INTRODUCTION 



Development of blister rust-resistant western white pine (Pinus monticola) has 

 been underway in the Inland Northwest since 1950. The first 25 years, known as the 

 phase I program, resulted in the establishment of three seed orchards. The trees in 

 these orchards are the results of two cycles of selection. The level of resistance, 

 under nursery conditions, is expected to be about 60 percent (Hoff and others 1973) 

 and field resistance will probably be as high as 80 percent (Bingham and others 

 1973). Selection of the phase I material was based mostly upon testing candidate 

 trees with four tester trees. Candidates with high ability to transmit resistance 

 were chosen (Bingham and others 1969). 



During the early selection work on western white pine, a considerable knowledge 

 was accumulated on the mechanisms of resistance and the existence of blister rust 

 races (Bingham and others 1971). This knowledge was available early enough to enable 

 us to do some last minute selection changes in the proportion of the types of resistance 

 going into the phase I orchards. We had found that one mechanism of resistance 

 (premature needle shed) was disproportionately high in a previously selected F2 

 population (Hoff and others 1973). Adjustments were made and now only 30-40 percent 

 of the resistance in the phase I seed orchards will result from this mechanism. 



This knowledge also made us aware that resistance in western white pine to 

 blister rust is due to many mechanisms of resistance. Some mechanisms are controlled 

 by single genes, others are controlled by many genes (Bingham and others 1971; table 

 4). This knowledge, together with the need to provide a larger gene base to enable 

 us to select for growth and form and to maintain adaptability to its environment, 

 including native pests, resulted in the initiation of a new program to develop 

 resistance in western white pine to blister rust -- phase II. 



The purpose of this paper is to review resistance in western white pine to 

 blister rust and describe a breeding program that has a high chance of stabilizing 

 the resistance but at the same time maintaining the native adaptability of western 

 white pine. 



The breeding program includes four main elements. One element is a nursery test 

 that will provide data on resistance and secondarily on growth since the nursery 

 phase will keep trees until 6 years old. The 15-25 percent slowest growing families 

 will be excluded. A second element is a field test, mainly for growth and form, but 

 also for comparing resistance to blister rust in the nursery and field. A third 

 element is a plan to allocate the resistant strain according to the degree of blister 

 rust hazard. And the fourth element is to describe a method for developing resistance 

 using natural selections. 



LIFE CYCLE OF WHITE PINE BLISTER RUST 



The heteroecious, full cycle white pine blister rust requires two hosts--white 

 pines and Ribes spp., i.e., currants and gooseberries. Dicaryotic aeciospores are 

 produced on pine, and infect the leaves of Ribes bushes. These spores have two 

 nuclei per cell and are believed to behave genetically as 2N. The Ribes infection 

 produces urediospores which aid in the spread of the fungus on the Ribes host. They 

 are also dicarytic and behave genetically as 2N. 



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