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Effect of Meloidogyne incognita Inoculum Density and Application Rate of Paecilomyces lilacinus Strain 251 on Biocontrol Efficacy and Colonization of Egg Masses Analyzed by Real-Time Quantitative PCR

First and fourth authors: Research Station Agroscope Changins-Waedenswil ACW, Plant Protection and Extension Fruit and Vegetables. Schloss P.O. Box, 8820 Waedenswil, Switzerland; and second and third authors: Institute for Crop Science and Resource Conservation, INRES, University of Bonn, Nussallee 9, D-53115 Bonn, Germany.

The fungal biocontrol agent, Paecilomyces lilacinus strain 251 (PL251), was evaluated for its potential to control the root-knot nematode Meloidogyne incognita on tomato at varying application rates and inoculum densities. Conversely to previous studies, significant dose-response relationships could not be established. However, we demonstrated that a preplanting soil treatment with the lowest dose of commercially formulated PL251 (2 × 10⁵ CFU/g soil) was already sufficient to reduce root galling by 45% and number of egg masses by 69% when averaged over inoculum densities of 100 to 1,600 eggs and infective juveniles per 100 cm³ of soil. To determine the role of colonization of M. incognita egg masses by PL251 for biocontrol efficacy, a real-time quantitative polymerase chain reaction (PCR) assay with a detection limit of 10 CFU/egg mass was used. Real-time PCR revealed a significant relationship between egg mass colonization by PL251 and the dose of product applied to soil but no correlation was found between fungal density and biocontrol efficacy or nematode inoculum level. These results demonstrate that rhizosphere competence is not the key mode of action for PL251 in controlling M. incognita on tomato.

Additional keywords: egg-pathogenic fungus, plant-parasitic nematodes.