Oct. 2, 1920.] Agricultural Gazette of N.S.W. 1\ 



Crown-gall of Fruit Trees* 



VV. A. BIRMINGHAM, Biologist's Assistant. 



The organism responsible for the production of ''crown-gall" {Psendomonas 

 tumefa -iens) is a microscopic plant belonging to the bacterial group, illus- 

 trated in the little sketch on this page. 



It is decidedly contagious, infection often taking place through wounds 

 induced by grafting and by careless cultivation. The disease shows its effects 

 by enlargements near the crown, or on the roots of various plants, as shown 

 in the accompanying illustration. These galls vary in size, ranging from 

 the size of a marble to an ai'ea that can be measured in inches. 



In most cases infection takes place in the nursery, and the disease passes 

 unnoticed by the grower when planting out his trees. Crown-gall greatly 

 retards the growth activities of the tree, and the amount of injury is affected 

 by the length of time the tree has been galled, and by the location and 

 extent of the injury. The disease is one which pi'ogressej slowly, stunting 

 the plant first, and finally destroying it. 



The organism rpsjjunsible is remarkable for the great 

 variety of plants that it attacks. In America it is to be 

 found on apple and pear, all stone fruits, grapes, berries, 

 walnut, beet, tomato, tobacco, &c. It occurs in Europe, 

 South America, and 8outh Africa ; and in New 8onth 

 Wales we have from time to time received specimens ^, „ , „ ^ 



" Flagella of Ps udo- 



showing similar conditions on pear and peach trees. monas tumefaciem 



All our attempts to isolate the causal organism from (after Loeffler). 

 specimens received have, so far, failed, probably owing to the age and hard, 

 woody nature of the galls. 



A " hairy-root " condition of apple-tr-ees has been shown by Erwin Smith, 

 Brown and Townsend, to be due to an organism indistinguishable from that 

 causing crown-gall. The organism is nor, located in the hairy roots them- 

 .selves, but in the flattened tumour from which such roots arise. The disease 

 can be communicated in a number of ways : — 



1. By the water of irrigation. 



2. By the implements used in cultivation, and 



3. By insects. 



rreventive Measures. 



No satisfactory method of treating the disease has been devised. Cutting 

 out the galls and treating the cut surfaces with germicides has failed to arrest 

 the develojjment of the disease. 



When detected, diseased trees should be dug out and burnt, and any 

 implements used in the operation should be dipped in a bucket containing 

 5 parts of formalin to 100 parts of water, before use elsewhere. 



B 



