BIOCONTROL OF BACTERIAL SPECK (Pseudomonas syringae pv. tomato DC3000) OF TOMATO SEEDLINGS BY Pseudomonas spp. STRAINS SVBP6 AND RBAN4

MANSILLA, A.Y.; AGARAS, B.; WALL, L.G.; CASALONGUÉ, C.A.; VALVERDE, C.

Rosario, Santa Fe

Congreso; IX Congreso de Microbiologia General; 2013

Sociedad Argentina de Microbiologia general

Pseudomonas syringae pv. tomato DC3000 (Pto DC3000) is the cause of bacterial speck in tomato(Solanum lycopersicum). This bacterium represents an important model in molecular plant pathology.Tomato is one of the most important vegetable crops worldwide. The effective controls of bacterialspeck are currently explored in crop plants. In response to the high environmental pollution caused bytoxic agrochemicals, new ecological alternatives such as biological control are being developed andimplemented for the control of plant diseases.Pseudomonas spp. strains are widely recognized for their ability to antagonize the growth ofpathogens and to induce systemic disease resistance in plants. The Pseudomonas putida-relatedstrain SVBP6 was isolated from an agricultural bulk soil and the Pseudomonas koreensis-relatedRBAN4 strain is a rhizospheric isolate from native pasture of a non agricultural soil. In this work, theability of SVBP6 and RBAN4 strains to reduce the incidence of bacterial speck in tomato seedlingswas tested. Four-day-old seedlings of the susceptible genotype cv. Platense, were placed onMurashige and Skoog?s medium (MS) containing 0.5 % agar and the corresponding bacterialsuspension. The bioassays were set up independently with the strains SVBP6 or RBAN4 (OD600 = 0.1on the plate). After 4 days of treatment, seedlings were placed on MS-agar plates (0.8% agar) andinfected with 1×108 cells ml-1 Pto DC3000 by flooding method. Symptoms of bacterial damage intomato seedlings were evaluated at 7 days post-infection. Pretreatment of tomato seedlings with eitherPseudomonas strain before inoculation with Pto DC3000 significantly decreased the infected area ofcotyledons compared with controls (no treatment or Escherichia coli treatment). To evaluate the PtoDC3000 load, disks were cut from SVBP6- or RBAN4-pretreated cotyledons, homogenized in steriledistilled water, and serial dilutions were plated onto KB agar medium to measure the number ofColony Forming Units (CFU). In SVBP6- or RBAN4-pretreated seedlings the number of CFU were2.14 ± 1.65 x 107 and 3.15 ± 1.89 x 106 CFU ml-1, respectively compared with non-pretreatedseedlings (8.93 ± 0.995 x 109 CFU ml-1). Accumulation of the antioxidant enzyme, ascorbateperoxidase (APX) protein, and of chitinase as a pathogenesis-related protein, was detected in SVBP6-and RBAN4-pretreated seedlings compared with controls, suggesting that both Pseudomonas strainscould trigger inducible defense mechanisms in planta. Currently, our goal is to elucidate themechanism underlying the biological control of Pto DC3000 by SVBP6 or RBAN4 strains in tomato.Supported by UNMdP, UNQ, ANPCyT and CONICET.IX