bluuebunny/crossref_metadata_2025 huggingface dataset:
Outbreak of Erwinia carotovora on Zantedischia spp. in South Africa
Authors: Mansvelt E. L. , Carstens E.
Published: May 2007

In South Africa, summer-flowering Arum lilies are grown for the tuber, potted plant, and cut flower markets. In 1998, an outbreak of soft rot was detected on Zantedischia oculata cv. Black Magic and Z. elliottiana plants from several nurseries. Crop losses of up to 25% were incurred. The initial symptom was wilting of leaves. When plants were lifted from the soil, soft rot of the tuber was found. Tuber rot usually developed on one side, and plants developing from affected tubers wilted and died. No discoloration of leaf or tuber tissues was found. Isolations from diseased tissues consistently yielded bacterial colonies that were translucent, white, and glistening and that had entire margins on nutrient agar. Ten representative isolates were chosen for further characterization. Erwinia carotovora subsp. carotovora strain B56 was included as a reference strain. All isolates were gram-negative rods, oxidase and arginine dihydrolase negative, catalase positive, and facultatively anaerobic. They degraded pectate and rotted potato slices but did not hydrolyze starch. All isolates fermented glucose, reduced nitrates to nitrites, and grew at a maximum temperature of 37°C. Isolates produced acids from D(+)-glucose, D(+)-cellobiose, melibiose, amygdalin, L(+)-arabinose, D-mannitol, L(+)-rhamnose, sucrose, ribose, D(-)xylose, and D(-)glucose but not from D-arabinose, D-sorbitol, or maltose. Isolates liquefied gelatin and used citrate, arbutine, esculin, salicin, and cellobiose as the sole carbon source. Pathogenicity to Zantedischia spp. was tested by injection of tubers with an inoculum suspension containing 108 CFU/ml. Control plants were inoculated with sterile distilled water. Inoculated plants were kept in a greenhouse at 24°C. Symptoms developed 2 days after inoculation with the pathogen and appeared to be identical to those observed on diseased material in nurseries. Control plants did not rot. The bacterium was readily reisolated from diseased plants, confirmed to be the inoculated pathogen, and identified as E. carotovora, based on morphological, biochemical, and physiological characteristics and pathogenicity. E. aroideae has been reported to cause soft rot of rhizomes of winter-flowering Arum lilies (Z. aethiopica) in South Africa (1). However, this is the first report of soft rot caused by E. carotovora subsp. carotovora on tubers of Z. oculata and Z. elliottiana plants in South Africa.

Reference: (1) V. Wager. 1970. Flower Garden Diseases and Pests. Purnell, Cape Town, South Africa.
Fluctuations of Prunus Necrotic Ringspot Virus (PNRSV) at Various Phenological Stages in Peach Cultivars
Authors: Zotto A. Dal , Nome S. F. , Di Rienzo J. A. , Docampo D. M.
Published: May 2007

Fluctuations in Prunus necrotic ringspot virus (PNRSV) concentration were researched in single plants of six peach (Prunus persicae) cultivars—Kurakata, Red Haven, Nectar Red, Start Delicious, Meadowlark, and Loadel—by double antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) of dormant buds (May, June), flowers (September), new sprouts (November), and mature leaves (January) (Southern Hemisphere). The optimum extract dilution (sample weight per buffer volume) to detect the virus was also quantified. The average absorbance patterns of the six cultivars show a steady increase in virus concentration, ranging from A 405nm 0.61 in May to A 405nm 0.86 in July for dormant buds, to A 405nm 1.22 in September in flowers, to 1.53 in November in new sprouts, where the highest concentration was found. Virus concentrations in mature leaves drop to values similar to those of noninfected plants in January ( A405nm 0.12). The yearly average (six noninfected peach trees) ranged from A405nm 0.04 to A405nm 0.08. This drop coincides with an increase in summer temperature and attenuates foliation symptoms caused by PNRSV. Analysis of dormants buds, flowers, or new sprouts with 5-cm-long leaves was reliable to differentiate infected from noninfected plants. Cluster analysis of absorbance profiles for single plants of cvs. Loadel and Meadowlark, however, showed a comparatively low profile, with a drop at flowering time (A405nm 0.20 in September) close to the average of healthy controls. The difference between infected and healthy plants did not become apparent in all cultivars from the analysis of plants at a given phenological stage, for example by the analysis of flower only, the material most preferred to diagnose the virus. Therefore, plants should be analyzed during flowering and sprouting or flowering and dormancy (dormant buds).
First Report of Leaf Blight on Sweet Persimmon Tree by Pestalotiopsis theae in Spain
Authors: Tuset J. J. , Hinarejos C. , Mira J. L.
Published: May 2007

During July 1998, a leaf blight caused by Pestalotiopsis theae (Saw.) Stey. was observed at an incidence of 18 to 20% in sweet persimmon (Diospyros kaki L.fil.) orchards in Huelva Province (southwestern Spain). Symptoms appeared on leaves as large grayish brown circular ringspots. Usually, they were solitary, but occasionally, two to three spots occurred on an affected leaf. In severe cases, lesions developed on more than one-third of the leaf, resulting in defoliation. Small black acervular conidiomata were visible in the surface of spots. These conidiomata produced fusiform conidia that were straight or rarely curved, four five-celled euseptate, including three olivaceous or dark brown median cells, and hyaline apical and basal cells with appendages that were slightly constricted at septa. Conidiomata were up to 240 μm in diameter; conidiogenous cells were 6 to 13 × 1.2 to 2.8 μm; conidia were 24.7 × 7.8 μm; three median cells were 16.7 μm long; two to three apical appendages (rarely four) were 28.3 μm long; and straight basal appendage was 5.7 μm. P. theae was consistently isolated on potato dextrose agar from diseased leaves and conidiomata. To confirm pathogenicity, both mycelial plugs and a conidial suspension (1.5 × 106 conidia per ml) of the fungus were used as inocula. Young completely developed leaves from persimmon tree cvs. Sharon and Hanafuyu were inoculated in the laboratory and maintained in a moist chamber for 5 days. Lesions resembling symptoms that occurred in the field were observed on leaves after 5 days. Symptoms were not observed on control leaves inoculated with agar media or sprayed with water. The fungus reisolated from diseased leaves was identical to the original isolates. Based on the morphological characteristics of conidiomata and conidia as well as pathogenicity, the fungus was identified as P. theae (1). This is the first report of this fungus as a pathogen of D. kaki in Europe. Possibly the introduction of P. theae to Spain has been through young imported persimmon plants. Unusual climatic conditions (heavy rainfalls during 1997 in southwestern Spain) have been favorable for disease development. The hot and dry conditions that usually occur during flowering, growing, and maturation of persimmon fruits normally prevent dissemination of inoculum and infection of leaves. For these reasons, the wet areas of southwestern Spain could be more favorable for “grey blight” of persimmon trees.

Reference: (1) T.-H. Chang et al. Korean J. Plant Pathol. 12:377, 1996.
First Report of Glomerella Leaf Spot (Glomerella cingulata) of Apple in the United States
Authors: González E. , Sutton T. B.
Published: May 2007

In August 1998, severe leaf spot, resulting in extensive defoliation, was observed on cv. Gala apple trees in two orchards in eastern Tennessee. Symptoms were similar to those reported in Brazil for Glomerella leaf spot on Gala (1), and Glomerella cingulata (Stoneman) Spauld. & H. Schrenk was observed fruiting in lesions. Single-ascospore isolates were obtained by placing individual perithecia from different lesions on microscope slides in a drop of sterilized distilled water. Perithecia were crushed, and the spore and mycelial suspension was distributed on the surface of petri dishes containing acid-water agar (AWA). Petri dishes were incubated at 24°C in light for 24 h. Germinated ascospores were transferred to petri dishes containing AWA. Cultures were transferred to potato dextrose agar and grown at 24°C in light for 14 days to induce sporulation. Four isolates (TN-1A, TN-1B, TN-2A, and TN-2B) were selected for pathogenicity tests. Three virulent isolates from Brazil (FK6, R-11, and 2VGE) also were included. Trees of apple cvs. Gala and Golden Delicious were placed in humidity chambers before inoculation. After 24 h, shoots on three trees of each cultivar were sprayed with an aqueous spore suspension of each isolate (1× 105 spores per ml) and maintained at 100% relative humidity (RH) and ≈22°C for 2 days. Shoots on three trees sprayed with sterilized distilled water and maintained at 100% RH served as a control. All isolates from Brazil and isolates TN-1A and TN-1B caused symptoms characteristic of Glomerella leaf spot on both cultivars after 2 days. Five days after inoculation disease severity on each leaf was visually rated on a scale of 0 to 5 (where 0 = no lesions and 5 = 25 to 50% of leaf surface covered with lesions). FK6 and R-11 were the most aggressive isolates on both cultivars. 2VGE and TN-1B were the least aggressive isolates.

Reference: (1) T. B. Sutton and R.M. Sanhueza. Plant Dis. 82:267, 1998.
Assessment of Soil Suppressiveness to Aphanomyces Root Rot of Pea
Authors: Persson L. , Larsson-Wikström M. , Gerhardson B.
Published: May 2007

The ability of field soils to suppress pea root rot caused by Aphanomyces euteiches was assessed in field soil samples in a greenhouse bioassay and in field experiments sown with pea in monoculture for four years. In the bioassay, an inoculum of oospores in talcum powder was added to the test soils 1 week prior to sowing of pea seeds. The rate of infection was assessed 4 weeks after sowing. The field experiments were placed in six localities with varying degrees of soil suppressiveness to pea root rot and the pea yield and number of oospores of A. euteiches in root tissue were measured each year. A large variation in disease suppression was found in 24 arbitrarily chosen soils, sampled in the vining pea growing area in southern Sweden, and some soils were found to be strongly disease suppressive. The pea root rot development was also clearly different between the field experiments, depending on the soil. In an experiment on a soil showing low disease suppressiveness in the greenhouse bioassay, the crop failed in the second year, the number of oospores in root tissue increased rapidly over time, and no yield at all could be taken the fourth year. In contrast, on a soil with a high disease suppressiveness in the bioassay, the pea monoculture led to a slow build-up of oospores in root tissue and a steady high yield of 5,300 kg/ha the fourth year.
Root Colonization of Soybean Cultivars in the Field by Fusarium solani f. sp. glycines
Authors: Luo Y. , Myers O. , Lightfoot D. A. , Schmidt M. E.
Published: May 2007

Soybean sudden death syndrome (SDS), caused by Fusarium solani f. sp. glycines, is a problem in some soybean-growing areas in the United States. Resistance is an important control strategy. In this study, root colonization of six soybean cultivars by F. solani f. sp. glycines was determined. Cultivars included susceptible P3981, CM497, and Spencer and field resistant LS90-1920, Pharaoh, and Ripley. All cultivars were tested in field experiments at different locations in southern Illinois in 1997 and 1998. Roots were collected at six sampling times and were dried and ground to isolate and enumerate the pathogen on a selective medium. SDS foliar disease index (FDX), the area under the F. solani f. sp. glycines population curve (AUPC), the incidence of colonized roots at 45 days after planting (RCI45), and the root colonization rate (RCR) were used to compare cultivars. FDX on the three resistant cultivars was significantly lower than on the three susceptible cultivars. Means of AUPC on the three resistant cultivars were significantly lower than those on the susceptible CM497 and P3981. RCI45 of Pharaoh was significantly lower than those of P3981 and Spencer. RCRs of all three resistant cultivars were significantly lower than that of P3981, and RCR of Ripley was also significantly lower than that of CM497. Based on combination of all cultivars, AUPC was significantly correlated with RCI45 and RCR.
Comparison of Assays for Measuring Sensitivity of Phytophthora infestans Isolates to Fungicides
Authors: Sedegui M. , Carroll R. B. , Morehart A. L. , Hamlen R. A. , Power R. J.
Published: May 2007

Pathogenic strains of Phytophthora infestans insensitive to phenylamide have been reported from around the world and are responsible for a lack of late blight control in both potatoes and tomatoes. In vivo laboratory assay methods used to determine the sensitivity of P. infestans to fungicides include floating of leaflet disks on fungicide suspension and the use of potato tuber disks. In our study, these two methods were compared with a new detached-leaf assay. The fungicides chlorothalonil (protective), oxadixyl and metalaxyl (systemic), and cymoxanil (locally systemic) were utilized. Phenylamide-insensitive and -sensitive genotypes of P. infestans were used as inoculum. Significant differences between preventive and systemic fungicides were found, and all assay methods differentiated between phenylamide-sensitive and -insensitive genotypes of P. infestans. Differences among assays were significant when comparing mean inhibitory values. There was no significant difference between the detached leaf and the tuber disk assay, but both methods were significantly different from the floating-leaflet disk assay.
First Report of Bacterial Blight of Mulberries Caused by Pseudomonas syringae pv. mori in the Eastern Anatolia Region of Turkey
Authors: Sahin F. , Kotan R. , Dönmez M. F.
Published: May 2007

During spring 1999, a severe bacterial blight disease was observed on white mulberry (Morus alba L.) trees grown in the Erzincan, Erzurum, and Artvin provinces in the eastern Anatolia region of Turkey. Initial symptoms appeared as small, water-soaked spots on leaves and shoots. The spots eventually expanded and resulted in dark brown to black, elongated, stripe-like lesions on shoots. Diseased leaves wilted at the twig tips and later died. Disease incidence was close to 100% in the regions surveyed. Fluorescent bacteria were isolated consistently from lesions on diseased leaves and shoots on King's medium B. Morphological and biochemical characteristics of 16 presumptive strains tested were rod-shaped, aerobic, gram negative, oxidase negative, and catalase and levan positive. None of the strains reduced nitrate or hydrolyzed gelatin. All strains were confirmed as Pseudomonas syringae by gas-chromatography fatty acid methyl ester (GC-FAME) analysis, with a similarity index ranging from 0.82 to 0.94. The pathogen was identified as P. syringae pv. mori based on pathogenicity tests performed by spray-inoculating healthy leaves (M. alba cv. Beyaz Dut) on 1-year-old host twigs with suspensions of 108 CFU/ml each strain (2). Inoculated plants and sterile water-sprayed controls were maintained in a greenhouse at 18 to 28°C. Plants were covered with polyethylene bags for 48 h after inoculation. Within 7 to 10 days, necrotic spots typical of those found in the nursery were observed on inoculated leaves. No symptoms were seen on control plants. The pathogen was reisolated from lesions on inoculated leaves. Recovered strains were identical to initial strains, based on morphological and biochemical tests and GC-FAME analysis. To our knowledge, the occurrence and incidence of this disease in different geographic regions of Turkey, except the central Anatolia and Aegean regions, have not been studied (1). This is the first report of bacterial blight of mulberries at high incidence in the eastern Anatolia region of Turkey.

References: (1) K. Türkolu and Y. E. Öktem. Plant Prot. Bull 13:19, 1973. (2) J. M. Young et al. N. Z.J. Agric. Res. 21:159, 1978.
Widespread Occurrence of Common Rust, Caused by Puccinia sorghi, on Rp-Resistant Sweet Corn in the Midwestern United States
Authors: Pataky J. K. , Tracy W. F.
Published: May 2007

Single, dominant resistance genes have been used successfully for the past 15 years to control common rust, caused by Puccinia sorghi, on sweet corn in the United States. Most sweet corn hybrids grown in the Midwest for mid- to late-season processing have Rp resistance, which is expressed as hypersensitive reactions resulting in chlorotic or necrotic flecks with little or no formation of urediniospores. Many, but not all, Rp-resistant sweet corn hybrids carry the gene Rp1D. Biotypes of P. sorghi in North America have been avirulent on plants with the Rp1D gene, except for an isolate collected in Kansas in 1990 (1). In a sweet corn nursery in Urbana, IL, in 1997, small uredinia of P. sorghi occurred on 27 of 79 Rp-resistant sweet corn hybrids that also were infected severely with southern rust caused by P. polysora (2). During August and September 1999, small uredinia or fully susceptible reactions to common rust were observed on several Rp-resistant sweet corn hybrids grown in an area bounded by Mendota, IL, Ripon, WI, and Le Sueur, MN. Southern rust also was prevalent and frequently severe in the area. Isolates of P. sorghi from Rp-resistant corn were collected during September 1999 from Mendota, Rock Falls, and Dekalb, IL; Sun Prairie, Madison, and Ripon, WI; and Rochester, Stanton, and Le Sueur, MN. Ten two-leaved seedlings of one susceptible sweet corn hybrid and five Rp-resistant hybrids, including hybrids known to carry the gene Rp1D, were inoculated in greenhouse trials. Each location (collection) was a separate trial. Inocula were prepared from several uredinia of P. sorghi per location. One set of seedlings also was inoculated with P. polysora. Susceptible reactions (uredinia with urediniospores) were observed on all inoculated seedlings. Uredinia and urediniospores of P. sorghi and P. polysora from seedlings inoculated in the greenhouse were compared directly. All isolates of P. sorghi were confirmed based on 6- to 7-day latent periods, formation of uredinia on both leaf surfaces, and urediniospores that were mostly spherical, cinnamon colored, and moderately echinulate. This is the first widespread occurrence in North America of a biotype of P. sorghi that is virulent on Rp-resistant sweet corn.

References: (1) S. H. Hulbert et al. Plant Dis. 75:1130, 1991. (2) J. K. Pataky et al. Purdue Univ. AES Bull. No. 758:99, 1997.
Influence of Ammonium Sulfate and Rotation Crops on Strawberry Black Root Rot
Authors: Elmer Wade H. , LaMondia James A.
Published: May 2007

The combined effects of rotation crops and nitrogen fertilizers were examined on the strawberry black root rot disease complex. In July 1995, microplots were filled with soil that had a history of strawberry black root rot and seeded with two types of oats (Avena strigosa ‘Saia oats’ or A. sativa ‘Garry oats’) or with sorgho-sudangrass (Sorghum bicolor × S. sudanense ‘Triple S’). Microplots planted with 1-year-old ‘Honeoye’ strawberry crowns served as the controls. In May 1996, the crops were chopped and incorporated into the soil. The soil was re-planted with 1-year-old strawberry ‘Honeoye’ crowns and then fertilized with (NH4)2SO4 or Ca(NO3)2 at equivalent rates of N. Two months later, (NH4)2SO4-treated plants had 36% more leaf area and 41% more runners than strawberries treated with Ca(NO3)2 Strawberries that had been pre- cropped with ‘Saia’ oats had 135% more runners and 38% more early fruit yield than strawberries grown in control microplots. Total fruit yield was not affected by the treatments. Compared to Ca(NO3)2, the (NH4)2SO4 treatment reduced the percentage of blackened roots. The influence of the cover crops on growth and disease was stronger with (NH4)2SO4 fertilization than with Ca(NO3)2 fertilization. Combining ‘Saia’ oats or sorgho-sudangrass rotation with (NH4)2SO4 fertilization reduced lesion nematode (Pratylenchus penetrans) numbers in subsequent strawberry roots when compared to controls. Also, the combination of ‘Saia’ or ‘Garry’ oats as a pre-crop with applications of (NH4)2SO4 reduced black root rot severity when compared to controls. Only the ‘Garry’ oat rotation reduced strawberry root colonization by Rhizoctonia fragariae when compared to controls. Other effects were associated with using (NH4)2SO4. The (NH4)2SO4 treatment lowered the rhizosphere soil pH by 0.2 units, reduced the numbers of fluorescent pseudomonads in the rhizosphere by 10- to 15-fold, and produced leaves that had more N, K, S, Mn, and Zn content than plants treated with Ca(NO3)2. Rotation with ‘Saia’ oats combined with (NH4)2SO4 fertilization may suppress strawberry black root rot and increase yields through multiple effects on the host, pathogens, and associated microflora.
Evaluation of Broccoli Residue Incorporation into Field Soil for Verticillium Wilt Control in Cauliflower
Authors: Subbarao Krishna V. , Hubbard Judith C. , Koike Steven T.
Published: May 2007

Wilt incited by Verticillium dahliae has recently become an important disease on cauliflower in the Salinas Valley. Although broccoli is closely related to cauliflower, wilt has not occurred on this host and V. dahliae isolates from cauliflower were weakly pathogenic on broccoli in greenhouse inoculations. In this study, the effectiveness of broccoli residues on propagule attrition in soil and wilt incidence on cauliflower was determined in a commercial field infested with V. dahliae microsclerotia. The treatments were broccoli residue with tarp, broccoli residue without tarp, chloropicrin, metham sodium, control with tarp, control without tarp, cauliflower followed by cauliflower, and cauliflower followed by fallow. Approximately 200 kg of chopped broccoli was uniformly disk incorporated into the corresponding plots (36 m2). Densities of V. dahliae microsclerotia were determined at 0, 30, 90, and 145 days after treatment in 1993 and 0, 30, 74, 109, and 140 days after treatment in 1994 using the modified Anderson sampler technique. Cauliflower cultivar White Rock was planted in all plots. Plant height, number of marketable heads, head weight, and wilt severity were determined at maturity. Even though the pre-treatment number of V. dahliae propagules in broccoli-treated and control plots were similar, by the end of the cauliflower cropping season numbers either were the same or increased in control plots compared with a reduction in numbers in broccoli residue-treated plots during both seasons. There were no differences between tarped and non-tarped plots either in broccoli residue-treated or control plots. In fumigated plots, propagules declined initially but later returned to pre-treatment levels by the end of the cropping season. Continuous cauliflower or fallowing after one cauliflower crop resulted in stable or increased levels of microsclerotia. Verticillium wilt severity was lowest in metham sodium-treated plots, followed by broccoli residue-treated plots and chloropicrin in both years. Plant height, marketable heads, and head weight were higher in broccoli-treated than in control plots. These results suggest that broccoli residues reduce V. dahliae microsclerotia in soil and wilt of cauliflower as much as or more than chloropicrin and metham sodium, and that rotation with broccoli may be a feasible approach to manage Verticillium wilt in cauliflower and other susceptible crops.
Comparison of Fumonisin Concentrations in Kernels of Transgenic Bt Maize Hybrids and Nontransgenic Hybrids
Authors: Munkvold Gary P. , Hellmich Richard L. , Rice Larry G.
Published: May 2007

Maize hybrids genetically engineered with genes from the bacterium Bacillus thuringiensis (Bt maize) express CryIA(b) and other Cry proteins that are toxic to certain insects, particularly the European corn borer (Ostrinia nubilalis). Maize kernel feeding by O. nubilalis often leads to infection by fungi in the genus Fusarium, including the fumonisin-producing species F. verticillioides and F. proliferatum. In field experiments in 1995, 1996, and 1997, transgenic maize hybrids and near-isogenic, nontransgenic hybrids were manually infested with neonatal European corn borer larvae. Manual infestation increased Fusarium ear rot severity and fumonisin concentrations in kernels of nontransgenic hybrids. Transgenic hybrids with kernel expression of CryIA(b) consistently experienced less insect feeding on kernels and less Fusarium ear rot than their nontransgenic counterparts. In manually infested treatments, these hybrids also exhibited lower concentrations of fumonisins in kernels compared with their nontransgenic counterparts. In manually infested treatments in 1995, mean fumonisin B1 concentrations were 8.8 μg/g in the nontransgenic hybrid and 6.7 or 3.0 μg/g in transgenic hybrids. In 1996, mean fumonisin B1 concentrations in manually infested treatments were 4.9 μg/g (range 2.3 to 8.8) for nontransgenic and 1.2 μg/g (range 1.0 to 1.3) for transgenic hybrids with kernel expression. Mean total fumonisin concentrations (fumonisin B1 + B2 + B3) were 7.0 μg/g (range 3.0 to 12.2) for nontransgenic and 1.7 μg/g (range 1.5 to 1.9) for transgenic hybrids with kernel expression. In 1997, mean fumonisin B1 concentrations in manually infested treatments were 11.8 μg/g (range 7.6 to 17.3) for nontransgenic and 1.3 μg/g (range 0.8 to 2.2) for transgenic hybrids with kernel expression of CryIA(b) or Cry9C. Mean total fumonisin concentrations were 16.5 μg/g (range 10.7 to 24.0) for nontransgenic and 2.1 μg/g (range 1.5 to 3.1) for transgenic hybrids with kernel expression. Transgenic hybrids that do not express CryIA(b) or Cry9C in kernels did not consistently have fumonisin concentrations different from the nontransgenic hybrids. Higher fumonisin concentrations in nontransgenic hybrids were associated with high European corn borer populations during the early reproductive stages of the maize plants. These results indicate that under some conditions, genetic engineering of maize for insect resistance may enhance its safety for animal and human consumption.
Fusarium Head Blight of Cultivated and Natural Wild Rice (Zizania palustris) in Minnesota Caused by Fusarium graminearum and Associated Fusarium spp.
Authors: Nyvall R. F. , Percich J. A. , Mirocha C. J.
Published: May 2007

Symptoms of Fusarium head blight on diseased wild rice seed from both cultivated fields and natural stands are shrunken, light weight seeds discolored light tan to light brown with infrequent light pink due to mycelial growth of Fusarium spp. F. graminearum was the predominant species isolated from whole seed at all growth stages, and from shattered seed gathered from four fields in 1994 to 1995. F. anthophilum and F. subglutinans were also frequently isolated at most growth stages, whereas F. acuminatum, F. culmorum, F. solani, and F. semitectum were infrequently isolated at one or more growth stages, and F. camptoceras was isolated only from shattered seed. F. graminearum was the only species isolated from processed seed, although rarely. Fusarium spp. were isolated at the highest percentage from shattered seed. The highest percentage of total Fusarium spp. isolated during seed development was at the milk and dough stages in a cultivated field and at the milk stage in a natural stand; the percentage then declined until the ripe stage in seed from both sites. There were no significant differences in the percentages of Fusarium spp. isolated at growth stages between seed from the cultivated field and from the natural stand. Fusarium spp. were isolated most frequently from whole seed grown in three cultivated fields, compared with the palea and lemma, and caryopsis. F. graminearum and F. anthophilum were frequently isolated from whole seed and all seed structures, whereas F. culmorum and F. sporotrichioides were isolated only from whole seed, F. moniliforme from whole seed, palea and lemma, and caryopsis, and F. subglutinans from whole seed and the palea and lemma only. Deoxynivalenol and nivalenol were identified in three isolates of F. graminearum; however, none of the seed samples from which the isolates were obtained yielded either mycotoxin. Survival of Fusarium spp. in diseased seed was similar from both cultivated and natural sources and occurs in whole seed not immersed in water but not in seed immersed in water.Survival was better in seed stored at 4°C than at −20°C. F. graminearum was reisolated from 81% of seed from inoculated plants but not from seed of noninoculated plants. Pathogenicity of other Fusarium spp. remains to be demonstrated.
Bacterial Blight of Leek: A New Disease in California Caused by Pseudomonas syringae
Authors: Koike Steven T. , Barak Jeri D. , Henderson Diana M. , Gilbertson Robert L.
Published: May 2007

During 1996 and 1997, a new and damaging disease of leek (Allium porrum) was observed on greenhouse-produced transplants and field-grown plants in California. Symptoms were water-soaked lesions at leaf tips, which eventually expanded down the length of the leaf and resulted in brown, elongated, stripe-like lesions with yellow margins. Diseased leaves eventually wilted. A blue fluorescent pseudomonad was consistently recovered from lesions, and biochemical and physiological tests indicated that it was Pseudomonas syringae. Pathogenicity tests established that representative strains of this P. syringae induced disease symptoms in leek that were similar to those observed on leek plants in the greenhouse and field, and that this bacterium caused similar symptoms in onion, chives, and garlic plants. Representative strains were further characterized by fatty acid analysis, repetitive bacterial sequence-polymerase chain reaction (rep-PCR), and rDNA sequencing. Fatty acid analysis confirmed that these isolates were P. syringae, but did not provide a clear pathovar designation. Rep-PCR analysis revealed that all the California leek P. syringae strains had identical DNA fingerprints and that these strains were indistinguishable from those of known strains of P. syringae pv. porri. In addition, the rDNA sequence of the spacer region between 16S and 23S rDNA genes was identical among the California leek P. syringae strains and P. syringae pv. porri. Together, these results established that the new leek disease in California is caused by P. syringae pv. porri. P. syringae pv. porri was recovered from a commercial leek seed lot imported into California, which suggests that the pathogen was introduced in association with seed. Commercial leek production in California is favorable for development of this disease because transplants are produced in greenhouses with high plant densities, overhead irrigation, and mowing of plants.
A Closterovirus (Family: Closteroviridae) Isolated from Tobacco Crops in Northern Greece (Macedonia)
Authors: Chatzivassiliou E. K. , Katis N. I. , Tchomguia M. , Peters D.
Published: May 2007

In 1997, viruslike symptoms similar to those caused by potato potyvirus Y (PVY) were observed in tobacco (Nicotiana tabacum ) plants of the cv. Basmas in the area of Drama (Macedonia) in northern Greece. Diseased plants showed vein clearing and necrosis of the petioles and main veins, and were severely stunted. Serological tests with polyclonal antibodies prepared against PVY, cucumber mosaic cucumovirus (CMV), alfalfa mosaic alfamovirus (AMV), and tomato spotted wilt tospovirus (TSWV) gave negative results. The virus was mechanically transmitted from infected field tobacco plants to plants of N. tabacum cvs. White Burley, Samsun NN, Xanthi, Christie, and Basmas, and to plants of the species N. benthamiana, N. clevelandii, N. glutinosa, N. roselata, and N. rustica. All tobacco species and cultivars generally reacted with chlorotic local lesions on the inoculated leaves followed by systemic vein clearing, often veinal necrosis, leaf curling, and severe stunting. Similar symptoms were produced on Petunia hybrida. Other plant species such as beet, faba beans, lettuce, tomato, Datura stramonium, and watermelon were not infected by the virus. Aphid transmission studies with Myzus persicae showed that the virus was transmitted in a semi-persistent manner. Electron microscopic observations of leaf squash preparations from infected plants revealed the presence of long, filamentous, virus particles of 1,600 to 1,800 nm in length, typical for the family Closteroviridae. The virus was partially purified in a process in which the extract was treated with Triton for 1 h at 4°C, followed by two cycles of high-speed centifugation on a 20-40-60 % sucrose cushion. The virus was denaturated on CsCl or CsSO 4 gradients. The results show that the virus isolated is the first member in the Closteroviridae reported to naturally infect N. tabacum.
Spring Dead Spot of Buffalograss Caused by Ophiosphaerella herpotricha in Kansas and Oklahoma
Authors: Tisserat N. , Wetzel H. , Fry J. , Martin D. L.
Published: May 2007

Buffalograss (Buchloe dactyloides) is widely planted in the Great Plains region of the United States as an amenity turfgrass. In May 1993, we observed circular dead spots in buffalograss lawns that were resuming growth following winter dormancy. The dead spots, 12 to 40 cm in diameter, were slowly filled in by buffalograss during the summer but reappeared in the same locations the following spring. Roots and stolons at the patch margins were colonized by darkly pigmented, ectotrophic fungal hyphae. Ophiosphaerella herpotricha, a cause of spring dead spot disease of bermudagrass (Cynodon spp.), was consistently isolated from diseased buffalograss roots collected in Kansas and Oklahoma. Identification of O. herpotricha was confirmed by the use of species-specific polymerase chain reaction (PCR) primers. To complete Koch's postulates, a 3-year-old stand of buffalograss cv. Sharp's Improved located in Manhattan, KS, was inoculated in September 1994 with O. herpotricha. Eleven soil cores, 10 cm in diameter × 8 cm deep, were removed at 1.2-m intervals across the turf. Five grams of oat seed infested with O. herpotricha (isolate KS221) wasadded to each hole and the soil plug was reinserted. For controls, 5 g of sterile oat seed was inserted in the bottom of each of 11 additional holes. No symptoms developed the following spring, but circular dead spots, ranging in size from 18 to 43 cm in diameter, were observed at 10 of 11 and 6 of 11 inoculation sites in May 1996 and 1997, respectively. No spots were noted in areas amended with sterile oats. O. herpotricha was consistently isolated from the roots at the margins of the patches. This is the first report of O. herpotricha causing spring dead spot in buffalograss.
Epidemiology of Mango Malformation in Guerrero, México, with Traditional and Integrated Management
Authors: Noriega-Cantú D. H. , Téliz D. , Mora-Aguilera G. , Rodríguez-Alcazar J. , Zavaleta-Mejía E. , Otero-Colinas G. , Campbell C. Lee
Published: May 2007

The temporal progress of malformation (MM) of mango (Mangifera indica) was studied from 1993 to 1995 with three management technologies applied to commercial plantations in North Guerrero, Mexico. Management influenced shoot production and thus determined the dynamics of epidemics. Environmental factors also affected disease incidence, particularly through an apparent effect on inoculum dispersal. In general, integrated management (IM), consisting of pruning, acaricide, and fungicide sprays, resulted in slower rates of epidemic development, lower levels of initial and final disease, and lesser areas under the disease progress curves. In the first cycle, IM increased yield per tree by 51% in relation to high technology (HT) and 74% in relation to lower traditional technology (LT), representing a benefit-cost rate of 2.8 and 3.3, respectively. Change of malformation incidence was correlated positively with the number of macroconidia of Fusarium sp. trapped in the canopy (r = 0.90, P = 0.0001) and wind speed (r = 0.83, P = 0.0001); both variables lagged over a 4-month period. The greatest change in malformation occurred during the main vegetative flush, which occurred 3 to 6 months after picking the fruit (May). The accumulated proportion of diseased shoots was correlated with the following variables measured over a 1-week period: average maximum daily temperature (r = -0.68, P = 0. 01), average temperature per hour (r = -0.59, P = 0.04), average number of hours with relative humidity ≥60% (r = -0.82, P = 0.001), and wind speed (r = 0.94, P = 0.0001). In general, the greatest spore density was found during the rainy season, with a morning periodicity showing the highest correlation with wind speed (r = 0.812, P = 0.0001). F. subglutinans was isolated consistently from diseased (86%) and asymptomatic (5%) vegetative and flowering shoots.
Comparison of Greenhouse and Field Testing to Identify Wheat Resistant to Tan Spot
Authors: Evans C. K. , Hunger R. M. , Siegerist W. C.
Published: May 2007

Incorporation of tan spot resistance into adapted wheat (Triticum aestivum) lines requires screening procedures in the greenhouse and field that correctly identify reaction to tan spot. This study compares greenhouse (seedling) and field (adult plants) testing of wheat lines for reaction to tan spot following inoculation with conidia by Pyrenophora tritici-repentis. Mistirrigation was used to provide adequate moisture for infection by P. tritici-repentis in the greenhouse and in the field. Reaction of seedlings to tan spot in the greenhouse was measured by lesion length. Area under the disease progress curve (AUDPC) was used to determine reaction in the field. The effect of tan spot on grain yield and kernel weight was determined by comparing inoculated with fungicide-sprayed split-plot values. In greenhouse tests, lesion length ranged from 1.2 to 4.1 mm. Lesions were 1.2 mm long on Red Chief, a tan spot-resistant check. Lesions were 3.6 mm long on TAM 105, a tan spot-susceptible check. Four breeder lines had levels of seedling (greenhouse) resistance nearly equal to that of Red Chief. Ranks of lesion length and field assessments of the AUDPC were significantly correlated (r = 0.75 to 0.93, P ≤0.05). Thus, greenhouse assessment was useful for screening large numbers of wheat genotypes for reaction to tan spot and identifying selected entries for further screening in the field. Mean grain yield from P. tritici-repentis inoculated plots was approximately 15% less than yield from fungicide-sprayed plots. Kernel weight was reduced an average of 7 and 13% at two field locations.
The Relationship of Gin Date to Aflatoxin Contamination of Cottonseed in Arizona
Authors: Bock C. H. , Cotty P. J.
Published: May 2007

During 1995 and 1996, a commercial gin in western Arizona ginned seed cotton on a field-by-field basis. Seed from each field was kept separate until sampled and analyzed for aflatoxin content according to Arizona Commercial Feed Law. This gave a comprehensive view of field-to-field variability in aflatoxin content as the season progressed. Regression analysis indicated significant relationships between gin date and aflatoxin content in both years: aflatoxin increased with later ginnning. Overall, 89 and 79% of seed lots exceeded 20 ppb in 1995 and 1996, respectively. No field ginned after Julian Day (JD) 273 in 1995 or after JD 267 in 1996 had an aflatoxin content <20 ppb. Means separation confirmed later ginned crops had significantly greater aflatoxin content (P = 0.05). In 1996, transgenic Bt and non-Bt cottonseed were similarly contaminated. Mean aflatoxin content of Bt cottonseed in 1996 was 413 ppb and that of non-Bt cottonseed was 598 ppb. These observations suggest that, in Arizona, losses from aflatoxin contamination of cottonseed can be reduced by early harvest.
A New Virus on Maize in Nigeria: Maize Mild Mottle Virus
Authors: Thottappilly G. , Qiu W. P. , Batten J. S. , Hughes J. N. , Scholthof K.-B. G.
Published: May 2007

Maize (Zea mays) and itch grass (Rottboellia cochinchinensis) plants exhibiting a mild mosaic or mottle were collected from a farmer's field near Mokwa, Nigeria, in 1993. Icosahedral virions (approximately 28 to 30 nm) were purified from symptomatic tissue by differential centrifugation in 0.1 M phosphate buffer, pH 7.0. The virions are composed of one single-stranded positive-sense RNA of approximately 4,000 nucleotides and, as estimated by 12.5% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), a capsid protein of approximately 28 kDa. The virus was readily detected in infected plants by enzyme-linked immunosorbent assay and immunoblot assays with a polyclonal rabbit antibody derived from purified virions. A partial cDNA library was generated with random primers. Sequence analyses of a cDNA clone representing a portion of the putative replicase gene aligned most closely with related sequences of viruses within the Tombusviridae. In particular, a region of 78 predicted amino acids surrounding the “GDD” replicase motif shares 73% identity with panicum mosaic virus and 61% identity with maize chlorotic mottle virus. The virus is readily transmitted by mechanical inoculation to sweet and dent corn, millet, and wheat. Currently it is not considered of economic importance in Nigeria. The data suggest that “maize mild mottle virus” is a newly identified virus infecting maize.
Occurrence of Witches'-Broom, a New Phytoplasma Disease of Acid Lime (Citrus aurantifolia) in India
Authors: Ghosh D. K. , Das A. K. , Singh Shyam , Singh S. J. , Ahlawat Y. S.
Published: May 2007

In India, acid lime (Citrus aurantifolia (L.) Swingle) is one of the most important citrus fruits grown. It constitutes nearly 20% of the total citrus production. During 1995, an unusual type of disease was observed on a 6-year-old acid lime plant in an orchard in the Nagpur District in eastern Maharashtra. It was named witches'-broom disease (WBD) to reflect the most conspicuous symptom. Other symptoms included small chlorotic leaves, highly proliferated shoots, and shortened internodes. Leaves dropped prematurely and infected twigs were distorted. In advanced stages, infected branches had dieback symptoms. WBD of lime has been reported from Oman and UAE (1) and the causal phytoplasma was designated “Candidatus Phytoplasma aurantifolia” (2). Subsequent surveys in 1995-1998 revealed disease incidences as high as 5% in Maharashtra and in other major acid-lime-growing states—Andhra Pradesh, Tamilnadu, and Karnataka. After the grafting of infected acid lime shoots, disease symptoms developed on Troyer citrange, rough lemon, and Rangpur lime, but not on sweet orange (mosambi), mandarin (Nagpur), or trifoliate orange. The WBD agent was transmitted from infected acid lime to periwinkle (Catharanthus roseus) plants and vice versa by dodder (Cuscuta reflexa). Ultrathin sections of leaf midrib of infected acid lime plants were fixed on copper grids, stained with uranyl acetate and lead acetate, and examined in a JEM 100S transmission electron microscope. Numerous bodies having the characteristic morphology of phytoplasmas were observed in phloem sieve tubes of acid lime in diseased but not in healthy leaves. The phytoplasmal bodies ranged from 100 to 800 nm in diameter and were bounded by a poorly defined membrance. Freehand transverse sections of young internode regions of a WBD-infected periwinkle plant were stained in DAPI (4′, 6 diamidino-2-phenylindole; 1.0 μg/ml) and were observed with a fluorescent microscope (Leica). An intense bluish-white fluorescence in the phloem elements of diseased periwinkle and its absence in healthy samples were consistent with the presence of phytoplasmas. This is the first report of phytoplasma-induced witches'-broom disease of acid lime in India.

References: (1) M. Garnier et al. Plant Dis. 75:546, 1991. (2) L. Zreik et al. Int. J. Syst. Bacteriol. 45:449,1995.
First Report of Tomato Yellow Leaf Curl Virus in Réunion Island
Authors: Peterschmitt M. , Granier M. , Mekdoud R. , Dalmon A. , Gambin O. , Vayssieres J. F. , Reynaud B.
Published: May 2007

In September 1997, stunting, reduced leaf size, leaf curling, and yellow margins were observed on tomato plants on a farm on the south coast of Réunion, a French island belonging to the Mascarenes archipelago. To our knowledge, these symptoms appeared to be characteristic of a tomato yellow leaf curl virus (TYLCV) infection. Diseased plants gave positive reactions with a triple antibody sandwich-enzyme-linked immunosorbent assay (TAS-ELISA), using ADGEN antibodies specific for begomoviruses (1). The serological results were confirmed by polymerase chain reaction (PCR) with a pair of degenerate primers—MP16, 5′-CCTCTAGATAATATTAC(C/T)(G/T)(G/A)(A/T)(T/G)G(G/A)CC-3′ and MP82, 5′-CGGAATTC(T/C)TGNAC(C/T)TT(G/A)CANGGNCC(T/C)T C(G/A)CA-3′—designed by Malla Padidam (ILTAB, San Diego, CA) to amplify a region of the A component of begomoviruses, between the intergenic conserved nonanucleotide sequence (TAATATTAC) and the first 5′ quarter of the capsid protein gene. A 500-bp PCR product was obtained from a symptomatic plant but not from a healthy looking one. After cloning the PCR product in a pGEM-T Easy vector (Promega, Madison, WI) and sequencing it with plasmid-specific primers (SP6, T7), the sequence was compared with the sequences of the NCBI data base, with the use of BLAST. Nineteen sequences among those producing the highest scoring segment pairs were compared with each other and with the 500-bp PCR product from Réunion by the Clustal method of MegAlign (DNASTAR, London). The Réunion sequence (AJ010790) was at least 94% similar to sequences of TYLCV isolates from the Dominican Republic (AF024715), Cuba (AJ223505), and Israel (X15656, X76319 for the mild clone). Based on these results, it appeared that the analyzed tomato plant was infected by a geminivirus isolate belonging to the Israeli species of TYLCV. A preliminary survey was carried out from December 1997 to April 1998 in both outdoor and protected tomato crops. Infected plants were detected by TAS-ELISA in 52 of the 123 locations visited. Severe economic losses were observed: 14 locations with 60 to 100% yield reduction and 11 locations with 40 to 60% yield reduction. All the infected samples were collected in the leeward coast, which is the driest region of the island. Although Bemisia tabaci (Gennadius) has been recorded since 1938 in Réunion (2), it has been observed on tomato crops only since 1997 and population levels were low compared with those of Trialeurodes vaporariorum Westwood. During the first six months of 1998, B. tabaci was found on Euphorbia heterophylla L., Lantana camara L., Solanum melongena L., S. nigrum L., and Phaseolus vulgaris L. These host plants often occur near infected tomato crops.

References: (1) S. Macintosh et al. Ann. Appl. Biol. 121:297, 1992. (2) L. Russell and J. Etienne. Proc. Entomol. Soc. Wash. 87:202, 1985.
Rust Disease on Lemongrass in California
Authors: Koike S. T. , Molinar R. H.
Published: May 2007

Lemongrass (Cymbopogon citratus) is a minor crop grown for its edible stem and oil. The plant is grown both commercially, by specialty producers, and noncommercially, particularly by homeowners of various Asian communities. For several years, a rust disease has affected the lemongrass plantings in coastal and inland California. Symptoms consist of elongated, stripelike, dark brown lesions that develop on both sides of leaf surfaces. Only lesions on abaxial leaf surfaces erupt and develop dark cinnamon brown uredinial pustules. Lesion development can be substantial, and coalescing lesions result in significant foliage death. Ellipsoidal urediniospores measured 22 to 28 μm by 22 to 25 μm and contained 3 to 4 germ pores in an equatorial configuration. Uredinia contained clavate paraphyses. Teliospores were not observed. Based on the morphology of the uredinia and urediniospores, the rust was identified as Puccinia nakanishikii (1). Rust on lemongrass has been observed during various seasons, but this is the first report identifying the causal pathogen in California. A Darluca mycoparasite species was often observed in uredinia of infected lemongrass from the coastal counties. In the United States, P. nakanishikii has also been reported on lemongrass in Hawaii (2).

References: (1) G. B. Cummins. 1971. The Rust Fungi of Cereals, Grasses, and Bamboos, Springer-Verlag, New York. (2) D. E. Gardner. Plant Dis. 69:1100, 1985.