Genetic characteristics of <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> from corn in the Philippines

Fusarium verticillioides (teleomorph: Gibberella moniliformis = G. fujikuroi mating population A) is one of the most important fungal pathogens of corn worldwide. The pathogen produces fumonisins, mycotoxins that are potentially harmful to humans and animals. Thirty-five Fusarium isolates from Laguna and Isabela, Philippines were identified morphologically and molecularly as F. verticillioides and characterized by PCR for mating type (MAT). Twenty-six isolates were MAT1-2, while nine isolates were MAT1-1. The isolates from Isabela were tested for aggressiveness, rated according to a disease index (%) on ‘Super Sweet’ corn IPB variety 1 under field conditions across two trials using the toothpick inoculation method. Other aggressiveness traits such as inhibition of seedling emergence, decrease of seedling height, fresh and dry mass were also determined in two greenhouse trials. All isolates were pathogenic to corn seedlings and mature plants compared to the noninoculated control. Significant genotypic variation was observed (P = 0.01) in trial, isolate, and isolate × trial interaction for all traits across two greenhouse trials and that aggressiveness was highly influenced by the trial conditions. Similarly, significant genotypic variation was observed in trial, replication within trial and isolate × trial interaction. Heritability was high for the five traits in the greenhouse (h ² = 0.80–0.90) but moderate for disease index in the field (h ² = 0.49). In an analysis of fumonisin production in corn culture by high performance liquid chromatography, 30 of 35 strains produced a detectable level of fumonisins, varying from 0.44 to 742 μg FB₁/g corn, 0.51–222 μg FB₂/g and 0.12–37 μg FB₃/g. Isabela isolates produced more fumonisins than the Laguna isolates did. In vitro fumonisin production had little correlation with the field disease index (r = 0.32) or with greenhouse seedling germination (0.25).     

Spore cell wall components ofAspergillus niger elicit downy mildew disease resistance in pearl millet

Elicitors derived from the cell wall of fungi are shown to be active in eliciting resistance in plants against a wide range of pathogens. In the present study carbohydrate components from the autoclaved spore cell wall ofAspergillus niger were prepared as aqueous suspensions and tested for defense response in pearl millet (Pennisetum glaucum (L.) R.Br.) against the oomycetous downy mildew pathogenSclerospora graminicola (Sacc.) Schroet. The aqueous suspension derived from the spore cell wall ofA. niger was used as a seed soak treatment at concentrations of 0.25, 0.5, 1.0, 1.5 and 2.0 mg ml⁻¹ for time intervals of 3, 6, 9 and 12 h. The concentration of 0.5 mg ml⁻¹ for a 6 h soaking period offered 94% seed germination and seedling vigor index increased to 1526. The seed germination and the seedling vigor were significantly higher than the untreated check. Spore cell wall suspension as seed treatment at a concentration of 0.5 mg ml⁻¹ required a 3-day time interval to provide 67% protection against downy mildew. Histological and biochemical studies were conducted to elucidate the mechanism of defense response in treated seedlings uponS. graminicola infection. Resistance host response was detected in the form of lignin and callose deposition in the epidermal cell wall of pearl millet seedlings, which is the site ofS. graminicola infection. A time course study showed rapid and localized deposition of lignin and callose in epidermal cell wall of carbohydrate components-treated pearl millet seedling coleoptiles. Increased levels of the defense-related enzyme peroxidase were detected in the treated seedlings. Peroxidase activity in elicitor-treated samples reached a peak at 8 h post-infection, which was 45% more than in their respective uninoculated control. Characterization of peroxidase isoforms by isoelectric focusing revealed 16 different isoforms, of which pI 6.8, 7.2 and 8.7 increased in elicitor-treated samples uponS. graminicola infection. http://www.phytoparasitica.org posting Nov. 14, 2005.     

Factors affecting the seed germination and seedling emergence of muskweed (Myagrum perfoliatum)

Myagrum perfoliatum is a noxious broad‐leaved weed in western Iranian farming systems. A better understanding of the timing of seedling emergence would facilitate the development of better control strategies for this weed. Therefore, the objective of this study was to examine the effects of different factors on muskweed seed germination. Only 2.8% of the seeds of this species, which are encapsulated in siliques, germinated by, while the seeds that had been removed from the siliques had a 50% germination rate. The immersion of muskweed fruits in concentrated sulfuric acid for 110 min was the best treatment for promoting germination. Gibberellic acid stimulated the germination of the naked seeds by 29.1%, potassium nitrate (40 mmol L^‐1) increased the germination rate to 71%, while higher concentrations of potassium nitrate inhibited germination. The optimum germination temperature for the naked seeds was 20/10°C (day/night) and light was not required for germination. No seedling emerged when the seeds were buried 6 cm deep. The seeds were sensitive to both osmotic and salinity stress, but they germinated to 46–49% over a pH range of 4–10. The results of this study revealed that the seeds of M . perfoliatum have physiological dormancy and that it is slowly broken via after‐ripening. However, the fruit wall can prevent germination after physiological dormancy is broken. Thus, this species has the potential to form a persistent seed bank because of the presence of the fruit wall.     

Effect of Three Seed-dressing Fungicides on the Germination of Cowpea,Groundnut and Maize

Abstract

Agrosan 5W, Fernasan D and Quinolate 15/40 significantly improved the germination, under field conditions, of the seeds of cowpea (variety Mezed), groundnut (variety Chimbuila) and maize (variety NSI), but not that of cowpea (variety New era) and groundnut (variety Spanish 205).

In those cases where the application of seed-dressing was effective, treatment with Agrosan 5W appeared to give better germination than treatment with either Fernasan D or Quinolate 15/40. Maize seeds treated with Quinolate 15/40 germinated slightly better than those treated with Fernasan D, whereas treatment of cowpea and groundnut seeds with Fernasan D gave better germination than treatment with Quinolate 15/40.

A similar trend was observed in tests in vitro.     

Resistance to metalaxyl-M and cymoxanil in a dominant clonal lineage of <Emphasis Type="Italic">Phytophthora infestans</Emphasis> in Huánuco,Peru, an area of continuous potato production

Fifty-eight isolates of Phytophthora infestans were evaluated in vitro and on detached leaves of potato for their sensitivities to metalaxyl-M and cymoxanil. The isolates belonged to the clonal lineage, EC-1, which is dominant on potato in Peru and Ecuador. All isolates were collected in Huánuco, Peru, an area of year-round potato production, where the potential for development of fungicide resistance is high. All isolates were resistant to metalaxyl-M, with in vitro EC₅₀ values ranging from 468.30—813.57 mg l⁻¹. In contrast, we found no evidence for resistance to cymoxanil for which in vitro EC₅₀ values ranged from 0.03—1.11 mg l⁻¹. Resistance to each fungicide was also evaluated for five isolates in a detached leaf assay in which the fungicide was sprayed on the leaf surface prior to inoculation. With metalaxyl-M, the range of EC₅₀ values was 158.85—828.29 mg l⁻¹, similar to that for the in vitro assay. For cymoxanil, EC₅₀ values ranged from 1.41 to 2.31 mg l⁻¹, which was higher than in the in vitro assay but still two orders of magnitude lower than the concentration applied by farmers in the field.     

Germination response of Orobanche seeds subjected to conditioning temperature, water potential and growth regulator treatments

Broomrapes (Orobanche spp.) are parasitic weeds that cause significant losses of crop yield. Experiments were conducted to investigate the seed response to the artificial germination stimulant GR₂₄ in three species of Orobanche subjected to preconditioning under various temperatures, water potentials and with plant growth regulators. The highest germination percentages were observed in Orobanche ramosa, Orobanche aegyptiaca and Orobanche minor seeds conditioned at 18°C for 7 days followed by germination stimulation at 18°C. With the increase of the conditioning period (7, 14, 21 and 28 days), the germination percentage of O. ramosa and O. aegyptiaca progressively decreased. When conditioned at −2 MPa, the germination percentage was lower than at 0 and −1 MPa, especially at 13 and 28°C. Orobanche minor seeds could retain relatively high germination if conditioned at 18, 23 or 28°C, even after significantly extended conditioning periods (up to 84 days). GA₃ (30–100 mg L⁻¹), norflurazon and fluridone (10–100 mg L⁻¹), and brassinolide (0.5–1.0 mg L⁻¹) increased seed germination, while 0.01 mg L⁻¹ uniconazole significantly reduced germination rates of all three Orobanche spp. The promotional effects of GA₃ and norflurazon and the inhibitory effect of uniconazole were evident, even when they were treated for 3 days. Germination of Orobanche seeds was much lower when the unconditioned seeds were directly exposed to GR₂₄ at 10⁻⁶ m . This early GR₂₄-induced inhibition was however alleviated or even eliminated by the inclusion of GA₃ or norflurazon (10–50 mg L⁻¹) in the conditioning medium. On the contrary, the inclusion of uniconazole increased the inhibitory effect of GR₂₄, particularly in the case of O. ramosa.     

<Emphasis Type="Italic">Paecilomyces lilacinus</Emphasis>, a potential biocontrol agent on apple rust mite <Emphasis Type="Italic">Aculus,schlechtendali</Emphasis> and interactions with some fungicides <Emphasis Type="Italic">in vitro</Emphasis>

The apple rust mite Aculus schlechtendali (Nal.) (Acari: Eriophyidae), is a main pest in apple-growing areas in Ankara, Turkey, and chemical control applications have some limitations. Entomopathogenic fungi have a potential for biological control of mites. In this study, an entomopathogenic fungus, Paecilomyces lilacinus (Thom) Samson (Deuteromycota: Hyphomycetes), was first isolated from the mite cadavers on Japanese crab apple leaves and pathogenicity of the fungus was observed in different inoculum densities and relative humidities. The pathogen caused up to 98.22% mortality of the mite population. The effects of some fungicides on the entomopathogenic fungus were determined in in vitro studies. Carbendazim, penconazole and tebuconazole were the most effective fungicides on mycelial growth of P. lilacinus, with EC₅₀ values under 3 μg ml⁻¹. In spore germination tests, captan, mancozeb, propineb were the most effective fungicides, followed by tebuconazole, penconazole, nuarimol and chlorothalonil. Sulphur could not inhibit the conidia germination totally at 5,000 μg ml⁻¹. Copper oxychloride and fosetyl-al prevented conidia formation at concentrations above 1,000 μg ml⁻¹.     

Sensitivity of Lasiodiplodia theobromae from Brazilian papaya orchards to MBC and DMI fungicides

Stem rot caused by Lasiodiplodia theobromae is an important postharvest disease of papaya in Brazil, responsible for reducing the quality and quantity of fruits. Fungicide use is one of the main disease management measures. However, there are no estimates available of pathogen sensitivity to commonly employed fungicides. Therefore, the EC₅₀ from 120 isolates of L. theobromae from northeastern Brazil, representative of six populations of the pathogen, was estimated in vitro for fungicides of the methyl benzimidazole carbamates—MBC (benomyl and thiabendazole) and demethylation-inhibiting—DMI (imazalil, prochloraz, tebuconazole) groups. Mycelial growth on fungicide-free media and virulence on papaya fruits of the MBC-sensitive and non-sensitive isolates were compared. For MBCs, 8.4% of isolates were non-sensitive to fungicides. For the remaining 91.6%, the mean EC₅₀ ranged from 0.002 to 0.13 μg ml⁻¹ and 0.36 to 1.27 μg ml⁻¹ for benomyl and thiabendazole, respectively. For DMIs, the mean EC₅₀ range for imazalil was 0.001 to 2.27 μg ml⁻¹, 0.04 to 1.75 μg ml⁻¹ for prochloraz, and 0.14 to 4.05 μg ml⁻¹ for tebuconazole. The EC₅₀ values of non-sensitive isolates were significantly (P≤0.05) higher those for the sensitive isolates for each of the DMI fungicides. Differences (P≤0.05) were found in the levels of sensitivity to DMI fungicides among the isolate populations associated with orchards. The populations from two orchards were less sensitive to DMIs. No solid evidence was found for fitness costs relating to MBC non-sensitive isolates because mycelial growth in fungicide-free media and virulence on papaya fruits were similar to those of sensitive isolates.     

Karrikins promote germination of physiologically dormant seeds of Chrysanthemoides monilifera ssp. monilifera (boneseed)

Physiological dormancy in weed species has significant implications for weed management, as viable seeds may persist in soil seedbanks for many years. The major stimulatory compound in smoke, karrikinolide (KAR₁), promotes germination in a range of physiologically dormant weed species allowing targeted eradication methods to be employed. Control of Chrysanthemoides monilifera ssp. monilifera (boneseed), a Weed of National Significance in Australia, may benefit from adopting such an approach. In this study, we hypothesised that seeds of C. monilifera ssp. monilifera exhibit physiological dormancy, germinate more rapidly as dormancy is alleviated, show fluctuations in sensitivity to KAR₁ and form a persistent soil seedbank. Seeds responded to 1 μM KAR₁ (40–60% germination) even during months (i.e. March, April, July, August) when seeds were observed to be more deeply dormant (control germination: 7–20%). Seeds germinated readily over a range of cooler temperatures (i.e. 10, 15, 20, 20/10 and 25/15°C) and were responsive to KAR₂ (~50% germination) as well. Eradication efforts for C. monilifera ssp. monilifera may benefit from use of karrikins to achieve synchronised germination from soil seedbanks, even at times of the year when C. monilifera ssp. monilifera seeds would be less likely to germinate, allowing more rapid depletion of the soil seedbank and targeted control of young plants.     

Selection,characterization and genetic analysis of laboratory mutants of <Emphasis Type="Italic">Botryotinia fuckeliana</Emphasis> (<Emphasis Type="Italic">Botrytis cinerea</Emphasis>) resistant to the fungicide boscalid

Resistance to the fungicide boscalid in laboratory mutants of Botryotinia fuckeliana (Botrytis cinerea) was investigated. The baseline sensitivity to boscalid was evaluated in terms of colony growth (EC₅₀ = 0.3–3 μg ml⁻¹; MIC = 10–30 μg ml⁻¹) and conidial germination (EC₅₀ = 0.03–0.1 μg ml⁻¹; MIC = 1–3 μg ml⁻¹) tests. Mutants were selected in vitro from wild-type strains of the fungus on a fungicide-amended medium containing acetate as a carbon source. Mutants showed two different levels of resistance to boscalid, distinguishable through the conidial germination tests: low (EC₅₀ ∼ 0.3 μg ml⁻¹, ranging from 0.03 to 1 μg ml⁻¹; MIC > 100 μg ml⁻¹) and high (EC₅₀ > 100 μg ml⁻¹) resistance. Analysis of meiotic progeny from crosses between resistant mutants and sensitive reference strains showed that resistant phenotypes were due to mutations in single major gene(s) inherited in a Mendelian fashion, and linked with both the Daf1 and Mbc1 genes, responsible for resistance to dicarboximide and benzimidazole fungicides, respectively. Gene sequence analysis of the four sub-units of the boscalid-target protein, the succinate dehydrogenase enzyme, revealed that single or double point mutations in the highly conserved regions of the iron-sulphur protein (Ip) gene were associated with resistance. Mutations resulted in proline to leucine or phenylalanine replacements at position 225 (P225L or P225F) in high resistant mutants, and in a histidine to tyrosine replacement at position 272 (H272Y) in low resistant mutants. Sequences of the flavoprotein and the two transmembrane sub-units of succinate dehydrogenase were never affected.     

Actions of sodium hypochlorite and hydrogen peroxide on seed dormancy and germination of wild oats, Avena fatua L.

Sodium hypochlorite (NaOCl) can release dormancy of imbibed wild oat (Avena fatua L.) seeds. Treatments found effective included (i) immersing intact seeds in 800 mm NaOCl for 1 h followed by incubation on 5 × 10^?4m gibberellin A₃(GA₃); (ii) immersing dehulled seeds in 800 mm NaOCl for 1 min followed by incubation on 5 × 10^?4m GA₃; (iii) immersion of dehulled seeds in much lower concentrations of NaOCl, e.g. 13 4 mm for 3 h followed by incubation on water; or (iv) incubating dehulled seeds on a low concentration of NaOCl. Based on the concentrations of each of the reagents required to produce equivalent responses, NaOCl is approximately 4–6 times more effective than hydrogen peroxide (H₂O₂) in triggering the onset of germination, and 6 times as effective in causing growth inhibition in the roots. These results suggest the modes of action of NaOCl and H₂O₂ in the termination of dormancy reside in a modification of the properties of the hull and seed coat membranes, and in the provision of additional oxygen to the seed.     

Factors affecting the activity of ethephon in stimulating seed germination of Striga hermonthica (Del.) Benth.

Ethephon (2-chloroethylphosphonic acid), which generates ethylene, stimulated the germination of pre-conditioned seeds of Striga hermonthica when it was added to the alkaline Gezira clay soil at concentrations of 2.5 to 30 mg kg^?1. As little as 5 min contact with treated soil was enough to stimulate germination. Ethephon in soil did not cause germination of unconditioned seeds for periods of up to 12 days and also had an adverse effect on seed germination when such seeds were given a second ethephon exposure after a storage period which was adequate, in untreated soil, to give the necessary pre-conditioning. Ethephon activity persisted in air-dry soil but declined over a 14 day period in moist soil. In the field ethephon at 0.6 to 4.8 kg ha^?1 decreased the number of Striga shoots and increased sorghum height and flowering.     

Germination behaviour of Cenchrus pauciflorus seeds across a range of salinities

Cenchrus pauciflorus (field sandbur) is an annual weed native to South America and Africa that has become an invasive plant in farmland and pastures around the globe. It forms two types of seeds that are different in shape and mass, defined as big seeds (M) and small seeds (P). This study examined effects of salinity and seed type on germination efficiency of C. pauciflorus. Increased concentration of salinity solutions (NaCl, Na₂SO₄ and Na₂CO₃) reduced germination rate and final germination percentage (FGP) of both seed types, while prolonging the mean final germination time (T_FG). M seeds tolerated salinity levels below 400 mmol (NaCl), 350 mmol (Na₂SO₄) and 300 mmol (Na₂CO₃), while P seeds tolerated salinity levels below 350 mmol (NaCl), 250 mmol (Na₂SO₄) and 150 mmol (Na₂CO₃). Furthermore, M seeds were less sensitive than P seeds, confirmed via increased germination rate (61%, 42% and 40%), FGP (36%, 29% and 26%), and shorter T_FG (37%, 19% and 16%) in NaCl, Na₂SO₄ and Na₂CO₃ solutions respectively. Moreover, the germination threshold values of M and P seeds were 426 and 365 mmol for NaCl, 354 and 264 mmol for Na₂SO₄ and 308 and 149 mmol for Na₂CO₃ respectively. These results add to our understanding of the germination strategy of different seed types of C. pauciflorus. This information on germination ecology may indicate a potential to invade regions with little or no salt stress.     

Chemical and environmental factors driving germination of Solanum americanum seeds

Solanum americanum Mill. is a weed that occurs with a number of crops, and it is known for its high seed production and its staggered germination. The objective of this work was to evaluate the germination behavior of S. americanum seeds under the influence of chemical and environmental factors. In the laboratory, we tested the effect on germination of (i) constant and alternating temperatures, (ii) seed washing, (iii) exposure time and concentration of chemical treatments and (iv) seeding depth and soil covered with plant residue on seedling emergence. The variables analyzed were germination percentage, germination rate index, seedling emergence and length of the seedlings. The results indicated that alternating temperatures are the main way to promote germination of S. americanum; however, chemical treatments can help to increase the germination percentage and rate index. There was no increase in germination with seed washing, with the exception of KNO₃ application. A GA₃ concentration of 0.84 g L^?1 and an exposure time of 21.22 h in 0.2% of KNO₃ promoted the highest germination of S. americanum. Germination occurs when seeds remain on the soil surface and are not covered by crop residue.     

Note: Survey of seedborne fungi of sudanese cultivars of onion,with new records

Through incubation of onion (Allium cepa L.) seed samples on potato dextrose agar and moist filter papers at 28±2°C, 32 species and four varieties belonging to 19 genera of fungi were determined as seedborne in this crop. Among them, 23 species are new reports to the mycoflora of onion seeds.Aspergillus (11 species and three varieties, ∼42.1% of the total colony count of fungi) was the most prevalent genus:A. niger (∼19.7%) was found at the highest rate in the seeds, followed byA. parasiticus (∼17.3%,A. oryzae (∼17.3%) andA. flavus (∼14.5%). The genusAspergillus was followed byPenicillium (∼12.4%),Sclerotium (∼7.1%),Fennellia, Rhizopus, Chaetomium, Drechslera andAlternaria (∼12.4%),Fusarium, Emericella andByssochlamys (∼7.1%), whereas the remaining eight genera displayed a low level of infection (∼10%). Twenty-seven species, three varieties and 12 genera represent Hyphomycetes; four genera, three species and one variety — Ascomycotina; one genus and one species — Zygomycotina; two genera and two species — other Deuteromycotina; and one genus — Oomycetes. Some species, which are known to cause devastating pre- and postharvest diseases to onion crops, were recovered from the seeds of this crop, suggesting the high possibility of their transmission by seed. http://www.phytoparasitica.org posting July 14, 2004.     

Effects of some fungicides on <Emphasis Type="Italic">Isaria farinosa</Emphasis>, and <Emphasis Type="Italic">in vitro</Emphasis> growth and infection rate on <Emphasis Type="Italic">Planococcus citri</Emphasis>

The effects of some fungicides used against citrus diseases, on mycelial growth and conidial germination of Isaria farinosa (Holmsk.) Fries [Sordariomycetes: Hypocreales] and also on the pathogenicity of the fungus on citrus mealybug, Planococcus citri (Risso), were determined. Systemic fungicides such as tebuconazole, penconazole and nuarimol were the most effective as regards both conidial germination and mycelial growth. Protective fungicides such as captan, chlorothalonil, mancozeb and propineb inhibited conidial germination at between 1 and 5 μg ml⁻¹ concentration, but captan, chlorothalonil and propineb did not inhibit the mycelial growth at 5,000 μg ml⁻¹. Mancozeb inhibited mycelial growth between 2,500 and 5,000 μg ml⁻¹. Sulphur and copper oxychloride did not inhibit the fungus even at very high concentrations. Sulphur, copper oxychloride, fosetyl-al, chlorothalonil and carbendazim did not decrease the mortality percentage caused by I. farinosa. Tebuconazole, penconazole and mancozeb were the most effective and respectively reduced the mortality from 83% to 33%, 28% and 30% in the ovisacs, from 81% to 29%, 27% and 29% in the 1st instar larvae, and from 84% to 34% in the adult females.     

Efficacy and dose–response relationship in biocontrol of Fusarium disease in maize by Streptomyces spp.

Two isolates of Streptomyces spp. DAUFPE 11470 and DAUFPE 14632 were evaluated to determine the antagonist–pathogen inoculum concentration relationship under greenhouse conditions. Pathogen and antagonist concentration, significantly (P < 0.05) affected development of Fusarium disease in maize with a significant interaction between pathogen and antagonist concentration. Dose–response relationship also differed significantly (P < 0.05) between the two isolates, but both isolates demonstrated effective control of Fusarium disease, regardless of pathogen concentration. The isolate DAUFPE 11470 provided the most effective control. The lowest value for disease incidence occurred at low pathogen (10³ chlamydospore g⁻¹ soil) and high antagonist concentration (10⁶ cfu ml⁻¹) for both isolates. The disease incidence for control plants ranged from 19% to 76%. However, in relation to control the lowest disease reduction occurred at low pathogen (10³ chlamydospore g⁻¹ soil) and high antagonist concentrations (10⁶ cfu ml⁻¹). These reductions were 10.6% and 13% for DAUFPE 14632 and DAUFPE 11470, respectively. The highest disease reductions, in relation to control plants, occurred at high pathogen (10⁶ chlamydospore g⁻¹ soil) and antagonist (10⁶ cfu ml⁻¹) concentrations for both isolates. These values were 55% and 62.2% for DAUFPE 14632 and DAUFPE 11470, respectively. The chlamydospore germination of Fusarium moniliforme was affected by glucose addition, antagonist isolates and type of inoculum. The lowest chlamydospore germination was observed with bacterial suspensions of the isolates, for all glucose additions. The results suggested that both Streptomyces spp. isolates were effective at different doses as biocontrol agents against F. moniliforme. Also, there was evidence for at least two mechanisms of biocontrol and that apparently, both isolates showed the same mechanisms of biocontrol action related to production of bioactive compounds and competition for carbon. Further studies will be developed to improve the level and effectiveness of control by these isolates.     

Sensitivity of <Emphasis Type="Italic">Botrytis cinerea</Emphasis> to propamidine: in vitro determination of baseline sensitivity and the risk of resistance

The baseline sensitivity of Botrytis cinerea to propamidine and assessment of the risk of propamidine resistance in vitro are presented in this article. The baseline sensitivities of 41 wild-type strains were distributed as a unimodal curve with EC₅₀ values of mycelial growth ranging from 0.182 to 1.460 μg ml⁻¹, with a mean of 0.79 ± 0.27 μg ml⁻¹. A total of 10 resistant mutants, obtained from one parental strain, were induced by UV irradiation and selected for resistance to propamidine with an average frequency of 1.98 × 10⁻⁹ and 0.025 respectively. These mutants were divided into three classes of resistant phenotypes with low (LR), moderate (MR) and high (HR) levels of resistance, determined by the EC₅₀ values of 5.0–15.0 μg ml⁻¹, 15.1–75.0 μg ml⁻¹ and more than 75.0 μg ml⁻¹ respectively. Neither positive cross-resistance nor negative cross-resistance was detected between propamidine and the fungicides, benzimidazole carbendazim, anilino-pyrimidine pyrimethanil, dicarboximide iprodione or procymidone. All 10 propamidine-resistant mutants showed reduced mycelial growth in vitro, sporulation, spore germination and pathogenicity when compared with the parental strain. These studies demonstrated that propamidine possesses a low risk of resistance developing. However, as B. cinerea is a high-risk pathogen, appropriate precautions against resistance development should be taken.     

球孢白僵菌孢子萌发促进剂的筛选及其对杀蚜效果的增强作用

以生物学相容性较好的聚乙二醇辛基苯基醚为乳化剂,从五大类生化营养基质中筛选出海藻糖、葡萄糖、蛋白胨、酪氨酸和菜籽油作为孢子萌发促进剂的基本成份,采用5因子正交旋转组合设计并实施了36个组配试验以优化配方。将所获孢子萌发促进剂加入球孢白僵菌(Beauveria bassiana)孢子乳悬液中喷雾接种桃蚜(Myzus persicae)无翅成蚜,在20℃和12L:12D的条件下饲养并逐日观察发病死亡数。所获数据经时间-剂量-死亡率模型模拟分析,桃蚜接种后第4～6天为死亡高峰,在10~6～10~8个孢子/ml的浓度下喷雾处理6天后的累计死亡率为62.9％～88.7％,LT_(50)估计值为3.8～4.8天,接种后第4、5和6天的LD_(50)估计值分别为3.75×10~7、3.73×10~5和2.08×10~5个孢子/ml。在连续6天的观察中,接种成蚜日均产若蚜数比对照分别下降了40.7％～85.0％,下降幅度随孢子乳悬液浓度提高而增大。这些结果表明,以上孢子萌发促进剂具有作为球孢白僵菌孢子制剂添加剂的应用潜力。     

Possible function of isoleucine in the methyl jasmonate response of <Emphasis Type="Italic">Arabidopsis</Emphasis> to <Emphasis Type="Italic">Phelipanche aegyptiaca</Emphasis>

Resistance of Arabidopsis thaliana to Phelipanche aegyptiaca (syn. Orobanche aegyptiaca) can be induced by exposure of the host to low concentrations of gaseous methyl jasmonate, in a concentration-dependent fashion. Application of methyl jasmonate at marginal concentrations, 10⁻⁸ M, for 12 h reduced infection by 50%. However, if the host plants were supplied with isoleucine at 10⁻³ M, and the isoleucine removed prior to exposure to methyl jasmonate, infection was reduced to less than 20%. The presence of isoleucine throughout the experiment—before, during and after exposure to methyl jasmonate—reduced infection of the host to almost zero. These results suggest that when Arabidopsis is exposed to methyl jasmonate, full activation of the defense mechanisms, including formation of the isoleucine jasmonic acid conjugate, might be limited by the availability of isoleucine in the host. These findings add another factor to the complex interaction between infecting parasite, and evocation of host defense mechanisms.