Germination Of Sporangia Research Articles

Coelomomyces psorophorae vartasmaniensis Couch+Laird (1988) (Coelomomycetaeceae: Blastocladiales), a fungal pathogen of the mosquitoAedes australis

The germination of sporangia in Coelomomyces psorophorae var tasmaniensis (C. p. tas.) is uncoordinated and thus there is a mixture of developmental stages in any given population. Continuous urografin gradients separated out the critical stages of germinating sporangia giving four bands, each band representing a consecutive stage of germination. These stages were investigated for changes in the sporangial wall using Transmission Electron Microscopy (TEM). The sporangia have a typical two-layered wall, an electron dense outer layer which can be divided into three distinct sub-layers D1, D2, and D3 and an inner electron transparent secondary wall. Stage 3 sporangia have an intact D1 layer on their outer wall. In the subsequent stages (4 & 4b) there is a progressive breakdown of this layer.

Coelomomyces psorophorae vartasmaniensis Couch+Laird (1988) (Coelomomycetaeceae: Blastocladiales), a fungal pathogen of the mosquitoAedes australis

The presence of synaptonemal complexes were checked in dividing chromosomes as evidence for meiotic division in germinating sporangia. Continuous urografin gradients were used to separate out the various phases of germinating sporangia, the nuclei were removed and embedded for ultrastructural studies. Meiotic inhibitors were applied to germinating sporangia to retard meiotic division to highlight the synaptonemal complexes. At an early phase of sporangial differentiation dividing nuclei developed with synaptonemal complexes. Meiotic inhibitors and stimulators may be used to control sporangial germination for an induction of a high meiospore count. This may be of crucial importance in the utilization of Coelomomyces spp. as a biological control agent of mosquito species.

Influence of tobacco leaf surface chemicals on germination ofPeronospora tabacina adam sporangia

Chromatographic procedures were utilized to isolate and purify components of tobacco cuticular extracts and leaf surface chemicals.In vitro microbial bioassays determined the influence of these leaf surface compounds on germination and germ tube morphology ofP. tabacina sporangia, the tobacco blue mold pathogen, and to a lesser extentAlternaria alternata, the tobacco brown spot pathogen. Exposure to 10 μg/cm(2) of α- and β-duvatrienemonols, sucrose esters, or hydrocarbons did not inhibit germination, whereas germination was significantly decreased bycis-abienol.cis-Abienol did not inhibit sporangial germination when combined with sucrose esters or hydrocarbons at a combined 10 μg/cm(2). Germination of sporangia was completely inhibited by α- and β-duvatrienediols. In contrast to a previous report, α-DVT-diol was more inhibitory than the β isomer. Toxic effects of the DVT-diols were not altered by pH. Diluting the DVT-diols to less than 0.1 μg/cm(2) resulted in a small but significant stimulation of germination. Previously, the DVT-diols had been identified only as inhibitory toP. tabacina. None of the leaf surface chemicals affected germination ofA. alternata conidia.

Effect of temperature and light on sporangial germination and zoospore infectivity inSclerospora graminicolaon pearl millet

The effects of temp. on germination of S. graminicola sporangia (zoospore release), zoospore viability and germ tube growth, and of light and temp. on zoospore infectivity and downy mildew development in pearl millet (Pennisetum glaucum [P. americanum]) were studied. Germination of sporangia was highest at c. 30 deg C and little germination occurred after 2 h 40 min. Germ tubes grew at 15-35 deg . Zoospores retained high infectivity ( more than or equal to 70% systemic infection ) for 4 h at 30 deg C, and for a longer time at lower temp. Zoospore infectivity was not affected by light. The shortest incubation period (3 d) and the highest infectivity (66%) were obtained at 30 deg . Although both roots and shoots of young seedlings were susceptible, incidence of downy mildew was highest when both were inoculated

Toxicity of propamocarb to the late blight fungus on potato

Propamocarb (Previcur-N; propyl-[3-dimethylamino-propyl] carbamate-monohydrochloride) was testedin vivo against 32 field isolates ofPhytophthora infestans from six countries. Fungicide dosages required to achieve 90% control of the blight ranged between 676 and 1530 ppm a.i. in potted potato (cv. ‘Alpha’) plants and between 1135 and 2648 ppm in potato tuber slices. Isolates from Israel were less sensitive to the fungicide than isolates from Europe or North America. Toxicity of propamocarb was not related to resistance or sensitivity to phenylamide fungicides (e.g. metalaxyl). Nevertheless, most metalaxyl-resistant isolates from Israel were less sensitive to propamocarb than most metalaxyl-sensitive isolates from this country. Monocyclic epidemics conducted with the 20 Israeli isolates in the field showed that 1081–2012 ppm of the fungicide was required to achieve 90% control of the disease. Laboratory experiments revealed that the fungicide was poorly active against sporangial germination and had a limited curative efficacy. It exhibited a translaminar translocation in leaves but a poor acropetal or basipetal systemicity from foliage. Propamocarb + mancozeb mixtures (1:1, v/w) were synergistically effective in controlling the blight. Growers in Israel use tank mixtures of propamocarb (Dynone) and mancozeb to combat late blight in potato fields where phenylamide-resistant isolates ofP. infestans are prevalent.

Effect of Extracellular Metabolites fromGliocladium virenson Germination of Sporangia and Mycelial Growth ofPythium ultimum

Culture supernatants from G.v. grown in 5% bran extract or in minimal medium supplemented with autoclaved hyphae of P.u. inhibited sporangial germination and mycelial growth of P.u. They contained gliotoxin and laminarinase, amylase, carboxymethylcellulase, chitinase and protease activities. They remained inhibitory after the above enzyme activities were inactivated by heating or removed by size-fractionation. Grown in the supplemented minimal medium, which did not contain these enzyme activities, they strongly inhibited sporangial germination and mycelial growth (...)

Infectivity to Potato, Sporangial Germination, and Respiration of Isolates ofPhytophthora infestansfrom Metalaxyl-Sensitive and Metalaxyl-Resistant Populations

Lesions developed on significantly larger proportions of inoculated leaflets on plants inoculated with metalaxyl-resistant (MR) isolates and maintained for 3, 6, or 9 hr in a moisture-saturated atmosphere than on plants similarly inoculated with metalaxyl-sensitive (MS) isolates. Germination tests in distilled water at 16 C revealed a significantly faster rate of zoospore liberation from MR than from MS sporangia at 60-150 min, but not at 240 min. Sporangia of the MR isolates consumed more than three times as much oxygen during zoosporogenesis as sporangia of the MS isolates. We propose that the greater infectivity of MR sporangia compared with MS sporangia results from faster indirect germination

The formation of secondary sporangia by Pythium ultimum: The influence of organic amendments and Pythium nunn

Sporangia of Pythium ultimum were placed in polycarbonate membrane sandwiches and buried in raw Nunn sandy loam amended with increasing concentrations of bean leaves, oatmeal, glucose + l-asparagine (4:1 w/w) or glucose alone. After 24 h, there was a significant negative correlation between the concentration of substrates added to the soil and the formation of secondary sporangia. Glucose + l-asparagine also inhibited the formation of secondary sporangia in an axenic system. The formation of secondary sporangia in soil amended with P. nunn (300 cfu g −) + 0.3% (w/w), bean-leaf or oatmeal was significantly greater than in the amended treatments without P. nunn at 7, 14 and 21 days after amendments were added to the soil. Results suggest that competitive saprophytric activity of P. nunn rapidly depletes substrates usually utilized by P. uttimum. This results in sporangial germination then immediate formation of survival structures (in some instance of lower inoculum potential) by the latter fungus.

Studies on the mechanism of action of cymoxanil in Phytophthora infestans

Colony growth and germ tube emergence of sporangia and encysted zoospores of Phytophthora infestans were highly sensitive to cymoxanil (ED 50 0.5–1.5 μg/ml), whereas differentiation of sporangia and zoospore release were insensitive at concentrations up to 100 μg/ml. Treated sporangia did not show distorted germ tubes. Oxygen consumption for glucose oxidation by germinating sporangia and zoospore motility were not inhibited at concentrations up to 100 μg/ml. Cymoxanil hardly affected the uptake of radiolabeled precursors of DNA, RNA, and protein at concentrations up to 100 μg/ml. Incorporation of [ 14C]phenylalanine into protein was completely insensitive. RNA synthesis as measured by [ 3H]uridine incorporation was differentially inhibited in the various developmental stages of the fungus. Inhibition did not occur at differentiation of sporangia, whereas at cyst and sporangial germination and mycelial growth this process was inhibited 20–45% at a concentration of 100 μg cymoxanil/ml. Endogenous RNA polymerase activity of isolated nuclei was not inhibited by cymoxanil. DNA synthesis as measured by [ methyl- 3H]thymidine incorporation was inhibited 20–80% at the various stages of development at cymoxanil concentrations higher than 10 μg/ml. Metalaxyl, a specific inhibitor of ribosomal RNA synthesis, inhibited [ 3H]uridine incorporation 40–60% at all developmental stages. The data suggest that although DNA synthesis is affected more than RNA synthesis, inhibition of both biosynthetic processes is a secondary effect. The primary mode of action of cymoxanil thus remains unknown.

Factors affecting the survival of metalaxyl-resistant strains ofPhytophthora infestans (Mont.) de Bary in Ireland

Five metalaxyl-resistant and five sensitive isolates ofPhytophthora infestans were compared for sporangium production per unit leaf area, sporangium germination and virulence to foliage and to tubers. Differences between the two groups of isolates were significant for sporangium production per unit leaf area only. The metalaxyl-resistant strains produced fewer sporangia per unit leaf area than the metalaxyl-sensitive strains. The implications under field conditions are discussed.

Removal of duvatrienediols from the surface of tobacco leaves increases their susceptibility to blue mold

Dipping leaf strips of greenhouse or field-grown tobacco ( Nicotiana tabacum L., cv. Ky-14) plants into acetone for 1 s, prior to inoculation with sporangia of Peronospora tabacina Adam, increased their susceptibility to blue mold. Disease severity and sporangial production on leaf discs from acetone-treated leaves were markedly increased compared to those on discs from untreated leaves. Treatment with acetone also decreased variation in susceptibility of leaves from plants of various ages. Disease severity on discs obtained from attached leaves which were dipped in acetone for 1 s was three times greater up to 15 days after dipping than on discs from leaves that were not dipped. TLC and GLC analyses of the acetone extracts indicated that 95% or more of the major cuticular diterpenoids, α- and β-4,8,13-duvatriene-1,3-diols (DVT), were removed from the surface by dipping for 1 s. These compounds had not reappeared on the leaf surface 15 days after leaves were dipped in acetone for 1 s. Aqueous suspensions of the acetone-soluble constituents as well as authentic DVT, inhibited sporangial germination of P. tabacina (ED 100 = 25 ppm) and the antifungal activity was accounted for by DVT. When DVT was removed from a leaf surface and added back to the same leaf strip, the resistance of the leaf tissue was restored. As tobacco plants aged, their susceptibility to blue mold decreased and the quantity of DVT on the leaf surface increased. The data support a role for DVT in the resistance of tobacco against blue mold.

Influence of Acidity Level in Simulated Rain on Disease Progress and Sporangial Germination, Infection Efficiency, Lesion Expansion, and Sporulation in the Potato Late Blight System

Influence of Acidity Level in Simulated Rain on Disease Progress and Sporangial Germination, Infection Efficiency, Lesion Expansion, and Sporulation in the Potato Late Blight System

Effect of Aliette on Bremia lactucae on lettuce

Aliette is a systemic fungicide effective against diseases caused by lower fungi but there is some question whether it acts directly on pathogens or indirectly via host defence. Downy mildew development on lettuce cotyledons was markedly decreased by application of 100–500 μg Aliette, active ingredient (a.i.), ml −1 to roots. Sporangial germination on glass and cotyledons was prevented by direct application of 10 and 25 μg Aliette ml −1 respectively. Germ-tube growth and penetration into cotyledons were markedly decreased when 25 μg Aliette ml −1 was applied directly 2 h after sporangial inoculation. The size of secondary vesicles and growth of intercellular hyphae in cotyledons were markedly affected when 250 μg Aliette ml −1 was applied 4 h after sporangial inoculation. Hyphal growth was seen to be affected 24 h later; a low incidence of necrosis of host cells was observed after a further 24 h. The findings gave reason to believe that Aliette acted directly on the pathogen in this system.

Activation of superoxide generation and enhancement of resistance against compatible races of Phytophthora infestans in potato plants treated with digitonin

Application of digitonin to the leaf surface of potato plants was demonstrated to activate O 2 − generation of the leaf tissues as determined by extracellular cytochrome c reduction which was inhibited by superoxide dismutase (SOD). Protoplasts prepared from stem shoots of potato enhanced NADPH-dependent reduction of extracellular cytochrome c immediately after being treated with digitonin. The reduction was also inhibited by SOD. The similar activation of SOD-sensitive cytochrome c reducing activity was observed in leaves or protoplasts of some other plants treated with digitonin. Potato leaf tissues pre-treated with digitonin by application to the upper or lower surfaces, or through the petiole, were protected from disease caused by infection with compatible races of Phytophthora infestans. Treatment of the wound surface ofpotato tuber tissue with digitonin induced the generation of the superoxide anion and, at the same time, sporangial germination, appressorial formation and invasion by P. infestans was greatly reduced. This effect was partially negated by the presence of SOD in the inoculum and seemed not to depend on antifungal compounds. These results suggest that plant tissues possess an O 2 − generating NADPH oxidase which is activated by digitonin and that its activation in potato may contribute to an enhanced resistance against attack by compatible races of P. infestans at pre- or post-infection stages.

Comparative Studies of the in Vitro Activity of the Fungicides Oxadixyl and Metalaxyl

The two phenylamide fungicides oxadixyl and metalaxyl were compared in vitro with respect to their activity against a diversity of zoosporic fungi and representative higher fungi. The spectrum of activity of these fungicides, formerly thought to inhibit only members of the Peronosporales, was expanded to include Pythiopsis cymosa in the Saprolegniales and Lagenidium giganteum in the Lagenidiales, both fungi that cannot synthesize their own sterols as is the case with members of the Peronosporales. Zoophagus insidians, a member of the Peronosporales that makes ergosterol, was insensitive to oxadixyl and metalaxyl. The Hyphochytriomycetes showed a sensitivity intermediate between that of sensitive fungi and that of the higher fungi. Different genera and different species among sensitive fungi had varying degrees of sensitivity to oxadixyl and metalaxyl. Sensitivity was also influenced by incubation time, growth medium, and incubation temperature. Stages in the life cycle of Phytophthora palmivora that were sensitive to oxadixyl and metalaxyl included vegetative growth, sporan? gium formation, and sporangium germination. Zoospore behavior, encystment, and cyst germination were not influenced by the two fungicides. Inhibition of germling growth by metalaxyl began less than 90 min after cyst germination. Mitotic divisions occurred at con? centrations ofthe fungicides that gave a 50% inhibition of growth. The results are compared with those of other workers and the significance of the results with respect to control and possible mechanisms of action is discussed.

Effect of Chloramphenicol and Streptomycin on Developmental Stages of Phytophthom infestans

Chloramphenicol and streptomycin inhibited vegetative growth and sporulation of wild-type isolates of Phytophthora infestans (B.25, C1234, respectively) but not the corresponding resistant isolates (Cr, Sr), or a streptomycin-dependent mutant (Sd); in the latter streptomycin was stimulatory. Chloramphenicol inhibited zoospore release in B.25 and Cr but direct sporangial germination of Cr was reduced only at high concentrations. Streptomycin inhibited zoospore release and direct sporangial germination equally in wild-type and Sr. Chloramphenicol was fungistatic, whereas streptomycin was fungistatic or fungicidal, depending on its concentration and length of incubation with the fungus. Delayed addition of antibiotics to liquid cultures of the wild-type isolates reduced growth inhibition.

Effects of atmospheric water potentials, free water, and temperature on production and germination of sporangia inPeronospora parasitica

Effects of atmospheric water potentials, free water, and temperature on production and germination of sporangia in<i>Peronospora parasitica</i>

Control of pearl millet downy mildew caused by Sclerospora graminicola with systemic fungicides in an artificially‐contaminated plot

SUMMARYAmong four fungicides, viz. metalaxyl (two formulations), fosetyl‐Al, pro‐pamocarb and cyomaxanil tested in vitro against sporangial germination inhibition of Sclerospora graminicola, cyomaxanil was found to be most inhibitory. In an artificially contaminated plot, when used as seed treatment or foliar spray for the control of downy mildew of pearl millet, only metalaxyl was effective.Metalaxyl 25 (Ridomil) and metalaxyl 35 (Apron) seed treatments protected the pearl millet plants from downy mildew up to 30 days. As a foliar spray, metalaxyl 25 used once at 20 days or twice after 20 and 38 days of plant growth gave less disease at harvest time. Seed treatment (metalaxyl 25 or 35) followed by one metalaxyl 25 spray was found to be effective in controlling the downy mildew. These treatments improved the growth of plants and yield significantly.

Screening soils for suppressiveness to Rhizoctonia solani and Pythium splendens.

Growth of mycelia and germination of sporangia amended with root extract on soil surface were used to detect soils suppressive to Rhizoctonia solani and Pythium splendens, respectively. In tests with 30 soil samples collected from various locations in Hawaii, 5 inhibited growth of R. solani more than 50% and 8 inhibited sporangial germination of P. splendens more than 50% as compared with conducive soil. Three of the soils were suppressive to both R. solani and P. splendens. Steaming the soil for 10-15min at 97-98C eliminated suppressiveness as evidenced by no reduction of either mycelial growth of R. solani or sporangial germination of P. splendens. Steam treatment reduced populations of fungi, actinomycetes, and bacteria in suppressive soils to approximately 0.04%, 1% and 5%, respectively, of the original numbers. Propylene oxide treatment and autoclaving increased inhibition on some soils. Similar effects were not found on steam-treated soils. The results indicate that suppressive soils may exist in small islands in a field and that the degree of suppressivenss variees from location to location.

Viability and infectivity of zoospores ofSclerospora graminicola (Sacc.) Schroet in the soil

In the present study an attempt has been made to establish the fate of sporangia ofSclerospora graminicola (Sacc.) Schroet deposited in the soil. A technique has been standardised to demonstrate the germination of sporangia and the viability and infectivity of zoospores in the soil under laboratory conditions. For how long the zoospores remain motile in the soil is one of the many unanswered questions in the zoospore biology. From the present study it is seen that, the sporangia can germinate in the soil and liberate zoospores. The zoospores can move against gravity, remain viable and infective for 5 hrs in the soil. Survival of zoospores in the soil indicated that, they may serve as a potential secondary source of inoculum through soil under field conditions.