Browsing by Author "Usall, Josep"
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- Biocontrol of postharvest decay using a new strain of Pseudomonas syringae CPA-5 in different cultivars of pome fruitsPublication . Nunes, Carla; Usall, Josep; Teixido, Neus; Abadias, Isabel; Asensio, Angels; Vinas, InmaculaEpiphytic micro-organisms isolated from fruits and leaves surfaces of apples from different orchards were screened for antagonistic activity against Penicillium expansum. From all micro-organisms tested the new strain CPA-5 of Pseudomonas syringae, isolated from organic orchard, was selected. This strain was very effective against Botrytis cinerea, P expansum and Rhizopus stolonifer at various antagonist and pathogen concentrations on 'Golden Delicious' apple, and 'Blanquilla', 'Rocha' and 'Conference' pear. Under cold storage conditions and in semi-commercial trials R syringae (CPA-5) significantly reduced development of P expansum and B. cinerea on 'Golden Delicious' apple, and 'Blanquilla' and 'Rocha' pears. Control of P expansum equal to the fungicide imazalil was obtained with CPA-5 at 10(8)cfu ml(-1) on 'Gold Delicious' apple and 'Rocha' pear. The populations of P syringae CPA-5 increased more than 100-fold during the first 50 days, and then remained stable on apple, and slightly decreased on pears. This indicates the high capacity of this antagonist to colonize wound surfaces of pome fruits under cold storage conditions.
- Development and application of a SCAR marker to monitor and quantify populations of the postharvest biocontrol agent Pantoea agglomerans CPA-2Publication . Nunes, Carla; Bajji, Mohammed; Stepien, Valerie; Manso, Teresa; Torres, Rosario; Usall, Josep; Jijakli, M. HaissamPantoea agglomerans CPA-2 is an effective biocontrol agent of postharvest diseases of citrus and pome fruit. A monitoring technique was developed for its identification and to quantify its populations. The methodology used consisted of (i) searching for a semi-selective medium, (ii) identification of molecular markers and (iii) monitoring population dynamics in a commercial trial. As a semi-selective medium, Malonate Broth Agar supplemented with tetracycline hydroxychloricle and incubation at high temperature (max. of 40 degrees C) facilitated the selective recovery of P agglomerans CPA-2 colonies. The RAPD technique was applied to a collection of 13 strains of P. agglomerans, including CPA-2. Among the 12 primers tested, OPL-11 amplified a fragment (about 720 bp) specific to strain CPA-2. On the basis of this fragment, two SCAR markers were amplified using a primer pair derived from OPL-11 elongation. A first SCAR marker of 720 bp was specifically amplified for the strain CPA-2 and a second one of 270bp was obtained for all P. agglomerans strains tested, including CPA-2. Commercial trials demonstrated a significant reduction of decay with the treatment of formulated cells of R agglomerans CPA-2. Population dynamics of CPA-2 in commercial trials were determined on fruit surfaces and in the environment using both the classical plating technique and PCR with SCAR primers. In general, no significant differences were observed between results obtained from the two methods. On fruit surfaces, 1 day after CPA-2 applied its population by classical methods was 4.37 x 10(6) cfu wound(-1) and at the end of the experiment the population increased to 5.8 x 10(5) cfu wound(-1). The percentages of colonies identified as P agglomerans CPA-2 at these sampling times using SCAR primers were 90 and 95%, respectively. Population dynamics in the environment to evaluate the environmental fate of R agglomerans CPA-2 showed that it has a limited persistence and limited capacity for dispersion. (c) 2007 Published by Elsevier B.V.
- Is it possible to improve biocontrol agents to practical applications? the pantoea agglomerans CPA-2 examplePublication . Teixidó, Neus; Cañamás, Teresa Paula; Torres, Rosario; Usall, Josep; Viñas, Inma; Nunes, CarlaA major hurdle in exploitation of biocontrol agents is the limited tolerance of fluctuating environmental conditions practically and the difficulties in developing a shelf-stable formulated product as effective as fresh cells. Most of microorganisms are very sensitive to drying processes involved in formulation and biological control is usually limited by the narrow range of conditions below microorganisms are able to survive, establish and effectively control pests and diseases. P. agglomerans cells grown at low water activities using NaCl exhibited osmotic adaptation and also demonstrated thermotolerance and desiccation tolerance after spray drying, freeze drying and fluidized bed drying. Different formulation strategies of P. agglomerans cells were tested in order to improve survival under field conditions and efficacy in controlling postharvest rots, including lyophilised cells, osmotic adaptation by NaCl treatments and additives. In general, osmotic adapted and lyophilised P. agglomerans cells showed greater survival rates than non-osmotic adapted or fresh cells when these bacterial treatments were sprayed at field conditions. However, this superiority was only found when additive Fungicover was added to suspension treatments. The improved formulation of P. agglomerans provided an effective control for oranges against natural postharvest pathogens infections and P. digitatum artificial infections. These results allowed us to conclude that it is possible to improve environmental stress tolerance and ecological competence of P. agglomerans by integrating certain formulation strategies. Enhancing stress tolerance and formulation strategies could be appropriate approaches to obtain consistency and broaden the spectrum of use of biocontrol agents.