Effects of selected tropical tree sawdust extracts on mycelial growth of seedborne pathogens of sunflower (Helianthus annuus, L.)
Sixteen sawdust samples obtained from sixteen tropical trees were evaluated in vitro for their potential to reduce the mycelial growth of the seedborne pathogens; Alternaria helianthi, Fusarium oxysporum and Aspergillus flavus. Sawdust samples were collected from the saw mill industries and heat sterilized (Gallenkamp hot air oven, 160°C for 5 h) to eliminate the resident mycobiota. Fungal pathogens used were isolated from sunflower via blotter test or agar plate methods. Each pathogen was inoculated on Petri dishes containing Potato dextrose agar media amended with sawdust extract while unamended media plates were used as control. Inoculated media were incubated for 7 days under room temperature at 28 °C ± 1 °C. Diameter of the fungal colony was measured using a meter rule along two diagonal lines drawn on the reverse side of each Petri dish seven days after inoculation. Gmelina arborea and Ficus exasperata sawdust induced up to 84.89% and 84.48% reduction in mycelial growth of the test pathogens. Sawdust samples from Esogordonia papaverifera, Piptadeniastrum africanum and Sterculia rhinopetela exhibited mycelial growth reduction of above 60.0% across the test pathogens. Fungitoxicity of Bombax spp., Brachystegia spp. and Terminalia superb was weak, inducing below 50.0% mycelial growth reduction across all pathogens. This study showed the prospect of sawdust in the control of seedborne pathogens and a possible alternative to chemical pesticides.