INFLUENCE OF CARBON/NITROGEN RATIO ON PYTHIUM APHANIDERMATUM AND ON PYTHIUMINDUCED DAMPINGOFF OF RADISH
A. Al-Azizi, A.M. Al-Sadi, H. Dietz, F.A. Al-Said, M.L. Deadman
A study was conducted to investigate the effect of fertilizers with different carbon/nitrogen ratios (no carbon, NC; low carbon/nitrogen ratio, LC; high carbon/nitrogen ratio, HC) on Pythium aphanidermatum and on radish damping-off. The ratio of carbon to nitrogen applied in the field was 29, 22 and 0 in 2007 and 22, 17 and 0 in 2008 for HC, LC (as cattle manure) and NC, respectively. Field experiments over two growing seasons provided evidence for the lowest mortalities due to Pythium-induced radish damping-off to be in soil amended with LC (P < 0.05). Isolations from diseased plants yielded P. aphanidermatum. When radish seedlings were planted in autoclaved soil artificially infested with P. aphanidermatum, the highest mortalities were observed in soil amended with HC and NC, while the significantly lowest mortalities were in soil amended with LC. Change in the inoculum density of P. aphanidermatum over time was not significant between soils treated with NC, LC and HC (P> 0.05), which may imply a lack of evidence for the effect of carbon/nitrogen ratio on reproduction in P. aphanidermatum.