Pathogenic Variability in F2 Generation of Cochliobolus Sativus (S. Ito & Kurib.)

Abstract

A total of 24 isolates of F2 generation of Cochliobolussativus (S. Ito &Kurib.) [anamorph, Bipolarissorokiniana (Sacc. In Sorok)] the causal pathogen of spot blotch of wheat were collected from Plant Pathology Laboratory,Agotechnology discipline, Khulna University, Khulna; for determining vindence spectra following pathogenic variability test.A susceptible wheat cultivar "Kanchan" was used inpathogenic variability test of those isolates of F2 generation of C. sativus. Seven components of disease development like infection frequency (IF), lesion size (LS), lesion cover (LC), necrosis (NEC), secondary spore production (SPD), disease severity (DS) and percent disease index (PDI) were studied. Wheat seedlings were inoculated and data on those seven disease development components were checked. After performing multivariate analysisa positive correlation was found among the seven components of disease development, where DS was strongly related with PDI. However, LS and IF did not show any significant relaüon to cause disease. After conducting a principal component analysis (PCA) infection frequency and lesion size were most promoting components to create variabilityand also in a Biplot, isolates with high infection frequency and lesion size were closely situated.lsolate CSF2-32 was found to be most virulent and isolate CSF2-58 was most virulent and aggressive ones by producing highest percent disease index (64.44) and secondary spore (2444.44), respectively.A clusteranalysis indicated that the isolates exhibited distinct differential virulence patterns with five groups supported by a dendrogram figure. Cluster Ill contains 16.66% of total isolates with the most virulent isolates (CSFr32, CSF2-27, CSF2-67, and CSFŽ- 58). Cluster I (16.66%) contains least virulent isolates (CSF2-10, CSFŽ-16, CSFŽ-61 and CSF233). This result also reflected in mean cluster distance by showing maximum distance (2080.63) between cluster I and cluster Ill. Findings of the present study reveal that seven disease development components are significantly differed to each other showing difference among the isolates; positive correlation is found among the disease development components; in PCA analysis, cumulatively Infection frequency and lesion size are the most atfributing components to create variability; and five major goups of F2 generation of C. sativus isolates have been found through cluster analysis.