Standardized Plant Disease Evaluations Will Enhance Resistance Gene Discovery

Gene discovery and marker development using DNA based tools require plant populations with well-documented phenotypes. Related crops such as apples and pears may share a number of genes, for example resistance to common diseases, and data mining in one crop may reveal genes for the other. However, unless consistent phenotype evaluation methods or data scoring techniques are employed, data mining for marker-trait associations is difficult. Fire blight resistance evaluations for apples may use a scale of 1-5 and pear evaluations may use 1-9. Some reports use a low numerical rating to indicate low susceptibility and others to indicate low resistance. Still others may report disease resistance as greater than or less than that of a standard cultivar. Environment, pathogen isolate and whether disease ratings are the result of natural infection or artificial inoculation also have strong impacts on disease resistance ratings. Before disease resistance phenotype data can be correlated with genetic data, the rating scale and evaluation environment must be standardized to the extent possible. Examples of pome fruit disease evaluations will be presented and a standardized disease rating system will be proposed.