bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Citrus Greening Disease and Associated Bacterium “Candidatus Liberibacter asiaticus” from Bhutan
Authors: Ahlawat Y. S. , Baranwal V. K. , Thinlay  , Doe Doe  , Majumder S.
Published: May 2007

During July 2002, surveys of mandarin orchards were conducted in Punakha Valley and Wangdue districts of Bhutan. Symptoms of the greening disease were observed in most of the orchard. The incidence of disease was recorded up to 30% in 24 private orchards with more than 5,000 trees total. Affected trees were generally stunted with leaves showing symptoms of mottling. Sometimes, symptoms were seen only on one part of the canopy. The greening disease is caused by a fastidious phloem restricted bacterium, “Candidatus Liberibacter asiaticus” in Asian countries and “Candidatus Liberibacter africanus” in African countries. To confirm the presence of this bacterium causing greening disease in Bhutan, 33 leaf samples were collected from seven locations in Bhutan and stored at -80°C. Petioles and midribs were used for extraction of DNA using DNeasy Plant Mini Kit (Qiagen Gmbh, Hilden, Germany). Polymerase chain reaction (PCR) was initially performed with a sample from Rimchu, Bhutan using primer pair 5′TATAAAGGTTGACCTTTCGAGTTT/5′ACAAAAGCAGAAATAGCACGAACAA previously designed for amplification of ribosomal protein genes of β-operon of two liberibacter species (1). An amplicon of approximately 700 bp was obtained. The size of the PCR product is similar to that amplified from “Candidatus Liberibacter asiaticus”. The amplicon was cloned in pGEM-T easy vector and sequenced. The clone was 703 nt long and showed 100% sequence homology with the corresponding sequence of “Candidatus Liberibacter asiaticus” confirming that “Candidatus Liberibacter asiaticus” is the cause of greening disease in Bhutan. Later, one sample from each location was analyzed and found to be positive to greening. To our knowledge, this is the first report of this bacterium and greening disease in Bhutan, and citrus greening appears to be the main cause of declining citrus in the Punakha Region of Bhutan.

Reference: (1) A. Jocquellet et al. Page 363 in: Proc. Conf. Int. Organ. Citrus Virol. 14th. IOCV, Riverside, CA, 2000.
Pathogenicity on Chile Pepper of Vertcillium dahliae Recovered from Three Weed Hosts in New Mexico
Authors: Sanogo S. , Clary M.
Published: May 2007

In July 2002, in the course of field surveys for Verticillium dahliae in chile pepper (Capsicum annuum), three weed species, Physalis wrightii (Wright groundcherry), Anoda cristata (spurred anoda), and Proboscidea louisianica (devil's-claw), were found with symptoms of vascular necrosis in three fields in Luna County and two fields in each Hidalgo and Doña Ana counties in southern New Mexico. Across the three weed species, vascular area with necrosis was approximately 5 to 15%, and was rated on longitudinal crown and stem sections (1). Except for a few plants of P. wrightii that had leaves with necrotic margins in one field in Luna County, no other symptoms were observed. The three weed species were at growth stages between flowering and fruit set. Isolates recovered from the vascular tissue were identified as V. dahliae based on morphological features when cultured on prune extract medium (2). Two isolates of V. dahliae from each weed species, along with an isolate from chile pepper, were grown on potato dextrose agar at 20, 25, or 30°C for 12 days. There was no significant difference in radial growth among isolates at the three temperatures, and maximum radial growth occurred at 25°C. The isolates were tested for pathogenicity on the chile pepper cv. NM 6-4 in the greenhouse. In each of the three trials, 15 plants were inoculated each by root dipping (1) in 20 ml conidial suspension (106 conidia/ml) of each V. dahliae isolate. Control plants were root dipped in sterile distilled water. Symptoms of foliar wilting with 75 to 100% vascular necrosis (1) were observed in all plants 4 weeks after inoculation. V. dahliae was recovered from symptomatic plants (2). To our knowledge, this is the first report that V. dahliae recovered from P. wrightii, A. cristata, and Proboscidea louisianica is pathogenic to chile pepper. Control of Wright groundcherry, spurred anoda, and devil's-claw may be important in the management of V. dahliae in chile pepper.

References: (1) R. G. Bhat and K. V. Subbarao. Phytopathology 89:1218, 1999. (2) P. W. Talboys. Plant Pathol. 9:57, 1960.
Use of a Plastic Rain Shield Reduces Fruit Decay and Need for Fungicides in Sweet Cherry
Authors: Børve Jorunn , Stensvand Arne
Published: May 2007

It has been shown previously that covering sweet cherry trees (Prunus avium L.) with rain shields made of polyethylene or other waterproof, light-transmitting material prior to harvest to prevent fruit cracking will reduce fruit decay by various fungi. In the present work, the effects of extending the covering period on fruit decay, fruit quality, and the potential reduction in number of fungicide applications were investigated. In six of eight trials, there were significant reductions in fruit decay in covered fruit compared with fruit that were not covered. The most prevalent fruit-decaying fungi were Monilinia laxa and Botrytis cinerea. Mucor piriformis and Colletotrichum gloeosporioides occurred in high amounts in one trial each. The treatments included covering during rain periods until harvest was over from (i) bloom (bloom-cover), (ii) 6 to 7 weeks prior to harvest (early-fruit-cover), (iii) 3 to 4 weeks prior to harvest (late-fruit-cover), and (iv) not covered. In two trials, the number of fungicide applications was similar between different covering times (bloom-cover not included), and in one trial no fungicides were applied at all (all treatments included). There was a significant effect of covering on fruit decay in all three trials, but there was no difference between covering 6 to 7 and 3 to 4 weeks prior to harvest. In the sprayed fields, the incidence of decay was 48% in fruit that were not covered compared with from 6 to 11% in covered fruit. In the unsprayed field, covering from bloom resulted in 14% fruit decay compared with 23 to 26% in the other two cover treatments. In five trials, all covering regimes were included, and the number of fungicide applications varied with time of covering. The number of fungicide applications for the different treatments were: bloom-cover, 0; early-fruit-cover, 1 to 4; late-fruit-cover, 2 to 5; uncovered, 3 to 6. The mean incidence of fruit decay at harvest for the five trials (range in parentheses) was 3.4 (2.0 to 4.3), 1.8 (0.4 to 4.0), 3.8 (1.8 to 7.7), and 16.5% (2.5 to 39.7), respectively, for the covering times listed. There were no significant differences in decay after storage (3 to 7 days at 4°C followed by 2 to 4 days at 20°C) among the different covering times in the six experiments where fruit were stored. The results indicate that fungicide applications were not needed if fruit were covered during rainy periods from bloom until the end of harvest, and it was possible to omit 1 fungicide application if the covering period was increased from 3 to 4 weeks to 6 to 7 weeks. The fruit quality was not reduced by increasing the covering period from the normal 3 to 4 weeks in any of the experiments.
Planting Date and Cultivar Effects on Soybean Yield, Seed Quality, and Phomopsis sp. Seed Infection
Authors: Wrather J. A. , Sleper D. A. , Stevens W. E. , Shannon J. G. , Wilson R. F.
Published: May 2007

Incidence of Phomopsis seed decay is frequently high and quality low in seed from early-maturing maturity group III and IV soybean cultivars planted in early to mid-April in the southern United States. Cultivars resistant to this disease have not been available until the recent release of germ plasm lines SS 93-6012 and SS 93-6181. Our objective was to determine the effects of planting dates with these lines and one Phomopsis seed decay-susceptible soybean cultivar, Asgrow 3834, on seed infection by Phomopsis spp. and on yield and the correlation between percentage of Asgrow 3834 infected with Phomopsis spp. and seed quality. Generally, yields averaged over years were significantly greater for mid-April than mid-June plantings, and yields of cultivars were similar within a planting date. Soybean lines SS 93-6012 and SS 93-6181 were highly resistant to Phomopsis seed decay compared with the susceptible cultivar, Asgrow 3834. There was a significant, negative correlation between germination of seed from mid-April plantings of Asgrow 3834 and percentage of these seed infected with Phomopsis spp. Moreover, there were significant correlations between fatty acid composition of Asgrow 3834 seed and the percentage of these seed infected with Phomopsis spp. This altered composition of fatty acids may be responsible for reduced quality of oil derived from seed infected with this fungus. Phomopsis seed decay-resistant soybean lines SS 93-6012 and SS 93-6181 should be useful in breeding programs focused on developing high-yielding cultivars resistant to this disease.
Temperature, Moisture, and Seed Treatment Effects on Rhizoctonia solani Root Rot of Soybean
Authors: Dorrance A. E. , Kleinhenz M. D. , McClure S. A. , Tuttle N. T.
Published: May 2007

The effects of temperature and soil moisture on infection and disease development by Rhizoctonia solani on soybean were studied individually. In addition, the anastomosis group of R. solani isolates recovered from soybean from 35 fields in 15 counties was determined. All of the 44 isolates recovered in this study were AG-2-2 IIIB. Five isolates of R. solani were able to infect and colonize soybean roots and hypocotyls at 20, 24, 28, and 32°C in growth chamber studies. The temperatures evaluated in this study were not limiting to the isolates tested. In greenhouse studies, nine R. solani isolates and a noninoculated control were evaluated at 25, 50, 75, and 100% soil moisture holding capacity (MHC). Root weights were greater and percent stand averages higher at 50 and 75% than at 25 or 100% MHC; however, as percentage of control, the main effect on percent moisture for percent stand, plant height, or root weight was not significant. There were significant differences among the isolates for the percent stand, root rot rating, and root fresh weight of soybean in each study. In both temperature and moisture studies, the R. solani isolates could be separated as predominantly causing (i) seed rot, as detected by greatly reduced plant stand; (ii) root rot generally having no effect on plant stand but a high root rot rating and low root weight; or (iii) hypocotyl lesions, having no effect on plant stand, a low root rot score, and a high number of red lesions on the hypocotyl. In the greenhouse seed treatment evaluations of five fungicides, there was no fungicide by isolate interaction using these pathogenic types of R. solani. None of the seed treatments evaluated in this study provided 100% control of the four isolates tested. Due to the wide range of environmental factors that permit R. solani infection and disease on soybeans, other control measures that last all season, such as host resistance, should be emphasized.
Identification and Cultivar Reaction to Three New Races of the Spinach Downy Mildew Pathogen from the United States and Europe
Authors: Irish B. M. , Correll J. C. , Koike S. T. , Schafer J. , Morelock T. E.
Published: May 2007

Since 1996, commercial spinach cultivars with resistance to four previously described races of Peronospora farinosa f. sp. spinaciae (races 1, 2, 3, and 4) were observed with high incidences of downy mildew both in California and Europe. Isolates of P. farinosa f. sp. spinaciae collected in California between 1997 and 2001, Arizona in 1999, and a single isolate collected in the Netherlands in 1996 were examined for their disease reaction on differential spinach cultivars and a set of commercial spinach cultivars. Disease reactions on the differential cultivars indicated the occurrence of three new races of P. farinosa f. sp. spinaciae. Two newly identified races, designated race 5 (isolate CA1) and race 6 (isolate SP1), were detected in the United States. The isolate from the Netherlands also was distinct and designated race 7 (isolate JVN7). Some cultivars with resistance to races 1, 2, 3, and 4 were susceptible to race 5, whereas others were resistant, indicating that resistance to a given race may be governed by different genes (or alleles) depending on the source of resistance. A survey of races in California indicated that races 5 and 6 predominated. Although the majority of the cultivars examined were susceptible to race 6 based on the traditional qualitative cotyledon inoculation assay, significant quantitative differences in resistance to race 6 were observed using a true-leaf greenhouse screening procedure. Although more work is needed to confirm the results of the true-leaf assays, the quantitative resistance observed using this procedure appears to be race specific.
Sensitivity of Botrytis squamosa to Different Classes of Fungicides
Authors: Tremblay D. M. , Talbot B. G. , Carisse O.
Published: May 2007

An automated quantitative (AQ) assay was compared with radial growth on solid media and with dry weight in liquid culture for assaying fungicide sensitivity in Botrytis squamosa, the causal agent of onion leaf blight. Five isolates of B. squamosa were assayed for sensitivity to mancozeb (Dithane DG) and iprodione (Rovral) at five concentrations (0.5, 1.0, 5.0, 10.0, and 50 ppm). For mancozeb, the correlations between 50% effective concentration (EC50) values obtained with the three assays were not significant; however for iprodione, correlations between EC50 values for AQ and radial growth and for AQ and dry weight were significant (r = 0.98 and 0.99, respectively). The AQ method was less time consuming and more reliable than the two standard assays. The AQ method was used to evaluate the sensitivity of 35 field isolates of B. squamosa to mancozeb (Dithane DG), iprodione (Rovral), vinclozolin (Ronilan DF), and chlorothalonil (Bravo 500). All isolates were sensitive to mancozeb (EC50 ranged from 3.36 to 12.97) and chlorothalonil (EC50 < 1.5 μg/ml), but four isolates were insensitive to both iprodione (EC50 ≥ 3.98 μg/ml) and vinclozolin (EC50 ≥ 17.49 μg/ml). The ratio of the EC50 values of the least-sensitive and the most-sensitive isolates of B. squamosa was 1.08, 3.86, 6.98, and 37.59 for chlorothalonil, mancozeb, iprodione, and vinclozolin, respectively. Cross-resistance was observed for the two dicarboximide fungicides, iprodione and vinclozolin, with a significant correlation (r = 0.94) in the sensitivity of the 35 isolates to these two fungicides.
Effects of Temperature, Wetness Duration, and Leaflet Age on Infection of Strawberry Foliage by Phomopsis obscurans
Authors: Nita M. , Ellis M. A. , Madden L. V.
Published: May 2007

Temperature, leaf wetness, and leaflet age effects on infection of strawberry foliage by Phomopsis obscurans were examined in controlled-environment experiments. A mid-season (‘Honeoye’) and early-season (‘Earliglow’) cultivar were used. Tested temperatures were 10, 15, 20, 25, 30, and 35°C, and tested wetness periods were 5, 10, 15, 20, 25, and 35 h. Leaflets were labeled based on age: 0 to 1, 2 to 6, and 7 to 14 days old. Effects of temperature, wetness duration, and leaflet age on the logit of disease incidence and severity were quantified using a linear mixed model analysis of variance (ANOVA). Age, wetness duration, and their interaction significantly affected these measures of disease. Disease intensity decreased dramatically with increasing leaflet age at the time of infection, indicating a decrease in susceptibility with maturation of foliage, and increased with increasing wetness duration. Temperature only affected disease incidence with ‘Honeoye’. A prediction model was developed for leaflet infection based on ANOVA results. Coefficients of determination were approximately 0.8 for both cultivars and measures of disease (incidence and severity), indicating that disease could be described accurately based on environmental conditions and leaflet age.
First Report of Sharp Eyespot of Wheat in Egypt
Authors: Hammouda A. M.
Published: May 2007

In 1998 and 1999, Rhizoctonia solani Kühn and R. cerealis van der Hoeven were isolated from lesions on basal leaf sheaths (2 to 4 cm above the soil level) of 48 wheat plants (Triticum aestivum L. em. Thell.). Plants were collected from 16 locations in Egypt in December 1998 (seedling stage) and March 1999 (adult stage). Disease incidence was approximately 20 and 30% during the 1998 to 1999 and 1999 to 2000 seasons, respectively. Mycelium was white to deep brown, branched at right angles with a septum near the branch, and a slight constriction at the branch base. Multinucleate cells and the production of irregular, brown black sclerotia in culture and on host plants were diagnostic of R. solani (1). Anastomosis groups AG-4 (30 isolates) and AG-1 (6 isolates) of R. solani, distinguished on the basis of hyphal fusion, were recovered. R. cerealis (12 isolates belonging to the anastomosis group CAG-1), which were slow-growing on potato dextrose agar, produced binucleate hyphal cells and yellow sclerotia. The 48 isolates were tested in the greenhouse for pathogenicity using cornmeal and sand inoculum prepared by mixing 3 g of infested cornmeal, 100 g of sand, and 20 ml of distilled water and incubating for 20 days at 28°C. Fifty milliliters of inoculum were added to 500 g of sterile soil in a 15-cm-diameter pot. There were six pots per isolate. Six pots containing noninfested soil were included as checks. Wheat (cv. Giza 160) seeds were disinfested by placing them in 5% of sodium hypochlorite for 5 min, and 10 seeds were planted in each pot. Twenty-five days after planting, an average of five plants survived in the pots treated with R. solani, and seven plants survived in pots treated with R. cerealis. All 10 plants in the noninfested pots survived and were symptomless. The surviving plants treated with R. solani developed a tan cortical rot of the root system and tan zonate lesions on the basal leaf sheaths. The lesions were oriented longitudinally with the stem and were irregular in shape with a white or light tan center surrounded by a wide, dark brown margin. Isolates of R. cerelis caused lesions on the base of the stem of young and mature plants. The lesions, which were larger than those caused by R. solani, were elliptic or “eye” shaped with a pale yellow center and sharply defined narrow border. The fungi were reisolated from the symptomatic tissue.

Reference: (1) J. D. S. Clarkson and M. J. Griffin. Plant Pathol. 26:98, 1977.
First Report of Natural Infection of Luffa acutangula by Watermelon bud necrosis virus in India
Authors: Mandal B. , Jain R. K. , Chaudhary V. , Varma A.
Published: May 2007

In August 2002, ridge gourd (Luffa acutangula) plant samples exhibiting yellowing of leaves were collected from the experimental farm of Tamil Nadu Agricultural University, Coimbatore, India. Mechanical inoculations of ridge gourd seedlings using the above samples resulted in chlorotic spots on inoculated leaves and vein clearing followed by chlorotic rings and yellow netting along veins of newly developed leaves. The virus was reisolated from the chlorotic spots of the seedlings. Extracts from the field samples as well as mechanically inoculated seedlings reacted with antiserum to Watermelon silver mottle virus (WSMoV) in direct antigen coating enzyme-linked immunosorbent assay, suggesting the association of a tospovirus belonging to WSMoV serogroup (2). Symptomatic leaves from the second mechanical passage exhibiting yellow netting along the veins were subjected to reverse transcription-polymerase chain reaction (1) to identify the genus Tospovirus. Using the primer pair (5′TCTGTCCT(C/T) TTGAA (G/T) GTCCA3′ and 5′AGAGCAATCGAGGCGCT3′) derived from the conserved sequences of Groundnut bud necrosis virus (GBNV) and WSMoV, part of the nucleocapsid (N) protein gene and the complete noncoding region upstream of the N gene's coding sequence were cloned and sequenced. Comparative sequence analysis of 291-bp region of the N gene revealed that the genus Tospovirus infecting ridge gourd shared maximum identity both at nucleotide (94%) and amino acid (97%) levels with the corresponding region of Watermelon bud necrosis virus (WBNV), which is a distinct species of WSMoV serogroup infecting watermelon in India (1). In contrast, only 76 to 81% and 82% identity at nucleotide and amino acid levels, respectively, was observed with the corresponding region of the N genes of GBNV and WSMoV. Natural infection of WBNV in cucurbits except watermelon in India is not known. To our knowledge, this is the first report of natural infection of ridge gourd by WBNV.

References: (1) R. K. Jain et al. Arch. Virol. 143:1637, 1998. (2) J. W. Moyer. Tospoviruses (Bunyaviridae). Pages 1803–1807 in: Encyclopedia of Virology. A. Granoff and R. G. Webster, eds. Academic Press, New York, 1999.
First Report of an Elm Yellows Subgroup 16SrV-C Phytoplasma Infecting Grapevine in Serbia
Authors: Duduk B. , Ivanovic M. , Dukic N. , Botti S. , Bertaccini A.
Published: May 2007

During a 2002 survey in Serbia, samples of grapevine (Vitis vinifera) were collected from plants showing typical phytoplasma-like symptoms: leaf roll, leaf redness, vein chlorosis and necrosis, and absence of lignification. The material was collected from one viticultural region (Zupa Aleksandrovac), where the disease was recorded in 2000 and showed an increasing percentage of symptomatic plants every year. Total nucleic acid was extracted separately from leaf midveins and stem bark collected from 10 symptomatic and 2 asymptomatic plants. Phytoplasma infection was detected using polymerase chain reaction (PCR) assays with universal primer pair P1/P7 for the amplification of phytoplasma 16S rRNA gene, and primer pair FD9f2/FD9r followed by FD9f3/FD9r2 in nested PCR for specific amplification of the FD9 nonribosomal DNA fragment of the EY-group (1). Phytoplasmas were detected in 9 of 10 midvein extracts from symptomatic grapevines (three of cv. Plovdina, two of cv. Smederevka, and four of cv. Gamé). Also, 6 of 10 bark preparations representing stem collections from the same plants were positive (two samples of cv. Plovdina, both samples of cv. Smederevka, and two samples of cv. Gamé). Both collections of midveins and bark tissues from asymptomatic plants were negative. Fragments amplified with universal P1/P7 primers (16S-23S rDNA) were analyzed by restriction fragment length polymorphism with TruI and TaqI restriction enzymes. The phytoplasmas produced identical restriction profiles to those of 16SrV Elm Yellows group and 16SrV-C Flavescence doreé subgroup (2). To our knowledge, this is the first report of phytoplasma infecting grapevines in Serbia, and the first survey in progress to verify the presence of Scaphoideus titanus to determine if this grapevine yellows could be defined as Flavescence dorée.

References: (1) E. Angelini et al. Vitis 40:79, 2001. (2) M. Martini et al. Mol. Cell. Probes 16:197, 2002.
First Report of a Field Outbreak of a Bacterial Leaf Spot of Cantaloupe and Squash Caused by Pseudomonas syringae pv. syringae in Georgia
Authors: Langston D. B. , Sanders F. H. , Brock J. H. , Gitaitis R. D. , Flanders J. T. , Beard G. H.
Published: May 2007

In March 2000, a leaf spot was reported affecting yellow summer squash (Cucurbita pepo) and cantaloupe (Cucumis melo) in commercial fields in Colquitt, Echols, and Grady counties in Georgia. All of the crops affected were reported within a 10-day period, and average temperatures during that time were 8 to 22.5°C, which is very close to the 50-year normal temperatures for these areas located in southwest Georgia. Incidence in affected fields was 100%. Lesions on squash leaves appeared irregularly shaped, dark, water soaked, somewhat vein restricted, and were 5 to 10 mm in diameter. Lesions on cantaloupe were angular, light tan, and necrotic with a lesion diameter of 2 to 5 mm. A general chlorosis was observed around lesions of both crops. Leaf distortion was observed on squash. Four isolates collected were used in biochemical, pathogenicity, and physiological tests. Gram-negative, rod-shaped bacteria were isolated from diseased tissue from squash and cantaloupes. Bacteria were aerobic, catalase-positive, fluorescent on King's medium B (1), oxidase-negative, nonpectolytic on potato, arginine dihydrolase-negative, utilized sucrose as a carbon source, produced levan, and gave a hypersensitivity response on tobacco (HR). Analysis of fatty acid methyl ester (FAME) profiles using the Microbial identification system (Sherlock version 3.1, Microbial identification system, Newark, DE) characterized representative strains as Pseudomonas syringae (similarity indices 0.65 to 0.80). Upon further characterization, the strains were negative for l (+)-tartarate utilization but utilized l-lactate and betaine and also exhibited ice nucleation activity. These characteristics are consistent with those of Pseudomonas syringae pv. syringae. Squash and cantaloupes were grown in a greenhouse for 4 weeks. Bacteria were grown in nutrient broth, resuspended in sterile tap water, and standardized using a spectrophotometer. Plants were inoculated by infiltrating leaves with 1 ml of bacterial suspensions (1 × 107 CFU/ml) using sterile syringes. Sterile water was used as a negative control, and 1 ml was infiltrated into leaves of squash and cantaloupes. Water-soaked lesions developed in 4 to 6 days on squash and cantaloupes inoculated with bacterial suspensions, and Pseudomonas syringae pv. syringae was isolated from diseased tissue. No symptoms developed on squash and cantaloupes used as negative controls. This outbreak of Pseudomonas syringae pv. syringae did not cause significant economic damage to either crop as symptoms subsided once daily high temperatures reached 28 to 32°C. This disease has been isolated from several cucurbit transplants reared in greenhouses, but to our knowledge, this is the first report of this disease occurring in the field.

Reference: (1) E. O. King et al. J. Lab. Clin. Med. 44:301, 1954.
Long-Term Monitoring for Resistance of Botryotinia fuckeliana to Anilinopyrimidine, Phenylpyrrole, and Hydroxyanilide Fungicides in Switzerland
Authors: Baroffio Catherine A. , Siegfried Werner , Hilber Urs W.
Published: May 2007

In Switzerland, the use of phenylpyrrole, anilinopyrimidine, and hydroxyanilide fungicides for control of Botryotinia fuckeliana, causal agent of gray mold in grapes, has been restricted to one treatment per fungicide class per year as part of an anti-resistance strategy. Resistance development in B. fuckeliana was monitored from 1995 to 2001 for the anilinopyrimidine cyprodinil and the phenylpyrrole fludioxonil and from 1997 to 2001 for the hydroxyanilide fenhexamid in experimental vineyards in Richterswil and Stäfa, Switzerland. In total, over 2,400 field isolates were tested. In 1996, the first case of field resistance to anilinopyrimidines was encountered in Richterswil. Efficacy of the anilinopyrimidine cyprodinil decreased significantly, and 54% of the isolates were resistant to anilinopyrimidines. During 7 years of monitoring, one field isolate was found that showed a slightly decreased sensitivity to the phenylpyrrole fludioxonil. Resistance to the hydroxyanilide fenhexamid was not found in 1997 and 1998. From 1999 to 2001, the level of fenhexamid-resistant isolates increased to 100% in Stäfa. The analysis of monitoring and efficacy data showed that subpopulations of B. fuckeliana resistant to cyprodinil and fenhexamid have increased significantly; however, the efficacy of a mixture of fludioxonil and cyprodinil and of fenhexamid alone was still effective. The objective of this study was to initiate long-term monitoring in order to establish an early resistance-detection system as a tool to assess the effectiveness of the anti-resistance strategy used in Switzerland.
Increase in Populations of Rhizoctonia solani and Wirestem of Collard with Velvet Bean Cover Crop Mulch
Authors: Keinath Anthony P. , Harrison Howard F. , Marino Paul C. , Jackson D. Michael , Pullaro Thomas C.
Published: May 2007

Velvet bean has been used traditionally as a summer cover crop in the southeastern United States. We investigated the use of killed velvet bean as a cover crop mulch left on the soil surface before collard was transplanted in the fall. Control treatments were weed-free fallow and velvet bean that was killed and disked into the soil before transplanting. Incidence of wirestem, caused by Rhizoctonia solani, reached a maximum of 25% in 2000 but only 4% in 2001 in cover crop mulch treatments. Nevertheless, in both years, the infection rate, area under the disease progress curve, and final incidence were significantly greater with cover crop mulch than in the fallow or disked treatments. Wirestem incidence did not differ between the disked and fallow treatments in either year. Populations of R. solani in soil were greater after cover crop mulch than in fallow plots in both years and greater in the disked treatment than in fallow soil in 2000 but not 2001. Velvet bean does not appear to be suitable as an organic mulch for fall collard production, but could be used as a summer cover crop if disked into the soil before transplanting collard.
Environmental Factors Affecting Rose Downy Mildew and Development of a Forecasting Model for a Nursery Production System
Authors: Aegerter B. J. , Nuñez J. J. , Davis R. M.
Published: May 2007

The effect of various environmental parameters on rose downy mildew caused by Peronospora sparsa was determined under controlled conditions and in the field. In growth chambers, optimal temperatures for infection and colonization of rose leaves were 15 to 20°C and 20 to 25°C, respectively. At optimal temperatures, infection required only 2 h of leaf wetness, although disease severity increased significantly with an increasing duration of leaf wetness up to 10 h. Infection of leaves occurred at temperatures as low as 5°C with 8 h of leaf wetness. The latent period of infection varied from 4 to 7 days. Weather and disease incidence data collected from natural field epidemics were used in the development of a predictive model of rose downy mildew. Logistic regression was used to identify those weather variables that explained the largest portion of the variation in disease incidence. The optimum regression model incorporated three weather variables calculated as cumulative totals over the previous 10 days: (i) hours of leaf wetness when temperatures were less than 20°C (positive correlation); (ii) hours between 15 and 20°C (negative correlation); and (iii) hours when temperatures exceeded 30°C (negative correlation). The simplest model, which was also a good fit, included only the 10-day cumulative number of hours of leaf wetness. The critical number of hours of leaf wetness for disease development was an average of 8.4 h per day over 10 days.
Outbreaks of Alternaria Brown Spot of Citrus in Brazil and Argentina
Authors: Peres N. A. R. , Agostini J. P. , Timmer L. W.
Published: May 2007

Alternaria alternata (Fr.) Keissler causes lesions on leaves, twigs, and fruit and reduces yield and fruit quality of many tangerines (Citrus reticulata) and their hybrids (2). Severe outbreaks of Alternaria brown spot were observed on ‘Murcott’ tangor (Citrus reticulata × Citrus sinensis) trees in southern São Paulo, southern Minas Gerais states in Brazil, and in Misiones and Corrientes provinces in Argentina. A single diseased ‘Fortune’ tangerine tree was observed in a grove in Misiones. On young leaves, brown-to-black lesions often expanded to cover large parts of the leaf, causing abscission of young shoots and dieback of twigs. Lesions were often surrounded by yellow halos. On fruit, dark specks from 0.2 to 0.5 cm were observed, and severe infection caused premature fruit abscission. Isolations were made on potato dextrose agar (PDA) after surface sterilization of leaf and fruit tissues in 1.5% sodium hypochlorite for 1 min. Plates were incubated at 27°C in the dark for 1 week. Isolated colonies were olive brown to black, and the fungus was stimulated to form conidia by scraping the surface of the mycelium. The pathogen was a typical small-spored Alternaria species, and the morphological characteristics of the conidia and conidiophores fit the description of A. alternata. Inoculation of three detached young shoots of ‘Murcott’ with a conidial suspension (105 conidia per ml) confirmed pathogenicity of three isolates obtained from widely separated groves in southern and eastern São Paulo State in Brazil and one from Misiones Province in Argentina. A control treatment with an equal number of shoots was sprayed with distilled water only. After 48 h, all isolates caused dark lesions on the leaves, characteristic of the disease. Symptoms were observed on inoculated, but not on control shoots. Koch's postulates were satisfied by reisolation of the fungus from symptomatic tissue in all cases. Although Alternaria brown spot was reported previously in neighboring Rio de Janeiro, Brazil on ‘Dancy’ and ‘Ponkan’ tangerines (1), serious disease problems now occur on ‘Murcott’, an important commercial variety in the major production area in Brazil. To our knowledge, this is the first report of Alternaria brown spot in Argentina.

References: (1) A. de Goes et al. Fitopatologia Brasileira 26(Suppl.):386, 2001. (2) L. W. Timmer et al. Pages 19–21 in: Compendium of Citrus Diseases. 2nd ed. L. W. Timmer, S. M. Garnsey, and J. H. Graham, eds. The American Phytopathological Society, St. Paul, MN, 2000.
Detection ofPyricularia griseaCausing Gray Leaf Spot of Perennial Ryegrass Turf by a Rapid Immuno-Recognition Assay
Authors: Uddin W. , Viji G. , Schumann G. L. , Boyd S. H.
Published: May 2007

An immuno-recognition assay using a monoclonal antibody was developed to detect Pyricularia grisea, the causal agent of gray leaf spot of perennial ryegrass (Lolium perenne). In vitro assays with isolates of P. grisea from perennial ryegrass, tall fescue (Festuca arundinacea), St. Augustinegrass (Stenotaphrum secundatum), crabgrass (Digitaria sanguinalis), finger millet (Eleusine coracana), wheat (Triticum aestivum), triticale (× Triticosecale rimpaui), and rice (Oryza sativa) showed positive reactions; however, the strength of the reactions differed among isolates. Reactions were more intense with isolates from perennial ryegrass, wheat, and triticale. All P. grisea isolates from perennial ryegrass collected from various regions of the United States showed positive reactions. P. grisea was detected at antigen dilution rates of 0.5×, 0.25×, 0.13×, 0.06×, and 0.03×. Dot-blot assays with Bipolaris sorokiniana, Colletotrichum graminicola, Curvularia lunata, Microdochium nivale, Pythium aphanidermatum, Rhizoctonia solani, or Sclerotinia homoeocarpa isolated from turfgrasses were negative. In vivo assays of symptomatic leaves of perennial ryegrass plants inoculated with P. grisea also showed positive reactions, and those inoculated with B. sorokiniana, P. aphanidermatum, R. solani, or S. homoeocarpa were negative. Intensity of reaction between the monoclonal antibody and P. grisea was proportional to disease severity in perennial ryegrass inoculated with P. grisea; however, there was no reaction in dot blots of leaf tissue collected during the latent period. P. grisea was detected in perennial ryegrass samples from golf course fairways affected by gray leaf spot in Connecticut, Massachusetts, Maine, New Jersey, Pennsylvania, and Rhode Island using this procedure. The monoclonal antibody recognition system is highly sensitive to P. grisea and can be used effectively for the rapid diagnosis of gray leaf spot of perennial ryegrass turf.
Application of Azoxystrobin for Control of Benomyl-Resistant Guignardia citricarpa on ‘Valencia’ Oranges in South Africa
Authors: Schutte G. C. , Mansfield R. I. , Smith H. , Beeton K. V.
Published: May 2007

Azoxystrobin was evaluated in replicated small-plot trials from 1995 to 1999 for control of citrus black spot (CBS) on ‘Valencia’ oranges caused by Guignardia citricarpa. Applications of different rates of tank mixes of azoxystrobin and mancozeb during the susceptible period from October to January were compared with an untreated control as well as the standard four applications of mancozeb with or without mineral oil (1.20 g a.i./liter + 0.5% [vol/vol]/liter and 1.60 g a.i./liter of water, respectively). Two applications of azoxystrobin in tank mixtures with mancozeb and mineral oil (0.5% [vol/vol]/liter) in mid-November and mid-January at rates of 0.10, 0.15, and 0.20 g a.i./liter controlled CBS by more than 98 to 99%, 99 to 100% and 95 to 98%, respectively. Concomitantly, where mineral oil was not added to the fungicide mixture, azoxystrobin and mancozeb resulted only in 73 to 95%, 74 to 93% and 92.2 to 92.3% CBS control, respectively. Tank mixtures of benomyl, mancozeb, and mineral oil reduced CBS by only 29%, which could be attributed to the presence of benomyl-resistant pathogen isolates in the experimental orchard. Azoxystrobin applied at rates of 0.05, 0.075, and 0.10 g a.i./liter in tank mixtures with mancozeb (1.2 g a.i./liter) and mineral oil (0.5% [vol/vol]/liter of water) or Agral 90 (0.5% [vol/vol]/liter of water) were equally effective, reducing CBS by more than 99%. When mineral oil was compared to different adjuvants in tank mixtures with azoxystrobin and mancozeb, only mineral oil resulted in 100% clean exportable fruit. There was no difference between Sunspray 6E and Bac oil when mixed with azoxystrobin and mancozeb on the degree of disease control. Furthermore, the concentration of mineral oil in water can be lowered from 0.5% (vol/vol)/liter of water to 0.3% (vol/vol)/liter of water without a loss in efficacy against CBS. It is therefore, recommended that azoxystrobin (0.075 g a.i./liter) must be applied in tank mixtures with mancozeb (1.2 g a.i./liter) and mineral oil, which can be applied at either 0.5% (vol/vol)/liter of water or 0.3% (vol/vol)/liter of water.
Biological Control of Septoria Leaf Spot Disease of Hybrid Poplar in the Field
Authors: Gyenis Laszlo , Anderson Neil A. , Ostry Michael E.
Published: May 2007

Biological control of Septoria leaf spot of hybrid poplars was investigated using disease-suppressive Streptomyces strains. Field experiments were conducted in 1998 and 1999 on potted trees placed in a hybrid poplar plantation near Rosemount, MN, and on field-planted trees in 1998 at St. Paul. At both locations, one resistant and three susceptible hybrid poplar clones were sprayed with Streptomyces spore suspensions and exposed to natural field inoculum of Septoria musiva. In the 1998 potted-tree experiment, strains GS-93-3, 93, and Mycostop in Tergitol or Triton X-100 solutions applied every 7 days significantly reduced leaf disease by 29 to 83% compared with the controls. In the 1999 potted-tree experiment, Streptomyces strain mixtures in Tergitol solution applied every 5 days significantly reduced leaf disease by 50 to 87% compared with the controls. In the 1998 plantation experiment, strains GS-93-3, 93, or Mycostop in Tergitol solution applied weekly, bi-monthly, or monthly significantly reduced leaf disease in all treatments by 64 to 78% compared with the controls.
Fusarium Head Blight Inoculum: Species Prevalence and Gibberella zeae Spore Type
Authors: Markell S. G. , Francl L. J.
Published: May 2007

The objectives of this study were to examine the relative abundance of Gibberella zeae ascospores and conidia and other Fusarium species on wheat spikes in a field environment, to relate inoculum counts of G. zeae to airborne spore counts, and to evaluate an inoculum bioassay technique. The inoculum levels of Fusarium species and airborne spores of G. zeae were measured in North Dakota during the 1999, 2000, and 2001 growing seasons. Spores were collected from wheat spikes in a 24-h potted-plant bioassay in a fallowed field and in a spring wheat plot bioassay. Inoculum levels of Fusarium species were assessed by placing a solution recovered from bioassays on selective medium; meanwhile, ascospores and conidia of G. zeae were enumerated microscopically. A Burkard cyclonic sampler measured airborne spore levels in the fallowed field. Wheat spikes were inoculated with known concentrations of conidia or ascospores, and rinsate was put on selective medium at different intervals to compare recovery rates. Known concentrations of both spore types were also applied directly to selective medium to compare with recovery of spore types from inoculated spikes. Fusarium graminearum was the most prevalent Fusarium species on wheat spikes, although F. moniliforme and F. poae counts were highest on some days. Approximately twice as many ascospores were recovered in both the 24-h potted-plant field bioassay and the cyclonic sampler as were conidia. Significantly more colonies were recovered from wheat spikes after conidial inoculation than after ascospore inoculation at an identical concentration regardless of time of rinsate collection. Colony numbers did not differ significantly following application of ascospores and conidia to selective medium. Results confirm the predominance of G. zeae inoculum in North America but indicate conidia play an important role in the primary disease cycle.
Effect of Crop Rotation on the Survival of Phytophthora capsici in Michigan
Authors: Lamour K. H. , Hausbeck M. K.
Published: May 2007

Phytophthora capsici is a limiting factor for some vegetable producers in Michigan despite crop rotation and fungicide applications. Our objective was to assess the effect of crop rotation on the survival of P. capsici at a naturally infested site in Michigan planted to cucumbers in 1998, corn in 1999 and 2000, and tomatoes in 2001. Isolates were characterized for compatibility type (CT), mefenoxam sensitivity, and amplified fragment length polymorphism (AFLP) marker profiles, and compared with isolates recovered from other locations in Michigan during the same time period. The A1:A2 CT ratio was 1:1, and approximately 60% of the isolates recovered in both years were intermediately sensitive or insensitive to mefenoxam. The majority of the isolates (89%) had unique AFLP fingerprints, and no members of the same clonal lineage were recovered among years. Isolates from this location were more similar to each other than to isolates from other locations in Michigan, and it was not possible to distinguish isolates based on the year of isolation. Genetic similarity analyses indicate that isolates from this location are part of a genetically distinct outcrossing population. These data indicate that P. capsici persisted as oospores for the 2 years between cucumbers and tomatoes, and that crop rotation and mefenoxam are not likely to provide economic control.
Occurrence of Nigrospora Lint Rot Caused by Nigrospora oryzae on Cotton in Alabama
Authors: Palmateer A. J. , McLean K. S. , van Santen E. , Morgan-Jones G.
Published: May 2007

During 2000 and 2001, a lint rot of cotton bolls (Gossypium hirsutum L.) was reported in the coastal region of Alabama when precipitation was 55% lower than the 5-year average. Bolls at an early stage of opening contained gray mycelium within the locules. At maturity, the lint within the infected locules was discolored, and the fibers were compact resulting in the characteristic “gray lock” sign and symptom attributed to Nigrospora oryzae (Berk. & Broome) Petch. Roots, petioles, leaves, and bolls when present were sampled at the seedling, first bloom, full bloom, and maturity stages of cotton development. A total of 640 sections of tissue (approximately 5 mm2) were surface sterilized for 20 s in 95% ethanol followed by 60 s in 0.525% NaOCl and aseptically plated on potato dextrose agar. Plates were incubated in the dark at 25°C for 3 to 10 days. N. oryzae was isolated at low frequencies from all plant tissues beginning at first bloom. Developing bolls at full bloom were colonized at a frequency of 48%. N. oryzae conidiophores were branched, flexuous, and pallid to brown with smooth walls 4 to 7 (5) μm thick. Conidiogenous cells were monoblastic, single, and 6 to 9 (7.5) μm in diameter. Conidia were single, smooth, broadly ellipsoidal, dark brown to black, single-celled, and 11 to 16 (14) μm in diameter (2). Principal component analysis was used to examine the relationship between disease incidence and weather parameters. Weather data was obtained from Auburn University Mesonet located in fields where the samples were collected. Principal components from weather data were ambient and soil maximum, minimum, and average temperature, maximum, minimum, and average relative humidity and precipitation. The first principal component, which is temperature, accounted for 61% of total joint variation among original observations. The second principal component, which was related to the moisture variables, accounted for 19% of the variation. The abundance of N. oryzae was correlated with the principal component factor moisture (r = -0.78**). The dry conditions experienced in this region were conducive to N. oryzae lint rot of cotton. This disease has been reported on cotton primarily in arid climates typical of the southwestern United States (1). To our knowledge, this is the first report of N. oryzae lint rot in the southeastern United States.

References: (1) W. E. Batson. Boll rots. Pages 36–38 in: Compendium of Cotton Diseases. T. L. Kirkpatrick and C. S. Rothrock, eds. The American Phytopathological Society, St. Paul, MN. 2001. (2) M. B. Ellis. Dematiaceous Hyphomycetes, CAB, Kew, Surrey, England, 1971.
First Report of Web Blight on Yellow-Sage (Lantana camara) Caused by Rhizoctonia solani in Europe
Authors: Garibaldi A. , Minuto A. , Bertetti D. , Nicoletti R. , Gullino M. L.
Published: May 2007

Lantana camara is increasingly grown in northern Italy as a potted plant and contributes to the diversification of offerings in the ornamental market. During the spring of 2001, selections of L. camara cuttings growing at a commercial farm located at Albenga (Riviera coast) exhibited tan leaf spots of irregular size and shape. Spots were at first isolated, 4 to 8 mm in diameter, and later coalesced and affected the entire plant. Heavily infected leaves, stems, and branches became blighted and were killed. Infected rooted cuttings also eventually died. Diseased cuttings showed a progressive reduction (to less than 20%) in rooting ability. Isolations from infected leaves and stems on potato dextrose agar (PDA), supplemented with 100 mg/liter of streptomycin sulphate, consistently yielded a fungus with mycelial and cultural characteristics resembling Rhizoctonia solani. The fungal isolates were further characterized as R. solani Kühn AG-4 based on hyphal anastomoses with several AG-4 tester isolates. Pathogenicity tests were performed by placing 5-day-old-fungal mycelial plugs, grown on PDA, at the base of five healthy yellow-sage stems and holding plants in a dew chamber at 18 to 22°C. After 2 days, foliage blight appeared on leaves of inoculated plants, and after 3 days, stems also became infected and entire plants wilted. Five noninoculated plants remained healthy. The fungal pathogen was reisolated from all inoculated plants. R. solani has been observed on L. camara in the United States (1) and the Philippines (2). To our knowledge, this is the first report of R. solani on L. camara in Europe.

References: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989. (2) F. T. Orillo and R. B. Valdez. Philipp. Agric. A. 42:292, 1958.