Ren.(lIcloirJ.):2 



Ro tylenchulus reinformis , is the predoininant type, and this soil is 

 apparently too heavy for root-knot. The sting nematode, Belonolirmrup 

 gracilis, the kidney-shaped nematode, and the two root-knot species, 

 M. incognita and H. acrits, are all important in providing openings for 

 the Fu.sarium wilt pathogen of cotton. Root-knot is the predominant 

 species and covers the widest range of soil textures, but the sting 

 nematode and kidney-shaped nematode infest lighter and heavier soils, 

 respectively. 



The Problem of Root-Knot Species 



Considerable confusion was created among root-knot resistance breeders 

 by the publication of Chitwood's revision of the genus in 19h9. Perhaps 

 this tended to delay the work somevjhat temporarily in some cases. Uow- 

 ever, this remarkable piece of work has placed breeding on a firm founda- 

 tion, and greater progress can now be anticipated for the future. 



I'LTiile it is necessary when initiating a breeding program to consider the 

 five species of Meloidogyne as independent species, it has often been 

 found that one gene or group of genes provides resistance to two or more 

 species. Hare, working with peppers, and Crittenden, working with soy- 

 beans, found that certain varieties were resistant to M. incognita , H. 

 incognita acrita , M. javanica , and M. arenaria. In neither crop none of 

 the varieties were resistant to M. hapla. Thus, M, hapla , the northern 

 root-knot species, appears somewhat removed from the resistance stand- 

 point from the other four species. Once the range of resistance is 

 determined for a set of genes in a given host then testing in the breed- 

 ing progrsjn may be limited to one species. To illustrate this point, in 

 cotton M. incognita acrita gives the best differentiation for resistance 

 in segregating populations. With tomatoes M. incognita apparently gives 

 the better differentiation and is preferred for testing. 



Procedure for Breeding for Root-knot Resistance 



While much of the breeding for root-knot resistance in the past has been 

 done by small increments and in dispersed particles, it is now apparent 

 that a well defined formula can be outlined for breeding for resistance. 

 This formula consists of six distinct and well defined operations as 

 f ollovjs : 



1. Determination of the species of Meloidogyne involved by 

 testing with pure cultures of the nema; survey area of 

 the host range for prevalence and species. 



2. Develop techniques for infecting all plants in progeny 

 populations. 



a) Satisfactory greenhouse techniques have been developed 

 for several crops xifhich may be ndnpt.nble to a.ddition;-il 

 crops. 



