Potatoes

Characterization of Streptomyces scabies

causing Common Scab of Potatoes

By

Sania Shoukat

Potatoes

CONTENTS

Introduction (Potatoes)

Characterization

Streptomyces scabies

INTRODUCTIO

N

(POTATOES)

“The potato is on the frontline in the fight

against world hunger and poverty.”

(Jacques DioufDirector-General, FAO)

Potato •Papa (Latin Americans), patata (Spaniards),potato...•The potato is a tuber, not a “tubular”

•Scientific Name : Solanum tuberosum•Family :Solanaceae (or nightshade family of flowering plants (Korpan et al.,2004)

•largest genus, with over 1000 species (OECD, 2008)•world's fourth most important food crop

Potatoes

Potatoes as staple food

“ Solanum tuberosum, the “humble tuber”

that spread from its Andean birthplace across six continents, staving off hunger,

fuelling economic developmentand changing the course of world history. ”

world’s number one non-grain food commodityvaluable cash crop for millions of farmers.

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POTATOES ARE GOOD FOR YOU

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International Year of Potato (IYP) 2008

The IYP mission: raise awareness of the importance of the

potato– and that of agriculture in general –in addressing issues of global concern,

including hunger, poverty and threats to the environment

IYP presented unique opportunity to make a valid and effective contribution

towards meeting the Millennium Development Goals

Potatoes

Potato productionglobal production of 314 million

T. (FAO, 2008).total production of 2542

thousand tonnes (Anonymous, 2008-2009)

Production estimated in 2009-10 to 3.14 million T in Pakistan.

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THREATS

Ralstonia solanacearum (brown rot or bacterial wilt)S

Phytophthora

infestans (late

blight);

Erwinia carotovora(black leg

and Erwinia rot)

Clavibacter michiganense (ring rot)

Streptomyces scabies (common scab)

Alternaria solani (early blight)

Pathogenic problems includes

(Kabeil et al., 2008)

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Streptomyces

scabies

(Common scab

of potato)

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Common scab of potato

One of the major bacterial pathogensPathogen: Streptomyces scabies

(gram-positive actinomycetes)Order: ActinomycetalesFamily:StreptomycetaceaeGenus :StreptomycesHosts: including radish, beet ,carrot,

potato (Solanum tuberosum) (Goyer and Beaulieu 1997).

Common scab pathogen – Streptomyces scabies

Potatoes

Potatoes

Losses caused by StreptomycesSerious disease of potatoesPrevalent in about 90% of the potato fields

in all potato growing areas of Pakistanaffecting the quality and market valuee95 % incidence in Taxila and Rawalpindi

region(Shazia et al., 2009-2010)

maximum incidence in Gujar Gabral in Swat(Khan etal., 1985)

Potatoes

When should I expect it?

Dry, alkaline, sandy or chalky

soils

Hot dry summers

disease is an like a bacterium, but with threads of mycelium-like fungi. It lives in the soil,

infecting tubers through natural openings such as lenticels

Characterization

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Potatoes

Characterization

(Loria et al. 1997).

over 400 identified species of Streptomyces

and only a fraction of these

are pathogenic on potato tubers

(Bouchek-Mechiche et al ., 2000Song et al., 2004.).

streptomycetes have been

classified into a number of species

by various scientific studies

based on 16s ribosomal DNA (rDNA) sequence,

biochemical characteristics

Potatoes

S.scabies were identified by the following biochemical tests

Gram stain (Gregerson, 1978) Melanin production on peptone yeast extract-iron agar

and tyrosine agar medium; starch Hydrolysis ; hydrogene sulfide production Nitrate reduction gelatin liquification Catalase production oxydase reaction urease production 3 and 5% sodium chloride(NaCl) tolerance.

(Schaad et al, 2001) Streptomyces scabies negative response for oxidase,

urease, indole production and nitrate reducatase and positive for production of hydrogene sulfide.

(BENCHEIKH et al., 2007)

Potatoes

Characterization continued………………..

Streptomyces scabies

(synonym, S. scabiei)

best-described species of scab

causing scab it has recently been

divided into several morphologically

similar but genetically distinct

species

(Bouchek-Mechiche, et

al., 2000)

scabies was first described by Thaxter

(1892) re-proposed by Lambert and Loria

(1989) as the predominant

species

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Characterization continued………………..

At present, streptomycetes causing common scab in potato are

classified into

at least 10 different species (Park, et

al., 2003)

at least three additional species cause netted scab in Europe or russet

scab in North America

Another species

causes scab on sweet potatoes

(Clark, et al., 1998)

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Potatoes

Characterization continued………………..

A distinct acid-tolerant species, S. acidiscabies, induces symptoms similar to S.

scabies.(Lambert and Loria, 1989)

S. europaeisca

biei

S. stelliscabie

i

cause common scab of potato

(Bouchek-

Mechiche et al., 2000).

S. reticuliscabiei

was identified as a causal pathogen of netted scab in France.

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Differences between„pathogens“ /PASCO; 2004/

Common scab

Netted scab

Occurrence soil-borne soil-borne

Soil temperature

20° C 17° C

Soil moisture low high

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Characteristics of numerous potato scab-inducing not

consistent with description of S.

scabies or S.acidiscabies.

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.

(Doering-Saad et al., 1992) divided potato scab-inducing strains into three phenotypic

groups

Spore chain morphology ranged from

spiral to flexuous to retinaculum-

apertum to rectus

Spore ornamentation ranged from

smooth to warty to spiny

Potatoes

What can I do about common scab?

Once the crop is affected there is no cure for this

disease. The tubers may look unappetising but they are

still edible. Peeling removes the damaged parts. Storage

is not affected.

Can common scab be avoided?

Potatoes

Use plenty of organic

matter such as compost, leaf mould

and manure

Most effective control is use of resistant variety

Avoid sowing infected seed

disease is very widespread in most soils and so is hard to avoid.

Don't compost diseased peelings or old potatoes.

Potatoes

CONCLUSIONAlthough the scab symptoms caused

by other species do not differ from those caused by S. scabies, but the phenotypic characteristics of this organism clearly differ from those of other pathogens.

S. scabies is the predominant species responsible for the disease other than S. acidiscabies and is limiting factor in potato production.

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Potatoes