B. P. I>— 682. 



4 SPOT DISEASE OF CAULIFLOWER,. 



INTRODUCTION. 



In April and again in May, 1909, diseased cauliflower plants were 

 sent to the Laboratory of Plant Pathology from a farm in southeast- 

 ern Virginia. In both lots the leaves were closely covered with 

 brownish to purplish gray spots 1 to 3 millimeters in diameter (PI. I). 

 There were also larger diseased areas due to the coalescing of spots. 

 All parts of the leaves were affected. Where the midribs and veins 

 were badly attacked the tissues had contracted, giving a puckered 

 appearance to the leaves (PI. II). From the spots a bacterium was 

 secured in pure cultures by means of petri-dish poured plates on agar, 

 and subcultures from colonies thus obtained were used for inoculating 

 healthy cauliflower plants. 



The cauliflower heads from the same plants were not in good con- 

 dition, but no success attended the efforts to secure from them the 

 same kind of bacterium that was found in the leaf spots. 



What appears to be the same disease was also received once on 

 cauliflower from Florida. 



INOCULATIONS. 



All moculations were made by spraying the plants mth pure cul- 

 tures of the bacterium suspended in water (24 to 48 hour agar slants 

 washed off in sterile water). Young, healthy cauliflower plants 6 to 

 10 inches high were used, some being kept in infection cages and 

 some merely on a bench in the greenhouse. 



The infection shows first on the lower surface of the leaves as 

 sunken water-soaked spots.^ These are visible on the third day 

 after inoculation. In 4 or 5 days the spots are dark purplish-gray 

 and show on both surfaces. In transmitted light the centers are 

 tliin, almost colorless, and surrounded by a dark border. In size 

 they vary from mere points to spots 1 .5 millimeters in diameter. In 

 shape they are irregularly angled; the spread of the disease appears 

 to be stopped or hindered by the veins of the leaf. The individual 



1 Some infections from old cultures that had probably lost much of their virulence were first indicated 

 after 6 to 8 days by tiny water-soaked elevations. As the disease progressed the tissues collapsed and 

 a sunken spot resulted. 



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