BLISTER RUST RESISTANCE OF WHITE PINES IN ASIA 255 



FLOOR DISCUSSION 



Discussion here concerns all 3 papers in the panel on "Relative 

 Blister Rust Resistance of Native and Introduced White Pines of Europe and 

 Asia," i.e., also for the preceding papers by Bent F. S0egaard and John 

 Gremmen. Dr. Bakshi's paper was read by his coworker Dr. S. Kedharnath, 

 since Dr. Bakshi was unable to attend the Advanced Study Institute. 



HEIMBURGER: Mr. Gremmen points out that you must have healthy root- 

 stocks if you would use grafts to test for resistance to white pine 

 blister rust. This is a very important factor in our work in Ontario, 

 and we handle it in the following way. We take potted, 4-year-old 

 seedling stock and we graft them in the greenhouse as close to the ground 

 as possible. Then we plant them out in a nursery the following spring, 

 planting them deep so that the place of grafting is underground. Often 

 new roots will come from the graft callus, and the original stock may 

 die. Therefore, if the original rootstock had been infected with blister 

 rust the danger of this disappears. This technique may be valuable in 

 Mr. Gremmen' s program for testing resistance of white pine. 



BINGHAM: Dr. S^egaard, could you describe the nature of the blister 

 rust bark lesions in your "class Z", where the branch was infected but 

 the lesion died out? 



S0EGAARD: The branches were successfully invaded by the rust, some- 

 times pycnia appeared, but aecia (in successive years) did not and 

 eventually the cankers died. 



BINGHAM: We've had some interesting suggestions in Dr. Bakshi's 

 paper on the possible existence of autoecism in the white pine blister 

 rust. I would like to address an inquiry to Dr. Hyun, concerning the 

 P. koraiensis plantations where autoecism might be involved. Dr. Hyun, 

 in the case mentioned where P. koraiensis became infected in the apparent 

 absence of alternate host Ribes spp. , how thorough a search of the planta- 

 tion vicinity was made to ascertain that Ribes was absent? 



HYUN: Yes, I think that is a very important question. The infected 

 plantation was observed in 1967, 1968, and 1969. I'm not saying that 

 absolutely no Ribes were present; possibly there were some. A thorough 

 search was made of the plantation area and of the 500-meters surrounding 

 it, yet we failed to find any. 



VAN ARSDEL : I'd like to make a related comment here. One time, in 

 the Mississippi River valley between Wisconsin and Minnesota (an area 

 generally considered to be climatically free of blister rust) , I found 

 a white pine just covered with rust. I was very interested in the tree 

 and observed it for several years. It was at the mouth of a canyon, or 

 deep valley, where there was a nighttime cold air drainage. Ribes 

 occurred high on the hill at a great distance. This kind of air drainage 

 can occur, and it can carry quite a few C. ribiaola spores in from a 

 great distance. It can be very specific and hit one area. 



BINGHAM: Yes, I would second this remark for distant infection of 

 western white pine, based on studies by Merle Lloyd, formerly of my 

 Experiment Station. We have similar, long-distance air drainage patterns, 

 and apparently we can receive infection from great distances. However, 

 like Dr. Hyun, I would hate to say we had no Ribes within these areas. 



