The effect of a mixture of seed-borne Microdochium nivale var. majus and Microdochium nivale var. nivale infection on Fusarium seedling blight severity and subsequent stem colonisation and growth of winter wheat in pot experiments

Greenhouse experiments were conducted in order to determine the impact of seed-borne Microdochium nivale var. nivale and var. majus inoculum, and seed treatment with a carboxin+thiram mixture, on the development of seedling blight, and on subsequent stem colonisation and growth of winter wheat (cv. Cadenza). Experiments were conducted at temperatures favourable (3°C) and unfavourable (22°C) to M. nivale. Seed-borne inoculum resulted in seedling blight symptom development when plants were grown at 3°C, but not when plants were grown at 22°C. For seedlings grown at 3°C, plants arising from heavily blighted seedlings developed more severe symptoms of stem colonisation, when compared with those arising from seedlings from carboxin+thiram treated seeds. In addition, the vigour of such plants (assessed by determining the number of tillers and ears per plant, stem length, green leaf area, dry weight and yield) was also significantly lower than for plants arising from carboxin+thiram treated seeds. Microdochium nivale var. majus and var. nivale appeared to have little effect on plant vigour from seedlings grown at 22°C. This is the first recorded incidence of seedling blight affecting subsequent plant growth. Microdochium nivale var. majus and var. nivale stem colonisation increased from growth stage (GS) 40–49 to harvest in plants raised from seedlings grown at both temperatures. Microdochium nivale var. majus and var. nivale were isolated from the second node at GS 40–49 and the third node at harvest of plants from seedlings grown at 3°C. For plants from seedlings raised at 22°C, M. nivale var. majus and var. nivale were isolated from the first node at GS 40–49 and the second node at harvest. Carboxin+thiram seed treatment decreased the extent and severity of stem colonisation on plants from seedlings grown at 22°C.     

Carboxin resistance in the haploid,the heterozygous diploid,and the plant-parasitic dicaryotic phase of Ustilago maydis

Respiration and growth of a diploid strain of Ustilago maydis, heterozygous at the oxr-1 locus for resistance to carboxin and carboxin analogs, were less sensitive to the fungicide than the corresponding processes in the wild type haploid. Data on the inhibition of succinate-2,6-dichlorophenolindophenol reductase indicate that the mitochondria of the heterozygous diploid probably contain a mixture of carboxin-sensitive and carboxin-resistant succinic dehydrogenase complexes. This hypothesis is supported by the results of temperature aging experiments: When mitochondria of the heterozygous diploid were subjected to incubation at 30°C which destroyed the enzyme activity of mitochondria from the mutant haploid, the remaining succinate-2,6-dichlorophenol-indophenol reductase activity exhibited a carboxin sensitivity similar to that of mitochondria from the wild type haploid.Carboxin gave very good control of corn smut in seedlings artificially inoculated with two wild type compatible strains but not when both strains were mutant for carboxin resistance, which indicates high resistance in the dicaryon. In a heterozygous cross, the dicaryon seemed to exhibit considerable resistance, if sufficient time was allowed for its formation between inoculation and carboxin treatment of soil.     

Bioassay evaluation of the systemic properties of carboxin in lemon seedlings

Carboxin was toxic to the fungus Deuterophoma tracheiphila. Uptake and translocation of carboxin (2,3-dihydro-6-methyl-5-phenylcarbamoyl-1,4-oxathiin) in lemon seedlings were assessed in plant extracts by a bioassay technique. Root uptake and translocation to stem and leaves were demonstrated from both an aqueous solution and drenched soil. Leaf uptake was lower than root uptake, and could be enhanced by removing the epicuticular wax. Chromatographic tests suggested that the compound responsible for fungitoxicity within plant tissues may have been carboxin itself.     

Differences in light stability of some carboxylic acid anilide fungicides in relation to their applicability for seed and foliar treatment

Irradiation of carboxin, furcarbanil, pyracarbolid, cyclafuramid, benodanil, mebenil and oxycarboxin by u.v. light (254 nm) for 4 h resulted in 97, 64, 58, 50, 20, 18 and 15% inactivation, respectively. Photoinactivation of the different compounds in aqueous solution or in the solid state was much slower in sunlight than in u.v. light and stability increased in the following order: carboxin < furcarbanil ≤ cyclafuramid ≤ pyracarbolid < mebenil ≤ benodanil < oxycarboxin. The residues of carboxin and furcarbanil on the leaf surface of bean plants were almost completely inactivated after 40 h exposure to sunlight; cyclafuramid lost 85% of its activity. The toxicity of leaf deposits of pyracarbolid, mebenil, benodanil and oxycarboxin decreased by 83, 53, 50 and 41%, respectively after 80 h in sunlight. The compounds with low photostability (e.g. carboxin, furcarbanil and cyclafuramid) are recommended mainly for controlling seed- and soil-borne fungi; pyracarbolid, mebenil, oxycarboxin and benodanil, which proved to be more photostable, appear to be useful fungicides to control rust diseases. Among several photochemical decomposition products of carboxin detected, the sulphoxide and sulphone were identified.     

Effect of seed treatment in preventing transmission of dwarf bunt of winter wheat to new areas

The effectiveness of various fungicide formulations containing carboxin and thiabendazole in eradicating teliospores of Tilletia controversa (dwarf bunt) from winter wheat seed was evaluated in the laboratory and the field. In the laboratory tests, the viability of teliospores washed from treated infested seed was greatly reduced as compared to the viability of teliospores washed from untreated infested seed, suggesting that carboxin and thiabendazole were primarily fungicidal. Field tests in two different years were established to determine if teliospores from treated infested seed could infect nearby untreated noninfested seed. Formulations containing carboxin were highly effective in reducing infection of healthy seed. No dwarf bunt infected plants developed in either year from seed treated with ‘Vitaflo 250’. Furthermore, seedborne common bunt caused by Tilletia foetida was nearly eradicated by carboxin-containing formulations in one field test. Carboxin treatment of winter wheat seed infested with dwarf bunt teliospores will greatly reduce the danger of introducing this pathogen into new areas.     

Control of bottom rot disease of lettuce (Rhizoctonia solani) using preparations of Trichoderma viride, T. harzianum or tolclofos-methyl

Isolates of Trichoderma were tested for their ability to control Rhizoctonia solani in lettuce seedlings and mature plants in a glasshouse. The best isolate (T. viride IMI 298375) was tested for its ability to control bottom rot disease in mature lettuce plants grown in polythene tunnels. Control was achieved in several trials but there was little evidence for much improvement after repeated applications and control with Trichoderma was poorer than that obtained with a standard treatment with tolclofos-methyl. Evidence was obtained to suggest however that enhanced growth of lettuce plants following treatment with Trichoderma can produce marketable yields of lettuce similar to those obtained with tolclofos-methyl.     

Inheritance of Carboxin Resistance in a European Field Isolate of Ustilago nuda

ABSTRACT Two carboxin-resistant field isolates of Ustilago nuda from Europe were crossed with a carboxin-sensitive field isolate from North America. Meiotic tetrads isolated from germinating F(1) teliospores of one of the hybrids were tested for carboxin resistance and mating type. Carboxin resistance was shown to be controlled by a single gene (CBX1R), because a 1:1 segregation of carboxin resistance was observed in all 27 tetrads. Tetrad analysis indicated that the loci for carboxin resistance (Cbx1) and mating type (MAT1) segregate independently but may be located on the same chromosome. Tetrad analysis was not possible with the F(1) hybrid of he other field isolate, and its resistance cannot yet be attributed to CBX1R. Carboxin resistance was qualitatively dominant to sensitivity in vitro, as demonstrated by triad analysis of germinating F(1) teliospores. Quantitative in planta infection percents supported the conclusion that CBX1R is dominant, although incompletely, in the F(1) hybrid of one of the field isolates. Also, fewer than expected carboxin-sensitive F(2) individuals were observed in planta. However, inoculations of host plants with U. nuda have resulted in similar, unexpected variation in the past.     

Oxathiin carboxamides highly active against carboxin-resistant succinic dehydrogenase complexes from carboxin-selected mutants of Ustilago maydis and Aspergillus nidulans

The systemic fungicide carboxin (5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxanilide) and structurally related analogs are powerful inhibitors of succinate oxidation in mitochondria isolated from a variety of sources. The site of action which is, apparently, also that for thenoyltrifluoracetone, is in the complex II (succinate-ubiquinone reductase) region of the mitochondrial electron transfer chain. The succinic dehydrogenase complex (SDC) in mitochondria from carbon-resistant mutant strains of Ustilago maydis and Aspergillus nidulans is resistant to the fungicide in vitro. The current study shows that certain oxathiin carboxamides are selectively active against particular mutated SDCs of U. maydis and A. nidulans. Molecular structures affecting the phenotypic expression of mutation to carboxin resistance in U. maydis do not appear to affect similarly such expression in A. nidulans and vice versa. Of particular interest was the discovery of oxathiin carboxamides, e.g., 4′-phenylcarboxin, which were more inhibitory to the enzyme complex from one category of carboxin-resistant mutants of U. maydis than from the wild-type strain. Although such negative correlation between carboxin and other carboxin analogs has not been observed in studies with other categories of mutants, structures which drastically lower the resistance level were found in all cases. It appears that for any given mutation affecting carboxin sensitivity of the SDC in fungi, a specific structural group of carboxamides (or even a specific carboxamide) may be found which will alleviate or reverse the effect of the mutation in terms of inhibition of the SDC. If the mutations alter a protein receptor site for carboxamides, such mutations might be expected to influence the binding of carboxins of different structure. In essence, then, different molecular structures can “recognize” different alterations in the mutated enzyme complex and inhibit effectively. With few exceptions, the inhibition by carboxamides of cell growth of wild-type and carboxin-resistant strains of U. maydis and A. nidulans closely paralleded the inhibition of their respective SDCs. Although the few analogs tested were found unable to control corn smut systemically in seedlings artificially inoculated with compatible carboxin-resistant strains, control of naturally occurring carboxin-resistant strains of pathogenic fungi may be possible using particular structural analogs of carboxin which selectively inhibit the mutant organisms.     

Biological effects of combining carboxin,organomercury fungicides and insecticides as seed dressings for wheat,and the effect of these combinations on adherence of the pesticides to the seed

When seeds of winter wheat were carefully dressed in the laboratory with combinations of fungicides (organomercury alone or organomercury plus the systemic fungicide carboxin) and insecticides (aldrin, carbophenothion or chlorfenvinphos as liquid formulations, or a γ-BHC powder formulation) so as to ensure that nearly all the recommended amounts of the active ingredients stuck to them, the insecticides gave good insect control, but γ-BHC with organomercury fungicide decreased the number of plants that germinated, and γ-BHC with carboxin and organomercury was even more damaging. Commercially dressed seeds had only about 30 to 60% of the target dose of fungicides, but more than 80% of the target doses of the liquid insecticides aldrin, carbophenothion and chlorfenvinphos. With combinations of powder fungicide and liquid insecticide, greater amounts of pesticide on the seed were obtained if the insecticide was put on first. Because of unusually late sowings and little fungal infestation, neither laboratory nor commercially treated seeds provided good tests for control of smut.     

Mode of action of oxathiin systemic fungicides : III. Effect on mitochondrial activities

Carboxin (5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxanilide) was tested for its effect on the activities of mitochondria from several fungi, pinto beans and rat liver. Succinate oxidation by mitochondria from the sensitive fungus Ustilago maydis was inhibited by low concentrations of carboxin, the K_i being 0.32 μM. The inhibition was of a noncompetitive nature. Succinate oxidation was also inhibited in the mitochondria from other sources but not to the extent as in those from U. maydis. Carboxin had little effect on the oxidation of reduced nicotinamide adenine dinucleotide. The dioxide of carboxin, oxycarboxin, was not as effective in inhibiting succinate oxidation as was carboxin, but was more effective than the monoxide. Carboxin did not appear to uncouple oxidative phosphorylation in the presence of succinate in tightly coupled rat liver mitochondria but did decrease the respiratory control ratio. Carboxin was ineffective in releasing oligomycin inhibition in coupled rat liver mitochondria while dinitrophenol and salicylanilide were effective in this respect. It is believed that carboxin inhibits mitochondrial respiration at or close to the site of succinate oxidation and does not greatly affect the remaining portion of the electron transport system or the coupled phosphorylation reactions.     

Plant-pathogen interactions of sunflower and Macrophomina phaseolina in vitro and in vivo

The relative pathogenicity of isolates of Macrophomina phaseolina was comparable both on sunflower tissue cultures and on mature plants and seedlings. The relative susceptibility of the different sunflower lines in vitro showed a similar pattern for cotyledon callus cultures, but not for immature embryo cultures. Although these protocols appear to be unsuitable for the selection of novel disease resistance, they do offer the potential for a rapid, non-destructive screen for resistant material.     

Alfalfa mosaic virus in lucerne seed during seed maturation and storage, and in seedlings

The incidence of alfalfa mosaic virus (AMV) in lucerne seed and pods during maturation, when monitored by sap transmission to Phaseolus (infective virus) and ELISA (AMV antigen), showed that infective virus incidence decreased rapidly with maturation, whereas antigen incidence declined slowly and was always higher than infective virus. Infective virus and antigen incidence were higher in mature seed of cv. Maris Kabul than cv. Europe because virus inactivation/degradation were more rapid in cv. Europe. Seed infection with virus originating from pollen, ovules or both was found in pods and seeds 12–15 days after pollination between healthy or AMV-infected plants; this was before maturation-associated virus inactivation. Ovule transmission was more frequent than pollen transmission. AMV antigen was present in embryos and testas of mature seed; infective virus only in embryos. Non-infective but ELISA-positive antigen in testa extracts accounted for the higher incidence of 'seed-borne AMV' compared with embryo-associated seed transmission to seedlings. Tests with dry mature seed either underestimated (infectivity tests) or overestimated (ELISA) eventual seedling infection. Infectivity and ELISA tests gave identical incidence values for 17 to 29-day-old seedlings.     

Inactivation of seed-treatment fungicides by Rhizobium

2-Methoxyethylmercury chloride (MEMC) applied to cowpea seeds with Rhizobium provided little or no control of seedling rot caused by Rhizoctonia solani; similar treatment, but without Rhizobium, gave >40% control of disease. Treating seeds with quintozene and then with Rhizobium rendered the fungicide completely ineffective against R. solani infections; disease control was >70% when seeds were treated with quintozene only, and >60% when seeds were coated first with Rhizobium and then with quintozene; treatment with quintozene+Rhizobium gave about 25% control. Simultaneous treatment with Rhizobium considerably reduced the efficacy of captafol, chloroneb, carbendazim and thiophanate-methyl. Disease control by carboxin, benomyl and thiabendazole remained unaltered in the presence of Rhizobium, but only thiabendazole gave good control. Seeds treated with MEMC and Rhizobium produced seedlings without root nodules; nodulation was also decreased by captafol and by carboxin but six other fungicides had no effect. The implications of Rhizobium-fungicides interactions are discussed in the context of fungicidal control of root diseases.     

大白菜软腐细菌从幼根侵染的组织病理学研究

 将大白菜种子置于培养皿内的滤纸上发芽。滤纸用不同浓度的洗涤与不洗涤的软腐欧氏杆菌(Erwinia carotovora pv.carotovoar Dye)悬浮液,离心上清液,培养基浸出液和灭菌生理盐水浸润。在25℃下培养26小时后,用细菌悬浮液处理的幼芽发病率为8-95%不等。病苗生长量为对照(用生理盐水处理)的17-80%。扫描电镜观察的结果指出,接种后病原细菌首先在根毛区发现,以后才在伸长区和成熟区发现大量病菌。成熟区表皮细胞与细胞交界处的细胞壁有被分解的迹象。在幼苗的导管及其附近的薄壁细胞内均发现了病原细菌,检出率分别为16%和3%。在病苗组织内和幼根表面的病菌可产生微纤丝。病苗幼茎经压气处理24小时后,对其断面进行扫描电镜观察,结果表明,病菌可将导管的外壁与纹孔膜分解而使导管解体仅剩螺蚊加厚部分或呈网孔状。     

A new class of carboxin-resistant mutants of Ustilago maydis

A small percentage of mutants of Ustilago maydis, selected on medium containing 40 μM carboxin, are distinctly more resistant than the mutants previously described, with an ED₅₀ at least 100 times higher than that of wild type strains. Nine mutants of this category were studied. Crosses involving any one of these mutants gave Mendelian ratios in all cases and no transgressive segregation for level of tolerance was observed. All nine mutants were found to carry a mutation at the locus previously designated as oxr-1. In all cases carboxin resistance in vivo could be related to the resistance of the succinic dehydrogenase system in mitochondrial preparations and no other mechanism of resistance has been recognized. It appears that two allelic mutant genes at the oxr-1 locus code for two altered types of the succinic dehydrogenase complex distinguished by the level of carboxin tolerance.     

Induction of phenylalanine ammonia-lyase (PAL) in insect damaged and neighboring undamaged cotton and maize seedlings

There has been scepticism about plants responding to information from their damaged neighbor plants since it was first reported, although a growing body of evidence indicates that interplant communication may play a key role in the resistance of plants. Cotton aphids and corn borer are important insects in cotton and maize, respectively. The resistance of healthy cotton and maize plants induced by their neighbor damaged plants was investigated in this study. Phenylalanine ammonia-lyase (PAL) is a chemical marker of induced resistance in many plants. The enzymatic activity and gene expression of PAL were determined in cotton and maize seedlings damaged by wounding, aphid and corn borer attack and in intact undamaged maize and cotton seedlings growing nearby. The enzymatic activity and gene expression of PAL were significantly increased in the cotton and corn seedlings damaged by wounding or by aphid and corn borer. Furthermore, undamaged neighboring cotton and maize seedlings also showed elevated enzymatic activity and gene expression of PAL. These inductions of PAL enzymatic activity and gene expression in the damaged and undamaged seedlings suggest inter-species communication between cotton and maize.     

<Emphasis Type="Italic">Brassica napus</Emphasis> plants infected by <Emphasis Type="Italic">Leptosphaeria maculans</Emphasis> after the third to fifth leaf growth stage in south-eastern Australia do not develop blackleg stem canker

Blackleg (Phoma stem canker) caused by Leptosphaeria maculans is the most damaging disease of Brassica napus (canola, rapeseed, colza) worldwide and is controlled by sowing blackleg resistant cultivars and crop management strategies that reduce exposure to inoculum and fungicide application. In experiments in south-eastern Australia, canola cultivars inoculated after the three to five leaf growth stage did not develop stem canker. Although mature canola plants are known to be less susceptible to blackleg than seedlings, this highlights for the first time the specific importance of protecting seedlings up to the three to five leaf growth stage in Australia. This would typically correspond to a period of four to six weeks after emergence. Canola plants are likely to be significantly less vulnerable to infection after this growth stage. However, this timing may vary due to the influence of environmental conditions.     

The biology of Bassia birchii (F. Muell.) F. Muell.

The native perennial shrub, Bassia birchii. occurs as a weed over large areas of semi-arid eastern Australia. Its germination requirements and seedling growth were investigated and related to field observations and to possible means of control. Seeds cannot germinate until the woody fruit has broken down. Laboratory experiments showed that seeds would germinate throughout the year with most germinating at autumn and spring temperatures. Seedling deaths in the field are attributed to poor root growth, before the effects of water stress occurs. The spasmodic appearance of Bassia birchii infestations, particularly after droughts, is related to the dependence on the death of mature plants to provide propagules and fruit breakdown for germination. The unpredictable infestation pattern and the early development of spined fruits and basal buds on seedlings hinder control. Short period rotational or strategic grazing are suggested as possible means of control of seedlings in areas where perennial pastures can be established.     

含双病原物诱导启动子无选择标记转基因烟草的获得

Transgenic plants are controversial for their edible and environmental security. Marker-free transgenic plants can be produced by the construction and transformation of plant expression vectors carrying twin T-DNAs. The construction of plant expression vectors harboring twin T-DNAs and two pathogen-inducible promoters was previously reported. These vector plasmids were introduced into tobacco plants and the transgenic tobacco plants were obtained. In this paper we report that T₁ transgenic tobacco seedlings were produced through classical genetics approach. Analysis of the seedlings demonstrated that some of them were marker-free lines. The segregation of exogenous genes in T₁ transgenic tobacco seedlings was tested by using two methods. Firstly, the ability of resistance to kanamycin was analyzed in T₁ transgenic tobacco seedlings from 14 transgenic plant lines. It was found that the segregation ratio of NPTII genes met well with Mendel’s law in 13 transgenic tobacco lines. So it was deduced that NPTII gene was as a single copy integrated into one of the homologous chromosomes. Then the NPTII genes and uidA genes of 130 T₁ transgenic seedlings were detected from the above 13 tobacco lines. The results showed that uidA genes were only detected in 20.77% of the seedlings, NPTII genes were solely detected in 22.31% of the seedlings, but both exogenous genes were in 53.85% of the seedlings. The segregation ratio of the two genes was consistent with the law of independent assortment (9∶3∶3∶1). These results suggested that the selective marker gene had no linkage with the reporter gene and they were segregated independently in the T₁ transgenic tobacco plants. This method, as compared with traditional backcross, is confirmed a more easy and rapid way to eliminate the antibiotic resistance gene used as a selective marker in transgenic plants.     

Analysis of quantitative trait Loci for resistance to southern leaf blight in juvenile maize

ABSTRACT A set of 192 maize recombinant inbred lines (RILs), derived from a cross between the inbred lines Mo17 and B73, were evaluated as 3-week-old seedlings in the greenhouse for resistance to southern leaf blight, caused by Cochliobolus heterostrophus race O. Six significant (LOD >3.1) quantitative trait loci (QTL) were identified for disease resistance, located on chromosomes 1, 2, 3, 6, 7, and 8. Results were compared with a previous study that had used the same RIL population and pathogen isolate, but had examined resistance in mature rather than juvenile plants. There was a very weak but significant correlation between the overall resistance phenotypes of the RILs scored as mature and juvenile plants. Two QTL were found in similar positions on chromosomes 1 and 3 at both growth stages. Other QTL were specific to one growth stage or the other. Twenty-three of these RILs, together with the parental lines, were inoculated in the greenhouse with four C. heterostrophus isolates. Results indicated that the quantitative resistance observed was largely isolate non-specific.