Heter: k 



the soil until a root conies close by and stimulates hatching. It is 

 not known for certain that root exudates are necessary in the soil to 

 stimulate hatching. Personally, I think there is a lot of spontaneous 

 hatching going on in the soil. We must not get the idea that diffusates 

 are absolutely essential. In this matter of response to diffusates we 

 can divide the nematodes into a number of categories. There is first of 

 all those types which just do not respond to the diffusates at all. In 

 H. major at certain times of the year you vrill get no response at all, 

 but if you collect cysts from the soil in the spring and keep them moist, 

 this is quite important with this nematode, and incubate them at the 

 temperat-ore of 55°C. then you can get perfectly good hatch. Using grass 

 root diffusates makes no difference. It is apparently only the water 

 which is operative. There is another group, although I don't know you 

 can call these groups yet because in some there is only a single species, 

 in which there is another type of response. This is exemplified by the 

 pea root eelworm, H. gottingjp na , in which you can get no hatch whatsoever. 

 This is quite a puzzle, for if you take exudates from pea roots and ex- 

 pose H. trifol ii to them you do get a stimulation of hatching. Let me 

 remind you thaT this is xjith a diffusate from a plant which is not a host 

 for the H. t rifo lii, and so we have another puzzle. The point is, the 

 pea roots do produce a substance which is capable of inducing hatching 

 but the pea root eelwom does not respond to it. In the field there 

 are some leguminous plants which can reduce cyst nematode populations. 

 These plants are non-hosts, but they do stimulate hatching. VJe can con- 

 firm this in the laboratory. 



Another group based on hatching response is what I call the H. 

 sch£chtii group and I think H. trifolii falls into this group. In it 

 one f jjids quite a marked water hatch j quite a lot of larvae come out. 

 As a sideline^ ri. scha chtii is therefore a very useful laboratory animal 

 because you can do work in hatching studies without having to rely on 

 root diffusate which would complicate the experimental work. In this 

 group there is a much higher hatch with diffusates from host plants and 

 from some non-host plants within the same family. That is, we have a 

 high water hatch with a much higher hatch from host diffusates. 



Then we come to the last group which we may regard as more highly 

 adapted parasites. The water hatch is very low and the host hatch is 

 very high. In that group will come H. rostochiensis , H. carotae , H. 

 crucifera e, and H. humuli. So you see we have in all these groups 

 mentioned a range of physiological responses to root diffusates. 



One can look at this thing in two ways. That is, we can propose 

 two hypotheses. One is that these diffusates are a single class of 

 substance and that the minor differences in specificity are due to 

 modifications of the same molecule; we have one kind of basic material 

 rd-th some differences in structure. Alternatively, one can consider 

 the hypothesis -l-hat we are not dealing with a single kind of material. 



