Isolation and screening of endophytic fusarium oxysporum for biological control of nematodes in tissue culture bananas

Abstract

Two major banana growing regions namely Meru district (Altitude: 1050 Masl, 06' 34S, 037o46' 23 E) and Kilifi (17 Masl 03'4S 0" 039° 40' 0" E) district) were identified as sampling sites for banana plants to be used for endophytic fungi isolation. Healthy appearing plants in heavily infested fields were sampled for endophytic fungi isolation. Endophytic fungi were isolated from the plant roots, the corm, pseudostem and the pseudostem base. A total of 2,455 Fusarium spp isolates were isolated from the two regions. Fusarium oxysporum species was the most prevalent endophytic fungi from banana roots and corm. They constituted 15.5% and 44.6% of all fungal isolates from Meru and Kilifi districts, respectively. Twelve isolates belonging to F. oxysporum were selected for in vitro bioassays against two major species of banana parasitic nematodes in the two regions namely Pratylenchus goodeyi and Helicotylenchus multicintus. The selected species of the endophytic fungi were cultured in Potato Dextrose Broth (PDB) media for seven days. Fungal filtrates from the twelve isolates were obtained after sieving and centrifuging the PDB media. One millilitre of the filtrate was used for each treatment consisting of one hundred nematodes suspended in 1 ml of distilled sterile water in sterile 5ml Bjorn bottles. Each treatment was replicated three times and the experiment laid out in complete randomised design. Mortality and paralysis were recorded after 3, 6 and 24 hours time intervals. Corrected mortalities were calculated using Abbott’s formula. The mortality significantly (p<0.0001) varied with the time of exposure. Culture xiv filtrates of F. oxysporum isolates significantly (p<0.0001) differed on their mortality effects to the nematodes. Out of the total thirteen endophytic isolates from Meru district, five isolates produced consistent mortalities and paralysis to both P. goodeyi and H. multicinctus. These isolates included 5JTOC134, 5SOPB11, 4M0C321, 4SIC132 and 5MR11. Similarly five fungal isolates from Kilifi district which demonstrated consistency in causing mortality and paralysis were 7MIC334, 8SIC334, 11MOC143, 11SR23 and 11MOC353. The isolates demonstrated potential biological activity against the major banana parasitic nematodes, and can further be investigates as biological control agents against these nematodes.