bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of Tall Fescue Genotypes to a New Strain of Brome mosaic virus
Authors: Mian M. A. Rouf , Zwonitzer J. C. , Hopkins A. A. , Ding X. S. , Nelson R. S.
Published: May 2007

Brome mosaic virus (BMV) infects many different species within the Poaceae family. A new strain of BMV, named F-BMV, was identified in a tall fescue (Festuca arundinacea Schreb.) plant. Here, we report the identification and characterization of tall fescue plants resistant to F-BMV, and the effects of F-BMV infection on their growth and development. Susceptible plants infected with F-BMV produced 40% fewer tillers and 42% less dry matter compared with virus-resistant plants in a greenhouse study. In the field, susceptible plants infected with F-BMV produced 25% fewer tillers, 36% less dry matter, 10% less plant height, and 40% lower seed yield compared with virus-resistant plants. In a field evaluation of a tall fescue mapping population, the virus symptom scores were negatively correlated with production of dry matter (r = -0.55), plant height (r = -0.55), and seed yield (r = -0.33). Thus, F-BMV has the potential to cause significant economic damage to susceptible tall fescue plants. These results indicate that the virus can present a serious challenge for long-term maintenance of valuable plant materials. A survey of tall fescue plants from Arkansas, Oklahoma, and Oregon indicated that the prevalence F-BMV in the field was very low.
Vegetative Compatibility Groups ofFusarium oxysporumf. sp.lactucaefrom Lettuce
Authors: Pasquali Matias , Dematheis Flavia , Gilardi Giovanna , Gullino Maria Lodovica , Garibaldi Angelo
Published: May 2007

Fusarium oxysporum f. sp. lactucae, the causal agent of Fusarium wilt of lettuce, has been reported in three continents in the last 10 years. Forty-seven isolates obtained from infected plants and seed in Italy, the United States, Japan, and Taiwan were evaluated for pathogenicity and vegetative compatibility. Chlorate-resistant, nitrate-nonutilizing mutants were used to determine genetic relatedness among isolates from different locations. Using the vegetative compatibility group (VCG) approach, all Italian and American isolates, type 2 Taiwanese isolates, and a Japanese race 1 were assigned to the major VCG 0300. Taiwanese isolates type 1 were assigned to VCG 0301. The hypothesis that propagules of Fusarium oxysporum f. sp. lactucae that caused epidemics on lettuce in 2001-02 in Italian fields might have spread via import and use of contaminated seeds is discussed.
Effects of Phosphonate and Mefenoxam Treatments on Development of Perennial Cankers Caused by Two Phytophthora spp. on Almond
Authors: Browne G. T. , Viveros M. A.
Published: May 2007

Orchard experiments were conducted to evaluate chemical treatments for management of perennial cankers caused by Phytophthora cactorum and P. citricola on almond (Prunus dulcis) in the San Joaquin Valley of California. Single preventive foliar sprays with phosphonate were tested by wounding and inoculating tree trunks and branches with either pathogen at time intervals from 15 days to 5 months after spraying. One to 3 months after inoculation, resulting cankers were measured. Preventive foliar sprays with phosphonate in the fall or spring suppressed development of cankers for up to 5 months after treatment; mean canker lengths on the trees sprayed with phosphonate before inoculation were 22 to 98% smaller than those on trees that received no phosphonate. In subsequent tests, preventive chemigation with phosphonate in spring or summer also inhibited canker expansion. A curative topical treatment with either fosetyl-Al or mefenoxam on cankers caused by P. cactorum or P. citricola reduced canker expansion by 36 to 88%. Neither preventive nor therapeutic treatments eradicated the pathogens from the diseased tissues, but disease ratings made 1 year after the treatments indicated extended disease suppression. Phosphonate and mefenoxam treatments can effectively manage almond scion cankers caused by P. cactorum or P. citricola.
First Incidence of Plum Pox Virus on Apricot Trees in China
Authors: Navratil M. , Safarova D. , Karesova R. , Petrzik K.
Published: May 2007

Plum pox disease, caused by Plum pox virus (PPV), is the most severe virus disease of plums, apricots, and peaches. The disease causes heavy losses for fruit growers and the international trade of propagation materials and fresh fruits. PPV was first reported in Bulgaria in 1917 (1). It is now widespread in Europe and has been reported from Cyprus, Syria, Egypt, India, Kazakhstan, Chile, the United States, and Canada. Leaves on symptomatic apricot trees (Prunus armeniaca cvs. Hong Mei and Bai Mei and a selected genotype) in the Hunan Province of China showed typical yellow rings and diffused chlorotic spots. Samples from three suspected trees were repeatedly analyzed using double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and reverse transcription-polymerase chain reaction (RT-PCR) in the summers of 2001-2003. PPV was detected in leaves, bark, and leaf buds of all three trees using ELISA with polyclonal and monoclonal antibodies provided by M. Navratil, Palacky University, Olomouc, Czech Republic (3). The results were confirmed using RT-PCR amplification of a 243-bp of the coat protein gene with a PPV-specific primer pair (2). BLAST analysis of two RT-PCR product sequences (GenBank Accession Nos. AY750961 and AY795603) showed 100% homology to multiple sequences of the PPV-D strain (GenBank Accession Nos. X81080, AF440743, and AF401295). The third sequence (GenBank Accession No. AY795602) had a C at position 112 rather than the T found in the other sequences. The ELISA, RT-PCR, and sequence results indicate that PPV-D was present in the apricot trees. To our knowledge, this is the first indication of PPV occurrence in China. This sporadic incidence of PPV on apricot trees requires addressing problems with the occurrence and spread of plum pox diseases in China and starting an eradication program.

References: (1) D. Atanasoff. Annu. Univ. Sofia Fac. Agron. et Sylvic. 11:49, 1932. (2) T. Candresse et al. Phytopathology. 88:198, 1998. (3) I. Hilgert et al. Hybridoma. 12:215, 1993.
First Report of Pythium Root Rot of Rau Ram (Polygonum odoratum)
Authors: Rosskopf E. N. , Yandoc C. B. , Stange B. , Lamb E. M. , Mitchell D. J.
Published: May 2007

Polygonum odoratum (= Persicaria odorata), known as rau ram or sang hum, is native to southeastern Asia and is a common herb in Vietnamese cuisine (1). It has been studied most extensively for its aromatic compound content (2). In Florida, rau ram commonly is grown hydroponically in greenhouses using large, cement beds with recirculated water. The plants form dense mats from which new growth is trimmed for market. During January of 2002, a severe dieback was observed in one production house in Saint Lucie County, FL. Plants with less severe symptoms were yellowed and stunted. Roots of symptomatic plants were largely decayed with root symptoms beginning as a tip necrosis. The cortex of severely affected roots slipped off easily, leaving a stringy vascular system. Plating of symptomatic tissue from 20 randomly selected plant samples was performed with multiple general and selective media including potato dextrose agar, corn meal agar with pimaricin, ampicillin, rifampicin, and pentachloronitrobenzene (PARP) (3). All colonies produced were identified as Pythium helicoides Drechsler on the basis of sporangial, oogonial, and antheridial characteristics (4). Isolates had proliferous, obovoid, papillate sporangia, and were homothallic with smooth-walled oogonia and thick-walled, aplerotic oospores. Multiple antheridial attachments per oogonium were common with the antheridium attached along its entire length. Pathogenicity tests were conducted using P. odoratum plants grown from commercial transplants. Two tests were performed. Each test was conducted using eight inoculated and eight control plants. In the first test, plants were maintained in 10-cm pots immersed in sterilized pond water for the duration of the test. Plants were inoculated with five 7- × 70-mm sections of freshly growing mycelial culture per plant using 10-day-old cultures of Pythium helicoides grown on water agar. Chlorosis was observed at approximately 2 months after inoculation. Root necrosis was observed in inoculated plants approximately 5 months after inoculation. This test was performed in the greenhouse with temperatures ranging from 20 to 30°C. The second test was performed in growth chambers at 35 to 40°C. Plants were maintained in 10-cm pots immersed in Hoagland's solution and were inoculated with four 6-mm plugs per plant. Symptoms were observed on inoculated plants at this temperature within 1 week of inoculation. No chlorosis or root decay was observed in noninoculated, immersed plants. The pathogen was reisolated from inoculated, symptomatic tissue. To our knowledge, this is the first report of root rot of P. odoratum caused by Pythium helicoides.

References: (1) R. E. Bond. Herbarist 55:34, 1989. (2) N. X. Dung et al. J. Essent. Oil Res. 7:339, 1995. (3) M. E. Kannwischer and D. J. Mitchell. Phytopathology 68:1760, 1978. (4) A. J. van der Plaats-Niterink. Monograph of the Genus Pythium. Vol. 21, Studies in Mycology. Centraalbureau voor Schimmelcutltures, Baarn, The Netherlands, 1981.
Characterization of California Isolates of Fusarium oxysporum f. sp. vasinfectum
Authors: Kim Y. , Hutmacher R. B. , Davis R. M.
Published: May 2007

Thirty isolates of Fusarium oxysporum f. sp. vasinfectum from California, Australia, China, and the American Type Culture Collection were characterized by partial sequences of translational elongation factor (EF-1α), phosphate permase (PHO), and beta-tubulin (BT) genes, restriction digests of the intergenic spacer (IGS) region of nuclear rDNA, and pathogenicity tests. Based on phylogenetic analysis of combined sequences of EF-1α, PHO, and BT genes, California isolates represented four lineages. Lineage I contained race 3, lineage II contained races 1, 2, and 6, lineage III contained race 8, and lineage IV contained race 4. The Australian isolates formed a strongly supported independent clade. There were nine haplotypes based on restriction digests of the IGS region. In greenhouse pathogenicity tests with California isolates, those from the race 4 lineage were highly aggressive on certain Pima cotton (Gossypium barbadense) cultivars and less aggressive on Upland cotton (Gossypium hirsutum) cultivars. All isolates belonging to the other lineages caused relatively mild symptoms on both Pima and Upland cultivars. This is the first report of the occurrence of races 3, 4, and 8 in California.
Evaluation of Components of Fusarium Head Blight Resistance in Soft Red Winter Wheat Germ Plasm Using a Detached Leaf Assay
Authors: Browne R. A. , Murphy J. P. , Cooke B. M. , Devaney D. , Walsh E. J. , Griffey C. A. , Hancock J. A. , Harrison S. A. , Hart P. , Kolb F. L. , McKendry A. L. , Milus E. A. , Sneller C. , Van Sanford D. A.
Published: May 2007

A large environmental influence on phenotypic estimates of disease resistance and the complex polygenic nature of Fusarium head blight (FHB) resistance in wheat (Triticum aestivum) are impediments to developing resistant cultivars. The objective of this research was to investigate the utility of a detached leaf assay, inoculated using inoculum from isolates of Microdochium nivale var. majus, to identify components of FHB resistance among 30 entries of U.S. soft red winter wheat in the 2002 Uniform Southern FHB Nursery (USFHBN). Whole plant FHB resistance of the USFHBN entries was evaluated in replicated, mist-irrigated field trials at 10 locations in eight states during the 2001-2002 season. Incubation period (days from inoculation to the first appearance of a dull gray-green water-soaked lesion) was the only detached leaf variable significantly correlated across all FHB resistance parameters accounting for 45% of the variation in FHB incidence, 27% of FHB severity, 30% of Fusarium damaged kernels, and 26% of the variation in grain deoxynivalenol (DON) concentration. The results for incubation period contrasted with previous studies of moderately resistant European cultivars, in that longer incubation period was correlated with greater FHB susceptibility, but agreed with previous findings for the Chinese cultivar Sumai 3 and CIMMYT germ plasm containing diverse sources of FHB resistance. The results support the view that the detached leaf assay method has potential for use to distinguish between specific sources of FHB resistance when combined with data on FHB reaction and pedigree information. For example, entry 28, a di-haploid line from the cross between the moderately resistant U.S. cultivar Roane and the resistant Chinese line W14, exhibited detached leaf parameters that suggested a combination of both sources of FHB resistance. The USFHBN represents the combination of adapted and exotic germ plasm, but four moderately resistant U.S. commercial cultivars (Roane, McCormick, NC-Neuse, and Pat) had long incubation and latent periods and short lesion lengths in the detached leaf assay as observed in moderately FHB resistant European cultivars. The dichotomy in the relationship between incubation period and FHB resistance indicates that this may need to be considered to effectively combine exotic and existing/adapted sources of FHB resistance.
Vector Transmission ofXylella fastidiosato Dormant Grape
Authors: Almeida R. P. P. , Wistrom C. , Hill B. L. , Hashim J. , Purcell A. H.
Published: May 2007

Homalodisca coagulata (Say) is a sharpshooter leafhopper vector of the bacterial plant pathogen Xylella fastidiosa. Introduced into California about 15 years ago, this insect triggered recent outbreaks of Pierce's disease of grapevine in the state. H. coagulata has been observed feeding on dormant grapevines during the winter, raising the possibility of X. fastidiosa transmission during that season. We tested whether H. coagulata can acquire X. fastidiosa from and inoculate the bacterium to dormant grape (Vitis vinifera) in the laboratory and in the field. Usually, >90% of H. coagulata survived on dormant plants in the laboratory and field. Field experiments showed that H. coagulata can inoculate X. fastidiosa into dormant plants, yet field acquisition experiments did not result in transmission. Transmission to dormant plants during the winter is a potential problem in California vineyards adjacent to citrus groves or other habitats with large overwintering populations of H. coagulata. Because dormant plants have positive root pressure, our findings provide evidence that X. fastidiosa transmission does not require negative pressure in plant xylem to be inoculated into plants.
Shoot Blight of Forsythia × intermedia in Virginia Nurseries Caused by Phytophthora nicotianae
Authors: Hong C. X. , Richardson P. A. , Kong P.
Published: May 2007

A severe blighting of shoots on Forsythia × intermedia cv. Lynwood Gold plants was observed at several commercial nurseries in Virginia from 2001 to 2004. Crop losses ranged from 10 to 35%. Symptoms first occurred at the tips of shoots, including those that were trimmed and not trimmed, and then progressed downward. Diseased shoots wilted quickly and usually turned black, and foliage on these shoots withered and became necrotic. With PARP-V8 selective medium (2), a species of Phytophthora was isolated consistently from symptomatic shoots (including tissues from shoot tips, leaves, and stems) as well as from apparently healthy roots. These isolates produced arachnoid mycelia and numerous noncaducous, papillate sporangia but did not produce sexual structures on isolation plates; these morphological characters are consistent with those of Phytophthora nicotianae. All isolates produced a single-strand conformation polymorphism pattern typical of P. nicotianae (3). To test pathogenicity, 1-year-old, healthy-appearing cv. Lynwood Gold forsythia plants (canopy size = 100 cm × 60 cm) in four 12-liter containers were sheared. Two plants were inoculated by spraying each plant with 200 ml of a zoospore suspension (1.6 × 104 spores per ml, prepared from one isolate), and the other two plants were not treated and served as controls. Plants were covered with plastic bags overnight to encourage infection and then were grown in a field (temperature range = 20 to 33°C). Severe blight developed on trimmed shoots and new shoot tips of inoculated plants within 1 week after inoculation. The same pathogen was isolated from all blighted leaf and stem pieces assayed. Blight symptoms were not observed on control plants during a 1-month observation period. Phytophthora nicotianae has been reported to attack F. viridissima in Italy (1) causing root and collar rot but not shoot blight. To our knowledge, this is the first report of shoot blight on Forsythia spp. caused by P. nicotianae and the first report of P. nicotianae on Forsythia spp. in the United States.

References: (1) S. O. Cacciola et al. Plant Dis. 78:525, 1994. (2) A. J. Ferguson and S. N. Jeffers. Plant Dis. 83:1129, 1999. (3) P. Kong et al. Fun. Gen. Biol. 39:238, 2003.
First Report of Plectosporium Blight on Pumpkin and Squash Caused by Plectosporium tabacinum in New York
Authors: Jimenez P. , Zitter T. A.
Published: May 2007

In early August 2004, pumpkin and zucchini squash (Cucurbita pepo) plants grown in conventional and organic commercial operations in Orange and Dutchess counties, respectively, showed spindle-shaped lesions on vegetative tissues and silver russeting and spots on fruit, typical of Plectosporium blight. Approximately 20% of pumpkin fruit were affected at this early time in yield development, while the zucchini planting had been abandoned due to disease. Symptomatic pieces of stem, petioles, and main leaf veins were excised, surface disinfected with 0.5% sodium hypochlorite, placed on one-quarter-strength potato dextrose agar, and incubated at 21°C with a 12-h photoperiod. Pale pink colonies with pinkish, hyaline, aerial mycelium developed from the tissues. When examined microscopically, simple and branched conidiophores with apical phialides were observed, as well as non- and one-septate ellipsoidal to slightly curved conidia that measured 7.5 to 13.0 × 2.5 to 3.3 μm. The fungus fits the description of Plectosporium tabacinum (van Beyma) M.E. Palm, W. Gams, & H.I. Nirenberg (synonyms Microdochium tabacinum (von Arx, 1984) and Fusarium tabacinum (Gams & Gerlagh, 1968) (1). Pathogenicity was tested on 10 seedlings each of pumpkin, zucchini, gourd (C. pepo), winter squash (C. moschata), and cucumber (Cucumis sativa). Plants were spray inoculated at the three true-leaf stage with a spore suspension at 104 conidia/ml in water with 1% gelatin. Plants were held overnight in a moist chamber and then transplanted into 12-cm-diameter pots and kept in the greenhouse for the rest of the experiment. P. tabacinum was reisolated from all inoculated plants which completes Koch's postulates. Symptoms were noted 3 days after inoculation on pumpkin, zucchini, and gourd, with typical spindle-shaped lesions on the main stem, petioles, and main leaf veins (2). Symptoms developed after 1 week on winter squash, and lesions were mostly concentrated on the older portion of the stem with occasional lesions on the petiole and main leaf veins. Symptoms on cucumber, however, did not develop until 2 weeks after inoculation and appeared as an inconspicuous line of coalesced lesions on the ridges of the main stem only. These symptoms could easily be misidentified as physical abrasions from handling or from wind scarring. These results confirm the high susceptibility of C. pepo species, and indicate that other cucurbits are susceptible, albeit at a lower level. To our knowledge, this is the first report of P. tabacinum in New York. A voucher specimen has been deposited in the Cornell Plant Pathology Herbarium (Accession No. CUP 67504).

References: (1) M. E. Palm et al. Mycologia 87:397, 1995; (2) T. A. Zitter. Microdochium blight. Page 28 in: Compendium of Cucurbit Diseases. T. A. Zitter, D. L. Hopkins, and C. E. Thomas, eds. The American Phytopathological Society, St. Paul, MN, 1996.
First Report of Anthracnose Fruit Rot Caused by Colletotrichum acutatum on Strawberry in Denmark
Authors: Sundelin T. , Schiller M. , Lübeck M. , Jensen D. F. , Paaske K. , Petersen B. D.
Published: May 2007

Strawberry (Fragaria × ananassa) is the most important small fruit crop in Denmark. The quarantine pathogen Colletotrichum acutatum was detected for the first time in June 2000 in Denmark in a production field on the island of Falster. Strawberry plants of cv. Kimberly showed typical symptoms of anthracnose fruit rot. On mature fruits, brown-to-black lesions with spore masses that were orange to salmon in color were observed. Mummified berries were also observed. The fungus was isolated and identified on the basis of morphological characteristics, and identification was confirmed using enzyme-linked immunosorbent assay at the Central Science Laboratory, York, U.K. Species-specific polymerase chain reaction with the C. acutatum-specific primer pairs acut1/col2 (1) and CaInt2/ITS4 (3) also supported the identification. Additionally, the internal transcribed spacer regions, ITS1 and ITS2, of the ribosomal DNA were sequenced in both directions (GenBank Accession No. AY818361). Homology searches with this sequence using BLAST also confirmed the identity. Colonies grown on potato dextrose agar developed white-to-grey aerial mycelium with salmon-colored spore masses, and were beige to black on the reverse side. Conidia were 11.3 (7.3 to 16.6) μm × 3.9 (2.5 to 5.2) μm, hyaline, cylindrical with at least one pointed end, and aseptate. Mycelial growth rate was 8.4 mm per day at 25°C which is similar to earlier reports (2). Spray-inoculated (106 conidia per ml) strawberry fruits cv. Elsanta developed brown, sunken, irregular lesions with salmon-colored acervuli after 2 to 5 days at 25°C. Koch's postulates were fulfilled since the reisolated fungus from these lesions developed the same morphological characteristics as described above. To our knowledge, this is the first report of C. acutatum in Denmark.

References: (1) P. V. Martinez-Culebras et al. J. Phytopathol. 151:135, 2003. (2) B. J. Smith et al. Plant Dis. 74:69, 1990. (3) S. Sreenivasaprasad et al. Plant Pathol. 45:650, 1996.
First Report on the Natural Occurrence of Cherry virus A in Mirabelle Plum (Prunus domestica var. insititia)
Authors: Svanella-Dumas L. , Marais A. , Gentit P. , Lamorte J. , Candresse T.
Published: May 2007

Cherry virus A (CVA) is a member of the Capillovirus genus (2). It was discovered serendipitously during cloning of the little cherry agent (2) and has since been shown to be relatively widespread in sweet and sour cherry (Prunus cerasus and P. avium) (2,3). It is currently unclear whether CVA is associated with any specific symptoms in these hosts. Although it can be transmitted by grafting and thus propagated in peach, it has not been reported to naturally infect any host other than cherry. Using a degenerate reverse transcription-polymerase chain reaction (RT-PCR) technique targeting a conserved region of the RNA-dependent RNA polymerase (RdRp) and allowing the amplification of members of the Trichovirus, Capillovirus, and Foveavirus genera of filamentous plant viruses (1), a number of symptomatic Prunus spp. germplasm were evaluated. Among these, a cv. Mirabelle dorée accession (Prunus domestica var. insititia P332) of French origin exhibited severe symptoms of rosetting, severe leaf and fruit deformation, and yellow mosaic occasionally turning necrotic. RT-PCR conducted on symptomatic samples produced an amplification product of the expected size (362 bp) in several independent experiments. Sequencing of these products yielded a single sequence (GenBank Accession No. AY792509) with 88.1% nucleotide identity and 93.2% amino acid identity with the type strain of CVA (2). Presence of a CVA isolate was independently confirmed using a CVA-specific PCR assay directly on the original plum material or following experimental transmission by grafting on several new hosts including apricot (P. armeniaca cv. Priana) and plum (P. domestica cv. Prune d'Ente). To our knowledge, this is the first report of natural infection of CVA in plum. The symptoms observed in the infected plum are reminiscent of those caused by severe Prune dwarf virus (PDV) strains. Infection by PDV was confirmed using a PDV-specific PCR assay. The contribution, if any, of CVA to the symptoms observed remains to be evaluated. These findings suggest that the possible presence of CVA in noncherry Prunus spp. hosts should be taken into consideration by quarantine and certification programs.

References: (1) X. Foissac et al. Acta Hortic. 550:3743, 2001. (2) W. Jelkmann. J. Gen. Virol. 76:2015, 1995. (3) M. J. Kirby et al. Plant Pathol. 50:6, 2001.
Seedling and Adult Plant Resistance to Powdery Mildew in Chinese Bread Wheat Cultivars and Lines
Authors: Wang Z. L. , Li L. H. , He Z. H. , Duan X. Y. , Zhou Y. L. , Chen X. M. , Lillemo M. , Singh R. P. , Wang H. , Xia X. C.
Published: May 2007

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is a widespread wheat disease in China. Identification of race-specific genes and adult plant resistance (APR) is of major importance in breeding for an efficient genetic control strategy. The objectives of this study were to (i) identify genes that confer seedling resistance to powdery mildew in Chinese bread wheat cultivars and introductions used by breeding programs in China and (ii) evaluate their APR in the field. The results showed that (i) 98 of 192 tested wheat cultivars and lines appear to have one or more resistance genes to powdery mildew; (ii) Pm8 and Pm4b are the most common resistance genes in Chinese wheat cultivars, whereas Pm8 and Pm3d are present most frequently in wheat cultivars introduced from CIMMYT, the United States, and European countries; (iii) genotypes carrying Pm1, Pm3e, Pm5, and Pm7 were susceptible, whereas those carrying Pm12, Pm16, and Pm20 were highly resistant to almost all isolates of B. graminis f. sp. tritici tested; and (iv) 22 genotypes expressed APR. Our data showed that the area under the disease progress curve, maximum disease severity on the penultimate leaf, and the disease index are good indicators of the degree of APR in the field. It may be a good choice to combine major resistance genes and APR genes in wheat breeding to obtain effective resistance to powdery mildew.
Meso- and Microscale Patterns of Fusarium Head Blight in Spring Wheat Fields in Minnesota
Authors: Wilhelm K. P. , Jones R. K.
Published: May 2007

Several techniques were used to study the spatial distribution of Fusarium head blight (FHB) in spring wheat fields in the Red River Valley of Minnesota in 2001 and 2002. Four scales of study were analyzed, ranging from countywide comparisons down to adjacent heads. Agreement to frequency distributions and the departure from randomness, along with the autocorrelation of FHB clusters, were calculated at each scale. Regression analysis also was used to describe any edge affects that might exist. Finally, the optimal number of samples to adequately assess a 32.4-ha (80-acre) field was determined to a precision of ±5% disease incidence (DI). The analysis showed that DI had a random pattern at scales smaller than 32.4-ha fields, including quadrats of 6,561, 729, and 9 m2, as well 0.8-m transects involving consecutive heads within drill rows. There was no difference in DI associated with edges of fields compared with the incidence of FHB in transects within fields. Analysis of the spatial distribution at the mesoscale (county and township) showed no association in FHB DI between fields based on proximity. Differences were attributed to previous crop and in-field residue. Disease incidence was most accurately assessed on a field-by-field basis. The optimal sampling size (with <5% error) for surveying for the incidence of FHB in a standard commercial field was seven 20-head samples. Regional disease estimates would improve from including more fields at the expense of fewer samples per field.
Evaluation of Thymol as Biofumigant for Control of Bacterial Wilt of Tomato Under Field Conditions
Authors: Ji P. , Momol M. T. , Olson S. M. , Pradhanang P. M. , Jones J. B.
Published: May 2007

Volatile plant essential oils thymol and palmarosa oil, used at a concentration of 0.7%, were evaluated under field conditions for control of bacterial wilt of tomato caused by Ralstonia solanacearum. The experimental fields were artificially infested with the bacterial pathogen. Two hours after infestation, the plant essential oils were applied, then the plots were sealed with plastic mulch for 3 or 6 days. Tomato seedlings were transplanted into the field 7 days later. In fall of 2002, 92.5% of tomato plants (cv. Equinox) wilted in the untreated control plots. Both thymol and palmarosa oil soil treatments reduced bacterial wilt incidence significantly. Thymol was more effective than palmarosa oil based on the final assessment, when 33.1 and 48.1% of the plants had wilted in plots treated with thymol and palmarosa oil, respectively. Soil treatment with either thymol or palmarosa oil produced significantly higher yield of tomato than the untreated control. In 2003, only thymol was evaluated. Thymol application significantly reduced bacterial wilt incidence on the susceptible cultivar Solar Set. Disease incidence in untreated plots reached 65.5%, while in thymol treated plots only 12% of plants wilted. Thymol treatment also increased yield of Solar Set significantly compared with the untreated control. This is the first report on the use of thymol for controlling a plant disease under field conditions, which indicated that this compound provided effective control of bacterial wilt on susceptible tomato cultivars when used as preplant treatment of soils. Because of its volatile property and broad-spectrum functions, thymol shows potential to be used as a soil biofumigant for the management of various plant pathogens.
First Report of the Root-Knot Nematode Meloidogyne floridensis on Tomato (Lycopersicon esculentum) in Florida
Authors: Church G. T.
Published: May 2007

The state of Florida is the largest producer of fresh market tomato (Lycopersicon esculentum L.) in the United States with 2003 yields of 634 million kg on 17,700 ha valued at 516 million dollars. Effective crop management is essential for production of vegetables in Florida because of the presence of intense pest pressure. The identification of the pests present is the first step in the development of a successful IPM (integrated pest management) program. Root-knot nematodes (Meloidogyne spp.) are common nematodes that parasitize vegetables in Florida and cause significant yield reductions when not properly managed. In 2003 field experiments, soil was collected from two research farms in Saint Lucie and Seminole counties in Florida. Galling caused by root-knot nematode was observed on tomato at both locations. Since females suitable for identification are difficult to obtain from field-grown roots, field soil was placed in pots in the greenhouse and planted with Lycopersicon esculentum cv. Rutgers. Standard morphological techniques, differential host tests, and isozyme phenotypes were used in nematode identification. Female root-knot nematodes were extracted from tomato roots and placed in extraction buffer (10% wt/vol sucrose, 2% vol/vol Triton X-100, 0.01% wt/vol bromophenol blue). The females were crushed, loaded on a polyacrylamide gel, and separated by electrophoresis using the PhastSystem (Amersham Biosciences, Piscataway, NJ). The activities of malate dehydrogenase and esterase enzymes were detected using standard techniques. Isozyme phenotypes consistent with Meloidogyne incognita (Kofoid and White) Chitwood and M. javanica (Treub) Chitwood as well as with the newly described M. floridensis Handoo (1) were observed at both locations. To our knowledge, this is the first report of M. floridensis naturally occurring on tomato in Florida. The identification and distribution of M. floridensis in vegetable production fields is important for disease management throughout the state since the host range is likely different from other Meloidogyne spp.

Reference: (1) Z. A. Handoo et al. J. Nematol. 36:20, 2004.
First Report of the Root-Knot Nematode Meloidogyne arenaria on Tropical Soda Apple (Solanum viarum) in Florida
Authors: Church G. T. , Rosskopf E. N.
Published: May 2007

Tropical soda apple (TSA), Solanum viarum Dunal, is an invasive, noxious, perennial weed that has invaded large areas of the southeastern United States. TSA is found growing in pasture lands and is spread by cattle, wildlife, and in the movement of sod and hay. Pasture land is commonly rotated into vegetable production. In November 2003, numerous TSA plants were collected from a vegetable farm growing cucumbers and tomatoes. This land in Martin County, Florida was previously used for pasture for grazing cattle. Root galling caused by root-knot nematode (Meloidogyne sp.) was observed. Female Meloidogyne sp. were randomly extracted from the roots and placed in extraction buffer (10% wt/vol sucrose, 2% vol/vol Triton X-100, 0.01% wt/vol bromophenol blue). The females were crushed, loaded on a polyacrylamide gel, and separated by electrophoresis using the PhastSystem (Amersham Biosciences, Piscataway, NJ) (1). The activities of malate dehydrogenase and esterase enzymes were detected using standard techniques (2). Isozyme phenotype and perineal patterns consistent with Meloidogyne arenaria (Neal) Chitwood were observed. Root galling consisted of round, bead-like galls that coalesced as the infection level increased. This is consistent with galling of tomato roots by M. arenaria. Thus, TSA is a potential reservoir for M. arenaria in Florida and throughout the southern United States. The large host range of root-knot nematodes implies that multiple crops may be affected if TSA is not managed in prior land uses. To our knowledge, this is the first report of M. arenaria occurring on tropical soda apple, S. viarum.

References: (1) P. R. Esbenshade and A. C. Triantaphyllou. J. Nematol. 22:10, 1990. (2) H. Harris and D. A. Hopkinson. Handbook of Enzyme Electrophoresis in Human Genetics. North-Holland Publishing, New York, 1976.
First Report of Orobanche foetida on Common Vetch (Vicia sativa) in Morocco
Authors: Rubiales D. , Sadiki M. , Román B.
Published: May 2007

Broomrapes (Orobanche spp.) are obligate parasites that infect roots of dicotyledoneous plants. Orobanche spp. are particularly important in southern and eastern Europe, the Middle East, and north Africa. O. crenata causes severe damage to legume crops, O. cumana threatens sunflower, O. ramosa attacks potato, tobacco, tomato, and hemp, O. aegyptiaca is severe on legumes and vegetables, and other broomrapes such as O. minor are widespread on forage legumes (3). O. foetida Poir. is considered important as an agricultural parasite of faba bean (Vicia faba) and common vetch (V. sativa) crops in the Beja Region of Tunisia (1). Aside from that, it has never been found infecting crops, even where it is widely distributed in the western Mediterranean area (Portugal, Spain, Morocco, Algeria, and Tunisia) parasitizing wild herbaceous leguminosae in the genera Anthyllis, Astragalus, Ebenus, Lotus, Medicago, Ononis, Scorpiurus, and Trifolium (2). In May 2004, we found O. foetida commonly occurring in Morocco infecting wild leguminosae. It was not seen infecting legume crops such as faba beans, chickpeas, or lentils, even where O. foetida was abundant in the close proximity to the crop fields, or in the field itself. In these instances, we verified that O. foetida was infecting weeds such as Scorpiurus spp. and not the crop plants themselves by gently pulling out the plants and examining the roots. However, O. foetida was identified infecting common vetch (V. sativa) on a small farm in Taounate, Saiss Region, 50 km north of Fes. Infection of vetch plants was confirmed by digging up the plants to verify the attachment of the broomrape plant to the vetch roots. The level of infection was moderate (0.1 to 0.2 broomrape plants per vetch plant). The farmer stated that he had observed this problem only in the last 3 years. Morphology was typical of O. foetida, i.e., dark reddish plant, 20 to 50 cm tall, corolla 12 to 20 mm, dark, purplish-red, lower lip not ciliate, filaments inserted 3 to 7 mm above base of corolla, and stigma deep yellow at anthesis (2). Voucher specimens were deposited in the Herbarium of the University of Córdoba. To our knowledge, this is the first report of O. foetida infecting common vetch and it is relevant since it indicates the first introduction of this parasite into crops in Morocco. The spread of this new crop parasite population should be monitored because it could represent a further constraint for legume production in this area.

References: (1) M. Kharrat et al. FABIS Newsl. 30:46, 1992. (2) A. J. Pujadas-Salvá. Pages 187–193 in: Resistance to Orobanche: The State of the Art. Junta de Andalucía, Spain, 1999. (3) D. Rubiales. Grain Legumes 33:10, 2001.
First Report of Witches'-Broom Disease of Chinese Wingnut in China and its Association with a Phytoplasma of Aster Yellows Group (16SrI)
Authors: Liu Q. , Sun Q. , Wu T. , Davis R. E. , Zhao Y.
Published: May 2007

Pterocarya stenoptera C. DC., commonly known as Chinese wingnut, is a fast-growing deciduous tree with tough bark and attractive foliage. Because of its tolerance of compact and nutritionally poor soil, drought, and heat, Chinese wingnut is an important component of the biological diversity in natural ecosystems and is a favorable shade tree in China. Chinese wingnut has also been used as a rootstock for walnuts because of its high resistance to soilborne Phytophthora spp. In the spring of 2004, a disease characterized by witches'-broom symptoms was observed affecting Chinese wingnut trees growing in suburban Taian, Shandong, China. The diseased trees developed dense clusters of highly proliferating branches with shortened internodes, leaves on the affected branches were significantly smaller, and some branches and twigs suffered dieback. Phytoplasma infection was suspected as the cause of this Chinese wingnut witches'-broom (CWWB) disease because the disease occurred in an area where phytoplasmal diseases, such as paulownia witches'-broom (PaWB) and jujube witches'-broom (JWB), are common (3). Nested polymerase chain reactions (PCR) were performed on DNA samples extracted from leaves of six diseased trees using phytoplasma-universal 16S rDNA primers (R16mF2/R16mR1 and R16F2n/ R16R2) (1,2). Results revealed that all diseased trees examined were infected by phytoplasma, whereas PCR assays of leaf samples from two nearby symptomless Chinese wingnut trees were negative. Subsequent restriction fragment length polymorphism analysis of the PCR-amplified 16S rDNA indicated that all diseased trees contained the same phytoplasma and that the CWWB phytoplasma belongs to subgroup B of the “Candidatus Phytoplasma asteris” (AY) group (16SrI). Nucleotide sequence analysis of a 16S rRNA gene cloned from CWWB phytoplasma (GenBank Accession No. AY831966) suggested that this phytoplasma is closely related to, but distinct from, PaWB phytoplasma, another member of group16SrI. To our knowledge, this is the first report of Chinese wingnut witches'-broom disease and of its association with a phytoplasma. Further work is being undertaken to examine the ecological and evolutionary relationship between CWWB phytoplasma and other phytoplasmas in the region and to assess the impact of CWWB on walnut rootstock selection.

References: (1) D. E. Gundersen and I.-M. Lee. Phytopathol. Mediterr. 35:144, 1996. (2) C. D. Smart et al. Appl. Environ. Microbiol. 62:2988, 1996. (3) S. Zhu et al. Acta Hortic. 472:701, 1998.
The Developmental Anatomy of Pierce's Disease Symptoms in Grapevines: Green Islands and Matchsticks
Authors: Stevenson Joshua F. , Matthews Mark A. , Rost Thomas L.
Published: May 2007

Symptoms of Pierce's disease were studied in an anatomical context from infected grapevines (Vitis species) collected from field sites within Napa Valley, CA. Two symptoms, green islands and matchsticks, are reported in this study. Green islands formed as a result of incomplete initiation of the phellogen. In regions of the stem where a phellogen and subsequent periderm arose, immediately exterior tissue was cut off, causing it to brown. In regions of the stem where no periderm is formed, the exterior tissues remained green. Consequently, the stem is mottled with both green living epidermis and brown dying epidermis as determined by the presence or absence of an underlying periderm. Matchsticks formed when the leaf lamina separated from the petiole, and the petiole remained attached to the stem. Lamina broke off from the petioles consistently in a fracture zone where xylem from the petiole anastomoses into the five major veins of the leaf. No separation layer was found to explain this pseudoabscission.
Lateral Clipping of Canopy Influences the Microclimate and Development of Apothecia ofSclerotinia sclerotiorumin Carrots
Authors: Kora Cezarina , McDonald Mary Ruth , Boland Greg J.
Published: May 2007

Four canopy management treatments were evaluated in carrot (Daucus carota) production in Bradford Marsh, Ontario, in 2001 and 2002: (i) unclipped control; (ii) unclipped canopy with manual removal of collapsed senescing leaves at 2-week intervals following the first appearance on the soil; (iii) lateral clipping of the canopy at the initial emergence of apothecia, leaving the debris in the furrow, and (iv) lateral clipping of the canopy with manual removal of the debris from the furrow. Clipping reduced the canopy width by ca. 20% on both sides of the carrot bed by cutting off overlapping leaves above the furrow and senescing foliage on the soil surface. Maximum air and soil temperatures were up to 9.2 and 3.1°C lower, respectively, and relative humidity was up to 30% higher in unclipped canopies than in clipped canopies. The total number of apothecia in clipped plots was reduced by 74 and 76% compared with unclipped plots in 2001 and 2002, respectively. Canopy clipping reduced the quantity of apothecia in the crop by creating an unfavorable microclimate for the development of S. sclerotiorum without affecting the fresh foliar and root weights of carrot at harvest. The presence of clipped foliar debris in the furrow affected the number of apothecia in 2001; however, apothecia under the debris are unlikely to contribute to the overall inoculum in the crop. Lateral clipping also appeared to control Sclerotinia rot of carrot where it occurred (in 2001). This is the first report that documents and quantifies the effects of canopy architecture on the microclimate, development of apothecia of S. sclerotiorum, and Sclerotinia rot in carrot crops.
Severity of Citrus tristeza virus Isolates from Texas
Authors: Herron C.M. , Mirkov T.E. , N. Solís-Gracia N. , Kahlke C.J. , Skaria M. , da Graça J. V.
Published: May 2007

Citrus tristeza virus (CTV) isolates collected from the Lower Rio Grande Valley in south Texas and east Texas were characterized using citrus indicators and molecular methods. The citrus indicators were Mexican lime (Citrus aurantifolia), sour orange (C. aurantium), sweet orange (C. sinensis) grafted to sour orange, Duncan grapefruit (C. × paradisi), and Madam Vinous sweet orange, with some CTV isolates additionally indexed using the Texas commercial grapefruit cvs. Rio Red and Star Ruby, and Marrs and N-33 sweet orange. Severity ratings used 11 biotype groups or cumulative mean relative indices. Molecular characterization was carried out using poly- and monoclonal antibodies, seven strain-specific probes and single-stranded conformational polymorphism, and all were based on the CTV major coat protein or gene. All Texas CTV isolates produced vein clearing symptoms on inoculated Mexican lime plants. Over half of the CTV isolates tested were placed in biotype groups IX and X (causing decline of sweet orange on sour orange, seedling yellows on sour orange and grapefruit seedlings, and stem pitting of grapefruit or sweet orange), and one isolate was in biotype I (mild).
Cotton Tolerance to Hoplolaimus columbus and Impact on Population Densities
Authors: Koenning S. R. , Bowman D. T.
Published: May 2007

Glyphosate-tolerant transgenic-cotton cultivars were evaluated for tolerance to Hoplolaimus columbus in field experiments conducted from 2001 to 2003. The studies were arranged in a split-plot design that included treatment with 1,3-dichloropropene at 42 liter/ha to establish fumigated versus nonfumigated subplots with cultivars as whole plots. Cotton cultivars were divided by relative maturity into two separate but adjacent experiments in order to facilitate cotton defoliation, with 10 early-maturity and 5 late-maturity cultivars. Fumigation was effective in suppressing H. columbus population densities and increased cotton lint yield. The cultivar-fumigation interaction was significant for early-season cotton cultivars but not for late-season cultivars. A tolerance index ([yield of nontreated/yield of treated] × 100) was used to compare cultivar differences. Both groups of cultivars expressed significant levels of tolerance to H. columbus, but late-season cultivars tended to yield more than early-season cultivars in infested fields.
A Member of the Closteroviridae from Mint with Similarities to All Three Genera of the Family
Authors: Tzanetakis Ioannis E. , Postman Joseph D. , Martin Robert R.
Published: May 2007

Mentha × gracilis ‘Variegata’, described more than 200 years ago, is still being used as an ornamental. The bright vein-banding symptoms that confer the ornamental value to ‘Variegata’ clones are graft transmissible and can be eliminated after heat therapy and apical meristem culture. This observation led us to investigate the possibility that symptoms are virus-induced. Double-stranded RNA extracted from a ‘Variegata’ clone was cloned. One of the viruses identified was a member of the Closteroviridae family. This virus, designated Mint vein-banding associated virus, shares sequence similarities with all three genera of the family, making it an important link among the genera of the Closteroviridae. A detection protocol has been developed that readily detects the virus in other mint clones that exhibit vein-banding symptoms.
Assessment of Epidemic Potential of Soybean Rust in the United States
Authors: Pivonia S. , Yang X. B. , Pan Z.
Published: May 2007

This article assesses the epidemic potential of soybean rust (Phakopsora pachyrhizi) in the United States. In the assessment, there are three critical components of uncertainty: (i) suitability of climate conditions in production areas for soybean rust epidemics; (ii) likelihood of establishment of the fungus in North America; and (iii) the seasonal dispersal potential of the pathogen from overwintering regions to major soybean production regions. Assessments on the first and second components suggest soybean rust epidemics are likely in the United States, and the certainty of the third component is yet to be determined. Comparison of epidemiological factors for soybean rust in soybean production regions between China and the United States shows a complicated picture with the United States having factors that both increase and decrease risk. Future investigation of risk components—incipience in the field and long-distance dispersal—is needed.