Germination Of Sporangia Research Articles

Mode of action of the systemic fungicides furalaxyl, metalaxyl and ofurace

AbstractThe systemic fungicides furalaxyl, metalaxyl and ofurace,Ofurace is the proposed BSI and ISO common name for α‐(2‐chloro‐N‐2,6‐xylylacetamido)‐γ‐butyrolactone. used to control diseases caused by phycomycetes, were extremely active in vitro against Pythium ultimum, Phytophthora nicotianae and Phytophthora palmivora. Sporangia production was reduced more than mycelial growth but germination of sporangia and zoospores was relatively unaffected. Less than 1% of the metalaxyl or furalaxyl, present in media at the ED50 for hyphal growth, was firmly absorbed by Phyt. palmivora mycelium; uptake was against a concentration gradient and was characterised by a rapid accumulation followed by a more gradual release. Respiration and wall synthesis were not inhibited, whilst membrane permeability was unaffected. Lipid patterns were altered but these changes were probably of secondary importance. The fungicides inhibited protein and nucleic acid synthesis; RNA production was particularly affected. There was some evidence of a reduction in nuclear division. The primary effect of furalaxyl and metalaxyl probably involves impaired biosynthesis of RNA so that mitosis is inhibited; ofurace may act in the same way.

Two New Members of the Blastocladiaceae. II. Morphogenetic Responses to O 2 and CO 2

The development of Microallomyces dendroideus and Allomyces reticulatus was studied under various mixtures of O2, CO2 and N2. All thalli grown in broth or agar media in air produce abundant resistant sporangia but rarely produce any zoosporangia. In both fungi, the proportion of zoosporangia borne by the thalli increases as the oxygen level decreases. In addition, increased CO2 strongly stimulates resistant sporangium germination in M. dendroideus. Neither fungus grows in the absence of oxygen; therefore, they seem to be adapted for rapid multiplication in a microaerophilic niche.

TWO NEW MEMBERS OF THE BLASTOCLADIACEAE. II. MORPHOGENETIC RESPONSES TO O2 AND CO2

The development of Microallomyces dendroideus and Allomyces reticulatus was studied under various mixtures of O2, CO2 and N2. All thalli grown in broth or agar media in air produce abundant resistant sporangia but rarely produce any zoosporangia. In both fungi, the proportion of zoosporangia borne by the thalli increases as the oxygen level decreases. In addition, increased CO2 strongly stimulates resistant sporangium germination in M. dendroideus. Neither fungus grows in the absence of oxygen; therefore, they seem to be adapted for rapid multiplication in a microaerophilic niche.

Sporangium Germination of Peronophythora litchii, the Causal Organism of Litchi Downy Blight

SUMMARYLitchi downy blight (name proposed) is induced by Peronophythora litchii. The fungus causes fruit rot in litchi (Litchi chinensis). The cardinal temperatures for growth are 12, 28, and 32 C and for sporangium germination are 12, 28, and 36 C. The sporangia germinate by normal germ tube (direct germination) on V-8-juice agar, and by releasing zoospores (indirect germination) in water. On 2% water agar with 0–10% dextrose, more sporangia germinate directly by a normal germ tube and by production of secondary sporangia as dextrose concentration increases. As dextrose concentration decreases, more sporangia germinate by a “thin” germ tube. Germination by zoospores remains constant. Percent germination decreases as the culture ages. The chilling effect on zoospore release is most evident at 16 C for 30 min when the culture was grown at 26 C and at 12 C for that grown at 16 C. The morphology of the fungus is described briefly.

Allomyces neo-moniliformis gametogenesis

InAllomyces neo-moniliformis meiosis takes place during resting sporangium germination. The meiospores are characteristically binucleate and biflagellate as described byEmerson (1938) andTeter (1944). A variation in the number of nuclei and flagella per meiospore from two is correlated with germination of the resting sporangia under reduced oxygen tension. The meiospores are extremely poor swimmers and are typically amoeboid. At encystment the gamma bodies of the cell are mobilized and appear involved in cyst wall synthesis. A single mitotic division of each nucleus gives rise to four nuclei. Gamete cleavage is as described for spore cleavage inBlastocladiella (Lessie andLovett 1968). The assembly of the nuclear cap and side body complex of the spore are extremely late processes in gametogenesis. The gametes are released when the single papilla dissolves. The gametes fuse in pairs and after zygote formation the cell is uninucleate with two flagella. The biflagellate zygote is an active swimming cell. The presence of homothallism or hetero-thallism inA. neo-moniliformis is discussed.

Behaviour of zoosporangia and zoospores of Albugo tragopogonis in relation to infection of Senecio squalidus

Effects of temperature, light and sporangial density on sporangial germination in the Senecio race of Albugo tragopogonis were studied. In addition, the influence of inoculum density and leaf age on disease development were investigated. Patterns of zoospore encystment on the leaf surface were also noted. Optimum temperatures for sporangial germination were 10–15° and germination was unaffected by either light or sporangial density. Increasing inoculum density accelerated disease development and increased its final severity. Zoospores encysted in a non-random manner and there was evidence for the selection of stomata as settling sites. Results are discussed in relation to the behaviour of other Albugo species, particularly that of the Helianthus race of A. tragopogonis .

Behaviour of Phytophthora infestans (Mont.) de Bary on potato tubers in relation to lenticel resistance

On potato tuber surfaces at 12° and 20 °C indirect germination of sporangia of Phytophthora infestans was stimulated to levels above those in distilled water. Following indirect sporangial germination, zoospores accumulated preferentially on the lenticels. As the tuber developed and lenticels became more resistant, the number of zoospores accumulating and the proportion subsequently germinating decreased. Differences in the proportion of zoospores germinating on different cultivars were related to cultivar resistance at 20 °C but not at 12 °C. Accumulation of zoospores involved a response to a diffusible stimulus produced by the lenticels.

Uptake of streptomycin by sporangia of Pseudoperonospora humuli and the inhibition of uptake by divalent metal cations

[14C] streptomycin HCl-CaCl2 complex and streptomycin sulphate were equally toxic to sporangia of Pseudoperonospora humuli. Uptake of [14C]strepto-mycin by sporangia was rapid and was not affected by temperature between 1° and 37°. Uptake was dependent upon density of sporangia and streptomycin concentration. Heat-killed sporangia sorbed more than viable ones. Uptake was markedly reduced in the presence of divalent metal cations whereas monovalent metal cations had no effect. Ninety-five per cent of sorbed [14C]-streptomycin was removed by washing sporangia with divalent metal salts. Low concentrations of a number of divalent metal cations also prevented or reduced the inhibitory effect of streptomycin on sporangium germination whereas monovalent metal cations had less effect. The degree of interference with streptomycin inhibition of germination was dependent on salt concentration, antibiotic concentration, density of sporangia, incubation temperature and the length of time sporangia were suspended in streptomycin before the addition of metal cations. Pretreatment of sporangia of P. humuli with streptomycin markedly reduced their electrophoretic mobility. The work suggests that at least 95% of streptomycin sorbed by sporangia is bound as unchanged antibiotic to negatively charged receptor sites on the sporangium case.

Parthenin: A growth inhibitor behaviour in different organisms

Differential behavior of a growth inhibitor parthenin, has been observed. It inhibits sporangial germination and zoospore motility inSclerospora graminicola and does not exercise the same activity in the conidial development ofAspergillus flavus at the same or greater concentration.

Viability of sporangia of Phytophthora infestans in relation to drying

The effect of drying on the viability of detached sporangia of Phytophthora infestons was studied at 95 % r.h., 90 % r.h. and in a saturated atmosphere. Sporangia produced on potato plugs bore a water film which influenced the rate at which sporangial germination was eliminated. In the presence of a water film no germination occurred after drying at 95 % r.h. for 20 min whereas in the absence of this film sporangia failed to germinate after drying at g5 % r.h. for 5 min or at 90% r.h. for 2·5 min. Slow rewetting of dried sporangia which failed to germinate, or exposure to chemicals, media or host tissue failed to induce germination. Dried sporangia which failed to germinate were found to be vacuolated and the cell membranes were damaged.

Flagellum Degeneration in the Fungus Phytophthora palmivora (formerly Phytophthora parasitica)

SUMMARY: Direct sporangial germination in Phytophthora palmivora (formerly Phytophthora parasitica) is accompanied by a regular series of events leading to the complete breakdown of all flagella present in the mature sporangia. Electron microscopy of thin sections shows that the breakdown involves the cleavage of the ensheathing flagellar vacuoles into small vesicles, thus leaving the axonemes unenclosed in the cytoplasm. In a second stage the axonemal microtubules lose their parallel arrangement and gradually disintegrate. The central microtubules break down first and thus appear to be more fragile than the peripheral ones.

Coelomomyces opifexi (Pillai & Smith). Coelomomycetaceae: Blastocladiales II. Experiments in sporangial germination

Laboratory experiments on sporangial germination and zoospore activity in Coelomomyces opifexi which utilises a suparlittoral environment are described. Sporangial germination depends upon (a) salinity of the medium used and (b) whether the sporangia were derived from living or deceased larvae. Sporangia from living larvae germinated almost instantaneously in distilled, tap, brackish pond and sea water with a salinity of 4.2‰ There was only partial germination at a salinity of 17‰, and none at all in 35‰ (full sea water). Sporangia from deceased larvae required a conditioning of 7 days or more under moisture at 23°C or 28°C before germination. Sporangia from living and moribund larvae became thick-walled and darker when exposed to a salinity of 8.5‰ or higher. These, likewise, required a conditioning period for germination. The biological and ecological significance of these observations are discussed.

Some Effects of Streptomycin on Pseudoperonospora humuli, the Downy Mildew of Hop

SUMMARY: Two sprays of streptomycin (1000 μg./ml.) considerably reduce sporulation of the hop downy mildew fungus, Pseudoperonospora humuli, on leaves of primary systemically infected shoots. Streptomycin markedly inhibited germination of its sporangia in vitro. Toxicity was dependent on sporangial concentration, incubation temperature and the cleanliness of the suspension but was independent of sporangial age. There were no marked differences in sensitivity to streptomycin between sporangia from five different isolates of Ps. humuli. Two commercial formulations of streptomycin were as inhibitory to sporangial germination as pure streptomycin sulphate. Sublethal concentrations of streptomycin interfered with cleavage of sporangial cytoplasm and increased the proportion of multiflagellate zoospores.The proportion of multiflagellate multinucleate zoospores liberated was dependent on streptomycin concentration. Germination of multiflagellate zoospores was observed. Streptomycin was very inhibitory to zoospore germination but had little effect on zoospore motility and germ-tube growth at concentrations which caused a high incidence of cyst lysis. Streptomycin was as toxic to sporangia of Phytophthora infestans as to those of Ps. humuli, whereas sporangia of Plasmopara viticola and Peronospora parasitica were less sensitive to the antibiotic.

Influence of temperature upon growth and sporulation in two species of Phytophthora

The paper deals with the influence of temperature on the growth and sporulation of two species ofPhytophthora, viz.,P. palmivoraButl. andP. parasiticaDast. var.macrosporaAshby, the causal agents of fruit rots ofAchras sapota L. andAnona squamosa L. respectively. Germination of sporangia at different temperatures were also undertaken. There was marked variation in growth and sporulation of these two organisms. Isolate C (Phytophthora palmivora) showed no growth at 5° and 35°C, scanty growth at 10° and 32.5° with an optimum temperature between 26–28°C. On the other hand, Isolate S (Phytophthora parasitica var.macroscora) showed no growth at 10°C, but slight growth even at 37°C. Eight days exposure at 37°C completely stopped the growth of this Isolate. It showed best growth at 30°C and hence this was its optimum temperature. In general, Isolate C sporulated abundantly at all temperatures tested but reached its maximum at 25°C. On the other hand Isolate S showed best growth but failed to sporulate at any of the temperatures in 98 hours growth, although it sporulated freely when the incubation period extended up to two weeks. On the basis of temperature toleration the twoPhytophthora isolates are distinguished from each other as two different species. This confirms the earlier observations and nomenclature criterion as emphasized and formulated byTucker (1931). In the germination studies, it was observed that the indirect germination with the formation of abundant zoospores started from 5° and continued even up to 35°C, reaching maximum at 20°C. High temperature was not favourable for indirect germination. As the temperature proceeded increasing, the percentage of direct germination by formation of germ tubes also increased. Direct germination was observed from 10° which continued up to 37°C, with a maximum reach at 30°C. This confirms the epidemic of fruit rots in nature during monsoon season which is prevalent with the persistence of high humidity and rainfall.

Presence of a fungal inhibitor in the pericarps of Acer saccharum fruits

The present data suggest that the pericarps of Acer saccharum contain a water-soluble fungal inhibitor that protects the fruit from fungal pathogens. Aqueous pericarp extracts effectively inhibited mycelial growth of several pathogenic soil fungi, particularly species of Pythium and Rhizoctonia. The extract also controlled damping-off of Pinus resinosa seedlings and inhibited microbial respiration in nursery soil. Even at relatively low concentrations (0.003% w/v), the extract lysed germ tubes and induced morphological abnormalities. Bioassays of chromatographically partitioned extracts indicated that four major compounds were present, one capable of markedly inhibiting germination of sporangia of Pythium irregulare. Two-dimensional paper chromatography of heat-treated extracts indicated that three additional spots were present. One spot showed characteristics of gallic acid; this suggests that the inhibitor is a gallotannin.

Factors affecting sporangial germination in Albugo ipomoeae-aquaticae

Sporangia of Albugo ipomoeae-aquaticae Sawada were found to germinate indirectly by release of zoospores. At relatively low temperatures direct germination of a few sporangia was observed. Penetration of the host (Ipomoea aquatica) occurred only through the stomata. Experiments on factors affecting sporangial germination showed that, in general, sporangia of A. ipomoeae-aquaticae behaved similarly to sporangia of other Albugo spp. which have been investigated. The single exception was the effect of temperature on germination: A. ipomoeae-aquaticae sporangia germinated only between 12 and 30° C, with an optimum of about 25°. This relatively high temperature range was confirmed by inoculation studies; exposing host plants to inoculum at 25° for as little as 2 h resulted in heavy infection. The pathogen appears to be well adapted to local climatic conditions at the time when the host is most abundant.

Effect of seed exudates ofPinus resinosa on the germination of sporangia and on the population ofPythium irregulare in the soil

Exudates from germinating seed ofP. resinosa stimulated the germination of sporangia and increased thePythium populations in soil. Sporangia ofP. irregulare did not germinate in natural soil and needed exogenous nutrition for their germination. Different components of the exudate, particularly glucose and asparagine, effectively stimulated sporangial germination. This is in agreement with an earlier finding withPythium ultimum 3.

Effects of hydrogen ion concentration on Phytophthora palmivora from Piper nigrum

Three-month old pepper cuttings in nutrient solutions of pH 3·0–8·0 were inoculated with Phytophthora palmivora (Butl.) Bud. on triturated pepper roots. Death occurred after 13 days at pH 6·0, 16 days at pH 8·0 and 23 days at pH 4·5. No infection occurred at pH 3·0. In the majority of twenty isolates of the causal organism kept in Petri's solution of pH 3·0–8·0, no sporangia were produced at pH 3·0, some sporangia were produced at pH 4·5, maximum sporulation occurred at pH 6·0 and declined at pH 8·0. It is suggested that disease development is prevented at low pH due to suppression of sporulation and sporangial germination.

Phytophthora infestans sporangial germination and tuber rot reduced by soil residues of fungicides

Foliar sprays of Difolatan were equal to or slightly better than those of maneb for the control of late blight when applied at equivalent rates of active ingredient. Difolatan foliar sprays, in general, resulted in less late blight tuber rot than did maneb sprays. Foliar sprays of Bordeaux mixture or Difolatan produced residues of these fungicides in the soil. These residues were greater in the surface soil (0 to 1/2 inch depth) than in the 1 to 2 inch layer, but were not sufficient to inhibit indirect germination of the sporangia ofP. infestans in soil leachates. Similar results were obtained with applications of Bordeux mixture or Difolatan to the soil in the absence of any foliar spray. Residues from foliar sprays of Difolatan plus soil treatments of Difolatan or Bordeaux mixture, made before and after the last cultivation, inhibited indirect germination ofP. infestans sporangia in soil leachates from the surface soil, but not from the 1 to 2 inch layer of soil. Application of foliar sprays of Bordeaux mixture to plots given soil treatments of Difolatan before the last cultivation resulted in fungitoxic residues in the surface soil and in the 1- to 2-inch layer of soil, but not when Difolatan soil treatments were made after the last cultivation. Similar results were obtained when maneb foliar sprays were applied to plots that had received soil applications of Difolatan.

Accumulation of hypoxanthine in potato leaves and its effect on spore germination in Phytophthora infestans

The accumulation of hypoxanthine (6-hydroxypurine) in blighted potato leaves and its effect on spore germination in the late blight organism, Phytophthora infestans, were investigated. Preliminary experiments on the translocation of this compound in whole plants and detached leaves were also conducted.Under in vitro and in vivo conditions, hypoxanthine had a pronounced stimulatory effect on the indirect germination of sporangia. Studies on the movement of this base indicate that it is freely translocated, but fails to be exported from detached leaves into aqueous solution. These observations, coupled with the finding that hypoxanthine readily accumulated in blighted leaves, suggest that this compound could be of importance in predisposing uninfected portions of the host to invasion by the pathogen.