Susceptibility scale to Phytophthora infestans in potato genotypes Manuel Gastelo Global Trial Data Management System Workshop Nairobi, June Global Trial Data Management System Workshop Nairobi, June

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 disease Intensity: 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 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

How to measure resistance to LB AUDPC : 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