INOCULATION OF EASTERN WHITE PINE WITH BLISTER RUST 377 



Tissue Grafts 



Bark patch grafts: Where large numbers of relatively uniform stem 

 cankers are required for experimental purposes, bark -patch grafting may 

 be the answer. About 75% overall success with young susceptible stock 

 was obtained by Patton (1962). Initial infection and subsequent canker 

 development were influenced by the type and degree of resistance of the 

 individual selection. 



In patch grafting a successful "take" of the patch is not necessary 

 for infection. The major requirement for transfer of the fungus from 

 patch to understock apparently is contact of patch and stock over a 

 relatively large surface area of inner bark tissues. With such a method 

 technique is important, and the major warning that might be given novices 

 is to avoid making cuts so deep that the cambium is exposed. This is 

 hardly possible on stems smaller than about 5 mm in diameter. With such 

 material it is advisable to make the graft at least 2 to 3 cm long, if 

 possible . 



A modification of the bark patch is the bark ring described by 

 Ahlgren (1961). Disadvantages of this method include death of the tree 

 by girdling caused by failure of the bark ring to "take", the greater 

 difficulty in obtaining close contact between edges of the infected and 

 healthy bark tissues, and the need for much more infected material for 

 use in making the rings. 



A major consideration in the use of bark-patch grafting is that it 

 bypasses all resistance to initial needle infection and the early stages 

 of establishment. This could be a disadvantage in judging overall resis- 

 tance of a tree but, on the other hand, might be of help in differentiatinj 

 needle and bark resistance on an experimental basis. The method has too 

 many disadvantages for use in large-scale testing but it could be useful, 

 for example, in propagating a large number of infections of a single 

 clone in race studies, or in studying the nature of bark resistance. 



Needle tissue grafts : Seeking an alternative to foliage inoculation 

 with basidiospores , Boyer (1964) made grafts with infected needle tissue. 

 Small segments of diseased leaves from 0.5 to 5 mm long were inserted 

 into vertical incisions in the stems of young white pine seedlings. 

 Transfer of the fungus was most successful with leaf segments 5 mm long 

 containing the fungus at both ends, while the seedlings were held in a 

 moist chamber for 30 days. Use of this method might prove of value in 

 identification or separation and propagation of different pathogenic 

 races on pine. 



The success of all tissue grafting methods seems to depend largely 

 on (1) providing as much opportunity as possible for growth of the fungus 

 from infected to healthy tissues held in close contact, and (2) providing 

 a food base (bark patch or needle segment) large enough to sustain the 

 fungus until it becomes well established in the exposed tissue of the 

 new host . 



