2. Morphological variability in F2 generation of Cochliobolus sativus

Leaf blotch, caused by Cochliobolus sativus, is a devastating foliar disease of wheat in Bangladesh. To develop effective disease management strategy against Cochliobolus sativus, knowledge of morphological variability of the fungal pathogen is essential for breeding program. For considering this fact present experiment was carried out in the Plant Pathology Laboratory of Agrotechnology Discipline, Khulna University, Khulna during June to August, 2019 to determine the morphological variation among the isolates of Cochliobolus sativus in F₂ generation. Twenty five isolates of F₂ generation of Cochliobolus sativus were used for observation of morphological variation. The experiment was laid out Complete Randomized Design with three replications. In morphological study, eleven morphological components viz. colony color, colony margin, colony growth behavior, radial growth, number of zonation, conidial color, conidial shape, septation number, length and width of conidia and conidia production cm^-2 were considered. Highest coefficient of variation (114.77) was observed among the number of zonation formation among the F₂ generation of Cochliobolus sativus. Five distinct clusters were found from cluster analysis based on eleven morphological components. Four distinct colony colors (whitish, blackish grey, ash grey and greenish black), three types of colony margin (regular, irregular and wavy), three types of colony growth behavior (fluffy, suppressed and too much suppressed), three types of conidial color (olive, brown and dark brown) and three types of conidial shape (straight, slightly curved cylindrical) were observed. Based on mean of five cluster centers, maximum spore producing and radial growth isolates were belonged in cluster 5. Between the clusters, maximum cluster distance was found between cluster IV and V (61.59) and minimum distance was observed between cluster II and IV (20.06). Higher correlation was observed among width of conidia, length of conidia, shape of conidia, conidial color and septation number. Principal component analysis (PCA) represented that colony color, colony margin and growth behavior contributed more than 80% of the variation among the eleven morphological components. PCA biplot showed that most of the highest sporulating isolates belonged to the same group and they produced olive colored conidia. 

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