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  • 1
    Online Resource
    Online Resource
    The Effect of Pythium ultimum and Soil Flooding on Two Soybean Cultivars
    Scientific Societies ; 2006
    In:  Plant Disease Vol. 90, No. 5 ( 2006-05), p. 597-602
    Details
    In: Plant Disease, Scientific Societies, Vol. 90, No. 5 ( 2006-05), p. 597-602
    Abstract: The effect of flooding and Pythium ultimum on soybean, Glycine max, was determined in a series of greenhouse experiments using the cultivars Hutcheson and Archer. Seeds were planted into pasteurized soil either not infested or infested with sand-cornmeal inoculum of P. ultimum and either flooded at emergence for 2 days or at the four leaf node stage (V4) for 5 days. A nonflooded control was included in each experiment. Seeds placed directly into infested soil resulted in little or no stand for Hutcheson regardless of flood treatment, whereas stand was reduced for Archer only in the flooded infested soil treatment. Additional experiments were conducted by placing seed onto a 2- to 5-mm layer of pathogen-free soil on top of the infested soil. Flooding at emergence reduced plant height, growth stage, and top dry weight for Hutcheson and root fresh weight for both cultivars. Greater reductions for Hutcheson in root weight, and top dry weight in P. ultimum-infested soil in the soil layer experiments, also indicated that Hutcheson was more susceptible than Archer. Flooding alone decreased root weights, and infestation with P. ultimum reduced weights further resulting in an additive effect. This also was the case for plant height, growth stage, and top dry weight for Hutcheson for flooding at emergence. Root discoloration was greatly increased for both cultivars in infested soil flooded at emergence. Similar results were found when plants were flooded at V4; however, the effect was not as great as with flooding at emergence. These studies indicate that Pythium damping-off and root rot may account for a portion of the negative response of soybean to flooding. The results also indicate that Archer has some resistance to P. ultimum.
    Type of Medium: Online Resource
    ISSN: 0191-2917 , 1943-7692
    URL: Article
    DOI: 10.1094/PD-90-0597
    Language: English
    Publisher: Scientific Societies
    Publication Date: 2006
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  • 2
    Online Resource
    Online Resource
    Identification of Phytoplasma Taxa and Insect Vectors of Peach Yellow Leaf Roll Disease in California
    Scientific Societies ; 2002
    In:  Plant Disease Vol. 86, No. 7 ( 2002-07), p. 759-763
    Details
    In: Plant Disease, Scientific Societies, Vol. 86, No. 7 ( 2002-07), p. 759-763
    Abstract: Two peach diseases in California, western X-disease (WX) and peach yellow leaf roll (PYLR) are caused by two genetically distinct phytoplasmas. Based on symptoms alone, WX and PYLR cannot be reliably distinguished. The objectives of this study were to determine which phytoplasma was causing PYLR disease in peach orchards planted near pear orchards and which phytoplasmas were present in potential insect vectors captured in both peach and pear orchards. Leafhoppers and pear psylla were collected from yellow sticky traps placed in three pear orchards and four peach orchards located in the Sacramento Valley from 1994 to 1996. DNA was extracted from potential vectors and suspect diseased trees, and analyzed for the presence of the WX and PYLR phytoplasmas using strain-specific DNA hybridization or polymerase chain reaction (PCR) assays. The most abundant phytoplasma detected in diseased peach trees was the PYLR phytoplasma. In 1994 and 1995, 10 to 25% of groups of pear psylla tested positive for the PYLR phytoplasma, while no psylla groups tested positive for the WX phytoplasma. Only one captured leafhopper tested positive for the WX phytoplasma. These results indicate the pear psylla is the primary vector of PYLR in northern California.
    Type of Medium: Online Resource
    ISSN: 0191-2917 , 1943-7692
    URL: Article
    DOI: 10.1094/PDIS.2002.86.7.759
    Language: English
    Publisher: Scientific Societies
    Publication Date: 2002
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  • 3
    Online Resource
    Online Resource
    Soybean Response to Flooded Soil Conditions and the Association with Soilborne Plant Pathogenic Genera
    Scientific Societies ; 2006
    In:  Plant Disease Vol. 90, No. 5 ( 2006-05), p. 592-596
    Details
    In: Plant Disease, Scientific Societies, Vol. 90, No. 5 ( 2006-05), p. 592-596
    Abstract: The role of soilborne pathogens in flood damage on soybeans, Glycine max, was examined using six genotypes representing a reputed range of flood tolerances. Genotypes were planted in single-row plots from 1996 to 1998 with flood treatments of no flood, flood at emergence (3-day duration), or flood at the fourth leaf node growth stage (7-day duration). Three or four days after removing each flood treatment, plant stands were estimated and 15 plants were collected from each plot, weighed, and rated for root discoloration. Roots were assayed for the presence of fungi and other filamentous eukaryotic organisms. Plant stands were reduced by flooding at emergence compared with the nonflooded control. Flooding at both growth stages caused significant increases in root discoloration compared with nonflooded soybeans. Plant weights were reduced in 2 of 3 years for flooding at emergence. Pythium was the only genus of filamentous organisms whose isolation frequency increased with flooding. Of the 60 Pythium isolates evaluated representing the different cultural groups based on appearance and growth rate on potato dextrose agar, cornmeal agar, and V8 agar, 47% were moderately to highly virulent on soybean. Pythium spp. isolated from soybean included the pathogenic species P. ultimum, P. aphanidermatum, P. irregulare, and P. vexans and Group HS. Nonpathogenic P. oligandrum also was isolated from soybean.
    Type of Medium: Online Resource
    ISSN: 0191-2917 , 1943-7692
    URL: Article
    DOI: 10.1094/PD-90-0592
    Language: English
    Publisher: Scientific Societies
    Publication Date: 2006
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  • 4
    Online Resource
    Online Resource
    Importance of Fungicide Seed Treatment and Environment on Seedling Diseases of Cotton
    Scientific Societies ; 2012
    In:  Plant Disease Vol. 96, No. 12 ( 2012-12), p. 1805-1817
    Details
    In: Plant Disease, Scientific Societies, Vol. 96, No. 12 ( 2012-12), p. 1805-1817
    Abstract: The importance of fungicide seed treatments on cotton was examined using a series of standardized fungicide trials from 1993 to 2004. Fungicide seed treatments increased stands over those from seed not treated with fungicides in 119 of 211 trials. Metalaxyl increased stands compared to nontreated seed in 40 of 119 trials having significant fungicide responses, demonstrating the importance of Pythium spp. on stand establishment. Similarly, PCNB seed treatment increased stands compared to nontreated seed for 44 of 119 trials with a significant response, indicating the importance of Rhizoctonia solani in stand losses. Benefits from the use of newer seed treatment chemistries, azoxystrobin and triazoles, were demonstrated by comparison with a historic standard seed treatment, carboxin + PCNB + metalaxyl. Little to no stand improvement was found when minimal soil temperatures averaged 25°C the first 3 days after planting. Stand losses due to seedling pathogens increased dramatically as minimal soil temperatures decreased to 12°C and rainfall increased. The importance of Pythium increased dramatically as minimal soil temperature decreased and rainfall increased, while the importance of R. solani was not affected greatly by planting environment. These multi-year data support the widespread use of seed treatment fungicides for the control of the seedling disease complex on cotton.
    Type of Medium: Online Resource
    ISSN: 0191-2917 , 1943-7692
    URL: Article
    DOI: 10.1094/PDIS-01-12-0031-SR
    Language: English
    Publisher: Scientific Societies
    Publication Date: 2012
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  • 5
    Online Resource
    Online Resource
    The Effect of pH on Spore Germination, Growth, and Infection of Strawberry Roots by Fusarium oxysporum f. sp. fragariae , Cause of Fusarium wilt of Strawberry
    Scientific Societies ; 2019
    In:  Plant Disease Vol. 103, No. 4 ( 2019-04), p. 697-704
    Details
    In: Plant Disease, Scientific Societies, Vol. 103, No. 4 ( 2019-04), p. 697-704
    Abstract: Previous work has shown that raising the pH of acidic soil to near neutrality can reduce the incidence of Fusarium wilt. The basis for this effect has not been established. The present study assessed effects of pH on spore germination, growth, and infection of strawberry roots by Fusarium oxysporum f. sp. fragariae, the cause of Fusarium wilt of strawberry. There was not a significant effect of pH (5 versus 7) on the rate of spore germination at either 20 or 25°C for any of the three tested isolates (one representative of each clonal lineage of F. oxysporum f. sp. fragariae found in California). Likewise, pH did not have a significant effect on fungal growth at 20°C. At 25°C, two isolates grew faster at pH 7 than at pH 5. Growth of the third isolate was unaffected by the difference in pH. For the strawberry cultivar Albion, the frequency of root infection was significantly higher for plants grown in acidified soil (near pH 5) than for plants grown in soil near neutrality. The higher frequency of root infection in acidified soil was associated with a lower level of microbial activity, as measured by hydrolysis of fluorescein diacetate.
    Type of Medium: Online Resource
    ISSN: 0191-2917 , 1943-7692
    URL: Article
    DOI: 10.1094/PDIS-08-18-1296-RE
    Language: English
    Publisher: Scientific Societies
    Publication Date: 2019
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  • 6
    Online Resource
    Online Resource
    Fusarium oxysporum f. sp. mori , a New Forma Specialis Causing Fusarium Wilt of Blackberry
    Scientific Societies ; 2017
    In:  Plant Disease Vol. 101, No. 12 ( 2017-12), p. 2066-2072
    Details
    In: Plant Disease, Scientific Societies, Vol. 101, No. 12 ( 2017-12), p. 2066-2072
    Abstract: Fusarium oxysporum has recently been identified as the cause of a wilt disease affecting blackberry in California and Mexico. Thirty-six isolates of F. oxysporum obtained from symptomatic blackberry plants in California and Mexico were comprised of nine distinct somatic compatibility groups (SCGs). Phylogenetic analysis of a concatenated data set, consisting of sequences of the translation elongation factor 1-α and β-tubulin genes and the intergenic spacer of the ribosomal DNA, identified nine three-locus sequence types, each of which corresponded to an SCG. Six SCGs were present only in California, two only in Mexico, and one in both California and Mexico. An isolate associated with the most common SCG in California was tested for pathogenicity on blueberry, raspberry, strawberry, and lettuce. All blueberry, raspberry, and lettuce plants that were inoculated remained healthy, but two of the five strawberry cultivars tested developed symptoms. The three strawberry cultivars that were resistant to the blackberry pathogen were also resistant to F. oxysporum f. sp. fragariae, the cause of Fusarium wilt of strawberry. We propose to designate strains of F. oxysporum that are pathogenic to blackberry as Fusarium oxysporum f. sp. mori forma specialis nov.
    Type of Medium: Online Resource
    ISSN: 0191-2917 , 1943-7692
    URL: Article
    DOI: 10.1094/PDIS-03-17-0428-RE
    Language: English
    Publisher: Scientific Societies
    Publication Date: 2017
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  • 7
    Online Resource
    Online Resource
    The Population of Fusarium oxysporum f. sp. fragariae , Cause of Fusarium Wilt of Strawberry, in California
    Scientific Societies ; 2017
    In:  Plant Disease Vol. 101, No. 4 ( 2017-04), p. 550-556
    Details
    In: Plant Disease, Scientific Societies, Vol. 101, No. 4 ( 2017-04), p. 550-556
    Abstract: The objectives of this study were to investigate the structure of the population of Fusarium oxysporum f. sp. fragariae in California and to evaluate methods for its detection. Fifty-nine isolates of F. oxysporum f. sp. fragariae were obtained from diseased strawberry plants and their identity was confirmed by pathogenicity testing. The full nuclear ribosomal intergenic spacer (IGS) and elongation factor 1-α gene (EF-1α) were amplified by polymerase chain reaction (PCR) and sequenced to elucidate phylogenetic relationships among isolates. IGS and EF-1α sequences revealed three main lineages, which corresponded to three somatic compatibility groups. Primers designed to detect F. oxysporum f. sp. fragariae in Japan amplified a 239-bp product from 55 of 59 California isolates of F. oxysporum f. sp. fragariae and from no nonpathogenic isolates of F. oxysporum. The sequence of this PCR product was identical to the sequence obtained from F. oxysporum f. sp. fragariae isolates in Japan. Intensive sampling at two locations in California showed results of tests based on PCR and somatic compatibility to be in agreement for 97% (257 of 264) of isolates tested. Our findings revealed considerable diversity in the California population of F. oxysporum f. sp. fragariae, and indications that horizontal gene transfer may have occurred.
    Type of Medium: Online Resource
    ISSN: 0191-2917 , 1943-7692
    URL: Article
    DOI: 10.1094/PDIS-07-16-1058-RE
    Language: English
    Publisher: Scientific Societies
    Publication Date: 2017
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  • 8
    Online Resource
    Online Resource
    Analysis of Xylem Fluid Components in Almond Cultivars Differing in Resistance to Almond Leaf Scorch Disease
    Scientific Societies ; 2011
    In:  Plant Disease Vol. 95, No. 2 ( 2011-02), p. 166-172
    Details
    In: Plant Disease, Scientific Societies, Vol. 95, No. 2 ( 2011-02), p. 166-172
    Abstract: Almond leaf scorch (ALS) is caused by the pathogenic bacterium Xylella fastidiosa and poses a threat to the California almond industry. Almond cultivars are differentially resistant or susceptible to ALS. X. fastidiosa can infect but does not overwinter in resistant cultivars in sufficient numbers to cause symptoms or be detected by polymerase chain reaction. To better understand the biochemical or morphological factors mediating resistance, we extracted and analyzed almond xylem fluid from four almond cultivars differing in ALS susceptibility, including Butte and Carmel cultivars that are field resistant and Peerless and Sonora that are ALS susceptible. Xylem fluid was collected over winter months in 2007 to 2009, as well as July 2008 and April 2009, and analyzed for the following: pH, osmolarity, concentrations of sugars, calcium, magnesium, organic acids, and total phenolics. For most of these analyses, we found no clear differences in xylem fluid from resistant and susceptible almond cultivars. However, during the winter months, resistant cultivars tended to have higher concentrations of total phenolic compounds compared with susceptible cultivars (P = 0.05). In February 2009, Carmel had the highest total phenolic concentration measured, 233 μg/ml of gallic acid equivalents. The lowest phenolic concentrations occurred in April 2009. The cross-sectional areas of xylem vessels in Butte (resistant) and Peerless (susceptible) trees were not significantly different between cultivars.
    Type of Medium: Online Resource
    ISSN: 0191-2917 , 1943-7692
    URL: Article
    DOI: 10.1094/PDIS-05-10-0328
    Language: English
    Publisher: Scientific Societies
    Publication Date: 2011
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  • 9
    Online Resource
    Online Resource
    First Report of a Wilt Disease of Blackberry Caused by Fusarium oxysporum in California
    Scientific Societies ; 2016
    In:  Plant Disease Vol. 100, No. 5 ( 2016-05), p. 1018-1018
    Details
    In: Plant Disease, Scientific Societies, Vol. 100, No. 5 ( 2016-05), p. 1018-1018
    Type of Medium: Online Resource
    ISSN: 0191-2917 , 1943-7692
    URL: Article
    DOI: 10.1094/PDIS-07-15-0784-PDN
    Language: English
    Publisher: Scientific Societies
    Publication Date: 2016
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  • 10
    Online Resource
    Online Resource
    Frequency and Seasonal Distribution of Pear Psylla Infected with the Pear Decline Phytoplasma in California Pear Orchards
    Scientific Societies ; 2002
    In:  Phytopathology® Vol. 92, No. 11 ( 2002-11), p. 1218-1226
    Details
    In: Phytopathology®, Scientific Societies, Vol. 92, No. 11 ( 2002-11), p. 1218-1226
    Abstract: Pear decline (PD) is an important disease of Pyrus communis fruiting cultivars in Europe, Asia, and the Americas. PD is caused by a phloem-limited phytoplasma that, in California, is transmitted from diseased to healthy trees by pear psylla, Cacopsylla pyricola. The percentage of phytoplasma-infected pear psylla has never been assessed in the United States in field-collected insects. Pear psylla were collected monthly from PD-infected trees from three orchards in northern California. Individual psylla were tested for the presence of PD phytoplasma, using both a quantitative DNA hybridization and PD phytoplasma-specific polymerase chain reaction (PCR) assays. The percentage of infected psylla ranged from 0 to 45% depending on the orchard, the month and year collected, and the method of detection. The PD phytoplasma was detected in both the winterform and summerform pear psylla. Significantly more infected psylla were detected with PCR than with DNA hybridization analysis in two of the three orchards. The number of PD phytoplasma per pear psylla was estimated to range from 1 × 10 6 to 8.2 × 10 7 . The percentage of PD-infected pear psylla found in the three northern California pear orchards suggests that both winterform and summerform pear psylla could be important in the transmission of PD.
    Type of Medium: Online Resource
    ISSN: 0031-949X , 1943-7684
    URL: Article
    DOI: 10.1094/PHYTO.2002.92.11.1218
    Language: English
    Publisher: Scientific Societies
    Publication Date: 2002
    detail.hit.zdb_id: 2037027-1
    SSG: 12
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