Methods for Sampling and Assessment of Phoma Stem Canker

Methods for Sampling and Assessment in Relation to the Spatial Pattern of Phoma Stem Canker in Oilseed Rape.

A sound assessment of phoma stem canker symptoms is needed to develop epidemiological, agronomical and physiological studies on the pathosystem.

A specific analysis was therefore carried out to:

  • compare four methods of crown canker assessment;
  • test the among and within assessor repeatability of one of the methods compared;
  • characterise the spatial pattern of the disease;
  • define the sample size required to achieve a given level of disease assessment precision.

The methods compared examined the symptoms with different procedures and graded the plants observed into six severity classes. A disease index (DI) summarised the severity distribution observed. Examination of crown cross-sections was the most precise method for assessing crown cankers. The method was repeatable, though an 'assessor effect' was apparent. The disease generally had a random pattern although significant spatial correlations were detected for four out of the fifteen plots studied at the scales examined. A relationship between the coefficient of variation of the DI and the sample size was established, evaluated with experimental field data and exemplified for typical severity distributions.

Authors: Aubertot JN., Schott JJ., Penaud A., Brun H., Doré T.

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Modification date : 25 April 2023 | Publication date : 16 September 2013 | Redactor : IPM network, contributor: Jean-Noël AUBERTOT (INRA).