Genetic control of growth traits and inheritance of resistance to bacterial leaf scorch in American sycamore

Abstract

Open-pollinated progeny tests of American sycamore (Platanus occidentalis L.), which included 55 open-pollinated families selected from several prior Westva - co progeny tests and seed orchards and six control-pollinated families were established in 2002 and 2003. The half-sibling families were planted at two sites in western Kentucky and southeastern Missouri. The six full-sibling families, generated from selections based on exhibition of parental disease resistance and susceptibility to a variety of diseases, were also planted near Stoneville, MS at the US Forest Service Center for Bottomland Hardwoods Research. All full-sibling families planted at the Stoneville site were inoculated in the fall 2002 with the leaf-scorch-causing bacterium, Xylella fastidiosa. Diameter and height data for trees of both half- and full-sibling families were recorded at ages three, five, seven, and nine at the various sites. Bacterial leaf scorch disease presence was also recorded as symptomatic or asymptomatic/ mildly symptomatic. Average family heritability across ages was 0.58, 0.50, and 0.55 for height, diameter, and volume, respectively, indicating that increased growth traits can be gained from family selection. In conjunction with derived age-age correlations, selection based on age-five data results in the greatest gain per unit time for age nine gains for half-sibling families. Breeding for bacterial leaf scorch resistance can also be successfully undertaken if proper selection and breeding of two resistant parents are undertaken which can result in a 4.5 fold decrease in the probability in symptoms of offspring by age nine. Results indicate a large potential for increased growth and disease resistance in American sycamore through traditional breeding.