Pathogenicity of Fusariumoxysporumon upland New Rice for Africa NERICA Varieties and its Management with Botanical Extracts

Abstract

Studies were carried out to investigate the pathogenicity of Fusariumoxysporum on nine Nerica rice cultivars (Nerica 1, 2, 4, 7, 8, 10, 11, 14, 15), in comparison with WAB 56/104 and OS6. In vitro and in vivo investigations were also conducted to evaluate the crude extracts of Azadirachtaindica, Moringaoleifera and Vernoniaamygdalinafor the control of the fungus. Rice seeds were planted in sterilized soil and inoculated with (2.3 x 10⁶) spores of F. oxysporumfour weeks after planting. The plants were arranged in Completely Randomized Design (CRD) and replicated six times. Susceptible OS6 rice cultivar was planted in 5 kg pots filled with sterile top soil and inoculated with spores of F. oxysporum. Water extracts of the botanicals were then applied into the soil after 24 hours. It was arranged in Completely Randomized Design and replicated four times. Data were collected as above. Extracts of botanicals were applied at 25, 50 and 75 % concentrations respectively in vitro on Potato Dextrose Agar (PDA) and observed for percentage fungal growth inhibition. Fusariumoxysporum significantly (P<0.05) reduced plant height, number of leaves and number of tillers in the inoculated plants compared to the uninoculated plants.Nerica 1, 7, 8, WAB 56/104 and OS6 were found to be susceptible while Nerica 2, 4, 10, 11, 14, and 15 showed levels of resistance. At 75 % botanical concentration, leaf chlorosis ranged between 1-10 %, while at 25 % concentration it ranged between 11-35 %. Leaf extracts were significantly more effective in reducing the radial growth of the pathogen at higher concentrations. Bitter leaf extracts (75 %), Neem extracts (75 %) and Moringa extracts (75 %) inhibited radial growth of F. oxysporum by 99.3, 93.5 and 81.1 % respectively. Fusariumoxysporumwas confirmed to be pathogenic on NERICA rice; therefore, adequate control measures such as use of antagonistic botanical extracts can be recommended.