Dwarf mistletoe resistant ponderosa pines in Oregon
1991
Scharpf, R.F. (Pacific Southwest Forest and Range Experiment Station, Berkeley, California (USA). Forest Disease Project) | Roth, L.F. (Oregon State University, Corvallis, Oregon (USA). Department Botany and Plant Pathology)
Several ponderosa pines (Pinus ponderosa) on the Deshutes, Ochoco, and Rogue River National Forests in Oregon were selected for resistance to dwarf mistletoe (Arceuthobium campylopodum). About 12 to 15 grafts were made on young, potted pines from each of 30 resistant and 8 susceptible parent selections. Sixty five seedlings from susceptible parents were used as controls. All the trees were planted on plots at random under an infected overstory of pines on the Pringle Buttle Experimental Forest in central Oregon. Data were analyzed to determine: 1) differences in levels of infection and percentage of trees infected between resistant and susceptible selections, 2) the relationship between tree survival and level of infection and, 3) the influence of tree heighy and total length of branches on proportion of trees infected and intensity of infection. After 20 years, 76 (%) of the resistant trees were still alive, whereas only 48 (%) of the susceptible were alive. Grafts from most resistant selections were either uninfected or were less than 50 (%) infected. For the susceptible selections, 70 (%) or more of the grafts and seedlings were infected. Resistant grafts also bore fewer infections on the average than the susceptible grafts and seedlings. Tree height and total length of branches were not correlated with percentage of trees infected or number of infections. We belive strong resistance to dwarf mistletoe occurs among certain ponderosa pines in central Oregon
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