INOCULATION OF WESTERN WHITE PINE WITH BLISTER RUST 369 



Remaining differences in progeny average heights were considered to 

 be male, female, or male x female effects (i.e., genetic), so adjustments 

 of observed needle-lesion values for variation in seedling height were not 

 attempted. 



Another indirect effect of plant height on infection, especially where 

 seedlings grew quite close together when inoculated, could be the inter- 

 ception of basidiospores falling from above (screening) by foliage of the 

 larger and taller adjacent plants (Fig. 2B) . However, in the experiment 

 examined, partial correlation analysis showed that intensity of foliar 

 infection, independent of screening, was again significantly correlated 

 with 2-year-old seedling height (r = .430, 5% level). Screening itself 

 (scored I /8th for each of the overtopping adjacent seedlings, see Fig. 2B) , 

 however, independent of height, had no significant effects on spotting 

 intensity. 



PLANT AGE RELATED TO SUSCEPTIBILITY 



For some time now it has been recognized that resistance of white 

 pines increases directly with host age, at least up to the age of 4 years 

 (Heimburger, 1958; Patton, 1961; Patton and Riker, 1966; Bingham, et at., 

 1969). Thus, difficulties occurred when we attempted to reduce test time 

 by inoculating the 1-year-old instead of 2-year-old seedlings. In fact, 

 we practically decimated some tests where we had inoculated extremely sus- 

 ceptible 1-year-old seedlings. Seedlings of the most resistant 1-year- 

 old progenies survived at levels barely discernible above controls (i.e., 

 5-10% versus the 25-35% usually found in tests inoculated at 2 years age). 



These results on 1-year-old seedlings caused us to quit inoculating 

 progeny tests the first fall after sowing. Nevertheless, because of the 

 severe dormancy problems of P. montioola seed, we are still faced with 

 the age problem. In all progeny tests inoculated at a seedling age of 

 2 years, 20 to 50% of the germinable seed simply fail to germinate the 

 first spring after sowing. They germinate a full year later, so that our 

 tests are. always confounded by the presence of both 1- and 2 -year-old 

 seedlings . 



The year's delay in germination is often strongly associated with 

 progenies of certain mother trees; but late sowing (November or December) 

 of the normally October-sown seed definitely increases the problem in all 

 seed lots. The only advantage of this situation is the weighty data pro- 

 vided on the difference in susceptibility of 1- versus 2-year-old seedlings 



A comparison of infection in seedlings either 1 or 2 years old when 

 inoculated was possible within full-sib progenies of several progeny 

 tests. In two of the largest tests (1964 and 1965), an analysis of infec- 

 tion was made in all progenies having 20 or more seedlings of both ages, 

 where those seedlings occurred in at least 5 of the 10 randomized progeny 

 row-plots of the test. Results are shown in Table 2. 



It can be seen that in the 1964 test, 11% more of the 1-year-old 

 seedlings bore needle lesions, and 29% more bore bark lesions than did the 

 2-year-olds. Similarly, in the 1965 test, 20% more of the 1-year-olds 

 bore needle lesions, 48% more bore bark lesions. The control seedlings 

 exhibited less difference in infection between 1- and 2-year-old plants. 

 One-year-olds were only 3 to 13% more heavily needle spotted, or 11 to 

 28% more heavily cankered than the 2-year-olds. 



