Influence of Culture Media on the Antimicrobial Activity of Fluorescents Pseudomonas Crude Supernatants Extracts against Phytophthora colocasiae, the Causal Agent of the Taro Leaf Blight

Crude supernatant extracts of two fluorescent Pseudomonas DS15V and DS17R obtained by monoculture under King B (KB), Luria Bertanie (LB), Nutrient Broth Yeast, (NBY), Succinate medium (SM), Tryptic Soy Broth (TSB) and Potato Dextrose Broth (PDB) culture media were evaluated for their antimicrobial potential against Phytophthora colocasiae (PC). Co-culture supernatant extracts with PC (PCo) were also tested. Moreover, the thermostability of extracts, inhibition of zoospore potential and in situ activity were estimated by the disc leaf test. The results showed that crude supernatant extracts from KB, LB and MS significantly inhibited mycelia growth (80-100%) at concentrations of 1:1 (v/v) and/or 1:2 (v/v) which correspond to Inhibitory Activity Unit (IAU). Furthermore, these supernatant extracts were highly thermosensitive and decreased significantly their antagonistic potential against P. colocasiae mycelia at high temperatures (100 and 121°C). On the other side, supernatant extracts obtained from monoculture and co-culture in potato liquid medium (PDB) demonstrated significant activity by IAU values at concentration of 1:3 (v/v) against mycelia growth for both DS15V and DS17R. For the zoospores growth, supernatants from PDB (PCo and PMo) presented high inhibition at low concentrations (1:3 v/v) especially 17Pco which shows 100% inhibition at concentration of 1:4 (v/v). In addition, these extracts were thermoresistant and maintained their antimicrobial potential against P. colocasiae without a significant difference. The four supernatants crude extract belong to co-culture on PDB medium (15PCo, 17PMo and 17PCo) used as best extracts on disc leaf test promoted 100% leaf disc prevention against P. colocasiae at concentration of 1:1 (v/v) and exhibited it curative effect at the same concentration after 4 days of treatment thereby stabilizing the development of necrosis on leaf disc.