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ABSTRACT
Hevea brasiliensisis affected by a myriad of leaf diseases caused by pathogens that are both microscopic and visible parasites as well as by others of non-pathogenic origin. This study was carried out to evaluate the effect of Plant extracts and chemical fungicides on the mycelial growth inhibition of Corynespora casiicola of rubber leaf (Hevea brasiliensis). The fungal isolate was isolated from naturally diseased leaf of Hevea brasiliensis collected from Rubber Research Institute of Nigeria’s plantation in Iyanomo, Benin City. Ten plant leaves were extracted using crude method and the extract was tested against C. casiicola to monitor the effect on conidial germination and mycelial growth. Four commercially available chemical fungicides were also evaluated for their effect against C. casiicola. Mycelia inhibition was observed for C. casiicola when whole commercially available fungicides were challenged with the pathogen with the control (14.25±0.00 cm) having more mycelia growth compared to the commercial fungicides such as Azoxystrobin (3.41±2.01 cm), Metalaxyl (5.34±3.29 cm), mancozeb (12.68±1.67 cm) and spiroxamine (8.63±3.08 cm). There was more observable antifungal effect when the concentrations of the fungicides were varied with azoxystrobin and Metalaxyl having more potent antifungal activity at 15 ppm concentration for both fungicides. Of the ten plant extracts used in the study, only four (Allium sativum, Ageratum cornyzoides, Amaranthus viridis and Ocimum basilicum) were found to have significant antifungal effect against the pathogen. The mycelia inhibition of the four active plant extracts revealed a better antifungal effect at 100% for O. basilicum and A. sativum. The minimum inhibitory concentration of the plant extract against the tested pathogen showed A. viridis (32%) and O. basilicum (33%). The percentage of mycelia inhibition of fungicides and active plant extracts revealed a favourable comparison with the usage of commercial fungicides and as result plant extracts can serve as a viable alternative to the use of chemical fungicides.
