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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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