634 SECTIONAL TRANSACTIONS.— M. 



Mr. D. G. O'Brien. — The Endotrophic Mycorrhiza of the Strawberry and 

 its Significance. 



The paper contains the results of a mycological investigation, undertaken in the 

 years 1926 and 1927, into a serious disease of strawberries in the Clyde Valley of 

 Scotland, known locally as ' The Lanarkshire Strawberry Disease.' The investigation 

 was first confined to the disease as it occurs in Lanarkshire, but later was extended 

 to include strawberry-growing districts throughout Great Britain, as evidence was 

 forthcoming to show that the symptoms throughout the country had various points 

 in common. 



In view of the complex nature and widespread occurrence of the trouble, it should 

 be understood that much research work still remains to be done before the problem 

 is finally solved ; meantime, on the evidence presented in this paper, the authors 

 have come to the following conclusions as to the cause and nature of the 

 disease : — 



1. The disease of strawberries, best defined as ' root weakness,' is a general one. 



2. Diseased plants are characterised by a paucity of absorbing rootlets. The other 

 symptoms of the disease are but signs of starvation consequent upon this. 



3. The only constant organism found in the living roots of unhealthy plants is an 

 endotrophic mycorrhizal fungus of the type bearing arbuscules and vesicules. 



4. This organism invades chiefly the fine absorbing roots of the strawberry plant. 



5. At or about flowering time of the strawberry plant, fine fibrous roots are produced 

 in great amoimt and, coincident with this, the maximum infestation occurs. Tho 

 disease is most destructive at this critical stage. 



6. Starch and other materials are removed from the root tissues by the action of 

 the arbuscules, and there is no evidence of any return of starch to cells when once 

 depleted of their contents. The vitality of the roots is therefore lowered. 



7. The arbuscules are never completely digested by the host ceUs, so that the 

 fungus benefits at the expense of the plant. 



8. At the points where strong infestation occurs the finer rootlets are ruptured 

 and drop off into the soil. To this we ascribe the poverty of absorbing roots noted 

 on diseased strawberry plants. 



9. We regard this endotrophic mycorrhizal fungus as a parasite, and believe it to 

 be the fundamental cause of the disease. 



10. The disease tends to be slow-acting and chronic in its nature, but the fungus 

 is capable of bringing about death of the plant if infection is severe. 



11. The disease assumes really serious proportions when aggravated by conditions 

 inimical to the growth of the strawberry plant. But, according as the mycorrhizal 

 attack is severe or slight, and as conditions are unfavourable or favourable for plant 

 growth, so is the ultimate damage greater or less. 



12. The so-called ' Lanarkshire Strawberry Disease ' represents this trouble in 

 its most serious form. 



13. The endotrophic mycorrhizal fungus paves the way for the entry of secondary 

 fungi and bacteria which, under certain conditions, may invade the weakened root 

 tissues and intensify the disease. 



14. The root fragments, which are broken off from diseased plants, serve to infect 

 the surrounding soil. 



15. Young runners from affected plants are free from disease imtU they strike 

 root in the soil, when their roots become infected. 



16. The disease is transmitted by infected runners. 



17. Some evidence is produced to show that the fungus is not specific to the 

 strawberry, but may invade other plants such as grasses and clovers. Infection'of 

 the strawberry crop may be traced to such sources. 



18. Control measures are outUned. 



Saturday, September 8^ 



Excursion (motor charabanc) to Ayr via Johnston, Dairy, Barassie, 

 Loans, Troon, Monkton, to view soil profiles, small holdings, etc. Return 

 via Auchincruive, Holmes Farm, Rowallan Castle (tea), Lugton. 



