398 



W. A. BECKER AND M. A. MARSDEN 



1964 the seed from these crosses were sown in a randomized block design 

 in the nursery at the Intermountain Forest and Range Experiment Station, 

 Moscow, Idaho. Concurrently, along with the pedigree matings , control 

 seeds collected from 10 random sources were planted in the nursery. The 

 conditions followed were the same as those reported for the 1960, 1962, 

 and 1963 progeny tests (Bingham et at. , 1969) except that the seedlings 

 were exposed to white pine blister rust (Cronartium ribicola J.C. Fisch. 

 ex Rabenh.) during their second seedling year rather than during their 

 first seedling year. 



The seedlings were examined 1 and 2 years after exposure to the 

 blister rust disease pathogen (Cronartium ribicola) . 



There were three stages to which selection could have been carried 

 out in this breeding program, each stage culminating in progressively 

 better seed orchards (Fig. 1) . For stage A, the blister-rust-free candi- 

 date trees could have been selected from among dead and diseased trees 

 in heavily rusted natural stands in the forest, and seed orchard "A" 

 established by grafting from all selected trees. The second stage (B) 

 could have been attained by progeny testing of the candidates and 

 establishing seed orchards by grafting only from those trees selected 

 for general combining ability (i.e., having all 4 test-cross progenies 

 exhibiting above-average survival levels) . The third stage (C) could 

 have been attained by exposing the progeny of the stage B matings to the 

 disease pathogen, selecting those seedlings that survived exposure, and 

 mating them in a seedling seed orchard. 













Base Population 





AGE 









A 



A 



seed orchards 



Selection of Candidates 













B 



B 



seed orchards 



Progeny Selection of Candidates 















C 



C 



seed orchards 



<;p1prtinn nf Seedlings 













Figure 1. Alternative breeding and seed orchard establish- 

 ment schemes. 



