A Bacterial Disease of Stone Fruits 423 



plums show the greatest variation. The majority of the American va- 

 rieties suffer little, if at all, while nearly all the Japanese varieties, es- 

 pecially Abundance and Burbank, are severely injured, in some cases the 

 disease resulting in the formation of deep limb and trunk cankers and in 

 eventual death of the tree. Similar wounds are occasionally formed also 

 on some varieties of apricot, nectarine, and peach, but they are far more 

 abundant on Japanese varieties of plum. 



The fruits of different varieties of the four kinds of hosts also show 

 considerable variation in susceptibility. The nectarines suffer the greatest 

 injury, the fruits of all the varieties of this host in Missouri being so badly 

 cracked that they are usually destroyed by the various rot-producing 

 organisms while still green. The effects of the disease on the fruits of 

 Japanese plums, especially Abundance and Burbank, are nearly as severe 

 as on the nectarines. The greater proportion of the fruits are badly 

 distorted and cracked and the small number that are not rotted before 

 they ripen are so badly injured that they are worthless for market. As 

 a rule, apricot fruits are injured to a less extent than those of the nec- 

 tarine or plum, but the variety Royal is severely affected. Though the 

 fruits of some varieties of peaches, particularly Elberta, are severely 

 injured, they are as a rule less badly disfigured than are the fruits of the 

 nectarine or the Japanese varieties of plum (Fig. 63c). 



In addition to this variation in susceptibility of the different varieties, 

 there is also considerable variation in the amount of injury to the fruits 

 of a given variety during different seasons. The real significance of these 

 latter variations is not always easy to explain, but in most cases the age 

 of the fruit and the weather conditions determine largely, the percentage 

 of infection. 



In table 1 is given a list of the apricot, nectarine, peach, and plum trees 

 in the variety orchard of the Missouri State Fruit Experiment Station, 

 showing the nature and degree of susceptibility of the different varieties. 

 These figures represent the average record for the year 1909. An estimate 

 of the percentage of infection on leaves, twigs, and fruit was made by 

 passing through the orchard, estimating and recording the injury. After 

 the estimates had been made several trees in different parts of the orchard 

 were carefully examined and the actual percentage of infection was ob- 

 tained by counting the diseased leaves, twigs, and fruits. The difference 

 found between the actual and the estimated percentages of infection 



