الملخص الإنجليزي
Damping-off disease was characterized as the most destructive disease in greenhouse cucumber in the Sultanate of Oman. Economically, the disease causes a great loss in cucumber production. The current study was conducted mainly to evaluate potential biological alternatives to chemical fungicides for the control of Pythium damping-off disease by the mean of antagonistic bacteria. It was carried out in two experiments. The purpose of the first study was to illustrate factors influencing growth of Pythium aphanidermatum (P085); causal agent of damping off. Radial growth rate of P. aphanidermatum was evaluated under three varying
environmental factors: temperature (35, 30, 25, and 20°C), soil water content (19.88, 18.30, 16.67%), and salinity (0.0252, 2.44, 5.97, 12.03 ds/ m and 0.0124 ds/ m was included as a control). Sand growth assay was used to evaluate fungus growth rate A temperature of 35oC significantly increased the radial growth rate of P. aphanidermatum (0.59 mm/hr). The highest level of water content (19.88%) showed an increase in expansion rate of the fungus. The growth rate at this water level was 0.68mm/hr. No correlation was found between radial growth rate of the fungus and salinity level. The maximum growth rate was observed when applied water was 20 ml (19.88%) at 35°C.
The second study was conducted to evaluate the potential of twenty one isolates of Pseudomonas aeruginosa strains to suppress Pythium aphanidermatum inducing cucumber damping-off. Paper disk assays were used to assess bacterial antagonism in vitro. Bacterial growth and activity were evaluated under different temperatures and levels of salinity. A bioassay demonstrating suppression of damping-off of cucumber seedlings was done under greenhouse conditions. Seven isolates were superior in inhibiting radial growth of P. aphanidermatum on PDA. Bacterial isolates showed optimal growth at 30°C, whereas a temperature of 37°C favored bacterial antagonistic activity. Bacterial growth was inhibited at 12.03 ds/m for the seven isolates. All the selected isolates enhanced the growth of cucumber seedlings (height, fresh weight, root length, root weight and number of leaves). Isolates 7,38, 48, 49, 94 and 95 appeared to have potential to control damping-off disease.
