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Life sciences Leaflets 3:47 – 53, 2010. ISSN 0976 - 1098

http://lifesciencesleaflets.ning.com/ Page | 47

STUDY ON PLANT PATHOGENIC

FUNGAL DISEASES AFFECTING

SOLANUM TUBEROSUM (POTATOES)

IN THE REGION OF DEHGAM

(CENTRAL GUJARAT)

V. N. Patel, T. H. Patel and S. C. Parikh1

Dept. of Microbiology, Smt.S.S.Patel Nootan Sci. & Comm. College, Visnagar, Gujarat, India

1P.G.Centre in Microbiology, Smt.S.M.Panchal Science College, Talod, Gujarat, India

Email: [email protected]

ABSTRACT:A brief study on the plant pathogens affecting the potatoes was made in order to

ascertain the level of preservation and effective measures taken by cold storages for

maintaining the potatoes during their shelf life. Various samples were taken to screen for

the presence of a specific disease in the crop of potatoes during, after & before

preservation. Eight villages nearby Dehgam were selected for testing plant pathogenic

activities in their potatoes. Diseased samples were analyzed for the occurrence of fungal

infections. The infections were identified on the basis of symptoms & were classified

relevant to the different seasons of their emergence.

Key words: Plant Pathogens, Potatoes, Potato Scab Disease, Phytopathogenic fungi, dry

rot, late blight

INTRODUCTION:

In the recent years, the production of potatoes is increased dramatically in Gujarat

(India). Especially after 1995, the production has quadrupled in the region of Dehgam

and nearby villages. The average production of potatoes in the year 1975 was 500,000

tons/annum as compared to 25, 00,000 tons/annum in the year 2007. Due to excessive

cultivation, storage and consumption, this crop needs special attention for preservation

from losses. However various microbial interactions are responsible for spoilage and

losses resulting in decreased productivity of potatoes. Local cold storages in the nearby





area can play a vital role for the preservation from losses caused by spoilage of potatoes.

The present study was conducted in eight main villages nearby Dehgam in order to

survey and identify the fungal pathogens affecting potatoes during last one year.

Infections caused may belong to various body parts of potatoes and further may be

caused by bacteria, fungi, viruses and others.

We have mainly focussed on fungal diseases occurring in potatoes in this study.

Potatoes being rich in biological polysaccharides such as starch and some other sugars,

serve as a natural media for the cultivation of some of the well-known phytopathogens.

Every year several tons of potatoes are thrown away due to inherent spoilage caused

during their storage and preservation in some of the well-known cold storages in thenearby area such as Rakhial, Sampa, Palaiya, Vahelal, Dehgam, Babalpura, Ahmedpura

and Zak.

MATERIALS and METHOD:

Eight field trips were made to survey potato fungal infections in the eight potato

producing regions of Central Gujarat i.e. Rakhial, Sampa, Palaiya, Vahelal, Dehgam,

Babalpura, Ahmedpura, Zak. Two trips were made each season. The first trip was made

10-12 days before potato harvesting. The second trip was made prior to the harvesting

and storage in the cold storages.

A sample of potato is collected from the cold storage and also from the out side of

the cold storage (near the cold storage), and labelled it and placed it in the polyethylene

bags for maintaining samples until completion of the survey mission.

The surfaces of infected potatoes were rinsed with sterile water, and then infected

portions were streaked/ spreaded on the Potato Dextrose Agar (PDA), Rose Bengal Agar

(RBA) and Nutrient Agar (NA). The plates were incubated in the dark at 25-28 oC and

examined periodically for identification of the isolated fungi.

Upon Cultivation of plant pathogenic fungi using the aforesaid microbiological

media, the organisms were further identified on the basis of their morphological & other

studies.

RESULTS and DISCUSSION:





Out of 100 samples analyzed for plant pathogenic activities, 39 were unidentified,

15 samples were having late blight disease of potatoes caused by Phytophthora sp., 29

samples were known to have stem canker & black scurf caused by Rhizoctonia sp., and

17 samples of potatoes were suffering from dry rot caused by Fusarium sp.

Table-1: Diversity of Fungal Phytopathogens and their geographical analysis

However the causative agents mentioned here were not the only species found on

cultivation media, but the higher colony forming units of these species comparative to

other fungal species, and the symptomatology of the fungal disease in these potatoes

helped us to designate them as the actual causative agents of the disease.

(1)Late Blight of Potatoes:

Area/

Type of Disease & Pathogen D e h g a m

R a k h i a l

V a h e l a l

Z a k

P a l a i y a

S a m p a

B a b a l p u r a

A h m e d p u r a

T o t a l

Total samples taken foranalysis 18 15 11 05 17 15 12 07 100

Unidentified 07 04 05 01 07 08 04 03 39

Dry rot

(by Fusarium sp.)02 04 01 01 03 03 02 01 17

Stem canker & Black scurf

(by Rhizoctonia sp.)06 05 04 01 04 03 05 01 29

Late blight

(by Phytophthora sp.)03 02 01 02 03 01 01 02 15





Water-soaked lesions appear on foliage that, within a few days, becomes necrotic,

turning brown when dry or black when wet. Under damp conditions, white mildew like

sporulation is visible, especially on the lower surface of leaves.

A pale yellow margin often forms around leaf lesions. Lesions on stems and

petioles are black or brown. Stem lesions are brittle and stems frequently break at the

point of the lesion. Under certain conditions, wilting can occur on stems with lesions.

Disease is favored by temperatures between 10 and 25°C, accompanied by heavy

dew or rain.

Tubers infected by spores washed by rain from the leaves and stems into the soil

have brownish surface discoloration. Sections cut through tubers show brown, necrotictissues not clearly differentiated from the healthy portions. Later secondary rot organisms

develop in blighted tissue and rots spread in storage.

(2) Stem Canker & Black Scurf Disease:

Lesions on sprout tips cause delayed emergence or failure to emerge. Slightly

sunken brown cankers of variable size and shape affect stolons and stems at or below the

soil line.

Cankers may girdle stems and result in aerial tuber formation, plant wilt, and

death. Girdled stolons may fail to produce tubers. Hard, dark brown or black sclerotia

(fungus-resting bodies) of irregular size and shape form on the tuber surface. A white

mycelial mat may develop on the stem base, but does little harm to the plant.

(3) Dry Rot of Potatoes:





Externally, tubers may have sunken or wrinkled areas and an occasional white or

pink fungal growth. Internally, tubers develop a crumbly dry decay ranging from dark

brown (chocolate colored) to black. In addition, cavities often develop in the rotted tissue

that contains the white or pink fungal growth.

A moist rot may occur if tubers are invaded by a secondary infection with soft rot

bacteria.

Unidentified

Late blight

Stem canker &

black scurf Dry rot

Fig.-1: Pie Chart indicating the occurrence & distribution of fungal diseases in

potatoes





The above pie chart indicates the occurrence & distribution of various fungal

pathogens affecting the potatoes in the region of Dehgam (Central Gujarat, India).

Among the diseased specimens Stem Canker and Black Scurf dominates over the dry rot

and late blight disease of the crop variety. However, a major part of the samples are

remaining undetectable as they are infected by mixed/ unknown type of infections (other

than fungal infections).

Fig.2: Occurrence & Distribution of various fungal diseases in the areas selected for

study.

CONCLUSION:

From this comprehensive study on phytopathogens of potatoes, it can be

concluded that most of the pathogens invade the host while moist & humid conditions are

present during their storage. The fungal pathogens that cause productivity loss to the crop

of potatoes are mostly the inherent soil microflora but under special circumstances they

cause a variety of diseases such as dry rot, stem canker, black scurf & late blight of





potatoes. Preventive measures that can be suggested are proper aeration, humidity control

& application of antifungal agents as a spray in the preservation area during their shelf

life.

ACKNOWLEDGEMENT:

We acknowledge the kind support and guidance provided by various cold storage

owners and local farmers of the affected crop variety of the region. We are really thankful

to the people of the selected areas for helping us to collect the specimens and providing

us useful information regarding the local terminology and outcome of specific potato

diseases affecting its productivity.

REFERENCES:

Suleiman M. Al-Kherb, Zaidan M. Abul-Hayja and Ibrahim Al-Shahwan(1996), “Potato

Fungal Diseases in the Kingdom of Saudi Arabia”, J. King Saud. Univ., Vol-8,

Agri. Sci.(1) 147,156

Row, C. (1986) “Managing Potato Production for Optimal Plant Health” Plant Disease,

70, 354-356.

Webster, J. (1980), Introduction to Fungi, 2nd (Ed.). Cambridge, UK, Cambridge

University Press ,669

Tuite, J.C. (1969) Plant Pathological Methods, Minneapolis, Burgess Publishing Co.,

Rich, A.E. Potato Diseases, NewYork: Academic Press,(1983)

Managing Late Blight on Irrigated Potatoes in the Pacific Northwest,( 2003). PNW

555Available Online at (http://www.info.ag.uidaho.edu/pdf/pnw/pnw0555.pdf )

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