bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of the Bemisia tabaci B Biotype in India and an Associated Tomato leaf curl virus Disease Epidemic
Authors: Banks G. K. , Colvin J. , Reddy R. V. Chowda , Maruthi M. N. , Muniyappa V. , Venkatesh H. M. , Kumar M. Kiran , Padmaja A. S. , Beitia F. J. , Seal S. E.
Published: May 2007

In May 1999, in the Kolar district of Karnataka State, Bemisia tabaci numbers on tomato increased by approximately 1,000-fold that observed previously (3). This was associated with an epidemic of severe tomato leaf curl disease that caused complete crop failure. DNAs extracted from 35 symptomatic tomato leaf samples collected within the epidemic region all gave the expected 500 to 600 bp amplicon with begomovirus-specific primers A/B (1). These primers amplify from the conserved nonanucleotide TAATATTAC in the common region of DNA-A to the conserved amino acid sequence CEGPCKYG within the coat protein gene. AluI and TaqI restriction patterns of all 35 polymerase chain reaction (PCR) products were identical. One PCR product from an epidemic (GenBank no. AF321929) and a non-epidemic (AF321930) site (Bangalore) were cloned and sequenced. The two 531-bp inserts showed 96% nucleotide identity to each other and 94% nucleotide identity to the equivalent region of Tomato leaf curl Bangalore virus (ToLCBV-Ban-4) (AF165098), suggesting that the epidemic was caused by an indigenous ToLCBV strain. Adult B. tabaci were collected from tomato plants at nine sites within the epidemic. DNA was extracted from 9 to 13 individuals per site and analyzed by RAPD-PCR using primers OpB20 and OpB11. Eighty to 100% of individuals per site had identical patterns to those of B biotype individuals from Israel and Florida, which were different to the patterns produced by the indigenous Indian B. tabaci. Adult B. tabaci from the epidemic and nonepidemic (Bangalore) regions were cultured separately on zucchini plants (n = 20) vars. Fordhook and Ambassador. Distinct silverleaf symptoms appeared in all plants fed on by the epidemic B. tabaci, but not on those fed on by the nonepidemic whiteflies. Irregular ripening of tomatoes was also a widespread problem in the epidemic area. Cytochrome oxidase I (COI) (720 bp) gene sequences were obtained for epidemic (AF321927) and nonepidemic (AF321928) B. tabaci, which had only 80% nucleotide identity to each other. A GenBank BLAST search showed that the former were most similar to B biotype whitefly from Israel (AF164667; 97%) and Texas (AF164675; 99%). The B biotype transmits Indian ToLCBV (2) and its introduction into India is of great concern as it is already associated with a devastating plant-disease epidemic.

References: (1) D. Deng et al. Ann. App. Biol. 125:327, 1994. (2) P. F. McGrath and B. D. Harrison. Ann. App. Biol. 126:307, 1995. (3) H. K. Ramappa et al. Ann. App. Biol. 133:187, 1998.
First Report of Phytoplasma Infection in Freesia Plant
Authors: Kamińska M. , Sliwa H. , Startek L.
Published: May 2007

Disease symptoms including leaf chlorotic and necrotic spots and stripes resembling freesia leaf necrosis (disease of unknown etiology [2]) were observed in freesia (Freesia × hybrida Klatt.) plants (cvs. Aladyn, Blue Lady, Cortine, Gompy, and White Rapid) naturally infected with Freesia mosaic virus (FMV) and grown in the greenhouse in Poland. The aim of this work was to study the association of the leaf symptoms occurring in freesia cultivars with phytoplasma infection and to identify it. To detect the possible presence of phytoplasmas in freesias, plants showing leaf symptoms (five cultivars) and symptomless plants (‘Blue Lady’, ‘Cortine’, and ‘Gompy’) were assayed for the presence of phytoplasma 16S rDNA fragment by polymerase chain reaction (PCR). For phytoplasma detection samples of young leaves and corms of 15 symptomatic and five symptomless freesias were taken. The samples were collected from the selected plants infected with FMV. In addition, leaf samples from healthy Catharanthus roseus plants and those infected with AKV reference strain of aster yellows (AY) phytoplasma group, subgroup I-B (supplied by W. Jarausch, INRA Bordeaux, France), were included for comparison. The amplification was performed using the universal—rA/fA or R16F1/R0 and group specific—R16(I)F1/R1 phytoplasma primer pairs (1). Phytoplasma identification was accompanied by digestion with AluI and MseI restriction endonucleases and restriction length polymorphism (RFLP) analysis of the R(I)F1/R1 or rA/fA products. DNA amplification product was observed in all nested PCRs containing template DNA derived from the leaves and corms of all symptomatic as well as symptomless and FMV-affected freesias except symptomless freesia ‘Cortine’. Based on RFLP analysis of PCR products and the comparison of the RFLP patterns with those of the strain AKV of aster yellows phytoplasma group (AY I-B), the associated phytoplasmas were identified as phytoplasma 16S rRNA group I, subgroup B. This work provides the first evidence that freesias examined were naturally infected with aster yellows phytoplasma. Detection of phytoplasma in diseased and symptomless but FMV-affected freesias underlines the need to know the role of this pathogen in the etiology of freesia diseases.

References: (1) I.-M. Lee et al. Phytopathology 84:559, 1994. (2) H. J. M van Dorst. Neth. J. Plant Pathol. 79:130, 1973.
Seed Transmission of Cylindrocladium parasiticum in Peanut
Authors: Randall-Schadel B. L. , Bailey J. E. , Beute M. K.
Published: May 2007

Seedborne Cylindrocladium parasiticum has been reported in peanuts and the possibility of seed transmission postulated; however, seed transmission has not been documented. Cinnamon brown speckles on peanut testae were correlated with isolation of C. parasiticum. Microscopy indicated that seed were colonized by cinnamon brown colored hyphae and microsclerotia interspersed in and on lightened areas of testa. Speckled seed from commercial seed lots (cultivars NC 7, NC 10C) were planted, with or without a chemical seed treatment (1992, captan + carboxin + dicloran [45:18:15% of product]; 1993 to 1995, captan + PCNB + carboxin [45:15:10% of product]), in fumigated fields with no history of peanut production. Asymptomatic seed from noninfested seed lots (cultivar NC-V 11 or NC 7) were checks for soilborne inoculum. C. parasiticum was isolated from all symptomatic seed lots prior to planting (percentage ranged from 4 to 45%) but was not isolated from asymptomatic seed. Seed transmission occurred from seed both with chemical seed treatment (0.25 to 2.75%) and without seed treatment (0.25 to 6.0%), but not in all years. Asymptomatic seed planted 2.5 cm from speckled seed increased the number of plants with Cylindrocladium black rot from two- to sixfold, illustrating the ability of disease to spread from colonized seed to uninfected plants. It was concluded that seed transmission of C. parasiticum is an important means by which this disease is spread within the seed industry.
Identification of Resistance Genes Effective Against Rice Bacterial Blight Pathogen in Eastern India
Authors: Shanti Marella Lalitha , George M. L. C. , Cruz C. M. Vera , Bernardo M. A. , Nelson R. J. , Leung H. , Reddy J. N. , Sridhar R.
Published: May 2007

Breeding for bacterial blight resistance in rice requires an understanding of the contemporary pathogen populations in the locations where resistance genes are to be deployed. We characterized 450 strains of Xanthomonas oryzae pv. oryzae collected from three states of India using polymerase chain reaction fingerprinting and virulence analysis. This pathogen collection was differentiated into 17 haplotypes (12 lineages at 80% similarity level). Significant differences in the distribution of haplotypes were observed among regions. Virulence analysis of the pathogen collection revealed nine pathotypes. Among the populations from three regions, the Orissa population was the most diverse, consisting of 11 out of 17 haplotypes and five out of nine pathotypes detected in the total collection. Representative pathotypes were used to evaluate seven near-isogenic lines carrying individual bacterial blight resistance genes (Xa3, Xa4, xa5, Xa7, Xa10, xa13, and Xa21) and gene pyramids. Pathogen strains compatible to individual genes were present in detectable frequencies, although no single strain could overcome all resistance genes. Gene combinations Xa4 + xa5, xa5 + Xa21, and Xa4 + xa5 + Xa21 conferred a broad spectrum of resistance to all the strains evaluated, supporting the strategy of pyramiding appropriate resistance genes.
First Report of a Furovirus Infecting Field-Grown Rye in North America
Authors: Momol M. T. , Blount A. , Kucharek T. A. , Petersen M. A. , Nielsen M. , Dankers W. , Barnett R. D.
Published: May 2007

Viral symptoms were present in a dwarf recurrent population (99RP17) of rye (Secale cereale) at the North Florida Research and Education Center in Quincy, Gadsden County, FL, during the winter and spring of 2000. Symptoms and distribution of the infected plants in the field were similar to those caused by Soilborne wheat mosaic virus (SBWMV; acronym WSBMV), which was first recognized in North America in 1919 (4) and found in Florida in wheat in 1970 (3). SBWMV has been observed based on symptoms in rye in North America (4). Interveinal, non-continuous, chlorotic areas of leaves and stunting of plants in patchy patterns occurred in four locations (0.8 to 1.6 km between locations). Incidences of the disease ranged from 3 to 15%. Leaves and roots of more than 25 plants were assessed. Using light microscopy, after staining with Calcomine Orange 2RS/Luxol Brilliant Green BL (1), amorphous, vacuolate inclusions were observed in all assayed leaves. With electron microscopy, rigid rods were present with a bimodal distribution of particle lengths that conformed to size distributions found originally in wheat in 1970 in Florida. Leaves with symptoms were sent to Agdia Inc. (Elkhart, IN) and samples were strongly positive for SBWMV using enzyme-linked immunosorbent assay. Cystosori of Polymyxa graminis were detected from a few roots from symptomatic plants. While these associations are suggestive of SBWMV, and rye is a reported host of SBWMV, the possibility of this virus being soilborne rye mosaic virus exists (2). Such a differentiation will require nucleotide sequence analysis. To our knowledge, this is the first report of a furovirus infecting field-grown rye in Florida and in North America.

References: (1) R. G. Christie and J. R. Edwardson. 1994. Light and Electron Microscopy of Plant Virus Inclusions Monogr. 9. University of Florida, Quincy. (2) R. Koenig et al. 1999. Arch. Virol. 144:2125–2140. (3) T. A. Kucharek and J. H. Walker. Plant Dis. Rep. 58:763–765, 1974. (4) H. H. McKinney. J. Agric. Res. 23:771–800, 1923.
Inheritance of Resistance to Phaeosphaeria Leaf Spot of Maize
Authors: Carson M. L.
Published: May 2007

Phaeosphaeria leaf spot is a potentially important maize disease that has recently appeared in the continental United States in winter breeding nurseries in southern Florida. Inbred lines re lated to B73 are particularly susceptible to Phaeosphaeria leaf spot, whereas inbreds related to Mo17 are highly resistant. The inheritance of resistance to Phaeosphaeria leaf spot was studied in the parents, F1, F2, and backcross generations derived from the cross B73 × Mo17. A replicated experiment was conducted over two winter nursery seasons in a southern Florida nursery Individual plants in plots were evaluated for Phaeosphaeria leaf spot severity (0 to 9 scale) at the mid-dent stage of kernel development. Variation in segregating generations appeared continuous, so generation mean analysis was used. Additive and, to a lesser extent, dominance gene action were determined to play a role in the inheritance of reaction to Phaeosphaeria leaf spot There was no evidence for epistatic gene interactions. Heritabilities (both narrow and broad sense) were high (0.70 to 0.85) and the magnitude of genotype × environment interactions was low. Estimates of the number of effective factors (genes) involved in the inheritance of resistance ranged from three to four. Selection should be highly effective in developing inbred lines with adequate levels of resistance to Phaeosphaeria leaf spot.
First Report of Fusarium oxysporum f. sp. lycopersici Race 3 on Tomato in Tennessee
Authors: Bost S. C.
Published: May 2007

In the summer of 2000, tomato (Lycopersicon esculentum Mill.) plants in several commercial fields in southeastern and eastern Tennessee exhibited symptoms of Fusarium wilt. All cultivars on which symptoms were observed are classified as resistant to races 1 and 2 of the causal fungus, Fusarium oxysporum Schlechtend.:Fr. f. sp. lycopersici (Sacc.) W.C. Snyder and H.N. Hansen. Race 3 has been reported from several areas (1), but not from Tennessee, a major producer of fresh market tomatoes. F. oxysporum was consistently isolated from discolored vascular tissue on potato dextrose agar (PDA). Pathogenicity and race determination tests for six isolates representing three counties were conducted by inoculating cultivars susceptible to races 1, 2, and 3 (Rutgers); resistant to race 1 (Bradley, Roma VF); resistant to races 1 and 2 (Conquest, Florida 47); or resistant to races 1, 2, and 3 (Floralina). Inoculum suspensions were obtained from 1-week-old cultures grown on PDA. Seedlings were grown in commercial potting mix for 3 weeks. The roots were rinsed and submerged for 30 s in inoculum suspensions (1 × 107 conidia per ml). Seedlings were then transplanted into potting mix in metal flats and placed in a greenhouse. Natural light conditions provided a 12-h photoperiod, and day and night temperatures averaged 29 and 17°C, respectively. Within 4 weeks after inoculation, all isolates caused symptoms of Fusarium wilt in all cultivars except Floralina, indicating that the isolates were race 3. The pathogen was reisolated from the discolored vascular tissue of diseased plants. Among the cultivars most severely affected by all six isolates was Conquest, which is resistant to F. oxysporum f. sp. radicis-lycopersici, the cause of Fusarium crown and root rot.

Reference: (1) M. L. Marlatt et al. Plant Dis. 80:1336, 1996.
First Report of Sugarcane yellow leaf virus (ScYLV) in Costa Rica
Authors: Avila R. , Arrieta M. C. , Villalobos W. , Moireira L. , Chavarría E. , Lockhart B. E. L. , Rivera C.
Published: May 2007

In Costa Rica, sugarcane plants with symptoms similar to those described for yellow leaf syndrome (YLS) (1,2) were first observed in 1994 in research plots of imported material in the midland areas of San Carlos and Turrialba. Recently, the same symptoms have been observed in commercial plantations in Turrialba. Symptomatic plants were characterized by yellowing of the leaves and central veins, the yellowing being more intense near the leaf tips. In severe cases, veins became reddish, and necrosis developed along the leaf edges, beginning at the leaf tip and extending to the base of the leaf. Growth of stems and roots was also reduced in infected plants. Minipurifications of six plants of four different varieties were examined by immunospecific electron microscopy (ISEM) using polyclonal antibodies (1). They were: one symptomatic plant each of the varieties H782313 and H608521; two symptomatic plants of H657052, and one asymptomatic plant each of H608521 and H827318. Isometric particles of approximately 28 nm were observed in the asymptomatic H827318 plant and in all symptomatic plants, with the exception of one plant of H657052. The size and morphology of the particles was similar to those reported for Sugarcane yellow leaf virus (ScYLV) (2). The presence of ScYLV was verified by indirect enzyme-linked immunosorbent assay (ELISA) using polyclonal antibodies (1). Twenty-two of 24 symptomatic plants and five of 13 asymptomatic plants were positive for ScYLV. These findings confirm the association of ScYLV with the yellows syndrome of sugarcane observed in Costa Rica. However, as was also reported by Scaglusi and Lockhart (1), ScYLV was not detected in several symptomatic plants, and research is continuing to determine whether other pathogens are associated with this syndrome in Costa Rica.

References: (1) S. Scagliusi and B. E. L. Lockhart. Phytopathology 90:120, 2000; (2) J. Vega et al. Plant Dis. 81:21, 1997.
First Report and Characterization of Rice yellow mottle virus in Central Africa
Authors: Traoré O. , Pinel A. , Fargette D. , Konaté G.
Published: May 2007

Rice yellow mottle virus (RYMV) of the genus Sobemovirus is the main virus infecting rice (Oryza sativa) in Africa. First reported in Kenya (East Africa), RYMV was later found in most countries of East and West Africa where rice is grown, and in Madagascar in the Indian Ocean. In Central Africa however, the disease had never been reported in rice fields. Ninety-eight field samples with typical yellow mottle symptoms from cultivated rice and two wild rice species (Oryza longistaminata and O. barthii) were collected in the Soudano-Sahelian zones, in the north of Cameroon and the south of Chad (Central Africa) in September 2000. RYMV was detected by ELISA with polyclonal antisera (1) in all samples. All virus isolates were also mechanically transmitted to rice cv. BG 90-2, which is highly susceptible to RYMV. Tests with monoclonal antibodies showed that most isolates from Central Africa were of the SI serotype, which is widespread in the Soudano-Sahelian zones of West Africa (1). The coat protein gene of 7 isolates was amplified by RT-PCR and the expected 720 bp fragment was obtained. Resulting sequences (AJ306735, AJ317949, AJ317950, AJ317951, AJ317952, AJ317953, AJ317954) shared over 95% sequence identity. They were compared to a set of sequences of RYMV isolates from cultivated rice of different geographical origins (2). Phylogenetic analyses by maximum parsimony (PAUP 4) showed that isolates from Central Africa belonged to a monophyletic group, a sister group of West African isolates from the Soudano-Sahelian zones, further supporting the geographic basis of RYMV diversity (2). RYMV incidence was generally less than 10% but reached 20% in some irrigated plots in the two countries.

References: (1) G. Konaté et al. Arch Virol. 142:1117, 1997. (2) A. Pinel et al. Arch. Virol. 145:1621, 2000.
Report of Sugarcane yellow leaf virus in Ecuador, Guatemala, and Nicaragua
Authors: Comstock J. C. , Pena M. , Vega J. , Fors A. , Lockhart B. E. L.
Published: May 2007

In 1998, sugarcane plants with symptoms similar to yellow leaf syndrome were observed in Ecuador, Guatemala, and Nicaragua. These plants showed yellowing of the central portion of the third to sixth leaves on the abaxial surface from the youngest expanding spindle leaf. Intense yellowing and necrosis of the leaf tip and the central portion of the leaf blade near the midrib occurred in severe cases. A tissue blot immunoassay was used to detect Sugarcane yellow leaf virus (SCYLV) in the midrib of the top visible dewlap leaf (2) using an antiserum specific to a Florida isolate of SCYLV (1). Since the virus can be detected in asymptomatic plants, leaf samples were collected from both symptomatic and asymptomatic plants. Symptom expression was most intense in plants at maturity that were under stress. Cut ends of leaf samples were imprinted on nitrocellulose membranes in the country of origin, and control samples of healthy and SCYLV-infected leaves were imprinted in Florida on each membrane prior to serological processing. The results from the following locations and cultivars, and the ratio of SCYLV-positive samples over the total samples is indicated: Milagro, Ecuador, PR 70-2085 (11/24) and PR 76-3385 (48/63) in 1999; Escuintla, Guatemala, CP 57-603 (1/10), CP 73-1547 (0/10), CP 72-2086 (120/308), PR 75-2002 (8/11), PR 78-294 (10/10), and PR 87-2080 (13/13) in both 2000 and 2001; Tipitapa, Nicaragua, L 68-40 (21/70) in 1998; and Chinandega, Nicaragua, CP 72-2086 (30/30) and CP 74-2005 (13/45) in 2000. CP 72-2086 is a major commercial cultivar in Central American countries and was infected in both Guatemala and Nicaragua. SCYLV was detected in 9 of 10 cultivars sampled. An exception was noticed in CP 73-1547 in Guatemala where none of the 10 plants tested were infected; however this cultivar has a high incidence of SCYLV in Florida. Only 1 of 10 samples of CP 57-603 was SCYLV positive in Guatemala; however, this cultivar has a low incidence of infection in Florida and is considered more resistant than the other CP cultivars sampled. To our knowledge, this is the first report SCYLV in Ecuador, Guatemala, and Nicaragua.

References: (1) S. M. Scagliusi and B. E. L. Lockhart. Phytopathology 90:120, 2000. (2) S. Schenck et al. Sugar Cane 4:5, 1997.
Reduction of Bacterial Spot Disease Severity on Tomato and Pepper Plants with Foliar Applications of Ammonium Lignosulfonate and Potassium Phosphate
Authors: Abbasi Pervaiz A. , Soltani Nader , Cuppels Diane A. , Lazarovits George
Published: May 2007

Bacterial spot is a serious and persistent disease problem of tomato and bell pepper in both the United States and Canada. Current disease management practices, based primarily on fixed copper bactericides, do not give consistent, effective protection. Foliar applications of ammonium lignosulfonate (ALS), derived from the wood pulping process, and the fertilizer potassium phosphate (KP) were tested for their ability to control this disease under both greenhouse and field conditions. Acibenzolar-S-methyl was included as a control. Greenhouse-grown tomato transplants treated with acibenzolar-S-methyl, 2 or 4% (vol/vol) ALS, 25 mM KP, or 2% ALS plus 10 mM KP and then inoculated with Xanthomonas campestris pv. vesicatoria had significantly less disease than the unprotected controls. Weekly foliar applications of acibenzolar-S-methyl, ALS, or KP significantly reduced disease severity on the foliage of inoculated field-grown tomato and pepper plants; although less disease appeared on the fruit of these plants, the effect was not always statistically significant except for the acibenzolar-S-methyl treatment. Acibenzolar-S-methyl increased the yield of marketable tomato fruit in 2 of 3 years of the study and that of pepper fruit in 1 of 2 years. There was a marked increase in the yield of marketable fruit on all ALS-treated pepper plants in 2001. None of the treatments significantly increased total tomato or pepper yield. ALS and KP had no observable phytotoxic effect on tomato or pepper foliage. Our results indicate that future integrated disease management programs for bacterial spot may be enhanced by including foliar sprays of these two products.
First Report of Phytophthora ramorum on Douglas-Fir in California
Authors: Davidson J. M. , Garbelotto M. , Koike S. T. , Rizzo D. M.
Published: May 2007

Phytophthora ramorum S. Werres & A.W.A.M. de Cock was isolated from three Douglas-fir (Pseudotsuga menziesii) saplings in a mixedevergreen forest in Sonoma County, California. Symptoms on these saplings included cankers on small branches (0.5 to 1 cm in diameter) resulting in wilting of new shoots, dieback of branches, and loss of leaves as much as 15 cm from the twig tip. Symptoms were observed on most saplings growing in the same area. On several smaller saplings (<1 m tall), P. ramorum infection resulted in the death of the leader and the top several whorls of branches. Isolates were identified as P. ramorum by their abundant chlamydospores and caducous, semi-papillate sporangia (2) and internal transcribed spacer rDNA sequences identical to those of isolates of P. ramorum from Quercus spp., Lithocarpus densiflorus, and Rhododendron (1,2). To test for pathogenicity, foliage inoculations were conducted on seedlings in two trials by misting 30 leaves per trial (five leaves per seedling plus controls) with sterile distilled water and pinning inoculum plugs, taken from the margin of P. ramorum cultures, to the upper surface of leaves. Inoculation resulted in lesions ranging between 1 and 12 mm long, and P. ramorum was recovered from 47% of inoculated leaves. Symptoms were not restricted to inoculated leaves, and in 26 single-leaf inoculations, lesions 17 to 85 mm long developed on branches (five mm in diameter) adjacent to the inoculated leaf. Isolation success from branch lesions was 50%, despite the fact that such lesions were apparently disjunct from the small 1-mm lesions developing on inoculated leaves. Stems of Douglas-fir seedlings (approximately 1 cm in diameter) were wound inoculated (1) in two trials consisting of 10 inoculated seedlings per trial plus 10 controls. After 6 weeks, lesion lengths in the cambium averaged 38 mm (range 12 to 62 mm), and three seedlings were completely girdled. P. ramorum was recovered from 75% of inoculated stems. Mean lesion lengths on seedlings inoculated with P. ramorum were significantly greater (P < 0.05) in both trials than those of control inoculations (mean 9 mm) based on analysis of variance. We have not observed unusual mortality or disease symptoms on overstory Douglas-fir trees in natural forests. The importance of P. ramorum branch tip dieback for growth and reproduction of Douglas-fir is unknown. Douglas-fir is present in many forests in California and Oregon already infested by P. ramorum, yet we have found infection of plants at only one location. At this site, symptomatic Douglas-fir saplings were surrounded by bay laurel (Umbellularia californica) trees with extremely high levels of P. ramorum infection. P. ramorum is known to sporulate prolifically on bay laurel leaves. More studies are necessary to determine if the incidence of P. ramorum in Douglas-fir extends to other locations or if it is limited to this one locale.

References: (1) D. M. Rizzo et al. Plant Disease 86:205, 2002. (2) S. Werres et al. Mycol. Res. 105:1155, 2001.
Differential Transmission of Isolates of the High Plains virus by Different Sources of Wheat Curl Mites
Authors: Seifers Dallas L. , Harvey Tom L. , Louie Raymond , Gordon D. T. , Martin T. J.
Published: May 2007

High Plains virus (HPV) isolates from Colorado, Idaho, Kansas, Texas, and Utah were serologically related, had similar relative molecular masses (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) for the 32-kDa diagnostic HPV protein, and were transmissible and maintained free of Wheat streak mosaic virus (WSMV) by vascular puncture inoculation. Collections of wheat curl mites (Aceria tosichella Keifer; WCM) from Kansas, Montana, Nebraska, South Dakota, and Texas differentially transmitted these isolates. For collections from South Dakota and Texas, little or no HPV transmission occurred, whereas WCM from Nebraska and Montana transmitted all five isolates. The collection from Kansas mostly transmitted only one HPV isolate. Aviruliferous or viruliferous WSMV Nebraska WCM transmitted HPV at similar rates and aviruliferous Montana WCM transmitted HPV at lower levels than viruliferous Montana WCM.
First Report of Xanthomonas Leaf Blight of Onion in California
Authors: Nunez J. J. , Gilbertson R. L. , Meng X. , Davis R. M.
Published: May 2007

In 2000 and 2001, severe leaf blight of fresh market onions occurred in several fields in the Antelope Valley of California, a high desert area located in northern Los Angeles County. In at least two fields, 70% of the canopy was affected, which resulted in an estimated yield reduction of over 50%. Both organically and conventionally grown onions were affected. Symptoms included numerous small chlorotic lesions that appeared first on older leaves. Lesions were often surrounded by water-soaked margins. As the season progressed, the lesions became elongated and necrotic. Entire leaf blades were often killed. The disease never progressed into the bulbs, but bulbs of infected plants never grew to full size. Yellow mucoid bacterial colonies were recovered on yeast extractdextrose-CaCO3 agar from symptomatic tissue. All isolates were gram-negative rods with single polar flagella. Two representative isolates were identified as Xanthomonas campestris based on their carbon utilization profile (similarity index of 0.784 and 0.850; Biolog, Hayward, CA), fatty acid profile (similarity index of 0.588; MIS-TSBA, version 4.10, MIDI Inc., Newark, DE), and 16S-23S intergenic spacer DNA sequences (98% sequence identify with strains of X. campestris). In greenhouse pathogenicity tests, eight white globe onion plants were inoculated with a bacterial suspension (106 CFU/ml) of each of the two isolates. Plants were inoculated by spraying the suspension on leaves lightly injured by rubbing with Carborundum or puncturing with needles dipped in the suspension. Controls were inoculated with water. All plants inoculated with the bacteria developed symptoms in 6 days. The bacterium was reisolated from all inoculated plants and confirmed as Xanthomonas. The trial was conducted twice. To our knowledge, this is the first report of Xanthomonas leaf blight of onion in California. In the United States, the disease has been reported in Texas and Colorado (1,2).

References: 1. T. Isakeit et al. Plant Dis. 84:201, 2000. 2. H. F. Schwartz and K. Otto. Plant Dis. 84:922, 2000.
Factors Associated with Foliar Disease of Staked Fresh Market Tomatoes Grown Under Differing Bed Strategies
Authors: Mills Douglas J. , Coffman C. Benjamin , Teasdale John R. , Everts Kathryne L. , Anderson James D.
Published: May 2007

The use of mulch or compost to reduce foliar disease in fresh market tomato could reduce fungicide use. Between 1997 and 1999, foliar disease was monitored in tomatoes grown in beds with bare soil, black polyethylene, composted dairy manure, or hairy vetch. Early blight was reduced in plots with vetch compared with bare soil or compost in all years and compared with polyethylene cover in 1 year. Early blight was reduced in plots with polyethylene versus compost and bare soil in 1 and 2 years, respectively. Septoria leaf spot was reduced in plots with vetch versus other bed strategies in 1998 and bare soil or compost in 1999. This disease was reduced in plots with polyethylene versus bare soil or compost in 1998 and 1999. Soil coverage of tomato leaflets and soil particle dispersal were reduced in plots with polyethylene or vetch versus bare soil or compost in both years that these variables were assessed. Sensor wetness duration was reduced in plots with polyethylene or vetch versus bare soil or compost in one of two years. These findings suggest that foliar disease reduction in mulch was associated with reduced splash dispersal and, in one year, reduced leaf wetness.
Effect of Metalaxyl Resistance and Cultivar Resistance on Control of Phytophthora nicotianae in Tobacco
Authors: van Jaarsveld E. , Wingfield M. J. , Drenth A.
Published: May 2007

Phytophthora nicotianae is a devastating root and stem pathogen of tobacco (Nicotiana tabacum) in South Africa. Growers strive to control the resulting disease, known as black shank, with metalaxyl treatments and resistant cultivars. The aim of this study was to consider whether development of metalaxyl resistance in P. nicotianae has contributed to poor disease control and if recently developed cultivars with high levels of resistance require metalaxyl for effective control. One hundred and thirty-two isolates of P. nicotianae were screened for sensitivity to metalaxyl. P. nicotianae isolates from most tobacco farms were metalaxyl sensitive. Growth of most isolates was inhibited completely at 1.0 μg a.i./ml. However, isolates from the MKTV tobacco producing area showed EC50 values ranging from 1.02 μg a.i./ml to 3.57 μg a.i./ml. Twenty-one tobacco cultivars were planted and treated with and without metalaxyl in two different growing seasons to evaluate their resistance to P. nicotianae and the value of using metalaxyl. Hicks was the most susceptible cultivar. Vuma/3/46, LK30/40/60-1, and LK33/60 exhibited the greatest resistance to P. nicotianae. Use of metalaxyl in combination with moderately resistant cultivars such as NC60 × TL33 and LK10/80/60 effectively reduced black shank in the field. Resistant cultivars were healthy and no significant difference between metalaxyl treated and untreated plants was observed.
Report of Root Rot Caused by Pythium F-Group on Hydroponically Grown Celery in South Africa
Authors: Labuchagne N. , Gull C. , Wehner F. C. , Botha W. J.
Published: May 2007

Celery (Apium graveolens) is commonly grown in hydroponic systems in South Africa. During the warm summer months, plants often become stunted or die, with mortality as high as 70% in some systems. Affected plants show severe root rot and yellowing of the foliage. Root segments excised from symptomatic celery plants collected from various hydroponic systems in Gauteng Province, South Africa, were rinsed in sterile distilled water and plated on PARP medium (2). Pythium was isolated consistently from both rotted and symptomless roots. Isolates produced only noninflated filamentous sporangia and no oospores, conforming to the description of Pythium F-group (1). Koch's postulates were confirmed by inoculating 4-week-old celery seedlings cultivated in aerated nutrient solution in a hydroculture system in the greenhouse. A zoospore suspension (105 zoospores per ml) of Pythium F-group cultured on V8 juice agar was added to the nutrient solution at the rate of 3 ml/1iter. Control plants received no inoculum, and the experiment was repeated once. Plants were assessed after 4 weeks. All inoculated plants showed symptoms of root rot, stunting, and yellowing, whereas control plants remained healthy. Pythium F-group was recovered on PARP medium only from the roots of inoculated plants. Pythium F-group has been described as a pathogen of celery elsewhere, but to our knowledge, this is the first report of root rot caused by the fungus on celery in South Africa.

References: (1) M. W. Dick. Keys to Pythium. University of Reading Press, Reading, UK, 1990. (2) S. N. Jeffers and S. B. Martin. Plant Dis. 70:1038, 1986.
Coryneum Twig Canker on Southern Live Oak in Florida
Authors: Wood A. K. , Tainter F. H.
Published: May 2007

In May 2001, following several years of severe drought, a depressed twig canker was observed on southern live oak (Quercus virginiana) in central Florida. Disease symptoms included twig and branch canker and dieback, distortion of young leaves, and premature leaf drop. Observation of conidia from sporulating acervuli revealed that Coryneum japonicum was associated with the cankers (1,2). The fungus produced abundant, subepidermal, dark brown, linearly arranged acervuli on affected tissues. Conidia were light brown, narrowly fusiform, often curved, and tapered toward an obtuse apex. The conidia had truncate bases and were five to seven distoseptate. Septa were medium to dark brown and sometimes prominent. The length to width ratio of conidia was >4:1. Under normal weather conditions, twig elongation of live oak trees is usually 30 to 60 cm per growing season; however, only 7 to 10 cm was observed on trees affected by C. japonicum. The fungus has been reported on bark and dead twigs of Quercus macrocarpa, Q. gambelii, Q. dilatata, and other species of Quercus in Canada, Pakistan, and the United States (2). To our knowledge, this is the first report of C. japonicum in Florida and on southern live oak trees. A specimen has been deposited in the U.S. National Fungus Collections (BPI number 841441).

References: (1) B. C. Sutton. Mycol. Pap. 138:33, 1975. (2) B. C. Sutton. The Coelomycetes, CMI, Kew, England, 1980.
First Confirmation of Phytophthora quercina on Oaks in Asia
Authors: Balci Y. , Halmschlager E.
Published: May 2007

During surveys of forests in the Asian Region of Turkey in 1999, 2000, and 2001, mature trees of several oak species were observed to have symptoms of decline, including thinning of the crown, yellowing and wilting of leaves, dieback of branches, and growth of epicormic shoots on branches and the main trunk. Observations over time confirmed a slow progress of tree mortality. To isolate Phytophthora spp. that might be associated with the decline, samples of rhizosphere soil including fine roots with necrotic lesions, were collected from around the bases of individual trees. Young leaflets from Quercus robur, Q. petraea, and Q. hartwissiana were used in a bioassay to bait flooded soil subsamples. After 3 to 5 days, baits were transferred to plates of PARPNH, a medium selective for Phytophthora spp. (1). Phytophthora spp. were recovered from 38 of 51 sites investigated (75%). In all, 10 species of Phytophthora were isolated; P. quercina was detected most frequently and was obtained from 29 (57%) sampled sites. Identification of isolates of P. quercina was based on comparisons of cultural and morphological characteristics to the description of the holotype (2) and to authentic cultures. Slight differences from the description of the holotype were observed for the size of sporangia, oogonia, and chlamydospores. On V8 agar most of the colonies showed an optimal radial growth at 22.5°C, with a growth rate ranging from 4.5 to 5.6 mm per day. Isolates from Turkey showed a lower optimal temperature and a higher growth rate compared with European strains. Recent studies have shown that many Phytophthora species, including P. quercina, occur in declining oak stands in Europe. In pathogenicity tests of infested soil, P. quercina isolates proved to be one of the more pathogenic species to roots of young Q. robur plants (2). Previously, P. quercina was only found in Europe. New hosts species for P. quercina include Q. hartwissiana, Q. frainetto, and the endemic species Q. vulcanica. Observations suggest that P. quercina is widespread in Turkey and occurs within the natural range of oak, which raises the question of the role of P. quercina in the oak decline syndrome.

References: (1) T. Jung et al. Eur. J. For. Pathol. 26:253, 1996. (2) T. Jung et al. Mycol. Res. 103:785, 1999.
Races of Puccinia graminis in the United States During 1997 and 1998
Authors: McVey D. V. , Long D. L. , Roberts J. J.
Published: May 2007

Wheat stem rust caused negligible yield losses in 1997 and 1998. Overwintering sites were found in central and east-central Louisiana in 1997, and in northwestern Florida, northeastern Louisiana, and central Texas in 1998. Race Pgt-TPMK predominated in 1997 with 69% of 100 isolates with race RCRS next at 11%. In 1998, race RCRS predominated with 55% of 132 isolates, and TPMK occurred at 10%. Race QFCS occurred at 8% in 1997 and 31% in 1998. Races QCCS and QTHJ were found in 1997, and races QFBS, RKMQ, RKQQ, and RCMS were found in 1998. Race QCCJ, virulent to barley with the Rpg1 gene for stem rust resistance, was not found from wheat in 1997 or 1998. No virulence was found to wheat lines with Sr 13, 22, 24, 25, 26, 27, 29, 30, 31, 32, 37, Gt, or Wld-1. Oat stem rust was found earlier in 1997 than 1998, but was more widespread in 1998. Race NA27, virulent to Pg-1, -2, -3, -4, and -8, was the predominant race in the United States in 1997 (79% of 116 isolates) and again in 1998 (79% of 116 isolates). NA16, virulent to Pg-1, -3, and -8, was found in the south (1997 and 1998), and NA5, virulent to Pg-2 and -15, and NA10, virulent to Pg-2, -3, and -15, were found in the west (1997).
First Report of Violet Root Rot Caused by Rhizoctonia crocorum on Alfalfa in Iran
Authors: Naseri B.
Published: May 2007

In August 2000, violet root rot of alfalfa (Medicago sativa L.) was observed in circular to irregular patches of alfalfa. Affected alfalfa plants turned yellow to brown in fields in the Zanjan Province of Iran. Diseased roots had a compact felt cloak of violet mycelium with white or purple strands. Samples of symptomatic roots were collected from 11 locations in the province and cultured on potato dextrose agar and malt-extract agar. The morphology of fungi isolated from pieces of alfalfa root with infection cushions from each location was consistent with Rhizoctonia crocorum (Pers.:Fr.) DC. (teleomorph Helicobasidium brebissonii (Desm.) Donk) (1). Seeds of alfalfa cv. Hamadani were sown in soil infested with inoculum of one isolate of R. crocorum prepared on a sandrye grain-water medium (20 g per pot) (2). Under 10 h of light at 22°C, destroyed taproots were evident after 8 months on 64 of 100 inoculated plants, and R. crocorum was reisolated from all 64 plants. Fifty noninoculated plants showed no symptoms. This is the first report of violet root rot of alfalfa in Iran.

References: (1) P. Roberts. Pages 157–158 in: Rhizoctonia-Forming Fungi. The Trustees, Royal Botanic Garden, Kew, UK, 1999. (2) P. G. Valder. Tran. Br. Mycol. Soc. 41:283, 1958.
Sensitivity of North American Isolates of Phytophthora erythroseptica and Pythium ultimum to Mefenoxam (Metalaxyl)
Authors: Taylor R. J. , Salas B. , Secor G. A. , Rivera V. , Gudmestad N. C.
Published: May 2007

A 4-year study (1997 to 2000) was conducted to determine the sensitivities of the potato tuber rot pathogens, Phytophthora erythroseptica and Pythium ultimum, to mefenoxam (metalaxyl). A total of 2,277 tubers showing symptoms of “water rot” were collected from 16 states and 2 Canadian provinces. From these, 849 isolates of P. erythroseptica and 213 isolates of P. ultimum were obtained, and 805 and 190 isolates, respectively, were tested for their ability to grow on V8 medium amended at 0.01 to 100 μg/ml with fungicide. Isolates ranged widely in their responses to mefenoxam. The presence of resistant isolates (EC50 > 100 μg ml-1) of P. erythroseptica in the potato producing areas of Maine was confirmed. The presence of P. erythroseptica isolates in Idaho and Minnesota resistant to mefenoxam is reported for the first time. The proportion of P. erythroseptica isolates resistant to mefenoxam varied from 2.9 to 36.2% between 1997 and 2000. The proportion of resistant P. ultimum isolates represented only a small proportion of the isolates tested (3.7%). A single resistant P. ultimum isolate was recovered from Washington, whereas most of the resistant isolates obtained (5 of 7) were collected in Minnesota during the final year of the study. This is the first report of resistance in P. ultimum pathogenic to potato tubers. These observations suggest that pink rot and leak could become significant problems in the future, particularly in those areas where resistance has been detected. Our results have implications for the effective management of water rot. Monitoring the sensitivity of the pathogen population to mefenoxam in all production areas should be considered and integrated as a part of the overall disease management strategy.
Evaluation of Pearl Millet Grain Hybrids for Resistance to Meloidogyne spp. and Leaf Blight Caused by Pyricularia grisea
Authors: Timper P. , Wilson J. P. , Johnson A. W. , Hanna W. W.
Published: May 2007

Pearl millet, Pennisetum glaucum, has potential as a grain crop in the southeastern United States. Our objectives were to (i) determine the resistance and/or tolerance of pearl millet hybrids to Meloidogyne incognita race 3 and M. arenaria race 1; (ii) compare reproduction of Meloidogyne spp. on pearl millet and corn; and (iii) determine the disease severity of leaf blight caused primarily by Pyricularia grisea. In a field naturally infested with M. incognita, experimental pearl millet hybrids with inbreds 114 and 117 as the pollinators had fewer numbers of second-stage juveniles and more severe leaf blight than did HGM-100, a nematode-susceptible hybrid; hybrids with inbred 115 as the pollinator were similar to HGM-100 in both nematode numbers and foliar disease severity. Grain yields in pearl millet were greater in plots treated with 1,3-dichloropropene than in control plots and were negatively correlated with leaf blight severity. In a greenhouse experiment, both M. incognita and M. arenaria produced fewer eggs on pearl millet hybrids with pollinators 114, 117, 101, 102, and 103 than on hybrid HGM-100. Reproduction of M. incognita was less on the resistant pearl millet hybrids than on corn. Because both M. incognita and P. grisea can reduce grain yield of pearl millet, hybrids developed for the southeastern United States should be resistant to both pathogens.
First Confirmation of Sphaerotheca macularis on Strawberry Plants in Southwestern Spain
Authors: Santos B. de los , Blanco C. , Porras M. , Barrau C. , Romero F.
Published: May 2007

In February 2001, in seven small tunnel production fields in southwestern Spain, symptoms and signs of powdery mildew were detected on strawberry (Fragaria × ananassa) cvs. Camarosa, Andana, and Carisma. On ‘Camarosa’ plants, white patches of mycelium developed on the lower leaf surface. Later, the leaf edges rolled upward, and reddish or necrotic irregular spots appeared on the lower leaf surface. Some immature fruits were abnormally hard and covered with a dense white mycelium. Symptoms were much less severe on ‘Andana’ and ‘Carisma’. Microscopic observations revealed conidia in chains, ellipsoidal to barrel-shaped, with fibrosin granules. Mean dimensions of conidia (N= 70) were 31.2 μm ± 2.8 × 20.39 μm ± 4.1. Cleistothecia were not detected. Based on these characteristics, the causal agent was identified as Sphaerotheca macularis (Wallr.:Fr.) Lind. (1). Pathogenicity was confirmed by inoculating leaves of 2-month-old potted ‘Camarosa’ plants. S. macularis obtained from field-grown plants was maintained on ‘Camarosa’ strawberry leaves in a growth chamber (20°C and 100% relative humidity). Inoculum was obtained from freshly sporulating infected leaves 11 days after inoculation. Conidia of S. macularis were gently brushed into 100-ml distilled water containing two drops of Tween 20. Ten strawberry ‘Camarosa’ plants were inoculated by misting with a conidial suspension (104 conidia per ml) (2). The plants were incubated at 100% relative humidity for 48 h in the greenhouse (15 to 25°C). Colonies of powdery mildew were observed on leaves after 18 days. To our knowledge, this is the first confirmation of S. macularis on strawberry in Spain.

References: (1) K. G. Mukerji. No. 188 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, UK, 1968. (2) R. Reuveni et al. Crop Prot. 19:335, 2000.
Homalodisca coagulata (Hemiptera, Cicadellidae) Transmission of Xylella fastidiosa to Almond
Authors: Almeida R. P. P. , Purcell A. H.
Published: May 2007

Almond leaf scorch (ALS) is caused by the bacterium Xylella fastidiosa, transmitted by sharpshooter leafhoppers and spittlebugs. The recent invasion of a X. fastidiosa vector, Homalodisca coagulata (Hemiptera, Cicadellidae), into California may have major consequences to the spread of ALS because this insect feeds readily on trees, including stone fruit species. We found that, under laboratory conditions, H. coagulata acquired X. fastidiosa from symptomatic almond plants with low efficiency relative to grape (3.3 to 10% per individual per day). Inoculation efficiency also was low, approximately 4% per insect per day. H. coagulata inoculated 1-year-old woody tissues of almond plants at similar rates as green shoots. H. coagulata transmitted two X. fastidiosa grape strains from grape source plants to grape and almond. We also observed X. fastidiosa transmission to dormant almond plants. X. fastidiosa populations in the petioles of field-collected symptomatic almond leaves were not higher than 107 CFU/g of tissue, suggesting that low bacterial populations within almond are partially responsible for the lower acquisition rates observed from diseased almond compared with diseased grape, which are usually within the range of 108 to 109 CFU/g. The relevance of our findings to ALS epidemiology, considering H. coagulata as a vector, is discussed.