S2.4. Genetic and Morphological Diversity in Exserohilum Turcicum, Incitant of Turcicum Leaf Blight in Maize
Genetic and Morphological Diversity in Exserohilum Turcicum, Incitant of Turcicum Leaf Blight in MaizeSangit 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.
Morphological variability in the isolates of E. turcicumIsolates N08 NO6 N05 A08 A06 A05 AO5a AO5b AO5c Para.Col. of Mouse Light Mouse Light Mouse Light grey Light greyculture grey grey grey grey br. grey grey brown grey brown br.Culture Radia Radia Radia Irre Radi Radia Radia Radia Irregu.orien. ting ting ting gular ating ting ting tingConidia Less High high Mod. Less Less high Mod. Suppreintensity ssed Mod. Br. – Brown, Orien. – Orientation Mod. - Moderate
Isolates N08 NO6 N05 A08 A06 A05 AO5a AO5b AO5c Para.Conidia 1-7 1-10 1-11 1-9 1-7 1-9 1-10 1-11 1-10spetaColor of stra Dark light Dark straw dark dark dark darkconidia w straw straw straw straw straw straw strawConidia 35X 20X90 35X120 20X90 20X90 20X90 20X70 20X90 20X90(µm) 120Conidia Sligh Straig. Slight. Straig. straight Slight Slight. Slight. Slight.shape tly curv. curv. curv. curv. curv. curv. Long beakChlamy high Mod. high Mod. Mod. Mod. Less High Lessdosporeintensity
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 Germination after 2 hours 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.
Dendrogram of isolates of Exserohilum turcicum based on morphological traits• 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.
L N08 N06 N05 A08 A06 A05 A05a A05b A05c L N08 N06 N05 A08 A06 A05 A05a A05b A05c (a) 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)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
Results1. 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 tomore 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.
Conclusions1. 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.
AcknowledgementThe authors gratefully acknowledgewith thanks the contribution of Dr. K. T.Pandurangegowda, Professor, UAS,Bangalore and Dr. S. K. Pant, Sr.Scientist Plant Pathology for providingthe isolates and infected samples fromNagenahalli (Karnataka) and Almora(Uttarakhand) in India respectively forpresent study.