Morphocultural Characterization and Aggressiveness of Fusarium stilboides Isolates from Four Coffee Growing Regions in Tanzania

Fusarium stilboides , the causative agent of Fusarium bark disease (FBD) in Coffea arabica , poses a significant threat to coffee production. Despite its impact, limited research has explored the pathogen’s morphological diversity and pathogenic variability in Tanzania. This study aimed to characterize the morphocultural traits and aggressiveness of F. stilboides isolates collected from four coffee-growing regions in Tanzania: Suji (Same District- Kilimanjaro region), Mahande and Mbangamao (Mbinga DC- Ruvuma region), Ayalabe (Karatu District- Arusha), and Bara (Mbozi District- Songwe region). Five isolates were obtained from symptomatic coffee trees. They were then cultured on Potato Dextrose Agar (PDA), and assessed for colony morphology, pigmentation, growth rate, and sporulation. Evaluation of pathogenicity was through stem injection and soil-drenching methods of inoculation on C. arabica seedlings, with disease severity monitored over 112 days. Results revealed significant variations in colony color, texture, and growth rate among isolates. Sporulation capacity also differed significantly, with isolates KSS24 and SVB24 exhibiting abundant sporulation, while RMM24 had the lowest. Pathogenicity assays showed a significant difference (P < 0.05). Isolate KSS24 was the most aggressive, reaching a mean disease severity score of 3.00 by 63 days after inoculation, whereas AKA24 exhibited the lowest severity (0.67). These findings highlight the morphological and pathogenic variability of F. stilboides in Tanzania, underscoring the need for further studies on molecular characterization and environmental interactions influencing pathogenicity, which could further inform breeding programs aimed at developing resistant coffee varieties.