Hes. (Keloid. ):3 



b) Develop field techniques for testing crops which -'jre 

 not well adapted to greenhouse production. 



3. Determine the type of resistance involved and method of 

 evaluation of resistance. 



a) Type of resistance: 



(1) Limited entrance. 



(2) Limited development and reproduction after 

 entrance. 



(3) Tolerance due to rapid root extension downward 

 or laterly. 



b) Evaluation of resistance by: 



(1) Disease index, yield, green weight, other. 



h. Search for resistant parental material in: 



i) Established commercial varieties or closely related 

 material. 



b) Wild material and related species. 



5. Determine the inheritance of resistance as a guide for 

 breeding. 



6. Cross and backcross until the desired types are estab- 

 lished. 



Inheritance of Resistance, Chromosome Numbers and 

 Polyploidy in Crops Bred for Root-Knot Resistance 



The table at the end of the paper summarizes the available information 

 on number of factors involved, dominance or recessiveness, basic number 

 of chromosomes and polyploidy in breeding for resistance to Meloidogyne. 

 From this table it can be seen that good information on inheritance of 

 resistance is rather sparse. The problem of transferring resistance is 

 not difficult in most cases where one or two dominant factors are 

 involved. However, with crops such as tobacco and sweet potato where 

 tetraploids and hexaploids are involved the problem is more complex. In 

 cotton, an amphidiploid, where several recessive factors are involved, 

 considerable difficulty in transfer of resistance is anticipated. With 

 tomatoes where a single dominant gene is involved the transfer of resist- 

 ance from the wild peruviajium has been difficiJ.t because of the linkage 

 of resistance with undesirable commerical traits. This work is now 

 perhaps in the 25th generation, with numerous backcrosses, and no com- 

 merical varieties have yet been released. 



Perhaps the work of Hanson, Robinson, and Wells on the heritability of 

 resistance to root-knot in Lespedeza represents a more practical 

 approach to the genetics of resistance where inheritance is complex. 



