bluuebunny/crossref_metadata_2025 huggingface dataset:
Managing the Race Structure of Phytophthora parasitica var. nicotianae with Cultivar Rotation
Authors: Sullivan M. J. , Melton T. A. , Shew H. D.
Published: May 2007

Deployment of tobacco cultivars with single-gene, complete resistance to race 0 of the tobacco black shank pathogen, Phytophthora parasitica var. nicotianae, has resulted in a rapid increase in the occurrence of race 1 of the pathogen in North Carolina. Cultivar-rotation studies were conducted in three fields to assess how different levels and types of resistance affected the race structure and population dynamics of the pathogen when deployed in fields initially containing single or mixed races of the pathogen. In a field with both races present, a high level of partial resistance in cv. K 346 was most effective in reducing disease and decreasing the proportion of race 1 in the pathogen population. The deployment of complete resistance in cv. NC 71 resulted in intermediate levels of disease control and race 1 became the predominate race. The cv. K 326, with a low level of partial resistance, had the highest levels of disease, and race 0 was the dominant race recovered. In a field where no race 1 was detected initially, disease incidence was high with the use of partial resistance. Complete resistance was very effective in suppressing disease, but race 1 was recovered after only one growing season. By the end of the third growing season, race 1 was recovered from most treatments where single-gene resistance was deployed. A high level of partial resistance was most effective in suppressing disease in a field where race 1 initially was the predominant race. A rotation between cultivars with single-gene resistance and cultivars with a high level of partial resistance should provide the most effective approach to black shank management. This rotation will reduce disease incidence and minimize race shifts in the pathogen and, over time, should prolong the usefulness of the Ph gene for black shank control in commercial production of tobacco.
Efficacy of Hot Water and Chlorine for Eradication ofCladosporium variabile,Stemphylium botryosum, andVerticillium dahliaefrom Spinach Seed
Authors: du Toit Lindsey J. , Hernandez-Perez Pablo
Published: May 2007

Cladosporium variabile, Stemphylium botryosum, and Verticillium dahliae are seedborne and seed-transmitted pathogens of spinach. Spinach seed treatments in 1.2% NaOCl for 10 to 60 min, or hot water (40, 45, 50, 55, and 60°C) for 10 to 40 min, were evaluated for eradication of these fungi from seed. C. variabile and V. dahliae were largely eradicated by chlorine treatment for ≥ 10 min. Although chlorine treatment reduced the incidence of S. botryosum, this fungus was not eradicated after 60 min in chlorine. Seed germination was not affected adversely by chlorine treatment, even after 60 min. In contrast, germination was reduced significantly by hot water treatment at 50°C for ≥30 min or 55 or 60°C for ≥10 min. C. variabile was eradicated from seed treated in 40°C water for 10 min. V. dahliaewas eradicated from seed treated at 55°C for ≥30 min or 60 °C for ≥10 min. S. botryosum was eradicated from a lightly infected seed lot (5% incidence) by hot water treatment at 55 or 60 °C for ≥10 min, but could not be eradicated from two heavily infected lots (>65% incidence), even at 60°C for 40 min. Using precisely controlled parameters, chlorine or hot water seed treatments can be used to eradicate C. variabile and reduce the incidence of S. botryosum and V. dahliae in spinach seed without damaging germination.
Dispersal Improvement of a Powder Formulation of Penicillium oxalicum, a Biocontrol Agent of Tomato Wilt
Authors: Sabuquillo P. , De Cal A. , Melgarejo P.
Published: May 2007

Sugars, polyalcohols, inorganic salts, and detergents were added to conidia of Penicillium oxalicum at three different points of the production-formulation process to improve water dispersal. Effects also were tested on conidial germination and production. Conidial germination without additives ranged from 51 to 79%. Additives did not reduce conidial germination except for 50% polyethylene glycol (PEG) 300 and 10% CaCl2. Sunflower oil and sodium alginate, sucrose (0.5, 15, 30, and 60%), D-sorbitol (30 and 60%), glycerol (2, 5, 20, and 30%), 30% PEG 300, CaCl2 (0.01 to 1%), Tween 20 (0.01, 0.02, 0.5, and 1%), and Tween 80 (0.01 to 1%) enhanced conidial germination. Production without additives ranged from 0.57 to 4.58 conidia × 108 g-1 substrate. Additives did not affect conidial production except for reduction by 60% D-sorbitol, 60% fructose, and 10% CaCl2. Conidial dispersal in water improved when 1.5% sodium alginate was added to substrate in bags before production, and when 1.5% sodium alginate, 60% sucrose, 60% D-sorbitol, 60% fructose, 5 to 20% PEG 8000, or 20% glycerol were added to conidia before drying. Dispersal of dried conidia was enhanced with 1% Tween 20, 1% Tween 80, 1% Trition X-100, 10% Agral, and 1.5% sunflower oil. Two P. oxalicum formulations (conidial suspensions maintained with 60% sucrose or 1.5% sodium alginate for 10 min before drying) significantly reduced tomato wilt caused by Fusarium spp. under greenhouse conditions and, in a preliminary trial, by Verticillium spp. in a field assay.
Comparison of Techniques to Sample Xanthomonas axonopodis pv. citri in Windblown Spray
Authors: Parker P. E. , Bock C. H. , Gottwald T. R.
Published: May 2007

Four techniques were evaluated to sample windblown splash from canker-infected citrus plants. Two volumetric cyclone samplers (PAS450 and Burkard Cyclone) and two passive samplers (funnels and panels) were evaluated. The PAS450 collected no detectable bacteria in any trial. The Burkard cyclone consistently collected spray, but was found to do so even when the power was turned off. Thus, the Burkard cyclone essentially functioned passively, negating the advantage of a volumetric sampler for this application. Panels collected the greatest volume of splash followed by funnel samplers. CFU of Xanthomonas axonopodis pv. citri per ml collected were significantly different between Burkards and panel samplers, but panels and funnels collected similar concentrations (Burkards, funnels, and panels collected 1,182, 1,426, and 2,667 CFU per ml, respectively). Positive correlations were found between the volume and the total X. axonopodis pv. citri collected, and between CFU per ml and total collected for panel and funnel samples. However, there was no correlation between CFU per ml and volume collected for either sampler. The Burkard sample showed a strong positive correlation (P < 0.01) between volume collected, total number of X. axonopodis pv. citri collected, and CFU per ml. The CFU per ml collected by the panels and funnels were similar (coefficient of determination, R2 = 0.97), compared with the relationship between the Burkard and panel catches (R2 = 0.68), or between the Burkard and funnel catches (R2 = 0.62). Panels collected the greatest volume, and effectively collected bacteria-laden windblown splash. The greater sampling area of the panels allowed a more representative sample than the other methods tested.
Molecular, Physiological, and Host-Range Characterization of Acidovorax avenae subsp. citrulli Isolates from Watermelon and Melon in Israel
Authors: Burdman Saul , Kots Nadia , Kritzman Giora , Kopelowitz June
Published: May 2007

Bacterial fruit blotch (BFB), caused by Acidovorax avenae subsp. citrulli, is a serious disease of cucurbit plants. The first important occurrence of BFB in Israel was during 2000 to 2003 on watermelon and melon. Twelve bacterial isolates associated with these outbreaks were confirmed as A. avenae subsp. citrulli by pathogenicity assays, gas chromatography of fatty-acid methyl esters, and substrate-utilization profiles. The isolates were characterized in terms of their aggressiveness in different hosts by seed, seedling, and fruit inoculations, and according to their DNA fingerprinting profiles using pulse-field gel electrophoresis (PFGE) and repetitive-PCR approaches. Results from the present work agree with previous studies supporting the existence of two differentiated groups within A. avenae subsp. citrulli, one including strains that are more associated with watermelon (group II), the other consisting of strains that are usually associated with nonwatermelon cucurbits (group I). This study indicates that isolates from both groups have been introduced to Israel. PFGE analysis revealed that the 12 analyzed isolates can be divided into five different haplotypes, of which four were previously unreported. Additional differentiating features between group I and II strains are presented.
First Report of Leaf Spot of Spinach Caused by Stemphylium botryosum in Arizona
Authors: Koike S. T. , Matheron M. E. , du Toit L. J.
Published: May 2007

During the winter (December through February) of 2003-2004, and again during 2004-2005, spinach (Spinacia oleracea) crops in the Yuma region of Arizona developed a foliar disease that previously had not been diagnosed in this geographic area. The problem was found on only a few acres and severity was low. The first symptoms consisted of round to oval leaf spots that were gray to olive green and visible from both adaxial and abaxial leaf surfaces. The spots were 3 to 6 mm in diameter but expanded up to as much as 10 mm. As disease progressed, leaf spots became tan and dry and papery in texture. Fungal growth was not observed on the spots. Isolations from the edges of surface-sterilized lesions onto V8 juice agar consistently resulted in fungal colonies. The fungus was identified as Stemphylium botryosum based on the following morphological characteristics of isolates incubated under fluorescent lights: dark green-to-brown mycelial growth, unbranched conidiophores with distinctly swollen apical cells that had dark bands, and dictyoconidia. The conidia were brown, ellipsoidal to ovoid, verrucose, borne singly, and measured 17 to 28 × 13 to 19 μm. To test pathogenicity, inoculum of each of five isolates (approximately 1 × 105 conidia/ml) was sprayed separately onto 20 to 25 plants each of spinach cvs. Whitney, Rushmore, Lion, Springfield, Nordic IV, and Unipak 144. Inoculated plants were incubated in a humidity chamber for 48 h and then maintained in a greenhouse (24 to 26°C). After 10 to 14 days, leaf spots resembling those seen in the field developed on all inoculated plants, and S. botryosum was reisolated from the spots. Control plants were similarly inoculated with water but did not develop symptoms. To our knowledge, this is the first report of leaf spot of spinach caused by S. botryosum in Arizona. The possibility of seedborne S. botryosum (3) may account for the development of this disease in winter spinach crops in this arid region. Leaf spot could be damaging to spinach grown in this region if rainfall is higher than normal, such as in 2004-2005. This disease has been reported in production spinach crops in California, Delaware, Florida, and Maryland (2,4) and in spinach seed crops in Washington (1).

References: (1) L. J. du Toit and M. L. Derie. Plant Dis. 85:920, 2001. (2) K. L. Everts and D. K. Armentrout. Plant Dis. 85:1209, 2001. (3) P. Hernandez-Perez and L. J. du Toit. (Abstr.) Phytopathology 95:S41, 2005. (4) R. N. Raid and T. Kucharek. 2003 Florida Plant Disease Management Guide: Spinach. University of Florida, Gainesville, 2003.
Bacterial Wilt of Beans (Phaseolus vulgaris) Caused by Curtobacterium flaccumfaciens in Southeastern Spain
Authors: González A. J. , Tello J. C. , Rodicio M. R.
Published: May 2007

Symptoms of bacterial wilt were observed on common beans (cv. Donna) in southeastern Spain. From samples collected in four different fields (coast of Granada), a bacterium was isolated with the following characteristics: gram positive, aerobic rods with yellow colonies, strictly oxidative, oxidase negative, galactose, sucrose, erythritol, mannitol, sorbitol and m-inositol were not used as a sole carbon source, and hydrolysis of casein was positive. These results coincide with what is expected for Curtobacterium flaccumfaciens pv flaccumfaciens (3). One isolate from each field was selected for pathogenicity tests using two different methods. Bacterial suspensions (approximately 108 CFU/ml) were spray inoculated on bean seedlings of cv. Andecha (10 plants with three true leaves for each isolate). Beans were covered with transparent plastic bags for 2 days and held at 25°C and 80% relative humidity with a 12-h photoperiod. In addition, 10 healthy seeds of cv. Andecha were soaked in bacterial suspensions (approximately 108 CFU/ml) for 1 h and incubated at 25°C (2). Seedlings sprayed with distilled sterile water and seeds soaked in water served as controls. With both methods of inoculation, assays were conducted twice. Results were recorded after 3 weeks. Symptoms that developed on plants after infection with the four isolates were similar to those observed in the field. They included golden yellow necrotic leaf lesions and wilting. Wilting was more pronounced in the field and when inoculation was performed by spraying seedlings rather than by soaking seeds. Control plants did not develop symptoms and grew bigger than the inoculated plants. Two pathogenic isolates were identified through sequencing of the 16S rRNA gene. The genes were amplified by polymerase chain reaction (1) and their nucleotide sequences (1,418 bp) proved to be identical (Accession No. AJ879110). Comparison of these sequences with databases showed that they were also identical to those of C. flaccumfaciens strains LMG 3645 and P 259/26 (Accession Nos. AJ312209 and AJ310414) and Curtobacterium sp. strains 2384 and 3426 (Accession Nos. AY688359 and AY688360). In Spain, the bean pathogen C. flaccumfaciens was first isolated from seeds during 2001 (4). However, to our knowledge, this is the first report of damage caused by this bacterium in the field. Bacterial wilt has been recorded, but often not substantiated, in several countries from North and South America, Africa, Asia, Oceania, and Europe.

References: (1) U. Edwards et al. Nucleic Acid Res. 17:7843, 1989. (2) T. F. Hsieh et al. Plant Dis. 86:1275. 2002. (3) K. Komagata and K.-I. Suzuki. Pages 1313–1317 in: Bergey's Manual of Systematic Bacteriology. Vol. 2. Williams and Wilkins, Baltimore, MD, 1986. (4) J. L. Palomo et al. Page 154 in: XI Congreso de la Sociedad Española de Fitopatología, Almería, 2002.
Occurrence of Pestalotiopsis uvicola Causing Leaf Spots and Stem Blight on Bay Laurel (Laurus nobilis) in Sicily
Authors: Vitale A. , Polizzi G.
Published: May 2007

In the spring of 2004, during a disease survey in three nurseries of eastern Sicily, a new leaf and stem problem was observed on 20 to 40% of young (2- to 6-month-old) container-grown bay laurel (Laurus nobilis L.). Affected plants exhibited sporadic water-soaked leaf spots on leaf edges that subsequently enlarged and turned into necrotic lesions. These spots were always bordered by a dark brownish margin. Frequently, these necrotic lesions expanded into stems causing blight of young shoots. No symptoms were observed on 2- to 3-year-old plants. Small portions (1 to 2 cm) of symptomatic tissue were surface disinfested for 30 s in 1% NaOCl, rinsed in sterile distilled water, placed on potato dextrose agar (PDA), and incubated at 22 ± 2°C. A fungus consistently isolated from affected tissues was identified as Pestalotiopsis uvicola (Speg.) Bissett based on morphological characters (1). Acervular conidiomata (as much as 250 μm in diameter) appeared in cultures on PDA at 24 ± 2°C over a period of 13 days. All isolates had 4-septate fusiform to narrow ellipsoid conidia with 2 to 4 apical appendages, often aggregated, and averaging 8 μm long. Conidia ranged from 20 to 25 μm long and 6 to 7 μm wide. Basal appendage was single, attenuated, and as much as 3 μm long. Three isolates of P. uvicola were selected for pathogenicity tests. Leaves and stems of 6-week-old seedlings of bay laurel were lightly wounded with a hypodermic needle, and a PDA mycelial plug (5 mm in diameter) was placed on the surface of wounded tissues. Sterile agar plugs were placed on control plants. This method was used to inoculate 6 plants for each isolate. All plants were incubated at 95 to 100% relative humidity and 25 ± 1°C. After 7 days, leaf spots and necrotic lesions on the stem similar to those observed in nurseries were observed. Control plants remained symptomless. Koch's postulates were fulfilled by reisolation of the fungus from affected tissues. Although found in only a few nurseries, the infections could be a threat to an important production area of bay laurel in Sicily. To our knowledge, this is the first report of P. uvicola on bay laurel in the world.

Reference: (1) T. R. Nag Raj. Mycotaxon 26:211, 1986.
Occurrence of the Perfect Stage of Powdery Mildew of Sugar Beets in Southern Montana in 2003
Authors: Jacobsen B. , Johnston M. R. , Weltzien H. C.
Published: May 2007

Wide spread powdery mildew infections on sugar beets were observed at the Southern Agricultural Experiment Station in Huntley, MT during September, 2003. Throughout the area, lower leaves were frequently heavily covered by the vegetative stage of the fungus with plants at the edge of the field having clearly visible abundant mature (black) and immature (brown) globose ascocarps on the leaf surfaces and stems. The fruiting structures had mostly branched appendages and were imbedded in the superficial mycelium. Their diameter ranged from 70 to 100 μm. Each ascocarp contained five to eight asci with one to four ascospores (mostly three) per ascus. Elliptical ascospores were hyaline and measured 20 to 25 μm long and 12 to 20 μm wide. On the basis of the descriptions given for isolates from Idaho and Colorado (1) and the usage of Erysiphe polygoni DC for powdery mildew on sugar beet in the United States, this isolate may be classified as E. polygoni DC. However, measurements taken show that ascocarps, asci, and ascospores also fall within the range of E. betae (Vanha) Weltz. as described by Weltzien (2). We strongly suggest that these species be compared by using rDNA analysis of the ITS region to determine whether they are separate species. If survival of the ascocarps and the viability and pathogenicity of the ascospores can be confirmed, epidemics of sugar beet powdery mildew could be understood as local and regional events that are not dependant on long distance dispersal of conidiospores. The occurrence of the perfect stage also could lead to the more frequent appearance of new races through genetic recombination.

References: (1) J. J Gallian and L. E. Hanson. Plant Dis. 87:200, 2003. (2) H. C. Weltzien. Phytopathol. Z. 47:123, 1963.
First Report of Powdery Mildew Caused by Podosphaera aphanis var. aphanis on Potentilla fruticosa in Italy
Authors: Garibaldi A. , Bertetti D. , Gullino M. L.
Published: May 2007

Potentilla fruticosa L. (bush cinquefoil), belonging to the family Rosaceae, is an ornamental plant used in parks and gardens. During the spring and summer of 2005, severe outbreaks of a previously unknown powdery mildew were observed in several private gardens located near Biella (northern Italy). The adaxial and abaxial surfaces of leaves as well as the stems were covered with white mycelium. Buds and flowers also were affected. As disease progressed, infected leaves turned yellow and dehisced. Conidia formed in chains and were hyaline, ovoid, and measured 24.0 to 36.0 × 15.8 to 24.0 μm (average 30.1 × 20.0 μm). Fibrosin bodies were present. Chasmothecia were numerous, sphaerical, amber colored, and diameters ranged from 84.0 to 98.4 μm (average 90.4 μm). Each chasmothecium contained one ascus with eight ascospores. Ascospores measured 26.5 to 27.2 × 13.2 to 15.6 μm (average 26.8 × 14.0 μm). On the basis of its morphology, the causal agent was determined to be Podosphaera aphanis (Wallr.) U. Braun & S. Takamatsu var. aphanis U. Braun (1). Pathogenicity was confirmed through inoculations by gently pressing diseased leaves onto leaves of healthy P. fruticosa plants. Three plants were inoculated. Three noninoculated plants served as a control. Plants were maintained at temperatures ranging from 12 to 23°C. Ten days after inoculation, typical symptoms of powdery mildew developed on inoculated plants. Noninoculated plants did not show symptoms. The pathogenicity test was carried out twice. To our knowledge, this is the first report of powdery mildew on P. fruticosa in Italy. Erysiphe polygoni D.C. and Sphaerotheca macularis (Wallr.:Fr.) Lind were observed in the United States on P. fruticosa (2), while in Japan, the presence of S. aphanis var aphanis was reported (3). Voucher specimens are available at the AGROINNOVA Collection, University of Torino.

References: (1) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000 (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St Paul, MN, 1989. (3) S. Tanda et al. J. Agric. Sci. 39:258, 1995.
Host—Pathogen Interactions Between Phytophthora infestans and the Solanaceous Hosts Calibrachoa × hybridus, Petunia × hybrida, and Nicotiana benthamiana
Authors: Becktell M. C. , Smart C. D. , Haney C. H. , Fry W. E.
Published: May 2007

Late blight, caused by the pathogen Phytophthora infestans, is a devastating disease of potato and tomato, but can also damage other solanaceous hosts. To gain a better understanding of the interaction between P. infestans and these other hosts, the susceptibility of species in three solanaceous genera was investigated. Of the 10 Calibrachoa × hybridus cultivars tested, four were susceptible and six were resistant to the pathogen; susceptible cultivars supported only very limited growth of P. infestans. The majority of the Petunia × hybrida (petunia) cultivars were susceptible, although less so than susceptible potatoes or tomatoes. Two petunia cultivars displayed differential resistance, suggesting the presence of R genes against P. infestans. The hypersensitive response was present in susceptible, partially resistant, and resistant petunia-P. infestans interactions, but was predominant in the resistant interaction. Young petunias (3 weeks) were more susceptible than older petunias (7 weeks). Nicotiana benthamiana was susceptible to all four P. infestans isolates tested in the lab and became infected during a field epidemic. Several of these isolates were tested for the presence of the inf1 gene, and were found to have and express the gene in vitro. In addition, culture filtrate from these isolates contained 10-kDa proteins and also elicited the hypersensitive response in Nicotiana tabacum and N. benthamiana.
Inheritance of Resistance to Fusarium Wilt in Sweet Basil
Authors: Chaimovitsh D. , Dudai N. , Putievsky E. , Ashri A.
Published: May 2007

Fusarium wilt, caused by Fusarium oxysporum f. sp. bacilici, is a severe disease of sweet basil (Ocimum basilicum L.) and has become acute mainly due to the intensive monoculture in green-houses and, recently, to prohibition of methyl bromide application. In a previous work, we selected a resistant cultivar, Nufar, to address this problem. The mode of inheritance of resistance to F. oxysporum f. sp. bacilici in sweet basil was examined in progenies derived from crosses of the homogeneous resistant cv. Nufar and the susceptible homogenous cv. Chen. Artificial inoculation of seedlings with a high concentration of a microconidial suspension of a virulent isolate of F. oxysporum f. sp. bacilici revealed no difference between reciprocal backcrosses. The nuclear resistance analysis and dominant characteristics of the resistance of backcross progenies of different parental lines and the segregation for resistance in F2 combinations fitted the expected Mendelian ratio for a single dominant gene with two alleles that confer resistance to Fusarium wilt in basil. These results indicate the usefulness of utilizing this resistance to F. oxysporum f.sp. bacilici in the production of new hybrids and cultivars of basil.
Detection and Variability of Begomoviruses in Tomato from the Andean States of Venezuela
Authors: Nava A. R. , Patte C. P. , Hiebert E. , Polston J. E.
Published: May 2007

The three Andean states of Mérida, Táchira, and Trujillo in Venezuela produce tomatoes (Lycopersicon esculentum) year-round with a high frequency of virus-like symptoms. Polymerase chain reaction amplification using degenerate primers detected begomoviruses in 18% of leaf samples collected from tomato plants showing virus-like symptoms in commercial fields in these states between 1993 and 1994. A comparison of the sequences of the amplified DNA products revealed a diversity of begomovirus sequences in tomato plants from this region. Partial A component sequences (approximately 1,100 bp) clustered in four groups based on BLAST, GAP, phylogenetic analyses of the nucleic acid sequences, and comparisons of iteron sequences with known begomoviruses. Two groups of sequences were closely related to Potato yellow mosaic virus—Venezuela strain tomato and Tomato Venezuela virus, respectively, begomoviruses previously reported from other Venezuelan states. The other two groups of sequences appear to belong to two new begomovirus species.
First Report of Tomato severe rugose virus in Chili Pepper in Brazil
Authors: Bezerra-Agasie I. C. , Ferreira G. B. , de Ávila A. C. , Inoue-Nagata A. K.
Published: May 2007

Three definitive and three tentative begomovirus species have been reported in tomato fields in Brazil according to a recent review (1). Extensive surveys have been conducted since the 1990s in solanaceous weeds and other crops planted close to tomato fields, but no tomato-infecting geminiviruses have been reported on those crops. During November 2003, leaves of one chili pepper plant “dedo-de-moça” (Capsicum baccatum var. pendulum) showing symptoms of yellow mosaic and leaf distortion were collected in Petrolina de Goiás (Goiás State). Serological analyses were carried out with polyclonal antisera produced in our laboratory against the following viruses: Potato virus Y (PVY), Pepper yellow mosaic virus (PepYMV), Tomato spotted wilt virus (TSWV), Tomato chlorotic spot virus (TCSV), Groundnut ringspot virus (GRSV), and Chrysanthemum stem necrosis virus (CSNV). Serological data showed that the plant was not infected with any of these viruses. A begomovirus-specific DNA-A fragment of 1.3 kb was amplified by polymerase chain reaction (PCR) from the analyzed plant. The fragment shared 98% identity to the partial coat protein coding region (CP), 94% to the intergenic region (IR), and 95% to the partial AC1 coding region of Tomato severe rugose virus (ToSRV) (GenBank Accession No. AY029750). Total DNA from the original infected plant was used to biolistically inoculate healthy plants of C. annuum and C. baccatum var. pendulum. Four resulting symptomatic plants, two from C. annuum and two from C. baccatum, were tested using PCR for begomovirus, and the nucleotide sequence of the amplified fragment confirmed they were infected with ToSRV. Whitefly inoculation of C. annuum, C. baccatum, and tomato was also performed, and all plants expressing symptoms were confirmed to be infected with ToSRV by sequencing a begomovirus-specific amplified fragment. Cloning of the complete DNA-A was achieved by using TempliPhi (Amersham Biosciences, Piscataway, NJ) amplification and digestion with a single cutting restriction endonuclease (2). Sequencing of several clones showed that the complete DNA-A (GenBank Accession No. DQ207749) was 97% identical to ToSRV, confirming the results of the previous PCR analysis. The deduced amino acid sequences showed identities of 97% to the CP, 95% to AC1, 96% to AC2, 96% to AC3, and 88% to AC4 of ToSRV. Although begomoviruses have not yet been causing any significant losses in chili pepper in Brazil, they may be of potential importance. Moreover, chili pepper, a plant commonly found in gardens throughout the country, may serve as an alternate host in tomato-producing areas. To our knowledge, this is the first report of a begomovirus infecting chili pepper in Brazil.

References: (1) C. M. Fauquet et al. Arch. Virol. 148:405, 2003. (2). A. K. Inoue-Nagata et al. J Virol Methods 116:209, 2004.
Major Gene Resistance to Blackleg in Brassica napus Overcome Within Three Years of Commercial Production in Southeastern Australia
Authors: Sprague S. J. , Marcroft S. J. , Hayden H. L. , Howlett B. J.
Published: May 2007

The infection by Leptosphaeria maculans of Brassica napus cultivars with major gene resistance derived from Brassica rapa subsp. sylvestris was studied in southeastern Australia. Following the commercial release of these cultivars in Australia in 2000, plants with stem cankers were first reported in 2002 at two geographically isolated regions in South Australia and New South Wales. In 2003, this study showed that the major gene resistance had been overcome in an area of approximately 50,000 ha in South Australia and in two fields in New South Wales (0.5 and 30 ha). There was no relationship between disease severity and incidence in 2003 and the proximity to the sites where resistance breakdown occurred in 2002. At some locations, the frequency of isolates able to overcome the B. rapa subsp. sylvestris-derived resistance had increased between 2002 and 2003. Isolates cultured from canola cultivars with either B. rapa subsp. sylvestris-derived resistance or polygenic resistance showed host specificity when inoculated onto cultivars with B. rapa subsp. sylvestris-derived or polygenic resistance, respectively. The most likely cause of the resistance breakdown was the rapid increase in frequency of L. maculans isolates virulent on this particular resistance source. The selection pressure leading to this increased frequency was probably mediated by the planting of cultivars harboring the major resistance gene in the same locations for a 3-year period, and the ability of the pathogen to produce large numbers of asexual and sexual spores.
Fertility and Mating Type Frequency in Indian Isolates of Sclerospora graminicola, the Downy Mildew Pathogen of Pearl Millet
Authors: Pushpavathi B. , Thakur R. P. , Rao K. Chandrashekara
Published: May 2007

Sclerospora graminicola, the downy mildew pathogen of pearl millet, is an oomycetous obligate parasite which reproduces by both sexual and asexual means. Fertility and mating type frequencies were studied in 70 single-zoospore isolates (SZIs) obtained from seven representative oo-sporic isolates (Sg 021, Sg 048, Sg 110, Sg 139, Sg 149, Sg 152, and Sg 153) of S. graminicola collected from major pearl millet-growing states of India. Of the 70 SZIs tested for fertility according to oospore production potential, 62 were self-sterile and 8 were self-fertile, indicating the low occurrence of homothallism in the S. graminicola populations. The sexual mating type test of the 70 SZIs, conducted by pairing each isolate with the two standard mating type tester isolates PT2 (Mat A) and PT 3 (Mat B), revealed 28 (40.0%) isolates of Mat A, 33 (47.14%) of Mat B, 8 (11.43%) of both Mat A and Mat B, and 1 (1.43%) as unknown. The frequencies of Mat A and Mat B were in approximately equal proportions among the isolates tested, except in three parental isolates. Implications of these results in understanding the dynamic genetic structure of S. graminicola population and potential for evolution of new virulence in the pathogen are discussed.
Genetic Analysis of Partial Resistance to Powdery Mildew in Bread Wheat Line Saar
Authors: Lillemo M. , Skinnes H. , Singh R. P. , van Ginkel M.
Published: May 2007

Powdery mildew, caused by Blumeria graminis (syn. Erysiphe graminis) f. sp. tritici, is an important disease of bread wheat (Triticum aestivum) in many countries. The CIMMYT bread wheat line Saar has exhibited a high level of partial resistance to powdery mildew in field trials conducted in Europe, Asia, and South America, and represents a valuable source of resistance in wheat breeding. A set of 114 random F5 inbred lines from the cross Saar × Avocet-YrA (susceptible) were evaluated in replicated field trials at two locations in southeastern Norway to determine the number of genes involved in partial resistance to powdery mildew. Narrow-sense heritability estimates were high (0.83 to 0.92). Based on both quantitative and qualitative genetic analyses, the minimum number of genes with additive effects segregating for powdery mildew resistance in the population was four. Transgressive segregation indicated that Avocet-YrA might have contributed one minor gene for resistance. It is concluded that partial resistance to powdery mildew in Saar is controlled by at least three genes. Such resistance conferred by multiple genes having additive effects is expected to be durable.
Host Resistance toMirafiori lettuce big-vein virusandLettuce big-vein associated virusand Virus Sequence Diversity and Frequency in California
Authors: Hayes Ryan J. , Wintermantel William M. , Nicely Patricia A. , Ryder, Edward J.
Published: May 2007

Big vein is an economically damaging disease of lettuce (Lactuca sativa) caused by the Olpidium brassicae-vectored Mirafiori lettuce big-vein virus (MLBVV). Lettuce big-vein associated virus (LBVaV) is also frequently identified in symptomatic plants, but no causal relationship has been demonstrated. Although big vein is a perennial problem in the United States, the extent of MLBVV and LBVaV infection and diversity is unknown. Lettuce cultivars partially resistant to big vein reduce losses, but do not eliminate disease. While Lactuca virosa does not develop big vein symptoms, it has not been tested for infection with MLBVV or LBVaV. Lettuce cultivars Great Lakes 65, Pavane, Margarita, and L. virosa accession IVT280 were evaluated for big vein incidence and virus infection in inoculated greenhouse trials. Additional lettuce samples were collected from field sites in California, classified for symptom severity, and evaluated for virus infection. Reverse transcription-polymerase chain reaction and nucleotide sequencing were used to determine infection with MLBVV and LBVaV, and sequence diversity among viral isolates, respectively. Infections with MLBVV and MLBVV/LBVaV were dependent on big vein symptom expression in California production areas, and isolates were closely related to those found in Europe and Japan. Partial big vein resistance was identified in Margarita and Pavane; however, MLBVV infection was found in asymptomatic plants. L. virosa IVT280 remained symptomless and virus free, suggesting that it is immune to MLBVV and LBVaV.
Distribution and Incidence of Some Aphid and Leafhopper Transmitted Viruses Infecting Sugar Beets in Iran
Authors: Farzadfar Sh. , Pourrahim R. , Golnaraghi A. R. , Ahoonmanesh A.
Published: May 2007

The main areas for field-grown sugar beet (Beta vulgaris) production in Iran were surveyed to study the occurrence and incidence of Alfalfa mosaic virus (AlMV), Beet curly top virus (BCTV), Beet mosaic virus (BtMV), Beet western yellows virus (BWYV), Beet yellows virus (BYV), Chickpea chlorotic dwarf virus (CpCDV), Cucumber mosaic virus (CMV), and Turnip mosaic virus (TuMV) during the growing season of 2001. A total of 5,292 random leaf samples in addition to 1,294 symptomatic leaves were collected from nine commercial sugar beet growing provinces of Iran and tested by tissue-blot immunoassay (TBIA). Serological diagnoses were confirmed by electron microscopy and host range studies. The highest virus incidence among the surveyed provinces was recorded in Qazvin, followed by Fars, Esfahan, Azarbayejan-e-gharbi, Khorasan, Kermanshah, Semnan, and Hamedan. According to the TBIA results, viruses in decreasing order of incidence in sugar beet were BCTV (27.9%), followed by BWYV (17.4%), CpCDV (12.5%), BYV (10.6%), BtMV (7.4%), TuMV (2.9%), AlMV (1.3%), and CMV (1.2%). Nearly 35% of sugar beets in Iran were infected by one or both of the two leafhopper-transmitted viruses (BCTV and CpCDV). Moreover, about 28% were infected by at least one of the six aphid-transmitted viruses (AlMV, BWYV, BtMV, BYV, CMV, and TuMV). Overall, one or more of the eight viruses assayed were detected in 45.5% of the plants surveyed. Several plants (35%) displaying virus-like symptoms did not react with the virus antisera used, suggesting that more viruses or virus-like agents are infecting sugar beets in Iran. In reference to the earlier reports, this is the first report of AlMV and TuMV in sugar beet fields of Iran. Also, this is the first detection of CpCDV as a pathogen of sugar beet.
Sodium Silicate Reduces Postharvest Decay on Hami Melons: Induced Resistance and Fungistatic Effects
Authors: Bi Y. , Tian S. P. , Guo Y. R. , Ge Y. H. , Qin G. Z.
Published: May 2007

The effect of sodium silicate (Si) for control of decay was tested in Hami melons (Cucumis melo L. var. inodorus Jacq.). Si significantly inhibited mycelial growth of Alternaria alternata, Fusarium semitectum, and Trichothecium roseum in vitro. Si at 100 mM was more effective than Si at 25 or 50 mM at controlling the diseases caused by the three pathogens, whereas Si at 200 mM was phytotoxic. Si treatments applied at 100 mM pre-inoculation with T. roseum had lower decay incidence and severity than treatments applied post-inoculation. The protection of Si was correlated with the activation of two families of defense-related enzymes, peroxidase and chitinase. Accumulation of both enzymes was induced in fruit treated with Si and challenged by T. roseum 24 h later, and was sustained for at least 9 days in ‘New Queen’ and 10 days in ‘8601’ at room temperature. It appeared that induced resistance was an important mechanism of disease control in Hami melons treated with Si.
Incidence of Phytophthora Blight and Verticillium Wilt Within Chile Pepper Fields in New Mexico
Authors: Sanogo S. , Carpenter J.
Published: May 2007

Statewide surveys of commercial chile pepper (Capsicum annuum) fields were conducted in New Mexico from 2002 to 2004 to gain information on the incidence of diseases with wilt symptoms and their causative agents. Fifty-nine fields were surveyed during the course of this 3-year study when chile pepper plants were at growth stages from green fruit to beginning red fruit. All fields were affected by diseases with wilt symptoms. The proportion of total field area exhibiting symptoms of wilt spanned from less than 1% to over 80%. Field diagnostics along with laboratory assays of wilted plants revealed that the wilting was caused by Phytophthora capsici and Verticillium dahliae. The two pathogens were both found in 80% of the fields, and occurred together in some wilted plants in 12% of the fields. Average incidence of plant infection (number of plants infected with P. capsici or V. dahliae out of 5 to 25 wilted plants sampled) varied from approximately 40 to 90% for P. capsici, and from 18 to 65% for V. dahliae. Incidence of plant infection by P. capsici was approximately 40% less in fields with drip irrigation than in fields with furrow irrigation. In contrast, incidence of plant infection by V. dahliae was approximately 32% greater under drip irrigation than under furrow irrigation. In pathogenicity tests, isolates of P. capsici and V. dahliae caused symptoms in inoculated chile pepper identical to those in field-grown chile pepper plants. Results indicate that diseases with wilt symptoms are well established in chile pepper production fields, with P. capsici and V. dahliae posing the most serious challenge to chile pepper producers in New Mexico.
Effects of Zoospore Concentration and Application Pressure on Foliage Blight ofCatharanthus roseusCaused byPhytophthora nicotianae
Authors: Banko T. J. , Richardson P. A. , Hong C. X.
Published: May 2007

This study investigated the effects of inoculum concentration, application pressure, use of carbon dioxide (CO2), and agitation associated with passage through a spray nozzle on zoospore survival and on foliage blight caused by Phytophthora nicotianae. In a greenhouse experiment, plants of Catharanthus roseus were inoculated by spraying zoospore suspensions at pressures of 210, 420, and 630 kPa (30, 60, and 90 lbs/in2[psi]). A low-pressure 35-kPa (5-psi) control inoculation was provided with a hand-operated aspirator-type mister. There was a consistent reduction in level of disease with increased application pressure, regardless of the zoospore concentration. To determine the source of this disease reduction, laboratory assays were conducted. Zoospore suspensions were pressurized to 210, 420, and 630 kPa with CO2or air, then transferred from the pressure bottle into a flask by either spraying or pouring. From the flask, the suspensions were spread over plates of PARP-V8 agar and incubated for 72 h, at which time total colony numbers were recorded. CO2significantly reduced zoospore survival. Pressure strength and method of spore transfer out of pressure bottles also impacted survival to lesser extents. There were significant interactions between pressure source and means of spore suspension transfer, and between pressure strength and means of spore transfer. These results may lead to development of alternative methods of water decontamination to prevent inoculum from entering crop systems through irrigation water.
A Species-Specific PCR Assay for Detection of Diplodia pinea and D. scrobiculata in Dead Red and Jack Pines with Collar Rot Symptoms
Authors: Smith Denise R. , Stanosz Glen R.
Published: May 2007

A polymerase chain reaction (PCR)-based assay was developed for the specific detection of the fungal pathogens Diplodia pinea and D. scrobiculata from pine host tissues. Variation among mitochondrial small subunit ribosome gene (mt SSU rDNA) sequences of Botryosphaeria species and related anamorphic fungi was exploited to design primer pairs. Forward primer DpF and forward primer DsF, each when used with the nonspecific reverse primer BotR, amplified DNA of D. pinea or D. scrobiculata, respectively. Specificity was confirmed using multiple isolates of each of these two species and those of closely related fungi including Botryosphaeria obtusa. The detection limits for DNA of each pathogen in red and jack pine bark were 50 to 100 pg μl-1 and 1 pg μl-1 in red and jack pine wood. The assay was tested using naturally occurring red and jack pine seedlings and saplings exhibiting symptoms of Diplodia collar rot. Samples from lower stems/root collars of 10 dead trees of each species from each of three sites at each of two locations were tested. Results were positive for D. pinea or D. scrobiculata for the large majorities of symptomatic bark and wood samples from both locations. For positive samples, however, there were effects of location and host species on detection of D. pinea (more frequent on red pine) and D. scrobiculata (more frequent on jack pine) (P < 0.01 in both cases). These results indicate that these new primers are potentially useful for studies in areas or hosts in which both pathogens may be present.
Heritability of Resistance to Verticillium Wilt in Alfalfa
Authors: Vandemark George J. , Larsen Richard C. , Hughes Teresa J.
Published: May 2007

Verticillium wilt of alfalfa, caused by Verticillium albo-atrum, may reduce forage yields by up to 50% in alfalfa-producing areas of the northern United States and Canada. It has been suggested that cultivars require at least 60% resistant plants to afford maximum protection against disease. Our objective was to calculate heritability estimates of resistance to Verticillium wilt in alfalfa. Estimates were generated for two alfalfa populations developed from the cvs. Affinity + Z and Depend + EV. Heritability on a half-sib progeny means basis was calculated based on data from greenhouse pathogenicity tests. Estimates based on repeated experiments conducted for single years (2004 and 2005) were high for both populations, ranging from 0.86 to 0.92. The heritability estimate based on data collected over 2 years was 0.26 for Affinity + Z and 0.66 for Depend + EV. Disease was more severe in 2005 than in 2004. However, the Spearman rank correlation between mean disease severity index values for half-sib families over 2 years was positive and significant for both populations. Results of pathogenicity tests suggested that neither cultivar had resistance levels approaching 60%. The heritability estimates suggest that resistance levels in both Affinity + Z and Depend + EV could be improved further through selection.
Reaction of Sorghum Lines Genetically Modified for Reduced Lignin Content to Infection by Fusarium and Alternaria spp.
Authors: Funnell Deanna L. , Pedersen Jeffrey F.
Published: May 2007

Two genes conferring the brown midrib (bmr) trait had been backcrossed into six elite sorghum lines, resulting in reduced lignin in the bmr lines when compared with the wild-type parent. Seed and leaf tissue from field-grown plants, planted at two locations, were screened for Alternaria spp. and Fusarium spp. on semi-selective media. The results suggest that bmr lines do not have increased susceptibility to colonization by Alternaria spp. However, significantly fewer colonies of Fusarium spp., including Fusarium moniliforme, were recovered from seed of reduced lignin lines from two genetic backgrounds. That the bmr trait in some genetic backgrounds might enable increased resistance to colonization by F. moniliforme was further supported by greenhouse experiments in which peduncles of developing heads were inoculated with F. moniliforme. Mean lesion measurements on bmr lines were significantly lower than those resulting from inoculations on wild-type lines. Analysis of near-isogenic lines revealed that mean lesion lengths on bmr lines were significantly less than those produced on their wild-type counterparts in four of the six genetic backgrounds. These results suggest that reduced lignin lines exhibit, in some cases, increased resistance to Fusarium spp., including F. moniliforme.