bluuebunny/crossref_metadata_2025 huggingface dataset:
Triazole Seed Treatments Suppress Spore Production by Puccinia recondita, Septoria tritici, and Stagonospora nodorum from Wheat Leaves
Authors: Sundin D. R. , Bockus W. W. , Eversmeyer M. G.
Published: May 2007

Treatments of winter wheat seed with the systemic triazole fungicides triadimenol (31 g a.i./100 kg = Baytan 30F at 1.5 fl oz/cwt) and difenoconazole (24 g a.i./100 kg = Dividend 3FS at 1.0 fl. oz/cwt) were tested for effect on asexual sporulation by Puccinia recondita, Septoria tritici, and Stagonospora nodorum. Spore production was measured on seedlings grown in a growth chamber (24°C day/15°C night, 12-h photoperiod) and inoculated with the pathogens 3, 5, or 7 weeks after sowing. Spore production was converted to a percentage of the non-treated control and regressed against weeks after planting when plants were inoculated. Linear models fit data for both fungicides against all three pathogens. According to the models, difenoconazole suppressed sporulation levels of P. recondita and Septoria tritici to 10% of the levels on plants from non-treated seed for about 3 weeks after sowing. Spore production for all three fungi was suppressed to 25% of the non-treated level for at least 4.2 weeks and to 50% for at least 6.5 weeks. Similarly, triadimenol suppressed all three pathogens to 50% of the non-treated level for at least 3.2 weeks. The two fungicides showed similar effects against S. tritici; however, difenoconazole showed significantly greater suppression of sporulation by P. recondita and Stagonospora nodorum compared with triadimenol. Responses occurred even though large concentrations of spores were used to inoculate plants and environmental conditions were optimized for spore production. Reduced sporulation should help protect fall-planted wheat seedlings and may significantly delay epidemics in the following spring.
Host Range of Oidium lycopersicum on Selected Solanaceous Species in Connecticut
Authors: LaMondia J. A. , Smith V. L. , Douglas S. M.
Published: May 2007

Powdery mildew of tomato in Connecticut was identified as Oidium lycopersicum based on anamorph characteristics. On tomato, conidia were most often formed singly or in pairs on unbranched conidiophores. Mycelium was hyaline and measured 5 to 7 μm. Cleistothecia were not found. This fungus caused disease on a number of tomato cultivars ranging in size from seedlings to mature plants under greenhouse and field conditions. Eastern black nightshade, eggplant, tobacco, and potato were infected in the greenhouse. Reciprocal inoculation experiments between tomato and nightshade and eggplant and tobacco demonstrated cross-infectivity, but the size and number of conidia per conidiophore varied between hosts. Conidia from tobacco, eggplant, and nightshade averaged 37.8 by 19.1 μm (SE = 0.5 and 0.2, respectively) with a 95% confidence interval (CI) of 35.5 to 40.0 by 18.1 to 20.3 μm (n = 300). Conidia from tomato were smaller, averaging 33.6 by 18.2 μm (SE = 0.3 and 0.2, respectively) with a 95% CI of 32.7 to 34.4 by 17.5 to 18.9 μm (n = 300). Conidia from potato averaged 32.4 by 16.6 μm (SE = 0.4 and 0.2, respectively) with a 95% CI of 31.5 to 33.3 by 16.3 to 17.0 μm (n = 100). There were significant differences in percent leaf infection and powdery mildew disease ratings between Lycopersicon esculentum cultivars and Lycopersicon breeding lines under both greenhouse and field conditions. Most commercial tomato cultivars were severely affected by powdery mildew. Cultivars such as Rutgers were not as extensively colonized by O. lycopersicum, compared to cultivars such as Celebrity and Nema 1200, but the severity of powdery mildew was still quite high. L. hirsutum and the tomato breeding line Hirol 3-21 were the only plants tested that were resistant to O. lycopersicum.
Characterization of a Tospovirus Isolate of Iris Yellow Spot Virus Associated with a Disease in Onion Fields in Brazil
Authors: Pozzer L. , Bezerra I. C. , Kormelink R. , Prins M. , Peters D. , Resende R. de O. , de Ávila A. C.
Published: May 2007

A tospovirus from onion causing a disease known as “sapeca” by growers in Brazil was characterized. Symptoms on onion consisted of numerous eyelike spots on the leaves and flower stalks resulting in flower abortion. Nicotiana benthamiana and N. rustica were the only systemic hosts experimentally found. Double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) experiments demonstrated that this virus was serologically related to iris yellow spot virus (IYSV), a tospovirus recently described in the Netherlands. This virus, from onion, based on an amino acid sequence identity of 90.5% for the N gene protein, is regarded as a strain of IYSV and is designated IYSVBR This 10% divergence in the nucleocapsid protein may represent an adaptation of the virus to distinct ecological niches.
Systemic Insecticides and Plant Age Affect Beet Curly Top Virus Transmission to Selected Host Plants
Authors: Wang Heping , de A. Gurusinghe P. , Falk Bryce W.
Published: May 2007

Greenhouse and field studies were conducted to assess the effects of systemic insecticides and plant age on beet curly top virus (BCTV) transmission to sugar beet, tomato, pepper, melon, and cowpea. Sugar beets were the most susceptible to BCTV infection. For all BCTV-susceptible plants tested, younger plants showed greater susceptibility to infection than did older plants, even when inoculations were delayed by only 1 week. Systemic insecticides applied to test plants resulted in increased beet leafhopper (Circulifer tenellus) mortality and decreased the percent BCTV transmission. Soil treatment with imidacloprid (250 g a.i./ha) gave significantly better reductions in BCTV transmission than did dimethoate foliar sprays (280 g a.i./ha). These data suggest that the use of specific systemic insecticides only when crop plants are most susceptible to BCTV infection could be an effective alternative component of the curly top disease control program.
The Influence of Compost Amendment or Straw Mulch on the Reduction of Gas Exchange in Potato by Verticillium dahliae and Pratylenchus penetrans
Authors: Gent M. P. N. , LaMondia J. A. , Ferrandino F. J. , Elmer W. H. , Stoner K. A.
Published: May 2007

Single potato plants (Solanum tuberosum cv. Superior) were grown in microplots in soil that was fumigated and then infested with Verticillium dahliae, Pratylenchus penetrans, or both to evaluate the effects of these pathogens and of cultural treatments with spent mushroom compost or straw mulch on gas exchange of potato leaves. Photosynthesis and transpiration of terminal leaflets of a cohort of similar-aged leaves were measured once a week from the time of expansion until they senesced. Over all measurements, gas exchange per unit leaf area was less for plants in microplots infested with V. dahliae or P. penetrans than for those in uninfested plots. For leaves that expanded in early June, gas exchange was similar immediately after leaf expansion but declined more quickly when microplots were infested with one or both pathogens compared to no infestation. Overall, leaf gas exchange was increased by compost amendment but not affected by straw mulch. Compost amendment prevented some of the decline in gas exchange due to infestation by one or both pathogens. For leaves that expanded in July, compost increased the gas exchange immediately after expansion in both infested and non-infested plots.
Predicting Wheat Leaf Rust Severity Using Planting Date, Genetic Resistance, and Weather Variables
Authors: Moschini R. C. , Pérez B. A.
Published: May 2007

Leaf rust epidemics of wheat, caused by Puccinia recondita f. sp. tritici, were analyzed for the 1972 to 1990 growing seasons. The disease severity values recorded for leaf rust in early and late bread-wheat planting dates at Pergamino were used to identify the best genetic and environmental predictors of disease severity. Leaf rust severity (early planting date) could be predicted (R2 = 0.88) as a function of heat accumulation (base daily mean temperature >12°C), days with relative humidity >70% without precipitation, and a cultivar resistance index. For late planting date, the predictive value of meteorological variables decreased, while the importance of the resistance index increased over that found for the early seeded trials. In general, predicted and observed leaf rust severity levels agreed during 1994 to 1996 at Pergamino, and for trials (1991) that were grown at some distance from the area where the original data for model development were recorded.
Prescreening Slash Pine and Cronartium Pedigrees for Evaluation of Complementary Gene Action in Fusiform Rust Disease
Authors: Stelzer H. E. , Doudrick R. L. , Kubisiak T. L. , Nelson C. D.
Published: May 2007

Single-urediniospore cultures of the fusiform rust fungus were used to inoculate seedlings from 10 full-sib families of a five-parent slash pine diallel at two different times in 1994. The presence or absence of fusiform rust galls was recorded for each inoculated seedling at 9 months postinoculation, and percent infection levels for each family-inoculum-time combination were used for detecting differences among host families and fungal cultures and for identifying differential interactions. The existence of differential interactions between two or more fungal cultures and two or more host families verifies that complementary gene action does exist in this pathosystem. Some host families may be excluded from more detailed interaction studies on the basis of their redundancy and lack of participation in differential interactions.
First Report of Heterobasidion annosum on Native European Pinus cembra
Authors: Nicolotti G. , Gonthier P. , Varese G. C.
Published: May 2007

Heterobasidion annosum (Fr.:Fr.) Bref. is one of the most widespread and damaging root and butt rot agents on conifers. In the summer of 1998, H. annosum was observed for the first time on the Swiss Stone Pine (Pinus cembra L.) in its natural range (1) at 1,900 m in the Aosta Valley in the northwestern Italian Alps. The affected tree was 14 m tall and about 60 years old. It was growing in a mixed spruce (Picea) and larch (Larix) forest severely affected by H. annosum. There were no clear crown symptoms but, after felling, an extensive butt rot was noticed up to 4 m from the collar. The pathogen was isolated from a disk cut at a height of about 40 cm. Its anamorphic form (Spiniger meineckellum (A. Olson) Stalpers) developed on this disk after 8 days of incubation at 20°C. H. annosum was also isolated from the central cylinder of the tree's primary roots and on the other roots down to a diameter of 0.5 cm. Sexual mating tests with single-spore testers for the P, S, and F intersterile groups (ISGs) showed that the isolate belonged to S-ISG. Biomolecular tests on this strain are in progress to confirm this.

Reference: (1) T. G. Tutin et al. 1993. Flora Europaea. Cambridge University Press, Cambridge.
The Identification of the Vector Species of Iris Yellow Spot Tospovirus Occurring on Onion in Brazil
Authors: Nagata Tatsuya , Almeida Ana Carla L. , Resende Renato de O. , Ávila Antonio C. de
Published: May 2007

In Brazil, tospoviruses have been reported in several horticultural and ornamental plants. In the northeast region of Brazil, a tospovirus has emerged as a devastating virus on onion cultures. Based on serology and the sequence of nucleocapsid (N) protein gene, this pathogen was identified as a strain of iris yellow spot tospovirus (IYSV) (1). This virus was first identified on iris and leek in The Netherlands and later on onion in Israel. For an effective integrated management of tospoviruses in Brazil, identification of IYSV vector is essential. Three thrips species, Thrips tabaci, Frankliniella schultzei, and F. occidentalis, that are major vegetable and floral crop pests in the Federal District, Brazil, were tested for their ability to transmit the virus by leaf disk assay (2). All thrips, up to 8 h old, were given an acquisition access period of 48 h at 25°C on IYSV-infected Nicotiana benthamiana plants in Tashiro-cages. Thrips were then reared on uninfected Datura stramonium detached leaves until the adult stage. These adults were transferred individually to microcentrifuge tubes containing an N. benthamiana leaf disk and were incubated for 48 h for virus inoculation. The leaf disks were then incubated 4 more days to allow development of the virus infection, and the presence of virus was evaluated by Dot-enzyme-linked immunosorbent assay (Dot-ELISA) with polyclonal antibodies against N protein of IYSV. Adult thrips were also used for direct inoculation to N. benthamiana plants, three thrips per plant. By the leaf disk assay, 45.8% (22 out of 48) of T. tabaci transmitted the virus, but F. schultzei (n = 48) and F. occidentalis (n = 32) did not transmit it. All plants (4 out of 4) directly inoculated by T. tabaci showed symptoms and infection by Dot-ELISA, while no plants inoculated with F. schultzei (n = 5) and F. occidentalis (n = 3) were positive, either by symptom observation or by Dot-ELISA. Only T. tabaci showed potential for a high capacity to transmit the IYSV onion isolate. In the field, considering the host preference of thrips, T. tabaci was considered the most important vector species of IYSV on onion.

References: (1) L. Pozzer et al. Plant Dis. (In press.) (2) I. Wijkamp and D. Peters. Phytopathology 83:986, 1993.
Two New Hosts for Poinsettia Mosaic Virus
Authors: Floeistad E. , Blystad D. R.
Published: May 2007

Poinsettia mosaic virus (PnMV), a possible member of the genus Tymovirus, commonly infects the potted flower crop Euphorbia pulcherrima Willd. ex Klotzsch (1). Two new host species for this virus were identified during grafting experiments with E. pulcherrima and other Euphorbia spp. E. cornastra (Dressler) A. Radcliffe-Smith was reciprocally grafted with PnMV-positive E. pulcherrima cv. Eckespoint Lilo. PnMV was detected by double antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) in E. cornastra leaves directly below the graft union 4 weeks after grafting. Infection was not fully systemic 6 weeks after grafting when screened by DAS-ELISA with antibodies specific to PnMV (DSMZ, Braunschweig, Germany). The symptomless infection in E. cornastra persisted in cuttings from grafted plants after a 1-year observation period. E. bubalina Boiss. anatomy differs from that of E. pulcherrima. The two species did not produce a viable graft union. However, in an experiment with two attempted graftings, the E. pulcherrima scions remained turgid for 14 to 18 days. As a result of one grafting, the E. bubalina rootstock tested positive for PnMV. The virus induced a mild mosaic in E. bubalina, but no reduction in growth. To confirm virus presence in E. cornastra and E. bubalina, both DAS-ELISA and immunosorbent electron microscopy were used. Non-grafted controls remained PnMV negative. PnMV was re-isolated from both species by sap inoculation to Nicotiana benthamiana. E. coulescens Haw., E. xylophyllides Brogn. ex Lem., E. marlothiana N. E. Br., and Ricinus communis L. were not infected by PnMV after similar grafting attempts.

Reference: (1) A. A. Brunt et al., eds. 1996. Viruses of Plants. CAB Int., Wallingford, UK.
Temperature, Leaf Wetness, and Isolate Effects on Infection of Minneola Tangelo Leaves by Alternaria sp.
Authors: Canihos Y. , Peever T. L. , Timmer L. W.
Published: May 2007

Alternaria brown spot causes necrotic lesions on immature leaves, twigs, and fruit of tangerines and their hybrids, reducing yield and fruit quality. The effect of temperature, leaf wetness, and isolate was evaluated in an in vitro system using immature detached leaves of Minneola tangelo Infection was greatest at 27°C, decreased gradually as the temperature declined to 24, 20, and 17°C, and dropped sharply at 32°C. Levels of infection were low at 4 and 8 h of leaf wetness and continued to increase with longer wetting periods up to 36 h. A polynomial equation was developed that provided a good fit for the data (adjusted R2 = 0.93). Isolates differed in aggressiveness, but there was no significant difference among isolates in their response to temperature and leaf wetness duration.
Vulnerability of U.S. Maize Germ Plasm to Phaeosphaeria Leaf Spot
Authors: Carson M. L.
Published: May 2007

Phaeosphaeria leaf spot (PLS) is a potentially important maize disease that has recently appeared in the continental United States in winter breeding nurseries in southern Florida. To better predict the potential of this newly introduced disease to inflict damage on the U.S. maize crop, 64 public and private inbred lines and 80 proprietary commercial maize hybrids representing the genetic diversity in the U.S. maize crop were evaluated for resistance to PLS in the 1996-97 and 1997-98 winter nursery seasons. Plots were evaluated for PLS severity (0 to 9 scale) at the early to mid dent stages of kernel development. Relatively few hybrids or inbreds were free from PLS at this growth stage. Inbred lines related to B73 were particularly susceptible to PLS. Relatively few commercial hybrids were as severely diseased as a susceptible check hybrid, indicating that U.S. maize production is not particularly vulnerable to damage from PLS at this time. However, the susceptibility of several widely used parental inbred lines makes PLS a potential concern to the seed industry should it become established in areas of hybrid seed production.
Easy and Efficient DNA Extraction from Woody Plants for the Detection of Phytoplasmas by Polymerase Chain Reaction
Authors: Green Margaret J. , Thompson Dan A. , MacKenzie Donald J.
Published: May 2007

A simple and efficient procedure for the extraction of high-quality DNA from phytoplasma-infected woody and herbaceous plants for polymerase chain reaction (PCR) detection is described. This procedure does not require phenol, chloroform, or alcohol for the precipitation of nucleic acids. Herbaceous and woody plant material are extracted in an identical manner with no additional purification or enrichment steps required. The method utilizes commercially available microspin-column matrices, and the extraction of total DNA can be achieved in less than 1 h. The method has been used to successfully purify phytoplasma DNA from whole leaves, leaf petioles and midribs, roots, and dormant wood from a diverse selection of plant material. The phytoplasmas detected by PCR include pear decline, western X-disease, peach yellow leaf roll, peach rosette, apple proliferation, Australian grapevine yellows, and Vaccinium witches'-broom.
First Report of Mimosa Wilt Disease of Silk Tree (Albizia julibrissin) in California Caused by Fusarium oxysporum f. sp. Perniciosum
Authors: Nesbitt R. B. , Tidwell T. E. , Stipes R. J. , Griffin G. J.
Published: May 2007

A Fusarium sp. was isolated from a 12-year-old Silk Tree (Albizia julibrissin) in a residential area of Redlands, CA. The scaffold branches and trunk exhibited gummosis, the sap oozing from fissures or intact bark. Internally the wood exhibited brown to black broad streaks of discoloration from the scaffold branches down into lateral roots below the root crown, similar to symptoms observed in Virginia (2). Wilted and dried foliage remained on the scaffold branches. Two-week-old cultures of the isolate grown on Komada (1) and acidified potato dextrose agar media developed short conidiophores, macroconidia, and colony morphology typical of Fusarium oxysporum. To complete Koch's postulates, 1-month-old seedlings were root-dip inoculated with a water suspension of macro- and microconidia (106 per ml). Two weeks after inoculation, typical Fusarium wilt symptoms developed in all inoculated seedlings. The fungus was reisolated from symptomatic seedlings. This is the first report of mimosa wilt disease in California. The disease has the potential to adversely impact California's nursery and landscape industry.

References: (1) H. Komada. Rev. Plant Prot. Res. 8:114, 1975. (2) R. J. Stipes and P. M. Phipps. Phytopathology 65:188, 1975.
First Report of Occurrence of Potato Tuber Necrotic Ringspot Disease in Greece
Authors: Bem F. , Varveri C. , Eleftheriadis I. , Karafyllidis D.
Published: May 2007

Potato tuber necrotic ringspot disease (PTNRD), caused by potato Y potyvirus isolate NTN (PVYNTN) of the N virus strain group, was first described in Hungary in 1980. It has spread throughout Europe, with the most recent reports from Portugal and Italy in 1997 to 1998 (1). Superficial necrotic ringspot areas on tubers, typical of PTNRD, were first observed in commercial potato fields of the Nevrokopi region in northern Greece in 1994. Affected cultivars included Timate and, to a lesser extent Spunta, the original seed of which came from the Netherlands. PVY was identified from all tubers tested by indexing on Nicotiana tabacum and subsequent testing of the plants by double antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA). The potato seed lots were rejected by the local authorities. PTNRD reappeared in the same area in 1998 in a more aggressive manner. Cultivar Hermes, imported from Scotland, was most affected, with very severe symptoms in 80% of the tubers. Symptoms appeared in early September, 40 days after defoliation of the plants. Other cultivars were affected at lower rates; cv. Spunta showed typical symptoms and cvs. Fabola, Santana, and Irvila exhibited atypical cracks and blisters. In all cases, PVY was isolated in N. tabacum and its presence confirmed by DAS-ELISA. Immunocapture-reverse transcription-polymerase chain reaction with specific PVYNTN primers (2) detected the characteristic 835-bp product in all cultivars tested. The incidence of PTNRD seems to be expanding in northern Greece, where it has become a threat to potato production. PTNRD symptoms were also observed in southern Greece (Ahaia) in experimental “crossing” fields of seed stocks. In this case, the disease seems to have spread especially in cv. Marfona.

References: (1) L. Tomassoli et al. Plant Dis. 82:350, 1998. (2) H. L. Wiedemann and E. Maiss. Z. Pflanzenkrankh. Pflanzenschutz 103:337, 1996.
Effect of Colletotrichum coccodes on Potato Yield, Tuber Quality, and Stem Colonization During Spring and Autumn
Authors: Tsror (Lahkim) Leah , Erlich Orly , Hazanovsky Marina
Published: May 2007

The response of five potato cultivars to Colletotrichum coccodes was tested in artificially inoculated fields for three consecutive spring and autumn seasons during 1994 to 1996. Significant yield reductions (22 to 30%) were observed in all tested cultivars. Results varied between years, but yield losses were more severe in autumn than in spring. Stem infections of plants were observed 90 days after planting on the surface of the stem and in vascular tissue. C. coccodes inoculation also resulted in reduction of the quality of daughter tubers. Cultivars Cara and Nicola were found to be less susceptible to tuber infection than Alpha, Desiree, and Agria. The incidence of diseased daughter tubers was higher when the soil was infested than when the foliage was inoculated. C. coccodes contamination of dry stems at harvest (in inoculated plots) was relatively high in all cultivars, with no difference between inoculation methods. Thus, C. coccodes infection not only affects potato yield and the quality of potatoes for seed and consumption, but also contaminates soil and serves as an important source of inoculum for future potato crops.
Reaction of Sweet Corn to Inoculation with Barley Yellow Dwarf Virus RMV-IL
Authors: Itnyre Ronald L. C. , D'Arcy Cleora J. , Pedersen W. L. , Sweets Laura E.
Published: May 2007

The reaction of five sweet corn hybrids to barley yellow dwarf virus (BYDV-RMV-IL) was determined in 1992 and 1993. In 1992, symptoms were observed in three of the five hybrids planted 20 May and four of the five hybrids planted 20 June. No symptoms were observed in hybrids planted June or July 1993. The mean virus incidences of RMV-IL determined by enzyme-linked immunosorbent assay (ELISA) in all plots for the May and June 1992 planting dates were 3.5 and 21%, respectively. The mean virus incidence for the inoculated plots for the June 1992 planting date was significantly higher than incidence for the control plots (29 versus 13%). Ear weights were significantly lower for inoculated plots than for the control plots (1.2 kg versus 1.4 k/10 ears). The mean virus incidences of RMV-IL in all plots for the June and July 1993 planting dates were 31 and 23%, respectively. The mean virus incidence for the inoculated plots for the June 1993 planting date was significantly higher than incidence for the control plots (49 versus 14%). Plots inoculated in June 1993 also had a significantly lower ear weight than the control plots (1.8 kg versus 2.0 kg/10 ears). A range of symptoms, infection levels, and yield responses of sweet corn hybrids to BYD-RMV-IL was demonstrated in this study. Hybrid susceptibility to this strain of BYDV should be considered when planting sweet corn from middle to late June in order to limit potential yield losses.
The Phytoplasma Associated with Ramu Stunt Disease of Sugarcane Is Closely Related to the White Leaf Phytoplasma Group
Authors: Cronjé C. P. R. , Bailey R. A. , Jones P. , Suma S.
Published: May 2007

Ramu stunt disease of sugarcane (ScRS) was responsible for large yield losses in commercial sugarcane varieties (interspecific hybrids of Saccharum spp.) in the Ramu Valley in northeast Papua New Guinea during the late 1980s. Losses were total in the cultivar Ragnar; Q90 and Yasawa were also affected but Cadmus and Q107 were resistant. Since that time, replanting with resistant cultivars has kept the disease under control. The disease spreads rapidly in susceptible cultivars, where it results in severe stunting of the cane and a yellow mottled striping of the leaves. Although several attempts have been made to detect a viral pathogen, no evidence for viral etiology exists and the causal agent remains unknown. With a nested polymerase chain reaction (PCR) of general phytoplasma primers from the 16S rDNA (1), phytoplasma-specific products were consistently amplified from the leaves of field-grown sugarcane, from sugarcane with ScRS symptoms grown in the glasshouse at IACR-Rothamsted, UK, and from samples of the putative vector collected at Ramu, the delphacid plant hopper Eumetopina flavipes Muir, which had been found to transmit symptoms of Ramu stunt in pot trials (2). Digestion of the amplimers with restriction enzymes RsaI and HaeIII gave profiles that matched those of members of the sugarcane white leaf (SCWL) phytoplasma group. The DNA sequence of the intergenic spacer region of the phytoplasma associated with ScRS showed a 95.98% homology with that of SCWL, suggesting that this newly discovered phytoplasma can provisionally be placed in this group. The 16S-23S intergenic spacer sequence has been submitted to GenBank (accession no. AF 106061).

References: (1) C. P. R. Cronjé et al. Ann. Appl. Biol. 133:177, 1998; (2) L. S. Kuniata et al. J. Aust. Entomol. Soc. 33:185, 1994.
Yield Loss Caused by Bacterial Streak in Winter Wheat
Authors: Tillman B. L. , Kursell W. S. , Harrison S. A. , Russin J. S.
Published: May 2007

The relationship between severity of bacterial streak and yield in winter wheat was studied in field plots and using a single-tiller method. Regression analysis from single-tiller studies showed that the grain weight per spike decreased as bacterial streak severity increased in cvs. Florida 304 and Savannah. The number of kernels per spike decreased as bacterial streak severity increased in Savannah but not in Florida 304. There was no difference in slope of the regression line between different years, locations, or cultivars for grain weight per spike. However, grain weight per spike at 0% bacterial streak (intercept) was different for different years, locations, and cultivars. The average reduction in grain weight per spike was 0.012 g for every 1% increase in bacterial streak severity. Using this relationship for cv. Savannah, average bacterial streak severity of 10% would result in about a 9% reduction in the grain weight per spike. In Florida 304, bacterial streak severity of 10% would result in about a 7% reduction in the grain weight per spike. During 1993-94, the largest difference in bacterial streak severity between inoculated and noninoculated plots was 4% in cv. Pioneer 2548, and the smallest difference was less than 1% in cvs. Terral 101 and Florida 304. There were no yield differences between inoculated and noninoculated treatments for any genotype. In field plot studies at two locations during 1989-90, bacterial streak severity did not differ between inoculated and noninoculated plots in Alexandria, Louisiana; but in Winnsboro, Louisiana, bacterial streak severity was 18 to 40% in inoculated plots and less than 5% in noninoculated plots. Differences in yield between inoculated and noninoculated plots ranged from 1,370 kg/ha (24% loss) to -121 kg/ha in Winns-boro. During the three seasons in which these studies were conducted, bacterial streak severity averaged about 10% or less in susceptible cultivars in all experiments except one. Based on the relationships derived from single-tiller studies, this suggests that yield loss is likely to be low most years. As indicated by the experiment in Winnsboro, however, more severe yield reductions could occur in a susceptible cultivar if weather conditions are favorable for disease development.
Effects of Silk Maturity and Pollination on Infection of Maize Ears by Ustilago maydis
Authors: du Toit Lindsey J. , Pataky Jerald K.
Published: May 2007

Host resistance is the most efficient method of controlling common smut of maize (Zea mays), caused by Ustilago maydis. Precise timing of ear inoculations with U. maydis relative to silk maturity and pollination may improve the ability to screen maize germ plasm for resistance. The objectives of this study were to determine the length of time maize kernels can be infected by U. maydis through silks, and to examine the effects of pollination on infection through silks. Two field studies were done in 1995, 1996, and 1997 at the University of Illinois South Farms. In the date-of-inoculation study, ears were inoculated at 2- to 3-day intervals from early silk emergence until 16 days after silk emergence. In the date-of-planting study, hybrids were planted on four dates and ears were inoculated on the same day for all planting dates. In each study, ear shoots were covered with shoot bags prior to silk emergence to prevent pollination, or ear shoots were left uncovered to allow silks to be pollinated normally. Maize ears were susceptible to infection by U. maydis from silk emergence until 8 to 14 days after silk emergence. During this period of susceptibility, incidence of ears with galls decreased as silks aged. Incidence of ears with galls on plants inoculated 7 days apart differed by as much as 70%. The period that maize ears were susceptible to infection by U. maydis was shorter and incidence of ears with galls decreased more rapidly when silks were exposed to pollen than when silks were not exposed. The silk channel method of inoculating for common smut does not appear to be practical for large-scale evaluations of numerous lines. The method is practical for evaluating a limited number of lines or for inducing ear galls for commercial production of huitlacoche (smut galls eaten at an immature stage).
Comparative Slow-Blasting in Rice Grown Under Upland and Flooded Blast Nursery Culture
Authors: Lai X. H. , Marchetti M. A. , Petersen H. D.
Published: May 2007

Evaluation of rice for resistance to rice blast disease caused by Pyricularia grisea usually is conducted in upland (nonflooded) disease nurseries, although all commercial U.S. rice is produced under flood irrigation. Upland rice is more susceptible to leaf blast than is flooded rice, and the magnitude of this differential susceptibility can vary among cultivars. This 2-year study was undertaken to determine (i) the relationship between rates of disease development (slow-blasting) in upland and flooded rice and (ii) the value to a rice breeding program of establishing a flooded blast nursery, a facility far more difficult to manage than an upland nursery. Among 200 rice lines compared for leaf blast susceptibility under upland and flooded cultures, only 7 were rated as slightly more resistant under upland culture and 136 rated more resistant under flooded culture. Disease ratings under upland and flooded cultures were highly correlated (R = 0.819). Among 14 preselected cultivars over 2 years, disease development curves under upland and flooded cultures were highly correlated (R = 0.990). The cultivars with intermediate susceptibility under upland culture appeared to benefit most from flooded culture. Upland culture provided more opportunities to assess slow-blasting than did flooded culture, since many lines that produced susceptible-type lesions in upland culture failed to do so under flooded culture. It was concluded that adequate information on comparative leaf blast resistance among rice lines was attainable from upland blast nurseries and that routine evaluation of rice breeding lines for blast resistance in flooded nurseries was not necessary.
First Report of Powdery Mildew, Caused by Erysiphe cichoracearum, on Coneflowers
Authors: Sholberg P. L. , Ginns J. H. , Li T. S. C.
Published: May 2007

Purple coneflowers (Echinacea purpurea) are grown in North America and Europe for their medicinal properties and as ornamental plants. In September 1997 and again in 1998, a previously undescribed disease was noticed on fully grown coneflower plants in Summerland and Oliver, British Columbia. Mycelia were observed on stems, foliage, and flowers, and distinct dark red to black, round (approximately 5 mm in diameter) lesions were observed on the flower petals. The disease appeared similar to powdery mildews that have been reported on numerous genera of the Asteraceae. Samples of the diseased tissue were examined and the salient features of the fungus on two specimens were determined: cleistothecia infrequent, subglobose or flattened on the side next to the leaf surface, 121 to 209 μm in diameter; epidermal (surface) cells 20 μm in diameter; appendages hyphoid, 5 μm in diameter, up to 200 μm long; asci, 10 to 19 in each cleistothecium, broadly ellipsoid, 47 to 85 × 28 to 37 μm with a short stalk, about 8 to 13 μm long and 8 μm in diameter; ascospores, immature, two per ascus, ellipsoid to broadly ellipsoid, 17 to 25 × 11 to 13 μm, thin walled, hyaline, and smooth; conidia oblong with sides slightly convex and apices truncate, 27 to 40 × 14 to 20 μm, walls hyaline, thin, smooth. Based on the occurrence of asci that contained two ascospores and the hyphoid appendages on the cleistothecia we concluded that the fungus was Erysiphe cichoracearum DC. Damage due to this disease was minimal in 1997 and 1998 because it developed very late in the growing season and occurred sporadically within the plantings. In order to complete Koch's postulates, Echinacea purpurea plants grown in the greenhouse were inoculated with a conidial suspension (105 to 106 conidia per ml) from field-infected plants. Powdery mildew first appeared 3 months later, eventually infecting leaves and stems of 12 of 49 inoculated plants. It was distinctly white and in discrete patches on leaves, compared with coalescing dark brown areas on the stems. Microscopic examination of the conidia confirmed that they were E. cichoracearum. Although powdery mildew caused by E. cichoracearum has been widely reported on lettuce, safflower, and other cultivated and wild Compositae, we found no reference to it on Echinacea spp. in Canada (1,2), the U.S. (3), or elsewhere in the world (4). The specimens have been deposited in the National Mycological Herbarium of Canada (DAOM) with accession numbers 225933 and 225934 for Oliver and Summerland, B.C., respectively.

References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) I. L. Conners. 1967. An annotated index of plant diseases in Canada and fungi recorded on plants in Alaska, Canada, and Greenland. Canada Dept. of Agric. Pub. 1251. (3) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN. (4) J. Ginns. 1986. Compendium of plant disease and decay fungi in Canada, 1960-1980. Agriculture Canada Pub. 1813.
First Report of Fusarium oxysporum Causing a Leaf Twisting Disease on Allium cepa var. ascalonicum in Sri Lanka
Authors: Kuruppu P. U.
Published: May 2007

A disease of shallot onions, Allium cepa var. ascalonicum, that caused yield losses of up to 20 to 30% in some fields was reported from Kalpitiya Peninsula in the North Western Province of Sri Lanka in the late 1980s. Disease symptoms consisting of chlorosis followed by curling and twisting of leaves and abnormal elongation of the neck region appeared after germination of the onion bulbs, subsequently causing plant collapse. Symptomatic plants occurred randomly in most fields and the disease was prevalent throughout the year. Tissue pieces from leaves and the neck region of symptomatic plants plated on potato dextrose agar containing 1% streptomycin (PDAS) produced purplish pink fungal colonies identified as Fusarium oxysporum. Pathogenicity tests were performed with single-spore fungal isolates grown at 25°C for 14 days on PDAS. Shallot onion cv. Vathalan was inoculated by soaking bulbs, pierced with a sterilized needle, in a spore suspension containing 2 × 106 spores per ml for 10 min. Control bulbs were wounded, and soaked for 10 min in sterilized water. Bulbs were then planted in sterile sand and maintained in a green house at 25 to 28°C. After 2 to 3 weeks, typical symptoms, as observed in the field, developed in plants produced from bulbs inoculated with the F. oxysporum isolate. Symptoms were not observed on plants from the control bulbs. Koch's postulates were confirmed by reisolating the same fungus from the neck region of diseased plants. Onion twister disease described by Ebenebe (1) also had been observed in this region in Sri Lanka during 1992-1993. There were differences between these two diseases in disease symptoms and disease development in the field. Acer-vuli of Colletotrichum spp. were always detected in lesions of the neck region, as well as on leaf blades, of plants severely affected by onion twister disease. This disease developed from foci in fields that spread over time. Moreover, onion twister disease occurred only from October until January, coinciding with the rainy season.

Reference: (1) A. C. Ebenebe. Plant Dis. 64:1030, 1980.
Damping-off of Swiss Chard, Caused by Rhizoctonia solani, in California
Authors: Koike S. T. , Subbarao K. V.
Published: May 2007

In California, various leafy vegetables are planted at extremely high seeding rates (up to three million seed per acre), grown to the four- to eight-leaf stage, then mechanically clipped and bagged for market as “spring mix” or “baby leaf” salad products. The crops are planted in separate strips, usually four to 16 beds of each, and include Japanese mustard (Brassica campestris subsp. nipposinica), red mustard (Brassica juncea subsp. rugosa), tah tsai (Brassica campestris subsp. narinosa), multiple lettuce (Lactuca sativa) cultivars, spinach (Spinacia oleracea), arugula (Eruca sativa), and Swiss chard (Beta vulgaris subsp. cicla). In 1997 and 1998, severe damping-off disease of Swiss chard was observed in the Salinas Valley (Monterey County). Symptoms on emergent plants consisted of wilting, brown necrosis of crown tissue, and eventual death of seedlings. Because of the high plant density, disease incidence increased rapidly, affecting large numbers of plants. Rhizoctonia solani was isolated consistently from symptomatic plants. Pathogenicity was tested by placing agar plugs of representative isolates adjacent to crowns of potted Swiss chard at the two- to four-leaf stage. Brown stem necrosis and plant collapse occurred within 5 days after inoculation, and R. solani was reisolated. Control plants, inoculated with sterile agar plugs, did not develop disease. Tests were repeated and results were similar. Anastomosis group testing revealed that all five isolates belonged to AG3 (1). For California, this appears to be the first documentation of damping-off of Swiss chard caused by R. solani.

Reference: (1) B. Sneh et al. Identification of Rhizoctonia Species. American Phytopathological Society, St. Paul, MN, 1991.
First Report of Root Rot of Soybeans Caused by Corynespora cassiicola in Wisconsin
Authors: Raffel S. J. , Kazmar E. R. , Winberg R. , Oplinger E. S. , Handelsman J. , Goodman R. M. , Grau C. R.
Published: May 2007

Corynespora cassiicola (Berk. & M. A. Curtis) C. T. Wei was isolated from diseased soybean plants (Glycine max) collected in two fields near Racine and Arlington, WI. Plants sampled at seedling emergence (VC), late vegetative (V5), and mid-reproductive (R5) stages exhibited reddish to dark brown longitudinal lesions on the exterior of the tap root extending vertically on the hypocotyl to the soil line, and extensive necrosis of lateral roots. Sample size at each growth stage was 144 plants per site. Roots were surface sterilized in 0.5% sodium hypochlorite for 2 min and sections of symptomatic tissue placed on water agar (12 g/liter) containing 100 μg of streptomycin per ml. Sporulation occurred on lesions and on mycelium that had grown out from the plant tissue onto the water agar following a 2-week incubation at 24°C under fluorescent light (280 μmol s-1 m-2). Incidence of isolation of C. cassiicola at both sites was 40% of plants sampled at growth stage VC, 67% at V5, and 78% at R5. Conidia characteristic of C. cassiicola were particularly abundant on the surface of necrotic lateral root tissue. Elongated conidia produced on water agar were 151 ± 5 μm × 15 ± 0.5 μm with an average of 13 ± 0.4 cells separated by hyaline pseudosepta (1). To confirm pathogenicity, a 1-cm lateral slice into each of four 5-day-old soybean seedling roots was made and a plug of agar taken from the margin of a colony of C. cassiicola grown on potato dextrose agar was placed in each wound and incubated for 14 days at 24°C in a growth chamber. Symptoms similar to those of diseased field plants were observed and C. cassiicola was reisolated from all plants inoculated with C. cassiicola; all controls treated with agar alone had no symptoms and C. cassiicola was recovered from none of the noninoculated controls. This is the first report of root rot caused by C. cassiicola on soybean in Wisconsin.

Reference: (1) W. L. Seaman and R. A. Shoemaker. Can. J. Bot. 43:1461, 1965.
Geographical Distribution and Incidence of Orchardgrass Choke, Caused by Epichloë typhina, in Oregon
Authors: Pfender W. F. , Alderman S. C.
Published: May 2007

A 1998 survey was conducted in the Willamette Valley of Oregon, the major U.S. production area for orchardgrass seed, to determine the extent and severity of choke disease in Dactylis glomerata. This disease is a severe constraint to orchardgrass seed production in other parts of the world, but was unknown in Oregon prior to 1997. Thirty-seven fields, representing 27 cultivars and the geographical extent of production in the Willamette Valley, were selected from a list of fields registered for certification. Choke was found in 26 (70%) of the fields, and disease incidence ranged from <0.05 to 28% tillers affected. Five of the 37 fields had only trace levels of the disease, but four of the fields, representing three counties, had incidences >10%. In a survey of 16 fields located within 3.5 km of the 1997 discovery, choke was found in 14 fields, of which three had incidences >20%. Increase in disease incidence between 1997 and 1998 ranged from 2.1- to 3.3-fold in the three fields where disease increase was measured. One year after its presence was confirmed in Oregon, choke disease of orchardgrass is well-established throughout the orchardgrass seed producing region at damaging levels and is apparently able to increase and spread under the prevailing climatic and cultural conditions.
First Report of Powdery Mildew of Greenhouse Pepper Caused by Leveillula taurica in Canada
Authors: Cerkauskas R. F. , Brown J. , Ferguson G. , Khosla S.
Published: May 2007

In 1999, powdery mildew on cvs. Oberon and Triple 4 of greenhouse pepper (Capsicum annum L.) and cv. FireFlame of chili pepper was reported simultaneously in two commercial greenhouses at two separate locations, Leamington and Vineland, geographically separated by 290 km, in southern Ontario. Losses of 10 to 15% each in the 2 and 3.1 ha greenhouse pepper operations were noted. The greenhouse pepper industry in Canada consists of 89.4 ha with sales of $43.6 million (Canadian). Lesions appeared as a white, powdery coating on the abaxial leaf surface only, generally on the lower foliage of pepper plants, while diffuse chlorotic spots were present at corresponding locations on the adaxial surface. In chili pepper, this chlorosis was restricted to interveinal tissue, causing the leaves to have a somewhat netted appearance. In some cases, pale yellow spots appeared on the adaxial portion of the affected foliage during later stages of disease development. No cleistothecia were observed. Pyriform and cylindrical, hyaline, single-celled conidia were present in equal numbers. Both conidia had a network of crests and granules containing tiny, thornlike projections on the surface. These projections were also evident on the lower half of conidiophores. Pyriform conidia ranged in length from 61.6 to 84.0 μm (mean = 70.8, SE = 0.7) and in width from 14.0 to 25.8 μm (mean = 21.1, SE = 0.4, n = 50), with a mean length to width ratio of 3.4. Cylindrical conidia ranged in length from 54.9 to 80.1 μm (mean = 66.3, SE = 0.9) and in width from 15.7 to 24.1 μm (mean = 18.6, SE = 0.3, n = 50), with a mean length to width ratio of 3.1. Short conidial chains borne on conidiophores consisted of a pyriform conidium first followed by cylindrical conidium. Stomatal penetration and extensive endophytic mycelial growth in the mesophyll layer were evident in foliar tissue cleared with glacial acetic acid:EtOH (1:2) and stained with lactophenol cotton blue. To confirm pathogenicity, conidia from infected pepper leaves were dusted onto the water-misted abaxial leaf surface of 41-day-old greenhouse pepper cvs. Cubico and Edison, and onto the similarly treated adaxial leaf surface of 58-day-old field pepper cv. Renegade. Plants were enclosed in plastic bags for 24 h on a bench. Control plants were treated identically but not inoculated. Inoculated plants developed foliar powdery mildew symptoms, including sporulation similar to that of naturally infected plants. Occurrence of the fungus on the abaxial surface of pepper foliage, presence of endophytic mycelium, and the morphological characteristics of the imperfect state confirm the identity of the fungus. This is the first report of Leveillula taurica (Lév.) G. Arnaud on pepper in Canada.

Reference: J. Palti. Bot. Rev. 54:423, 1988.