R. T. BINGHAM 



VAN ARSDEL: Could I rephrase the question?' Do you get cankers 

 without needle spots, because we did get them with eastern white pine (P. 

 strobus)? In fact, I have always considered the needle spots as sort of 

 a resistance reaction. In other words, only some of the successful infec- 

 tions result in needle spots, and some that don't result in spots might 

 be causing the bark cankers you are seeing. 



MCDONALD: In our preliminary analysis I mentioned above, 99.6% of 

 the seedlings had needle spots we judged to be associated with successful 

 attack by Cronartium ribioola. Thus, we had little opportunity to observe 

 cankering in the absence of spotting. 



BINGHAM: Maybe I can shed a little light on the problem, Dr. Van 

 Arsdel. In certain of our annual, artificial inoculation runs, those 

 that have been less successful than the one Dr. McDonald discussed, there 

 has been a very good correlation between the presence of needle spots and 

 cankers or the absence of needle spots and the absence of cankers. 

 Perhaps your own Phytopathology publication, demonstrating that succulent 

 Pinus strobus stems could be infected in the absence of needles (cf . 

 Van Arsdel, E. P. Phytopathology 58: 512-514, 1968) might provide a 

 partial explanation to the phenomenon of cankers sans needle spots. Now 

 I have a question for you. Have you observed similar, unexplained cankers 

 in the in the non-needled portion of stem internodes in nature? 



VAN ARSDLL: Yes. 



BINGHAM: Then you suspect that with Pinus strobus the phenomenon is 

 also happening in nature. 



VAN ARSDEL: Yes. 



GERHOLD: I'm not sure that Dr. Kinloch's question was fully answered. 

 Were different resistance criteria used by various investigators, and how 

 were these taken into account when you established resistance rankings 

 for the white pine species? 



BINGHAM: In the Table 2 mentioned previously, results from Hirt, or 

 from Bingham and staff were expressed in percent of trees in the different 

 species that became infected in a given period of years. Bedwell and 

 Childs' data were based upon number of bark cankers per million needles, 

 but Spaulding's and Meyer's data were largely observational. If the 

 "tentative average blister rust resistance rankings" of the last column 

 of the table have any reliability, it comes from similarity of rankings 

 found by the 3 investigative teams who gave quantitative results. 



VAN ARSDEL: I have made a similar ranking, based on about the same 

 literature as Mr. Bingham's. I included Stuart Moir's bulletin (Moir, 

 W. Stuart. 1924. White-pine blister rust in western Europe. USDA Bull. 

 1186, 32 p.), and, as you know, I have written to obtain your rankings. 

 Except for 2 or 3 of these species with "muddy" coverage, our rankings 

 by literature review methods are very similar. Perley Spaulding and 

 others have published the same relationship for P. atbioaulis and 

 P. larribertiana in Europe, that you showed here. 



