SELECTING AND BREEDING PINES RESISTANT TO FUSIFORM RUST = SELECTING AND BREEDING PINES RESISTANT TO FUSIFORM RUST

다국어 초록 (Multilingual Abstract)

The most serious disease of slash and loblolly pines in the southern United States is fusiform rust, caused by Cronartium quercuum f. sp. fusiforme. Before World War II this disease was relatively innocuous, but since then, more intensive management practices have produced an intensification of the disease, resulting in an epidemic in some parts of the South. Rust is estimated to be increasing at 2 to 3 percent per year, and incidence of infection from 85 to 95 percent is common in many areas. Because of the impact of the disease on timber production, many research programs on disease resistance were begun during the 1960`s. The first breakthrough was finding four geographic areas around the periphery of the natural range of loblolly pine where bulk collections of seed provided considerable resistance to fusiform rust. Seed from one of these sources, from Livingston Parish, Louisiana, combines good growth and form with rust resistance and has been widely used in reforestation programs. In addition, many states and forest industries began to emphasize rust resistance in their tree improvement programs. Special rust-resistant orchards were developed by organizations that held lands in areas with high disease incidence. These were clonal orchards; however, the Georgia Forestry Commission - USDA Forest Service (GFC-USFS) orchard used a new approach - a seedling seed orchard made up of survivors of seedling-inoculation tests. At present, several rust-resistant orchards in the South are producing seed for reforestation programs. Most of these seed have sufficient rust resistance to reduce incidence of fusiform rust by 40 percent. The GFC-USFS seedling seed orchard, however, has produced seed with the highest rust resistance yet tested, and seedlings from this orchard should reduce field infection by one-half. The primary reason for the rapid advances in these programs on rust resistance was the development of a rapid artificial inoculation technique carried out under carefully controlled conditions. These inoculations, which correlate well with field results, provide results within 6 to 9 months instead of 5 years or longer in the field. During the past decade, additional developments have taken place in rust-control programs, including new planting strategies, the use of hybrids for increased rust resistance, research into the mechanisms of resistance, and micropropagation.