Number of 

 seedlings 



0, 

 



cankered 



Resistance 

 ranking 



207 



8.7 



High 



234 



5.9 



High 



172 



8.7 



High 



206 



9.7 



High 



173 



18.5 



Medium 



174 



14.9 



Medium 



209 



19.6 



Medium 



116 



21.5 



Medium 



205 



29.2 



Low 



PATHOLOGY AND GENETICS OF EUROPEAN PINE RUSTS 417 



Table 1. Percentage of seedlings from crosses of various P. 

 silvestris parent trees showing cankers 14 months after inocu- 

 lation with P. pini 



Crosses 



Healthy S 6226 x Healthy S 6205 

 Healthy S 6205 X Infected A 

 Healthy S 6205 X Infected B 

 Healthy S 6205 X Infected C 

 Healthy S 6226 x Infected A 

 Healthy S 6226 x Infected B 

 Healthy S 6226 X Infected C 

 Infected B X Infected A 

 Infected C X Infected A 



Shoots surrounding the terminal leader of 3-year-old plants were 

 inoculated with 2 spore samples of different geographical origin. The 

 percentage values refer to the total percent cankering from both spore 

 samples. The same pine is rarely receptive to both inoculations. Dif- 

 ferent pine progenies can thus vary in their degree of sensitivity to 

 Peridermiwm, but also Pevidermivm from different sources shows a certain 

 variability. This means that the choice of spores must be subject to 

 continuity. It can also be questioned how many and which types of spores 

 should be used in the tests. 



SUMMARY 



M. pinitorqua is a common parasite on a number of European pines. 

 Also many introduced American pines are susceptible. 



The establishment of the fungus on pine shoots depends on damp 

 weather conditions favorable for basidiospore formation during the axial 

 extension of succulent pine shoots. But it has also been proved that 

 pine shoots contain several substances that have an inhibiting effect on 

 Melampsora basidiospore germination. Other inhibitors have been traced 

 in leachates from the surface of pine shoots.- 



Pine material with differences in susceptibility to attack by 

 Melampsora pinitorqua has been described, but there is as yet no breedinj 

 work using this material. And the question of how to score attack by 

 the twist rust in an acceptable way for routine work is still to be 

 solved. There are no obvious morphological differences between host- 

 alternating Cvonavtiwn and P. pini. Attention is drawn to cytological 



