Ros.(Hetcr. j»3 



tub 



erosum . In breeding for resistance, it would 



active as that of 



obviously be an advantage" to have two types of resistant plant, one 

 producing little or no hatching factor, which would tend to 'guard' or 

 enhance resistance j and another type, producing much of the hatching 

 factor, which would make the ideal trap crop, after suitable breeding, 

 to give tubers of economic value, if only for feeding stock. The pre- 

 liminary experiments outlined above suggest that the first type is 

 more likely to be found by crossing with S. vernei than with S. andi - 

 gena . Unfortunately, however, active diffusates are produced quite 

 widely amongst Solanaceae, so that response is not highly specific to 

 hosts. 



The effect of resistant plants on soil populations has been investigated 

 in pot experiments and in the field. The results of a pot experiment 

 are shown in Figures 1 and 2. In Figure 1, the effect of five individual 

 resistant plants from each of the lines Hi, H3, and HU are compared with 

 fallow soil (O), susceptible S. andigena , and S. tuberosum seedlings 

 (H13 and HlU respectively), and with plants grmm from Gladstone tubers. 



Cyst populations of : 



H1 H3 H4 H13 H14 Gladstone 



Total egg and larval populations of pots 



nn nUnd. n n n fl n 



HI H3 H4 H13 H14 Gladstc 

 Seedlings ' Tuber 



Figure 1 



Hesults of a pot experiment, 

 itesistant plants have. reduced the soil population, 



