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Contribution à la protection des plants de pomme de terre contre les maladies dues aux bactéries pectinolytiques par l'évaluation de la susceptibilité des lots et par la lutte directe

Picture 1 : Symptom of black leg observed in the fields - Picture 2 : Rot on tubers caused by Erwinia

Contribution to the protection of seed potatoes against pectinolytics Erwinia soft rot diseases by susceptibility evaluation and by direct seed treatment

Context

This project began according to a demand of the potato seeds growers. The producers had more losses due to these soft rot bacteria during the last ten years. These losses can occur in the field (black leg or wilt to more than 10 % of the plants – picture 1) but also during the conservation or during the transport of the seed potatoes to their client location (rot of the potatoes that can cause the full loss of the lot – picture 2). Important financial losses are consecutive to the decrease of the production yield and production quality.

Objectives

In this project, we propose to complete the arsenal of the potatoes protection methods against the soft rot generally caused by the Erwinias. The first objective is to find susceptibility indicators of the seed lots (batches) to soft rot based on the measurement of the latent contamination level and identification of the responsible pathogenic. The most contaminated lots should be moved away. The indicators validity will be confirm by comparison with the damages in crops, during the conservation or in the descendants.

To propose a cheap and reliable system, several methods of assessment contamination levels will be tested concerning their sensitivity, specificity, repeatability, reproductibility and cost.

The second objective is to evaluate new systems to protect potato seeds. The identification of the candidate ingredients will be done by permanent review of the technical and scientific information sources. Most interesting ingredients will be bought and their efficiency will be tested on inoculated tubers following a standardised method. To evaluate this efficiency, we will use the available quantification method. Concerning the biological antagonists, we will verify their ability to colonize the descendants tubers and plants.

The third objective is to identify the risk factors in relation with the different production systems that could influence the soft rot developments. A sampling of 25 plots is organised during several successive years. The conservation and crop conditions and the contamination level is registered at each stage of the production process.

The analysis of the investigation results will contribute to a progressive reduction of the latent contamination level of the potato seeds. So, it will be possible to drastically reduce the risk of soft rot development in the fields and during the conservation of the potato seed tubers.

Expected results

The serological quantification method and the quantitative inoculation method will have to be validated.

The others objectives will be achieved during a project prolongation.

Results obtained

A new serological method is tested (Enrichment ELISA or E-ELISA). in order to quantify the bacterial inoculum infecting the contaminated tubers. It will be compared to two others method. The first is based on counting bacterial colonies on selective media and the other consists of counting macerated tubers after incubation of tubers samples.

The study of the 25 plots permitted us to identify several risk factors in relation with production conditions. The most important identified factors are linked on the bacterial quality of the seeds tubers, the climatic conditions, the edaphic characteristics of the cropped fields. The indicators regarding the harvest conditions, the preparation of the potatoes plots and the conservation will be precisely identified later.

From the incubation assays realised on the potatoes samples collected before harvest, we noticed that the 2003’s scorching summer had a positive effect by reducing the rate of macerated tubers. However, the same incubation assay realised on tubers collected at the end of conservation period showed that this positive effect was partial and couldn’t eradicate the bacterial contamination. The first collected data on the 2004’s production confirm the previous data and showed that the scorching effect was of short term.

A new quantitative inoculation system of healthy tubers by vacuum infiltration is about to be validated. This is the first step of any efficient evaluation of the different available protection systems.

Partners

Walloon Council of Seed Potatoes Producers

CRAW off coordinator

DUPUIS Brice (Attaché scientifique)

Systèmes agricoles

Rue de Serpont, 100

B-6800 Libramont

Tél : +32 61 23 10 10

Fax :+ 32 61 23 10 28

E-mail :dupuis@cra.wallonie.be

Funding

  • DGARNE
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