bluuebunny/crossref_metadata_2025 huggingface dataset:
DNA Analysis of Ralstonia solanacearum and Related Bacteria Based on 282-bp PCR-Amplified Fragment
Authors: Villa Joselito , Tsuchiya Kenichi , Horita Mitsuo , Natural Marina , Opina Nenita , Hyakumachi Mitsuro
Published: May 2007

Strains of Ralstonia solanacearum, Pseudomonas syzygii, and the blood disease bacterium (BDB) from different countries were tested for polymerase chain reaction amplification of the 282-bp fragment using the primer pair 759 and 760. These 282-bp fragments from 49 strains of R. solanacearum, six strains of P. syzygii, and two strains of BDB were sequenced. A phylogenetic tree was generated based on the sequence alignment. The R. solanacearum strains were divided into three groups. Group I was composed of strains belonging to biovars 3, 4, 5, and biovar N2 from Japan. Most of the strains from this group were of Asian origin except for two strains from Australia and Guyana (GMI 1000), the type strain. Group II was composed of strains belonging to biovars 1 and 2 and biovar N2 from Brazil. Group III was composed of strains belonging to biovar N2 from Japan and the Philippines. All strains of P. syzygii and BDB clustered in group III. Based on nucleotide differences of the 282-bp fragments, restriction enzyme NlaIII was capable of differentiating R. solanacearum strains into the three groups. Restriction analysis of 165 R. solanacearum isolates from the Philippines using NlaIII showed that all biovar 3 and 4 (group 1) strains had restriction fragments of 116 and 166 bp, strains belonging to biovars 1 and 2 (group 2) showed no restriction, and one strain belonging to biovar 2 (group 3) showed restriction fragments of 54 and 228 bp in size. Thus, NlaIII could be used for rapid differentiation of R. solanacearum strains. Additionally, other restriction enzymes, such as McrI, BsiEI, and MnlI could be used to differentiate R. solanacearum strains from P. syzygii strains.
Identification of Strains of Citrus tristeza virus by Subtraction Hybridization
Authors: Derrick K. S. , Beretta M. J. , Barthe G. A. , Kayim M. , Harakava R.
Published: May 2007

Citrus sudden death (CSD) appears to be a new disease that is a serious problem in Brazil. Symptoms of CSD include yellow stain in the phloem of the rootstock. The cause is not known, but it appears to be infectious and may only affect trees budded on Rangpur lime. In a survey in Brazil, in addition to CSD, we observed numerous trees on Rangpur lime that were obviously declining but had remained in production for several years. Trees with this disease, referred to as Rangpur lime decline (RLD) were different from those with citrus blight (CB). They had near-normal size fruit compared with the small fruit associated with CB and were negative in the serological test for the CB-associated protein (p12). Moreover, they did not have the yellow stain symptom and obviously were declining much more slowly than was reported for CSD. To determine what viruses or virus strains might be associated with CSD, double-stranded (ds)RNAs from fibrous roots of a tree with CSD and stem bark from greenhouse trees infected with Citrus tristeza virus (CTV) isolates T30 and T36 were used to make random primed cDNAs. A Clontech PCR-Select cDNA Subtraction Kit was used to subtract the CSD cDNA with cDNA from an equal mixture of dsRNA from T30 and T36. Of 28 clones that were sequenced, five were found to be significantly different from published CTV sequences. One clone (SDA-1) was found to be only 48% similar to CTV T30 based on amino acid sequence. Using samples collected in October 2001, hybridization assays with a DIG probe of SDA-1 were positive for RNA from roots of declining trees from an area where CSD is reported to occur and from a second area where trees were declining with what had been thought to be CB and are now considered to be RLD. The SDA-1 probe reacted weakly or not at all with RNA from stem bark of trees with CSD, collected in October 2001, or RNA from roots of trees that were declining with CB. Using samples collected in March 2003 from trees with severe decline (nearly dead), the SDA-1 probe reacted with all preparations from both stems and roots. Reactions to the SDA-1 probe also were observed in many stem or root samples from trees with RLD, with early symptoms of CSD, and nonsymptomatic trees. The SDA-1 probe did not react with samples from roots or stems of healthy or CB trees from Florida.
Comparison of Aflatoxin Production in Normal- and High-Oleic Backcross-Derived Peanut Lines
Authors: Xue H. Q. , Isleib T. G. , Payne G. A. , Wilson R. F. , Novitzky W. P. , O'Brian Greg
Published: May 2007

The effect of the high-oleate trait of peanut on aflatoxin production was tested by comparing normal oleic lines with high-oleic backcross-derived lines. Seeds were blanched, quartered, and inoculated with Aspergillus flavus conidia, placed on moistened filter paper in petri dishes, and incubated for 8 days. In one experiment, dishes were stacked in plastic bags in a Latin square design with bags and positions in stacks as blocking variables. High-oleic lines averaged nearly twice as much aflatoxin as normal lines. Background genotype had no significant effect on aflatoxin content, and interaction between background genotype and oleate level was not detected. In a second experiment, dishes were arranged on plastic trays enclosed in plastic bags and stacked with PVC spacers between trays. Fungal growth and aflatoxin production were greater than in the first experiment. Background genotype, oleate level, and their interaction were significant. The mean of high-oleic lines was almost twice that of normal lines, but the magnitude of the difference varied with background genotype. Special care should be taken with high-oleic lines to prevent growth of Aspergillus spp. and concomitant development of aflatoxin contamination.
Characterization of a New Potyvirus Naturally Infecting Chickpea
Authors: Larsen Richard C. , Kaiser Walter J. , Wyatt Stephen D. , Buxton-Druffel Keri L. , Berger Phillip H.
Published: May 2007

During the 1999 to 2001 growing seasons, symptoms consisting of mosaic, stunting, yellowing, wilting, shortening of internodes, and phloem discoloration were observed in chickpea (Cicer arietinum) grown in the Department of Chuquisaca in southern Bolivia. In some fields, approximately 10% of the plants exhibited viruslike symptoms and suffered greatly reduced seed yields. Lentil (Lens culinaris) was also observed to be infected but not pea (Pisum sativum) or faba bean (Vicia faba) growing in nearby fields. Infected chickpea tissue reacted positively to the potyvirus group-specific monoclonal antibody (MAb), but there was no serological reaction with antisera to the potyviruses Bean yellow mosaic virus, Clover yellow vein virus, Cowpea aphid-borne mosaic virus, Pea seedborne mosaic virus, Bean common mosaic virus, or Bean common mosaic necrosis virus. Western blots of total protein extracts probed with the potyvirus MAb revealed a single band ca. 32 kDa. Comparative sequence analysis of cDNA clones generated from the putative coat protein gene consisted of 282 amino acids (31.9 kDa) and showed moderate identities of 67, 66, 63, 63, and 61% with the coat proteins of potyviruses Pepper severe mosaic virus, Pepper yellow mosaic virus, Potato virus Y, Plum pox virus, and Pepper mottle virus, respectively. Phylogenetic analysis of the coat protein amino acid sequence revealed that this virus is a unique member of the family Potyviridae and is phylogenetically most closely related to a group of Solanaceae-infecting potyviruses rather than to other legumeinfecting potyviruses. The proposed name for the new causal agent is Chickpea yellow mosaic virus.
Virulence and Genetic Variability Among Isolates of Mycosphaerella pinodes
Authors: Zhang J. X. , Fernando W. G. D. , Xue A. G.
Published: May 2007

Fifty-eight isolates of Mycosphaerella pinodes, collected from western Canada, New Zealand, France, Australia, the United Kingdom, and Ireland, were analyzed for pathogenic and genetic variation according to their virulence on six differential cultivars of field pea (AC Tamor, Bohatyre, Danto, Majoret, Miko, and Radley) and amplified fragment length polymorphism markers. The 56 isolates were classified into 15 pathotypes. Pathotype 1 consisted of 31 isolates that were virulent on all six pea differential cultivars. Pathotypes 14 and 15 consisted of eight isolates that were avirulent on all six differential cultivars or virulent on one of six differential cultivars. The analysis of molecular variance showed that 57.2% of the total variation was caused by differences among populations, and 42.8% was due to molecular diversity within populations. Phylogenetic analysis of molecular variation of isolates showed that most of the Canadian isolates and four Australian isolates formed two clustered groups, respectively, regardless of virulence on the six differential cultivars. Isolates from New Zealand were geographically clustered into two groups. However, the isolates from France, Ireland, and the United Kingdom were clustered with the Canadian isolates.
Diversity and Sources of Multiple Disease Resistance in Hordeum spontaneum
Authors: Fetch T. G. , Steffenson B. J. , Nevo E.
Published: May 2007

Hordeum spontaneum, the progenitor of cultivated barley, is known to be a rich source of disease resistance genes. The objective of this study was to assess the diversity of H. spontaneum accessions from Israel and Jordan for their reaction to six fungal pathogens of importance to cultivated barley in the United States and Canada. Overall, a high level of macro-scale (across collection sites) and micro-scale (within a collection site) diversity for disease reaction was found in the 116 accessions of H. spontaneum evaluated at the seedling stage. Additionally, genetic heterozygosity for resistance loci was common in H. spontaneum. The frequency of resistance in accessions from Jordan and Israel was high for Septoria speckled leaf blotch (77 and 98%, respectively), leaf rust (70 and 90%), net blotch (72 and 68%), and powdery mildew (58 and 70%); intermediate for spot blotch (53 and 46%); and low for stem rust (2 and 26%). The level of disease resistance in H. spontaneum was not strongly correlated with any of the weather variables (temperature, precipitation, and humidity) monitored near the collection sites. However, in general, resistance was more often found in germ plasm from mesic (e.g., Mediterranean coast) than in xeric (e.g., Negev Desert) areas. Two H. spontaneum accessions (Shechem 12-32 and Damon 11-11) were resistant to all six pathogens and may be useful parents in programs breeding barley for multiple disease resistance. The high level of diversity and heterozygosity for disease reaction found in this study indicates that H. spontaneum is an extraordinarily rich and largely untapped source of unique disease resistance alleles for cultivated barley improvement.
First Report of Puccinia xanthii on Xanthium italicum in Eastern Hungary
Authors: Dávid I. , Harcz P. , Kövics G. J.
Published: May 2007

In 2002, in Debrecen, eastern Hungary, Puccinia xanthii Schwein. was detected on hunter burr, a geographically spreading, noxious weed species in row crops. Symptoms were found on leaves, stems, and petioles of plants collected from a competition experiment between sugarbeet and hunter burr. Density of the hunter burr population (6 plants per m2 or 20 plants per m2) influenced the rate of infection. In the low-density population, the number of rust pustules and infected leaves was lower than that in the high-density population, in which 70% infection was reached by September. First symptoms appeared at the end of July (high-density population) and in the beginning of August (low-density population) in the form of small, chlorotic raised spots on the underside of the leaves. Dark brown telia (3.8 mm in diameter or larger) developed on spots. Elliptical telia occurred at the rate of 0.02 to 2.37 pustules per cm2. Elongated pustules caused swelling and epidermal splitting on stems and petioles. Teliospores were brown, two-celled, and 35 to 56 × 15 to 21 μm, the walls were 0.8 to 1.0 μm at the side and 5 to 8 μm at the apex, the septum was 1 to 1.5 μm, and a persistant pedicel was 15 to 50 μm. Size and morphology of teliospores fit the description of P. xanthii (2). A pathogenicity test was conducted in the greenhouse (24°C with high relative humidity) according to the “leaf disc method” of Morin et al. (1) using freshly collected hunter burr leaves. Teliospores germinated immediately, producing metabasidia, and basidiospores were produced within 5 h. The first macroscopic symptoms on test plants were observed 4 days after inoculation. Approximately 8 days after inoculation, developing telia arose from the thallus and began to erupt through the epidermis. Developed teliospores on artificially inoculated plants were morphologically identical to those from leaves collected in the field. Control plants did not develop symptoms. This microcyclic rust occurs in several regions of the world, including several southern European countries. This rust is a potential biological agent for the control of Xanthium spp.; however, it can infect several cultivars of sunflower (1). To our knowledge, this is the first report of P. xanthii in Hungary.

References: (1) L. Morin et al. Can. J. Bot. 71:959, 1993. (2) J. A. Parmelee. Can. J. Bot. 47:1391, 1969.
First Report of Peach latent mosaic viroid and Hop stunt viroid Infecting Peach Trees in the Czech Republic
Authors: Hassan M. , Rysanek P. , Di Serio F.
Published: May 2007

Peach latent mosaic viroid (PLMVd) and Hop stunt viroid (HSVd) are known to naturally infect stone fruits, but their contemporary presence in peach trees has been reported only recently (3). During a field validation of detection methods developed for sanitary screening of propagation material, PLMVd and HSVd, alone or in mixed infections, were detected in peach trees grown in the trial orchard of the Czech University of Agriculture in Prague. Leaf samples were collected in September 2002 from symptomless trees of peach cultivars imported from the United States (cvs. Sunhaven, Redhaven, Fairhaven, Cresthaven, Dixired, Halehaven, and NJC 103), Slovakia (cv. Luna), and a tree of Chinese wild peach, Prunus davidiana, and analyzed by reverse transcription-polymerase chain reaction (RT-PCR). PLMVd cDNA was amplified as previously reported (2) or by using two sets of primer pairs designed to amplify partial cDNAs, one reverse primer R: GTTTCTACGG CGGTACCTGA, complementary to the nucleotide positions 204 to 223 and forward primers F1: CGTATCTCAACGCCTCATCA, homologous to the positions 109 to 128, and F2: CTGCAGTTCCCGCTAGAAAG, homologous to the positions 15 to 34 of PLMVd reference sequence (2). The two pairs using the R sequence produced the expected size PCR products of 115 and 209 bp, respectively. RT-PCR for HSVd detection was performed as reported (1). The same total RNA preparations were also analyzed by molecular hybridization with nonisotopic riboprobes specific for each viroid. With minor exceptions, both methods gave similar results. Of 66 tested trees, 5 were infected with PLMVd, 46 were infected with PLMVd and HSVd, and 15 were free of both viroids. Viroid free plants included cvs. Luna, Cresthaven, Dixired, and Halehaven and the species P. davidiana. The high number of infections by both viroids was unexpected because mixed infections are generally rare (3). Most likely, mixed infections occurred during field manipulations and propagation of infected materials. To our knowledge, this is the first report of PLMVd in the Czech Republic. Although further investigations are needed to ascertain the spread of stone fruit viroids in the Czech Republic, our results also report an unusually high incidence of mixed infections of peach trees in this country. These results stress the need for a certification program to help control the spread of stone fruit viroids in the Czech Republic.

References: (1) K. Amari et al. J. Gen. Virol. 82:953, 2001. (2) A. M. Shamloul et al. Acta Hort. 386:522, 1995. (3) M. Tessitori et al. Plant Dis. 86:329, 2001.
First Report of White Leaf Spot of Dry Bean Caused by Pseudocercosporella albida in North America
Authors: Río L. E. del , Bradley C. A. , Lamppa R. S.
Published: May 2007

In August 2002, white leaf spot disease was observed on red kidney bean (Phaseolus vulgaris L.) at three fields near Staples, MN. Disease incidence in these fields, calculated as the proportion of plants showing visible symptoms, ranged from 20 to 100%. Symptoms and signs consisted of abundant, white sporulation on the abaxial side of leaves that was limited by secondary veins, resulting in angular-shaped lesions. Corresponding with fungal growth, yellow, angular spots were observed on the upper leaf surface. In older leaves, lesions coalesced, covering most of their surface, while younger leaves were relatively free of symptoms. Heavily diseased plants senesced faster and defoliated earlier than nonsymptomatic plants. Identification of the pathogen was conducted by direct observation of infected plant tissues with light and electron microscopes. Conidia were hyaline, filiform, rounded at their apex, and with no visible scar at their point of attachment to the conidiophore. Conidia had one to four septa, were 57 to 68 μm long, and approximately 2.4 μm in diameter. Conidia were produced at the tip of colorless, short conidiophores that emerged through stomata in groups of five or more. These traits are in agreement with the description of Pseudocercosporella albida (Matta & Belliard) Deighton (1,2). A sample of infected tissues has been deposited at the U.S. National Fungus Collection (BPI 842303) at Beltsville, MD. The impact of this disease on bean yields in Minnesota was not estimated. However, in the cool highlands of Colombia, where white leaf spot is endemic, yields can be reduced by as much as 47% (3). To our knowledge, this is the first report of the presence of this pathogen on dry bean in North America.

References: (1) F. C. Deighton. Trans. Br. Mycol. Soc. 66:547, 1976. (2) A. Matta and L. Belliard. Phytopathol. Mediterr. 12:102, 1973. (3) H. F. Schwartz et al. Plant Dis. 65:494, 1981.
Determination of Host Responses to Magnaporthe grisea on Detached Rice Leaves Using a Spot Inoculation Method
Authors: Jia Y. , Valent B. , Lee F. N.
Published: May 2007

Through the use of standard assays, where conidia of the pathogen Magnaporthe grisea are sprayed onto rice, it is impossible to determine the exact number of conidia in any given area and to predict the locations of disease lesions in the rice blast system. To develop a localized, quantitative inoculation of M. grisea, a novel spot method was investigated. Serially diluted Tween 20 was added to M. grisea conidial suspensions in 0.25% (wt/vol) gelatin to promote adherence of conidia on detached rice leaves. Standard assays indicated no deleterious effects of Tween 20 to rice blast development and 0.02% (vol/vol) Tween 20 was necessary for promoting adherence of spore suspensions to the detached leaves. The spot method was evaluated using three well-characterized races of M. grisea and confirmed with standard assays. Disease reactions of rice to four predominant races of M. grisea were tested concurrently using the spot method and standard assays. Successful application of this assay will help identify novel sources of rice blast resistance and evaluate virulence of M. grisea to aid in breeding resistance to rice blast.
Reduction of Defoliation in Citrus Caused by Mycosphaerella citri with a Novel Biocompatible Fungicide
Authors: McGovern R. J. , Winston A. E. , Rouse R. E. , Welch A. W.
Published: May 2007

A novel, biocompatible fungicide, CD-2346, was evaluated for management of defoliation associated with greasy spot (Mycosphaerella citri Whiteside) in orange (Citrus sinensis (L.) Osbeck) and grapefruit (Citrus × paradisi Macfad.). This product contains potassium bicarbonate, potassium carbonate, urea, and a surfactant. CD-2346 (7.0 kg/ha) and a half-rate combination of CD-2346 + benomyl (0.55 kg/ha) were compared with a higher rate of benomyl (1.1 kg/ha) and commercial standards of oil (petroleum distillate FC-435-66 [70 to 93.5 liters/ha]) or oil (46.8 liters/ha) + copper sulfate (2.2 to 2.8 kg/ha). Fungicide efficacy was assessed using the area under the defoliation progress curve (AUDPC) and final defoliation in entire trees or final greasy spot severity in individual leaves. All fungicide treatments reduced the AUDPC, and all but benomyl reduced either final defoliation percentage or disease severity in individual leaves. CD-2346 and the reduced-rate combination of CD-2346 + benomyl were generally equal or superior to the full rate of benomyl in decreasing the AUDPC; CD-2346 + benomyl was equivalent to oil in reducing the AUDPC. Oil and CD-2346 treatments similarly reduced final defoliation, but oil + copper sulfate was superior to CD-2346 in reducing the AUDPC and final greasy spot defoliation or severity.
The Perfect Stage of Powdery Mildew of Sugar Beets Found in Idaho and Colorado
Authors: Gallian J. J. , Hanson L. E.
Published: May 2007

Powdery mildew (Erysiphe polygoni DC [synonym E. betae {Vanha} Weltzien]) of sugar beet (Beta vulgaris L.) has been a significant problem in many sugar beet growing areas of the United States since the first serious epidemic in 1974. Disease has been attributed solely to the asexual stage of the pathogen in the United States, except for one report of the perfect stage in a single field in Washington coincidental with the 1974 epidemic (1). In August 2001, ascomata were observed in several fields in Owyhee County in southwestern Idaho near Grand View. The perfect stage was widespread and easily found, and in one field the surfaces of leaves collected from 50 randomly sampled plants were between 10 and 90% covered with ascomata. Subsequently, the ascigerous stage was found in September and October in multiple fields in three additional counties in southwestern and south-central Idaho and two counties in northern Colorado. Ascomata were found on 12 commercial varieties in the two states and six breeding lines in Colorado. Asci contained one to four hyaline or yellow-to-golden pigmented ascospores per ascus. Ascomata observed in Idaho and Colorado are similar to those described from Europe (2). Ascospores appeared intact after leaves were dried and stored at 4 to 7°C more than 4 weeks. However, after leaves with ascomata were dried and stored at 24 to 27°C for 1 week or more, ascomata and asci appeared intact microscopically, but ascospores were no longer delineated and appeared desiccated or degraded. Because the ascigerous stage provides a means of genetic recombination, there is the potential for races of the pathogen to arise with greater frequency. This has serious implications for managing fungicide resistance and breeding for disease resistance to sugar beet powdery mildew.

References: (1) D. L. Coyier et al. (Abstr.) Proc. Am. Phytopathol. Soc. 2:112, 1975. (2) S. Francis. Mol. Plant Pathol. 3:119, 2002.
Quercus canariensis, a New Host of Trabutia quercina
Authors: Trapero A. , Sánchez M. E.
Published: May 2007

Quercus canariensis Willd. is an oak species endemic to northwestern Africa and the Iberian Peninsula. This species is particularly abundant in the southwestern Andalucía Region of southern Spain. During a disease survey in this area from 1997 to 1998, we observed Q. canariensis trees affected by a tar spot disease. Tar spot lesions were clearly differentiated by a black, crustose, and shiny stromata (10 to 20 mm in diameter) on the upper surface of leaves mainly arranged along leaf veins but also scattered randomly over the leaf surface. On most leaves there was little necrosis, and on most trees the damage was not serious, although some trees located in the most humid areas were severely affected with leaf chlorosis and heavy defoliation. Other Quercus species in the area, such as Q. ilex and Q. suber, did not show signs of tar spot. One fungus species was consistently associated with tar spots. The fungus formed ascomata, 250 to 400 µm in diameter, embedded in the stromata. Asci were clavate or saccate, 45 to 55 × 17 to 22 µm, eight spored, and short stalked. The ascus apex was acute to obtuse. Ascospores were arranged irregularly, 20 to 25 (-30) × 5 to 8.5 µm, fusiform to ellipsoidal fusiform, often curved and flattened on one side, thin walled, hyaline, aseptate, and smooth without a gelatinous sheath or appendage. Based on these characteristics, the fungus was identified as Trabutia quercina (Rudolphi ex Fr.) Sacc. & Roum., a pathogen causing tar spot in several Quercus species in the Northern Hemisphere (1). Samples were deposited in the Plant Pathology Mycotheca at the University of Córdoba, Spain (MIC-888 to MIC-897). To our knowledge, this is the first report of T. quercina on Q. canariensis and the first report of this pathogen in Spain.

Reference: (1) P. F. Cannon. Mycopathologia 135:69, 1996.
First Report of Fusarium denticulatum from Sweet Potato in Venezuela
Authors: González M. S. , Fuenmayor F. , Godoy F. , Navas R.
Published: May 2007

During 2001and 2002, 53 accessions of sweet potato (Ipomoea batatas L.) from a germ plasm collection maintained in the field at Centro Nacional de Investigaciones Agropecuarias, Maracay, Venezuela, were evaluated for diseases. Sweet potato accessions Catemaco and 2878 were symptomatic for chlorotic leaf distortion with deformation of young leaves and stunted vines. Symptomatic nodes and shoot tips were excised, surface disinfested in 0.5% sodium hypochlorite, cultured on potato dextrose agar (PDA), and incubated at 28°C. Pale pink colonies with white aerial mycelium developed from symptomatic tissues. At 20°C, pure cultures on PDA developed slow-growing, aerial, white-to-pink mycelium. Pigmentation in reverse was light orange. Conidia aggregated in false heads, and orange sporodochia were abundant. Conidiophores in aerial mycelium were prostrate, short, and sometimes branched. Sporodochial conidiophores were branched. Phialides were mostly monophialidic but occasionally polyphialidic and averaged 25.0 × 3.0 µm. Microconidia were abundant, long, oval to allantoid, and 0 to 1 septate. Macroconidia were fusiform to falcate with a beaked apical cell and a footlike basal cell, 3 to 5 sepate, and 38 to 45 × 3.6 to 4.0 µm. Chlamydospores were absent. The fungus was identified as Fusarium denticulatum Nirenberg and O'Donnell (1). Ten 25-cm-long vine-tip cuttings of accessions Catemaco and 2878 were immersed in a conidial suspension (1 × 106 conidia per ml) of F. denticulatum. As a control, vines were immersed in sterile, distilled water. After inoculation, each cutting was planted in a 13-cm plastic pot containing a soil/sand (1:1) mixture. Inoculated plants were covered with plastic bags for 48 h and grown in a greenhouse at temperatures ranging from 30 to 38°C. After 3 months, three inoculated plants of accession Catemaco and two plants of accession 2878 developed purple terminals and moderate interveinal chlorosis. Leaf distortion was not observed. F. denticulatum was recovered from both symptomatic and asymptomatic inoculated plants. To our knowledge, this is the first report of F. denticulatum from sweet potato germ plasm in Venezuela. Dried, pure cultures and slides of the fungus are being deposited in the Albert S. Muller Herbario Micologico (VIA).

Reference: (1) H. I. Nirenberg and K. O'Donnell. Mycologia 90:434, 1998.
Characterization of the Reaction of North Dakota Dry Bean Cultivars to Three Races of Colletotrichum lindemuthianum
Authors: del Río L. E. , Lamppa R. S. , Gross P. L.
Published: May 2007

Colletotrichum lindemuthianum, causal agent of anthracnose, a serious disease of dry bean, had been prevalent mostly in the eastern United States and Michigan. In 2001, the disease was observed affecting several commercial bean fields in North Dakota. To assess the potential impact of this pathogen on the North Dakota dry bean industry, 30 of the most widely planted cultivars were inoculated with races 7, 73, and 89 of C. lindemuthianum. Race 73 is present in Michigan, and has been detected in recently North Dakota and Manitoba, while races 7 and 89 are currently present in Michigan and Ontario. All cultivars were spray inoculated with a suspension of 106 conidia/ml in the greenhouse and evaluated for disease reaction using a 0-to-9 scale 8 days after inoculation. Most kidney beans were susceptible to race 7, but resistant to races 73 and 89. ‘Isles’ and ‘Drake’ were the only kidney beans resistant to all three races. All pinto beans were susceptible to races 73 and 89 except ‘Topaz’, which was moderately resistant to race 73 but susceptible to race 89. Most pinto beans were resistant or moderately resistant to race 7. Navy bean cvs. Newport and Envoy were resistant to all three races; however, ‘Norstar’, the most widely planted navy bean cultivar, was susceptible to all three races. Research is being conducted to identify germplasm with resistance to these races. To reduce the possibility of spreading this pathogen to new fields in the region, the use of noncertified seed should be discouraged among producers, and fields used for seed production should be monitored very carefully.
Multiple Disease Resistance in Interspecific Hybrids of Potato
Authors: Jansky S. H. , Rouse D. I.
Published: May 2007

Wild species of Solanum are excellent sources of disease resistance genes that may be incorporated into S. tuberosum through breeding. This study was initiated to determine whether multiple forms of disease resistance could be identified in interspecific Solanum hybrids. Thirty-two clones were evaluated for resistance to soft rot, common scab, black scurf, Verticillium wilt, and early blight. Most of the clones originated from populations that were not initially selected for disease resistance traits. Comparisons with the cultivars Atlantic, Russet Norkotah, and Russet Burbank indicated that all clones were more resistant than at least one cultivar for at least one disease resistance trait. Clone C545, which exhibited improved resistance to soft rot, scab, pitted scab, early dying disease, and early blight, appears to be an especially valuable source of disease resistance. The use of interspecific hybridization at the diploid level, combined with sexual polyploidization to return to the tetraploid level, provides a method to introduce multiple forms of disease resistance into advanced clones.
Survival of Gibberella zeae in Fusarium-Damaged Wheat Kernels
Authors: Inch Sharon A. , Gilbert Jeannie
Published: May 2007

The survival of Gibberella zeae in Fusarium-damaged kernels was investigated under field conditions at Glenlea, Morden, Portage la Prairie, and Winnipeg, Manitoba, Canada. Fusarium-damaged kernels were either left on the soil surface or buried at 5 or 10 cm and monitored for 24 months. G. zeae was isolated after 24 months from Fusarium-damaged kernels under all conditions, with isolation frequency ranging from 85 to 99% of kernels. Perithecia developed on Fusarium-damaged kernels from all locations and treatments, but ascospores developed only in perithecia on kernels located at the soil surface. A similar experiment was conducted under controlled conditions to test survival of the fungus in kernels left at the surface or buried at 5 cm in heat-treated and nontreated soil at -10, 2, and 20°C. The fungus survived in 76 to 100% of kernels. When kernels were incubated at 20°C, G. zeae was recovered from 83 and 76% of kernels in heat-treated and nontreated soil, respectively. Perithecia developed on kernels incubated at 20 and 2°C, but ascospores developed only in perithecia on Fusarium-damaged kernels at 20°C on the soil surface. As survival of G. zeae in Fusarium-damaged kernels did not decrease after 24 months, rotations of at least 2 years are necessary to avoid infection of new crops by G. zeae originating from Fusarium-damaged kernels.
Impact ofRaspberry bushy dwarf viruson ‘Marion’ Blackberry
Authors: Strik Bernadine , Martin Robert R.
Published: May 2007

Raspberry bushy dwarf virus (RBDV), genus Idaeovirus, was first observed in 1997 in a planting of ‘Marion’ blackberry (a complex hybrid with Rubus idaeus, R. procerus, and R. ursinus in its background) established at the North Willamette Research and Extension Center (Aurora, OR) from tissue-cultured plants in 1993. RBDV was detected in 128 of the 280 plants. The incidence of RBDV in this planting did not increase from 1997 through 2001. In 1999 and 2000, we evaluated the impact of RBDV on yield, fruit quality, and plant growth of ‘Marion’ blackberry. RBDV had no effect on cane growth or fruit number, but it reduced yield (40 to 50%), fruit weight (23 to 40%), and drupelet number per fruit (36 to 39%) compared with uninfected plants. In 2000, we surveyed 32 commercial ‘Marion’ fields for RBDV using enzyme-linked immunosorbent assay. The locations of sampled fields were selected to reflect the acreage distribution of ‘Marion’ blackberry production in Oregon. RBDV-infected plants were detected in three fields.
Sweetpotato Virus Disease (SPVD): Distribution, Incidence, and Effect on Sweetpotato Yield in Peru
Authors: Gutiérrez D. L. , Fuentes S. , Salazar L. F.
Published: May 2007

Sweetpotato virus disease (SPVD), the most important disease affecting sweetpotato (Ipomoea batatas (L.) Lam), is caused by the synergistic interaction of the aphid-transmitted Sweetpotato feathery mottle virus (SPFMV) and whitefly-transmitted Sweetpotato chlorotic stunt virus (SPCSV). In this study, SPVD was the main disease in the Cañete Valley, the major sweetpotato-producing area in Peru. Studies on virus incidence showed that SPCSV and SPFMV were the most frequently identified viruses in Cañete Valley. Symptoms of different severity were associated with isolates of both viruses involved in the SPVD. Over 80% of plants infected with both SPFMV and SPCSV showed the symptoms (leaf reduction and deformation, vein clearing or mosaic, and stunting) typically attributed to SPVD elsewhere. SPFMV did not significantly affect the yield of the sweetpotato cultivars Jonathan and Costanero, but infection of these cultivars by SPCSV was associated with significant yield reduction. Double infection by the two viruses resulted in SPVD and greater yield reduction than for either alone. These results demonstrate that SPFMV and SPCSV interact synergistically and that the severity of SPVD symptoms also depends on the particular isolate of each virus.
Use of a Seed Scarifier for Detection and Enumeration of Galls of Anguina and Rathayibacter Species in Orchard Grass Seed
Authors: Alderman Steve C. , Bilsland Douglas M. , Griesbach John A. , Milbrath Gene M. , Schaad Norman W. , Postnikova Elena
Published: May 2007

Seed galls, caused by Anguina spp., are normally detected visually in cereals such as wheat and barley. However, in grasses such as orchard grass, the presence of galls induced by Anguina or Rathayibacter spp. are difficult to detect visually due to their infrequent occurrence and masking by lemmas and paleas. To develop improved seed assays for the presence of the nematode and bacterial galls, a small scarifier was used to remove lemmas and paleas without causing major damage to seeds or galls. Following scarification, the galls were visually identified and manually counted under a dissecting microscope. Using the scarifier, several orchard grass seed lots were screened for Anguina and Rathayibacter spp. The percentage of samples of orchard grass seed harvested in the Willamette Valley of Oregon during 1996, 1997, and 2000 containing galls of Anguina sp. were 37, 46, and 48, respectively. The percentage of samples containing bacterial galls with Rathayibacter sp. was 27, 31, and 40, respectively. Total galls with Anguina sp. per 25 g of orchard grass sample ranged from 1 to 24. The mean of Anguina sp. galls per sample in 1996, 1997, and 2000 were 4, 5, and 5, respectively. Total galls with bacteria per 25 g of sample ranged from 27 to 40; mean number of galls per sample in 1996, 1997, and 2000 were, 6, 5, and 11, respectively. This is the first report confirming the presence of Rathayibacter sp. galls in orchard grass in Oregon.
Viruses Infecting Cucurbits in Samsun, Turkey
Authors: Sevik M. A. , Arli-Sokmen M.
Published: May 2007

To detect cucurbit viruses and determine their incidence, surveys were conducted in 45 fields in 18 villages in Samsun province, Turkey from July to October in 1999 and 2000. Watermelon mosaic virus (WMV), Zucchini yellow mosaic virus (ZYMV), and Cucumber mosaic virus (CMV) were detected in cucurbits after analyzing 165 samples by enzyme-linked immunosorbent assay. WMV, ZYMV, and CMV were detected in 53.9, 38.8, and 20.6% of samples tested, respectively. ZYMV and WMV infections were detected in all cucurbit species, but CMV was not detected in any samples of watermelon and pumpkin.
Induced Resistance as a Possible Means to Control Diseases of Strawberry Caused by Phytophthora spp.
Authors: Eikemo H. , Stensvand A. , Tronsmo A. M.
Published: May 2007

Two putative elicitors of disease resistance (acibenzolar-S-methyl and chitosan) were tested for their effect on crown rot (Phytophthora cactorum) in strawberry. The effect of both compounds was enhanced when the time between treatment and inoculation was prolonged from 2 to 20 days. There were no significant differences between treatments when the concentration of acibenzolar-S-methyl was increased from 10 to 1,000 μg a.i./plant. The lowest tested concentrations of chitosan (10 and 50 μg a.i./plant) resulted in a lower disease score compared with the highest concentrations (250 or 1,000 μg a.i./plant). There were no differences in disease score between treatment with fosetyl-Al, acibenzolar-S-methyl, or chitosan when applied 5 or 15 days before inoculation. The effect of acibenzolar-S-methyl and chitosan also was tested against P. fragariae var. fragariae in alpine strawberry (Fragaria vesca var. alpina cv. Alexandria). Chitosan had no effect, whereas fosetyl-Al and all treatments with acibenzolar-S-methyl (50 or 250 μg a.i./plant; 5, 10, 20, or 40 days before inoculation) reduced the severity of the disease. There were no significant differences between acibenzolar-S-methyl and fosetyl-Al when applied at the same time. Acibenzolar-S-methyl and chitosan at concentrations of 0.5, 5, 50, and 500 μg a.i. ml-1 in V8 juice agar were tested for possible effects on P. cactorum and P. fragariae var. fragariae in vitro. Only chitosan at concentrations of 50 and 500 μg a.i. ml-1 had a growth-retarding effect on P. cactorum. Both acibenzolar-S-methyl and chitosan at a concentration of 500 μg a.i. ml-1 reduced the growth rate of P. fragariae var. fragariae.
Induction of Growth Promotion and Resistance Against Downy Mildew on Pearl Millet (Pennisetum glaucum) by Rhizobacteria
Authors: Raj S. Niranjan , Chaluvaraju G. , Amruthesh K. N. , Shetty H. S. , Reddy M. S. , Kloepper Joseph W.
Published: May 2007

A series of laboratory, greenhouse, and field experiments were conducted to evaluate seven strains of plant growth-promoting rhizobacteria (PGPR). The PGPR were tested as suspensions of fresh cultures and talc-based powder formulations. Evaluations were conducted on pearl millet (Pennisetum glaucum) for growth promotion and management of downy mildew caused by Sclerospora graminicola. All treatments with fresh suspensions and powdered formulations showed enhancement in germination and vigor index over the respective untreated controls. With fresh suspensions, maximum vigor index resulted from treatments by Bacillus pumilus strain INR7 followed by B. subtilis strain IN937b (64 and 38% higher than the untreated control, respectively). With powdered formulation, treatment with strain INR7 also resulted in the highest germination and vigor indexes, which were 10 and 63%, respectively, over the untreated control. Under experimental plot conditions, prominent enhancement in growth also was observed in the disease tests. Yield was enhanced 40 and 37% over the untreated control by seed treatment with powdered formulations of strains INR7 and SE34, respectively. The same strains also increased yield by 36 and 33%, respectively, when applied as fresh suspensions. Studies on downy mildew management resulted in varied degrees of protection by the PGPR both under greenhouse and field conditions. With fresh suspensions, treatment with INR7 resulted in the highest protection (57%), followed by B. pumilus strain SE34 and B. subtilis strain GBO3, which resulted in 50 and 43% protection, respectively, compared with the untreated control. With powdered formulation, PGPR strain INR7 suppressed downy mildew effectively, resulting in 67% protection, while SE34 resulted in 58% protection, followed by GBO3 with 56% protection. Treatment with Apron (Metalaxyl) resulted in the highest protection against downy mildew under both greenhouse and field conditions. Thus, the present study suggests that the tested PGPR, both as powdered formulations and fresh suspensions, can be used within pearl millet downy mildew management strategies and for plant growth promotion.
Population Race Structure of Pyrenophora tritici-repentis Prevalent on Wheat and Noncereal Grasses in the Great Plains
Authors: Ali Shaukat , Francl Leonard J.
Published: May 2007

The fungus Pyrenophora tritici-repentis, cause of tan spot of wheat, is an important foliar pathogen worldwide. Genetic variation in the fungal population prevalent in the Great Plains was studied by analysis of 270 single-spore isolates of P. tritici-repentis recovered from wheat, durum, and 10 noncereal grasses: Alti wild rye, barnyard grass, crested wheatgrass, intermediate wheatgrass, needle and thread grass, quackgrass, smooth bromegrass, sand reedgrass, slender wheatgrass, and wild barley. The isolates were grouped into five known races based on necrosis and/or chlorosis induction on standard differentials with two additional wheat genotypes ND495 and M-3. The isolates recovered from wheat were races 1, 2, and 4, while those from durum were races 1 and 5. Isolates from noncereal grasses were all race 4, except for the recovery of two isolates of race 1 from smooth bromegrass. Race 3 was not found in this study. This is the first record of barnyard grass and slender wheatgrass as alternative hosts for P. tritici-repentis. The recovery from noncereal grasses suggests that the fungus has a fairly wide host range; however, predominance of a race that is avirulent on wheat on these grasses tends to eliminate their significance in the disease epidemiology of wheat. The results indicate that P. tritici-repentis has a diverse population on wheat and noncereal grasses. For durable resistance, wheat lines should be tested against all virulent races found in the field.
First Report of Sclerotium rolfsii on Brassidium Hybrid Orchid
Authors: Pratt T. B. , McMillan R. T. , Graves W. R.
Published: May 2007

Brassidium hybrid orchid leaves were sent to the University of Florida Plant Disease Clinic in the summer of 2002. Symptoms on leaves were a spreading, cottony, white mass of mycelium with necrotic centers 3 to 5 × 5 to 9 mm. Approximately 1% of leaves submitted were affected. Sclerotium rolfsii Sacc. was isolated from the affected leaves using acid potato dextrose agar (APDA) (1). Two plastic boxes were lined with wet paper towels and 6 uninoculated leaves were placed in each. Three leaves in each box were treated as controls and received 3 mm2 of APDA, while the other three leaves in each box received 3 mm2 of S. rolfsii culture on APDA. All leaves were misted with water and enclosed to maintain humidity. Twenty-four hours later, infection was visible on two treated leaves. Within 72 h, significant infection was visible on three of the six inoculated leaves. All control leaves remained uninfected. S. rolfsii was consistently reisolated from the inoculated leaves, fulfilling Koch's postulates. Over the past 12 months, S. rolfsii has been detected in 30% of commercial orchid nurseries as well as homeowner orchid collections in Miami-Dade County, Florida. No resistance to this disease in orchids has been reported. To our knowledge, this is the first report of S. rolfsii on this orchid hybrid.

Reference: (1) J. Tuite. Media and nutrient solutions used by plant pathologist and mycologist. Page 53 in: Plant Pathological Methods Fungi and Bacteria. Burgess Publishing Company, Minneapolis, MN, 1969.
First Report of “Candidatus Liberibacter asiaticus”, the Agent of Citrus Huanglongbing (Ex-greening) in Bhutan
Authors: Doe Doe , Om Namgay , Dorji Chencho , Dorji Thinlay , Garnier M. , Jagoueix-Eveillard S. , Bové J. M.
Published: May 2007

Mandarin (Citrus reticulata) is the most important cash crop in Bhutan and plantations total approximately 1.8 million trees (Ministry of Agriculture, Thimphu, Bhutan, 2000). Most trees are a local mandarin variety. Seedlings trees are produced by local farmers or supplied by Druk Seed Nursery. Mandarin seedlings have also been introduced from India. In the mid-1990s, mandarin trees growing in Punakha Valley and Wangdue districts began showing symptoms of decline that included sparse yellow foliage and shoot die-back. After initial surveys in 2000, huanglongbing (HLB) was suspected as the cause of declining trees based on symptomatology and presence of the psyllid vector Diaphorina citri, but no confirmatory tests were carried out. In August 2002, we surveyed eight locations in the valley from Rimchu (North) to Kamichu (South). HLB-like leaf mottle symptoms were observed on declining mandarin trees at all locations at altitudes ranging from 700 to 1,450 m. Orchards around Punakha (1,350m) in the center of the valley were more severely affected. Symptoms were also observed on Mexican lime (Citrus aurantifolia), citron (Citrus medica), and on tangelo trees (Minneola, Seminola, and Iyo) introduced originally as certified HLB-free budwoods from Corsica, France and grafted onto Rangpur lime at the Wangdue Research Center (1,300m). Leaves were collected from symptomatic trees and three declining mandarin trees without characteristic leaf mottle symptoms. Two specific polymerase chain reaction (PCR) tests for the detection of HLB Liberibacter species (1,2) were carried out on 16 DNA samples extracted from leaf mid-veins of 10 mandarins, two Mexican limes, three tangelos, and one citron tree. “Candidatus Liberibacter asiaticus” was readily detected by both PCR assays in all but two samples (one mandarin with noncharacteristic symptoms and citron) and all sampled orchards. The presence in the Wangdue Research Center of liberibacter infected trees, propagated from certified HLB-free budwoods, suggests that natural spread of the HLB by D. citri is occuring, as the psyllid had been identified previously in the Punakha area by Bhutanese Entomologists. It is likely that the disease was originally introduced as infected planting material although its source has not been determined.

References: (1) A. Hocquellet et al. Mol. Cell. Probes 13:373, 1999. (2) S. Jagoueix et al. Mol. Cell.Probes 10:43,1996.