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Abstract
Crape myrtles (Lagerstroemia sp.) are an economically important crop planted in the southeastern United States for their showy flowers, bark, a foliage. This research was conducted to understand further the disease cercospora leaf spot and improve crape myrtles through mutagenesis. This research developed a method for inducing tetraploidy in crape myrtles using the chemical oryzalin. Tetraploid crape myrtles showed modified leaf and stomata morphology. Fungicides were tested in vitro for control of the causal agent of cercospora leaf spot, Pseudocercospora lythracearum. The fungicides thiophanate methyl (3336 WP), propiconazole (Banner Maxx II®), azoxystrobin (Heritage®), mancozeb (Dithane® 75DF), chlorothalonil (Daconil Ultrex®) were effective while the fungicide fludioxonil (Medallion 50WP) was not. Resistance to cercospora leaf spot exists among crape myrtle cultivars descended from a cross between L. indica and L. subcostata var fauriei. Cultivars most resistant to cercospora leaf spot are ‘Apalachee’, ‘Muskogee’, ‘Natchez’, and ‘Miami’. Cultivars least resistant to cercospora leaf spot are ‘Ozark Spring’, ‘Victor’, ‘Dynamite’, and ‘Pink Velour’.