The use of area under the disease progress curve to assess resistance to late blight in potato germplasm

Abstract

The multiple evaluation of potato cultivais and breeding selections (clones) for disease during the season can be costly and may not be necessary for accurate assessments of disease resistance or susceptiblity. For diseases whose progression can be described by sigmoid curves, an estimate of the area under the disease progress curve from two data points may provide as much information as from repeated assessments. Twentythree clones were planted in a randomized complete block design in Hastings, FL, in 1997 and evaluated for percent diseased foliage 14 times during a 31-day period after late blight was first noticed in the plots. The area under the disease progress curve (AUDPC) was calculated for all 14 assessments. The AUDPC was also calculated for nine sub-sets of the original data set. There was a high correlation between all the methods in the calculation of the AUDPC. The AUDPC calculated based on two dates (representing the beginning of the epidemic and the time until two of the clones were dead from late blight) was as informative as the AUDPC calculated on the entire data set. The AUDPC could be calculated based on any two dates from this time frame as long as one date was shortly after the epidemic started and the other date was as the epidemic was reaching its peak. Much information was lost if AUDPC was calculated based on dates involved only in the early part of the epidemic. A considerable savings in time and effort can be realized by only a few assessments.