scholarly journals Elephant Hide and Growth Cracking on Potato Tubers Caused by Rhizoctonia solani AG3-PT in South Africa

Plant Disease ◽  
2014 ◽  
Vol 98 (4) ◽  
pp. 570-570 ◽  
Author(s):  
N. Muzhinji ◽  
J. W. Woodhall ◽  
M. Truter ◽  
J. E. van der Waals
Keyword(s):  
South Africa ◽  
Rhizoctonia Solani ◽  
Black Scurf ◽  
Free State ◽  
Potato Tubers ◽  
Streptomyces Species ◽  
Koch’S Postulates ◽  
Plant Pathol ◽  
Barley Grains ◽  
Koch's Postulates

Rhizoctonia solani consists of 13 anastomosis groups (AGs) designated AG1 to 13. AG3-PT is considered the predominant AG in potatoes (4) and is associated with quantitative and qualitative yield losses. Qualitative losses are typically associated with the tuber blemish disease, black scurf. However, atypical tuber blemishes such as elephant hide consisting of corky lesions on the tuber surface (2) have also been attributed to Rhizoctonia. Such atypical blemishes are not considered specific to Rhizoctonia, making direct-cause effect estimates difficult (1). Koch's postulates for the elephant hide symptom and R. solani AG3-PT have not been completed. Recently, growth cracking and scab lesions were observed on potato tubers in South Africa and attributed to a new Streptomyces species (3). These lesions and cracks were similar to elephant hide symptoms attributed to R. solani AG3-PT. Therefore, the cause of the elephant hide symptom in South Africa was investigated further. Symptoms of elephant hide and cracking have been observed on tubers from the Eastern Free State, KwaZulu-Natal, Limpopo, Mpumalanga, North-Eastern Cape, Northern Cape, North West, Sandveld, and Western Free State growing regions. In 2012, three samples of potato tubers (cv. BP1) with elephant hide and cracking were selected for analysis. These samples were collected from Clanwilliam in the Sandveld potato growing region. Tubers were surface sterilized with 1% NaOCl; sections of affected tissue were excised and plated onto potato dextrose agar (PDA). Rhizoctonia-like colonies were identified and after further sub-culturing on PDA, three representative isolates (Rh3, Rh4, and Rh6) of R. solani from each sample were obtained. For each isolate, genomic DNA was extracted and the rDNA ITS region sequenced using ITS1-F and ITS4 (2). The resulting sequences (KF234142, KF234143, and KF234144) were at least 98% identical to other AG3-PT sequences on GenBank (JX27814 and KC157664). To confirm Koch's postulates, pathogenicity tests were conducted with the three isolates. PDA plugs of each isolate were added to 10 g of barley grains which were incubated for 14 days until fully colonized. The barley grains were then used to inoculate disease-free mini-tubers (cv. BP1) in 5l pots containing a sand-clay-pine bark mixture (1:1:1 ratio). Potato plants inoculated with sterile barley grains served as controls. Plants were held for 120 days in a greenhouse at 22°C with light for 12 h a day. Incidence of the elephant hide symptom for isolates Rh3, Rh4, and Rh6 was 58%, 33%, and 37.5%, respectively. Growth cracking and black scurf were also observed with each isolate. R. solani AG3-PT was successfully re-isolated from symptomatic tubers, confirming Koch's postulates. This is the first report of R. solani AG3-PT causing elephant hide in potato tubers in South Africa. Elephant hide caused by R. solani AG3-PT has been reported in tubers from France (2) and the United Kingdom (3), but Koch's postulates were not proven. In this study, Koch's postulates were proven for R. solani AG3-PT causing scab or elephant hide symptom and cracking in potato tubers. R. solani AG3-PT should thus be considered in addition to Streptomyces as a cause of this symptom and control strategies should also consider R. solani AG3-PT. References: (1) G. J. Banville et al. Pages 321-330 in: Rhizoctonia Species: Taxonomy, Molecular Biology, Ecology, Pathology and Disease Control, B. Sneh et al., eds. Kluwer Academic Publishers, Dordrecht, The Netherlands, 1996. (2) M. Fiers et al. Eur. J. Plant. Pathol. 128:353, 2010. (3) R. Gouws and A. McLeod. Plant Dis. 96:1223, 2012. (4) J. W. Woodhall et al. Eur. J. Plant. Pathol. 136:273, 2013.

scholarly journals First Report of Rhizoctonia solani AG 4HG-III Causing Potato Stem Canker in South Africa

Plant Disease ◽  
2014 ◽  
Vol 98 (6) ◽  
pp. 853-853 ◽  
Author(s):  
N. Muzhinji ◽  
J. W. Woodhall ◽  
M. Truter ◽  
J. E. van der Waals
Keyword(s):  
South Africa ◽  
Rhizoctonia Solani ◽  
Stem Canker ◽  
Black Scurf ◽  
Limpopo Province ◽  
Control Treatment ◽  
First Report ◽  
Potato Diseases ◽  
Plant Pathol ◽  
Barley Grains

Black scurf and stem canker caused by Rhizoctonia solani Kühn (teleomorph: Thanathephorus cucumeris Frank Donk) are potato diseases of worldwide economic importance (4). R. solani consists of 13 anastomosis groups (AGs) of which AG 3-PT is considered the dominant causal agent of potato diseases globally (1,4). However, other AGs such as AG 2-1, 5, and 8 have been reported to cause potato diseases (1,4). In February 2013, potato stem samples (cv. Mondial) displaying dark brown lesions resembling those caused by Rhizoctonia stem canker were obtained from a commercial field in Limpopo Province, South Africa. Symptomatic tissue was disinfected with 1% NaOCl for 1 min, rinsed in sterile water, and 4-mm stem pieces excised from the margins of symptomatic tissues and plated on 2% water agar supplemented with 20 mg/l of chloramphenicol. Single hyphal tips taken from fungal isolates identified as R. solani based on morphological traits (3) were transferred to potato dextrose agar. DNA was isolated from the resulting cultures and ITS region of rDNA was sequenced as previously described (2). The resulting sequences of three of the isolates, Rh 81, Rh 82, and Rh 83 (KF712285, KF712286, and KF712287), were 99% similar to those of AG 4 HG-III found in GenBank (DQ102449 and AF354077). Therefore, based on molecular methods, these three isolates were identified as R. solani AG4 HG-III. To determine pathogenicity of the AG4 HG-III isolates, certified disease free mini-tubers (Generation 0, cv. Mondial, produced in tunnels) were used in pot trials. PDA plugs of each isolate were added to 10 g of barley grains, which had been sterilized by autoclaving for two consecutive days at 121°C for 30 min, and were incubated for 14 days until fully colonized. Ten colonized barley grains were placed 10 mm above each mini-tuber planted in 5l pots containing sterile potting mixture of sand:clay:pinebark (1:1:1). Ten tubers were inoculated with each isolate. Uninoculated, sterile barley grains were applied to the control treatment. Mini-tubers were grown in a greenhouse maintained at 22°C with light for a 12 h day. After 7 weeks, five plants for each isolate were destructively sampled and assessed for stem canker symptoms. At 120 days after sowing, the remaining five plants per treatment were assessed for blemishes on progeny tubers. The stem canker incidences of plants inoculated with Rh 81, Rh 82, and Rh 83 were 25, 25, and 50%, respectively, whereas no symptoms were observed in control plants. Sclerotia formation and blemishes were not observed on any of the progeny tubers, which might indicate that these strains are only able to infect stems, or that environmental conditions were not suitable for tuber blemish or black scurf development. R. solani AG4 HG-III was consistently re-isolated from symptomatic stems displaying brown lesions, and the identity of the re-isolates were confirmed by molecular tests as previously described, thereby fulfilling Koch's postulates. To our knowledge, this is the first report of R. solani AG4 HG-III causing stem canker on potato in South Africa and worldwide. Knowledge of which AGs are present in crop production systems is important when considering disease management strategies such as crop rotation and fungicide treatments (3). References: (1) C. Campion et al. Eur. J. Plant. Pathol. 109:983, 2003. (2) N. Muzhinji et al. Plant Dis. 98:570, 2014. (3) L. Tsror. J. Phytopathol. 158:649, 2010. (4) J. W. Woodhall et al. Plant. Pathol. 56:286, 2007.

scholarly journals Rhizoctonia solani Anastomosis Group 3 is Predominant in Potato Tubers in Poland

Plant Disease ◽  
2013 ◽  
Vol 97 (9) ◽  
pp. 1245-1245 ◽  
Author(s):  
J. W. Woodhall ◽  
B. Lutomirska ◽  
J. C. Peters ◽  
P. S. Wharton
Keyword(s):  
Rhizoctonia Solani ◽  
Tap Water ◽  
Anastomosis Group ◽  
Black Scurf ◽  
Crop Rotations ◽  
Potato Tubers ◽  
Hyphal Fusion ◽  
Group 3 ◽  
Plant Pathol ◽  
Potato Crops

Rhizoctonia solani is a species complex of 13 related but genetically distinct anastomosis groups (AGs). In potato, R. solani can infect the stems, stolons, and roots, resulting in quantitative losses. It can also cause qualitative losses through blemishes occurring on progeny tubers, such as black scurf and elephant hide (corky cracking). Knowledge of the AG in local populations is important because they differ in host range, fungicide sensitivity, and disease severity (2). To determine the AGs present in Poland, 54 tuber samples displaying typical R. solani symptoms were taken from six different fields in 2011. The fields were representative of five different administrative regions of Poland and from at least 10 different varieties. Rhizoctonia was isolated from tubers by placing symptomatic material on to tap water agar amended with streptomycin and penicillin and after 2 to 3 days Rhizoctonia colonies were identified and hyphal tips of these transferred to potato dextrose agar. Rhizoctonia was successfully isolated from 48 tubers displaying black scurf and two tubers displaying elephant hide symptoms. DNA was extracted from Rhizoctonia cultures using a Wizard Food kit (Promega) and the AG was determined using specific real-time PCR assays (1). All Rhizoctonia isolates were determined to be AG3 and this was confirmed for 10 selected isolates by observing hyphal fusion with a known AG3 tester isolate (Rs08) as described previously (3). Pairings were also conducted amongst the 10 Polish isolates, C2 reactions were typically observed indicating numerous vegetative compatible groups are present. This study shows that AG3 is likely to be the predominant AG in potato tubers in Poland. This is similar to other studies in Europe, which have all determined that AG3 accounts for at least 92% of isolates from potato (2,3). AG2-1, 4, and 5 have also been found in tubers worldwide and climate and certain crop rotations can influence the presence of these other AGs in potato tubers (2). However, climate and crop rotations in Poland are similar to other parts of Europe so the predominance of AG3 is expected. AG3 was also isolated from elephant hide symptoms; however, it was more frequently isolated from sclerotia. The ability of AG3 to prolifically produce sclerotia and thereby survive on seed tubers may explain its predominance in potato crops (4). Therefore, studies focusing on the management of Rhizoctonia potato disease in Poland should consider AG3 in the first instance. References: (1) G. E. Budge et al. Plant Pathol. 58:1071, 2009. (2) L. Tsror. J. Phytopathol. 158:649, 2010. (3) J. W. Woodhall et al. Plant Pathol. 56:286, 2007. (4) J. W. Woodhall et al. Plant Pathol. 57:5, 2008.

scholarly journals First Report of Rhizoctonia solani AG4 HG-II Infecting Potato Stems in Idaho

Plant Disease ◽  
2012 ◽  
Vol 96 (11) ◽  
pp. 1701-1701 ◽  
Author(s):  
J. W. Woodhall ◽  
P. S. Wharton ◽  
J. C. Peters
Keyword(s):  
Rhizoctonia Solani ◽  
Seed Tuber ◽  
Its Region ◽  
Stem Canker ◽  
Potato Production ◽  
Koch’S Postulates ◽  
First Report ◽  
Rdna Its ◽  
Plant Pathol ◽  
Koch's Postulates

The fungus Rhizoctonia solani is the causal agent of stem canker and black scurf of potato (Solanum tuberosum). R. solani is a species complex consisting of 13 anastomosis groups (AGs) designated AG1 to 13 (2, 3). Stems of potato (cv. Russet Norkotah) with brown lesions were recovered from one field in Kimberley, Idaho, in August 2011. Using previously described methods (3), R. solani was recovered from the symptomatic stems and one representative isolate (J15) was selected for further characterization. Sequencing of the rDNA ITS region of isolate J15 was undertaken as previously described (3) and the resulting rDNA ITS sequence (HE667745) was 99% identical to sequences of other AG4 HG-II isolates in GenBank (AF354072 and AF354074). Pathogenicity of the isolate was determined by conducting the following experiment. Mini-tubers of cv. Santé were planted individually in 1-liter pots containing John Innes Number 3 compost (John Innes Manufacturers Association, Reading, UK). Pots were either inoculated with J15, an isolate of AG3-PT (Rs08), or were not inoculated. Each treatment was replicated four times. Inoculum consisted of five 10-mm-diameter potato dextrose agar plugs, fully colonized by the appropriate isolate, placed in the compost approximately 40 mm above each seed tuber. Pots were held in a controlled environment room at 21°C with 50% relative humidity and watered as required. After 21 days, plants were assessed for disease. No symptoms of the disease were present in non-inoculated plants. In the Rs08 (AG3-PT) inoculated plants, all stems displayed large brown lesions and 20% of the stems had been killed. No stem death was observed in J15 (AG4 HG-II) inoculated plants. However, brown lesions were observed in three of the four J15 (AG4 HG-II) inoculated plants. These lesions were less severe than in plants inoculated with the Rs08(AG3-PT) inoculated plants and were present in 40% of the main stems. In the J15 (AG4 HG-II) inoculated pots, R. solani AG4 HG-II was reisolated from the five symptomatic stems, thereby satisfying Koch's postulates. To our knowledge, this is the first report of AG4 HG-II causing disease on potatoes in Idaho. AG4 has been isolated from potato previously from North Dakota, although the subgroup was not identified (1). The only previous report where AG4 HG-II was specifically determined to cause disease on potato was in Finland, but the isolate could not be maintained and Koch's postulates were not completed (3). The present study shows that AG4 HG-II can cause stem disease in potatoes, although disease does not develop as severely or as consistently as for AG3-PT. However, as demonstrated with isolates of AG2-1 and AG5, even mild stem infection can reduce tuber yield by as much as 12% (4). AG4 HG-II is a pathogen of sugar beet in Idaho, which was grown previously in this field. This history may have contributed to high levels of soilborne inoculum required to produce disease on potato. References: (1) N. C. Gudmestad et al. Page 247 in: J. Vos et al. eds. Effects of Crop Rotation on Potato Production in the Temperate Zones. Kluwer, Dordrecht, Netherlands, 1989. (2) M. J. Lehtonen et al. Agric. Food Sci. 18:223, 2009. (3) J. W. Woodhall et al. Plant Pathol. 56:286, 2007. (4) J. W. Woodhall et al. Plant Pathol. 57:897, 2008.

scholarly journals Anastomosis Groups and Pathogenicity of Rhizoctonia solani and Binucleate Rhizoctonia from Potato in South Africa

Plant Disease ◽  
2015 ◽  
Vol 99 (12) ◽  
pp. 1790-1802 ◽  
Author(s):  
N. Muzhinji ◽  
M. Truter ◽  
J. W. Woodhall ◽  
J. E. van der Waals
Keyword(s):  
South Africa ◽  
Rhizoctonia Solani ◽  
Stem Canker ◽  
Black Scurf ◽  
Bootstrap Support ◽  
Internal Transcribed Spacer Region ◽  
Binucleate Rhizoctonia ◽  
Anastomosis Groups ◽  
Potato Plants ◽  
Comprehensive Survey

A survey of anastomosis groups (AG) of Rhizoctonia spp. associated with potato diseases was conducted in South Africa. In total, 112 Rhizoctonia solani and 19 binucleate Rhizoctonia (BNR) isolates were recovered from diseased potato plants, characterized for AG and pathogenicity. The AG identity of the isolates was confirmed using phylogenetic analysis of the internal transcribed spacer region of ribosomal DNA. R. solani isolates recovered belonged to AG 3-PT, AG 2-2IIIB, AG 4HG-I, AG 4HG-III, and AG 5, while BNR isolates belonged to AG A and AG R, with frequencies of 74, 6.1, 2.3, 2.3, 0.8, 12.2, and 2.3%, respectively. R. solani AG 3-PT was the most predominant AG and occurred in all the potato-growing regions sampled, whereas the other AG occurred in distinct locations. Different AG grouped into distinct clades, with high maximum parsimony and maximum-likelihood bootstrap support for both R. solani and BNR. An experiment under greenhouse conditions with representative isolates from different AG showed differences in aggressiveness between and within AG. Isolates of AG 2-2IIIB, AG 4HG-III, and AG R were the most aggressive in causing stem canker while AG 3-PT, AG 5, and AG R caused black scurf. This is the first comprehensive survey of R. solani and BNR on potato in South Africa using a molecular-based approach. This is the first report of R. solani AG 2-2IIIB and AG 4 HG-I causing stem and stolon canker and BNR AG A and AG R causing stem canker and black scurf on potato in South Africa.

scholarly journals Anastomosis Grouping of Rhizoctonia solani Associated with Black Scurf and Stem Canker of Potato in South Africa

Plant Disease ◽  
2004 ◽  
Vol 88 (1) ◽  
pp. 83-83 ◽  
Author(s):  
M. Truter ◽  
F. C. Wehner
Keyword(s):  
South Africa ◽  
Rhizoctonia Solani ◽  
Rating Scale ◽  
Solanum Tuberosum L ◽  
Potato Cultivar ◽  
Stem Canker ◽  
Potato Production ◽  
Black Scurf ◽  
Chi Square ◽  
Chi Square Analysis

Rhizoctonia disease (black scurf of tubers and stem canker) of potato (Solanum tuberosum L.) caused by Rhizoctonia solani Kühn was first recorded in South Africa in 1918 (3). Although the sclerotial form on tubers is one of the most common potato diseases in the country, it is not known which anastomosis groups (AGs) of R. solani are involved. Between 1999 and 2001, R. solani was isolated from 28 plant and 56 soil samples collected in 7 (Eastern Free State, Gauteng, KwaZulu-Natal, Limpopo, Mpumalanga, Northern Cape, and Sandveld) of the 14 potato-production regions of South Africa and screened for hyphal anastomosis with tester strains of R. solani AG-1 to AG-10 according to Carling et al. (1). Of the 411 isolates from tubers with black scurf symptoms, 408 were AG-3 and three were AG-5. Symptomless tubers yielded two AG-3 isolates and three AG-5 isolates. Of 39 isolates from symptomatic stems and roots, 32 were AG-3, five were AG-4, and two were AG-5. Of the 127 isolates obtained from soil, 86, 28, 7, 3, and 3 were AG-3, AG-4, AG-5, AG-7, and AG-8, respectively. More than one AG was isolated from five of the seven regions. Virulence of 40 isolates representative of the above AGs was determined in triplicate on sprouts growing from seed tubers of potato cultivar Up-to-Date in a sand/soil mixture as described by Carling and Leiner (2) but using cultures grown in cornmeal/sand instead of colonized agar disks as inoculum. Damage to sprouts (lesions, girdling, and death) was assessed after 28 days at 16 to 28°C according to the 0 to 4 rating scale (2). Chi-square analysis of the data indicated that AG-3 was the most virulent, with isolates from sclerotia on tubers and lesions on stems more aggressive than those from symptomless tubers or soil. AG-4 and AG-5 caused significantly less disease than AG-3, but none of the AG-7 and AG-8 isolates showed any virulence to potato sprouts. References: (1) D. E. Carling et al. Phytopathology 77:1609, 1987. (2) D. E. Carling and R. H. Leiner. Phytopathology 80:930, 1990. (3) E. M. Doidge. S. Afr. Fruit Growers 5:6, 1918.

scholarly journals First Report of Black Scurf Caused by Rhizoctonia solani AG-3 on Potato Tubers in Mauritius

Plant Disease ◽  
2021 ◽  
Vol 105 (1) ◽  
pp. 213
Author(s):  
S. D. Takooree ◽  
H. Neetoo ◽  
V. M. Ranghoo-Sanmukhiya ◽  
S. Hardowar ◽  
J. E. van der Waals ◽  
...  
Keyword(s):  
Rhizoctonia Solani ◽  
Black Scurf ◽  
Potato Tubers ◽  
First Report

scholarly journals Streptomyces Species Associated with Fissure Scab of Potato in South Africa Including Description of S. Resiliuntiscabiei Sp. Nov.

2021 ◽  
Author(s):  
Elsie Margaretha Cruywagen ◽  
Rian Pierneef ◽  
Kgothatso Andronicah Chauke ◽  
Brightness Zama Nkosi ◽  
David Labeda ◽  
...  
Keyword(s):  
South Africa ◽  
Culture Media ◽  
Phylogenetic Analyses ◽  
Housekeeping Genes ◽  
Potato Tubers ◽  
Streptomyces Species ◽  
Culture Morphology ◽  
New Type ◽  
Genome Analyses ◽  
Phenotypic Tests

Abstract Streptomyces species are the causal agents of several scab diseases on potato tubers. A new type of scab symptom, caused by Streptomyces species, was observed in South Africa from 2010 onwards. The disease was initially thought to be caused by a single Streptomyces species, however, subsequent isolations from similar symptoms on other potato tubers revealed diversity of the Streptomyces isolates. The objective of this study was to characterise these isolates in order to determine which species are involved in the disease. This was done by sequencing and phylogenetic analyses of the 16S rDNA as well as five housekeeping genes, investigation of growth on different culture media, standard phenotypic tests and scanning electron microscopy of culture morphology. The presence of the pathogenicity island (PAI) present in plant pathogenic Streptomyces species was also investigated. The genomes of eight isolates selected from the three main clades identified, were sequenced and annotated to further clarify species boundaries. Two isolates of each of the three main clades were also inoculated onto susceptible potato cultivars in order to establish the pathogenicity of the species. The results of the phylogenetic and genome analyses revealed that there are three main species involved, namely, S. werraensis, S. pseudogriseolus and a novel Streptomyces species that is described here as Streptomyces resiliuntiscabiei sp. nov. The glasshouse trial results showed that all three of the Streptomyces species are capable of producing fissure scab symptoms. None of the Streptomyces isolates from fissure scab contained the full PAI and the mechanism of disease initiation still needs to be determined.

scholarly journals Formation of canker lesions on stems and black scurf on tubers in experimentally inoculated potato plants by isolates of AG2-1, AG3 and AG5 of Rhizoctonia solani: a pilot study and literature review

2008 ◽  
Vol 18 (3-4) ◽  
pp. 223 ◽  
Author(s):  
M.J. LEHTONEN ◽  
P.S. WILSON ◽  
P. AHVENNIEMI
Keyword(s):  
Pilot Study ◽  
Rhizoctonia Solani ◽  
Stem Canker ◽  
Potato Production ◽  
Anastomosis Group ◽  
Black Scurf ◽  
Potato Tubers ◽  
Potato Plants ◽  
Production Areas ◽  
Potato Crops

Development of black scurf on potato tubers (cv. Nicola) was compared in plants inoculated with isolates of Rhizoctonia solani of three anastomosis groups (AG2-1, AG3 and AG5) which occur in potato crops in Finland. All isolates induced stem canker lesions but only isolates of AG3 formed efficiently black scurf on progeny tubers. Among the AG2-1 and AG5 isolates tested, only one AG2-1 isolate formed a few sclerotia on 13.5 % of the progeny tubers in one experiment. The data indicate that isolates of AG3 differ from those of AG2-1 and AG5 in having a higher ability to form sclerotia on tubers. Therefore, while AG2-1 and AG5 isolates have a broader host range, AG3 is more efficient in producing black scurf, which provides this anastomosis group with more efficient means of dissemination on seed potatoes. These differences probably explain the predominance of AG3 (98.9 % of isolates) in potato crops in Finland and other northern potato production areas.;

scholarly journals Inhibition of Mycelial Growth of Rhizoctonia Solani by Chitosan in vitro and in vivo

2019 ◽  
Vol 13 (1) ◽  
pp. 156-161
Author(s):  
Sabah R. Mohammed ◽  
Elsayed M. Zeitar ◽  
Ivan D. Eskov
Keyword(s):  
Rhizoctonia Solani ◽  
Mycelial Growth ◽  
Phenylalanine Ammonia Lyase ◽  
Inhibitory Effect ◽  
Black Scurf ◽  
Potato Tubers ◽  
Antifungal Effect ◽  
Poisoned Food Technique

Objective: Evaluate the antifungal effect of chitosan against Rhizoctonia solani in vitro and the possible mechanisms of its induced activity in potato tubers to control black scurf disease. Methods: The in vitro influence of chitosan at different concentrations on mycelial growth of R. solani was tested by using the poisoned food technique in PDA medium. The effect of these concentrations on the development of lesion diameters in tubers inoculated with R. solani mycelium was assayed for 30 days. The concentration that showed the greatest inhibitory effect on lesion diameters was tested to assess the induced activity of defense-related enzymes in the infected tubers. Results: In the poisoned food technique, chitosan at 1% completely inhibited the growth of R. solani mycelium. In vivo tests showed that chitosan treatment at 0.5% effectively controlled the black scurf in tubers inoculated with R. solani mycelium. Chitosan increased the activities of defense-related enzymes such as Peroxidase (POD), Polyphenol Oxidase (PPO) and Phenylalanine Ammonia-lyase (PAL) in treated tubers of tested cultivars. Conclusion: This work demonstrated that chitosan directly inhibited the growth of R. solani, and potentially elicited defense reaction in potato tubers.

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