Genetic Variation Among Open-Pollinated Progeny of Eastern Cottonwood

Open-pollinated seed was collected in 1963 from 81 trees in natural stands along the Mississippi River between Clarkscfale and Vicksburg, Mississippi. Twenty-nine of the trees were chosen for outstanding growth and form; the remaining 52 were randomly selected. Seeds were cleaned, then stored at 38° F and 25 percent relative humidity until sown on August 5. They were sown in subirrigated plant bands filled with a mixture of equal parts of sand, peat, and loam. In late August, seedlings were thinned to six per band, and two bands per family were transplanted to each plot in a nursery experiment that followed a 9 X 9 balanced lattice design with 10 replications; this design was carried into the outplanting. Plants were lifted from the nursery in late February 1964, pruned to an 8-inch top, and bar-planted in the field with 2 inches of stem above the soil surface. A field plot consisted of a row of six trees randomly chosen from each nursery plot. Spacing was 4 X 4 feet. A two-row border was planted around the test site. The soil was Commerce loam underlain in some places by lenses of heavier soil. The trees were cultivated during the first growing season, and in the second growing season were irrigated twice in late summer. Survival averaged 97 percent. Total height was recorded after the 1964 and 1965 growing seasons; diameter at 1 foot abov~ soil surface was recorded in 1965. Incidence of leaf rust (Melampsora medusae THUM.) was recorded for each plant in late October 1964. A rating of 0 indicated no rust while a 5 indicated heavy infection (100 percent of leaf surface covered with sori). Distribut ion of ratings was normal. Foliation date the day on which the first leaves were ~",; inch out of buds was recorded on four replications in 1965 and 1966.