INVESTIGATIONS ON FUNGICIDES. I. FUNGICIDAL AND SYSTEMIC FUNGICIDAL ACTIVITY IN CERTAIN ARYLOXYALKANECARBOXYLIC ACIDS

Fifty-four aryloxyalkanecarboxylic acids have been examined as systemic fungicides. Of these, four which produced negligible damage in broad-bean seedlings yet conferred systemic fungicidal protection to broad beans against Botrytis fabae and to tomatoes against Alternaria solanixvere studied in detail. The direct fungicidal activity of twenty compounds was assessed against B. fabae and Pythium ultimum. No correlation between fungicidal and systemic fungicidal action toward B. fabae was established. Other possibilities regarding their mode of action as systemic fungicides are discussed. The systemic fungicidal activity of a-phenoxyziobutyric and 2:4:6-trichlorophenoxyacetic acids in beans and of the latter compound in tomato plants was found to depend upon seasonal factors, but for 3-phenoxybutyric and 5-phenoxycaproic acids such variation was not observed. Results obtained in the bean test by two methods of assessment were found to correlate. The potato petiole test (van Raalte) for assessing systemic fungicidal activity was studied and modified. Evidence was obtained that the results might be unreliable owing to toxic effects produced by the compounds on the petiole tissue. Attempts were made to avoid this complication, but when phytotoxicity was eliminated, little fungicidal activity was shown.     

INVESTIGATIONS ON FUNGICIDES II. ARYLOXY- AND ARYLTHIO-ALKANECARBOXYLIC ACIDS AND THEIR ACTIVITY AS FUNGICIDES AND SYSTEMIC FUNGICIDES

A wide range of aryloxyacetic acids and corresponding acids with alkyl groups in the side chain, their arylthio- analogues and the antibiotic griseofulvin have been assessed in the plate test for fungistatic effect on six fungi, and as systemic fungicides against Botrytis fabae in broad beans and Alternaria solani in tomatoes. The results indicate that in general, arylthio- derivatives are more fungicidal than their aryloxy- analogues. The systemic fungicidal performance of x-(2-chlorophenylthio)propionic acid in the tomato test at 1–100 p. p. m. was found to be of the same order as that shown by griseofulvin at 50–500 p. p. m. Variable results were obtained with griseofulvin in the tornato test and its performance in the bean test was consistently poor. Further evidence is presented which indicates that the protection conferred by certain compounds may not be due to activity per se .     

Induction of systemic protection against rust infection in broad bean by saccharin: effects on plant growth and development

Here, we examine the effect of saccharin on the induction of systemic resistance in broad bean (Vicia faba) to the rust fungus Uromyces viciae-fabae. Saccharin was applied to beans at the three-leaf stage, either as a soil drench or by painting the solution on to first leaves. Plants were then challenge inoculated with the rust 1, 6, 10 and 14 d following saccharin treatment, after which they were harvested, assessed for the intensity of rust infection and plant growth measurements conducted. Foliar application of saccharin did not induce systemic protection to rust infection until 14 d after application and was less effective than saccharin applied as a soil drench. When saccharin was applied as a drench, systemic protection was not observed until 6 d after application, but was still apparent in plants 14 d after application of the drench. Irrespective of the method of application, saccharin had no significant effect on fresh and dry weights or leaf area of the plants. Saccharin applied as a drench did, however, reduce the number of leaflets produced.     

INVESTIGATIONS ON FUNGICIDES

Twenty (aryloxythio)trichloromethanes were examined for in vitro fungicidal activity against six fungi. All compounds showed a direct fungistatic effect and some exhibited a marked fumigant action. Good protectant action against Alternaria solani on tomato and Botrytis fabae on broad bean was obtained with certain compounds, but none was better than the three standard protectants used for comparison. When supplied to plants through their roots, eight conferred significant systemic fungicidal protection against Alternaria solani in tomato, but there was no significant protection against Botrytis fabae in broad bean. In preliminary tests the 2:4:5-trichlorophenoxythio analogue gave promising results when examined as a fumigant fungicide for eradication of downy mildew in lettuce plants, for reducing lenticel rot in stored apples and for preventing blue-mould in oranges.     

Tobacco plants epigenetically suppressed in phenylalanine ammonia-lyase expression do not develop systemic acquired resistance in response to infection by tobacco mosaic virus

The response of tobacco (Nicotiana tabacum L. cv. Xanthinc) plants, epigenetically suppressed for phenylalanine ammonia-lyase (PAL) activity, was studied following infection by tobacco mosaic virus (TMV). These plants contain a bean PAL2 transgene in the sense orientation, and have reduced endogenous tobacco PAL mRNA and suppressed production of phenylpropanoid products. Lesions induced by TMV infection of PAL-suppressed plants are markedly different in appearance from those induced on control plants that have lost the bean transgene through segregation, with a reduced deposition of phenofics. However, they develop at the same rate as on control tobacco, and pathogenesis-related (PR) proteins are induced normally upon primary infection. The levels of free salicylic acid (SA) produced in primary inoculated leaves of PAL-suppressed plants are approximately fourfold lower than in control plants after 84 h, and a similar reduction is observed in systemic leaves. PR proteins are not induced in systemic leaves of PAL-suppressed plants, and secondary infection with TMV does not result in the restriction of lesion size and number seen in control plants undergoing systemic acquired resistance (SAR). In grafting experiments between wild-type and PAL-suppressed tobacco, the SAR response can be transmitted from a PAL-suppressed root-stock, but SAR is not observed if the scion is PAL-suppressed. This indicates that, even if SA is the systemic signal for establishment of SAR, the amount of pre-existing phenylpropanoid compounds in systemic leaves, or the ability to synthesize further phenylpropanoids in response to the systemic signal, may be important for the establishment of SAR. Treatment of PAL-suppressed plants with dichloro-isonicotinic acid (INA) induces PR protein expression and SAR against subsequent TMV infection. However, treatment with SA, while inducing PR proteins, only partially restores SAR, further suggesting that de novo synthesis of SA, and/or the presence or synthesis of other phenylpropanoids, is required for expression of resistance in systemic leaves.     

STUDIES ON SYSTEMIC FUNGICIDES

A number of mono-, di-and trichloro-β-naphthols and the corresponding naphthyloxy- n -carboxylic acids were prepared. They were tested as systemic fungicides against chocolate spot of broad bean ( Vicia faba ) caused by Botrytis fabae and as fungicides in vitro by their effect on the germination of spores of Sclerotinia laxa and the growth of the mycelium of Botrytis fabae.
The systemic fungicide tests showed no difference in the activity of the compounds associated with different side chains, though there were slight but significant effects associated with different chlorine substitutions in the naphthalene nucleus. The 3:4-dichloro-2-naphthol derivatives were more effective than the other compounds tested.
Fungicide tests with the 1:3-dichloro-2-naphthol derivatives suggested that there was some increase in toxicity to the spores of Sclerotinia laxa with increasing length of side chain. The effectiveness of the various chlorine-substituted compounds in suppressing growth of Botrytis fabae was in the following descending order, 1:3:4-trichloro-, 1:3-dichloro-, 1:4-dichloro-and 3:4-dichloro-compounds. The concentrations required in agar culture to induce reductions of B. fabae growth comparable to those found in the leaf could reasonably be expected to occur in the bean plants treated with the 2-naphthyloxyacetic acids at 10 p.p.m.     

THE ACTION OF MERCURY AS A SOIL FUNGICIDE

Metallic mercury and mercury compounds in the soil retard the growth of plants. The development of mosses and lichens is inhibited, and experimental evidence shows that the growth of toadstools on turf and the activity of ascomycetes is retarded by mercury. In vitro , mercury has no fungicidal action but the rate of growth of hyphae is reduced by mercury vapour.
The lack of fungicidal properties of mercury and its good performance in controlling certain soil-borne diseases are reconciled by assuming that a differential retardation disturbs the relationships necessary for infection. This assumption is supported by diagrams which treat the rates of growth of the parasite and the host as population characteristics normally distributed.     

Biological control of common blight of bean (Phaseolus vulgaris) causedby Xanthomonas axonopodis pv. phaseoli by using the bacteriumRahnella aquatilis

The aim of this study was to evaluate the bacterium Rahnella aquatilis (Ra) for protection of bean plants against common blight disease caused by Xanthomonas axonopodis pv. phaseoli (Xap). Xap isolates were isolated from a naturally blighted leaves of bean plants grown in Assiut governorate. The blight symptoms were produced by all three isolates, but the isolates differed in their degree of the pathogenicity. Xap1 was the most virulence one against bean plants. The effect of Ra against common blight of bean plant was tested. In vitro studies, Ra exhibited inhibitor effect against the pathogen. Under greenhouse and field conditions, beanvariety “Giza 6” treated by Ra resulted in marked disease suppression. Ahigh decrease of the disease was correlated with a reduction of the bacterial multiplication. In physiological studies, bean plants treated by Ra exhibited higher phenolic compounds contents and higher activity of peroxidase (PO) enzyme than untreated plants. In conclusion, application of Ra was effective and could be recommended for controlling the bean common blight disease.     

Partial application of insecticide to broad bean (Vicia fabae) as a means of controlling bean aphid (Aphis fabae) and bean weevil (Sitona lineatus)

The effects upon the nature of insect pest attack of treating only a certain proportion (0%, 25%, 50%, 75% and 100%) of the plants in a field bean (Vicia fabae) stand, with a systemic insecticide (aldicarb as Temik 10G, Rhone Poulenc Drugs Ltd; 10% a.i.) were assessed. Numbers of both the black bean aphid (Aphis fabae) and the bean weevil (Sitona lineatus) were proportionally reduced on untreated plants in plots with an increasing proportion of insecticide treated plants. A similar response was also observed with bean weevil leaf damage scores.
It is postulated that the observed effects are due to a reduction in insect numbers per plot brought about by redistribution of insects after initial invasion. Insects initially alighting on untreated plants later migrate to treated plants and either die or leave the plot altogether. This resulted in proportionally fewer insects on the untreated plants than would be expected.     

间作减轻蚕豆枯萎病的微生物和生理机制

通过田间小区试验,研究了小麦与蚕豆间作对蚕豆枯萎病发病率、病情指数、根际镰刀菌数量、蚕豆根系抗氧化酶活性和膜质过氧化的影响.采用Biolog ECO板分析了根际土壤微生物的代谢功能多样性,通过高效液相色谱(HPLC)测定了蚕豆根际土壤中酚酸含量.结果表明: 与单作蚕豆相比,小麦与蚕豆间作有降低蚕豆枯萎病发病率的趋势;发病盛期和发病末期,间作使蚕豆枯萎病的病情指数比单作显著降低15.8%和22.8%,明显提高了蚕豆根际微生物活性(AWCD值),根际微生物的Shannon多样性指数显著提高4.4%和5.3%,丰富度指数显著提高19.4%和37.1%.主成分分析表明,发病盛期和发病末期,间作明显改变了蚕豆根际微生物的群落结构,蚕豆根际镰刀菌数量分别降低53.8%和33.1%;并显著降低了蚕豆根际土壤中对羟基苯甲酸、香草酸、丁香酸、阿魏酸、苯甲酸和肉桂酸的含量.发病盛期和发病末期,间作蚕豆根系的过氧化物酶(POD)和过氧化氢酶(CAT)活性分别显著提高了20.0%、31.3%和38.5%、66.7%,丙二醛(MDA)含量显著降低36.3%和46.3%;发病初期间作对蚕豆根系的POD、CAT酶活性和MDA含量无显著影响.小麦与蚕豆间作显著提高了蚕豆根际微生物的活性、多样性和根系抗氧化酶活性,降低了蚕豆根际土壤中酚酸含量和膜质过氧化程度,减少了土壤镰刀菌的数量,从而提高了蚕豆对枯萎病的抗性,降低了枯萎病的危害程度.     

Different Dicer-like protein components required for intracellular and systemic antiviral silencing in Arabidopsis thaliana

Eukaryotes employ RNA silencing as an innate defense system against invading viruses. Dicer proteins play the most crucial role in initiating this antiviral pathway as they recognize and process incoming viral nucleic acids into small interfering RNAs. Generally, 2 successive infection stages constitute viral infection in plants. First, the virus multiplies in initially infected cells or organs after viral transmission and then the virus subsequently spreads systemically through the vasculature to distal plant tissues or organs. Thus, antiviral silencing in plants must cope with both local and systemic invasion of viruses. In a recent study using 2 sets of different experiments, we clearly demonstrated the differential requirement for Dicer-like 4 (DCL4) and DCL2 proteins in the inhibition of intracellular and systemic infection by potato virus X in Arabidopsis thaliana. Taken together with the results of other studies, here we further discuss the functional specificity of DCL proteins in the antiviral silencing pathway.     

THE PARASITISM OF STRIGA HERMONTHICA BENTH. ON LEGUMINOUS PLANTS

Pot experiments at the Gezira Research Farm showed that Striga hermonthica Benth. is not confined to the Gramineae but can also parasitize groundnuts, cowpea, dolichos bean and soya bean, causing a loss in yield in all but the last-named. The Striga plants developing on the roots of these hosts were small, apparently ill-nourished and did not grow more than 1 cm. above the ground, in contrast to the vigorous, flowering Striga plants that develop on sorghum. The greatest reduction in yield in these experiments was in dolichos bean, where the aerial growth was reduced 60%; no significant reduction in root weight was found in groundnuts, cowpea or soya bean. The last-named plant appeared to be feebly parasitized by S. hermonthica. A reduction in total nodule weight, but not in number of nodules, was obtained in groundnuts and cowpea. Parasitized dolichos bean showed a reduction in both the number of nodules and in nodule dry weight; in groundnuts, the later fruit production was seriously reduced.
The use of these leguminous crops to clean Striga -infested soil is discussed.     

Biochemical changes in French bean pods infected with Colletotrichum lindemuthianum*

Infection of bean pods with Colletotrichum lindemuthianum leads to the appearance in diffusates of a range of fluorescent and phenolic compounds and of at least two inhibitory compounds. These compounds were found to be absent or in reduced concentration in control diffusates, although the inhibitors were frequently observed to appear at low concentrations without infection. Although sugars and amino acids were found to be released into diffusates, variation in the concentration of these stimulants was found to have little effect on spore germination. Evidence from solvent partition, spectrophotometry and chromatography suggests that the two inhibitors can be tentatively identified with inhibitors previously described from French bean, and both appear to be phenolic substances. It is suggested that inhibitor production may be regarded as part of a general change in aromatic biosynthesis following infection.     

Role of dissimilatory fermentative iron-reducing bacteria in Fe uptake by common bean (Phaseolus vulgaris L.) plants grown in alkaline soil

Iron (Fe) is an essential element for plant growth and development. Some plant growth-promoting rhizobacteria can increase Fe uptake by plants through reduction of Fe(III) to Fe(II) at the root surface. The aim of this work was to identify novel bacterial strains with high Fe(III) reduction ability and to evaluate their role in plant Fe uptake. Four bacterial strains (UMCV1 to UMCV4) showing dissimilatory Fe-reducing activity were isolated from the rhizosphere of bean and maize plants and further identified by 16S rDNA amplification and sequence analysis. From these analyses, UMCV1 and UMCV2 isolates were identified as Bacillus megaterium and Arthrobacter spp., respectively, whereas UMCV3 and UMCV4 were identified as Stenotrophomonas maltophilia. All four isolates showed Fe reduction in a nonflooded soil and when associated with roots of bean plants grown in alkaline soil or in mineral medium. In addition, the bacterial isolates were able to stimulate plant growth in vitro and on a broad level, plants grown in inoculated soil were generally bigger and with higher Fe content than those grown in sterilized soil. These results indicate that bacterial species isolated from the rhizosphere of bean and maize plants contribute significantly to Fe uptake by plants likely through increased Fe(III) reduction in the rhizosphere.     

SYSTEMIC INSECTICIDAL ACTION OF NICOTINE AND CERTAIN OTHER ORGANIC BASES

Nicotine and nicotine salts are taken up by the roots of plants from solutions, and when 0.01–0.001 % nicotine is used the plants become toxic to Aphis fabae and to Pieris brassicae larvae and can be shown to contain nicotine. The results with Phaedon cochleariae adults and larvae are less satisfactory. No systemic action is observed when the nicotine is watered on to soil in which plants are growing and no nicotine can be detected in the plants. Apparently the nicotine is decomposed in the soil.
When applied several times to the upper surface of a bean leaf nicotine kills aphids on the underside. There is some evidence that nicotine can be translocated further through the plant following leaf applications, but the toxic action at any distance is very weak in the plants used in the present experiments and can only be produced by frequent applications of rather concentrated nicotine solutions. Leaf absorption and subsequent translocation has not been observed with nicotine salts.
The various organic bases, including some piperidine phosphonites and allied compounds tested, are of very little interest as contact or systemic insecticides against aphids.     

THE SYSTEMIC ACTION AGAINST PSEUDOMONAS MEDICAGINIS VAR. PHASEOLICOLA OF A STREPTOMYCIN SPRAY APPLIED TO DWARF BEANS

The prophylactic effect resulting from the localized application of streptomycin as a foliage spray on dwarf bean plants has been examined. Streptomycin sulphate solution applied to the primary leaves exhibited a marked and consistent systemic, antibacterial, prophylactic action even at sites as far removed from the point of application as the fourth trifoliate leaf. This systemic protection against the halo blight organism persisted for various periods up to a maximum of 11 days. Mannosidostreptomycin was much inferior to streptomycin in its systemic prophylactic action against halo blight.     

Effect of substrate Zn level on distribution of photo-assimilated C14 in maize and bean plants

Summary Maize and pea bean plants were grown for 2 weeks in Zn-deficient soil fertilized with varying levels of Fe and Zn. The plants were then exposed to C¹⁴O₂ for 2 minutes and after harvest the ethanolsoluble photosynthate was fractionated into carbohydrates, organic acids, and amino acids. There appeared to be a general increase in the CO₂ assimilation rate by maize with increasing rate of Zn; rates were slightly higher with applied Fe, at each Zn level. In contrast to maize, the rate of assimilation by pea beans was unaffected by substrate Zn and was slightly lower with application of Fe, especially in the carbohydrate fraction. Increasing rates of applied Zn had little effect on concentration of Fe and Mn in the maize or pea bean tops. However, application of Fe resulted in a depression in Zn concentration of maize. Despite the relatively high levels of Zn in the tissue of both species, there was no increase in total organic acids assimilated or any indication of gross metabolic imbalances.     

Systemic effects of neem on western flower thrips,Frankliniella occidentalis (Thysanoptera: Thripidae)

The systemic effects of neem on the western flower thrips, Frankliniella occidentalis (Pergande), were investigated in laboratory trials using green bean, Phaseolus vulgaris L., in arena and microcosm experiments. In arena experiments, systemic effects of neem against western flower thrips larvae on primary bean leaves were observed with maximum corrected mortality of 50.6%. In microcosm experiments using bean seedlings, higher efficacy in the control of western flower thrips were observed with soil applications of neem on a substrate mixture (i.e., Fruhstorfer Erde, Type P, and sand) in a 1:1 ratio (93% corrected mortality) compared with application on the commercial substrate only (76% corrected mortality). However, longer persistence of neem was observed with soil application on the commercial substrate, which showed effects against thrips for up to 6 d after application. In addition to systemic effects observed on all foliage-feeding stages of western flower thrips, mortality on contact and repellent effects were observed on soil-inhabiting stages after soil applications of neem. Finally, bean seedlings grown from seeds pregerminated for 3 d in neem emulsion were also toxic to western flower thrips.     

Effect of the molecular weight of chitosan on its antiviral activity in plants

The effect of the molecular weight of chitosan on its ability to suppress systemic infection of bean mild mosaic virus in bean (Phasoleus vulgaris L.) plants was studied. The enzymatic hydrolysate of low-molecular-weight chitosan was successively fractionated by ultrafiltration through membranes with decreasing pore size. In total, four chitosan fractions with a weight-average molecular weight varying from 1.2 to 40.4 kDa were obtained. It was shown that the treatments of bean plants with these fractions (chitosan concentration, 10 or 100 microg/ml) inhibited virus accumulation and systemic propagation. The degree of chitosan-induced antiviral resistance increased as the molecular weight of chitosan decreased. The monomers comprising the chitosan molecule-glucosamine and N-acetylglucosamine--exhibited no antiviral activity.