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. 2020 Sep 17;9(9):760.
doi: 10.3390/pathogens9090760.

Investigation of Streptomyces scabies Causing Potato Scab by Various Detection Techniques, Its Pathogenicity and Determination of Host-Disease Resistance in Potato Germplasm

Sohaib Ismail  1 , Bo Jiang  2 , Zohreh Nasimi  1 , M Inam-Ul-Haq  3 , Naoki Yamamoto  1 , Andrews Danso Ofori  1 , Nawab Khan  4 , Muhammad Arshad  5 , Kumail Abbas  6 , Aiping Zheng  1
Affiliations

Investigation of Streptomyces scabies Causing Potato Scab by Various Detection Techniques, Its Pathogenicity and Determination of Host-Disease Resistance in Potato Germplasm

Sohaib Ismail et al. Pathogens. .

Abstract

Streptomyces scabies is a Gram-positive bacterial pathogen that causes common scab disease to several crops, particularly in the potato. It is a soil borne pathogen, a very devastating scab pathogen and difficult to manage in the field. Streptomyces has several species that cause common scab such as S. scabiei, S. acidiscabies, S. europaeiscabiei, S. luridiscabiei, S. niveiscabiei, S. puniciscabiei, S. reticuliscabiei, S. stelliscabiei, S. turgidiscabies, S. ipomoeae. Common scab disease harmfully affects potato economic and market value due to the presence of black spots on the tuber. Owing to its genetic diversity and pathogenicity, the determination of pathogen presence in potato fields is still challenging. In this study, S. scabies genetic diversity was measured by surveying five potato-growing areas of Pakistan during the growing season 2019. A total of 50 Streptomyces isolates, including S. scabies, S. acidiscabies, S. griseoflavus were isolated and identified based on morphologic, biochemical and molecular analysis. Virulent confirmation assays confirmed ten virulent strains of Streptomyces spp. On the potato cultivars Cardinal and Santee. Among the Streptomyces species, S. scabies showed the highest scab index, followed by S. acidiscabies and S. griseoflavus by exhibiting the scab-like lesions on potato tubers. Ten potato cultivars were screened against these virulent isolates of Streptomyces. The Faisalabad white variety showed the highest scab index followed By Cardinal, Tourag, Kuroda, Santee, Lady Rosetta, Asterix, Diamant, Faisalabad red and Sadaf. Moreover, genetic diversity and pathogenicity of Streptomyces spp. on potato tubers were also likely diverse in different geographical regions and also potato cultivars. This study represents a contribution to understanding the local interaction between potatoes and Streptomyces spp. in Pakistan. It will aid in supporting a solution for the management of this pathogen around the world.

Keywords: Gram-positive bacteria; Streptomyces scabies; common scab disease; soil borne pathogen.

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Conflict of interest statement

The authors declare no conflict of interest in this work. All forms of financial support are acknowledged in the contribution. All authors have offered consent to submission.

Figures

Figure 1
Figure 1
Percent disease incidence and percent scab index in different areas of Pakistan; Taxila City, Rawalpindi; Hazro, Attock; Sialkot; Kasur; Okara; Faisalabad. The means obtained for various treatments with significant differences denoted by different letters, based on Duncan’s multiple test procedure at p < 0.05. Disease incidence in Taxila (c), Hazro (c), Sialkot (b), Kasur (a), Okara (a), Faisalabad (b) was observed statistically. Scab index % in Taxila (c), Hazro (c), Sialkot (b), Kasur (a), Okara (a), Faisalabad (b) was also observed statistically.
Figure 2
Figure 2
Isolation frequency of Streptomyces from potato tubers. Streptomyces were isolated and purified on King’s B medium, and the percentage of isolates obtained for each species of Streptomyces was calculated by comparison of means. Isolates; S. scabies (a), S. acidiscabies (b), S. turgidiscabiei (c), S. griseoflavus (c), S. europaeiscabiei (d) were observed statistically. The means obtained for various treatments with significant differences denoted by different letters, based on Duncan’s multiple test procedure at p < 0.05.
Figure 3
Figure 3
Diversity and distribution of various Streptomyces species from samples collected from different potato-growing areas during the 2019 survey.
Figure 4
Figure 4
Biochemical characterization of different Streptomyces isolates for confirmation. (A) Test-positive isolates confirmed by Gram-staining test (c), catalase oxidase test (b), loop test (b) and Kovac’s oxidase test (a) (B) Test-negative isolates confirmed by Gram-staining test (a), catalase oxidase test (c), loop test (b) and Kovac’s oxidase test (d). Means obtained for various treatments with significant differences denoted by different letters (a, b, c, d), based on Duncan’s multiple test procedure at p < 0.05.
Figure 5
Figure 5
Various biochemical responses of Streptomyces spp. (a) Microscopy diagram of S. scabies; (b) Levan test for confirmation of Streptomyces spp; (c) fluorescent pigment test for the presence of Gram-positive actinomycetes Streptomyces (d) oxidase test of Streptomyces.
Figure 6
Figure 6
Virulent confirmation/Pathogenicity tests for the confirmation of virulent strains of Streptomyces spp. on the potato cultivars. (A) Percentage of the mortality rate of Streptomyces spp. on the potato cultivar Cardinal; (B) percentage mortality rate of Streptomyces spp. on the potato cultivar Sante. Means obtained for various treatments with significant differences denoted by different letters, based on Duncan’s multiple test procedure at p < 0.05.
Figure 7
Figure 7
Determination of the Percent tuber area infected in two potato cultivars by pathogenicity assays (pin-prick method). (A) Percentage of tuber area infected by Streptomyces spp. on the potato cultivar Cardinal, Isolates such as CS-TAX02 (a), CS-HAZ14 (bc), CS-HAZ56 (c), CS-SIAL060 (d), CS-SIAL101 (ab), CS-OK010 (de), CS-OK126 (ef), CS-OK14 (de), CS-FSD124 (f), CS-FSD129 (ef) were observed statistically; (B) Percentage tuber area infected by Streptomyces spp. on the potato cultivar Santee, Isolates such as CS-TAX02 (b), CS-HAZ14 (c), CS-HAZ56 (d), CS-SIAL060 (b), CS-SIAL101 (a), CS-OK010 (f), CS-OK126 (e), CS-OK14 (c), CS-FSD124 (d), CS-FSD129 (f) were observed statistically. Means obtained for various treatments with significant differences denoted by different letters, based on Duncan’s multiple test procedure at p < 0.05.
Figure 8
Figure 8
Percent disease incidence and percent scab index of screened potato cultivars against Streptomyces scabies. (A) Disease incidence of 10 potato cultivars such as Cardinal (de), Santee (b), Lady Rosetta (f), Kuroda (a), Tourag (bc), Asterix (f), Diamant (cd), Fsd-white (f), Fsd-red (b), Sadaf (e) were observed statistically (B) Percent scab index of 10 potato cultivars such as Cardinal (b), Santee (a), Lady Rosetta (d), Kuroda (a), Tourag (ab), Asterix (d), Diamant (c), Fsd-white (d), Fsd-red (ab), Sadaf (c) were observed statistically. These parameters were measured based on the disease rating scale of potato scab. The means obtained for various treatments with significant differences are denoted by different letters, based on Duncan’s multiple test procedure at p < 0.05.
Figure 8
Figure 8
Percent disease incidence and percent scab index of screened potato cultivars against Streptomyces scabies. (A) Disease incidence of 10 potato cultivars such as Cardinal (de), Santee (b), Lady Rosetta (f), Kuroda (a), Tourag (bc), Asterix (f), Diamant (cd), Fsd-white (f), Fsd-red (b), Sadaf (e) were observed statistically (B) Percent scab index of 10 potato cultivars such as Cardinal (b), Santee (a), Lady Rosetta (d), Kuroda (a), Tourag (ab), Asterix (d), Diamant (c), Fsd-white (d), Fsd-red (ab), Sadaf (c) were observed statistically. These parameters were measured based on the disease rating scale of potato scab. The means obtained for various treatments with significant differences are denoted by different letters, based on Duncan’s multiple test procedure at p < 0.05.
Figure 9
Figure 9
Statistical analysis of the effect of Streptomyces scabies on different growth parameters of screened potato cultivars. (A) Different growth parameters such as No. of tubers in potato cultivars; Kuroda (a), Santee (a), Fsd-Red (a), Tourag (a), Diamant (a), Cardinal (a), Sadaf (a), Asterix (a), Fsd-white (a), Lady Rosetta (a), Root weight Kuroda (bc), Santee (bc), Fsd-Red (c), Tourag (abc), Diamant (ab), Cardinal (a), Sadaf (bc), Asterix (ab), Fsd-white (c), Lady Rosetta (ab) were observed statistically. Shoot weight in Kuroda (bc), Santee (bc), Fsd-Red (d), Tourag (bc), Diamant (ab), Cardinal (a), Sadaf (bc), Asterix (ab), Fsd-white (cd), Lady Rosetta (bc) were observed statistically. (B) Different growth parameters such as Root length for various varieties such as Kuroda (ab), Santee (ab), Fsd-Red (ab), Tourag (a), Diamant (ab), Cardinal (b), Sadaf (ab), Asterix (ab), Fsd-white (ab), Lady Rosetta (a) were observed statistically. Shoot length in Kuroda (ab), Santee (c), Fsd-Red (c), Tourag (c), Diamant (ab), Cardinal (c), Sadaf (c), Asterix (ab), Fsd-white (ab), Lady Rosetta (d) are described statistically. Means obtained for various treatments with significant differences denoted by different letters, based on Duncan’s multiple test procedure at p < 0.05.
Figure 9
Figure 9
Statistical analysis of the effect of Streptomyces scabies on different growth parameters of screened potato cultivars. (A) Different growth parameters such as No. of tubers in potato cultivars; Kuroda (a), Santee (a), Fsd-Red (a), Tourag (a), Diamant (a), Cardinal (a), Sadaf (a), Asterix (a), Fsd-white (a), Lady Rosetta (a), Root weight Kuroda (bc), Santee (bc), Fsd-Red (c), Tourag (abc), Diamant (ab), Cardinal (a), Sadaf (bc), Asterix (ab), Fsd-white (c), Lady Rosetta (ab) were observed statistically. Shoot weight in Kuroda (bc), Santee (bc), Fsd-Red (d), Tourag (bc), Diamant (ab), Cardinal (a), Sadaf (bc), Asterix (ab), Fsd-white (cd), Lady Rosetta (bc) were observed statistically. (B) Different growth parameters such as Root length for various varieties such as Kuroda (ab), Santee (ab), Fsd-Red (ab), Tourag (a), Diamant (ab), Cardinal (b), Sadaf (ab), Asterix (ab), Fsd-white (ab), Lady Rosetta (a) were observed statistically. Shoot length in Kuroda (ab), Santee (c), Fsd-Red (c), Tourag (c), Diamant (ab), Cardinal (c), Sadaf (c), Asterix (ab), Fsd-white (ab), Lady Rosetta (d) are described statistically. Means obtained for various treatments with significant differences denoted by different letters, based on Duncan’s multiple test procedure at p < 0.05.
Figure 10
Figure 10
DNA template detected from infected potato tubers and PCR amplification of Streptomyces scabies.
Figure 11
Figure 11
Phylogenetic tree of Streptomyces species associated with potato cultivars. The phylogenetic tree was constructed by the maximum-likelihood method by MEGA 7.0.26. Bootstrap support values were obtained from 1000 replications.
Figure 12
Figure 12
Potato-growing areas of Punjab, Pakistan were visited for sample collection.
Figure 13
Figure 13
A disease rating scale for the measurement of percent disease incidence of common scab of potato.
Figure 14
Figure 14
The disease rating scale of percent scab index of common potato scab.
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