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FLOOR DISCUSSION 



VAN ARSDEL: If you are determining races on the leaf spot stage of 

 your infection, how do you separate something like "Coleo-psorium jonesii" 

 from the rust if you have spores of that in your nursery, or do you carry 

 them through to maturity--to aeciospores? 



MCDONALD: Of course, we were initially very concerned about the 

 specific identity of these individual spots. We looked at 20,000 spots 

 in our nursery beds, and made histological collections of 100 of these 

 spots representing seven different lesion classes that we had defined at 

 that time. This past winter we carried out a microscopic analysis of 

 these sections and found the typical pseudosclerotium in four lesion types 

 that you saw yesterday. There were two types that did not have the 

 pseudosclerotium; therefore, we threw these out. Also, they represented 

 less than 1 percent of the 20,000 spots that we catalogued. 



VAN ARSDEL : How would you separate Cvonartiun mycelium from 

 Coleosporium mycelium? 



MCDONALD: There was another factor involved. We were able to 

 classify plants, individual seedlings, as having all red spots or all 

 yellow spots, and so on. Many of the plants supporting only red spots 

 and only yellow spots produced aeciospores this past spring. 



BEGA: Where did you get these different races? Were they from 

 geographically different areas? 



MCDONALD: The inoculum used in the 1964 progeny tests, on which the 

 race hypothesis is based, were obtained from a mile-long section of Hobo 

 Creek here in Northern Idaho. The principal Ribes species involved was 

 hudsonianvn var. ■petiotave. We collected from individual bushes and mixed 

 the leaves. Hopefully we had a fairly uniform distribution of inoculum over 

 the test. But, let me point out that while this race hypothesis was made 

 on the 1964 test it has subsequently been tested on the 1966 test. This 

 test was inoculated 2 years later with inoculum obtained from the same 

 area. We realize that we haven't really proven the existence of patho- 

 genic races, but we have hypothesized the system and tested it using 

 10,000 seedlings, 1,000 seedlings per family in ten families. 



