bluuebunny/crossref_metadata_2025 huggingface dataset:
Mycosphaerella dearnessii, a Needle-cast Pathogen on Mountain Pine (Pinus mugo) in Italy
Authors: La Porta N. , Capretti P.
Published: May 2007

The pathogen Mycosphaerella dearnessii Barr. (syn. Scirrhia acicola; anamorph Lecanosticta acicola), the causal agent of brown spot needle blight, was observed on Pinus mugo in the Botanical Garden in Gardone (Brescia), on the western side of Garda Lake in northeastern Italy. Symptoms were first noticed in the spring of 1997 by Klaus Lang (University of Freising, Germany). Two years later, all 12 of the P. mugo present in the Garden exhibited extensive necrosis, and defoliation of the crown starting from the bottom upward was more prevalent on the shaded portion of infected trees. The trees were about 50 years old and 2.0 to 2.5 m in height. Symptomatic needles were confined to the 2- and 3-year old internodes. Infected needles had several dark to purplish-brown spots surrounded by green tissue and usually had dead tips. Pycnidia and conidia of Lecanosticta acicola were observed. Conidia were 4-celled, curved, pointed at one end and blunt at the other, pale olive-brown and 20 to 30 × 3 to 4 μm. The fungus was isolated in pure culture. The pathogen causes serious losses in China, eastern United States, and central and South America, but was observed for the first time in Europe only 30 years ago. It is a major cause of needle blight on several European pine species, especially P. sylvestris, P. nigra, and P. mugo. In the last 7 years, there have been reports of the fungus in pine stands, first in France, Aquitaine, and the western Pyrenees on P. radiata (3), and more recently on P. mugo in the Alps in Austria (1), Switzerland (2), and southern Germany (4). This record of the fungus near Lake Garda poses a new serious threat especially for the pine plantations of P. nigra and P. sylvestris in the more humid locations in the Alps, Apennines, and elsewhere in the mountains of southern Europe where the climatic conditions are similar to that of central Europe. This is the first report of M. dearnessii on the southern slopes of the Alps and in Italy.

References: (1) M. Brandstetter and T. Cech. Oesterreichische Forstzeitung 110:35, 1999. (2) O. Holdenrieder and T. N. Sieber. Eur. J. For. Pathol. 25:293, 1995. (3) A. Levy and C. Lafaurie. Phytoma 463:33, 1994. (4) L. Pehl L. Nachrichtenbl. Dtsch. Pflanzenschutzdienstes 47:305, 1995.
First Report of a Leaf Blight of Onion Caused by Xanthomonas campestris in Colorado
Authors: Schwartz H. F. , Otto K.
Published: May 2007

Sweet Spanish onion (Allium cepa L.) cultivars in southern Colorado (Otero and Prowers counties) have been found with symptoms of a foliar blight since 1996, and the same symptoms have been observed in northern Colorado (Weld County) since 1997. This onion disease appears to be identical to that reported from Barbados in 1971, Hawaii in 1978, and Texas in 1998 (1). Leaf blighting in scattered fields began as linear, tan to brown, water-soaked lesions that rapidly coalesced and were often surrounded by chlorotic areas, causing a general discoloration and tip die-back of affected foliage. The disease occurs generally after periods of heavy rainfall or storms. Bulb size may be reduced, and 10 to 15% yield losses have been recorded from control plots in copper-based bactericide screening nurseries naturally infected primarily by this pathogen at Rocky Ford during 1996 to 1998. Disease progression into bulbs has not been observed. Gram negative, rod-shaped, yellow bacteria were consistently recovered from infected foliar and bulb tissues on nutrient agar. The bacterial isolates utilized glucose in an oxidative manner, were catalase positive, oxidase negative, and negative for the tetrazolium salt tolerance test (0.1 and 0.02%). Two strains, one recovered during 1996 and the other in 1997, were identified by Microbe Inotech Laboratories (St. Louis, MO) as Xanthomonas campestris based on fatty acid methyl ester analysis (similarity indices of 0.81 and 0.82). A literature search indicated that classification to pathovar is lacking (2). To prove pathogenicity, a suspension (108 CFU/ml sdw) of one of the strains was sprayed to runoff onto a flat of approximately 100 8-week-old plants. Inoculated plants were placed in a dew chamber for 24 h, and then transferred to a bench and maintained at 25 to 28°C with a 12-h photoperiod and misting period for 14 days. A sample of 10 randomly selected plants with symptoms of water-soaking and discoloration was collected from which X. campestris was reisolated. No symptoms developed on seedlings sprayed with water only. This is the first report of X. campestris from onions grown in Colorado and the western continental United States.

References: (1) T. Isakeit et al. Plant Dis. 84:201, 2000. (2) M. Van Den Mooter and J. Swings. Int. J. Syst. Bacteriol. 40:348–369, 1990.
Comparison of Five Fungicides on Development of Root, Crown, and Fruit Rot of Chile Pepper and Recovery of Phytophthora capsici from Soil
Authors: Matheron M. E. , Porchas M.
Published: May 2007

The activity of five fungicides, azoxystrobin, dimethomorph, fluazinam, fosetyl-Al, and metalaxyl (subsequently replaced with mefenoxam by the manufacturer), was compared for effects on the development of root, crown, and fruit rot of chile pepper and on recovery of Phytophthora capsici from naturally infested soil. When inoculated with zoospores, plants survived longer and shoot and root fresh weights were greater for plants drenched with metalaxyl at 10 μg/ml than for plants treated with the same rate of azoxystrobin or dimethomorph. At 100 μg/ml, the duration of plant survival was greater for dimethomorph and fluazinam than for azoxystrobin; however, shoot and root growth did not differ. In soil naturally infested with P. capsici, survival and growth of shoots and roots for plants treated with dimethomorph at 100 μg/ml were greater than for those treated with the same rate of azoxystrobin or fluazinam. The most effective compounds for inhibition of lesion development on stems and fruit were mefenoxam at 1,200 μg/ml and dimethomorph at 480 μg/ml. Recovery of P. capsici from soil treated with each of the five tested compounds was significantly less than that recorded for soil not receiving a fungicide. The potential and relative value of azoxystrobin, dimethomorph, fosetyl-Al, and fluazinam as chemical management tools for Phytophthora blight on chile pepper, in addition to metalaxyl (replaced with mefenoxam), has been demonstrated.
First Report of Anemone Plants Infected by Ranunculus white mottle virus
Authors: Vaira A. M. , Vecchiati M. , Lisa V. , Milne R. G.
Published: May 2007

Ranunculus white mottle virus (RWMV) (1), genus Ophiovirus, has been reported in crops of several cultivars of commercial ranunculus (Ranunculus asiaticus hybrids) during the 1990s in Liguria in Northwest Italy. Symptoms associated with RWMV in ranunculus are not clear-cut owing to the presence of mixed viral infections. During autumn 1999, a severe disease in commercial crops of anemone (Anemone coronaria) was noted in the same area. Plants appeared stunted with young leaves showing curling, deformation, and necrotic spotting. Disease incidence in some fields reached 40 to 50%. DAS- and TAS-enzyme-linked immunosorbent assays (ELISAs) for presence of RWMV and for the viruses most frequently infecting anemone in Italy were run on 24 field samples. Seven proved to be infected by RWMV in mixed infection with Cucumber mosaic virus subgroup II or with Tobacco necrosis virus. Ophiovirus-like particles were detected by negative staining and electron microscopy from sap extracts of field plants that were RWMV-positive by ELISA. Sap from these plants was also mechanically inoculated to indicator plants. Total RNAs were extracted from RWMV-infected field samples and from inoculated Nicotiana benthamiana and N. clevelandii and used in molecular tests. A DIG-DNA probe targeting the 1.8-kb RNA2 of RWMV was used in Northern blots and dot blots of total RNAs, confirming the infection in field samples and multiplication of the virus in test plants, unfortunately still in mixed infection. At present, it is difficult to evaluate RWMV symptomatology in anemone, but the presence of this virus in mixed infection seems to produce serious effects. This is the first report of RWMV in anemone.

Reference: (1) A. M. Vaira et al. Arch. Virol. 142:2131, 1997.
First Report of Cucumber mosaic virus in Garlic Mustard in Ohio
Authors: Boehm M. J. , Nameth S. T.
Published: May 2007

Garlic mustard (Alliaria officinalis) is a common weed species associated with woodland borders, hedge rows, and suburban gardens. Garlic mustard plants expressing foliar symptoms of leaf mosaic and vein banding were collected from Franklin and Cuyahoga counties in Ohio. Analysis of symptomatic tissue using viral-associated double-stranded RNA (dsRNA) analysis on 5% polyacrylamide gels and stained with ethidium bromide resulted in the production of a banding profile (four dsRNA bands with molecular weights of 2.6, 2.0, 1.5, and 0.7 × 106 daltons) similar to that of Cucumber mosaic virus (CMV) (1). Symptomatic tissue suspected of being infected with CMV was analyzed with an indirect enzyme-linked immunosorbent assay (iELISA) employing commercially produced antiserum (Agdia Inc.) against the common strain of CMV antiserum confirmed the presence of CMV. Nonsymptomatic tissue reacted negatively to CMV. This is the first report of CMV in garlic mustard in Ohio. Due to the extensive range of this weed and the wide host range of CMV in ornamental and food-plant species, garlic mustard could serve as an alternate host for CMV in many commercially important plant species.

Reference: (1) T. J. Morris et al. Plant Mol. Biol. Rep. 1:27–30, 1983.
Effects of Quadrat Size and Time of Year for Sampling of Verticillium dahliae and Lesion Nematodes in Potato Fields
Authors: Wheeler T. A. , Madden L. V. , Rowe R. C. , Riedel R. M.
Published: May 2007

Six potato fields were randomly sampled using quadrat areas ranging from 10 m2 to 4,000 m2. A composite soil sample consisting of 20 soil cores was taken from each of 20 quadrats of each unit area. All samples were assayed for Verticillium dahliae and nematodes. The area in which a composite sample was taken had little effect on estimated mean and variance of V. dahliae until quadrat size was ≥1,000 m2. Then variances dramatically increased with size. With Pratylenchus spp., there was no systematic relationship between quadrat size and variance. Seven additional fields were divided into 2,000 or 4,000 m2 grids, and each grid was sampled in both spring and fall for V. dahliae and plant-parasitic nematodes (Pratylenchus spp. and Meloidogyne hapla). Density of V. dahliae was lower, and in some cases, degree of aggregation was higher, in the spring than in the fall. Sampling for V. dahliae in the fall required 2 to 7 composite samples to estimate mean density within 25% of the true mean, while in the spring, 10 to 19 samples were required. Assays of Pratylenchus spp. required a similar number of samples in spring and fall surveys, while M. hapla required fewer samples with spring than with fall sampling when estimating densities >20 second-stage juveniles per 100 cm3 of soil.
Sudden Decline of Date Palm Trees Caused by Erwinia chrysanthemi
Authors: Abdalla M. Y.
Published: May 2007

A new bacterial disease of date palm ‘sudden decline’ was found in the Al-Qassim region, Saudi Arabia. It is characterized by a sudden loss of vigor in the affected trees with the appearance of some blighted inner leaves. Symptoms develop rapidly and the whole tree assumes a straw color in about 2 weeks. The bud union is killed, and massive amounts of slime in a gel-like matrix could be detected in the heart of the affected tree. Biological and physiological tests of the isolated bacterium suggested that it belongs to the species Erwinia chrysanthemi. Artificial inoculation of various date palm cultivars using the technique of infusion under reduced pressure demonstrated that E. chrysanthemi was the causal agent and that cv. Succary was the most susceptible cultivar, whereas cvs. Roshody and Helwa were resistant to infection with E. chrysanthemi.
Resistance of DiploidVacciniumspp. to the Fruit Rot Stage of Mummy Berry Disease
Authors: Stretch A. W. , Ehlenfeldt M. K. , Brewster V. , Vorsa N. , Polashock J.
Published: May 2007

Mummy berry disease caused by Monilinia vaccinii-corymbosi is the most widespread economically important problem of cultivated blueberry in North America. In an attempt to identify new sources of resistance to the fruit rot (mummification) phase of mummy berry, 140 accessions from a total of 21 populations from seven wild diploid species of blueberry were evaluated for resistance under greenhouse conditions. Six isolates of M. vaccinii-corymbosi from three states were used as inoculum. A highly resistant response to mummy berry fruit rot was exhibited by all accessions of Vaccinium boreale, V. myrtilloides, V. pallidum, and V. tenellum, and by most accessions of V. darrowi. Most of the V. corymbosum and V. elliottii accessions were moderately to highly susceptible. Introgression of the resistance found in the wild diploid species into horticulturally desirable cultivars could significantly improve available resistance.
Effect of Fungicide Applications Scheduled to Control Gummy Stem Blight on Yield and Quality of Watermelon Fruit
Authors: Keinath Anthony P.
Published: May 2007

Yield and quality reductions in watermelon infected with Didymella bryoniae may be attributed to reduced number or weight of fruit, sunburned fruit, fruit rot, or low sugar content due to gummy stem blight on foliage and black rot on fruit. Number, weight, soluble solids content, and external appearance of fruit were determined in four experiments conducted in fall 1996 and 1997 and spring 1997 and 1998. Severity of gummy stem blight was varied by applying no fungicide, mancozeb, or chlorothalonil according to different schedules. In the fall, when disease severity was high, total fruit weight, percent marketable fruit, and soluble solids content were lower and percent fruit with black rot was higher in nonsprayed than in sprayed treatments. Fungicide applications did not affect total fruit weight, soluble solids content, or black rot in the spring, when disease severity was moderate to low. Percent sunburned fruit was greater in treatments sprayed every 14 days than in those sprayed weekly. In fall experiments, the number of healthy, unblemished fruit increased linearly as the number of fungicide applications was increased from zero to nine per season. Yield losses in watermelon to gummy stem blight and black rot resulted primarily from a reduction in total fruit weight and an increase in number of diseased and sunburned fruit.
The Effect of Solute Potential and Water Stress on Black Scorch Caused by Chalara paradoxa and Chalara radicicola on Date Palms
Authors: Suleman Patrice , Al-Musallam Azza , Menezes Cynthia A.
Published: May 2007

Date palm trees (Phoenix dactylifera) were found to be infected with Chalara radicicola and Chalara (Thielaviopsis) paradoxa in 1992. Compared with healthy palms, most of the diseased palms appeared to be drought stressed and poorly maintained in landscape settings and nurseries. Water potential studies conducted in growth chambers with 5- to 6-leaf seedling plants subjected to water stress at -2.3 MPa had relatively larger necrotic lesions that developed into cankers, death of buds, and eventually plant death. Tissue necrosis was directly related to water potential. Histological studies showed many necrotic islands of parenchyma tissue in drought-stressed infected plants. Only a few inoculated plants in the growth chamber study died without developing extensive cankers, apparently due to the invasion of the crown or terminal bud by the pathogens. In vitro studies with potato dextrose agar amended with glycerol, NaCl, and KCl to decrease the osmotic matrix-based water potential of the media (-4.25 MPa) resulted in a decrease in the radial growth, biomass, and the sporulation of C. radicicola and T. paradoxa. Solute potential of -0.35 to -1.97 MPa, however, favored the growth of both fungi. Sodium chloride had the greatest effect on the growth characteristics of both fungal species. These studies indicate that in parts of Kuwait where drought and salinity prevail, opportunistic pathogens such as C. radicicola and T. paradoxa could become aggressive and cause serious damage to date palms.
Effect of Imidacloprid on Incidence of Tomato yellow leaf curl virus
Authors: Ahmed N. E. , Kanan H. O. , Sugimoto Y. , Ma Y. Q. , Inanaga S.
Published: May 2007

Confidor, an imidacloprid insecticide, was used in two applications at four rates (47.6, 71.4, 95.2, and 119 g a.i./ha) for indirectly controlling Tomato yellow leaf curl virus (TYLCV) in field plantings of tomato. This spray regimen was compared with standard applications of cypermethrins at 10- to 15-day intervals throughout the growing season. In three field trials, a combination of integrated pest management (IPM) practices and two applications of Confidor at the two highest rates immediately after planting and 6 weeks later, protected tomato plants against the disease until 12 weeks after sowing. All rates of Confidor reduced disease incidence compared with standard chemical control applied in an integrated strategy, and quantitative efficacy increased with increase of insecticide rate. In the three seasons, the mean incidence of TYLCV 12 weeks after sowing was 42.7% in plots not adopting IPM compared with 15.7% in those that did. Disease incidence was reduced by Confidor treatments to 2.2 to 17%. Confidor-treated plots consistently had higher yields than control plots, and the yields decreased with the decrease in the rate of Confidor application. Confidor offers several advantages over standard applications of cypermethrins to control TYLCV. When applied immediately after planting, its long-lasting systemic activity protected the crop against the disease during early stages of growth. In addition, it reduced the number of sprays and increased tomato yield.
Basal Rot of Geraldton Waxplant Caused by Phytophthora boehmeriae
Authors: Wolcan S. , Lori G.
Published: May 2007

Geraldton waxplant (Chamaelauciun uncinatum Schauer.) is a shrub that produces flowered branches used in bouquets. Waxplant was introduced into Argentina (Buenos Aires province) in the 1990s and currently is cultivated in greenhouses. In the summer of 1995, a previously undescribed disease was observed on plants at different stages of growth. Plants showed a progressive yellowing of the branches from the base to the top of the stems. Leaves of diseased plants became grayish green, then yellow, and finally straw colored. Leaves remained attached to the branches after the plants died. Roots and stem discoloration was observed and the root cortex sloughed off. A Phytophthora sp. was isolated from the roots and lower stems of symptomatic plants. Koch's postulates were completed in a greenhouse at 28 to 34°C using the cvs. Snowflake, Violet, and Orchid. Inoculum was obtained by growing the fungus for 7 days in Petri dishes containing an autoclaved wet mixture of polished rice + wheat bran + V8 juice + perlite (1:1:1:1, by volume). The inoculum was mixed with soil (4:100, wt/wt) in pots, and 15 4-month-old plants per cultivar were transplanted into infested and noninfested soil. Plants of the cv. Snowflake were the most susceptible with symptoms starting 25 days after inoculation. At the end of the trial (five months) 86% of these plants died. Disease development was delayed on plants of cvs. Orchid and Violet and mortality was only 20% on Orchid and 26% on Violet. Control plants remained healthy. The Phytophthora sp. was reisolated from plants showing typical symptoms. The fungus was cultivated on potato-dextrose agar at 25°C and morphological characteristics were recorded. The colony diameter was 3.7 cm after 5 days. Ovoid, obturbinate and obpyriform to limoniform, papillate and caducous sporangia were observed. They averaged 42.1 ± 10.7 × 31.7 ± 9.2 μm (range 25.0 to 65.0 × 18.7 to 55.0 μm) with a length-breadth ratio = 1:1 to 1.81, av. 1.25:1. Many sporangia were distorted in their shapes and averaged 61.7 ± 30.5 × 24.8 ± 4.5 μm (range 27.5 to 125.0 × 20.0 to 32.5 μm) with a length-breadth ratio = 1.31:1 to 4.6:1, av. 2.1:1. After the zoospores were discharged, a narrow exit pore was observed (3.7 to 8.7 μm, av. 6.9 μm). Pedicels were not conspicuous or were short when present. Oogonia and amphigynous antheridia were readily observed in single culture. Spherical oospores nearly filling the oogonium and containing many subcellular inclusions averaged 29.7 ± 8.9 μm (range 17.5 to 47.5 μm). Terminal or intercalary, rounded to ovoid chlamydospores developed in smooth or swollen hyphae. Based on cultural and morphological characteristics, the species infecting waxplant was identified as P. boehmeriae Sawada (1). This is the first record of P. boehmeriae on geraldton waxplant.

References: (1) D. C. Erwin and O. K. Ribeiro. 1996. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN.
First Report of Natural Hybrids of Phytophthora nicotianae and P. cactorum on Loquat in Taiwan
Authors: Man in 't Veld W. A.
Published: May 2007

In 1995 loquat trees (Eriobotrya japonica [Thunb.] Lindl.) in several orchards in central Taiwan suffered from a severe stemrot and rootrot (2). Two populations of Phytophthora spp. isolates were recovered from diseased trees by placing pieces of plant tissue in a petri dish containing selective medium (2). One group of isolates possessed papillate sporangia, appeared to be heterothallic with amphigynous antheridia, and had a maximum growth temperature of 36°C. Upon mating, isolates of this group produced oogonia and oospores measuring 26.1 and 21.4 μm in diameter, respectively. These isolates were identified as typical strains of P. parasitica (=P. nicotianae) (2). The second group of isolates showed papillate sporangia, was homothallic with predominantly amphigynous antheridia, and had a maximum growth temperature of 34.5°C. However, the sizes of oogonia and oospores were considerably larger (average 34.7 and 30.3 μm in diameter, respectively) than those of P. nicotianae. Amplification of genomic DNA of one isolate (95023) of the second group by polymerase chain reaction (PCR) using P. nicotianae species specific primers PAR1 and PAR2, produced a special 1,000 bp sequence, indicating that the atypical isolates of second group were closely related to P. nicotianae. Isozyme analysis of two isolates (95023 and 95034, provided by L. L. Chern, Taiwan) of the second group, using the dimeric enzymes malic enzyme (MDHP; EC 1.1.1.40) and malate dehydrogenase (MDH; EC 1.1.1.37), was applied as described before (1,3). These two isolates generated the same three banded patterns using either enzyme (genotype: MDHP: 92/100; MDH-2: 93/100); the Mdhp92 allele and the Mdh-293 allele are diagnostic for P. cactorum, whereas the Mdhp100 allele and the Mdh-2100 allele are diagnostic for P. nicotianae. These well-defined heterozygous band patterns were exactly identical to those generated in atypical isolates which were identified earlier as hybrids of P. nicotianae and P. cactorum (1,3). Based on their atypical morphology and isozyme genotyping, it was concluded that these two isolates of the second group represent hybrids of P. nicotianae and P. cactorum. One of the parents, P. nicotianae, was also found closely associated with diseased loquat trees; the other parental species, P. cactorum, was not isolated from loquat in this study. It is the first time that natural hybrids of P. nicotianae and P. cactorum were found on loquat in Asia.

References: (1) P. J. M. Bonants et al. Phytopathology 90:867–874, 2000. (2) L. L. Chern et al. Plant Dis. 82:651–656, 1998. (3) W. A. Man in 't Veld et al. Phytopathology 88:922–929, 1998.
Effects of Nozzle Type and Spray Pressure on Control of Alternaria Leaf Blight of Muskmelon with Chlorothalonil
Authors: Egel Daniel S. , Harmon Philip
Published: May 2007

Methods of fungicide application were evaluated for their influence on the chemical control of Alternaria leaf blight of muskmelon in 1997, 1998, and 1999. Chlorothalonil was applied through either flat-fan or hollow-cone nozzles and with spray pressures ranging from 207 to 1,034 kPa. In all 3 years, unsprayed controls had significantly more disease than any of the sprayed treatments. There was no significant effect of nozzle type on disease severity or yield in any year. Spray pressures of 207, 414, or 620 kPa did not significantly affect disease severity or yield in 1997. In 1998, the 827-kPa pressure significantly lowered disease severity compared with the 207-kPa and 414-kPa pressures, but a similar decrease in the number of lesions per leaf did not occur. Yield responses in 1998 did not support a relationship between spray pressures and disease control. In 1999, spray pressure of 1,034 kPa did not significantly decrease the area under the disease progress curve as estimated from weekly ratings of the disease severity ratings or counts of lesions per leaf made on two dates. Results indicate no differences in disease control due to any of the application methods examined.
Occurrence, Distribution, Epidemiology, Cultivar Reaction, and Management of Rice Blast Disease in California
Authors: Greer C. A. , Webster R. K.
Published: May 2007

Rice blast, caused by Pyricularia grisea, was first found in California in 1996. Disease surveys have shown the blast disease is spreading at a moderate rate in California rice fields. Although no effective major resistance genes are known to occur in widely grown commercial California cultivars, there appear to be differences among the cultivars with respect to field susceptibility to the pathogen. P. grisea was recovered from rice crop residue and commercial seedlots which are suggested as possible sources of initial P. grisea inoculum in California rice fields. Examination of weather data indicates that environmental conditions in California rice-producing areas are permissive for rice blast but generally not optimal for epidemic development. Spore trapping determined that the majority of P. grisea conidia are generally not released until approximately 6:00 A.M. and would not have sufficient time for infection before leaf wetness periods end. Azoxystrobin showed positive results with respect to reduction of neck blast incidence and yield increases in small-plot and large-scale fungicide trials.
Virulence Composition of Phytophthora sojae in Michigan
Authors: Kaitany R. C. , Hart L. P. , Safir G. R.
Published: May 2007

Knowing the virulence composition of Phytophthora sojae is important for the management of Phytophthora root and stem rot of soybean. Plant samples were collected in Michigan from diseased plants in soybean fields with Phytophthora root and stem rot symptoms. Eighty-seven isolates of P. sojae were evaluated for virulence using 13 differential soybean cultivars. Rps 3b, 3a, 1b, 1k, and 6 were resistant to 81, 77, 74, 69, and 66% of the isolates, respectively, while Rps 1a and 7 were resistant to only 12 to 13% of the isolates. Races 2, 25, 41, and 44 of P. sojae were identified among the isolates and reported for the first time in Michigan. Virulence formulae of 69 isolates did not match those of currently known races of P. sojae. Nine isolates were considered nonpathogenic. Incorporating Rps genes 1b, 1k, 3a, 3b, and 6 in soybean cultivars with good field tolerance, in conjunction with other control measures, should offer improved protection of soybeans from Phytophthora root and stem rot in Michigan.
First Report of Cassava virus X in Cassava in Venezuela
Authors: Chaparro-Martínez E. I. , Trujillo-Pinto G.
Published: May 2007

Cassava (Manihot esculenta Crantz) is a vegetatively propagated tropical root crop. Viral infections have been identified as an important biotic component limiting cassava production (2). To survey for virus diseases, symptomatic samples of cassava plants were collected from the Venezuelan cassava production states Amazonas, Aragua, Barinas, Cojedes, Monagas, and Portuguesa. Mechanical transmissions to a differential host (Chenopodium quinoa) and a previously described double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) procedure (3) were used to test for the presence of Cassava virus X (CsVX). The DAS-ELISA procedure used gamma globulin diluted 1/2,000, conjugate diluted 1/2,000, and leaf sap extracts diluted 1/100 (1). CsVX and frog skin disease (detected graft inoculation tests with cultivar Secundina and electron microscopy) were detected in mixed infections in plants collected in Barinas. CsVX was not detected in any of the plants collected in the other surveyed areas. The low incidence of the virus (11.43%; 4 of 35 samples) suggests that CsVX has been introduced only recently via infected planting stock. Transmission of the virus is 100% when infected cuttings are used as propagation material. CsVX caused no symptoms on any of the cultivars examined in the field, and the occurrence of symptomless CsVX in Venezuela may result from the inadvertent use of cuttings from virus-infected plants. This is the first report of CsVX in cassava in Venezuela.

References: (1) B. L. Nolt et al. Ann. Appl. Biol. 118:105, 1991. (2) B. L. Nolt et al. Plant Pathol. 41:348, 1992. (3) A. C. Velasco et al. 1994. Prog. Virol. Yuca, CIAT, Cali, Colombia.
First Report of Psittacanthus angustifolius on Psidium guineense and Pinus tecunumanii in Honduras
Authors: Melgar J. , Berrios M. , Mathiasen R. , Howell B.
Published: May 2007

The mistletoe Psittacanthus angustifolius Kuijt (Loranthaceae) is a common parasite of pines in Central America and southern Mexico (1,2). In August 2000, we observed this mistletoe parasitizing a wild guava tree, Psidium guineense Sw., ≈5 km north of Yamaranguila, Department Intibuca, Honduras, at an elevation of 1,800 m. Only one plant was found on a single tree, and wild guava is apparently a rare host for this mistletoe because we have not observed this host-parasite combination in other areas where Psidium guineense occurs. This is the first report of P. angustifolius on a plant other than Pinus spp. In November 2000, we observed this mistletoe parasitizing Pinus tecunumanii (Schw.) Eguiluz et Perry ≈4 km north of Opatoro, Department La Paz, Honduras, at an elevation of 1,700 m. Several pines were infected, but no trees had more than five mistletoe infections. To our knowledge, this is the first report of P. angustifolius on P. tecunumanii in Honduras, although it is known to occur on this host in Chiapas, Mexico. Specimens of P. angustifolius from these hosts have been deposited at the Herbario, Escuela Nacional de Ciencias Forestales, Siguatepeque, Honduras.

References: (1) R. Mathiasen et al. Plant Dis. 84:203, 2000. (2) R. Mathiasen et al. Plant Dis. 84:808, 2000.
Effects of Rice Straw Management on Sclerotium oryzae Inoculum, Stem Rot Severity, and Yield of Rice in California
Authors: Cintas N. A. , Webster R. K.
Published: May 2007

Under continuous rice cropping, open field burning has been the primary means of rice residue disposal and of minimizing the carryover inoculum of Sclerotium oryzae, the cause of stem rot of rice. The phase down of open field burning in California has necessitated the development of alternatives to burning. In 1993, a continuous-year experiment was initiated in Colusa County to evaluate the effects of alternative residue management strategies on overwintering sclerotia of S. oryzae, stem rot incidence and severity, and yield. Treatments were arranged in a split-plot design with winter flooding and winter nonflooding as the main plots, and fall incorporation of the straw residue, rolling of the straw to enhance soil contact, baling and removal of residue, and fall burning as the subplots. S. oryzae inoculum and disease severity were significantly lower and yield was significantly higher in 5 out of 6 years in the winter-flooded main plots compared with the winter nonflooded plots. Over the duration of the trial, S. oryzae inoculum was consistently lower in burn subplots when compared with all other subplots. No consistent differences in disease incidence and severity or yield occurred in the subplots, although average yield over the 6 years was highest in burn subplots when compared with all other subplots. The results suggest that winter flooding is the best alternative to burning for stem rot management.
RT-PCR Detection of Seedborne Cowpea aphid-borne mosaic virus in Peanut
Authors: Gillaspie A. G. , Pio-Ribeiro G. , Andrade G. P. , Pappu H. R.
Published: May 2007

The Brazilian strain of Cowpea aphid-borne mosaic virus (CABMV) is a severe pathogen in peanut and a significant problem when distributing germ plasm to other countries. The virus is seedborne at approximately 0.15% in peanut, depending upon the cultivar, and its detection in seed lots would strengthen quarantine programs. Utilizing 3′ sequence data (GenBank Accession #AF241233), primers were designed from the coat protein region and evaluated by reverse transcription-polymerase chain reaction (RT-PCR). Use of the forward primer 5′-CGCTCAAACCCATTGTAGAA-3′ and reverse primer 5′-TATTGCTTCCCTTGCTCTTTC-3′ yielded a 221-bp product. Extracts of thick seed slices and a sample size of 12 to 25 seed showed no significant advantage of RT-PCR over enzyme-linked immunosorbent assay (ELISA) in tests of large seed lots. However, RT-PCR detected more virus in seed than in the number of infected seedlings normally arising in germination tests. Also, RT-PCR was extremely sensitive and detected 1 infected leaf among 99 healthy leaves. In contrast, ELISA detected only one infected leaf among nine healthy leaves.
Characterization of Rhizoctonia spp. Causing Root and Stem Rot of Miniature Rose
Authors: Priyatmojo A. , Yotani Y. , Hattori K. , Kageyama K. , Hyakumachi M.
Published: May 2007

Root and stem rot of miniature rose (Rosa hybrida L.) was observed in commercial glasshouse-grown roses in Gifu prefecture, Japan, during the summer and fall of 1997 and 1998. One hundred and fifty-three isolates of Rhizoctonia spp. were obtained from infected roots and stems. Of the 153 isolates, 9 had binucleate and 144 had multinucleate vegetative hyphal cells. Binucleate Rhizoctonia failed to anastomose with tester isolates of anastomosis groups (AG)-A through -S (not including AG-J and AG-M). Of 144 isolates identified as R. solani, 83.3% were AG 2-2 IIIB and 16.7% were AG 4 HG-I. Five isolates from each group caused severe rot and mortality on cuttings during rooting. Pathogenicity of Rhizoctonia spp. varied on three different ages of miniature roses cv. Silk. Isolates of AG 4 HG-I caused root and stem rot and mortality on 15-, 25-, and 40-day-old plants, whereas isolates of AG-2-2 IIIB caused root and stem rot and mortality on 15- and 25-day-old plants, but light root rot on 40-day-old plants. Isolates of binucleate Rhizoctonia caused root and stem rot and mortality only on 15-day-old plants.
First Report of Parietaria mottle virus on Tomato in Spain
Authors: Aramburu J.
Published: May 2007

During spring 2001, plants of different tomato (Lycopersicon esculentum) cultivars grown in several commercial fields in the eastern Catalonia Region of Spain had fruit with brown patches and young leaves with rings and a bright necrotic mosaic that progressed to stem necrosis of the apex, which might die and later develop new symptomless shoots. The symptoms were similar to those of Cucumber mosaic virus (CMV) and Tomato spotted wilt virus (TSWV). Sap of tomato sample R1 (in buffered saline [0.02 M sodium phosphate, 0.15 M NaCl at pH 7.2, containing 0.2% 2-mercaptoethanol]) was infective to Cucumis sativus (local necrosis), tomato cv. Marmande (systemic infection consisting of chlorotic local lesions and necrotic mosaic), Nicotiana clevelandii and N. benthamiana (chlorosis and rosetting), and Chenopodium quinoa (chlorotic local lesions, systemic mottle, and leaf distortion). The sap was not infective to N. glutinosa, N. tabacum cv. Xanthi, Datura stramonium, or Gomphrena globosa. The host range data indicated that the infective agent in sample R1 could be Parietaria mottle virus (PMoV) (1). Symptomatic plants inoculated in a greenhouse with the R1 isolate and symptomatic from tomato plants from the field were analyzed by indirect enzyme-linked immunosorbent assay (ELISA) and had minimum ELISA values at least 10-fold higher than healthy controls, using a polyclonal antiserum (provided by P. Roggero) of a tomato strain of PMoV denoted tomato virus 1 (2). The R1 isolate of PMoV was negative in ELISA when analyzed with commercial antisera to TSWV, CMV, Tomato mosaic virus, Tomato bushy stunt virus, Potato Y virus, Tobacco etch virus, Pelargonium zonate spot virus, and Tobacco streak virus.

References: (1) P. Caciagli et al. Plant Pathol. 38:577, 1989. (2) P. Roggero et al. J. Plant Pathol. 82:159, 2000.
Occurrence of Diaporthe phaseolorum var. meridionalis on Soybean in Illinois
Authors: Gravert C. E. , Li S. , Hartman G. L.
Published: May 2007

Both Diaporthe phaseolorum var. caulivora and D.phaseolorum var. meridionalis cause stem canker on soybean, with D. phaseolorum var. caulivora reported in the northern regions and D. phaseolorum var. meridionalis reported in the southern regions of the United States (1). During the 1999 and 2000 growing seasons, fungi were isolated from soybean plants from growers' fields exhibiting stem canker symptoms. Stem tissue along the margin of the canker was cut into 1- to 5-mm3 pieces, surface-disinfected for 4 min in 0.5% NaOCl solution, rinsed twice, and plated on water or potato dextrose agar (PDA). Fungi of interest were hyphal tipped, grown on PDA at 21°C with 24 h of light, and identified by culture and spore morphology after 3 to 4 weeks. Typical D. phaseolorum var. meridionalis isolates produced white, lanose colonies that turned tan with age. Most of the D. phaseolorum var. meridionalis isolates produced pycnidia with alpha spores and beaked perithecia after 25 to 30 days (2). Brown to black stromata formed in irregular shapes. Of the 16 D. phaseolorum var. meridionalis isolates identified, 11 were from Illinois, 1 each from Indiana and Ohio, and 3 from Kentucky. In Illinois, four isolates were from the northern part of the state, and the rest were from the central and southern areas of the state. In addition to D. phaseolorum var. meridionalis, other isolates obtained from soybean plants included D. phaseolorum var. caulivora, D. phaseolorum var. sojae, and Phomopsis longicolla.

References: (1) J. A. McGee and D. C. Biddle. Plant Dis. 71:620, 1987. (2) A. W. Zhang et al. Phytopathology 88:1306, 1998.
First Report of Frankliniella fusca as a Vector of Impatiens necrotic spot tospovirus
Authors: Naidu R. A. , Deom C. M. , Sherwood J. L.
Published: May 2007

Of more than a dozen members of the genus Tospovirus, Tomato spotted wilt virus (TSWV) and Impatiens necrotic spot virus (INSV) are among the most damaging viruses found in North America (3). TSWV is a major problem in vegetable and field crops, whereas INSV is commonly encountered in the floriculture and nursery industries. TSWV is transmitted by several thrips species, of which the western flower thrips (WFT, Frankliniella occidentalis Pergande) is the most predominant vector. INSV has been reported to be transmitted only by WFT (1). To determine if tobacco thrips (TT, F. fusca Hinds) can transmit INSV, a virus-free culture of TT was reared on detached peanut cv. Florunner leaves in 0.5-liter polypropylene cups with closed lids at 25 ± 2°C with constant light. Fresh peanut leaves were exchanged every 2 to 3 days to maintain the thrips colony. For transmission studies, adult thrips were confined on peanut leaves for 24 h for oviposition and then the peanut leaves, sans adults thrips, were transferred to a new cup. Leaves were examined daily for larval emergence, and similarly aged first instar larvae (<12 h old) were given an acquisition access period of 24 to 48 h on INSV-infected detached leaves of Emilia sonchifolia. The larvae were subsequently transferred to healthy peanut leaves and reared until adult emergence. Groups of 10 adults per plant were given a 48-h inoculation access period on 10-day-old healthy E. sonchifolia seedlings. Thrips were subsequently killed, and the plants were maintained in a growth chamber at 28 ± 2°C, and with a 16/8 light/dark photoperiod. Transmission studies were repeated 10 times with different sources of infected plants and different batches of larvae following acquisition access periods. Seven to ten days after inoculation, plants developed symptoms consisting of chlorotic spots, mosaic, and mottling. The presence of INSV in these symptomatic plants was confirmed by ELISA using INSV ImmunoStrip Test (Agdia, Inc., Elkhart, IN) and by reverse transcription-polymerase chain reaction assay with primers specific to the INSV-NSs gene. Our results demonstrate that TT can serve as a vector of INSV. INSV has been reported in peanut in the southeastern United States (2). WFT and TT transmit TSWV in peanuts, with the latter being the predominant vector species in Georgia and other parts of the region. TT transmission of INSV is of concern because of the increased incidence in recent years of INSV in peanuts and the potential for synergistic or gene exchange between TSWV and INSV, since mixed infections with both viruses have been observed (4).

References: (1) M. L. Daughtrey et al. Plant Dis. 81:1220, 1997. (2) S. S. Pappu et al. Plant Dis. 83:966, 1999. (3). J. L. Sherwood et al. Pages 1034–1040 in: Encyclopedia of Plant Pathology. C. Maloy and T. D. Murray, eds. John Wiley and Sons, Inc., New York, 2001. (4) L. Wells et al. Phytopathology (Abstr.) 94:S94, 2001.
Selection and Evaluation of Microorganisms for Biocontrol of Fusarium Head Blight of Wheat Incited by Gibberella zeae
Authors: Khan N. I. , Schisler D. A. , Boehm M. J. , Slininger P. J. , Bothast R. J.
Published: May 2007

Gibberella zeae incites Fusarium head blight (FHB), a devastating disease that causes extensive yield and quality losses to wheat and barley. Of over 700 microbial strains obtained from wheat anthers, 54 were able to utilize tartaric acid as a carbon source when the compound was supplied as choline bitartrate in liquid culture. Four tartaric acid-utilizing and three nonutilizing strains reduced FHB in initial tests and were selected for further assays. Antagonists were effective against three different isolates of G. zeae when single wheat florets were inoculated with pathogen and antagonist inoculum. All seven antagonists increased 100-kernel weight when applied simultaneously with G. zeae isolate Z3639 (P ≤ 0.05). Bacillus strains AS 43.3 and AS 43.4 and Cryptococcus strain OH 182.9 reduced disease severity by >77, 93, and 56%, respectively. Five antagonists increased 100-kernel weight of plants inoculated with G. zeae isolate DAOM 180378. All antagonists except one increased 100-kernel weight, and four of seven antagonists reduced disease severity (P ≤ 0.05) when tested against G. zeae isolate Fg-9-96. In spray-inoculation experiments, Bacillus strains AS 43.3 and AS 43.4 and Cryptococcus strains OH 71.4 and OH 182.9 reduced disease severity, regardless of the sequence, timing, and concentration of inoculum application (P ≤ 0.05), though 100-kernel weight did not always increase when antagonists were applied 4 h after inoculum of G. zeae. Overall, 4 of 54 isolates that utilized tartaric acid in vitro were effective against G. zeae versus only 3 of 170 isolates tested that did not utilize tartaric acid (P ≤ 0.05, χ-square test of goodness of fit), demonstrating the potential benefit of prescreening candidate antagonists of FHB for their ability to utilize tartaric acid. Biological control shows promise as part of an integrated pest management program for managing FHB.
Factors Affecting Mechanical Transmission of Tomato spotted wilt virus to Peanut (Arachis hypogaea)
Authors: Mandal B. , Pappu H. R. , Culbreath A. K.
Published: May 2007

Evaluation of peanut germ plasm for Tomato spotted wilt virus (TSWV) resistance has been slowed by the difficulty in achieving a high rate of mechanical transmission of the virus to peanut. In this study, improvements were made and a highly efficient mechanical transmission protocol was developed. Several factors that affect the transmission efficiency were identified. Use of two antioxidants (sodium sulfite and mercaptoethanol) and two abrasives (Celite and Carborundum) and application of the inoculum by rubbing with a cotton swab dipped in the inoculum as well as pricking with an inoculation needle resulted in a significantly higher transmission rate. The most susceptible growth stage of peanut to TSWV inoculation was 2 to 3 days after germination (6 to 7 days after planting). The inoculation protocol consistently resulted in a higher percentage of infected plants from different sources of inoculum such as infected peanut, tobacco, and tomato.
Effects of Sodium Chloride on Commercial Asparagus and of Alternative Forms of Chloride Salt on Fusarium Crown and Root Rot
Authors: Reid T. C. , Hausbeck M. K. , Kizilkaya K.
Published: May 2007

Experiments with applications of NaCl (560 and 1,120 kg/ha) and lime (6,719 kg/ha) were conducted in asparagus fields in commercial production (one healthy and one exhibiting symptoms of early decline), and an experiment with NaCl (1,120 kg/ha) was conducted in a badly declined research field at Michigan State University from 1998 to 2000 to determine whether these treatments control Fusarium crown and root rot of asparagus. Growth chamber and greenhouse studies were conducted to test the ability of alternative forms (CaCl2, NH4Cl, and MnCl2) of chloride salt to reduce disease caused by F. oxysporum f. sp. asparagi and F. proliferatum. NaCl applications increased yield and fern health in the research plot, but not in commercial fields. Soil tests in these fields indicated that NaCl did not decrease levels of calcium, magnesium, or potassium, and did not affect pH. In growth chamber studies with asparagus seedlings in Hoagland's agar test tubes, and in greenhouse studies with asparagus seedlings in soil, none of the alternative forms of chloride salt tested were more effective than NaCl in controlling Fusarium crown and root rot.
Levels of Stewart's Wilt Resistance Necessary to Prevent Reductions in Yield of Sweet Corn Hybrids
Authors: Freeman Noah D. , Pataky Jerald K.
Published: May 2007

Stewart's wilt reactions and yield of a total of 69 sweet corn hybrids were evaluated in trials in 1999 and 2000 in order to determine the level of Stewart's wilt resistance necessary to prevent reduction in yield of sweet corn hybrids. Plants at the 2- to 3-leaf stage were inoculated with Erwinia stewartii using the pinprick method. Stewart's wilt symptoms were rated from 1 to 9, and incidence of systemic infection was determined as a percentage for each experimental unit. Primary ears were harvested about 21 days after midsilk, and yield was measured as ear weight and number of marketable ears. Percent yield was calculated for each hybrid by dividing yield from inoculated treatments by yield from noninoculated treatments and multiplying by 100. Hybrid means for Stewart's wilt ratings in inoculated treatments ranged from 2.0 to 7.3. The relationships between percent yield and Stewart's wilt severity ratings were described best by curvilinear regressions, whereas percent yield decreased linearly with the incidence of systemic infection in 2000. Ear weights of hybrids with ratings below 3 or 3.5 were estimated from the regression equations to be within 95 or 92%, respectively, of those from noninoculated treatments of the same hybrid. The number of marketable ears from hybrids with ratings of 3 or below was estimated from the regression equations to be within 90% of those from noninoculated treatments of the same hybrid. A level of resistance that resulted in Stewart's wilt ratings below 3 or 3.5 corresponded to nonsystemic infection of most plants (i.e., incidence of systemic infection below 5 or 10%, respectively). The adverse effects of Stewart's wilt on ear weight and marketability appeared to be minor for sweet corn hybrids with levels of resistance that prevented or minimized systemic infection.