128 "Black Neck" or Wilt Disease of Asters 



and the medium sterilised in the autoclave. The other media were 

 prepared by the ordinary methods given in recent papers by Pethy- 

 bridge 1 , Dastur 2 and others. A more or less healthy growth of the 

 fungus was obtained on all these media but that on Quaker Oat agar 

 was by far the most vigorous. Here an aerial mycelium soon formed 

 a dense woolly felt over the surface of the medium, whilst on other 

 media the growth was much less rapid, aerial hyphae being only sparingly 

 produced. 



The fungus was isolated in the following way. A diseased plant was 

 well washed, first in water and then rapidly in a saturated solution of 

 corrosive sublimate. The portion of the stem near the upper limit 

 of infection, as indicated by the discoloration of the tissues, was cut 

 off with a razor previously sterilised. Sections were cut longitudinally 

 from this piece of stem and transferred to the surfaces of Aster agar 

 and Beerwort agar in Petri dishes. After 48 hours the mycelium had 

 spread a considerable distance over the surface of the medium and the 

 growth near its limits was free from bacteria and other fungi. From 

 this region portions of the mycelium were transferred to tubes and plates 

 of sterile media and the cultures in these remained pure. Owing to 

 the very rapid growth on Quaker Oat agar it was necessary on this 

 medium to start fresh sub-cultures fortnightly. New cultures were 

 also started from time to time, by the method described above, from 

 different diseased asters, and in every case the fungus isolated was 

 the Phytophthora already referred to. 



Although over a hundred artificial cultures have been made up 

 to the present, no mature sporangia have appeared on solid media. 

 The sporangia, however, were obtained in abundance by transferring 

 portions of vigorously growing mycelium to the roots of various seedlings 

 submerged in water in Petri dishes. Among seedlings used successfully 

 for this purpose were those of Aster, Helianthus, Gilia, Lycopersicum 

 esculenlum and Senecio vulgaris. After about three days very abundant 

 crops of sporangia were formed on these pieces of mycelium. The libera- 

 tion of zoospores was then easily observed by removing the hyphae 

 healing mature sporangia to hanging drops of fresh well-aerated tap 

 water. It is possible also to obtain sporangia by simply bringing 

 pieces of mycelium from pure cultures into tap water, but under these 

 conditions they do not appear for 10 to 21 days. 



1 8ci. Proc. Roy. Dublin Soc., L913 14. 

 - Mem. Dept. Agric, India. 1913. 



