Evaluation of the inhibitory effects of potato rhizosphere fluorescent pseudomonads against Globodera rostochiensis

The cyst nematode Globodera rostochiensis is one of the most important causal agents of disease on potato in Hamadan province which reduces crop yield every year. In this study, the biological control of the nematode by the fluorescent pseudomonads isolated from potato rhizosphere was investigated. Infested soils were collected from potato fields and the cysts were isolated. The nematode second juvenile stage was obtained by cyst exposure to potato root extract (variety Marfona) collected from excess water following plant watering. From potato healthy soil, 108 Pseudomonas strains were isolated by serial dilution method on King’s B medium. In a randomized design by three replicates, the effects of bacterial strain filtrate culture on nematode larva mortality were evaluated. Results indicated significant differences among the strains antagonistic activity. The upper score was obtained for Pseudomonas strain SN20 by 69.96% nematode mortality and the lowest score for Pseudomonas strain SN22 by 54.28% mortality. A total of five pseudomonas strains were selected for further investigation under green-house conditions in a complete block design by three replicates based on the results of the laboratory experiment. Significant differences among the strains 1% level were observed and  Pseudomonas strains SN17 and SN20 showed the highest effect with 42.47% disease severity reduction. Plant length was increased 55.10% by the Pseudomonas strain SN20. Characterization of the phenotypic features of the strains revealed their belonging to Pseudomonas fluorescens and P. putida.