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Influence of Temperature, Leaf Wetness Period, Leaf Age, and Spore Concentration on Infection of Pecan Leaves by Conidia of Cladosporium caryigenum. T. R. Gottwald, Research plant pathologist, USDA-ARS, Southeastern Fruit and Tree Nut Research Laboratory, P. O. Box 87, Byron, GA 31008; Phytopathology 75:190-194. Accepted for publication 8 September 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/Phyto-75-190.

To develop a method for rapidly screening a large number of pecan seedlings in a breeding program for resistance to pecan scab, a study was conducted to determine the greenhouse environmental optima for infection by the pathogen, Cladosporium caryigenum. Optimum temperature for infection of pecan foliage ranged from 15 to 25 C. Maximum lesion development occurred with 48 hr of continuous free foliar moisture. Foliar susceptibility decreased with increasing leaf age. Maximum foliar susceptibility occurred 7- 21 days after bud break. Foliage became relatively resistant to infection upon reaching full expansion. Lesion number and disease rating increased directly with inoculum concentration; the highest concentration, 2.5 x 106 conidia per milliliter, produced the most lesions. However, lower concentrations were adequate and more practical to produce for large-scale greenhouse scab screening.

Additional keywords: breeding for resistance.