380 ROBERT F. PATTON 



and the total environment (Bromfield, 1967) . I have emphasized in another 

 paper in these proceedings that spore germination and differentiation of 

 infection structures apparently require different conditions. Thus condi- 

 tions during some latter stage of inoculation may have to vary from those 

 provided in the beginning to reactivate the inoculum. It is here that 

 elements of technique in following a method could be of great importance 

 since the influence of many of the factors may be very subtle indeed. 



Effect of Age of Stock 



The susceptibility of eastern white pine to infection decreases with 

 increasing age of the stock (Patton, 1961) . This influence has been 

 discussed in regard to needle penetrations (Patton, 1967), and resistance 

 (Patton, 1967; Patton and Riker, 1966). In another paper in these 

 proceedings I have mentioned the possible relation of wax plugs in stomata 

 to differences in infection largely between primary and secondary needles, 

 also an age effect. The relation of age to infection seems clear (though 

 the reasons for it may not be) , and it seems essential that breeders take 

 it into account in evaluating progeny test results. Patton (1961) 

 pointed out some pros and cons in regard to progeny testing, and Patton 

 and Riker (1966) pointed out specifically in a discussion of the seedbed 

 testing method that, although many factors in progeny testing technique 

 are impossible to control, age of stock is one over which control is 

 possible . 



Effect of Fluctuating Temperatures 



During the years of work at Wisconsin to develop blister rust 

 resistance in eastern white pine, numerous inoculations have been made, 

 mostly outside and largely successful. In other experiments, inoculations 

 were made in the greenhouse. The criterion for inoculation was to obtain 

 temperatures (and moisture) that were ideal for basidiospore formation 

 and germination; this meant mainly a temperature of about 16°C and not 

 over 20°C. Some infection was obtained under these conditions but usually 

 much less than under outdoor conditions. Moreover, the effectiveness of 

 the inoculation was generally judged on the basis of the percentage of 

 trees that eventually developed cankers, regardless of whether these 

 resulted from a single penetration or from multiple needle infections. 



More recently, research was directed toward a study of the infection 

 process and the concern was with needle penetration. It became obvious 

 that, although a constant 16°C temperature was favorable both to casting 

 of basidiospores onto needles and to germination of the basidiospores on 

 the needle surface, infection did not occur at all or so rarely that it 

 was impossible to locate and study the histology of needle penetration. 



Finally, experiments on temperature fluctuation were conducted, first 

 in the greenhouse by moving inoculated plants between houses with dif- 

 ferent temperatures, and later in growth rooms in which the temperature 

 regime was programmed to duplicate as closely as possible representative 

 diurnal temperature fluctuations experienced during successful outdoor 

 inoculations in the Blister Rust Nursery. Outdoor inoculations have been 

 successful with the lower limit at about 4°C and the upper limits ranging 

 from near 16°C to as high, occasionally, as 26°C and even up to 32°C for 

 short periods. Many more or less "standard" runs ranged from about 4°C to 

 21°C. When the growth chamber was programmed to duplicate this range 

 over a 24-hour period, severe infection was obtained on seedlings ranging 

 in age from 1-1/2 months to more than 5 years. 



