GENETIC-VARIATION IN DISEASE RESISTANCE OF JUNIPERUS-VIRGINIANA AND JUNIPERUS-SCOPULORUM GROWN IN EASTERN NEBRASKA

Juniperus trees were examined in a plantation located in Horning State Farm, near Plattsmouth in eastern Nebraska, USA. Trees were grown fro m seeds collected from 131 open-pollinated families within 39 seed-zon es in eastern redcedar (J. virginiana L.) and 25 open-pollinated famil ies within 14 seed-zones in Rocky Mountain juniper (J. scopulorum SARG .) from their native ranges in the Great Plains of USA. The plantation was established in spring 1980 to examine genetic variation among gen otypes for resistance to Cercospora blight caused by Pseudocerospora j uniperi (ELLIS and EVERH.) SUTTON and HODGES, comb. nov. (formerly Cer cospora sequoiae var. juniperi), a major disease that threatens junipe r survival east of the Rocky Mountains. All plantation plots were inoc ulated with P. juniperi in 1982, 1984, 1985, and 1986. Infection was s cored in 1987. Kabatina tip blight caused by Kabatina juniperi SCHNEID ER and V. ARX, which occurred naturally, was scored also. Between the two juniper species, we found significant differences in survival and resistance to both diseases (P < 0.05). All traits differed among seed -zones and among families within seed-zones of eastern redcedar (P < 0 .01). With Rocky Mountain juniper, variation was significant among see d-zones for survival (P < 0.01), and among families within seed-zones for Cercospora blight and survival in 1994 (P < 0.05). Heritabilities and genetic correlations were high for both disease resistance traits in eastern redcedar. Geographic patterns of genetic variation were ide ntified; seed sources from southeastern collection sites of lower elev ations tended to exhibit higher resistance to both diseases than seed sources from north western collection sites of higher elevations. Dise ase resistance traits were not correlated with height growth (\r\ < 0. 20, P > 0.05) for either species. The relationship between Cercospora blight resistance and survival in 1994 was significant (r = 0.59, P < 0.05). Results indicate that Cercospora blight resistance in eastern r edcedar can be improved by selecting resistant seed sources or familie s for direct reforestation programs or future breeding programs in eas tern Nebraska. Additionally, Kabatina tip blight levels were lower on genotypes selected for resistance to Cercospora blight. Moreover, beca use resistance to Cercospora and Kabatina blights can be selected inde pendently of height growth and survival, there is apparently no need t o sacrifice growth and survival characteristics.