Abstract: The effect of Rhizobium isolates on sporulation, hyphal lysis and zoospore survival of P. cinnamomi was examined in extracts of suppressive and conducive soils. Varying degrees of inhibition of P. cinnamomi growth by fifteen Rhizobium isolates were observed on agar media. Inhibition of mycelial growth was enhanced when the rhizobia were inoculated into the agar as compared to the surface streak method. An isolate from nodules of Acacia pulchella was found to be the most antagonistic to mycelial growth. Sporulation and hyphal lysis were stimulated by three of the rhizobia tested, with both suppressive and conducive soils. There was no significant difference between the effects of type of soil on sporangial formation or hyphal lysis. Rhizobia isolated from root nodules of A. pulchella significantly reduced zoospore survival in both the non-sterile suppressive and conducive soil extracts. There was a slightly greater zoospore survival in the conducive yellow podsolic extract than in the suppressive red earth extract, possibly attributable to microbial components of the extracts. These results indicate that Rhizobium , in concert with other soil micro-organisms, actively suppresses the pathogen P. cinnamomi in vitro .

Abstract: Large aliquot water samples (30 ml) were enriched with nutrients, then gelled in the cold with Polycell (wallpapering paste) and incubated to derive Saprolegniaceae colonies and hence deduced spore counts, from water collections of about 1 litre. The Saprolegnia pathogen of fish was a component of the total recoveries; it was recognised on the basis of its secondary zoospore cyst ornamentation. Windermere water entering The Ferry House fish hatchery gave spore assays of 2 to 28 1−1 for the pathogen, a significant component of total Saprolegnia, which was 6–73 spores per litre.

Abstract: Summary: Citrus pectin induces highly synchronous differentiation in populations of Phytophthora cinnamomi zoospores in the absence of a host plant. This action is independent of the presence of Ca2+ in the zoospore suspension medium. Water-soluble, ethanol-insoluble material present on the surface of the plant roots also induces differentiation of P. cinnamomi zoospore populations with the same time course as pectin. It is proposed that this material provides the natural recognition signal which induces P. cinnamomi zoospores to differentiate, and that pectin is sufficiently similar in structure for it to mimic its action.

Abstract: Spizellomyces punctatum has been reported to be a mycoparasite on spores of vesiculararbuscular mycorrhizal fungi, and studies were undertaken to determine whether this species attacked viable or non-viable Gigaspora margarita azygospores incubated in sterile sand on nylon sieves and inoculated with zoospores of the fungus. (1) Spizellomyces puntatum mostly attacked non-germinated azygospores. (2) Inoculation of G. margarita azygospores with zoospores of S. punctatum did not significantly reduce the incidence of azygospore germination. (3) Pre-killing of azygospores with propylene oxide or heat greatly increased colonization by S. punctatum. (4) Water soluble exudates from propylene oxide-killed azygospores chemotactically attracted more S. punctatum zoospores than exudates from healthy azygospores. (5) High populations of the chytrid did not reduce infection or growth response by G. margarita when a zoospore suspension of S. punctatum was mixed with VAM inoculum and added to cotton plants in the greenhouse. Infection and growth response of citrus by Glomus fasciculatum similarly were not reduced. This evidence suggests that S. punctatum is primarily a saprophyte which attacks non-viable spores of VAM fungi.

Abstract: The removal of divalent cations from suspensions of zoospores of Phytophthora cinnamomi decreased cell viability. When zoospores were exposed to combinations of cations, the degree of zoospore encystment was reduced to the mean level of that stimulated by the two cations acting separately. When Ca2+ was present in mM concentrations, any damaging effect of the second cation was reduced. In the absence of added K+ and Ca2+, the ionophores valinomycin and A23187 induced zoospore encystment within minutes. The addition of Ca2+ to zoospores treated with A23187 induced germination of the cysts. Strontium at 25 mM was as effective as Ca2+ in stimulating germination. The calmodulin-inhibitory drugs trifluoperazine, imipramine hydrochloride and dibucaine reduced zoospore viability and, with the exception of dibucaine, were ineffective at inducing encystment.

Abstract: The ultrastructural organization of the primary (1°) and secondary (2°) cysts of Aphanomyces astaci and A. laevis is extremely similar, and similar to that of the 1° and 2° cysts of A. eutekhes as presented earlier by Hoch and Mitchell. Synchronous populations of 2° cysts can be induced by mechanical shock and encystment appears to be essentially instantaneous. The cyst coat–wall appears to be formed extremely rapidly from material from the peripheral vesicles with flocculent content. After encystment the microtubule cytoskeleton found in the zoospore is maintained in the 1° and 2° cyst (i.e. the single microtubules which extend along the pyriform nucleus from the ki–netosomes–centrioles and the bundles of closely appressed microtubules are retained). The peripheral vesicles with granular content found in the zoospore are not seen in the 1° or 2° cyst. Multivesicular bodies and lomasomes are observed in the 1° and 2° cyst which are not found in the zoospore. The peripheral cisternae of the zoospore are lost upon encystment and may be formed from dictyosome–derived vesicles during excystment of the 1° and 2° cyst. The U–body of A. astaci has a paracrystalline content while the U–body of A laevis and A eutekhes has a tubular content. A microbody–lipid body complex (sensu Powell) is found in the 1° and 2° cysts of A laevis but not in A astaci or A eutekhes. The significance of the presence of a microbody–lipid body complex in a biflagellate zoospore is discussed.

Abstract: The ultrastructure of the secondary zoospores of Aphanomyces astaci and A. laevis was compared. The general appearance of the organelles and their compartmental–ization is the same, but some subtle differences were found. A. laevis has a less distinct distribution of fuzzy vesicles around the border of the water expulsion apparatus than A. astaci. The content of the U–body of the A. astaci zoospore is paracrystalline but the A. laevis U–body has a tubular content. In the peripheral cytoplasm of both species are seen vesicles with a granular content. Flattened cisternae are found in a narrow zone just below the plasmalemma. These two structures are confined to the zoospore stage of the fungi. The lipid–microbody complex of A. laevis cysts is not present in the zoospore. The ultrastructural organization of uniflagellate and bi–flagellate zoospores is compared.

Abstract: Novel features observed of the ultrastructure of secondary zoospores of Plasmodiophora brassicae were; an angle between the flagella of 30–40°; a kinetosome only 0.5 μm long; a spore discharge mechanism through aborted zoosporangia; and marked amoeboid movement and pseudopodial development.

Abstract: The flagellar apparatus of the quadriflagellate zoospores of the marine cladophoralean alga, Chaetomorpha spiralis Okamura, was compared with that of other green algae. There is a general similarity, with some important differences, to the Ulvales and siphonous green algae so far studied. Common features are the presence of a cruciate root System (4-2-4-2 type), basal body overlap, the presence of terminal caps and displacement of the upper pair of the basal bodies and four microtubular roots. On the basis of these features, it is concluded that the taxonomic affinities of C. spiralis lie with the Ulvophyceae sensu Stewart and Mattox rather than with the Chlorophyceae sensu Stewart and Mattox. In this alga two pairs of basal bodies He at obviously different levels. Basal bodies of the upper pair are disposed relevant to each other in the 11/5 o'clock direction (counter-clockwise orientation), whereas basal bodies of the Iower pair are in the 1/7 o'clock direction (clockwise orientation). We discuss the terminology of the arrangements of the flagellar apparatus components. Characteristics of the striped fibres which connect the X-membered roots to basal bodies are also discussed and this is given the name \"X-membered root associated striped band (XSB)\" to distinguish it from the rhizoplast-type System II fibres.

Abstract: Citrus pectin induces highly synchronous differentiation in populations of Phytophthora cinnamomizoospores in the absence of a host plant. This action is independent of the presence of Ca2 + in the zoospore suspension medium. Water-soluble, ethanol-insoluble material present on the surface of the plant roots also induces differentiation of P. cinnamomi zoospore populations with the same time course iis pectin. It is proposed that this material provides the natural recognition signal which induces P. cinnamomi zoospores to differentiate, and that pectin is sufficiently similar in structure for it to mimic its action.