394 F. M. Rolfs 



On the fruit 



The disease does not ordinarily appear on the fruit until about the 

 middle of May. Injured fruits of all the four kinds of hosts, however, 

 have been collected early in May (Fig. 63). The first external signs of 

 the disease are numerous small gray specks just below the cuticle. These 

 specks enlarge slightly and soon take on a water-soaked appearance or a 

 purplish color. The skin over the spots is soon ruptured, producing 

 numerous straight or angular cracks which resemble the wounds on chapped 

 hands (Fig. 64). Usually individual spots do not » measure much more 

 than two millimeters in diameter, but they are often so numerous that 

 the cracks soon become confluent and frequently form a network, fissures 

 nearly an inch in length being developed in some cases. On young growing 

 fruit it is not uncommon to find rifts extending nearly the entire length 

 of the fruit. Such wounds mar its appearance and in many cases render 

 it worthless for market. 



On all kinds of fruit the disease results in the formation of these 

 small, more or less abundant, crack-like wounds, but certain varieties 

 of the nectarine are especially liable to this type of injury. In some 

 cases the spots gradually widen and extend for a considerable depth into 

 the tissue, forming roundish, sunken, black spots which finally measure 

 from one-fourth to one-half inch in diameter. Rifts develop in the 

 blackened tissue. These widen, and cracks appear throughout the dis- 

 eased area which often (especially when the disease is on young develop- 

 ing fruit) finally extend beyond the dead into the healthy tissue. In 

 many cases the fruit becomes so badly distorted and cracked that it is 

 worthless, and it is soon destroyed by various rot-producing organisms. 



ETIOLOGY 



Historical 



The pathogen causing this disease was first isolated by the writer in 

 1904 at the University of Florida. Many poured plate cultures were 

 made from the spots on injured leaves of both peach and plum. Cultures 

 made from the young water-soaked spots invariably gave numerous 

 yellow bacterial colonies, and in no case was a species of Cercospora or 

 Cylindrosporium obtained. Consequently it was concluded that the 

 disease was of bacterial origin. It was observed also that the defoliated 



