Meloid :b 



The next item is factors influencing the development. Just a word or 

 two about temperature, tiany years ago, Jocelyn Tyler, working with 

 root-knot in Galifornia, found that the optimum temperature for devel- 

 opment of the form with which she worked centered around about 05° F. 

 or about 29° C. But if she raised the soil temperature up about 92.3° P' 

 or thereabouts, or 33° C, the development ceased at that point; if she 

 dropped it to 60° F. , it also ceased. Recently Ferris has published 

 data to the effect that the optimum temperature for the development of 

 Rostochiensis centers around about 65° F. or 18.3° C., and if the soil 

 teniperatvire is raised to 85° F., development ceased. There, in fact, is 

 quite a difference in temperature relationships compared to the root- 

 knot nematodes with which Miss Tyler worked, at least. We do not know 

 what the root-knot species was, but it apparently was more nearly a hot 

 weather organism than one of its counterparts in the other genus. 



Let us now consider that we have the larvae hatched and we have them 

 more or less in the root. P'^rhaps, the next logical matter to comment 

 on would be some of the relationships with regard to factors that influ- 

 ence infection. One of the factors, of course, is the suitability of 

 the plant. Quite a long while ago, Godfrey and Oliveira pointed out 

 that it took considerably longer for the root-knot nematode with x\rhich 

 they were working to develop in the roots of pineapple than it did in 

 the roots of cowpeas. Further work, later on, has shown that there is 

 a big difference, other factors being equal, in the rate of development, 

 depending on the plant in which the parasite is developed and whether 

 it is what I choose to call a suitable host or an unsuitable host. 



^i-These illustrations are all of tomato roots. They are all photomicro- 

 graphs of galls of knoim ages, known to within 2U hours. A gallery may 

 be left in the tissues by the migration of a larva through the tip. It 

 is said that the larvae tend to pass between the cells, pushing them 

 apart. This can be seen clearly in sectioned material. Twenty-four 

 hours after infection it can also be seen that cells of the epidermis 

 are somewhat enlarged. Although the nematode's path may be between the 

 cells, many of the cells are crushed and destroyed. 



One of the effects of most plant-parasitic nematodes, and certainly 

 that of root-knot larvae, is the effect on the cell walls. One of the 

 first things you will see in many instances is a change in the staining 

 quality of the cell walls. In the case of root-knot, the cell wall 

 staining property changes, and then the wall begins to dissolve. Or, 

 at least, many of the cell walls do. They either dissolve or they are 



"fEditor's note: At this point. Dr. Christie's talk was based on dis- 

 cussion of lantern slides which were shoim to the group. As much as 

 possible of this portion of the talk which could be used without having 

 the pictures at hand is presented. It has been necessary to alter the 

 wording somewhat to fit this situation, but the content has not been 

 changed. 



