The next rust symptom is the appearance of cankers in the stem. The rate of 

 appearance of cankers varies with families (table 2) . This trait appears to be 

 controlled by several genes with a heritability of 46 percent. 



Table 2. --Number and percentage of blister rust cankers observed in the stems of 

 western white pine seedlings 1 year after inoculation 



Cankers following inoculation 



Family 1st year 2nd year 1st year/2nd year^ 4th year' 





Number 



Number 



Percent 



Percent 



17 X 121 



38 



60 



63 



63 



17 X 250 



11 



38 



30 



39 



17 X 57 



23 



65 



35 



74 



19 X 121 



18 



54 



33 



54 



19 X 250 



21 



61 



34 



61 



19 X 57 



14 



60 



23 



60 



22 X 121 



35 



61 



57 



61 



22 X 250 



26 



48 



54 



51 



22 X 57 



30 



62 



48 



65 



58 X 121 



37 



64 



58 



65 



58 X 250 



23 



65 



35 



66 



58 X 57 



2 



27 





27 



^Heritability 



(0.46) 



calculated from a 4 



X 10 factorial 



including thesi 



crosses (author's unpublished data). 



^By the 4th year after inoculation all cankers that will show up are 

 observable. 



After the fungus reaches the stem, a series of reactions can occur that-- 

 depending on individual and f amily--result in the death of the fungus. The effective- 

 ness of this resistance depends on two separate reactions: (1] the ability of a 

 seedling to initiate a necrotic response in the cortex after invasion by the rust; 

 (2) the ability of a seedling to rapidly produce a strong wound-periderm. We observe 

 in western white pine (unpublished information) and in Armand pine (Hoff and McDonald 

 1972), that only the host cells seem to be killed; the fungus, although not healthy, 

 appears still to be alive, at least the cytoplasm and the nucleous of the fungus was 

 not disrupted. Also, the small amount of data on Armand pine indicates that the 

 effectiveness of the resistance varies with the phenology, i.e., the necrotic reaction 

 is apparent when diameter growth begins and it is not operating during other periods. 



The rate of growth of the fungus in the stem varies with individuals and families. 

 In many trees, of the progeny tests set up by R. T. Bingham and A. E. Squillace in 

 1952 through 1955, the fungus had not girdled the stem by 1970, even though the 

 fungus had reached the stem of the seedlings probably by the time the seedlings were 

 2-3 years old, i.e., 1 year after artificial inoculation (table 3). 



4 



