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Susceptibility scale to Phytophthora infestans in potato genotypes
Manuel Gastelo
Global Trial Data Management System Workshop Nairobi, 26 - 28 June - 2013
Evaluation of diseases It is one of the most important tasks and usually more
difficult to perform A adequate evaluation method should give exact,
accurate and reproducible results
Terminologies in evaluation of diseaseIntensity: The amount of disease present in a plant or plant population
Incidence: The number of diseased plants in reference to the totality of plants evaluated
Severity: Area or volume the affected plant tissue in relation to the area or volume of the plant
Methods for evaluating disease
Horsfall-Barrant Scale: assigned to the plant, a numeric value according to the percentage of leaf area infected by the disease
Direct Estimation: Estimated percentage of severity directly
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PPercent
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LB Readings
AUDPC
How to measure resistance to LBAUDPC : has been used for a long time as a single measure to quantify the amount of disease (LB), but can not compare the AUDPCs of a clon in different years and locationes, so we seek standardized measure and was called audpc relative (AUDPCr)
AUDPCr : is calculated dividing the AUDPC of clone by AUDPC maximum potential.
The scale of susceptibility :
In 2009 Dr. Forbes et al established a scale of susceptibility to LB using the numbers 1 to 9.
This scale allows us to compare resistance of a clon in different yeras and locations.
This scale from 1 to 9 (resistant to suceptible) , gives numbers that are easier to remember and interpreted
How calculate Scale of susceptibility
=F2/$F$10*6
Thanks you