Efficacy of Pseudomonas fluorescens Root colonization on disease suppression of Pythium Root Rot of Cucumber [electronic resource].

Includes reference.

Three Pseudomonas fluorescens isolates termed 3, 5, and 6, biocontrol agents, were used to examine their efficacy on root colonization and reduction of Pythium root rot of cucumber seedlings. P. fluorescens was used as a seed coat at the rate of 5 X 10⁸ cfu ml⁻¹. Bacterial populations at 1 or 2 cm below the seed or 1 cm from the root tip were estimated after 14,21 and 28 days of planting. Bacterial populations at 1 cm below the seed were remained at the same level on the first 14 days of planting for the three bacterial isolates, i.e. 2x 10⁸, 7x10⁷ , and 5x10⁸, respectively. The bacterial populations were decreased significantly overtime and reached to 5x10² , 3x10², and 2x10³ , respectively after 28 days of planting. Pre- and post-emergence damping- off symptoms on cucumber was decreased significantly after coating the seeds with P.fluorescens. Examination of the effect of nitrogen source (NH₄⁺ or NO₃') in vitro revealed that NH₄+ amplified P. fluorescens growth than NO₃'. When different pH values i.e. 5, 6 and 7, were examined in combination with the nitrogen source, the results revealed that pH 6.0 and 7.0 enhanced the growth of bacterial population when NH₄+ was used as the nitrogen source, whereas pH 5.0 enhanced the growth when NO'₃ was used as the nitrogen source. The present results suggest that P. fluorescens populations were differed significantly on different root levels and towards external factors, nitrogen source, which may be added as plant fertilizer, and pH. Thus, it may be concluded that factors such as pH and the nitrogen form affect P. fluorescens population and subsequently suppression of Pythium ultimum, the causal agent of cucumber root rot.

Summary in Arabic.

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