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Resistance

Variation in Rust Susceptibility in Beans: Predicting Lesion Size from Leaf Developmental Stage Measured by Leaf Age, Length, and Plastochron Index. M. Shaik, Department of Botany, Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario, Canada M5S 2C6; T. A. Dickinson(2), and J. R. Steadman(3). (2)Department of Botany, Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario, Canada M5S 2C6; (3)Department of Plant Pathology, University of Nebraska, Lincoln 68583-0722. Phytopathology 79:1035-1042. Accepted for publication 17 May 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-1035.

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.