40 



PLASMODIOPHORALES 



OCTOMYXA 



Couch, Leitner, and Whiffen, 1939. Jour. Eli.sha 

 Mitchell Sci. Soc. 55: 400. Whiffen, 1939. 

 Ibid. p. 243. 



(PL.^TE .5, FIG. 27—10) 



Re.sting spore.s usually adhering in groups of 

 eight, sometimes in groups of six to nine; forming 

 zoospores whicli infect the host and develo]) into 

 vegetative plasmodia. Such plasmodia cleaving into 

 sporangiosori composed of numerous small zoospo- 

 rangia, which are sometimes conjoined by narrow 

 isthmuses ; exit papillae lacking on some zoosporan- 

 gia. Zoospores anteriorly bifiagellate and hetero- 

 cont. Sporogenous plasmodia cleaving into small 

 segments which in turn divide into eight uninucleate 

 spores. 



This monotypic genus is characterized by resting 

 spores wliich are grouped usually in clusters of eight 

 (fig. 38). As in other genera, the zoospores enter the 

 host hyphae directly and completely without leav- 

 ing a spore case on the outside. Infection may occur 

 at any place along the hyphae, but hypertrophy of 

 the host occurs only at or near the tip (fig. 27). The 

 young, naked parasite is surrounded by the host pro- 

 toplasm (fig. 28-29) and soon develops into a multi- 

 nucleate Plasmodium. As the latter develops, the 

 hyphal tip swells and attains its maximum size be- 

 fore the parasite is completely mature. As a result. 

 the Plasmodium lies in a vacuolate region (fig. 30) 

 of the swelling, surrounded by radiating strands of 

 host protoplasm along which small particles may be 

 seen moving toward the parasite. The latter thus 

 lives within and in intimate contact with the host 

 protoplasm, and in the early stages of development 

 the two protoplasts are indistinguishable. The plas- 

 modium usually develops from a single zoospore, but 

 Couch et al. believed several small plasmodia may 

 fuse to form a large one. 



The mature plasmodium, however formed, may 

 give rise to sporangesori or cytosori, but the latter 

 do not usually appear until the cultures are several 

 days old. The zoosporangia (fig. 31) are delimited 

 as globose or ovoid masses which soon develop thin, 

 hyaline walls. Sometimes cleavage may be incom- 

 plete, so that several sporangia are joined by nar- 

 row isthmuses. As the sporangia mature, exit papil- 

 lae are formed on those adjacent to the host wall and 

 on some in the center of the group or sorus. As a re- 

 sult, the zoospores may be discharged (fig. 32) di- 

 rectly to the outside or within the host cell. They 

 emerge from the zoosporangia singly and slowly, and 

 after moving about sluggishly for a few seconds at 

 the mouth of the exit papillae swim away. The two 

 unequal flagella are attached at or near the anterior 

 end, and during motility the shorter one extends for- 

 ward while the longer i)rojects backward. Occa- 

 sional zoospores witli four flagella occur (fig. 36), 

 which ajjpear to be the result of incomplete or un- 

 equal cleavage instead of fusion. 



The plasmodia which give rise to the resting 



spores arc indistinguishable from the zoosporangial 

 Plasmodia until after cleavage begins. Miss Whiffen 

 ('39) reported that the two are to be distinguisiied 

 cytologically by the fact that the nuclei of the rest- 

 ing spore plasmodia pass through the so-called akar- 

 yote stage and undergo reduction division. However, 

 she has not yet counted the chromosomes present 

 during the two meiotic divisions. The sporogenous 

 Plasmodia cleave into a number of comparatively 

 large masses, as in Tetrami/.ra, and these in turn 

 usually divide into eight uninucleate segments which 

 soon encyst in groups of two tetrads of resting 

 spores. This grouping, however, may frequently 

 vary from six to nine. Four normal-sized spores and 

 two larger ones may sometimes occur, while nine and 

 seven may be found in other groups. After a short 

 dormant period, the resting spores germinate, each 

 one giving rise to a single zoospore. The structure. 

 type of flagella, and method of swimming of these 

 zoospores are unknown. 

 O. ACHLYAE Couch, et al, I.e., PI. +7, 48. 



Resting spores spherical, 2. 1—3.2 /x, with smooth, 

 slightly thickened walls. Zoosporangia spherical, 

 ovoid, sometimes flattened by mutual pressure, 6-16 

 IX in diameter, hyaline and thin-walled; single exit 

 jjapilla on sporangia adjacent to host wall and in the 

 center of gall; deeper lying sporangia often dis- 

 charging zoospores through the peripheral sporan- 

 gia. Zoosjjores 6-11 in a sporangium, discharged di- 

 rectly to the outside and also within the host wall ; 

 oval; flagella attaciied to or near the anterior end, 

 the shorter one extending forward and the larger one 

 backward during swimming. 



Parasitic in Achli/a r/lomcrata in North Carolina, 

 U. S. A., causing marked enlargement of the hyphal 

 tips. 



This species appears to be an obligate parasite of 

 A. glomeraia. Couch, et al., attempted to transfer it 

 to Saprolegnia feraj', S. mef/asperma, .J. imperfecta, 

 A. flageUata, A. colorata, A. racemosa, A. deBary- 

 ana, Aphaiiomyces stellatus, Apodachlya brachi/- 

 nema, A. minima, and AUomyces arbii.^ciila, but all 

 results were negative. So far, this is the only known 

 species of the Plasmodiophoraceae parasitic in a 

 fungus. 



The life cycle of 0. Achli/ae seems to be almost 

 identical with that of JVoronina poli/cijstis as far as 

 both species are known at present, and it is not im- 

 probable that the two may prove to be related. Ac- 

 cording to Couch, et al., 0. Achylae differs from W. 

 polycy.<!ti.s by the fact that it usually causes spherical 

 swellings and does not lead to septation of the host 

 hy])hae. Furthermore, its cystosori are hyaline in- 

 stead of brown, and the resting spores are usually 

 grouped in clusters of eight rather than in spherical, 

 oval, elongate, and irregular masses. The first dif- 

 ference cited above is not very significant, since the 

 shape of the swellings is not a very fundamental di- 

 agnostic character. What seems more significant is 

 that the sporangia and resting spores of W. poly- 

 cy.iti.i- give a definite cellulose reaction, while those 

 of O. .ichiilae do not. 



