scholarly journals Relationship Between the Application of Foliar Chemicals to Reduce Common Scab Disease of Potato and Correlation with Thaxtomin A Toxicity

Plant Disease ◽  
2012 ◽  
Vol 96 (1) ◽  
pp. 97-103 ◽  
Author(s):  
Robert S. Tegg ◽  
Ross Corkrey ◽  
Calum R. Wilson

Production of the phytotoxin thaxtomin A by pathogenic Streptomyces spp. is essential for induction of common scab disease in potato. The disease can be significantly reduced by a range of chemicals applied as foliar sprays before tuber initiation. We tested a range of chemicals that had previously demonstrated varying capacities to reduce common scab for both disease suppression and their ability to inhibit thaxtomin A toxicity in both ‘Desiree’ and ‘Russet Burbank’ potato. Our results for disease suppression generally supported previous studies. Our tuber slice assays with thaxtomin A showed a strong correlation between the ability of the chemical to suppress common scab symptom development and the ability of the chemical to inhibit thaxtomin A toxicity. A Bayesian measurement error linear regression model was derived for each cultivar and trial and demonstrated a clear positive relationship between disease and thaxtomin-A-induced necrosis. The relationships obtained were much stronger than would have been obtained without adjustment for measurement error. This demonstrates that disease mitigation using chemical foliar sprays is strongly correlated with the ability of the chemical to inhibit thaxtomin A toxicity, suggesting this mechanism as a key mode of action for understanding this novel disease control strategy.

Plant Disease ◽  
2008 ◽  
Vol 92 (9) ◽  
pp. 1321-1328 ◽  
Author(s):  
Robert S. Tegg ◽  
Warwick M. Gill ◽  
Hannah K. Thompson ◽  
Noel W. Davies ◽  
John J. Ross ◽  
...  

Production of the phytotoxin thaxtomin A by pathogenic Streptomyces spp. is essential for induction of common scab disease in potato. Prior studies have shown that foliar application of sublethal concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) and other auxin or auxin-like compounds significantly reduced severity and occurrence of common scab in subsequently produced tubers. However, the means of disease suppression by these compounds was not known. We confirm the disease suppressive activity of 2,4-D. Detailed tuber physiological examination showed that lenticel numbers, lenticel external dimensions, and periderm thickness and structure, physiological features believed to be critical to Streptomyces scabiei infection, were not substantially changed by 2,4-D treatments, negating a possible mechanism for disease suppression through alteration of these structures. In contrast, our studies show accumulation of 2,4-D in tubers of treated plants occurs and is associated with an enhanced tolerance to thaxtomin A. Applying 2,4-D to cultures of S. scabiei did not significantly alter in vitro growth of the pathogen. Thaxtomin A production by the pathogen was inhibited by 2,4-D, but only at the highest rate tested (1.0 mM), which is at least 200-fold more than is found in 2,4-D treated tubers. These data suggest 2,4-D has no direct effect on the pathogen or its virulence. Confirmatory evidence from studies with Arabidopsis thaliana seedlings demonstrated that the auxins 2,4-D and IAA ameliorate thaxtomin A toxicity. The evidence presented whereby auxin treatment inhibits toxicity of thaxtomin A secreted by the pathogen suggests a novel indirect means of disease suppression.


Plant Disease ◽  
2009 ◽  
Vol 93 (12) ◽  
pp. 1329-1334 ◽  
Author(s):  
J. J. Hao ◽  
Q. X. Meng ◽  
J. F. Yin ◽  
W. W. Kirk

A novel strain of Streptomyces (named DS3024) was isolated from a potato field in Michigan in 2006. The taxonomy of the organism was determined by morphology, biochemistry, and genetic analysis. Analysis of the 16S ribosomal RNA gene sequence indicated that the organism was most similar to an isolate of Streptomyces sp., ME02-6979.3a, which is not pathogenic to potato tubers but is distinct from other known pathogenic Streptomyces spp. Strain DS3024 has genes that encode thaxtomin synthetase (txtAB), which is required for pathogenicity and virulence, and tomatinase (tomA), which is a common marker for many pathogenic Streptomyces spp. However, the nec1 gene (associated with virulence in most pathogenic Streptomyces spp.) was not detected. The new strain was capable of growth at pH 4.5, caused necrosis on potato tuber slices, and produced thaxtomin A. In greenhouse experiments, DS3024 caused scab symptoms on potato tubers similar to those caused by Streptomyces scabies on tubers of potato cv. Atlantic, which is scab susceptible. We propose that DS3024 is a new strain of Streptomyces capable of causing common scab on potato tubers. The prevalence of this strain of Streptomyces in potato-producing areas in the north-central United States has not been determined.


2016 ◽  
Vol 106 (2) ◽  
pp. 123-131 ◽  
Author(s):  
Joanna K. Fyans ◽  
Luke Bown ◽  
Dawn R. D. Bignell

Potato common scab (CS) is an economically important crop disease that is caused by several members of the genus Streptomyces. In this study, we characterized the plant-pathogenic Streptomyces spp. associated with CS-infected potato tubers harvested in Newfoundland, Canada. A total of 17 pathogenic Streptomyces isolates were recovered from potato scab lesions, of which eight were determined to be most similar to the known CS pathogen S. europaeiscabiei. All eight S. europaeiscabiei isolates were found to produce the thaxtomin A phytotoxin and to harbor the nec1 virulence gene, and most also carry the putative virulence gene tomA. The remaining isolates appear to be novel pathogenic species that do not produce thaxtomin A, and only two of these isolates were determined to harbor the nec1 or tomA genes. Of the non-thaxtomin-producing isolates, strain 11-1-2 was shown to exhibit a severe pathogenic phenotype against different plant hosts and to produce a novel, secreted phytotoxic substance. This is the first report documenting the plant-pathogenic Streptomyces spp. associated with CS disease in Newfoundland. Furthermore, our findings provide further evidence that phytotoxins other than thaxtomin A may also contribute to the development of CS by Streptomyces spp.


Plant Disease ◽  
2012 ◽  
Vol 96 (5) ◽  
pp. 718-725 ◽  
Author(s):  
Noah Rosenzweig ◽  
James M. Tiedje ◽  
John F. Quensen ◽  
Qingxiao Meng ◽  
Jianjun J. Hao

Potato common scab, caused by Streptomyces spp., is an annual production problem for potato growers, and not effectively controlled by current methods. A field with naturally occurring common scab suppression has been identified in Michigan, and confirmed to have a biological basis for this disease suppression. This field and an adjacent scab nursery conducive to disease were studied using pyrosequencing to compare the two microbial communities. Total DNA was extracted from both the disease-conducive and -suppressive soils. A phylogenetically taxon-informative region of the 16S rRNA gene was used to establish operational taxonomic units (OTUs) to characterize bacterial community richness and diversity. In total, 1,124 OTUs were detected and 565 OTUs (10% dissimilarity) were identified in disease-conducive soil and 859 in disease-suppressive soil, including 300 shared both between sites. Common phyla based on relative sequence abundance were Acidobacteria, Proteobacteria, and Firmicutes. Sequences of Lysobacter were found in significantly higher numbers in the disease-suppressive soil, as were sequences of group 4 and group 6 Acidobacteria. The relative abundance of sequences identified as the genus Bacillus was significantly higher by an order of magnitude in the disease-conducive soil.


1998 ◽  
Vol 44 (8) ◽  
pp. 768-776 ◽  
Author(s):  
Linda L Kinkel ◽  
John H Bowers ◽  
Kyoko Shimizu ◽  
Eric C Neeno-Eckwall ◽  
Janet L Schottel

Thaxtomin A production in culture, potato common scab severity (percentage of tuber surface infected or number of lesions per tuber), and fatty acid profiles were determined for 78 Streptomyces isolates. Only pathogenic Streptomyces spp. (n = 17) produced thaxtomin A in culture. Thaxtomin A production in culture (µg/mL) was significantly positively correlated with the percentage of tuber surface infected (R = 0.60; p = 0.017) but not with the number of lesions per tuber (R = 0.37; p = 0.17). An increase of 1 µg/mL in thaxtomin A production corresponded to an 11% increase in disease severity (percentage of tuber surface infected). The data indicate that quantitative information on the ability of a particular pathogen isolate or population to produce thaxtomin A may be critical to understanding and predicting the disease potential of that population. Using cluster analysis of fatty acid data, 94% of 67 unknown field isolates grouped with other field isolates having the same pathogenicity (plus or minus).Key words: thaxtomin A, phytotoxin, potato scab.


Plant Disease ◽  
2017 ◽  
Vol 101 (1) ◽  
pp. 224-232 ◽  
Author(s):  
Lea H. Hiltunen ◽  
Jani Kelloniemi ◽  
Jari P. T. Valkonen

Potato common scab caused by several Streptomyces spp. is an important disease with no effective methods of control. Suppressiveness against common scab can develop in soil as a result of long-term potato monoculture and has been associated with nonpathogenic Streptomyces spp. To determine whether the development of scab suppressiveness could be enhanced, the effect of repeated applications of an antagonistic Streptomyces strain on common scab was investigated in a long-term field trial over 5 years. Streptomyces strain 272 applied annually at planting consistently suppressed development of common scab symptoms. On scab-susceptible potato cultivar Bintje, strain 272 reduced disease severity, on average, by 43%; whereas, on the scab-tolerant Nicola, the strain reduced both disease incidence and severity by 43 and 59%, respectively. Regardless of disease pressure, the combined use of strain 272 and the tolerant cultivar reduced the scab coverage to a negligible level. After a single application of strain 272, efficient disease suppression did not persist in the soil to the following growing season. However, when strain 272 was applied in three or more consecutive years, the soil remained suppressive to scab for at least 2 years beyond the last application, suggesting that, with repeated applications, it may be possible to enhance development of scab suppression in soil.


2016 ◽  
Vol 106 (7) ◽  
pp. 719-728 ◽  
Author(s):  
Tsuyoshi Tomihama ◽  
Yatsuka Nishi ◽  
Kiyofumi Mori ◽  
Tsukasa Shirao ◽  
Toshiya Iida ◽  
...  

Potato common scab (PCS), caused by pathogenic Streptomyces spp., is a serious disease in potato production worldwide. Cultural practices, such as optimizing the soil pH and irrigation, are recommended but it is often difficult to establish stable disease reductions using these methods. Traditionally, local farmers in southwest Japan have amended soils with rice bran (RB) to suppress PCS. However, the scientific mechanism underlying disease suppression by RB has not been elucidated. The present study showed that RB amendment reduced PCS by repressing the pathogenic Streptomyces population in young tubers. Amplicon sequencing analyses of 16S ribosomal RNA genes from the rhizosphere microbiome revealed that RB amendment dramatically changed bacterial composition and led to an increase in the relative abundance of gram-positive bacteria such as Streptomyces spp., and this was negatively correlated with PCS disease severity. Most actinomycete isolates derived from the RB-amended soil showed antagonistic activity against pathogenic Streptomyces scabiei and S. turgidiscabies on R2A medium. Some of the Streptomyces isolates suppressed PCS when they were inoculated onto potato plants in a field experiment. These results suggest that RB amendment increases the levels of antagonistic bacteria against PCS pathogens in the potato rhizosphere.


2015 ◽  
Vol 105 (10) ◽  
pp. 1311-1317 ◽  
Author(s):  
Tanya Arseneault ◽  
Claudia Goyer ◽  
Martin Filion

Common scab of potato, caused by pathogenic Streptomyces spp., is an important disease not efficiently controlled by current methods. We previously demonstrated that Pseudomonas fluorescens LBUM223 reduces common scab development under controlled conditions through phenazine-1-carboxylic (PCA) production, leading to reduced thaxtomin A production by the pathogen, a key pathogenicity and virulence factor. Here, we aimed at determining if LBUM223 is able to increase potato yield and control common scab under field conditions, while characterizing the biocontrol mechanisms involved. We investigated if a reduction in pathogen soil populations, activation of induced systemic resistance in potato, and/or changes in txtA gene expression, involved in thaxtomin A biosynthesis in pathogenic Streptomyces spp. were involved in common scab control by LBUM223. Common scab symptoms were significantly reduced and total tuber weight increased by 46% using biweekly applications of LBUM223. LBUM223 did not reduce pathogen soil populations, nor was potato systemic defense-related gene expression significantly altered between treatments. However, a significant down-regulation of txtA expression occurred in the geocaulosphere. This is the first demonstration that a Pseudomonas strain can directly alter the transcriptional activity of a key pathogenesis gene in a plant pathogen under field conditions, contributing to disease control.


Plant Disease ◽  
2012 ◽  
Vol 96 (8) ◽  
pp. 1223-1223 ◽  
Author(s):  
R. Gouws ◽  
A. McLeod

Common scab caused by Streptomyces spp. is one of the major factors limiting successful potato (Solanum tuberosum) production in South Africa. Most potato cultivars are susceptible to the disease and huge losses are incurred due to a reduction in cosmetic value. Common scab symptoms that have been reported worldwide are variable, with circular, raised, tan-to-brown, corky lesions being the most common symptoms. However, a distinct atypical symptom was observed in isolated production regions (Western Free State and Mpumalanga) in South Africa since early 2010. Deep longitudinal fissures (3 to 12 mm) containing scab-like lesions were observed on the surface area of tubers from several potato cultivars (Mondial, BP1, and Buffelspoort). Lesions on Mondial were interesting since this cultivar, but not the susceptible BP1 and Buffelspoort cultivars, is tolerant to typical common scab in South Africa. Isolations were made from tuber lesions obtained from the two production regions and were plated onto yeast malt extract medium. Several pure culture strains were obtained that were positively identified as Streptomyces spp. based on morphology. Species identity of four strains was investigated using PCR primers targeting the 16S rRNA region of known species (3), which showed that the strains did not belong to any of the known pathogenic reference strains (S. scabiei, S. europascabiei, S. turgidiscabies, S. acidiscabies). Species identity of the strains was further investigated through sequencing of the 16S rRNA region (1.2 kb). The four strains had 100% sequence similarity (GenBank Accession. No. JQ241439) to each other and to 15 GenBank sequences that included several unknown Streptomyces spp., S. vinaceus, S. malachiticus, S. werraensis, S. cyaneus (the only published sequenced), and S. pseudogriseolus. The sequence of the isolates had only 95.5% identity to the most prevalent common scab pathogen, S. scabiei (GI154707840, [3]). The pathogenicity of the four strains, along with an S. scabiei reference isolate, was investigated using BP1 potato tubers and the double pot methodology (1). Fifteen-centimeter pots containing silica sand were each planted with one potato tuber and placed on top of a rectangular planting box (15 × 1.5 × 0.4 m) filled with native Hutton soil. The 15-cm pots were irrigated until the roots grew into the Hutton soil. Subsequently, irrigation was only applied to the Hutton soil, thus creating dry conditions in the tuber development area (15-cm pot), which is conducive for common scab development. The potato plants were inoculated with 10- to 14-day-old Streptomyces strains during the tuber initiation stage at a concentration of 1 × 106 spores/ml of sterile water, 10 ml per plant, and six replicates per strain. Ten weeks after inoculation, each of the four strains caused cracking and scabbing, similar to initial symptoms observed, on more than 90% of the tubers. The S. scabiei reference isolate caused typical circular, raised, brown, corky common scab lesions. Streptomyces was reisolated from the lesions, fulfilling Koch's postulates. To our knowledge, these results indicate that a previously unreported Streptomyces sp. is the causal agent of a new lesion type, fissure scab, on potato in South Africa that may lead to serious losses to the local potato industry. References: (1) L. Marais and R. Vorster. Potato Res. 31:401, 1988. (2) D. J. Theron. Page 1 in: Guide to Potato Production in South Africa, 2003. (3) L. Wanner. Phytopathology 96:1363, 2006.


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