Abstract

0, 75, 100, 125 and 150 ppm a.i. concentrations of benomyl in Green Cocoa Mucilage Agar (GCMA) plates were evaluated for suppression of Colletotrichum gloeosporioides inPhytophthora palmivora plates contaminated by C. gloeosporioides. To do this, GCMA plates amended with the above concentrations of benomyl were seeded with mycelia plugs from a contaminated P. palmivora culture and radial growth rates of the resulting P. palmivora colonies were recorded. Mycelial bits from the centres, middle and peripheries of such colonies were examined at 7 days interval for P. palmivora and the contaminating C. gloeosporioides. Growth rates of pure C. gloeosporioides cultures were also studied on benomyl plates. Growth rates of 7.15, 3.10, 2.30, 2.05 and 1.60 mm/day were obtained for P. palmivora on plates, respectively, containing 0, 75, 100, 125 and 150 ppm benomyl. Growth rates of 2.95, 1.65, 1.60, 1.60 and 1.55 mm/day were respectively, obtained for the pure cultures of C. gloeosporioides indicating that on contaminated plates, growth of C. gloeosporioides will lag behind that of P. palmivora.On plates with 0 to 125 ppm benomyl, P. palmivora was detected at the centres, middle and peripheries of all colonies within the first week but C. gloeosporioides was restricted to the centres and middle portions of such colonies due to its slower growth rate. When subcultures were made at day 7 from the peripheries of colonies on 0 to 125 ppm benomyl plates onto benomyl-free plates, C. gloesporioides was not detected from the resulting cultures which were clean.

Key words: Collectotrichum gloeosporioides, contamination, selective culturing, Phytophthora palmivora