CONFERENCE ON FRUIT-GROWING. 



6 7 



I. CONTROL OF DISEASE BY BREEDING. 



More attention should be paid to the breeding of varieties which 

 are immune or resistant to those diseases which are apt to ruin the 

 Crop. 



It may not be generally realized what great differences of " consti- 

 tution " exist in the forms or varieties of one species of plant. Let 

 me give you the facts which I have recently observed in the case of 

 the hop plant and its mildew (Sphaerotheca Hamuli). I obtained 

 seed of the " wild hop " from Italy, and during the past six years I 

 have raised some 600 seedlings, and tested their susceptibility to 

 mildew. The greater number of these seedlings have proved extremely 

 susceptible to mildew ; a small number are strongly resistant or 

 semi-immune, to the mildew, so that they suffer little harm from its 

 attacks ; and a small number are absolutely immune to mildew. 

 These seedlings do not shift from one class to another in different 

 seasons, but remain perfectly true to their " constitution " from year 

 to year. 



This year, I am testing the commercial varieties of hops in cultiva- 

 tion, and so far it does not appear that any of these were selected 

 originally for any resistance to mildew. 



And this is the first point which I wish to emphasize : that more 

 attention should be paid at the very start to combating disease ; this 

 can be done by the selection of varieties resistant to disease. 



With our present knowledge of the principles of heredity, we have 

 every reason to believe that the character of disease-resistance can 

 be, by the process of hybridization, united to the other desirable 

 characters. 



This work of breeding disease-resistant varieties is scarcely one, 

 I think, which the ordinary nurseryman can carry out, because it 

 requires the particular disease against which resistance is sought to 

 be always present in a virulent form — which is not a nice prospect 

 for a nursery ! 



Research institutions should be deputed to deal with the breeding 

 or testing of plants against particular diseases ; here the work would 

 be carried out under specialists who have an intimate knowledge of 

 the diseases in question. 



We have new varieties of potatos immune to " wart disease " being 

 raised by State help, and similar breeding work is urgently required 

 with regard to our various fruits. 



It is possible that the different stocks used in growing apples, pears, 

 plums, and cherries may affect their liability to disease. At the East 

 Mailing Fruit Experiment Station many different types of Paradise 

 stocks have been collected, and it is intended to investigate the influence 

 of each on the susceptibility to disease or otherwise of the grafted 

 tree. » 



