Genetic and Morphological Diversity in Exserohilum

Turcicum, Incitant of Turcicum Leaf Blight in Maize

Sangit Kumar, Meena Shekhar, Archana Sharma, B. M. Prasanna

Directorate of Maize Research, Pusa Campus IARI, New Delhi,

110012 India

1. Turcicum leaf blight or northern corn leaf blight

(TLB) is incited by the fungus Exserohilium

turcicum (Pass) Leonard and Sugs. (Synonyms;

Drechslera turcica (Pass.), Shoemaker.

Helminthosporium turcicum (Pass.)

2. It is a ubiquitous foliar disease of maize (Renfro

and Ullstrup 1976). TLB has worldwide

distribution.

3. Loss in grain yield range from 27.6 to 97.5% and

this loss was directly proportionate to the

intensity of the disease.

4. Two hot spots (Nagenahalli & Almora) for

Turcicum leaf blight identified for screening for

resistance in Peninsular India & Northern hills.

Turcicum leaf blight • Distribution – Jammu & Kashmir, Himachal Pradesh, Sikkim,

West Bengal, Meghalaya, Tripura, Assam, Rajasthan, Uttar akhand, Uttar pradesh (Rabi), Bihar (Rabi), Madhya Pradesh, Gujrat, Maharastra, Andhra Pradesh, Karnataka, Tamil Nadu

• Symptoms – Long, elliptical, grayish-green or tan lesions ranging from 2.5 to 15 cm in length develop on leaves. They may appear first on the lower leaves and later on the diseases progresses upward on the plant. The disease can develop rapidly after anthesis resulting in complete blighting of leaves.

• Predisposing Factors – cool/moderate humid conditions (18-27ºC) favors disease developments. When infection occurs prior to and at silking stage and conditions are optimum, it may cause significant economic damage.

The extent of morphological and genetic diversity among a set of isolates of E. turcicum, collected from two distinct agro climatic zones (Northern hill region and southern peninsular zone) in three different years from different maize cultivars were investigated.

For developing location specific disease management strategy, understanding the genetic variability among isolates of E. turcicum is essential.

S.

No.

Isolate Year of

collection Location

1 A05 2005 Almora (Hawalbagh -Him-4)

2 A05a 2005 Almora (Hawalbagh -Vivek-9)

3 A05b 2005 Almora (Hawalbagh -CML-142)

4 A05c 2005 Almora (Hawalbagh -DMR-617)

5 A06 2006 Almora (Sheetlakhet)

6 A08 2008 Almora (Hawalbagh)

7 N05 2005 Naganenhalli

8 N06 2006 Naganenhalli

9 N08 2008 Naganenhalli

Details of isolates used in present investigation

Isolates

Para.

N08 NO6 N05 A08 A06 A05 AO5a AO5b AO5c

Col. of

culture

Mouse

grey

Light

grey

br.

Mouse

grey

Light

grey br.

Mouse

grey

Light

grey

grey

brown

Light

grey

grey

brown

Culture

orien.

Radia

ting

Radia

ting

Radia

ting

Irre

gular

Radi

ating

Radia

ting

Radia

ting

Radia

ting

Irregu.

Conidia

intensity

Less High high Mod. Less Less high Mod. Suppre

ssed

Mod.

Morphological variability in the isolates of E. turcicum

Br. – Brown,

Orien. – Orientation

Mod. - Moderate

Isolates

Para.

N08 NO6 N05 A08 A06 A05 AO5a AO5b AO5c

Conidia

speta

1-7 1-10 1-11 1-9 1-7 1-9 1-10 1-11 1-10

Color of

conidia

stra

w

Dark

straw

light

straw

Dark

straw

straw dark

straw

dark

straw

dark

straw

dark

straw

Conidia

(µm)

35X

120

20X90 35X120 20X90 20X90 20X90 20X70 20X90 20X90

Conidia

shape

Sligh

tly

curv.

Straig. Slight.

curv.

Long

beak

Straig. straight Slight

curv.

Slight.

curv.

Slight.

curv.

Slight.

curv.

Chlamy

dospore

intensity

high Mod. high Mod. Mod. Mod. Less High Less

Cultural characteristics of the colonies of different isolates of E. turcicum

10 days old Cultures grown in PDA

Spore germination in different isolates of

Exserohilum turcicum

S. No Isolate Germination

after 2 hours

Germination

after 4 hours

1 NO8 - +

2 NO6 - +

3 NO5 - +

4 AO8 - +

5 AO6 + +

6 AO5 + +

7 AO5a + +

8 AO5b + +

9 AO5c + +

1. The isolates of E. turcirum exhibited variation in

mycelium color, with isolates N08, N05, A06 (mouse

grey) while isolates N06, A08 (light grey brown) and

isolates A05, A05a, A05b and A05c being light grey

to grey brown.

2. They varied significantly in their cultural,

morphological and physiological traits of colony

color shape, texture, conidia size and radial mycelia

growth on culture media. The optimum temperature

for the mycelia radial growth was 25°C and the

fungus was grown well in potato dextrose agar

(PDA).

Spore germination data revealed that

Almora isolates were more prolific in

comparison to Nagenahalli isolates in

terms of germ tube production. Though

the Nagenahalli isolates possessed higher

number of spores in culture media (PDA).

Progressive mycelial growth on culture

media revealed maximum coefficient of

variation in A05c while minimum in A05b

isolates.

The morphological observation showed that

all the isolates of E. turcicum had different

conidial traits.

Among them N05 sporulated better on PDA

medium. The mean length and breadth of

conidia ranged from 20x70 µm and (A05a,

A05c) and 35X120 µm (N05, N08), respectively.

Mean septa of conidia was maximum in isolate

N05, A05b and minimum in isolate A06 and

N08.

The highest mean radial growth was observed

in isolate N05 followed by N08 and the lowest

was observed in isolate A05c.

• Phenotypically all isolates belonged to four clusters

• maximum similarity of 64% in A05a and A05c

• N08and A06 again belonged to same cluster as in RAPD analysis.

Dendrogram of isolates of Exserohilum turcicum based on

morphological traits

L N08 N06 N05 A08 A06 A05 A05a A05b A05c L N08 N06 N05 A08 A06 A05 A05a A05b A05c

L N08 N06 N05 A08 A06 A05 A05aA05bA05c L N08 N06 N05 A08 A06 A05 A05a A05bA05c

(b)

L N08 N06 N05 A08 A06 A05 A05a A05b A05c L N08 N06 N05 A08 A06 A05 A05a A05b A05c

(c)

(a)

characterization of exserohilum turcicum with different primers; (a) OPP-10,

OPS-1, (b) OPO-10, OPO-12 (c) OPS-3, OPS-10

Dendrogram of isolates of E. turcicum based on RAPD analysis

Results

1. Thirty two primers out of eighty (40%) produced

reproducible PCR banding pattern with a total of

205 bands.

2. Each primer produced an average of six bands

ranging in size between 0.025-0.1 kb. Five percent of

the amplified bands were common to all individual

isolates, while 90% were polymorphic being specific to

more than one isolates.

3. These were considered “phylogenetically

informative” since they were useful for inferring

clustering relationships.

4.The most divergent isolate was N05 from Nagenahalli

with only 12% similarity with other isolates.

5. Isolates from Nagenahalli, N08 & Almora A06

are very similar to each other with 85%

similarity.

6. The morphological variability was observed

among these isolates.

7. The highest mean radial growth was

observed in isolate N05 followed by N08 and

the lowest was observed in isolate A05c.

8. Isolates belonging to same year from similar

location (A05, A05a, A05b and A05c) exhibited

enormous cultural variation in respect to

cultural characteristics & spore characters.

Conclusions

1. Dendrogram based on morphological traits

revealed diversity within the isolates collected

from the same geographical locations as well

from Nagenahalli and Almora.

2. Only a single isolate from Nagenhalli 05 was

out grouped with only 12% similarity with other

isolates. Isolate from Nagenahalli N08 and

Almora A06, are closely related with 85%

similarity. Gowda (1993) has reported that the

isolates from Almora and Nagenahalli belong to

race IV.

3. Genotypic and phenotypic variability

were not correlated from two locations.

4. Phenotypically all isolates were grouped

into four groups as compared to three

groups at genotypic level.

5. Further study with more number of

isolates is needed to establish the

relationship between genetic and

morphological traits.

Acknowledgement

The authors gratefully acknowledge

with thanks the contribution of Dr. K. T.

Pandurangegowda, Professor, UAS,

Bangalore and Dr. S. K. Pant, Sr.

Scientist Plant Pathology for providing

the isolates and infected samples from

Nagenahalli (Karnataka) and Almora

(Uttarakhand) in India respectively for

present study.