Screening for potential Rhizospheric Soil bacteria of oil palm against Ganoderma Boninense

Field: Agricultural and Biological Sciences (Life Sciences)

Ten culturable rhizospheric soil bacteria were isolated from the rhizosphere soil of oil palm sampled from oil palm plantation located at the School of Sustainable Agriculture, Sandakan campus of University Malaysia Sabah. The bacterial isolates were characterized based on morphological characteristics, including colony colour, colony surface, colony margin, colony elevation and appearance displayed on Potato Dextrose Agar (PDA) plate and Nutrient Agar (NA) plate. The bacterial isolates were Gram's negative and rod shape. Among the ten isolated rhizospheric soil bacteria, only six bacterial isolates (C, D, G, H, I and J) showed inhibition towards the growth of Ganoderma boninense in the screening test. The bacterial isolates (C, H and I) showed potential inhibitory effect against G. boninense in dual culture test with their percentage inhibition of mycelial growth recorded were more than 50%. There was significant higher in inhibitory effect (P<0.05) among the six bacterial isolates in dual culture test. The inhibition zone of G. boninense recorded growth by bacterial isolate C
was 5.23 cm, while the bacterial isolate H was 4.23 cm and bacterial isolate I was 4.07 cm. The inhibition zone of G. bomi7ense growth by bacterial isolates (C and H) was higher than bacterial isolate I. The rhizospheric soil bacteria isolated C and H were further investigated in culture filtrate test, mixture of PDA and bacterial culture test (in vitro) and nursery trial. The PI values of bacterial isolate C was 100%, while bacterial
isolate H was 17.47% in culture filtrate test. The bacteria C showed 100% inhibition of G. boninense, while bacteria H showed 96.78% inhibition mycelial growth in mixture of PDA and bacterial culture test. There was significant different in inhibition of G. boninense (P<0.05) in both culture filtrate test and mixture of PDA and bacterial culture test. The bacterial isolate H showed 17.47% inhibition of mycelial growth in
culture filtrate with absent of bacterial culture, while showed 96.78% inhibition of mycelial growth in mixture of PDA and bacterial culture test with present of bacterial
culture. The result showed that antimicrobial metabolites produced during antagonism between bacteria and pathogen. The bacterial isolate C and H caused malformation of
hyphae of G. boninense. The bacterial isolate C and H were further investigated in nursery trial with three months duration. The disease severity of G. boninense infected seedlings treated bacterial isolate C and H was no significant different with non-treated infected seedlings (P>0.05). The bacterial isolate C and H showed no effect on growth height of seedlings and plant biomass. There was no significant different between
infected seedling treated with bacterial isolate and non-treated infected seedlings (P>0.05). The abiotic factor, including soil condition, temperature and humidity
affected the inhibitory effect of rhizospheric soil bacteria C and H. Thus, the further field study of effects of abiotic factor on rhizospheric soil bacteria is required. The long study duration of nursery trial also recommended.