bluuebunny/crossref_metadata_2025 huggingface dataset:
Banana Die-Back Virus - a New Virus Infecting Banana in Nigeria
Authors: Hughes J. d'A. , Speijer P. R. , Olatunde O.
Published: May 2007

Two viruses naturally infect Musa in Nigeria: banana streak badnavirus (BSV) and cucumber mosaic cucumovirus (CMV). During a recent field survey at Ibadan (Nigeria), some severely stunted banana plants (cv. Valery) were found that tested negative for CMV, banana bunchy-top virus, and BSV. The plants had symptoms of leaf crinkling, leaf necrosis, and cigar-leaf die-back. Subsequent suckers from the same mats were progressively more stunted. A 28- to 30-nm isometric virus was purified, and used for the production of antibodies, from the affected plants with (NH4)2SO4 to precipitate the virus. The antiserum (titer of 1:10,000) was used in enzyme-linked immunosorbent assay and immunosorbent electron microscopy to detect the virus. Mechanical inoculation with partially purified virus preparations resulted in stunting and development of pinpoint chlorotic lesions on Vigna unguiculata TVu-76 and symptomless systemic infection of Nicotiana occidentalis. The virus was not mechanically transmissible from N. occidentalis to banana. A serological relationship between this virus, banana die-back virus (BDBV), and tobacco ringspot, tomato ringspot, and cacao necrosis nepoviruses was found. The nematode species around the affected banana plants were isolated: Helicotylenchus multicinctus (Cobb) Golden was the dominant species, low numbers of H. dihystera (Cobb) Sher were present, but no virustransmitting nematodes were found in soil or banana roots. Further studies are needed to determine the mode of spread of BDBV, the implications for banana/plantain production in sub-Saharan Africa, and the safe international movement of germplasm.
Effect of Temperature on Symptom Expression and Reliability of Banana Streak Badnavirus Detection in Naturally Infected Plantain and Banana (Musa spp.)
Authors: Dahal G. , Hughes J. d'A. , Thottappilly G. , Lockhart B. E. L.
Published: May 2007

The effect of temperature on symptom expression and detection of banana streak badnavirus (BSV) by immunosorbent electronmicroscopy (ISEM) and enzyme-linked immunosorbent assay of 12 in vitro-propagated plantain hybrids (genome AAB × AA), 3 ABB cooking banana, and 3 AAB plantain landraces was studied. Experiments were done for 2 years under two temperature regimes, 28 to 35°C in a screenhouse and 22°C in a temperature-controlled room. Most BSV-infected plants of plantain hybrids expressed symptoms under both conditions. Symptom expression was enhanced when plants were continuously grown at 22°C, but later became indiscernible when plants were continuously grown at 28 to 35°C. Plants grown at 22°C and showing severe symptoms contained significantly higher virus titer than plants grown at 28 to 35°C. When asymptomatic plants with very low virus titer at 28 to 35°C were transferred back to 22°C, there was a significant increase in both symptom severity and concentration of virus (greater than 3 to 5 times) in leaf tissues after 9 months. In contrast, the concentration of virus and symptom severity decreased in plants after transfer from 22°C to 28 to 35°C. Micropropagated plants of AAB plantain landrace cv. Mimi Abue and ABB cooking bananas (cvs. Bluggoe, Cardaba, and Pelipita) did not express visible symptoms under either temperature regime, but BSV was detected by ISEM in 23% of the plants. After 2 years at 22°C, virus was detected in 64% of the plants, but the concentration of virus remained low. Implications of these results on quarantine screening of in vitro plants and virus diagnosis are discussed.
Parasitism and Biological Control of Verticillium dahliae by Pythium oligandrum
Authors: Al-Rawahi A. K. , Hancock J. G.
Published: May 2007

Pythium oligandrum was a parasite of Verticillium dahliae in dual culture, impeding the latter's ability to grow and form microsclerotia. Variation occurred among isolates of P. oligandrum in their parasitism toward isolates of V. dahliae, and isolates of V. dahliae expressed a range of susceptibilities to parasitism by P. oligandrum. Temperature and matric potential significantly affected interactions between these fungi. Populations of P. oligandrum in the rhizosphere of pepper (Capsicum annuum) were similar in a potting soil infested and noninfested with V. dahliae, but the populations of V. dahliae in combined samples of rhizosphere and nonrhizosphere soil of pepper were significantly lower in the presence of P. oligandrum than in its absence. In greenhouse experiments with pepper grown in soil infested with V. dahliae, shoot and fruit weights were significantly higher in the presence of P. oligandrum than in its absence. However, when soil was infested only with P. oligandrum, fresh weights of shoots and fruits were 40 to 50% higher than when plants were grown in its absence, evidence that this fungus significantly promoted growth of this crop. Therefore, processes responsible for improved plant health associated with soil treatment with P. oligandrum could be the result of complex interactions between pathogen, host, and mycoparasite.
Histopathology and Within-Plant Distribution of the Phytoplasma Associated with Australian Papaya Dieback
Authors: Siddique A. B. M. , Guthrie J. N. , Walsh K. B. , White D. T. , Scott P. T.
Published: May 2007

Dieback-affected papaya plants were characterized by a discoloration of the contents of laticifers, while the anatomy of sieve elements was healthy in appearance until the necrotic stages of the disorder were reached. Laticifer discoloration was not always associated with the presence of phytoplasma in affected tissue, as judged by polymerase chain reaction (PCR) using primers based on the 16S rRNA gene and 16S-23S intergenic spacer region. Phytoplasma DNA was detected in a range of plant tissues, including roots, but not in mature leaves which would act as photoassimilate sources. As plants recovered from a dieback period, the extent of the distribution of both laticifer discoloration and phytoplasma DNA decreased. Phytoplasma cells were not observed in transmission electron microscopy studies of mature sieve elements of dieback-affected leaf, stem, or fruit tissue from plants at various stages of symptom expression, although PCR tests indicated the presence of phytoplasma DNA. Membrane-bound structures, similar in shape and size to phytoplasma cells but interpreted as autophagic vesicles or latex vesicles in immature laticifers, were observed within vacuoles of cells in phloem tissue in leaves displaying tissue breakdown in the form of a water-soaked appearance to veins (“X-Y” patterning). In contrast, phytoplasmas were readily observed in papaya leaves displaying symptoms of yellow crinkle. We conclude that phytoplasma cells are present in very low titer in dieback-affected tissues and that, while the plant appears to limit proliferation of the dieback-associated pathogen, this defense strategy is ultimately unsuccessful because it is associated with a rapid decline of the papaya plant.
Infection Studies of Mycosphaerella fijiensis on Banana and the Control of Black Sigatoka with Chlorothalonil
Authors: Washington J. R. , Cruz J. , Lopez F. , Fajardo M.
Published: May 2007

Infection studies with Mycosphaerella fijiensis, causal agent of black Sigatoka disease of banana (Musa AAA), demonstrated that the abaxial leaf surface is the primary infection site. Inoculation of banana plants with M. fijiensis ascospores on the abaxial surface of young leaves resulted in disease symptoms in 100% of the leaves inoculated within 18 to 30 days; whereas only 5% of the leaves inoculated on the adaxial surface showed black Sigatoka symptoms within 10 weeks. Disease symptoms appeared more rapidly on the new, emerging leaves than on the first and second fully expanded leaves. Application of chlorothalonil (1.08 kg a.i. ha-1) to the abaxial surface of emerging leaves resulted in 99 to 100% disease control in the treated area. When the emerging leaf was not sprayed until fully expanded, disease control was reduced to 76 to 80%. Application of chlorothalonil to the adaxial surface of banana leaves had little or no impact on disease control. Chlorothalonil arrested hyphal growth when applied to banana leaves after ascospores had already germinated and reduced the rate of lesion expansion when applied to the abaxial leaf surface after symptom appearance. Chlorothalonil was less effective than systemic fungicides in reducing production of M. fijiensis pseudothecia in infected tissue. When systemic and protectant fungicides were applied to infected leaf tissue, none of the fungicides affected the viability of ascospores that were discharged from pseudothecia produced in that tissue. For successful control of black Sigatoka with chlorothalonil, deposition of the fungicide on the abaxial leaf surface is essential.
Collar Rot of Peanut Caused by Lasiodiplodia theobromae
Authors: Phipps P. M. , Porter D. M.
Published: May 2007

In August and September of 1993, a collar rot disease of peanut was observed in several fields in Virginia and North Carolina. Only a few scattered plants exhibited symptoms and signs of the disease in Southampton County and Suffolk, Virginia, and Northampton County, North Carolina. The disease was severe at two farm sites in Dinwiddie County, Virginia where the affected areas exceeded 0.4 ha in size. Numerous plants were either chlorotic, wilted, or dead. Symptomatic plants exhibited blackened stem cankers and pods. Diseased stems and tap roots were easily shredded to reveal slate-gray to black internal tissues. Black, erumpent pycnidia were observed on stem lesions at the soil surface. Immature conidia were single-celled and hyaline. Mature conidia were two-celled and dark brown. Morphological features of the fungus on diseased plants and potato dextrose agar were consistent with descriptions of Lasiodiplodia theobromae (Diplodia gossypina). The fungus was isolated from discolored seed and asymptomatic seed from fields having plants which exhibited severe symptoms. Seed treatment with captan 1.125 g + pentachloronitrobenzene 0.375 g + carboxin 0.25 g a.i./kg reduced recovery of the fungus from seed, but did not eradicate the pathogen. This treatment on naturally infested seed provided significant early-season disease suppression and improved yield significantly in 1994. Season-long disease suppression and a significant yield increase were obtained in plots planted to fungicide-treated, commercial seed from non-infested fields. At-plant and mid-season applications of fungicides in 1994 and 1995 did not improve disease suppression over that of fungicide-treated, commercial seed. Overall, Virginia-type cultivars of peanut were more susceptible to collar rot than runner-type cultivars. Among the Virginia-type cultivars, NC-V 11 exhibited moderate susceptibility and the 79-X breeding line from Florida exhibited resistance. Georgia Browne and Southern Runner were the most resistant of the runner-type cultivars.
Resistance to Phytophthora citrophthora and P. parasitica and Nursery Characteristics of Several Citrus Rootstocks
Authors: Matheron M. E. , Wright G. C. , Porchas M.
Published: May 2007

Studies were conducted to compare existing and potential citrus rootstocks with respect to resistance to root rot and gummosis caused by Phytophthora citrophthora and P. parasitica in greenhouse and growth chamber experiments and horticultural performance under simulated nursery conditions. Depending upon rootstock and experiment, mean root weights resulting from inoculation with P. citrophthora were 27 to 96% lower than the comparable controls. In similar experiments with the same rootstocks, inoculation with P. parasitica resulted in root weights that were 38 to 95% less than weights of the noninoculated controls. During 1994 or 1995, mean root weight reduction compared with noninoculated plants among Citrus macrophylla, rough lemon, C. volkameriana, and Sunki mandarin × Flying Dragon trifoliate (62-109-19) attributable to P. citrophthora and mean root weight reduction among C. macrophylla, C. volkameriana, rough lemon, Sacaton citrumelo, Sunki mandarin × Flying Dragon trifoliate (62-109-19), African shaddock × Rubidoux trifoliate, and Shekwasha mandarin × English trifoliate attributable to P. parasitica were significantly less than those recorded for all other tested rootstocks. Rootstocks that sustained a low percentage of root weight reduction generally experienced a low percentage of shoot weight reduction and survived longer as well. In evaluation of resistance to gummosis, depending on rootstock and experiment, the mean length of stem lesions caused by P. citrophthora on rootstocks ranged from 0.2 to 25.0 mm, whereas values for P. parasitica ranged from 0.2 to 18.5 mm. Stem lesions smaller than 5 mm in length were recorded for 21 and 14 of 36 different rootstocks inoculated with P. citrophthora and P. parasitica, respectively. On the other hand, P. citrophthora and P. parasitica caused stem lesions of at least 10 mm in length on 8 and 16 citrus rootstocks, respectively. Desirable nursery characteristics, including vigorous growth, minimal branching, and high leaf chlorophyll content, were demonstrated most prominently by Gomiri rough lemon, C. volkameriana, and Benton citrange, and to a lesser degree by some other rootstocks. Possible factors that could account for inconsistent classification of some citrus rootstocks as susceptible or resistant to Phytophthora root rot and gummosis are discussed.
Seed Contamination Thresholds for Development of Carrot Bacterial Blight Caused by Xanthomonas campestris pv. carotae
Authors: Umesh K. C. , Davis R. M. , Gilbertson R. L.
Published: May 2007

The relationship between levels of carrot (Daucus carota subsp. sativus) seed contamination with Xanthomonas campestris pv. carotae and (i) establishment of populations of X. campestris pv. carotae on carrot leaves and (ii) the incidence and severity of carrot bacterial blight was determined in field plots in Davis, California, in 1995 and 1996. Levels of seed contamination ranged from 0 to 1.5 × 105 CFU/g in 1995 and from 0 to 1.5 × 107 CFU/g in 1996. Seed contamination levels were positively correlated with X. campestris pv. carotae populations detected on leaves and with the incidence and severity of carrot bacterial blight. The size of X. campestris pv. carotae populations on leaves was also directly related to disease incidence. In 1996, yields were significantly reduced in plots established with seed lots having the highest levels of X. campestris pv. carotae contamination. Under the conditions of this study (i.e., a location having low rainfall and relative humidity), the threshold of seed contamination for the establishment of X. campestris pv. carotae populations on leaves and for the development of carrot bacterial blight was unexpectedly high: 104 to 105 CFU/g of seed.
Serological Differentiation of the Citrus Tristeza Virus Isolates Causing Stem Pitting in Sweet Orange
Authors: Nikolaeva Olga V. , Karasev Alexander V. , Garnsey Stephen M. , Lee Richard F.
Published: May 2007

Citrus tristeza virus (CTV) complex comprises a number of isolates or strains producing several economically important disease syndromes in commercial Citrus spp. The stem pitting syndrome is the most important, and causes substantial losses in many citrus-producing regions of the world. In an attempt to develop a serological tool to rapidly differentiate stem pitting isolates of CTV, we evaluated many combinations of trapping and detecting antibodies in an indirect double-antibody sandwich (I-DAS) enzyme-linked immunosorbent assay (ELISA). Two combinations of trapping and detecting antibodies were found suitable for differentiating stem pitting isolates in extracts of infected sweet orange plants. One used a polyclonal serum raised against bacterially expressed CTV coat protein (CP) for trapping and a conformational monoclonal antibody 3E10 for detection, and the other used two polyclonal antisera generated against bacterially expressed CTV CP. Seventy-six CTV isolates from 20 countries, including 35 that cause stem pitting in sweet orange plants, were analyzed in I-DAS-ELISA using different combinations of polyclonal and monoclonal antibodies for trapping and as intermediate detecting antibodies. The ELISA format developed produces a strong positive signal for CTV isolates that cause stem pitting in sweet orange plants and a negative ELISA signal for CTV isolates that do not cause stem pitting. When combined with data on a universal ELISA format, i.e., reacting with a broad range of CTV isolates, these selective ELISA formats allowed reliable serological differentiation of CTV isolates that caused stem pitting in infected sweet orange plants.
A Tuber Rot of Cyperus esculentus Caused by Rosellinia necatrix
Authors: García-Jiménez J. , Busto J. , Vicent A. , Sales R. , Armengol J.
Published: May 2007

Tiger nut (Cyperus esculentus L.) is cultivated in Spain for the production of tiger nut milk. Over the past 5 years, important economic losses resulting from a new tuber rot have been observed near Valencia in eastern Spain. Affected tubers were covered by a white mycelium that turned black as the disease advanced, leading to a general rotting of tubers. Aboveground plant parts showed some early decay and under high-moisture environmental conditions the white mycelium was present on the soil surface. This mycelium showed pyriform swellings characteristic of Rosellinia necatrix Prill., and coremia were occasionally observed on external surfaces of tubers after incubation in a moist chamber for 1 to 2 months. Coremia produced small ellipsoid or obovoid single-celled conidia 3.7 to 5.0 × 2.0 to 2.2 μm. The teleomorph has not been observed. Pathogenicity tests were conducted with inoculum produced on wheat (Triticum aestivum L.) seeds that were soaked for 12 h in flasks filled with distilled water. Each flask contained 300 ml of seeds that were subsequently autoclaved after excess water was drained. Two fungal disks of a 2-week-old culture of R. necatrix grown on potato dextrose agar were placed aseptically in each flask. The flasks were incubated at 25°C for 4 weeks, and shaken once a week to avoid clustering of inoculum. Two plastic pots (35 cm in diameter) per isolate were filled with a sterilized mixture of equal portions (vol/vol) of soil, sand, and peat moss, and inoculum was added at a concentration of 30 g of infected wheat seeds per 1,200 g of substrate (1). Healthy tubers were surface disinfested in 1.5% (vol/vol) sodium hypochlorite for 1 min, washed twice in sterile water, sown, and subsequently thinned to one per pot after emergence. Plants were grown under field conditions. Six months after inoculation, symptomatic tubers appeared similar to those originally observed in the field. The fungus was reisolated from affected tubers, confirming Koch's postulates. Pathogenicity tests were also conducted on avocado (cv. Reed) and almond (cv. Garriges) seedlings, and apple rootstock (MM-106) as very susceptible host plants for R. necatrix (1). Inoculated plants showed symptoms of wilting and death 4 weeks after inoculation. The fungus was reisolated from affected plants. This is the first report of C. esculentus as a host of R. necatrix.

Reference: (1) A. Sztejnberg and Z. Madar. Plant Dis. 64: 662, 1980.
First Report of Pythium polymastum on Broccoli and Cauliflower in California
Authors: Aegerter B. J. , Davis R. M.
Published: May 2007

Damping-off of broccoli (Brassica oleracea var. italica) and cauliflower (B. oleracea var. botrytis) seedlings occurred in several greenhouses in Fresno, CA, in 1997. Symptoms included wilting and root and stem rot. Pythium polymastum was consistently isolated from symptomatic tissues placed on corn meal agar amended with 10 ppm pimaricin, 250 ppm ampicillin, 10 ppm rifampicin, and 25 ppm pentachloronitro-benzene. On grass leaves in water, the fungus produced numerous aplerotic oospores in oogonia 43 to 50 μm in diameter (average 46 μm) with spines about 7 μm long. Spherical sporangia were only rarely observed. In the greenhouse, 4-week-old broccoli and cauliflower seedlings were transplanted into potting mix amended with a colonized vermiculite/rye/V8 juice medium to produce approximately 2,500 CFUs per gram of potting medium. Control plants were transplanted into noninfested potting mix. There were six replicate pots per treatment and three plants per pot. After 12 days, the potting mix was gently washed from the roots and the seedlings were dried and weighed. Symptoms on inoculated plants included wilting, severe root rot, black streaks on the lower stems, and death. The fungus was recovered from symptomatic tissues. There were no symptoms on the control plants. Infection by P. polymastum reduced dry weights of surviving broccoli and cauliflower seedlings by 82 and 58%, respectively. Similar results were obtained in a second experiment. This fungus was previously characterized as a pathogen of both cultivated and wild crucifers in Canada (1). This is the first report of P. polymastum in California.

Reference: (1) T. C. Vanterpool. Can. J. Bot. 52:1205, 1974.
Rubus ellipticus, a Perennial Weed Host of Prunus Necrotic Ring Spot Virus in India
Authors: Sharma Anupama , Ram Raja , Zaidi A. A.
Published: May 2007

Rubus ellipticus is a perennial shrub occurring in natural vegetation of the temperate and subtropical Himalayas. For several years, plants of R. ellipticus in and around the Institute of Himalayan Bioresource Technology in Palampur were seen with mild mosaic and chlorotic symptoms on leaves followed by necrotic ring spots. Infected plants often recovered from the symptoms. The causal agent was mechanically transmissible to several herbaceous hosts including Cucumis sativus, Chenopodium album, C. quinoa, Cucurbita maxima, C. pepo, Melilotus alba, Trifolium repens, and Zinnia elegans. The virus incited chlorotic local lesions followed by systemic necrotic lesions or ring spots and severe stunting on C. sativus. Several aphid species (Myzus persicae, Aphis gossypii, A.fabae-solanella, Brevicoryne brassicae, and Macrosiphoniella sanbornii) were tried as viral vectors, but all failed to transmit the virus. Virus has been detected in pollen and fruit of infected plants. Ilarvirus-like particles, 27 nm in diameter, were observed in partially purified extracts of symptomatic plants of R. ellipticus and in experimentally infected C. sativus plants, but not in healthy plants. The isolate was distantly serologically related to apple mosaic virus and unrelated to tobacco streak virus. Presence of Prunus necrotic ring spot virus (PNRSV) in symptomatic plants was also confirmed by enzyme-linked immunosorbent assay with antiserum from American Type Culture Collection and Agdia, Inc. (Elkhart, IN). This is the first report of a viral disease in R. ellipticus. The presence of PNRSV in a new weed host may become an important constraint to production of susceptible agronomic crops around Palampur.
Integrated Management of Sclerotinia Blight in Peanut: Utilizing Canopy Morphology, Mechanical Pruning, and Fungicide Timing
Authors: Butzler Thomas M. , Bailey Jack , Beute Marvin K.
Published: May 2007

Sclerotinia blight of peanut, caused by Sclerotinia minor, generally becomes severe only after vines meet in the row middles and a dense canopy develops. Dense foliage appears to support a microclimate conducive to the colonization of peanut limbs by S. minor. Removal of excess foliage before and during a Sclerotinia blight epidemic on the susceptible genotype NC 7 has been shown to reduce the rate of disease progress. Field tests in 1993 and 1994 examined control of Sclerotinia blight among four peanut genotypes (NC 7, VA 93B, NC Ac 18016, and Tam-span 90) with diverse canopy morphologies. Each cultivar had foliage pruned with a rotary mower once (1993 and 1994) or twice (1994) during the season. Applications of fluazinam (9.2 kg a.i./ha) were imposed on the genotype × pruning treatments. Soil temperatures under the canopy of each genotype and pruning treatment were measured and compared. Disease data were collected weekly by counting the number of feet of plants exhibiting lesions with visible fungus growth. Tamspan 90, a resistant Spanish peanut, had the least Sclerotinia blight incidence. Pruning measurably affected soil temperature for approximately 2 weeks following pruning. Removal of foliage reduced disease and increased disease control affected by fluazi-nam in fields with high disease pressure. In some tests, yields were increased by pruning through a reduction in disease pressure. Yields were lower when peanuts were pruned excessively, especially late in the season. Pruning of excessive vine growth can be an alternative, or complement, to fungicide treatments when done in midseason during favorable weather when moderate to high disease pressure occurs.
Barley Yellow Dwarf Luteoviruses and Their Predominant Aphid Vectors in Winter Wheat Grown in South Carolina
Authors: Gray Stewart M. , Chapin Jay W. , Smith Dawn M. , Banerjee Nanditta , Thomas James S.
Published: May 2007

Barley yellow dwarf is recognized as an important disease problem in winter wheat production in the southeastern United States, but there is relatively little known about the ecology and epidemiology of barley yellow dwarf virus (BYDV) in this region. From 1991 to 1993, and in 1996 and 1997, winter wheat was sampled for BYDV throughout the principal wheat production areas in South Carolina. In addition, in 1997, a small number of samples were collected from fields in North Carolina and Kentucky. Plant samples were assayed to determine the BYDV serotype and, subsequently, coat protein sequences of isolates within the same serotype were compared using restriction fragment length polymorphisms. Representative BYDV isolates from South Carolina and type isolates from New York were compared in aphid transmission experiments using aphid species collected from South Carolina and laboratory colonies maintained in New York. The predominant BYDV serotype in South Carolina (in all years) was PAV, accounting for 94% of the total BYDV-infected samples analyzed. The RPV serotypes were more abundant in samples collected from western North Carolina and Kentucky. PAV isolates from all regions were identical to the New York BYDV-PAV in terms of serology and restriction fragment patterns. Furthermore, the aphid transmission phenotypes were similar for South Carolina and New York BYDV isolates. The predominant aphids colonizing winter wheat in South Carolina included Schizaphis graminum, Rhopalosiphum rufiabdominalis, R. padi, and Sitobion avenea. The South Carolina clones of R. padi and S. avenae were similar to the New York laboratory clones in their abilities to transmit various BYDV isolates from New York and South Carolina. In contrast to the New York clone of Schizaphis graminum that can vector SGV, PAV, and RPV, the S. graminum clone from South Carolina was not a vector of any BYDV serotype tested. R. rufiabdominalis was found to be an efficient vector of PAV, RPV, and RMV isolates, but did not transmit MAV or SGV.
Relationship Between Flag Leaf Symptoms Caused by Xanthomonas translucens pv. translucens and Subsequent Seed Transmission in Wheat
Authors: Tubajika K. M. , Tillman B. L. , Russin J. S. , Clark C. A. , Harrison S. A.
Published: May 2007

The relationship between foliar disease symptoms on parent plants, seed contamination by the causal bacterium (Xanthomonas translucens pv. translucens), and subsequent development of bacterial leaf streak in wheat was studied in microplots and in the laboratory to determine the role of seed transmission in disease epidemiology. Microplot experiments were carried out during the 1994-95 and 1995-96 growing seasons using seed harvested in Baton Rouge, Louisiana, in 1994 and 1995, respectively. Treatments were seed lots from plants with differing levels of bacterial leaf streak severity on the flag leaves of the parent tillers. X. translucens pv. translucens was detected in 1 to 20% of seed from susceptible cultivars Florida 304 and Savannah collected from plants with leaf streak symptoms. Correlations between seed contamination and disease on plants that developed from this seed were detected only when seed came from parent tillers that expressed flag leaf disease severity ≥15 to 20% in 1994-95 and ≥30 to 35% in 1995-96. However, symptoms of bacterial leaf streak on plants that developed from these seed were evident on only ≤3% of plants. Results suggest a possible threshold level for bacterial leaf streak on flag leaves that is necessary before X. translucens pv. translucens can be detected in seed. Seedling emergence in microplots correlated negatively with leaf streak severity on parent tiller flag leaves. Artificial infestation of seed with X. translucens pv. translucens also reduced seed germination, but this was more evident in Savannah than in Florida 304.
Occurrence of Pod Rot Pathogens in Peanuts Grown in North Carolina
Authors: Hollowell J. E. , Shew B. B. , Beute M. K. , Abad Z. G.
Published: May 2007

Pod rot diseases historically caused significant losses in peanut production in North Carolina. Advances in the understanding of pod rot diseases and changes in cultural practices minimized losses in the years since 1979. By the early 1990s, however, some peanut growers began to observe pod rot that apparently was not associated with infection by common soilborne pathogens. Incidence of pod rot also was high in research plots used to study conservation tillage methods. Selected farms were surveyed in the fall of 1994, 1995, and 1996 to identify the fungi associated with pod rot symptoms in North Carolina. Over the three years of the study, more than 6,000 symptomatic pods from 125 peanut fields were assayed for Rhizoctonia spp., Pythium spp., Cylindrocladium parasiticum, Sclerotium rolfsii, and Sclerotinia minor. All five pathogens were isolated during the field survey, with Pythium spp. and Rhizoctonia spp. isolated most frequently. Rhizoctonia spp. were the dominant pathogen in the majority of fields in 1994, whereas Pythium spp. predominated in 1995 and 1996. Combinations of pathogens were identified from 12 to 15% of pods; Rhizoctonia spp. + Pythium spp. and Pythium spp. + C. parasiti-cum were the most frequent combinations. The mean estimated incidence of pod rot was 6.6% in 1995 and 5.9% in 1996. The effects of cover crops and tillage on pod rot incidence were studied in microplots in 1995 and 1996. In 1995, winter cover crops (wheat, oat, rye, and fallow soil) did not affect pod rot incidence, but incidence was greater in no-till treatments compared to plots with conventional tillage. Pod rot incidence did not differ among infestation treatments and no interactions among pathogen, cover crop, or tillage treatments were significant. In contrast, significant (P = 0.04) interactions among winter cover crops and tillage occurred in 1996. Tillage did not affect pod rot incidence following wheat or oats, but incidence following rye was much greater in no-till than in tilled plots.
Effects of Onion Yellow Dwarf and Leek Yellow Stripe Viruses on Symptomatology and Yield Loss of Three French Garlic Cultivars
Authors: Lot Hervé , Chovelon Véronique , Souche Sylvie , Delecolle Brigitte
Published: May 2007

This study was conducted to determine the effect of two potyviruses, onion yellow dwarf virus (OYDV) and leek yellow stripe virus (LYSV), on the symptoms, growth, and potential yield loss of garlic (Allium sativum). For 2 consecutive years, the impact on leaf length, pseudostem diameter, and bulb weight was evaluated after mechanical inoculation of cultivars Messidrome, Germidour, and Printanor, the three main garlic cultivars grown in France. The reduction in bulb weight due to OYDV ranged from 39% for Germidour to about 60% for the two other cultivars. For LYSV, the reduction in bulb weight was less on Messidrome (17%) and Germidour (26%) than on Printanor (54%). Coinfection with both viruses further reduced growth and bulb weight. When cloves originating from bulbs infected by each virus alone or a mixture of both viruses were planted, results indicated that such chronic infection induced further yield reduction. An assay designed to evaluate the role of LYSV inoculation date on yield revealed that yield losses were the lowest for late-season infections. However, yield loss was greater than 30% when the inoculation was performed at the end of April, the time when natural contamination generally occurs in southern France. A comparison of the impact of mixed infections of OYDV and LYSV from different origins suggested that the isolates did not differ significantly in their effects on yield loss.
Partial Characterization of a Distinct Potyvirus Isolated from Watermelon in Florida
Authors: Purcifull D. E. , Hiebert E. , Petersen M. A. , Simone G. W. , Kucharek T. A. , Gooch M. D. , Crawford W. E. , Beckham K. A. , De Sa P. B.
Published: May 2007

Conspicuous, unusual nuclear inclusions in stained epidermal strips of leaves implicated a virus (designated isolate 2932) as the cause of foliar mosaic in a watermelon plant (Citrullus lanatus) received for analysis from South Florida in 1990. In greenhouse tests, mechanically inoculated plants of Cucurbita pepo (Small Sugar pumpkin and Early Prolific Straightneck squash) and watermelon (Crimson Sweet) developed mosaic or mottle symptoms. Isolate 2932 caused foliar symptoms in 16 cultivars of Cucurbita pepo, including Freedom II and Prelude II, and in six cultivars of watermelon. None of five cultivars of melon (Cucumis melo) or 11 cultivars of cucumber (Cucumis sativus) developed consistent, distinctive symptoms, but all of these cultivars were systemically infected based on back-inoculations to squash. No systemic infection of mechanically inoculated plants of 25 species representing 13 noncucurbitaceous plant families was detected. Crystalline nuclear inclusions, cytoplasmic amorphous inclusions, and cytoplasmic cylindrical inclusions were detected by light and electron microscopy in leaf tissues of infected squash and watermelon. Electron microscopy of squash leaf extracts revealed filamentous particles, and 86% of 159 particles measured ranged from 800 to 890 nm in length. The virus was transmitted in a nonpersistent manner by Myzus persicae from squash to squash in two of three trials. Immunodiffusion tests with polyclonal antisera prepared to partially purified 2932 or its capsid protein showed that the isolate was antigenically different from papaya ringspot virus type W, watermelon mosaic virus 2, and zucchini yellow mosaic virus. In limited testing of field samples of squash and watermelon since 1990, no additional isolates of the 2932 type have been found. The characteristics of isolate 2932 obtained thus far indicate that it is a distinct potyvirus. It is tentatively named watermelon leaf mottle virus to distinguish it from other potyviruses commonly isolated from cucurbits in Florida.
First Report of Anthracnose of Velvet Ash Caused by Discula fraxinea in Louisiana
Authors: Holcomb G. E.
Published: May 2007

Velvet ash (Fraxinus velutina Torr.), a native tree of the southwestern United States, was commonly planted in Louisiana and other southeastern states until horticulturalists lost interest in the plant due to insect and disease problems. For several years, velvet ash trees in Baton Rouge have exhibited necrotic leaf spots and blotches during March and April. Trees frequently have 10 to 25% foliage infection and those most severely infected may show 50% defoliation. Small hyaline conidia that averaged 9.0 × 3.8 μm were produced in acervuli in necrotic tissue on lower leaf surfaces of affected trees. A fungus that produced similar conidia was consistently isolated from infected leaves and grown on potato dextrose agar. Pathogenicity tests were performed by misting 3 × 106 conidia per ml on leaf surfaces of velvet ash seedlings that were then placed in a dew chamber maintained at 26°C for 48 h. Chlorotic leaf spots developed on inoculated plants in 4 to 6 days at 24°C and were followed by necrotic spots and blotches 4 days later. The fungus was reisolated and identified as Discula fraxinea (Peck) Redlin & Stack (previously known as Gloeosporium aridum Ellis & Holw.) (2). Velvet ash anthracnose was first reported from California in 1949 (1), but this is the first report of its occurrence in Louisiana.

References: (1) D. M. Coe and W. W. Wagener. Plant Dis. Rep. 33:232, 1949. (2) S. C. Redlin and R. W. Stack. Mycotaxon 32:175, 1988.
First Report of Peanut Stunt Cucumovirus Naturally Infecting Desmodium sp
Authors: Gillaspie A. G. , Ghabrial S. A.
Published: May 2007

Plant species in the genus Desmodium (Fabaceae) are used as forage and cover crops and include a number of common weeds such as beggarweed (D. tortuosum) and beggarlice (D. intortum). Accessions of the genus are part of the plant genetic resources collection maintained at Griffin, GA. Peanut stunt cucumovirus (PSV) was detected in naturally infected plants of Desmodium sp. PI 322505 (from Brazil) in a germ plasm regeneration plot by a direct antigen coating-enzyme-linked immunosorbent assay (DAC-ELISA) with an antiserum against PSV strain ER (subgroup I) originally isolated from cowpea in Georgia. The infected plants showed mild mosaic symptoms. Indicator host studies in the greenhouse revealed symptoms characteristic of PSV on Nicotiana tabacum cv. Burley 21 (ringspots and oak leaf pattern), Chenopodium album subsp. amaranticolor (chlorotic local lesions), and Vigna unguiculata (chlorotic spots followed by systemic mild mosaic). These symptomatic indicator plants tested positive for PSV by DAC-ELISA. Greenhousegrown plants of D. incanum (kaimi-clover) and D. uncinatum (Spanish tick-clover) were inoculated with the field isolate and the plants were tested for PSV by DAC-ELISA (10 infected of 10 tested and 3 infected of 9 tested, respectively). The PSV isolate infecting Desmodium spp. was found to contain satellite RNA and it generated the predicted products in reverse transcription-polymerase chain reactions (RT-PCRs) with primers based on specific PSV-ER sequences. The RT-PCR products were confirmed by restriction-enzyme digestion (1). This is the first report of PSV naturally infecting a member of the genus Desmodium. Because some members of this genus may grow as perennial weeds near peanut, cowpea, or other host crops, this genus may serve as an alternate/overwintering host for the virus.

Reference: (1) R. A. Naidu et al. Phytopathology 85:502, 1995.
First Report of Fire Blight on Indian Hawthorn Cultivar Olivia in Louisiana
Authors: Holcomb G. E.
Published: May 2007

Twig and branch death were observed on Indian hawthorn (Raphiolepis indica (L.) Lindl.) cv. Olivia in an experimental planting in May 1998. Symptoms resembled those of fire blight caused by Erwinia amylovora and included the release of large numbers of bacteria from stem sections placed in water drops. Small pieces of wood from surface-disinfected cv. Olivia twigs were crushed in drops of sterile water, dilutions made and streaked on yeast extract-dextrose-CaCO3 agar, and single colony cultures established. Pathogenicity tests were performed on immature pear (Pyrus communis L. ‘Kieffer’) and cherry laurel (Prunus caroliniana (Mill.) Aiton) fruits by injecting them with bacterial suspensions containing 105 CFU/ml. Twigs of cv. Olivia were inoculated with a needle that had been dipped in the bacterial cultures. Control inoculations were done with sterile water. Inoculated fruits (nine pear and eight cherry laurel) turned black and oozed bacteria after 5 to 10 days and seven of nine inoculated twigs developed leaf chlorosis followed by browning and death of foliage and twigs after 7 days. Control inoculations were negative. The bacterium was reisolated and identified as E. amylovora based on positive pathogenicity tests and results from Biolog Microplate tests. Although R. umbellata (Thunb.) Makino is a natural host of E. amylovora (1), R. indica was reported only as an experimental host (2) but is now generally recognized as a natural host of E. amylovora. Among nine Indian hawthorn cultivars. (total of 48 plants) in the Louisiana planting, only cv. Olivia was infected with fire blight and all six plants died by late summer.

References: (1) E. M. Hildebrand. Phytopathology 44:192, 1954. (2) H. E. Thomas and H. E. Thomas. Phytopathology 21:425, 1931.
Effect of Temperature on the Discharge and Germination of Ascospores by Apothecia of Monilinia fructicola
Authors: Hong Chuanxue , Michailides Themis J.
Published: May 2007

Naturally growing apothecia of Monilinia fructicola were collected from two commercial plum orchards near Reedley and Sanger, both in Fresno County, California. Ascospore discharges from 90 (1996) and 86 (1997) apothecia were monitored individually using spore traps at four constant temperatures. The period of discharge decreased as temperature increased from 10 to 25°C. However, daily discharge increased as temperature increased from 10 to 15°C and remained high at 20 and 25°C. The greatest discharge occurred with apothecia at 15°C, followed by those incubated at 20, 10, and 25°C. The germination of ascospores of M. fructicola and the length of germ tubes increased as temperature increased from 7 to 15°C; however, increasing temperatures above 15°C did not increase either ascospore germination or length of germ tubes. This information may help in the development of warning systems and management strategies for brown rot blossom blight of stone fruits.
Characterization of the Hyphal Swelling Group of Pythium: DNA Polymorphisms and Cultural and Morphological Characteristics
Authors: Kageyama K. , Uchino H. , Hyakumachi M.
Published: May 2007

The hyphal swelling (HS) group of Pythium species and P. ultimum were studied for cultural and morphological characteristics, restriction fragment length polymorphisms of the amplified internal transcribed spacer (ITS) region in nuclear rDNA, and random amplified polymorphic DNA (RAPD) analysis of genome DNA. The shape of sporangia was spherical to subspherical or lemoniform and averaged 18.1–23.0 μm. All isolates could grow at 5 to 35°C, and the rate at the optimal temperature, 30°C, was 29–34 mm/24 h. The size of the ITS region amplified by polymerase chain reaction and the banding patterns after digestion with the restriction enzymes showed no variation between the HS group and P. ultimum. No difference in banding patterns was shown between the HS group and P. ultimum by RAPD analysis with each of three primers. Isolates examined were from Japan, and results should be confirmed from other regions.
Tillage Effects onMacrophomina phaseolinaPopulation Density and Soybean Yield
Authors: Wrather J. A. , Kendig S. R. , Tyler D. D.
Published: May 2007

Reduced-tillage production systems have become popular with soybean farmers in the United States. During 1992 to 1994, soil and soybean root samples were collected from disk-tillage, no-tillage, and moldboard plow treatments in an experiment conducted since 1979 at the University of Tennessee in Jackson. The objective was to determine if reduced-tillage production systems affected charcoal rot incidence and severity. There were no differences at planting in soil population density of Macrophomina phaseolina in the 0- to 15-cm layer of soil among treatments. However, the soil population density of M. phaseolina in disk-tillage and no-tillage plots was significantly greater in the 0- to 7.5-cm layer of soil than in the 7.5- to 15-cm layer. Similarly, soil population densities were significantly greater in the 0- to 7.5-cm layer of soil in no-tillage than in either disk-tillage or moldboard plowed plots. Tillage did not affect the number of M. phaseolina infection sites in 6-week-old plant roots or the percentage of root segments of physiologically mature plants colonized by M. phaseolina. There was no significant correlation between soybean yield and M. phaseolina soil population density. These data suggest that long-term tillage did not affect charcoal rot incidence and severity.
Metalaxyl-Resistant Isolates of Phytophthora nicotianae: Occurrence, Sensitivity, and Competitive Parasitic Ability on Citrus
Authors: Timmer L. W. , Graham J. H. , Zitko S. E.
Published: May 2007

Phytophthora nicotianae was recovered from 8 of 11 nursery sites, and metalaxyl-resistant isolates were detected at 6 of the 8 positive sites. Resistant isolates comprised 31 to 59% of the population at those sites. Most resistant isolates grew well in the presence of 100 μg/ml of metalaxyl, whereas sensitive isolates did not grow at 1.0 μg/ml. Some isolates from mature citrus groves were intermediate in their sensitivity. Metalaxyl-drench treatments failed to control resistant isolates in greenhouse tests, but fosetyl-Al was usually effective. The replacement series technique was used to compare the relative competitive ability of resistant and sensitive isolates in greenhouse tests. Results varied according to the isolate used, but at least some metalaxyl-resistant isolates were able to compete favorably with sensitive isolates in the absence of metalaxyl. In a field test, a high percentage of the population remained resistant to metalaxyl even after 2.5 years without treatment with this fungicide. Excessive use of metalaxyl in nursery situations has reduced the future utility of the product in Florida citrus groves.
Two New Hosts of Xanthomonas campestris pv. vitians
Authors: Sahin F. , Miller S. A.
Published: May 2007

Bacterial leaf spot of lettuce (Lactuca sativa L.) caused by Xanthomonas campestris pv. vitians (proposed new names X. axonopodis pv. vitians / X. hortorum pv. vitians) is an economically important disease in many areas of the world (1,2). Serious outbreaks occurred in Ohio in 1995 and 1996. The primary sources of the causal agent are presumed to be contaminated seed and infected plant debris in the field. Once the disease is present in a field, crop rotation is required to decrease primary inoculum of the pathogen. Therefore, appropriate crop rotation sequences need to be determined based on the host range of the pathogen. Some vegetable crops, including tomato, pepper, cabbage, collard, kale, radish, and horseradish, were tested for susceptibility to four representative strains of X. campestris pv. vitians by spray inoculation in the greenhouse. Typical symptoms of bacterial leaf spot were observed on tomato and pepper plants 8 days after inoculation, whereas the other crops did not develop diagnostic symptoms. The pathogen was reisolated and Koch's postulates were completed on tomato and pepper. This is the first report that X. campestris pv. vitians strains can cause bacterial spot disease on tomato and pepper.

References: (1) C. L. Patterson et al. Plant Dis. 70:982, 1986. (2) L. Vauterin et al. Int. J. Syst. Bacteriol. 45:472, 1995.