He tor: 7 



partial diminution in p;rowth and not collanyini:' becauae of nematode 

 inj\)ry. So von see there are these tvjo attributes and they are both 

 very import<'int in connection with breedinf^. Most of our breeding pro- 

 grams so far have gone on the basis of host efficiency, but I thdjik we 

 ought to turn our attention to resistance to troubles due to invasion, 

 remembering that these two are hot necessarily the same thing. 



ECOLOGY 



Now to turn to something different. VJe can break down the Heterodera 

 life cycle into a number of phases. The first is the hatch from the egg 

 and the second is emergence from the cyst. I point out that there rnay 

 be conditions vjhich can effect emerf^ence even after hatching. It is 

 conceivable that there may be larva wiiich hatch within the cyst but are 

 TUiable to get out, so emergence can be a different phase from hatching. 

 The third phase is movement in the soil towards host roots. Fourth in 

 the series is the actual act of invasion. When infection is completed 

 the organism is out of the soil, but ud to that point it had been en- 

 tirely dependent upon the soil as its environment. 



It is true that the plant iself may be modified by certain con- 

 ditions such as length of day and by the soil as a medium for plant 

 growth, but after invasion occurs it is the plant primarily vrhich pro- 

 vides the environment for the nematode. Stage five is its remaining 

 development and then niating. There are times, of course, when the male 

 goes back into the soil environment and its actions and m.ovements are 

 there governed by the same conditions which regulate the earlier stages. 

 The process of producing eggs by the female is, I am sure, very depend- 

 ent upon the nutrition obtained from the plant. That then marks the 

 end of dependence on the plant for, I think, that once the eggs are 

 fertilized and have their egg shell aroimd them they become to a large 

 extent independent of both the plant and the soil. It is probable that 

 the embryo can go on developing up to the second stage, provided there 

 is enough moisture. 



These thoughts can be summarized as follows: 



Environment Life C ycle 



I Soil 1. Hatch 



2. Emergence 



3. Movement in soil 

 U. Invasion of plant 



II Plant 5. Remain jnc; development 



6. Mating (male may go back to ;.riil) 



7. Ovulation 



III More or less independent 8. PJmbryonation 

 of soil anf) plant. Needs 



moisture . 



