Meloidt? 



The term "super-sensitivity" has been used f' > :;uch relationships. I 

 flirt.ed with that idea quite awhile. It was an attractive theory, and 

 looking at some plants like peachns, where there is so much necrosis 

 around the nematodes, it looked as through there might be something to 

 the idea. Certainly, the matter required investigation. 



I repeated my work with tomatoes on marigolds to a considerable extent. 

 I used marigolds as a plant in w hi ch the parasites did not develop. I 

 very quickly found that there wa.s no necrosis around the head of the 

 parasite. It was just the opposite, nothing happened around the head 

 of the parasite, or, at least, very little happened up until about eight 

 or ten days after invasion. At the end, of about a time like that, I do 

 not remember the exact figure, there developed a condition that compared 

 favorably with the condition in a tomato root tip about two days after 

 larvae entered. That is as far as it went, because by that time the 

 parasites were dead. 



I think in those cases, and in the case of marigolds and probably Crota- 

 laria, that the reason the parasites fail to develop is because they do 

 not, or are not able to, modify the roots in such a manner that they 

 can feed on them, I offer that as a suggestion. 



What about the Caladium tubers T spoke of before? I suggest that in 

 some tissues like Caladium, for example, the parasite can feed on the 

 tissue without any changes whatever, just as it is. Therefore, it does 

 not make any difference whether they can modify or not modify it; it is 

 already in such condition that they can feed on it. 



Quite a long while ago when Mr. Machmer was in Beltsville, he was work- 

 ing with rose geraniums, one of the Pelargoniums . He was growing them 

 in root-knot nematode infested soil. Some little hard spots were pro- 

 duced on the roots which looked somewhat like galls. However, no root- 

 knot nematodes could be found in this tissue. All the plants were 

 grown from cuttings. One day he noticed at the base of one of the cut- 

 tings where the roots originated quite a little gob of tissue, a soft, 

 succulent tissue. I expect, perhaps, you would classify it as callus 

 tissue. It was found to be just loaded with females and lots of egg 

 masses. I suggest that the reason the parasites developed in that 

 tissue is because it was of such a nature the nematodes did not need to 

 do anything to it at all. The reason nematodes did not develop in the 

 roots is that the roots just went on in normal development and starved 

 the parasite out. 



Not long ago I had an occasion to look at some soybeans that one of the 

 experimental people in Gainesville was growing. He had several varieties 

 of soybeans that he considered to be fairly root-knot resistant. We 

 went out into the plots and began pulling up plants. There was one 

 varifty that certainly did look good. We could not see any galls on the 

 roo+s; they seemed to be free from galls. I took some plants back into 

 the laboratory to look at them a little more carefully. I found plenty 

 of female root-knot nematodes with egg masses in the bacterial nodules. 



