGTGCC ACATT-3′ (complementary to RNA 2 nucleotides 716–697). An immunocapture RT-PCR using this primer set and the coating antibody from the Adgen ELISA kit was also successful in detecting PMTV. In separate reactions, a second product of 646 bp was generated from the triple gene block on RNA 3 (4) using the primer pair PMTV 5 5′-GGTGAACACGAGGACAAGGT-3′ (RNA 3 nucleotides 1417–1436) and PMTV 7 5′-AACAGTCCGGTCTTGTGAAC-3′ (complementary to RNA 3 nucleotides 2063–2044). The sequence of these products was 98 to 100% identical to PMTV published sequences. The discovery of this virus will result in adjustments to U.S. and Canadian seed potato certification standards and symptom characterization for common North American cultivars.

References: (1) R. A. C. Jones and B. D. Harrison. Ann. Appl. Biol 63:1, 1969. (2) S. Kashiwazak et al. Virology 206:701, 1995. (3) M. Sandgren et al. Am. J. Potato Res. 79:205, 2002. (4) K. P. Scott et al. J. Gen. Virol.75:3561, 1994.
First Report of Anthracnose Caused by Colletotrichum gloeosporioides on Taxus mairei in Taiwan
Authors: Fu C. H. , Hsiao W. W. , Yao J. C.
Published: May 2007

Taxus mairei (Lemee & Levl.) S.Y. Hu ex Liu is a giant evergreen tree native to Taiwan. T. mairei and the Pacific yew, T. brevifolia, produce taxol, a highly effective antitumor drug. Anthracnose was observed on cuttings and seedlings of T. mairei in nurseries and on larger plants grown in plantations in Taiwan. Circular or irregular, brown leaf spots were associated with defoliation. Stems lesions and tip dieback were also observed. Colletotrichum gloeosporioides (Penz.) Sacc. was isolated from diseased tissues, and this fungus grew well on potato dextrose agar and malt extract agar (MEA), with a growth rate of 6.3 mm per day on MEA at 32°C in the dark. Colonies were white to grayish white and became dark gray with age. Acervuli produced on leaves were 115 to 155 μm in diameter, with one or several brown-to-black setae and pale salmon conidial masses. Conidia were guttulate, straight, cylindrical, obtuse at the apex and truncate at the base, and approximately 12 to 17 × 3.5 to 6.0 μm. The disease was reproduced by spraying T. mairei seedlings with a suspension of 104 to 105 conidia per ml, and the control plants were inoculated with distilled water. Inoculated plants were kept in a transparent moist chamber with a constant humidity near 100% (1). Symptoms appeared within 7 days when the temperature was over 32°C. When the temperature was below 24°C, symptoms were delayed. The fungus was reisolated from the inoculated plants, fulfilling Koch's postulates. To our knowledge, this is the first record of anthracnose on Taxus mairei (2), and anthracnose appears to be the most important disease on this plant in Taiwan. Voucher specimens have been deposited at the Division of Forest Protection, Taiwan Forest Research Institute as TFRIFCH Herbarium specimen 137.

References: (1) W. W. Hsiao et al. Taiwan J. For. Sci.17:119, 2002. (2) Y. P. Tsai, ed. List of plant diseases in Taiwan. The Plant Protection Society of the Republic of China and The Phytopathological Society of the Republic of China, 1991.
An Outbreak of a Leaf Spot Disease of Cabbage in Southern Florida Caused by Xanthomonas campestris pv. armoraciae
Authors: Pernezny K. , Jones J. B. , Roberts P. D. , Dickstein E.
Published: May 2007

From October to December 2001, a leaf spot disease was observed in numerous commercial fields of red and green cabbage (Brassica oleracea var. capitata L.) in the Everglades Agricultural Area, south and east of Lake Okeechobee and in the environs of Immokalee in southwestern Florida. Discrete water-soaked to greasy appearing spots were observed in the leaf blades with no evidence of marginal V-shaped lesions characteristic of black rot caused by Xanthomonas campestris pv. campestris. Profuse bacterial streaming was observed when cut leaf sections were examined microscopically. A bacterium that formed yellow colonies on nutrient agar was consistently isolated from these lesions. Ten bacteria were isolated, purified, and characterized. All strains were aerobic, gram-negative rods. Strains were positive for esculin hydrolysis, proteolysis in litmus milk, and gelatin liquefaction. Strains were negative for urease production, nitrate reduction, oxidase, and utilization of asparagine as a sole source of carbon and nitrogen. Fatty acid methyl ester analysis indicated a match with Florida library strains of X. campestris pv. raphani (similarity indices 0.605–0.738). Suspensions (2 × 107 CFU/ml in phosphate-buffered saline) of two Oklahoma strains identified as X. campestris pv. armoraciae provided by J. P. Damicone (3) and four representative Florida strains were applied to plants using a hand-held sprayer. Pathogenicity of the strains was tested on three replicate greenhouse-grown plants of the following: green cabbage cv. Market Early; red cabbage cv. Salad Delight; radish cv. Red Silk; tomato cv. Sunny; sweet bell pepper cv. Jupiter; and fresh horseradish roots purchased from a retail grocery chain. A strain of X. campestris pv. campestris originally isolated from Homestead, FL was also included in pathogenicity tests. All Florida and Oklahoma strains produced leaf spots, but no V-shaped lesions, on leaves of green cabbage, red cabbage, radish, tomato, and horseradish. Typical black rot symptoms were observed only in radish and green and red cabbage inoculated with the X. campestris pv. campestris strain. On the basis of these results, we identify the Florida strains as X. campestris pv. armoraciae (1,2,3), recognizing the precedent of X. campestris pv. armoraciae over X. campestris pv. raphani based on extensive genetic and serological data (1). Our strains appear to be more similar to those causing outbreaks on crucifers in Oklahoma (3) than those in Ohio (2), because Florida strains were pathogenic on tomato.

References: (1) A. M. Alvarez et al. Phytopathology 84:1449, 1994. (2) F. Sahin and S. A. Miller. Plant Dis. 81:1334, 1997. (3) Y. Zhao et al. Plant Dis. 84:1008, 2000.
First Report of Sclerotium rolfsii on Kenaf in South Africa
Authors: Swart W. J. , Tesfaendrias M. T. , Terblanche J.
Published: May 2007

Kenaf, Hibiscus cannabinus L. (Malvaceae), is being planted commercially in South Africa for the high quality cellulose fibers that it produces. In a January 2001 survey of 3-month-old kenaf plants grown from seed in experimental plots near Rustenburg, Northwest Province, 30% of plants were observed with severe wilting. Stems at ground level of all infected plants had sunken tan lesions, white mycelial strands, and small, dark brown, 1 to 2 mm diameter sclerotia. Isolations from diseased stem tissue on malt extract agar (MEA) consistently yielded a fungus conforming to the description of Sclerotium rolfsii Sacc. (teleomorph Athelia rolfsii (Curzi) Tu & Kimbrough). Pathogenicity tests were conducted by applying toothpick tips (5 mm) colonized by S. rolfsii on MEA to the stems of 120-day-old potted plants of 10 kenaf cultivars in the greenhouse. Five plants of each cultivar were wounded once using a sharp dissecting needle, and a colonized toothpick tip was placed on top of each wound. Control treatments consisted of five plants per cultivar each wounded and inoculated with sterile toothpick tips. All inoculation points were wrapped using Parafilm, and the experiment was conducted twice. Lesions were measured after 10 days. Mean lesion lengths for the 10 cultivars were as follows: Dowling (34.9 mm), Cuba 108 (38.6 mm), Gregg (41.1 mm), Everglades 41 (44.2 mm), SF459 (44.9 mm), Tainung 2 (45.8 mm), El Salvador (45.9 mm), Whitton (46.1 mm), Everglades 71 (46.4 mm), and Endora (54.0 mm). The Newman-Keuls multiple comparison test revealed that cvs. Dowling and Endora were significantly more resistant and more susceptible (P < 0.05), respectively, than the other cultivars. Lesions did not develop on control plants. The fungus was reisolated on MEA from all artificially inoculated plants. The pathogen is reported to cause serious losses in yield and fiber quality of kenaf (1). To our knowledge, this is the first report of S. rolfsii on kenaf in South Africa. Commercial plantings of kenaf in South Africa are expected to exceed 500 ha during the next 2 years, so its potential impact on kenaf production in this country will be significant if efficient disease control measures are not practiced.

References: (1) J. M. Dempsey. Kenaf. Pages 203–304 in: Fiber Crops. The University Press of Florida, Gainesville, 1975.
A New Tomato yellow leaf curl virus Strain in Southern Spain
Authors: Morilla G. , Antúnez C. , Bejarano E. R. , Janssen D. , Cuadrado I. M.
Published: May 2007

Tomato yellow leaf curl disease (TYLCD) has affected tomato crops annually in southern Spain since 1992 when Tomato yellow leaf curl Sardinia virus (TYLCSV-ES) was first described. In 1997, the presence of a different begomovirus species (TYLCV-[ES7297]) was reported in common bean (Phaseolus vulgaris). In 1999, TYLCV-[ES7297] was found in pepper (Capsicum annuum) (2). In September 2002, we observed tomato plants of TYLCD tolerant tomato cultivars (Kampala and Tiway) showing strong TYLCD symptoms (shortened internodes, curling of leaflet margins, and leaf blade reduction). Samples from 90 of these plants were collected from greenhouses located in the Province of Murcia and analyzed by Southern blot using the intergenic region of TYLCSV-ES[2] and TYLCV-[ES7297] as specific probes. Positive signals were obtained for TYLCV-[ES7297] and TYLCSV-ES[2] in 88 and 23 of the plants, respectively. Samples from eight TYLCV single-infected plants (four ‘Kampala’ and four ‘Tiway’) were analyzed by polymerase chain reaction using a pair of primers (OTYA7: GCTCCCTGAATGTTCGGATGGA and OTYA8: ATCATGGATTT ACGCACAGGGG) designed to amplify a 1.9-kb fragment of any isolate of TYLCV/TYLCSV. Subsequent restriction fragment length polymorphism analysis of the amplification products yielded a restriction pattern different from that obtained for TYLCV-[ES7297]. Fragments from the eight samples were sequenced and showed 97.9% identity to a TYLCV strain previously reported in Israel (X15656) (1) and only 92.7% identify with TYLCV-[ES7297]. To our knowledge, this is the first report that this strain of TYLCV has been detected in Spain.

References: (1) N. Navot et al. Virology 185(1), 151, 1991. (2) J. Reina et al. Plant Dis. 83:1176, 1999.
First Report of Leaf Blotch Caused by Marssonina coronaria on Apple in Italy
Authors: Tamietti G. , Matta A.
Published: May 2007

During the early summers of 2001 and 2002, in Forno Canavese in northwest Italy, a leaf disease was observed on the old apple cv. Furnas in a domestic orchard. Lesions on the upper side of the leaf were brownish, irregular in size and shape with somewhat dendritic margins, became black, and often coalesced with time. On the underside, lesions were smaller with more definite margins. Beginning in July, scattered acervuli (95 to 170 μm) were observed erupting through the epidermis on the upper side of leaves. Conidia were ampule shaped, 1-septate, constricted at the septum, hyaline, guttulate, and 6.1 to 8.4 × 14.6 to 22.0 μm. Severely diseased leaves abscised prematurely. The fungus was identified as Marssonina coronaria (Ellis & J.J. Davis) J.J. Davis, teleomorph Diplocarpon mali (1) although the conidia were slightly shorter than those originally described for this fungus. Monoconidial isolates were obtained by spreading mini-suspensions of conidia taken from acervuli on malt agar (MA) and transferring single-germinated conidia to MA, potato dextrose agar, V8 agar, or apple leaf agar (ALA). The fungus grew slowly, producing small colonies on V8 and ALA only. On ALA medium, after 3 months incubation at 20 to 22°C, the colonies were 5 to 7 mm in diameter with light brown, irregular margins and dark brown centers bearing acervuli. Conidia from pure cultures were collected, suspended in sterile, distilled water (250,000 ml-1), and sprayed on the leaves of three ‘Golden Delicious’ apple shoots maintained in a mist chamber at 20 to 25°C for 2 weeks. In two independent experiments, the fungus reproduced symptoms like those observed on ‘Furnas’ and was reisolated from acervuli. No symptoms were observed on water-treated controls. To our knowledge, apple leaf blotch has not previously been reported in Italy. Although now it is a minor disease, it could become more important in sustainable crops because of its relatively low sensitivity to copper fungicides (2), the only products that can be used under that program.

References: (1) Y. Harada et al. Ann. Phytopathol. Soc. Jpn. 40:412, 1974. (2) J. Ruide et al. China Fruits 2:51, 1997.
Characterization of Isolates of Phytophthora infestans from Southern and Southeastern Brazil from 1998 to 2000
Authors: Reis Ailton , Smart Christine D. , Fry William E. , Maffia Luiz A. , Mizubuti Eduardo S. G.
Published: May 2007

The population of Phytophthora infestans in Brazil was first characterized 12 years ago. In this research, isolates of P. infestans from potato (n = 184) and tomato (n = 267) collected in southern and southeastern Brazil were characterized to provide more detailed analysis of the current structure of the population. All 451 isolates were analyzed for mating type, and subsets of the isolates were analyzed for allozymes, restriction fragment length polymorphism fingerprint, mtDNA haplotypes, and metalaxyl resistance. Tomato isolates were all of A1 mating type, mtDNA Ib, and US-1 genotype or some variant within this clonal lineage. Of the potato isolates, 82% were A2 mating type, mtDNA IIa, BR-1 genotype, which is a new lineage of P. infestans. All A2 isolates were found on potato, whereas 91% of the A1 isolates were from tomato. A1 and A2 isolates were never found in the same field. The frequency of resistance to metalaxyl was higher in isolates from tomato (55%) than in isolates from potato (38%). After more than a decade of coexistence of isolates of the A1 and A2 mating types, the population was highly clonal, dominated by the BR-1 and US-1 clonal lineages.
Suppression of Bacterial Spot of Tomato with Foliar Sprays of Compost Extracts Under Greenhouse and Field Conditions
Authors: Al-Dahmani Jaber H. , Abbasi Pervaiz A. , Miller Sally A. , Hoitink Harry A. J.
Published: May 2007

The efficacy of foliar sprays with compost water extracts (compost extracts) in reducing the severity of bacterial spot of tomato caused by Xanthomonas vesicatoria was investigated. Extracts prepared from composted cow manure, composted pine bark, an organic farm compost, or composted yard waste, applied as foliar sprays on tomato transplants, resulted in a moderate but statistically significant reduction in the severity of bacterial spot. The population of X. vesicatoria in infected leaves was reduced significantly by extracts prepared from composted cow manure. Efficacy of the water extracts was not affected by oxygen concentrations in the suspension during extraction, compost maturity, or sterilization by filtration or autoclaving. The degree of control provided by foliar sprays with the most effective compost extracts did not differ from that obtained with the plant activator acibenzolar-S-methyl. In the field in two growing seasons, foliar sprays with compost water extracts did not reduce the severity of foliar diseases, including bacterial spot. During the 1997 season, when the severity of bacterial spot in the field was high, foliar sprays with compost water extracts significantly reduced the incidence of bacterial spot on tomato fruit. Amending plot soil with several rates of composted yard waste did not lead to additional control of fruit disease over those only sprayed with extracts. Foliar sprays with a mixture of chlorothalonil and copper hydroxide or with acibenzolar-S-methyl reduced the severity of bacterial spot as well as incidence of spot on fruit.
Control of Moldy-Core Decay in Apple Fruits by β-Aminobutyric Acids and Potassium Phosphites
Authors: Reuveni M. , Sheglov D. , Cohen Y.
Published: May 2007

Alternaria alternata is the predominant fungal pathogen responsible for moldy-core decay in the ‘Red Delicious’ apple fruits. The failure of registered fungicides to control the disease necessitated the search for alternative methods. Here we report that DL-β-aminobutyric acids (BABA) and potassium phosphite are capable of controlling moldy-core in apple fruits in the laboratory and the field. Laboratory tests involving inoculation of wounded mature fruits revealed that decay by A. alternata was 40 to 58% inhibited by 50 μg/ml and completely inhibited by 500 μg/ml of potassium phosphite. DL-BABA, R-BABA, and S-BABA at a concentration of 500 μg/ml inhibited decay formation by 82 to 90%. Potassium phosphite, BABA, and S-BABA inhibited decay formation even when applied 6 to 48 h postinoculation. In vitro tests indicated that BABA compounds did not affect conidial germination or mycelial growth, whereas potassium phosphite partially inhibited both developmental stages of the fungus. Results suggest that BABA inhibits fruit decay development indirectly, probably by inducing resistance in the host tissue, whereas potassium phosphite may act directly against the fungus. A preliminary field trial in a commercial apple orchard showed that three foliar applications of BABA or potassium phosphite, starting from the beginning of bloom until petal fall, reduced the number of fruits infected with moldy-core by 40 and 60%, respectively, relative to fruits from nontreated control trees. Results suggest that potassium phosphite and BABA could provide adequate control of moldy-core disease in apple.
Potential Involvement of Melon Fruit in the Long Distance Dissemination of Cucurbit Potyviruses
Authors: Lecoq Hervé , Desbiez Cécile , Wipf-Scheibel Catherine , Girard Myriam
Published: May 2007

Papaya ringspot virus (PRSV) and Zucchini yellow mosaic virus(ZYMV) are potyviruses frequently reported in cucurbits in Mediterranean, subtropical, and tropical regions. Occasionally, epidemics are also observed in more temperate regions, but the ways these viruses are introduced into new areas are not yet fully determined. We investigated the possibility that infected imported melon fruit could be a route for the introduction of PRSV and ZYMV. Imported melon fruits of the yellow canary type infected by ZYMV and PRSV were exposed in the fields next to healthy melon or squash bait plants. During this period, aphids were observed landing and probing on the fruits. In four independent experiments using different fruits, 3.1 to 25% of bait plants were infected by ZYMV and/or PRSV. PRSV was more frequently transmitted to bait plants than ZYMV. Comparison of partial sequences of the isolates from fruits and from bait plants showed a very high, if not complete, identity within each experiment, confirming that a natural transmission did occur from the fruit to the bait plants. These results suggest that globalization of melon production and international trade may be a factor in the spread of cucurbit potyviruses between countries or continents.
Potential Sources of Resistance for Melon to Nonpersistently Aphid-borne Viruses
Authors: Díaz Juan Antonio , Mallor Cristina , Soria Carmen , Camero Rocío , Garzo Elisa , Fereres Alberto , Alvarez José María , Gómez-Guillamón María Luisa , Luis-Arteaga Marisol , Moriones Enrique
Published: May 2007

Two hundred and sixty-eight Cucumis melo and wild relative accessions were evaluated for resistance to Cucumber mosaic virus (CMV), Papaya ringspot virus strain W (PRSV-W), Watermelon mosaic virus (WMV), and Zucchini yellow mosaic virus (ZYMV). Symptom development and systemic infection based on double antibody sandwich enzyme-linked immunosorbent assays were monitored. Sources of resistance were scarce. However, a number of them were found among the C. melo accessions tested. Thus, the accession C-189 behaved similarly to PI 161375 and showed resistance to “common” CMV strains although it was infected by a “song” type CMV. For WMV, the accessions C-768 and C-425, although infected, exhibited very mild symptoms, and recovery from infection occurred in some occasions in the former. A similar trait was also found in C-105, although in this case symptoms rarely appear and part of the plants are not infected. In addition, C-105 was highly resistant to virus transmission by Aphis gossypii, similarly to PI 161375. Accessions C-885 and C-769 exhibited resistance to PRSV-W, WMV, and ZYMV; therefore they are potential sources of multiple resistance. Resistance traits were also found in wild relatives that could be exploited when interspecific barriers with C. melo can be circumvented.
Resistance to Phialophora gregata Is Expressed in the Stems of Resistant Soybeans
Authors: Tabor G. M. , Tylka G. L. , Cianzio S. C. , Bronson C. R.
Published: May 2007

Growth chamber experiments were conducted to determine if resistance to Phialophora gregata, the causal agent of brown stem rot (BSR) of soybean, is expressed in the stems of resistant soybean genotypes. Upon introduction of the pathogen into the base of stems of 2-week-old seedlings, the fungus advanced with the growing tips of plants of susceptible genotypes but lagged behind in resistant genotypes. Five weeks after introduction of the pathogen, both mean percent stem length colonized by P. gregata and mean percentage of symptomatic trifoliate leaflets were significantly less for resistant than for susceptible genotypes. These results indicate that resistance can be expressed in the stems of resistant soybean plants and suggest that stem inoculation methods may be useful for assessing resistance to P. gregata. Also, in our experiments, internal stem discoloration was not as useful as colonization and foliar symptoms in discriminating resistant from susceptible genotypes.
Effect of Preharvest Application of Cyprodinil on Postharvest Decay of Apples Caused by Botrytis cinerea
Authors: Sholberg Peter L. , Bedford Karen E. , Stokes Sarah
Published: May 2007

Dry-eye rot and gray mold of apple are important diseases caused by Botrytis cinerea. Fungicides available for their control are lacking, and this study was conducted to determine if cyprodinil (Vangard) could be used for this purpose. The mean EC50 value of cyprodinil for 32 Botrytis spp. isolates (27 from apple) was 0.02 μg ml−l, indicating that apple isolates are generally very sensitive. Some of the isolates (19%) were less sensitive and had EC50 values greater than 0.03 μg ml−l, and one isolate from ‘Gala’ apple was considerably less sensitive at 0.095 μg ml−l. Bloom sprays of cyprodinil alone in 1998 and 1999 or in combination with myclobutanil or metiram in 1998 reduced Botrytis spp. infection on developing fruit. Postharvest application of cyprodinil in 1998 indicated that cyprodinil protected apples from gray mold for 3 months. Cyprodinil applied 2 to 3 weeks before harvest in 1999 reduced lesion diameters 68 and 62% on ‘Jonagold’ and ‘Gala’ apples, respectively, that had been wounded and inoculated with B. cinerea after storage at 1°C for 6 months. In similar trials on ‘Gala’ apples in 2000 and 2001, preharvest applications of cyprodinil consistently reduced gray mold incidence and lesion diameter on inoculated apples stored for 6 months. New preharvest use patterns for cyprodinil are discussed for control of postharvest diseases caused by B. cinerea.
New Considerations for Pruning in Management of Fire Blight in Pears
Authors: Shtienberg D. , Zilberstaine M. , Oppenheim D. , Levi S. , Shwartz H. , Kritzman G.
Published: May 2007

The efficacy of pruning infected pear tissues to combat fire blight (caused by Erwinia amylovora) was evaluated in two sets of experiments conducted during 1999 to 2001 in Israel. In the first set of two experiments, diseased tissues were removed soon after the observation of blossom infections. Pruning was effective in 0 to 50% of the treated trees, and resulted in complete eradication of E. amylovora. In the remaining trees, pruning not only did not result in eradication of the bacteria from the tree tissues, it made the situation worse, as the disease had invaded the main branches and limbs of a significantly larger proportion of pruned trees than of non-pruned ones, because of alteration of the physiological status of the host plant by pruning. In the five experiments of the second set, the efficacy of pruning fire blight infections on main branches and limbs was studied; the time of pruning varied among the experiments. Effectiveness of cutting and removing infected branches and limbs was linearly related to time of treatment: the efficacy of pruning improved significantly with lateness of the treatment. The best results were obtained when pruning was carried out while the trees were dormant, in December: none of these trees had a severely infected canopy the following spring. Based on the results obtained in this study, it was concluded that factors related to all three components of the disease triangle (i.e., pathogen, host, and environment), rather than only the actual presence of diseased tissues, should be taken into account in considering the need for cutting and removing fire blight—diseased tissues. Accordingly, recommendations for Israeli growers were revised and updated.