FIRE-BLIGHT OF APPLE, PEAR, ETC. I TYPE 365 



slime which oozes through natural openings (stomata and 

 lenticels) to the surface of stems, fruits (Fig. 284) and leaves 

 (Fig. 285) in great abundance, where it is visited by insects, and 

 from which is also drips readily to other parts of the tree 



In the shoots it is primarily a bark disease (Figs. 286, 287). 

 It disintegrates the green fruits by multiplying in the inter- 

 cellular spaces and dissolving the middle lamellae (Fig. 288) and 

 is enormously abundant in such fruits. 



In cultures I have not observed rapid loss of virulence. A 

 strain carried along on media in my laboratory for 7 years 

 (1908-1915) blighted pear shoots readily, even of a so-called 

 ''blight-proof" sort, when inoculated by needle pricks in June, 

 1915. Another strain on media 5 years w r as infectious in 1920. 



Fire-blight occurs destructively every year in some part of 

 the United States (Fig. 289), and in certain years (as in 1914 and 

 1915) sweeps over the whole country. It has been known for 

 a hundred and forty years in the eastern United States where 

 it was probably first present on wild shrubs, but its distribution 

 in other parts of the world remains uncertain. It has, how- 

 ever, been reported from Italy. I have been told also that it 

 now occurs in northern Japan on pear and apple, especially on 

 the Red Astrachan (Gentaro Yamada). In Cornwall, England, 

 I saw what looked at a little distance like fire-blight on apple 

 twigs, but on going into the orchard I found that the twigs had 

 been smothered by lichens. 



The disease can be controlled by prompt, intelligent and 

 severe pruning (Fig. 290). This is the only remedy known. To 

 avoid spreading the disease by means of the pruning tools they 

 must be disinfected after the removal of each infected limb. 

 The cut surface should also be disinfected (see Part I, page 71). 

 O'Gara recommends 1:1000 mercuric chloride in water applied 



FIG. 280. Blight on pear leaves due to Bacillus amylovorus. Introduced 

 to show how petioles and midribs often blight in advance of the leaf-blade. In 

 these leaves both petioles were blackened on their surface (except at X) and were 

 exuding bacterial droplets from numerous stomata, but enough fluid was still 

 passing through their vascular bundles to keep the leaf-blades green and turgid 

 except an extremely small portion of the base of B, and a much larger but still 

 relatively small area along the midrib of A. The invasion came from the bark 

 of the shoot, which was blighted. 



