Abstract
Dark leaf spot (Alternaria brassicae) is one of the important diseases in crucifers causing serious yield and quality loss in production due to the seed borne nature of the pathogen. Variation in morphology and cultural characteristics among 32 representative Indian geographical isolates of Alternaria brassicae, the causal agent of Alternaria blight of cauliflower (Vegetable) rapeseed-mustard (Oil seed), was studied. All the isolates showed high level of variability in vitro in respect of conidial length, width, and number of septa. Conidia of Uttar Pradesh isolate (CaAbU4) were smallest in size with lowest number of septa. Substantial variation was found in mycelial growth, sporulation among these isolates in different nutrient media. All the isolates did not grow and sporulate abundantly on the same nutrient medium. However, Potato Dextrose Agar, Cauliflower (Host) Agar medium and Carrot Potato Agar were good for all the cultures. Variation in mycelial growth, sporulation was also observed. Cluster analysis of data on cultural variability among thirty two A. brassicae isolates found a close relationship among isolates of both origins viz, from Cauliflower and mustard. Isolates from Uttar Pradesh, Delhi, Haryana and West Bengal were found to be more similar to each other whereas the Rajasthan isolates along with Tamil Nadu and Kerala isolate were distantly related to others. All the isolates were pathogenic in nature but not directly related to the cultural and the morphological characteristics. These isolates were further molecularly characterized by using internal transcribed spacer region where all the isolates were found 56% similar to each other and 99% similar to the A. brassicae isolates present in NCBI database. Key words: Dark leaf spot, Alternaria brassicae, morphology, cultural variability,pathogenicity, ITS analysis.
Highlights
Among several fungal diseases, severe damage of the foliage or seed germination in crucifers occurs due to Alternaria blight caused by Alternaria brassicae (Berk) (Tewari, 1983; Weiss, 1983; Kolte, 1985; Tewari, 1991; Verma and Saharan, 1994)
Some researchers have worked on cultural variability in Alternaria species in respect of mycelial growth and sporulation (Ansari et al, 1989), media (Patni et al, 2005)
In a recent report Goyal et al (2011) reported variation in conidial morphology, mycelial growth, sporulation of thirteen isolates of A. brassicae collected from different geographical zones were dependant on temperature and geographical origin
Summary
Severe damage of the foliage or seed germination in crucifers occurs due to Alternaria blight caused by Alternaria brassicae (Berk) (Tewari, 1983; Weiss, 1983; Kolte, 1985; Tewari, 1991; Verma and Saharan, 1994). Black spot of different crucifers viz-oil seed rape, cabbage, cauliflower and mustard have been reported in many countries; Italy (Tosi and Zazzerini, 1985), USA, UK and several other. Cauliflower (Brassicae oleracea var botrytis) and mustard (Brassicae juncea) are the two important crucifer crops of India which are facing serious yield and quality loss in production due to Alternaria brassicae (Berk) Sacc. Causing dark leaf spot disease (Sharma et al, 2013).
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