376 ROBERT F. PATTON 



For seedbed inoculations the bed was enclosed by a frame over which 

 wide mesh hardware-cloth screening was placed. A solid layer of ribes 

 leaves was placed over the wire mesh and covered by burlap and lath screens. 

 Long hose sprinklers kept the burlap constantly wet (Patton and Riker, 

 1966). 



Greenhouse or growth-room inoculation also have been made using the 

 same basic procedure. Generally such inoculations have been made in a 

 mist chamber in which moisture was constantly provided as a fine mist 

 from compressed air atomizers. For such individual tree inoculations, 

 Van Arsdel (1968) wrapped the ribes leaf completely around the pine 

 shoot. Enclosures of plastic films impermeable to water vapor have 

 sometimes been used, although it has often been difficult to keep tempera- 

 tures within the desired range unless they were used in a growth-room 

 where temperatures could be closely controlled. 



Most of the modifications of this basic procedure have been concerned 

 with maintaining the moisture and temperature conditions essential to 

 obtaining infection. Some infection has been attained on individual pine 

 seedlings inoculated in dew chambers at Wisconsin, but the dew chambers 

 have been less reliable so far than mist chambers or small burlap-covered 

 inoculation chambers in which the relative humidity can be maintained at 

 approximately 100%. 



A further modification was the use by Boyer (1962) of telial columns 

 pregerminated for 12 hours on water agar and then transferred to cotyledons 

 and needles of small seedlings. Here, viability of telia was assured by 

 production of basidiospores before transfer to the pines, but only about 

 3% infection was attained. No doubt other elements of the technique were 

 responsible for these poor results. Otherwise, it seems that use of 

 pregerminated telia might offer considerable advantage in reducing over- 

 all inoculation time necessary under controlled conditions of moisture 

 and temperature. 



Spore Suspensions 



For securing uniform coverage of plants with inoculum and standard- 

 izing the amount of inoculum applied, the use of spore suspensions seems 

 most appealing. As far as is known, however, such a method has not been 

 used with any great success with C. vibiaola. Trials with suspensions 

 of basidiospores cast on water during an overnight period, and with telia 

 prepared by chopping telia-bearing ribes leaves in a blender, were made 

 in the Blister Rust Nursery at Wisconsin. Sprays of basidiospores 

 essentially were failures while the level of infection with sprays of 

 telia ranged from bout 35 to 50%, well below that obtained with the usual 

 direct spore casts from ribes leaves. Examination of the trees sprayed 

 with a suspension of telia indicated that many telia were lodged on the 

 pine foliage and stems in drops of water and were unable to germinate 

 because of the low oxygen level. The reason basidiospore suspensions 

 failed to incite infection in trials both outdoors in the Blister Rust 

 Nursery and on trees in the greenhouse is unknown. Neither method has 

 been explored in great detail, however, and I believe some such method 

 as this may yet have promise. 



