492 E. P. VAN ARSDEL 



VAN ARSDEL: I think that probably you are right; the fungus needs 

 nitrogen, and is higher in protein than the hose material. At least, 

 those rodents that chew on cankers all the time are after something. I 

 think they are after protein nutrition (or nitrogen) . It shouldn't be 

 too difficult to analyze but I haven't done it. 



WEISSENBERG: In discussing the question of potential hazard areas 

 for blister rust, the Mediterranean countries have been mentioned. Miss 

 Emma Vecchi de Pellati mentioned at the FAO 2nd World Consultation on 

 Forest Genetics that the white pine blister rust has not occurred in Italy 

 although they have both the alternate host and P. gviffithii (syn. P. 

 walliahiana) and P. strobus. And Prof. Vidacovic mentioned that the 

 rust does not occur in Yugoslavia. I would like to know whether these areas 

 can at all be considered potential hazard areas. They might have both hosts 

 occurring sympatrically but the climate might not be suitable for the total 

 life cycle of the rust. 



VAN ARSDEL: Spaulding showed quite a gradation across Europe in his 

 paper of 1929 on conditions of rust in Europe. Harm has been done, I think, 

 to research work in the U.S. Forest Service, because people that went to 

 Switzerland were told by a Swiss forester that the rust wasn't very serious. 

 "We grow P. strobus and we get rust but it never hurts anything." Yugo- 

 slavia is in a warm climatic zone and I don't think you could grow the rust 

 in it if you wanted to, anymore than you could in southwest Texas, Ohio, or 

 Indiana. I haven't explained the mechanism of what happens after a little 

 rust gets into an area. Warmer weather is required for urediospores to 

 make a secondary spread after the initial ribes infections from a few 

 cankers on pines. They spread rapidly from ribes leaf to ribes leaf, 

 defoliating them in warm weather. When the cooler weather that permits 

 telial formation and germination comes in the fall, there are no ribes 

 leaves with rust on them to infect more pines. Thus the rust is controlling 

 itself. Farther north most infections on ribes come from aeciospores on 

 pines, without much uredial infection occurring. The aeciospore to telio- 

 spore cycle occurs in the cooler climates. The warm weather, heavy uredio- 

 spore spread that occurs in the warmer Lake States seems to occur in the 

 western U.S. The same type of infection gradient probably occurs in 

 Europe--high rust incidence in the cool north, low rust incidence in the 

 cooler part of the south. 



SCHUTT: Dr. Van Arsdel, you stated that we know that basidiospores 

 have only about 4 hours to germinate and penetrate before light kills them. 

 This is a very important factor since it could be useful in understanding 

 an early resistance mechanism. 



VAN ARSDEL: I think I'd better correct this. Many times the sporidia 

 have only 4-5 hours to reach the pine. Now let's get a point first. I'm 

 talking about epidemics. I'm not talking about the one or two in a hundred 

 ifnections, or the case when Ray Hirt says the spores would live through 

 a single hot day, he pointed out that 3 i 

 day. I'm not talking about this kind of 

 epidemic situations. You may release a 

 live through the next day. Most of them 



through the next day. There have been a lot of tests, some very bad, in 

 which they put a few dry spores on a glass slide, and let the sun shine on 

 it, and they died. You might die, too, but there is a difference. When 

 I worked out the gradients from zones of ribes out into the pine area I 

 found two gradients of spores. They are related to how long it takes for 

 the number of infections to take the square root of itself at a given 



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