Abstract
Alternaria blight (Alternaria brassicae) causes severe foliar damage to Indian mustard in Uttarakhand. Ten (10) isolates of A. brassicae were collected from different hosts and characterized for cultural, morphological, pathogenic and molecular variations. A. brassicae colonies varied in their cultural behaviour ranging from cottony, flurry to feathery, with smooth to rough margins. Colour of colonies ranged between white, off white to light brown. Colony growth varied from slow, medium to fast with fast growth in isolate KM and least in JD on the potato dextrose agar (PDA) medium. Significant morphological variations in conidia length, conidia width, and number of horizontal septa were observed in the isolates. Average conidial size ranged from 105 to 135 × 10 to 20 μm. Isolates exhibited variations in disease index, number and size of the lesions. The dendrogram analysis, based on molecular (random amplification of polymorphic DNA, RAPD) basis revealed two groups at 15% similarity coefficient. Group I was composed of seven isolates namely, VR, DV, P7, LM. P10, KR and ND with 18% similarity (82% dissimilarity) while group II was composed of only three isolates namely, JD, KA and AS with only 24% similarity (76% dissimilarity). Key words: Pathogenic variability, Brassica, Alternaria brassicae, RAPD-PCR.
Highlights
Alternaria brassicae (Berk.) Sacc., is an important necrotrophic pathogen causing Alternaria blight disease in Indian mustard [Brassica juncea (L.) Czern and Coss.]
Alternaria blight severity on oilseed Brassicas differ season to season, region to region and individual crop to crop in India (Chattopadhyay et al, 2005)
Plant material infected with A. brassicae was sampled randomly from different cultivars of B. juncea grown in the field of Crop Research Centre of G
Summary
Alternaria brassicae (Berk.) Sacc., is an important necrotrophic pathogen causing Alternaria blight disease in Indian mustard [Brassica juncea (L.) Czern and Coss.]. Alternaria blight severity on oilseed Brassicas differ season to season, region to region and individual crop to crop in India (Chattopadhyay et al, 2005) This might be due to the existence of variability among geographically similar isolates of A. brassicae. Reports are available who studied the genetic variation within and between Alternaria species by random amplified polymorphic DNA (RAPD) molecular marker (Sharma and Tewari, 1995, 1998; Pryor and Michailides, 2002; Kumar et al, 2008). Since the crop and disease are of paramount importance to the Uttarakhand state and no studies on pathogenic and genetic variability have been conducted Keeping this in mind, the present investigation focused on morphological, cultural, pathogenic and molecular variability of ten mustard isolates of A. brassicae in Uttarakhand. Characters like colony color, appearance, growth, shape, margin, sporulation and zonation were recorded by direct observation of culture-grown Petri plate on PDA which was incubated in B.O.D. incubator at 25°C temperature and 100% relative humidity
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