344 ROBERT A. SCHMIDT 



uncertain process. Although the time, expense, and space involved in the 

 establishment of meaningful field tests is considerable, their ability to 

 test geographic interactions is an extremely important advantage. 



2. Rust nursery — This technique is essentially one of natural 

 inoculation. Pines to be inoculated are planted between rows of suscep- 

 tible oaks which are inoculated with aeciospores of the fungus. Irriga- 

 tion maintains high moisture levels. Although the nursery cited in 

 Table 2 encompasses only one site location and has had erratic inoculation 

 success, the technique has the advantage of closely approximating a 

 natural situation under conditions which enhance the chance of successful 

 inoculation. 



3. Tent chambers over nursery beds, etc . --This method, which consists 

 of enclosing in a cheesecloth tent a nursery bed containing seedlings, is 

 used with good success. High moisture conditions within the tent are 

 maintained by a water mist system and abundant inoculum is provided by 

 branches of telia-bearing oak leaves. Inoculum density is difficult to 

 control and some aspects of geographic interaction are normally precluded. 



4. Screening shed. --This technique uses a large frame building with 

 screen sides and removable canvas covering. High moisture levels are 

 maintained by spraying water onto the canvas sides. Evaporation from the 

 wet canvas aids in maintaining favorable temperatures within. Seedlings 

 in greenhouse flats are placed on multi -shelved racks within the shed. 

 Abundant inoculum is provided by suspending branches of telia-laden oak 

 leaves above the shelves of flats containing the seedlings, or by placing 

 individual leaves on a wire shelf above the seedlings. This technique 

 can be used with good success to inoculate large numbers (10-15 thousand 

 per test) of seedlings for progeny tests. However, it requires considerable 

 labor to handle the seedlings and provides little opportunity for control 



of inoculum density or geographic interaction. 



5. Inoculation chambers . --In contrast to the large chambers just 

 discussed, several smaller inoculation chambers of various sizes and 

 construction are used to facilitate inoculation of pine. Although the 

 number of seedlings inoculated is relatively small (200-1000), several 

 have been used to screen progeny for disease resistance. Others are 

 designed to study the effects of environment or inoculum density on 

 disease development. These small chambers offer little prospect of 

 testing geographic interaction in relation to disease resistance. Their 

 chief advantages relate to their ability to control one or more of the 

 many variables involved in the inoculation process and, as such, are 

 extremely useful. One such chamber is described in this proceedings 

 (see Dwinell) . 



B. Individual Tree Inoculations 



Inoculation techniques for individual tree are of widely divergent 

 types and, with the exception of techniques No. 6 and 7, Table 2, bear 

 little resemblance to mass inoculations. Individual tree inoculations 

 are not efficient for rust resistance screening programs but are advan- 

 tageous in other investigations of disease resistance or epidemiology. 



6. Telia suspended above individual seedlings . --This technique does 

 not differ appreciably from some mass inoculation methods already 

 mentioned. Usually, oak leaves bearing mature telia are placed directly 



on each seedling to be inoculated. This method has been used in conjunction 



