Studies on the Fire-Blight Organism, Bacillus amylovorus 45 



were healthy. The center blossoms blighted as frequently as did the 

 lateral blossoms. Infection sometimes takes place in the blossom, the 

 apple develops, and when the fruit is about one-fourth inch in diameter 

 it is heavily charged with bacteria which ooze from the lenticels during 

 rainy periods. This was observed particularly in the 72- and the 96- 

 hour series. 



The test was repeated at Rochester in June, 1926. At the time when 

 the bags were tied about the branches, approximately 50 per cent of 

 the center blossoms of the clusters had opened and these were removed. 

 When the 72-, 96-, and 120-hour series were inoculated, from one-third 

 to four-fifths of the petals had fallen. The results were checked on 

 June 24, 1926, at which time some young fruits one-fourth inch in 

 diameter, and many blossoms, showed drops of bacterial ooze. The 

 results are presented in table 10. The weather record is given in 

 table 11. 



The results of 1926 give further evidence of the resistance of blos- 

 soms 120 hours after opening, as compared with newly opened 

 blossoms ; also, they give no definite evidence that pollinated blos- 

 soms are more resistant than unpollinated blossoms to invasion by 

 fire-blight bacteria. The results obtained on the Rhode Island Green- 

 ing and Baldwin varieties indicate that if pollination does exert an 

 influence on blossoms in relation to fire-blight infection, it is to augment 

 susceptibility rather than to increase resistance. The writer is of the 

 opinion that pollination has very little influence upon infection of 

 blossoms by fire-blight bacteria. 



RELATION OF TEMPERATURE TO RATE OF MIGRATION 



Most workers on fire blight- recognize that temperature is one of the 

 limiting factors in the rate of migration of the bacteria. D. H. Jones 

 (1909) states that the rate of progress of the disease depends largely 

 upon the "succulency of the twig and the atmospheric temperature," 

 warm days inducing rapid progress. Brooks (1926) was one of the 

 first to give particular attention to this phase of the problem. His 

 data (page 688 of reference cited) show that maximum progress was 

 made by the organism at about 25° C. 



The writer, in one experiment on the rate of migration (February 

 22, table 6, page 86), kept a thermographic record during the seven 

 days covered by the experiment. The greatest distances t fa versed by 

 the organism were recorded on the mornings following the warmest 

 days of the period (February 24 and 27, with a temperature at noon 

 of aboul 90 F.i. Cooler days, although their mean temperature was 

 near 70 F., seemed to he distinctly less favorable I'm- migration. These 

 somewhal fragmentary data are in keeping with the commonly observed 

 fact that fire blight is more destructive in warm than in cool climates. 



