(il.rtmiii'Mh \< i v r 



38 



rable 1. showing the host range of Ave species of Olpidioptu. Numerals Indicate number of monospure Infections at- 

 tempted; +■ and below numerals, success or failure to secure infection; and 11. the original hosi from which each 

 parasite was isolated. From Shanor, 1940. 



Hosts 

 >■ ~ ~- 



Parasites 



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- ? c 2r g g .3 ; §i -S2 2"S.a,e » 2 * ? ■-, - "8 I 



g> -S i £ « s i3 » "S. ~ a 3> § ». t - §s § g a E .§ ? -2 



f r ~ * ^ "* " •; : * t ■ "1 .i IS < g- £ I- ■= •£. s = 5 



i t 3 2 II 8 2 2 2 2 2 2 2 J J 2 2 2 2 2 2 2 2 2 2 



+ + 1- 1 1 



4. 4 3 J " H 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 



+ + + L ~_ 1 — 



-' - 2 2 2 2 2 2 2 2 2 2 2 2 1 4 4 2 2 H 1 1 1 12 



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22222222222222234221 1 H 1 12 



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Olpidioptit variant 



O. ftuiformit 



0. Baprolegniat 



O. mcrassata 



(). luxuriant 



(O. Aphanomt/cit) 



cross inoculation experiments involving numerous 

 host species of Saprolcgnia, Achlya, other related 

 genera, and Pythium. As is shown in table 1, Shanor 

 found that 0. ftuiformit and 0. variant are re- 

 stricted in host range to a few species of Achlya, 

 while 0. Aphanomycet (O. luxurious) is limited to 

 Aphanomycet laevis. .Miss Whiffen, however, found 

 a form of the latter species on ./. cladogamous which 

 would not infect ./. laevis. Olpidiopsis Saproleg- 

 niae and 0. mcrassata, on the other hand, are re- 

 stricted to the same species of .Saprolegnia and to 

 all hut one, I. eccentrica, of the same species of 

 Itoachlya, according to Shanor. The number of in- 

 fections attempted by Shanor. however, is small, 

 and more extensive tests may possibly give different 

 results. Furthermore, it is not evident from Shanor 's 

 account that temperature, pH concentration, and 

 other environmental conditions were controlled in 

 his experiments. Such factors have proven to be very 

 significant in infection and development of other 

 fungus diseases, and it is quite probable that they 

 operate in relation to Olpidiopsis also. Nonetheless, 

 the obligate parasitism and limited host range of 

 Olpidiopsis species which parasitize the Saproleg- 

 niaceae have been clearly established. Shanor's re- 

 sults are furthermore significant, because they sug- 

 gest that species which were formerly believed to 

 be distinct. 0. Aphanomycet and 0. luxuriant for 

 example, may be identical. This is further substan- 

 tiated by the observations that these species arc 

 not as distinct morphologically as they were earlier 

 reported to be. 



The data presented by McLarty and Shanor show 



Mry definitely that hasty observations and meager 



descriptions, of the kind so frequently made in the 

 past, without exact identification of the host and in- 



tensive study of the range of morphological varia- 

 tion, are practically worthless in the study of Olpi- 

 diopsis. Further studies on these parasites of sapro- 

 legniaceous hosts, if they are to be of value, must 

 comply with the following criteria: 1, Exact identi- 

 fication of the host from pure cultures ; 2, Mono- 

 spore infections of a pure culture of the host to de- 

 termine whether one or more parasite species are 

 present in the original host culture; 3, Intensive 

 study of monospore infection cultures of the para- 

 site to determine the variations in size, shape, and 

 echinulation or spininess of the sporangia, in the 

 degree of sexuality present, and in the character of 

 the outer resting spore wall; 1, Extensive inocula- 

 tion of saprolegniaceous hosts to determine the host 

 range. 



Development of Thalli and Zoosporangia 



The development and life cycle of Olpidiopsis 

 species are as follows: The zoospore comes to rest 

 on the host cell, develops a definite cellulose wall 

 ( fig. 8) and forms a conspicuous germ tube through 

 which the content of the spore passes into the host 

 (figs. 9-11). leaving the empty case on the outside. 

 Occasionally, the germ tube fails to penetrate the 

 host and may elongate and branch to a marked de- 

 gree. Figure 7 shows a spore which germinated in 

 water outside of the host and formed a branched 

 germ tube which is strikingly similar to the rhizoida] 

 system of a young rhizidiacous ehytrid thallus. The 

 newly-entered zoospores and young thalli are ap- 

 parently naked but immiscible with the host proto- 

 plasm. Even after ten hours following entrv into 

 tin host McLarty was unable to demonstrate the 



