ABSTRACT
Corynespora cassiicola is an important plant pathogen causing Corynespora leaf fall disease (CLF) of the rubber tree. Symptoms produced by Corynespora cassiicola on rubber vary with the type of the clone, stage of the maturity and the locality where the susceptible clone is planted. This ubiquitous fungus has more than 80 plant species as its hosts and shown to be having an intra-specific variation within the isolates. This study was done to determine the pathogenicity of Corynespora cassiicola on selected clones of rubber. The pathogenicity of the isolates on selected rubber clones was investigated. Leaf disc (30 mm diameter) were prepared from 10 rubber clones namely, NIG800, NIG 801, NIG802, NIG803, NIG901, NIG904, NIG908, NIG910, GT 1 and RRIM600 obtained from the bud wood nursery of Rubber Research Institute of Nigeria, Iyanomo, near Benin city. Cross infectivity study showed that all the ten isolates from rubber clones infected the Nigeria developed clones (NIG900), exotic clone (RRIM 601) and tomato plant. The growth rate of the ten isolates showed no significant variation on both culture medium (Potato Dextrose Agar and Malt Extract Agar). The biomass of the isolates showed no significant difference between the two media (PDA and MEA). The biomass of each isolate also shows no significant variation among the rubber clones except for GT 1(2.433) and RRIM 600 (2.367) that had the highest concentration. In conclusion, this study showed that RRIM 600 was very highly susceptible to Corynespora cassiicola attack while NIG 800, 801, 802, 803, 804, 901, 904, 908, 910 and GT 1were moderately susceptible to the pathogen attack.
