Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Protocol for field sampling

In disease surveys of field crops, a common practice is to collect samples at a constant interval along a path of predetermined shape. The sampling design along the X-shaped path of the field, used in this research to choose plants for estimating the mean OTA content of the vineyard, is considered by plant pathologists to be one of the best approaches.

High variability was observed in OTA content both among bunches and among plants in the two vineyards with different contamination levels. Very high amounts of OTA were detected in 1 or 2 strongly contaminated bunches in both vineyards. This variability is totally random; in fact, no relation was found between OTA content and the position of a bunch on the branch or the location of the plant in the vineyard.

Sampling design markedly influenced the assessment of must contamination. The best results were obtained when sampling involved 1 bunch per plant, in a pre-defined position, from at least 10 plants. The difference from reference OTA contamination decreased when the number of sampled plants increased. A reduction of variability was also obtained, as expected, increasing the number of sampled bunches.

Despite the large variability among OTA levels detected in bunches, estimated means obtained following different sampling design did not differ significantly from reference OTA content in both vineyards. If the true contamination in a vineyard is 2 µg Kg-1, the limit fixed in Europe for OTA content in must and wine, the range of OTA content assessed using the described sampling designs, should lie between 5 and 0.8 µg Kg-1 in the worst situation, when bunches were collected from 1-2 plants (SSC, n=10), and 2.9 and 1.4 in the best situation, e.g. when the basal bunch of the central shoot was collected (SSB_a, n=10), the position commonly suggested for the evaluation of quality characters at ripening.

The accuracy could be considered acceptable, even if there is a trend towards overestimation; in this case corrective actions must be taken and good indications can be obtained for the management of the must.

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