Identification and Morpho-Cultural Characterization of Colletotrichum sublineolum Causal Agent of Sorghum Anthracnose and Its Management with Extracts of Azadiracta indica in Dutsin-Ma, Nigeria

Abstract

This study investigated the isolation, identification, characterization, and control of Colletotrichum sublineolum, the fungus responsible for sorghum anthracnose, using neem (Azadirachta indica) extracts (seed, leaf, and bark) combined with methanol at concentrations of 0%, 10%, 20%, and 30%. Infected sorghum leaves were collected from local farms, and the fungus was isolated from five fields, resulting in five distinct isolates: DTMCOE, DTMHYG, DTMDRW, DTMSRB, and DTMSMQ. DTMSRB had the highest frequency of occurrence (12), followed by DTMDRW (8), while DTMSMQ was least frequent (4). Pathogenicity testing on detached sorghum leaves revealed that DTMSRB and DTMHYG isolates were highly virulent, producing severe infection symptoms. DTMDRW and DTMCOE isolates caused moderate infection, while DTMSMQ exhibited only slight symptoms. Isolates were further characterized on Potato Dextrose Agar (PDA) based on physical traits such as colony elevation, margin, texture, color, and conidia shape. Most isolates showed hyaline, smooth-walled, falcate conidia without septa and smooth colony margins, though a few had undulated margins. Morphological diversity among isolates indicated the possible presence of several C. sublineolum sub-species in the study area. In vitro evaluation showed that all neem-methanol extracts effectively controlled fungal growth, with neem bark extract having the most significant impact in reducing the radial growth of C. sublineolum compared to leaf and seed extracts. Variations in concentrations (especially higher levels) improved the antifungal efficacy of the neem extracts. The study suggests that neem-based treatments could be a viable approach for managing C. sublineolum and recommends formulating neem-methanol extracts for practical use in sorghum anthracnose control.