Methods for Sampling and Assessment in Relation to the Spatial Pattern of Phoma Stem Canker (Leptosphaeria maculans) in Oilseed Rape

Abstract : 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: (i) compare four methods of crown canker assessment; (ii) test the among and within assessor repeatability of one of the methods compared; (iii) characterise the spatial pattern of the disease; and (iv) 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.
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Submitted on : Saturday, September 10, 2016 - 3:31:23 PM
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Jean-Noël Aubertot, Jean-Jacques Schott, Annette Penaud, Hortense Brun, Thierry Doré. Methods for Sampling and Assessment in Relation to the Spatial Pattern of Phoma Stem Canker (Leptosphaeria maculans) in Oilseed Rape. European Journal of Plant Pathology, Springer Verlag, 2004, 110 (2), pp.183-192. ⟨10.1023/B:EJPP.0000015359.61910.3b⟩. ⟨hal-01363609⟩

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