Investigation on the optimal term of one-fold insecticide application for decreasing onion thrips ( Thrips tabaci Lindeman, Thysanoptera, Thripidae) damage on early white cabbage

An impact of the term of one-fold insecticide application to reduce the damage of the onion thrips in early white cabbage was established. During the growing season plants were treated with insecticide (abamectin) in three different terms (treatment 1: 9 June, treatment 2: 16 June, treatment 3: 23 June, and treatment 4: untreated). On the exterior leaves of cabbage heads, treated with the insecticide, statistically significantly lower mean index of damage was determined as compared to the untreated plants. No significant differences were found between three different terms of application. The majority of the economically important damages in all of the treatments was found between the 3rd and 6th exterior leaf in the head. The highest mean weight of heads (1517.3 g) and mean net weight of heads I = mean weight of heads - weight of damaged and removed leavesl (1166.3 g) were established in plants which were treated the last. These parameters were the lowest in untreated plants (1083.3 g / 805.6 g). The yield loss due to damaged leaves removal amounted from 22.9% (treatment 2) to 25.6% (treatment 4). Based on the results obtained in this research we concluded that yield loss due to onion thrips attack in plants with one-fold insecticide application is not substantially lower as in untreated plants (though statistically significant differences between them were established), because insecticide cannot reach the interior leaves in the head. Substantial differences in the total and net weight of heads between the treatments and especially between the treated and untreated plants are explained by the fact that feeding of numerous thrips populations in the heads and on the exterior cabbage leaves negatively affects plant physiology and yield. The highest average yield in plants which were treated the last indicates a possibility that insecticide also inhibits plant growth and development to a certain extent.     

Evaluation of some fungal diseases and yield of groundnut in groundnut-based cropping systems

A study on the evaluation of some fungal diseases and yield of groundnut in groundnut-based cropping systems was conducted in 2002 and 2003 planting seasons. Analysis of variance indicated that intercropping was highly significant on leaf spot disease severity 0.76; 0.75, rust 2.75; 2.69, as well as percentage defoliation 78.42%; 78.10% in 2002 and 2003, respectively. Plant population was significant on leaf spot severity 4.52, 4.60 rust 2.76; 366 and defoliation 226.5; 441.1 fungal as well as yield, while interactions were not significant on the fungal diseases and yield. Sole groundnut recorded significantly high severity of the fungal diseases investigated but low yield, when groundnut was intercropped with maize and melon and recorded the lowest yield in 2002 and 2003 respectively. 250,000 plants/ha recorded the lowest severity of the diseases investigated, while 444,444 plants/ha recorded the highest. Sole groundnut also recorded the highest percentage defoliation 79.37%, 79.25% when groundnut was intercropped with maize recorded the lowest 77.06%; 77.60%. 250,000 plants/ha had the lowest defoliation when 444,444 plants/ha had the highest 80.75% 82.13% in 2002 and 2003, respectively. Sole groundnut recorded the lowest in the majority of yields when intercropped with maize and with melon recorded a high yield and yield components in 2002 and 2003, respectively. The microorganisms identified were Cercospora spp., Aspergillus linked and Blastomyces.     

Induction of Systemic Resistance to Tobacco Powdery Mildew by Tobacco Mosaic Virus, Tobacco Necrosis Virus or Ethephon

Local infections of either TMV or TNV in tobacco plants cv. Havana 425 (hypersensitive to TMV) proved effective in inducing systemic resistance to subsequent inoculation with the powdery mildew fungus Erysiphe cichoracearum DC. The proportion of leaf surface invaded by this pathogen and the amount of conidia it produced were both significantly lower in virus inoculated plants than in non-inoculated controls. However, the decrease in sporulation rate was less regularly observed than the reduction in leaf area infected. TMV was more effective than TNV in protecting tobacco plants from powdery mildew. E. cichoracearum is thus added to the list of challenge pathogens to which TMV or TNV are known to induce resistance in the host plants. Necrotic lesions caused to the leaves by local treatment with Ethephon (an ethylene-releasing compound) also conferred to tobacco some degree of systemic resistance to the same fungal pathogen, more frequently visible as a reduction of leaf area invaded. The protection due to the Ethephon lesions was in present experiments less marked than that of TMV. No effects against subsequent powdery mildew infection were obtained when point freeze necrotic lesions were provoked on the plants.     

The bacterial microflora of witloof chicory (Cichorium intybus L. var.foliosum Hegi) leaves

The bacterial flora on the heads of four different witloof chicory varieties was examined. The 590 isolates were characterized by their SDS-PAGE protein profiles; they revealed 149 different protein fingerprint types. The fluorescentPseudomonas fingerprint type CH001 was abundantly found on all heads examined. Fourteen other fingerprint types occurred in high densities more than twice. Among these, the following were identified: fluorescentPseudomonas, nonfluorescentPseudomonas sp.,Erwinia herbicola, Erwinia sp., andFlavobacterium sp. The majority of the fingerprint types (90%) was found only once. It was also our objective to isolate bacteria applicable in the biological control of chicory phytopathogens. Isolates of all fingerprint types were tested for in vitro antagonistic activity and for possible deleterious effect on plant growth. FluorescentPseudomonas andSerratia liquefaciens isolates were antagonistic against fungi. Among the 161 fluorescentPseudomonas strains, five were able to produce disease symptoms on chicory leaves upon inoculation. Comparison of the results of this study with those obtained in two previous analyses revealed that the leaf microflora showed some similarities with the bacterial flora of chicory roots. The chicory seed microflora differed from that of both leaves and roots.     

Fluorescent Pseudomonas Isolates Pathogenic on Witloof Chicory Leaves

Nineteen phytopathogenic fluorescent Pseudomonas isolates were isolated from diseased witloof chicory (Cichorium intybus L. var. foliosum Hegi). They were compared with six Ps. fluorescens strains from culture collections, using SDS-PAGE of total cell proteins. The fluorescent pseudomonads examined showed seven different fingerprint types. The major group of phytopathogenic fluorescent pseudomonas revealed a fingerprint type which was frequently found on healthy chicory roots and leaves too. Some, but not all, of the isolates from healthy plants produced typical disease symptoms upon artificial inoculation of etiolated chicory leaves. Infectivity titrations showed a reduced efficiency of the latent pathogen PGSB-7228 to cause disease symptoms on the chicory leaves. The virulence of the latent pathogen is induced in the presence of wounded chicory tissue.     

Successful biological control of mist flower (Ageratina riparia) in New Zealand: Agent establishment, impact and benefits to the native flora

The white smut fungus (Entyloma ageratinae) and the gall fly (Procecidochares alani) were released in New Zealand in 1998 and 2001 respectively to suppress mist flower (Ageratina riparia). The fungus established and spread rapidly, crossing 80 km of sea to Great Barrier Island within 2 years. The mean number of P. alani galls increased exponentially to 1.96/stem at release sites, but dispersal was slow. The impact of the biocontrol agents was monitored once annually from 1998/99 to 2003/04, at up to 51 sites in the North Island. The mean percentage of live leaves infected with fungus rapidly reached nearly 60%. Maximum plant height declined significantly. In heavy infestations, mean percentage cover of mist flower declined from 81 to 1.5%. Galls were only recorded towards the end of the impact study, and at low mean numbers. As mist flower declined, the species richness and mean percentage cover of native plants increased. In contrast, the species richness and mean percentage cover of exotic plants (excluding mist flower) did not change significantly. Many plant species colonizing the plots were important native mid- or late-successional shrubs or trees. With few exceptions, the exotic plant species common in the plots were not weeds that appeared to threaten native forest habitats. There was only a weak “replacement weed effect” from the potentially serious invader African club moss (Selaginella kraussiana). These data, together with reports of reduced threats to rare endemic plants from mist flower, suggest this rapid, well-monitored weed biocontrol program was very successful.     

Impact of a disease and a defoliating insect on houndstongue (Cynoglossum officinale) growth: implications for weed biological control

The noxious weed houndstongue (Cynoglossum officinale) has become a major problem on the forested rangelands in the interior of British Columbia. However, recently the fungus Phoma pomorum and the ranchman's tigermoth (Platyprepia virginalis) were identified as potential biocontrol agents of this biennial weed. Infection by the fungus Ph. pomorum resulted in the formation of large brown lesions on leaves of houndstongue. In culture, the fungus readily produced pycnidia with pycnidiospores measuring 5.7 μm × 1.7 μm. The effect of Ph. pomorum and P. virginalis on the growth of houndstongue was examined over a six week period. Leaf age strongly influenced the intra plant distribution of insect feeding and lesion formation with Ph. pomorum primarily attacking the older leaves, while P. virginalis larvae preferred feeding on young leaves. Infection of leaves by Ph. pomorum resulted in their premature death. The effect of infection by Ph. pomorum on plant weight varied among tests, but the disease usually increased the number or percentage of dead leaves and reduced root biomass. A study of the effect of plant age and disease on houndstongue showed that younger plants infected with Ph. pomorum had a slightly higher percentage of dead leaves than older plants, but that reductions in live leaf weight and root weight were similar for different age groups. Six weeks after exposure to feeding damage by P. virginalis, there was no significant effect of P. virginalis on plant weight either acting alone or in combination with Ph. pomorum.     

The Genera and Species Spectrum of Cucumber Powdery Mildew in Czechoslovakia

In 1979 and 1980, the fungi causing cucumber powdery mildew were investigated in Czechoslovakia. In 37 localities in the major growing 102 samples of mildew were collected. Most of them came from cucumber leaves (especially from field cultures), few came from squash leaves. Studies of the imperfect stage served to identify, in the samples, two pathogen species, viz. Erysiphe cichoracearum and Sphaerotheca fuliginea have been found. E. cichoracearum predominated under field conditions; S. fuliginea was found in only two localities. In glasshouses S. fuliginea predominated.     

STUDIES ON SYSTEMIC FUNGICIDES. I. FUNGICIDAL PROPERTIES OF THE ARYLOXYALKYLCARBOXYLIC ACIDS

A method is described for assessing the systemic activity of compounds in checking the infection of broad bean ( Vicia faba ) by the fungi Botrytis cinerea or B. fabae. Treatment consisted in allowing the roots of young seedlings to stand in a solution containing 10 p.p.m. of the chemical for 2–3 weeks. The plants, together with controls, were then inoculated and when symptoms had had time to develop, the degree of chocolate spot infection was assessed. Several methods of disease assessment were examined and are critically discussed.
Certain phenoxyalkylcarboxylic acids tested by this method consistently gave a reduction in the mean size of fungus lesions on the bean leaves, clearly indicating systemic fungicidal action. The most promising substances were 2:4:6-trichlorophenoxyacetic, pentachlorophenoxyacetic and pentachlorophenoxy iso butyric acids. Further experiments with these compounds involving soil treatment, stem injection and spray application are described, and in most cases systemic fungicidal activity was clearly demonstrated. Certain compounds caused visible damage to the plants or resulted in a reduction in growth.
The results presented indicate that phenoxy acids can be fairly readily translocated in bean plants and that they tend to accumulate in actively growing tissues. It is considered unlikely, however, that they persist for long periods in plant tissue.
In the soil, the compounds appeared to remain effective for a considerable time, particularly the less soluble pentachloro acids, suggesting that soil application might provide a safe and useful method of treatment.     

Detoxification of SO2 derivatives in chloroplasts ofHardwickia binata

Intact chloroplasts isolated from sulphur dioxide fumigatedHardwickia binata leaves showed inhibition of PS II electron transport activity without any significant effect on photosystem I. Sulphur dioxide exposed leaves accumulated more hydrogen peroxide than those from non-fumigated plants and this was caused by increase in superoxide radical production. Hydrogen peroxide formation was inhibited by addition of cytochrome C and superoxide disrnutase. In sulphur dioxide fumigated leaves, increase in superoxide dismutase activity showed resistance to sulphite toxicity. The localization of ascorbate peroxidase, glutathione reductase and dehydroascorbate reductase activities in chloroplasts provide evidence for the photogeneration of ascorbate. The scavenging of hydrogen peroxide in chloroplast due to ascorbate regenerated from DHA by the system: PS I → Fd → NADP → glutathione. The system can be considered as a means for preliminary detoxification of sulphur dioxide by chloroplasts     

Gas transfer in floating-leaved plants

Pressurized gas transport with flow rates of 1.1 to 1.81 gas h^-1 plant^-1 have been detected in the floating-leaved aquatic macrophyte Euryale ferox on sunny days. The younger leaves gave the highest pressurization, but the gas flow was initiated mainly by the middle-aged leaves of the plants. The gas through-flow was shown to be highly beneficial for floating-leaved plants. It improved the oxygen level in the aerenchyma of the submerged organs of Nymphaea alba and Nymphoides peltata, and doubled the ATP level in the root tissues. On the other hand, the sulphur dioxide fumigation experiments on Nymphaea odorata indicated that the pressurized gas transport may adversely affect the floating-leaved plants, due to an increased contamination of the leaves leading to increased photo bleaching and impaired photosynthesis.Abbreviations ATP adenosine triphosphate - FW fresh weight - SO₂ sulphur dioxide     

The biological evaluation of Zato 50 WG in protection of carrot against Alternaria blight

Effectiveness of new fungicide Zato 50 WG (biologically active substances BAS - trifloxystrobin 50%) in the control of Alternaria blight on carrot was studied. Field experiments were carried out in the years 2003-2004 on carrot cv. Koral. As the standard fungicide Amistar 250 SC (BAS - azoxystrobin 250 g/dm3) was used. The results of health status of carrot leaves analysis in first and second year of experiment showed, that development of disease symptoms was lower on leaves of chemical protected plants than on leaves of control plants. The last estimation of infestation degree of carrot leaves made immediately before harvest showed, that standard fungicide Amistar had longer systemic influence on plants. This was confirmed the lower (statistically significant) infestation index of protected carrot in combination with Amistar. The estimations of health status of carrot roots were made directly after digging up indicate, that there wasn't difference of value of infestation index between protected combination and control. Experiment showed, significant effect of tested fungicides on crop quantity of carrot roots per 1 m2. Especially in the second year of study the crop of carrot roots in combination with Zato was higher - statistically significant - than in the rest combinations.     

High temperatures limit plant growth but hasten flowering in root chicory (Cichorium intybus) independently of vernalisation

An increase in mean and extreme summer temperatures is expected as a consequence of climate changes and this might have an impact on plant development in numerous species. Root chicory (Cichorium intybus L.) is a major crop in northern Europe, and it is cultivated as a source of inulin. This polysaccharide is stored in the tap root during the first growing season when the plant grows as a leafy rosette, whereas bolting and flowering occur in the second year after winter vernalisation. The impact of heat stress on plant phenology, water status, photosynthesis-related parameters, and inulin content was studied in the field and under controlled phytotron conditions. In the field, plants of the Crescendo cultivar were cultivated under a closed plastic-panelled greenhouse to investigate heat-stress conditions, while the control plants were shielded with a similar, but open, structure. In the phytotrons, the Crescendo and Fredonia cultivars were exposed to high temperatures (35 °C day/28 °C night) and compared to control conditions (17 °C) over 10 weeks. In the field, heat reduced the root weight, the inulin content of the root and its degree of polymerisation in non-bolting plants. Flowering was observed in 12% of the heat stressed plants during the first growing season in the field. In the phytotron, the heat stress increased the total number of leaves per plant, but reduced the mean leaf area. Photosynthesis efficiency was increased in these plants, whereas osmotic potential was decreased. High temperature was also found to induced flowering of up to 50% of these plants, especially for the Fredonia cultivar. In conclusion, high temperatures induced a reduction in the growth of root chicory, although photosynthesis is not affected. Flowering was also induced, which indicates that high temperatures can partly substitute for the vernalisation requirement for the flowering of root chicory.     

Acromyrmex octospinosus (Hymenoptera: Formicidae) management: effects of TRAMILs fungicidal plant extracts

Leaf-cutting ants, Acromyrmex octospinosus (Reich), are considering among the most important pest species of the New World. Until now, the main insecticides used for controlling these ants were synthetic chemicals. Leaf-cutting ants live in obligate symbiosis with abasidiomycete fungus, Leucocoprinus gongylophorus (Heim) Moeller. The crucial role of this symbiotic partner in the nest of leaf-cutting ants has prompted us to focus on A. octospinosus management through the use of fungicides in our study. Five parts of plants identified for their antifungal potential through TRAMIL ethnopharmacological surveys were tested: 1) bulbs of Allium cepa L.; 2) seed pods of Allium sativum L.; 3) green fruits of Lycopersicon esculentum L.; 4) leaves of Manihot esculenta Crantz; and 5) leaves of Senna alata (L.) Roxburgh. One plant extract with strong fungicidal activity (S. alata) against L. gongylophorus was found. The other extracts had lesser fungistatic or fungicidal effects depending on the concentrations used. The data presented in this study showed that TRAMILs fungicidal plant extracts have potential to control the symbiotic fungus of leaf cutting ants, in particular a foliage extract of S. alata.     

Antiviral activity of extracts of transgenic chicory and lettuce plants with the human interferon α2b gene

This paper studies the biological activity of protein extracts of the Cichorium intybus L. and Lactuca sativa L. transgenic plants with the human interferon ??2b gene againsf vesicular stomatitis virus. Extracts from transgenic lettuce and chicory roots, which were obtained after A. rhizogenes-mediated transformation, had antiviral activity in the range 1620?C5400 IU/g of weight; extracts from leaves of chicory plants transformed by A. tumefaciens, up to 9375 IU/g. The dependence of the antiviral activity of plant extracts from roots or leaves on the vector used for plant transformation is shown. The extracts of plant roots obtained by A. rhizogenes-mediated transformation had antiviral activity; at the same time, such activity was absent in the extracts from leaves.     

Water and temperature relations of softrot bacteria: growth and disease development

The effect of water availability and the temperature of the growth substrate on growth and disease development of softrot bacteria were studied using artificial media and plant material. Water availability was measured as the osmotic potential of a solution (ψ_osm) and was assessed for solutions of PEG4000 and KNO₃ as artificial osmotica and for plant tissue of chicory heads. Growth of softrot bacteria was found at water potentials from ψ= -0.12 MPa to ψ= -8.0 MPa but the lag phase of the growth curve increased with decreasing water potential. The relative growth rates of the three softrot pathogens showed a sigmoidal relationship with water potential, the relative growth rates decreasing rapidly at water potentials lower than ψ= -1.5 MPa. The water potential of harvested chicory heads decreased with storage time of the harvested crop but was still within the growth limits for softrot bacteria. In relation to temperature, the relative growth rate of Erwinia carotovora subsp. carotovora (Ecc) was highest at 10°C, of Erwinia carotovora subsp. atroseptica (Eca) at 15°C and of Pseudomonas marginalis (Pm) at 5°C. Chicory heads of two cultivars, Rumba and Salsa, inoculated with Ecc, had a significantly higher disease severity at 30°C (0.72 for Rumba and 0.47 for Salsa) than at lower or higher temperatures. In conclusion, temperature and water availability during forcing of chicory were not factors limiting populations of softrot bacteria. Possibilities for crop protection thus only avail during chicory root storage. During storage a high death rate combined with a low growth rate of the softrot bacteria may result in a decrease of bacterial populations below the minimum densities needed for infection during the forcing of chicory heads.     

The effect of take-all disease on gas-exchange rates and biomass in two winter wheat lines with different drought response

There have been no studies of the effect of take-all on leaf gas-exchange rates, despite the fact that take-all severely restricts plant water and nutrient uptake, which results in significant biomass and grain yield reduction. Here we describe the effect of inoculation with Gaeumannomyces graminis (Sacc.) var. tritici (Ggt) on carbon assimilation rate (A) and biomass production of wheat plants grown under two water regimes. We show that the impact of Ggt inoculation on plant growth and leaf A may be through reduced photosynthetic capacity of the leaves and not water stress per se. The nature of this reduced photosynthetic capacity remains uncertain but may involve nutrient deficiency and different enzymes produced by the fungus. In each of the 3 years the experiment was conducted, Ggt significantly reduced A, i.e. at anthesis by 18% in 2000, 15% in 2001, and 12% in 2002. In agreement with other field studies, Ggt reduced tiller number and production of all plant components, mostly root dry mass and grain mass per plant. Highly significant negative correlations were found between disease rating and A in all years, showing that at disease ratings equal or higher than 3 (on a scale from 1 to 4) A could practically be zero. While A decreased, intercellular CO₂ concentration increased or did not change, and stomatal conductance was relatively high. In addition, A was more reduced under high than under low soil moisture content. These results support the idea that water stress per se did not contribute to the observed reduction of A. The mechanism of photosynthetic capacity reduction due to the Ggt root-rotting fungus is of interest as it may lead to the molecular mechanisms of plant resistance and ultimately to the development of take-all resistant plants.     

Growth of Lucerne (Medicago sativa L.) Exposed to Sulphur Dioxide

The effect of exposure to sulphur dioxide (0 or 96 µgm^–3 SO₂) on the growth and sulphur content of lucerne(Medicago sativa L.) was examined in a period of 135 d duringwhich the plants were harvested four times. The lucerne wasgrown in pots of soil with and without the addition of sulphateand of nitrate. Evidence of sulphur deficiency, including areduction in the weight, the number and the sulphur contentof shoots, was found in plants grown without added sulphate.Deficiency was alleviated through exposure of plants to SO₂.Apart from reducing shoot weight at one harvest and generallyincreasimg the concentration of sulphur in the shoots, exposureto SO₂ had no significant effect on plants grown with addedsulphate. The yield of shoots was greater, and was reduced toa lesser extent with sulphur deficiency, in plants grown withadded nitrate than in those dependent on rhizobia. Whilst thetranspiration coefficient increased greatly in sulphur-deficientplants, it was reduced where otherwise similarly treated plantswere exposed to SO₂; this treatment did not alter the coefficientin plants with an adequate supply of sulphur from the soil.     

Efficacy of Metarhizium anisopliae in controlling the two‐spotted spider mite Tetranychus urticae on common bean in screenhouse and field experiments

The efficacy of aqueous and emulsifiable formulations of the fungus Metarhizium anisopliae isolate ICIPE78 was evaluated on the population density of Tetranychus urticae infesting common bean plants under screenhouse and field conditions. Synthetic acaricide abamectin was included as a check. Bean plants were artificially infested with T. urticae and allowed to multiply. Three treatments were applied in the screenhouse and 1 treatment in field trials. Mite density was recorded 2 d before spraying and weekly postspraying. The number of pods per plant, number of seeds per pod, and the dry weight of seeds per plant were recorded only in the screenhouse trials. In both screenhouse and field trials, fungal formulations applied at the concentration of 10⁸ conidia/mL and the acaricide reduced the population density of mites as compared to the controls. There were significant differences in T. urticae population densities between the treatments at the various post‐spraying sampling dates. In the screenhouse, the mite densities were near zero from 3‐week postspraying in the treated leaves. At 4‐week postspraying, there were no more leaves in the untreated control (T1) and in the control water + Silwet‐L77 (T2). Fungal formulations were as effective as abamectin in reducing mite densities in both screenhouse and field experiments. There were significant differences in the production parameters during the 2 screenhouse trials, with fungal and abamectin treatments generally having the highest yield. Results of this study underline the potential of the M. anisopliae isolate ICIPE78 as an alternative to acaricides for T. urticae management.     

Effects of anthracene on development of an arbuscular mycorrhizal fungus and contribution of the symbiotic association to pollutant dissipation

The influence of anthracene, a low molecular weight polycyclic aromatic hydrocarbon (PAH), on chicory root colonization by Glomus intraradices and the effect of the root colonization on PAH degradation were investigated in vitro. The fungus presented a reduced development of extraradical mycelium and a decrease in sporulation, root colonization, and spore germination when exposed to anthracene. Mycorrhization improved the growth of the roots in the medium supplemented containing 140 mg l⁻¹ anthracene, suggesting a positive contribution of G. intraradices to the PAH tolerance of roots. Anthracene disappearance from the culture medium was quantified; results suggested that nonmycorrhizal chicory roots growing in vitro were able to contribute to anthracene dissipation, and in addition, that mycorrhization significantly enhanced anthracene dissipation. These monoxenic experiments demonstrated a positive contribution of the symbiotic association to anthracene dissipation in the absence of other microorganisms. In addition to anthracene dissipation, intracellular accumulation of anthracene was detected in lipid bodies of plant cells and fungal hyphae, indicating intracellular storage capacity of the pollutant by the roots and the mycorrhizal fungus.