402 AGEICULTUKAL AND INDXJSTEIAL BACTERIOLOGY 



blight, SO destructive to the pear and affecting also others 

 of the pomaceous fruits such as the apple. The disease is 

 widely spread over the United States. 



Morphology. — The organism is a short rod, motile by 

 means of flagella; from 0.5 to l/j. in diameter and 1 to 1.8m 

 in length. It stains readily with the ordinary aniline dyes 

 and is Gram-negative. 



Cultural Characters. — The growth upon artificial media 

 is quite uniformly good; upon agar it produces a grayish 

 white, buttery growth. Slight liquefaction in gelatin occurs 

 after several weeks. There is some production of acid from 

 dextrose but no gas is developed. 



Pathogenesis. — It is believed that this organism is trans- 

 ferred from plant to plant by bees, by plant lice and by 

 other insects. The leaves turn brownish or black, the stem 

 turns black and the young twigs show a blackened bark. 

 The name "fire blight" is often given to this type of infec- 

 tion because the infected branches have a scorched appear- 

 ance. It may also invade the larger branches and trunk of 

 the tree, producing the so-called body blight. 



The disease is combated by pruning out all diseased wood. 

 Care must be used to remove all infected twigs and 

 branches, the cutting should take place some distance below 

 the visible infection inasmuch as the bacteria ordinarily, 

 at least, early in the season, are a considerable distance in 

 advance of the blackened area. The wood cut away should 

 be burned. Instruments used in cutting out wood should 

 be carefully disinfected, otherwise they may aid in spread- 

 ing the disease from tree to tree. 



Erwinia solanacearum 



Synonym. — Bacillus solanacearum. 



This organism is the cause of a wilt attacking many 

 plants belonging to the family Solanacew, particularly the 

 tomato, egg plant, potato and tobacco. 



