Biocontrol of the phytophagous nematode Nacobbus aberrans by Pseudomonas fluorescens strain CHA0

LAX, P., BECERRA, A., MARRO, N., AGARAS B, VALVERDE C. AND DOUCET, M.

Workshop; PGPR 9th International and 1st Latinamerican PGPR Workshop; 2012

Nacobbus aberrans is a sedentary endoparasite that induces galls in root systems. It has a high reproductive potential and it causes severe economical damage to different horticultural crops. In Argentina, this nematode affects greenhouse- and field-grown tomato. Several Pseudomonas strains produce extracellular secondary metabolites that are toxic for phytopathogenic fungi, certain protists and phytophagous nematodes, and are able to induce systemic resistance in plants. Strain ARQ1 is an isogenic gfp/KmR-tagged derivative from the biocontrol isolate P. fluorescens CHA0. We studied the effect of ARQ1 (BACT) on a N. aberrans population (NEM) from Lisandro Olmos (Buenos Aires, Argentina) in tomato seedlings (cv. Platense) grown in sterilized soil under greenhouse conditions. Four treatments (5 replicates) were set up: a) Control; b) BACT, c) NEM, d) NEM+BACT. The inocula consisted in 100 second-stage juveniles and/or 10 ml of a suspension of ARQ1 cells at OD600 = 0.1. At 60 days after inoculation (DAI), the number of galls (G) and egg masses (EM) produced by the nematode were determined. We observed a significant reduction (P<0.05) in both parameters in NEM+BACT plants (G=20; EM=11) compared to NEM plants (G=34; EM=19). At 15 DAI, the roots of NEM+BACT plants were colonized by ARQ1 cells at 1.0 ± 0.02 ´106 UFC/g whereas at 60 DAI, roots contained 3.0 ± 0.7 ´104 UFC/g. These results show that P. fluorescens strain CHA0 colonized tomato roots and had an antagonistic effect on the N. aberrans population.