Fungitoxic activity of some essential oils

Of the five essential oils screened against Helminthosporium oryzae, the oils of Cymbopogon martinii (ginger grass oil), Cymbopogon oliveri, Cymbopogon sp. (rosa sofia oil) and Trachyspermum ammi (dethymolysed oil) exhibited strong fungitoxicity and showed wide range of activity. The oils were found more active than some of the prevalent synthetic fungicides and thus might be exploited as natural fungicides if successful infield trials. Besides, these oils were found toxic to various human pathogens.     

Competitive ability and ethirimol sensitivity in strains of barley powdery mildew

Strains within field populations of barley powdery mildew (Erysiphe graminis f. sp. hordei) varied greatly in their response to ethirimol. Each strain remained stable whether the fungicide was present or not, and no evidence for adaptation was obtained. Strains of intermediate sensitivity were the most frequent within the pathogen population, and these also dominated model populations maintained in the laboratory. Ethirimol eliminated sensitive strains from laboratory mixtures, and increased the relative fitness of insensitive ones, but not sufficiently to oust the intermediate strains. Mildew from treated field plots was less sensitive than that from untreated plots, but only early in the epidemic. Insensitivity was not related to the level of ethirimol used and, at four times the rate used commercially, insensitive strains were no more frequent than at lower rates. As the complexity of mildew populations increased, changes in ethirimol sensitivity in response to selection became less pronounced, and it is suggested that strains of intermediate sensitivity to ethirimol exert a stabilising effect within natural populations. This could alter if the fitness of insensitive strains were to increase, perhaps through recombination. Consideration should be given to the effect ethirimol might have on the composition of the pathogen population if applied when sexual recombination occurs, and to the role ascospores play in disease development.     

Fungitoxic and Phytotoxic Studies with Essential Oil of Ocimum adscendens

On screening the leaf extracts of some higher plants for their volatile antifungal activity against the test organism Aspergillus flavus, the extract of Ocimum adscendens exhibited the strongest fungitoxicity. The leaves showed maximum, fungitoxicity as compared with other plant parts. The volatile fungitoxic fraction obtained as an essential oil was standardized by various physico-chemical properties. The oil showed its fungicidal nature and broad range of activity at its minimum inhibitory concentration. The oil was thermostable and the toxicity remained unchanged even on autoclaving and on storage for up to 360 days. Moreover, the oil proved more active than some prevalent synthetic fungicides and exhibited no phytotoxic effect onVigna radiata.     

Fungitoxic and phytotoxic effects of fungicides controlling powdery mildew on apple

Benomyl, pyrazophos (HOE 2873), triarimol, triforine and the non-systemic fungicide diethyl phthalimidophosphonothionate (Dowco 199) were sprayed at c. 200 gal/acre (2250 1/ha) at 14-day intervals from pink bud (late April/early May) on seven apple cultivars including Cox's Orange Pippin, Golden Delicious and Jonathan. Compared with binapacryl or dino-cap (and with elemental sulphur on the sulphur-tolerant cv. Golden Delicious), these compounds were more phytotoxic without substantially or consistently improving the control of Podosphaera leucotricha; fruit russet was increased and the crop and fruit size of some cultivars were reduced in some trials. In 1969 the inclusion of bis(dimethylthiocarbamoylthio)-methylarsine (44 ppm) as Urbacid^(R) in the sprays reduced russeting by benomyl and Dowco 199 so that these fungicides became as safe as captan on several cultivars; Dowco 199 was also safened by captan (500 ppm). Urbacid^(R) (88 ppm a.i.) safened benomyl and triarimol on fewer cultivars in 1970 when russet was less severe. The addition of Urbacid^(R) did not prevent yield losses caused by sprays in either year. The crop is most sensitive to spray damage from pink bud until late June. This is a crucial period for the control of mildew, and unless new fungicides are less phytotoxic, palliatives may become necessary adjuvants.     

Fluxes and accumulation of ethirimol in haustoria of Erysiphe pisi and protoplasts of Pisum sativum

Isolated purified fractions containing haustorial complexes and mesophyll protoplasts were used to investigate the relative affinities in vitro of the host-parasite interface and host for the mildew specific fungicide, ethirimol. Compounds labelled with [¹⁴C] were used throughout this study. Isolated haustorial complexes accumulated fungicide against a concentration gradient and, in 15 min, to much higher concentrations than they accumulated glucose, sucrose, uracil, glycine, ethanolamine hydrochloride, inulin carboxylic acid, thiocyanate ions or uridine diphosphate glucose. Accumulation of ethirimol ceased after 30 min when the internal concentration was over twenty times greater than in the ambient medium. Similar quantities were absorbed in 15 min at pH 4.2 and 6–2. The quantities absorbed during 1 h incubation were directly related to the ambient concentration (4–400 μm). Ethirimol introduced into haustorial complexes was easily removed by washing; one third was removed in the first 5 min and only one sixth of the original remained after 3 h. Analysis of the kinetics of ethirimol efflux showed that it was located in two compartments within the complexes; thus it most probably entered the fungal cytoplasam. Ethirimol entered pea mesophyll protoplasts showing biphasic kinetics with considerable uptake in the first 30 min and a more gradual influx during the following 18 h. It was not accumulated against a concentration gradient until 6 h and after 18 h the internal concentration exceeded that of the ambient by only 1.74 fold. Extraction and chromatography showed that only small proportions of the ethirimol were degraded by haustorial complexes and protoplasts during the experimental periods. These in vitro experiments indicate competitive accumulation of ethirimol by the host-parasite interface in vivo.     

Fungitoxic effect of some derivatives of substituted phenoxyacetic acids

Фунгистатическое действие соединс-н ий mетил-, этил-,-пропил-, изопро-п ил- и -бутил-эфиров следующих к0438;с-лот: 2-mетокс ифеноксиуксусной, 3-mето- ЗамеЧаниЯ по вопросу ΟτноШения между проницаемосτьы И жизнеспосое‐ Ηосτьы) Κлеτок дрожжей Л. ΜобаЧ Β. ΚоеаЧоеа При инкубации с дезоксихолаτом йлеτки дрожжей сτановяτся пронииае – мыми для солей янτарной кислоτы и для феррицицианида. Через некоτорое ремя клеτки погибаыτ И ок осн овными краси τлями. Так как кор – реляции между прони даемосτьы и окра– Шиваемосτьы клеτок не наблыдалось, выскаываеτся предположение, Чτо при ЧасτиЧном разр уШении барьера пр они – даемосτи клеτки в τеЧние некоτорого времени могуτ осτаваτься живыми.     

Comparative Fungitoxic and Plant Growth Regulating Properties of Triazole Derivatives

The triazol derivatives, S-3307, S-3308, triadimefon, triadimenoland paclobutrazol are recommended for use as either fungicidesor plant growth regulators. However, in varying degrees theyexhibit both properties. In a comparative study with 5 differentfungi, S-3308 followed by S-3307 were the most fungitoxic (invitro) whereas S-3307 and paclobutrazol were the most activeplant growth retardants in bean (Phaseolus vulgaris L.) andKentucky bluegrass (Poa pratensis L.). (Received September 24, 1985; Accepted November 26, 1985)     

Fungitoxic effects of extracts from some West African plants

Extracts from five West African plants were evaluated in vitro for fungitoxicity against Ustilago maydis, Ustilaginoidea virens, Curvularia lunata and Rhizopus sp. Steam distillate from leaves of Cymbopogon citratus completely inhibited the growth of all four fungi, and hot water extracts from fresh leaves of Ocimum gratissimum and Chromoleana odorata, and dry fruits of Xylopia aethiopica, reduced radial growth by 10–60%. A hot water extract from dry fruits of Monodera myrstica was ineffective as a fungitoxicant.     

Fungitoxic dihydrofuranoisoflavones and related compounds in white lupin,Lupinus albus

Chromatographic investigation of a methanolic extract of white lupin roots has revealed the presence of six new dihydrofuranoisoflavones (lupinisoflavones A-F). Three monoprenylated (3,3-dimethylallyl-substituted) isoflavones (wighteone, luteone and licoisoflavone A), two diprenylated isoflavones [6,3′-di(3,3-dimethylallyl)genistein (lupalbigenin) and 6,3′-di(3,3-dimethylallyl)-2′-hydroxygenistein (2′-hydroxylupalbigenin)] and two pyranoisoflavones (parvisoflavone B and licoisoflavone B) have also been isolated from the same source. In addition to genistein, leaf extracts of L. italbus contain 3′-O-methylorobol which is presumed to be the precursor of lupisoflavone [5,7,4′-trihydroxy-3′-methoxy-6-(3,3-dimethylallyl)isoflavone]. Probable biogenetic relationships between the prenylated, and dihydrofurano-and pyrano-substituted isoflavones in roots and leaves of L. albus are briefly discussed.     

Synergistic Mixtures of Fungitoxic Monochloro and Dichloro-8-Quinolinols against Five Fungi

Fourteen mono- and dichloro-8-quinolinols were tested against five fungi (Aspergillus niger, A. oryzae, Myrothecium verrucaria, Trichoderma viride, and Mucor circinelloides) and compared with the fungitoxicity of 8-quinolinol in Yeast Nitrogen Base containing 1% D-glucose and 0.088% L-asparagine. All of the compounds were more fungitoxic than 8-quinolinol except for the surprising activity of 8-quinolinol against A. oryzae. Mixtures of the MICs of monochloro- and dichloro-8-quinolinols in which the halogens were in different positions of the quinoline ring showed synergism. Comparable mixtures in which one position of each compound was occupied by the same halogen showed additive activity. In a different study we showed that 3,5,6-, 3,5,7-, 4,5,7-, and 5,6,7-trichloro-8-quinolinols were not toxic to M. circinelloides, whereas the combinations of the correspondingly substituted mono- and dichloro-8-quinolinols as well as 3,6-dichloro- and 5,7-dichloro-8-quinolinols were inhibitory. This indicated that a steric factor can be involved in affecting fungitoxicity.     

Germination and growth of single-pustule isolates of Erysiphe graminis tolerant and sensitive to tridemorph and ethirimol

The germination and colony growth of single-pustule Erysiphe graminis isolates tolerant and sensitive to tridemorph and ethirimol was studied on glass slides and on leaf segments sprayed with tridemorph or left untreated. In the absence of the fungicide, neither tridemorph- nor ethirimol-tolerant isolates differed from the sensitive in germination or colony growth. Germination percentages of all isolates were depressed by high temperature and low humidity, although some isolates grew well in less than optimum conditions. Differences between ethirimol- and tridemorph-tolerant and sensitive isolates for colony size on untreated plants of various cultivars reflected differences in virulence to the host rather than fungicide tolerance. The presence of tridemorph retarded the growth rate of colonies of tolerant and sensitive isolates, but the germination of tridemorph-tolerant isolates was greatly stimulated by low concentrations of tridemorph (50 mg/litre) and was less depressed than that of the sensitive isolates by high concentrations (200 mg/litre).     

Fungitoxic and phytotoxic effect of some surface-active agents applied for the control of apple powdery mildew

Mixtures of methyl esters of fatty acids (‘Off-Shoot O’) and mixtures of fatty alcohols (‘Off-Shoot T’), applied during the late autumn (November), eradicated apple powdery mildew (caused by Podosphaera leucotricha) from infected buds. Applications in the spring at bud-burst were less effective. The autumn sprays caused little damage to the cultivars Bramley's Seedling, Cox's Orange Pippin and Golden Delicious but on Worcester Pearmain 50% of the buds were killed by a 5% Off-Shoot O spray. The bud-burst sprays were damaging and reduced yield on the Cox and Bramley trees. A 5% a.i. mixture of nonanol/lissapol applied to a range of commercial cultivars was effective in eradicating powdery mildew but was more phytotoxic than the Off-Shoot compounds. Spraying Cox trees later in the winter failed to reduce the damage. Eradication of the overwintering stage of the disease resulted in low spore concentrations during the following spring and early summer, enabling some economies to be made in the summer mildew fungicide programme.     

Studies on the Mode of Action of Tomatine as a Fungitoxic Agent

Removal of 1 or more sugar residues from the alpha-tomatine molecule markedly decreased its fungitoxicity. While partial hydrolysis of alpha-tomatine did not greatly affect its surfactant properties, it did destroy the ability of this alkaloid to form a complex with cholesterol. Only unprotonated alpha-tomatine was capable of binding cholesterol; the protonated form did not. Since alpha-tomatine was far more toxic at a high pH than at a low pH, this suggests that the unprotonated alkaloid is the active form and that it acts by complexing with fungal sterols.     

Fungitoxic effects of some leaf extracts against rhizopus oryzae causing tuber rot of potato

Extracts of Cymbopogon citratus, Azadirachta indica (Neem) and Ocimum gratissimum were effective in controlling the growth of Rhizopus oryzae in vitro and in vivo. Neem was found to be the best followed by C. citratus and O. gratissimum. Alcohol extracts of these plant species were more effective than water extracts in reducing the growth of the pathogen in culture and in checking rot development in potato tuber by the fungus. A. indica and C. citratus have considerable disease control potential and their extracts can be exploited as a source of pesticide of plant origin to control the soft rot in stored potato incited by Rhizopus oryzae.     

Fungitoxic Effects of Extracts of Azadirachta Indica against Cochliobolus Miyabeanus causing Brown Spot Disease of Rice

The oil extract from seeds of Azadirachta indica as well as water and ethanol leaf extracts of the plant were effective in reducing the radial growth of Cochliobolus miyabeanus in culture and in checking the spread of brown spot disease in rice. The oil extract was found to be the most effective, followed by ethanol leaf extract, in inhibiting the growth of the pathogen in vitro and in checking the development of the disease in vivo . Although the cold water extract from the plant leaf reduced the radial growth of the pathogen in culture, it failed to reduce the incidence and severity of the disease as effectively as the oil and ethanol extracts. The oil and ethanol extracts compared favourably with carbendazim (Bavistin) at 0.1% a.i and have the potential for control of brown spot disease of rice in the field.     

Role of Zearalenone Lactonase in Protection of Gliocladium roseum from Fungitoxic Effects of the Mycotoxin Zearalenone

Zearalenone is a mycotoxin with estrogenic effects on mammals that is produced by several species of Fusarium. We found that zearalenone and its derivatives inhibit the growth of filamentous fungi on solid media at concentrations of ≤10 μg/ml. The fungitoxic effect declined in the order zearalenone > α-zearalenol > β-zearalenol. The mycoparasitic fungus Gliocladium roseum produces a zearalenone-specific lactonase which catalyzes the hydrolysis of zearalenone, followed by a spontaneous decarboxylation. The growth of G. roseum was not inhibited by zearalenone, and the lactonase may protect G. roseum from the toxic effects of this mycotoxin. We inactivated zes2, the gene encoding zearalenone lactonase in G. roseum, by inserting a hygromycin resistance cassette into the coding sequence of the gene by means of Agrobacterium tumefaciens-mediated genetic transformation. The zes2 disruption mutants could not hydrolyze the lactone bond of zearalenone and were more sensitive to zearalenone. These data are consistent with a hypothesis that resorcylic acid lactones exemplified by zearalenone act to reduce growth competition by preventing competing fungi from colonizing substrates occupied by zearalenone producers and suggest that they may play a role in fungal defense against mycoparasites.     

Fungitoxic properties of selected South African plant species against plant pathogens of economic importance in agriculture

Thirty‐nine plant species, representing 20 families from the subclasses Rosidae, Asteridae, Commelinidae and Liliidae, were collected from the Blyde River Canyon Nature Reserve, Mpumalanga, South Africa. Crude extracts were prepared and bioassayed, at equal concentrations, for their antifungal potential by determining the inhibitory effects on the mycelial growth of seven economically important plant pathogenic fungi. Statistically significant differences between plants and plant parts were observed as well as the resistance of different fungi to treatment with different plant extracts. The most significant mycelial growth inhibition was obtained with extracts from two species of the subclass Liliidae, namely Aristea ecklonii and Agapanthus inapertus. The crude extract of A. ecklonii performed best of all extracts as it totally inhibited the mycelial growth of all seven of the plant pathogenic test organisms and outperformed the inhibition by a broad spectrum synthetic fungicide (carbendazim/difenoconazole). Crude extracts of A. inapertus showed complete inhibition of four and strong inhibition of the remaining three plant pathogenic fungi. Although not as efficient as the previous two species, the extract of Anisopappus junodii, from the subclass Asteridae, also showed promising antifungal activity by completely inhibiting mycelial radial growth of two and strongly inhibiting that of the remaining five fungi.