Effect of Two Fungicides on Mycelial Growth of Fungi Causing Leaf Blight and Wilt of the Rubber Plant (Hevea brasiliensis Muell Arg.) in Cameroon

Rubber (Hevea brasiliensis Muell. Arg., Euphorbiaceae) is a tropical tree crop mainly grown for the industrial production of latex. The rubber sector in Cameroon is faced with the effects of global economic crisis and a drop in the yield of latex due to several pests and diseases. This study focused on leaf diseases caused by Fusarium oxysporum and Pestalotiopsis microspora. The fungi were isolated from the leaves of the rubber plant and cultured for characterization on two media (Potato Dextrose Agar (PDA) and Potato Carrot Dextrose Agar (PCDA)) at various temperature and pH levels. Using the poison food technique, an in vitro assay was done to assess the effect of two fungicides (Synthetic Fungicide 1 (SF1) and Synthetic Fungicide 2 (SF2)) at the respective doses of 0.006, 0.013 and 0.025 g.L-1, and 0.005, 0.01 and 0.02 g.L-1 on the growth of the two fungi. Results obtained show that PDA is most favourable for the growth of both fungi compared to PCDA. Both fungi attained optimal growth at pH 7 and at an incubation temperature of 25 oC. Neither F. oxysporum nor P. microspora grew on SF1-amended PDA and PCDA at all doses of the fungicide. SF2 significantly (P>0.05) inhibited the growth of P. microspora by 53.3% at the dose of 0.025 g.L-1 while F. oxysporum was less sensitive to the fungicide at all doses. In vitro pathogenicity test revealed similar disease symptoms as those observed in the field. This study shows that SF1 is the best fungicide against F. oxysporum and P. microspora as it gave 100% inhibition on the growth of both fungi.