CULTURES WITH MELAMPSORAE ON 

 POPULUS 



James R. Weir and Ernest E. Hubert 



Additional cultural results with the Mel lamps orae on species of 

 Populus have been secured since the positive results in 191 6 on 

 species of Larix with the rust known as Melampsora medusae 

 Thiim. found on Populus trichocarpa and P. tremuloides. 1 The 

 telial material on P. tremuloides used in 1916 was typical of M. 

 albertensis Arth., but owing to the fact that positive results were 

 secured on species of Larix only and negative results on Pseu- 

 dotsuga taxifolia 2 is was referred to M. medusae. 



In April, 1917, a large number of cultures were undertaken for 

 the purpose of checking the two rusts commonly found on Popu- 

 lus in the Northwest. The aecial stage known as M. albertensis 

 on Pseudotsuga taxifolia was found in July, 1916, at Darby, Mon- 

 tana, and at other points, but no successful check cultures had 

 been made for this region up to the present report. The results 

 of the 1917 cultures are presented in Table I. All cultures were 

 made under control conditions in the greenhouse at Missoula, 

 Montana, by the use of celluloid cylinders. An attempt was made 

 to use only those hosts having young susceptible needles. 



A study of the data in Table I shows that the sporidia of the 

 rusts known as M. albertensis and M. medusae infect species of 

 Larix and species of Pseudotsuga without any apparent pref- 

 erence on the part of either fungus for any particular host genus. 

 Teliospores from a small portion of an infected leaf of collection 

 No. 24 was used to inoculate both Larix occidentalis and Pseu- 

 dotsuga taxifolia with positive results in both cases. This was 

 done to eliminate so far as possible the chance of having two 



1 Weir, Jas. R., and Hubert, E. E. Recent cultures of forest tree rusts. 

 Phytopath. 7: 106-109. 1917. 



2 The negative results on Pseudotsuga taxifolia in the light of recent work 

 have since been attributed to the use of trial hosts with needles too far ad- 

 vanced in growth. It appears that the youngest and most tender needles are 

 the most susceptible to infection. 



194 



