Variation in rust susceptibility in beans: predicting lesion size from leaf developmental stage measured by leaf age, length, and plastochron index

The importance of controlling for leaf developmental stage at the time of inoculation in studies of lesion size was investigated. Significant differences were obtained between two cultivars. Pompadour Checa and Pinto 650, by regressing lesion size on leaf developmental stage at time of inoculation. Leaf developmental stage was recorded as leaf age (days from unfolding), as leaf length, and by means of a plastochron index. Of these three variables, leaf age and plastochron index were better predictors of lesion size than leaf length. Plastochron index is a superior indicator of leaf development since it integrates chronological age and increase in size and is easier to assess. The results reported here may explain certain aspects of the field resistance of Pompadour Checa