Meloidsl 



MELOIDOGYrre 



LIFE HISTOHY, BIOLOGY, KAC^S, PATHOGMIGITY, AND 

 OTHEK TOPICS DEALING V/ITH ROOT-KUOT NH-IATODE PiESEAHCH 



J. R. Christie 



I am going to begin without preliminaries but with a few generalities. 



The root-knot nematode has been long in that group of plant infecting 

 species that are sometimes referred to as sedentary parasites. There 

 have been named at least ten genera, the species of which belong in this 

 category. 



In every one of them the adult female, or the female once it has become 

 established in the tissues of the host, remains thereafter in a fixed 

 position, feeding on the tissues within reach of its head. In every 

 case, the female loses its original nematoid shape and becomes more or 

 less sac- like The final foim varys from what might be called sausage- 

 shape to almost spherical. 



In every one of these genera, the adult male retains its slender, nema- 

 toid form. 



In the genera Meloidogyne and Heterodera , larvae of both sexes enter 

 the plant. (Usually they enter the roots.) That is to say, larvae 

 destined to become males, as well as those destined to become females, 

 enter the plants. In early development, the male undergoes the same 

 changes as the female — the same widening of the body; but as it reaches 

 maturity, it undergoes a series of molts and a metamorphosis, from which 

 it emerges as a slender, nematoid form. This type of development for 

 the male is unique for these two genera, being found nowhere else in the 

 phylum Nematoda, so far as I am aware. 



The larvae of these two genera do not necessarily pass any stage of 

 their development in the soil. To be sure, they are in the soil, but 

 the sojourn in soil is strictly incidental. Larvae are ready to pene- 

 trate the roots at the time of hatching. They are, in both genera, 

 technically second stage larvae, because they have already molted in 

 the egg. 



In the genera Tylenchulus and Kotylenchulus , the larvae pass their en- 

 tire development in the soil. It is a hurried up development. They 

 pass through a series of quick molts, but they end up technically as 

 adults. Only the female enters the root; and the female, at the time 

 of penetration, is technically an adult, having completed its molts. 

 The male does not become parasitic. Both sexes pass through these early 

 staf^es with no appreciable change in size and apparently without feeding. 



This type of development, in which the male at least passes through its 



