The Take-all Disease of Cereals and Grasses 2] 



inoculated growing wheal with diseased straw or spore suspensions, 

 obtaining typical symptoms of the disease in every case. The first recorded 

 inoculations with the fungus from pure culture were made in New Zealand 

 by Waters (1920, a and b), on wheat seedlings grown from sterilized seed 

 on sterilized soil in test tubes. Inoculated plants died in from twenty- 

 eight to thirty-six days from the date of inoculation, while control plants 

 were in good condition after fifty-eight days. Inoculated culms of wheat 

 plants growing in pots did not become infected. 



In the present investigation the relation of Ophiobolus cariceti to take-all 

 has been clearly established. The fungus was found regularly associated 

 with the disease in each of the 205 infested fields of winter wheat observed 

 during the four years while this investigation was in progress. 



The fungus was isolated by the following methods: Bits of the host 

 tissue bearing one or more perithecia were immersed in a 1-2000 mercuric 

 chloride solution for from one to two minutes and then placed under a 

 binocular, where by means of needles individual perithecia were freed 

 from foreign matter. The perithecia were then crushed in a large drop 

 of sterile water, and this drop was diluted by the addition of sufficient 

 sterile water so that if individual small drops were taken each would 

 contain approximately one ascospore. Drops of this suspension were 

 then atomized on, or several drops were spread over, the surface of dex- 

 trose agar 6 in petri dishes. After twenty-four to forty-eight hours, when 

 the petri dishes were examined under the low power of the microscope, 

 the ascospores had started to germinate and single ascospores were 

 transferred with a needle to the surface of agar in petri dishes. During 

 the latter part of the investigation another method 7 was used to obtain 

 cultures from single spores. This consisted in placing individual drops 

 of the ascospore suspension on small pieces of sterile cover slips. The 

 drops on the slips were examined under the microscope, and only those 

 in which the drop contained one ascospore were transferred to the surface 

 of agar in petri dishes. Subsequent examinations were made daily, and 

 where no contamination developed, and the ascospore germinated and 

 produced a colony, a mycelial tip was taken. A third method of isolation 

 consisted in the planting of small bits of diseased host tissue in agar in 

 petri dishes, and the subsequent transfer of single mycelial tips to agar 

 in test tubes. 



The first and second methods were used when viable ascospores were 

 obtainable. 



Isolation of the fungus from tissue plantings is difficult, because of its 

 slow growth and the occurrence of other more rapidly growing organisms 

 in the tissue. Nevertheless the fungus was isolated from fifty tissue 

 plantings, and more than one hundred and ninety ascospore dilution 



6 Formula; 100 cubic centimeters water, 20 grams agar, 2 grams dextrose. 



7 This method, as well as the formula for the agar, was suggested to the writer by Dr. H. E. Thomas. 



