BREEDING POPLARS RESISTANT TO DISEASE 603 



POPULUS ZF~S?-CCA~2A 



The possibilities of using ?. trichocarpa in poplar plantations are 

 increasing since, with the help of the "Ride* test", we succeeded in 

 selecting several clones that are highly resistant to bacterial canker. 

 The same clones are also highly resistant to D. populea. 



POPULUS MAXIMOWICZII 



The clones of ?. maximowiczii, are somewhat susceptible to rust and 

 bacterial canker, and therefore not directly useful in our plantations. 

 However, we obtained interesting results from the interspecific crosses 

 with ?. delzzides and 7. zrichccarza. 



RESULTS OBTAINED KITH HALF-SIB CROSSINGS 



By simple selection in natural populations we succeeded in isolating 

 several clones of ?. deltoides and P. trichocarpa that seem to have 

 sufficient multiple resistance to the 'most important western European 

 diseases. These clones will be used in our commercial poplar plantations. 



At about 10 years of age, each of these plantations will be a 

 possible seed orchard. Here seed collections of half-sib and even full- 

 sib crosses may be collected at an extremely low cost. 



During summer 1969 we obtained about 3,500 seedlings for each of "5 

 different half-sib offsprings of selected P. deltoides parent trees. It 

 certainly seems possible that we can select, from these seedlings, a 

 number of clones with increasing multiple resistance to the various 

 diseases . 



There are similar possibilities within the species P. nigra and 

 jiczii. But since it is nearly impossible to establish in 

 Europe, economically valuable plantations with these two species, the 

 breeder will have to pay the total cost of experimental plantations and 

 seed orchards. 



RESULTS OBTAINED WITH FULL-SIB CROSSINGS 



For several years we have made many different intra- and interspecific 

 crosses between clones of P. nigra, P. deltoides 3 P. trichocarpa and P. 

 maximowiczii that show high multiple resistance (Table 1) . The seedlings 

 of these crosses are subjected to the diseases listed in Table 1 through 

 field tests except for bacterial canker. Later on, the best of these 

 seedlings are inoculated with bacterial canker. 



Pcpulus delzzides x Pzz^.lss deltoides 



Several Fi and F2 crosses have already been made between different 

 P. deltoides clones which are immune or highly resistant to all the 

 diseases listed in Table 1 except for bacterial canker. Multiple resis- 

 tance has remarkably increased for most of the second generation crosses, 



This means that the seedling plantations established with these 

 poplars at a latitude of 45° N, in an area free of bacterial canker, are 



