Pathogenicity-based Isolate Profiling of Macrophomina phaseolina Associated with Stem and Root Rot of Groundnut and Sunflower

Abstract

Aims: To characterize Macrophomina phaseolina isolates from groundnut and sunflower in Andhra Pradesh and Telangana, India, for cultural traits and pathogenic variability, and to develop an integrated Macrophomina Virulence Index (MVI) for profiling the isolates across hosts and assays in relation to pathogenicity. Study Design: Pathogenicity based isolate profiling using rolled paper towel and sick-soil pot culture assays, with multivariate analysis and hierarchical clustering. Place and Duration of Study: Infected groundnut and sunflower samples were collected from districts of Andhra Pradesh and Telangana. Laboratory assays and pathogenicity tests were conducted at ICAR-Indian Institute of Oilseeds Research, Hyderabad, during 2024-25. Methodology: Forty-one M. phaseolina isolates were isolated from symptomatic root and basal stem tissues. Isolates were characterized for colony morphology and microsclerotial production on PDA. Pathogenicity was evaluated on groundnut cv. K-6 and sunflower hybrid KBSH-44 using rolled paper towel (germination, seed rot, seedling blight, total infection) and sick-soil pot culture assays (germination, wilt incidence, root rot incidence, mean lesion length). Integrated Macrophomina Virulence Index (MVI) was computed across 16 pathogenicity components (2 hosts × 2 assays × 4 variables). Isolates were clustered hierarchically based on disease-response profiles. Results: All isolates produced typical M. phaseolina colonies with variation in colour, texture and growth. In rolled paper towel and pot assays, total infection and wilt incidence ranged from 0–100%, respectively. MVI values showed a continuous distribution, indicating a continuum of aggressiveness. Hierarchical clustering resolved isolates into three consensus clusters and distinguished broad-spectrum from host-preferential phenotypes. Conclusion: The study revealed substantial cultural and pathogenic diversity among Macrophomina phaseolina isolates from groundnut and sunflower in Andhra Pradesh and Telangana. The integrated MVI demonstrated a continuum of pathogenicity and identified both broadly aggressive and host-preferential isolates. These findings provide a useful foundation for resistance screening, pathogen characterization and sustainable disease management in oilseed crops.