Fulltext search in archive

This paper presents the results of a three-year research on the effect of perforated polyethylene foil and polypropylene fibre covers on the growth of early potato cultivars at various lengths of plant covering period (2 and 3 weeks after plant emergence). Plants grown under covers were higher, produced higher mass of above-ground parts, and were characterised by a smaller value of leaf weight ratio (LWR) and leaf area ratio (LAR) compared with the cultivation without covering. In the case of plant covering for 2 weeks after emergence the mass of leaves at the time of cover removal was on average almost 2 times higher and the mass of stems over 2.5 times higher than in the cultivation without covering; the values of LWR and LAR were however smaller by 0.094 and 0.137 m

The influence of seed inoculation with a bio-preparation of nodule bacteria Rhizobium leguminosarum, fertilization of 0, 40, 80, 120 kg N/ha and molybdenum topdressing on the yield of green mass, dry matter, seed, average number of pods per plant, average number of seeds per pod, average nodule number per plant, nodule dry weight as well as plant and seed protein concentration were studied during the two years of investigations on two soils - Mollic Gleysols and Eutric Cambisols. The highest values of all investigated parameters were obtained in the inoculated seed variants with molybdenum application, except the average nodule number per plant where the highest values were achieved in variants without molybdenum. The effect of nitrogen fertilization depended on the soil type, i.e. its chemical properties. The largest number of the investigated parameters obtained the highest values as a result of fertilization with 40 kg N/ha on Mollic Gleysols (3.96% humus). Thus, seed yield was 4.02 t/ha, nodule dry matter 0.482 g per plant whereas seed protein concentration was 26.91%. The largest number of the investigated parameters on Eutric Cambisols (1.07% humus) obtained the highest values with fertilization of 80 kg N/ha where seed yield amounted to 3.65 t/ha, nodule dry matter 0.456 g per plant while seed protein concentration was 26.48%.

Yacon [Smallanthus sonchifolius (Poepp. et Endl.) H. Robinson], a native plant of the Andes, belongs to the family Compositae (Asteraceae). It represents a traditional crop from the original population of Peru. Most of the tuberous root biomass is constituted by water (> 70% of the fresh weight). Saccharides, especially oligofructans, form 70-80% of their dry weight. Four yacon ecotypes originating from Bolivia, Ecuador, Germany and New Zealand were cultivated on the trial fields of the Czech University of Agriculture in Prague in 1995, 1996, 2000 and 2001. Considerable differences among the ecotypes were observed in their content of inulin (141-289 mg/kg d.m.) and lesser for fructose levels (195-217 mg/kg d.m.). No differences were found in glucose and saccharose contents. The highest inulin and fructose contents were found in the harvests from 2001 and 2000, similar trends were found for glucose. Statistically significant effect on the content of all saccharides has the year of cultivation. Tubers contained much higher levels of inulin (179 g/kg d.m.) and fructose (193 g/kg d.m.) in comparison with rhizomes. No significant differences were found for saccharose (higher in rhizomes) and glucose (lower in rhizomes). The contents of inulin and fructose in the upper and lower parts of tubers were reciprocal. During the storage period of 140 days at10°C and 75% a relative humidity inulin content decreased by 48.7% and monosaccharides content increased (fructose by 9.97%, glucose by 31.4%) due to hydrolysis. Likewise saccharose content increased by 12.9%.

Limited information is available regarding the source-sink alterations on soybean yield under whole plant light enriched conditions. The differential responses of yield components for two old and two new cultivars were investigated. The yield sensitivity of the old cultivars to the changes in source strength and light enriched conditions was much greater than that of the two new cultivars. The yield of the new cultivars was more likely sink-limited, and source-limited for the old cultivars. The increased yield by light enrichment was in part due to an increased branch contribution. Pod number per plant was more responsive than seed number per pod. The reduction in pod number by source-sink manipulation was more severe in the old cultivars. Light enrichment increased pod number in the two old cultivars but not in the two new cultivars. Seed size was responsive to changes in the source-sink ratio and changes in the environment. Both pod number or seed size may be increased or decreased if environmental conditions for seed filling are altered.

Growth response of sugar beet plants to drought stress applied at different growth stages has been investigated. Cessation of watering imposed moderate water stress and resulted in the reduction of the relative water content of young and old leaves maximally by 6%. However, water content in taproot was more drastically decreased than in the shoot. Water withholding reduced dry matter accumulation and leaf assimilatory expansion when imposed at successive growth stages, especially in the case of earlier stress application. Substantial change in distribution pattern was observed when stress affected foliar development, more than 80% of dry matter was accumulated in the taproots. Water shortage negatively influenced both taproot and sugar yield by 16-52%, depending on the stress timing in the season. Drought stress did not change the sucrose concentration but when occurred in foliar and early stage of root development, decreased the contents of important non-sugar compounds like potassium and -amino-N solutes in the final yield. Overall, data concerning the different water status in particular organs implies that a hydrodynamic equilibrium does not exist within the sugar beet plant as a response to water stress. Drought imposed on the earlier stage, most drastically influenced plant growth and final yield. When water stress occurs at the end of crop cycle, sugar beet plants had a higher ability to recovery their growth.

This study compares effects of 2,3,5-triiodobenzoic acid (TIBA) and flavonoid quercetine (Q). In spite of the fact that both these compounds are inhibitors of the polar transport of auxin, a number of experiments demonstrated that their properties are different. If the flax seedlings were decapitated and one cotyledon was removed, the axillary bud of the remaining cotyledon grew up more intensively while TIBA (0.5% applied in the form of a lanolin paste on the remaining cotyledon) induced a correlative reversal so that axillars of removed cotyledons grew up more intensively. However, when Q (0.5%) was applied on the remaining cotyledon in the form of a lanolin paste, this inhibition was not significant. In the lamina-deprived petioles of apple trees TIBA accelerated abscission while Q caused an inhibiting effect similar to that of auxin. TIBA applied on epicotyls of pea seedlings inhibited their growth by 35% while Q only by 15%. As far as the release of ethylene by pea seedlings is concerned, both compounds showed promoting effects similar to the effect of auxin.

Sequencing of cereal genomes is not a feasible task due to their large size and high content of repetitive DNA sequences. There are two basic approaches to simplify analysis of such genomes: reduced representation approaches, such as EST sequencing, methyl filtration and Cot-based cloning and sequencing; on the other side there is analysis of genomes in a step-wise manner, e.g. through creation of chromosome-specific genomic resources. Combination of both approaches - i.e. Cot-based cloning and sequencing of DNA obtained from a chromosome-arm-specific BAC library - was tested in this work.

Several fusarioid microorganisms were isolated as potential pathogens of hop (Humulus lupulus L.) but their virulence was not proved in inoculation trials in field conditions. Molecular search for other possible pathogens was then performed. Using terminal restriction fragment length polymorphism (TRFLP), Gibberella pulicaris (anamorph: Fusarium sambucinum) was identified as a probable cause of the hop wilting. The primary cause of the disease is wounding of hop crowns by feeding of rosy rustic moth (Hydraecia micacea) caterpillars or by defect pruning and other unfavourable circumstances. The specific primer HLf1 was designed that can be used to detect the pathogen in soil and in damaged plant tissues.

The goal of the investigations was to assess the average contents of heavy metals (Pb, Zn and Cd) in the surface soil layer (0-30 cm), in drainage water and their uptake by growing plants, in the experimental amelioration field for four different variants of drainpipe spacing (15, 20, 25 and 30 m) during the three-year period. Maize and winter wheat were grown in all variants throughout the trial period. In all variants of drainpipe spacing, heavy metals in soil, drainage water and plant material were within the limits. The highest average level of Pb was 13.5 mg/kg, Zn 88 mg/kg and Cd 0.7 mg/kg in soil. Drainage water concentration of heavy metals was below 50 µg/dm³ for Pb, below 2 µg/dm³ for Cd, while the highest average value of Zn amounted to 20 µg/dm³. In grain of the crops grown, the concentration of Pb was below 0.4 mg.kg-1 and that of Cd below 0.1 mg/kg.

The aim of the study was to determine the response of soil enzymes such as dehydrogenases, urease and acid and alkaline phosphatases to heating oil contaminating (0.0, 0.25, 0.5, 0.75, 1.0, 1.5% of soil) the experimental soil supplemented with lime and used for cultivation of yellow lupine of the Markiz variety. An increasing contamination of soil with heating oil stimulated the activity of dehydrogenases and acid and alkaline phosphatases but had a toxic effect on yellow lupine. Lime supplements did not have a significant effect on an average activity of soil dehydrogenases. However, such soil treatment had a significant effect on urease. Increasing heating oil doses in lime-supplemented soil stimulated urease activity, whereas in lime-free soil urease activity was inhibited. The activity of acid and alkaline phosphatase was lower in limed soil than in lime-free soil. The activity of dehydrogenases, urease and alkaline phosphatase in the soil with lupine cultivation was significantly higher than in the unsown soil.

Our objective was to determine which rhizome extract from Japanese knotweed, Giant knotweed or Bohemian knotweed has the most significant inhibition effect on the germinated seeds. The seeds of white mustard were incubated with the extracts for two days under laboratory conditions. We monitored differences in number of germinated seeds, length of radicles, hypocotyls and root/shoot ratio between the control and experimental seeds. Inhibitory effect of extracts from dried knotweed rhizomes was confirmed, but without differences among tested plants. A higher allelopathic effect was revealed in the case of extract from aboveground parts.

Incidences of powdery mildew were repeatedly evaluated for two years on 1 420 young seedlings of 20 progenies (of different levels of mildew susceptibility) in a green house, and then for 10 years on 642 seedlings in an orchard. Part of the seedlings in the orchard were pre-selected for the characteristic and others not. Except for the first scoring done in the first year, there was no correlation between mildew incidence on individual seedlings in the green house and their mean performance in the orchard. The seedlings with scores above 6 (resistant or tolerant) at the first stage of evaluation in the green house, however, yielded four times more desirable seedlings after final selection in the orchard than the mean of the total. The progenies that had a better healthy state as a whole yielded more partially resistant genotypes than those with low mean scores. Therefore, the progenies that most rapidly develop infestation on the whole lot should be discarded, whereas those that retain a healthy state longer should be subjected to individual selection according to the previous item.

In this work, the effects of double, triple and quadruple combinations of gibberellic acid, kinetin, 24-epibrassinolide and polyamines (cadaverine, putrescine, spermidine, spermine) on the stomata movements in the leaves of barley seedlings grown under saline conditions were studied. In the control seedlings, the stomata number, stomata index and stomata length increased in the upper surfaces of leaves in comparison with their lower surfaces. In addition, the epidermis cell number in the leaves of control plants were fewer in the upper surface than that in the lower surface, but the stomata were statistically in the equal width in both surfaces. As for the applyings, they generally decreased stomata number, stomata index, stomata length and epidermis cell number, while they increased the stomata width in the upper and especially in the lower surface according to the control. The growth regulators used may have served to adaptation of barley seedlings to saline conditions by causing a decrease in most of the mentioned parameters.

An average dry matter yield structure (three cuts per growing season) in relation to agronomically valuable characteristics of six forage grass species and a year of herbage utilization was studied over the period of 1989-2002 in Lithuania. The most productive species of the first cut of two years of herbage utilization were Phleum pratense (P < 0.01) and Festulolium hybrids (P < 0.05) (average dry matter yield were 7.42 and 6.66 t/ha, respectively), moderately productive - Festuca pratensis, Dactylis glomerata and Lolium perenne (5.58, 5.42 and 5.20 t/ha), significantly lower (P < 0.01) yielding was Poa pratensis (4.19 t/ha). During two years of herbage utilization Dactylis glomerata produced significantly (P < 0.01) higher dry matter yield of aftermath - 7.30 t/ha. Other grass species were ranked in the following order: Festulolium hybrids 5.85 t/ha, Festuca pratensis 4.94 t/ha, Poa pratensis 4.57 t/ha, Lolium perenne 4.48 t/ha, and Phleum pratense 3.92 t/ha. Dactylis glomerata and Poa pratensis distinguished by the highest aftermath percent in the structure of the annual dry matter yield (57.7 and 52.2%). Phleum pratense formed an especially poor aftermath - only 34.6%. An average annual dry matter yield data analysis of two years of herbage utilization over the period of 1989-2002 showed that Dactylis glomerata and Festulolium hybrids were most productive (P < 0.01) species.

Soil bacteria belonging to the genus Azotobacter, Pantoea and some unidentified soil isolates were tested in vitro for phytohormone production under laboratory and soil conditions. The German wheat variety Munk was inoculated by several soil bacteria with exogenously applied hormones (IAA, 2,4-D) and a flavonoid(naringenin) with a half of the amount of recommended doses of fertilizers under greenhouse conditions. Most of the soil bacteria tested were able to produce indole acetic acid (IAA), and stimulated a lateral root development and colonization by the addition of 2,4-D and IAA. A formation of paranodules on roots as a result of crack entry invasion was observed with 2,4-D as well as with IAA. We were able to reisolate the organism from the paranodules and could establish the same results. Analyses for root exudates and in vitro phytohormone production by various bacterial isolates were also carried out, revealing that 2,4-D can be replaced either by high IAA producing bacteria or by exogenous application of IAA. Bacterial survival in the rhizosphere as well as the root and shoot weight of wheat plants were positively affected also by the addition of IAA, 2,4-D and naringenin.

The effect of nitrogen fertilization on root length (RL) distribution of winter wheat (Triticum aestivum L.) was investigated. The study was conducted in Prague-Ruzyne on clay loam Chernozemic soil in the years 1996-2003. Two (N0, N1) and three (N0, N1, N2) treatments, unfertilized (N0), fertilized with 100 kg (N1) and 200 kg N/ha (N2) were studied in 1996-2000 and 2001-2003, respectively. Nitrogen rate 100 kg/ha had no effect on RL in soil layers (P > 0.1) in years 1996-2000 and 2002-2003 and there was not significant interaction between N treatment and soil layer except for year 1998 (P < 0.01). Nitrogen fertilization affected RL distribution significantly (P = 0.013) only in 2001 due to reduction of root growth in subsoil layers in treatment N2 (200 kg N/ha) in comparison with N0 and N1. The effect of N fertilization on total RL in rooted soil volume was insignificant. There was a significant effect of year on total RL (P < 0.01) but not of interaction of year and N treatment. Roots reached, with the exception of two years, the depth between 100 and 130 cm. Nitrogen fertilization (N1) had no effect (P = 0.59) on rooting depth (RD) in years 1996-2000 but there was a significant effect of interaction between year and N fertilization on RD (P < 0.01). In the second experimental series (2001-2003) N fertilization rate 200 kg N/ha significantly reduced maximum RD (P < 0.01) in comparison with N0 and N1. The year had highly significant effect on RD.

In several cases ethylenediaminetetraacetic acid (EDTA) proved to be an efficient mobilising amendment during chemically enhanced phytoextraction of heavy metals. The presence of Fe-(hydr)oxides and their dissolution after the addition of EDTA can limit the phytoextraction of the targeted heavy metals due to the high stability of the formed Fe(III)EDTA complexes. This study has focused on the influence of Fe- and Mn-oxides and hydroxides dissolution on heavy metal uptake by Zea mays in a two-year EDTA-enhanced phytoextraction process. Incubation experiments and speciation modelling proved the increased concentrations of Mn and Fe through the dissolution of Mn-and Fe-(hydr)oxides. Furthermore, increased Fe and Mn accumulation was observed in maize plants after the second year of the phytoextraction process. Therefore, the presence of Mn- and especially Fe-(hydr)oxides proved to be a limiting factor during EDTA-enhanced phytoextraction of heavy metals from contaminated soils.

The influence of N-S fertilizers on the copper content in the inter oilseed rape plants was studied in field experiments. The evaluation involved two treatments of a single rate for the first spring fertilizer application with 100 kg N/ha in the AN treatment (nitrochalk) and 100 kg N/ha + 50 kg S/ha in the ANS treatment (ammonium nitrate and ammonium sulphate). A positive influence of the ANS fertilizer on the copper contents in different parts of plants was determined. The highest Cu concentrations were determined in the leaves and inflorescences, the lowest ones occurred in the stem. The concentration of Cu ranged within the interval of 1.56-8.75 mg Cu/kg of dry matter depending on the growth period and the part of the plant. No differences in copper content were determined in the seeds of individual treatment. The highest uptake in the above-ground parts of the plants was recorded in the green pod period and amounted to 57.4 g Cu/ha for the ANS treatment.

Spatial variability of soil mineral nitrogen N_min (N-NH₄⁺, N-NO₃^-) in a soil profile down to 60 cm was determined in a 19-ha experimental field in Prague-Ruzyně for four years. Winter wheat was grown in the years 2000 and 2001, oats in 2002 and mustard in 2003. Root length distribution and depth of the crops were determined at four locations representing different soil conditions within the experimental field. The coefficient of variation as the measure of the variability of nitrate N in topsoil and subsoil (0-30 and 30-60 cm, respectively) in the experimental years ranged between 18-39 and 20-37%, respectively. It was mostly the same or slightly greater in subsoil than in topsoil in respective years. The variability of ammonium N in topsoil and subsoil ranged between 4-58 and 11-27%, respectively. It was similar in topsoil and subsoil, except for autumn 2000. There was a positive relation between nitrate content in top and subsoil on all sampling terms. We did not find a relationship between N_min contents in experimental years. Spatial dependencies were evaluated on the basis of model variogram parameters. The nugget value expressed as a percentage value of the total variogram's sill was used for the class of spatial dependence determination. When a spatial dependence of the observed factor was found it was within a range of medium-strong dependence. Only in two cases a strong spatial dependence was found. A considerable variability was also found out in the variogram's range, which was between 61 and396 m. All these facts pose a problem for further actions, such as appropriate design of a sampling grid, measured data spatial interpolation and application maps design.

Seeds are the primary sinks for photosynthates during reproductive growth. Variation in light intercepted during and after seed initiation has been found a major environmental determinant of soybean [Glycine max(L.) Merrill] seed size. We investigated the influence of light enrichment and shading on seed growth rate, effective filling, cotyledon cell number, cell volume and endogenousABA concentrations of cotyledons/testas during seed filling of soybean. Evans, an indeterminate Group 0 soybean, was subjected to light reduction and enrichment treatments from the beginning of pod formation until final harvest for two years inMassachusetts. Higher rates of seed growth, greater seed dry weight, and higher cotyledon cell number were all observed with light enrichment. There was a reduction in seed growth rate and cotyledon cell number, along with a significant lowering of endogenousABA levels in testa and cotyledon with shade. The level ofABAin cotyledon during seed development was significantly correlated with seed growth rates only under shade treatments. Both the growth rates and seed filling duration were influenced by variation in light interception by the soybean canopy. The effects of varying light treatment on seed size, within one genotype, were most likely due to the differences in seed growth rate and cotyledon cell number.

The monitoring was carried on in the years 1996-2000 in the international IOSDV (Internationale Ökologische Stickstoff Dauer Versuche) field trial running since 1983 in Lukavec, Pelhřimov district. In the given locality, there are low fertility sandy-loamy cambisoils, long-term average annual rainfall 653 mm, average annual temperature 7°C, altitude 620 m. In the field trials there were introduced different organic fertilizations and graduate N-doses. According to the complex diffusion analysis, statistically significant for the yields of winter wheat after potatoes was the impact of N fertilization, years, and double interactions, with the exception of different organic fertilization. The N doses up to 120 kg.ha^-1 after potatoes proved to be optimal from the viewpoint of winter wheat yields and quality. The situation was similar for winter barley. The results of diffusion analysis for individual years were analogical also in straw yields of both cereals. The highest N dose to potatoes (200 kg.ha^-1) resulted in the highest tuber yields, but the starch content was significantly lower. Graduated N doses increased in cereals the numbers of ears per m2, but the mass of 1000 grains mostly decreased. In addition, N content in grain and straw increased with N doses, while pH annually decreased by 0.1 to 0.4. On plots without organic fertilization the N-balance was equilibrated with the annual application of 120 kg N.ha^-1 with straw embedding after cereals at 90 kg N.ha^-1 and on plots with stall dung to potatoes already at 70 kg N.ha^-1. On plots without N fertilization, the balance was passive also in P and K on plots without organic fertilization. A balance surplus was obtained already with the annual application of 15 kg P.ha-1 and 83 kg K.ha^-1 and organic fertilization. With the annual fertilization with 22 kg P.ha^-1 and 83 kg K.ha^-1 and stall dung (30 t.ha^-1) once every three years the P and K content increased annually by 1 to 3 mg.kg^-1 of soil. Maximum levels of crop growing profitability were obtained with those doses of fertilizers with which also an equilibrated balance of nutrients was obtained.

Sewage sludge application in agriculture is the simplest method of its management. Its content of organic and inorganic toxic components is a barrier to such management. Particular attention should be paid to the content of heavy metals whose presence in sewage sludge and later in soil poses hazard for plants, animals and people. The investigations aimed to determine the effect of vermicomposts obtained from tannery sludge on development of the root system and biomass of shoots as well as heavy metal concentrations in these organs. In the first year after the vermicomposts application their effect on the maize biomass increase was equal to the farmyard manure treatment but significantly worse than the mineral fertilization. The consecutive fertilizer effect of vermicomposts of tannery sludge ted on the increase in biomass of the shoots and roots of winter rape, sunflower and oats was comparable with the farmyard manure effect but notably better than the mineral fertilization. Heavy metal concentrations in individual plants were diversified; in the plants from vermicompost treatment they were as a rule lower than in the plants from mineral or farmyard manure treatment. Absorbed heavy metals accumulated primarily in the root systems, whereas the extremely high chromium content in vermicomposts did not cause its excessive accumulation in the cultivated plants.

Microbial activities and counts of microorganisms were monitored as a part of research projects at 11 localities on arable land of different soil types during the years 2002-2006. The counts of microorganisms (total bacteria count, actinomycetes, micromycetes, Azotobacter, oligotrophic and spore-forming bacteria) and microbial activities (respiration, ammonification and nitrification tests) were evaluated using summary statistics, analysis of variance and correlation coefficients. The average counts of microorganisms corresponded with usual counts of microbes in arable soils. There were only some differences among localities in Azotobacter counts. Soil respiration is very often used as an indicator of soil microflora activity. Average values of basal respiration were slightly lower (0.45 mg CO₂ /h per 100 g dry soil) than usual values, potential respiration with glucose (G) or with ammonium and G (NG) responded to usual values (average G 4.27, NG 9.53 mg CO₂ /h per 100 g dry soil). All activities (except actual ammonification) were higher in spring season, but the differences were not significant. There were significant differences in correlation coefficients among the selected criteria; 66% from the total number of correlation coefficients were non-significant, 34% were significant (13% of them was at the significance level 0.05, 10% P < 0.01, and 11% P < 0.001).

Cadmium mobility in sewage sludge amended by four types of ameliorative materials (lime, limestone, bentonite and zeolite) incubated under aerobic and anaerobic conditions for eight months was studied in the experiment. The most statistically significant decrease of available Cd extracted by 0.01 mol/l CaCl₂ was recorded in sludge between second and fourth months of incubation. As most effective stabilizers were found limestone and bentonite added into the sludge incubated under aerobic and anaerobic conditions respectively. The presence of air reduced Cd mobility in individual sludges more than lack of air. Cadmium was separated by sequential extraction into five fractions as water soluble, exchangeable, bound with Fe and Mn oxides, organically bound, and residual fraction. Sequential analysis showed decrease of Cd in exchangeable and oxide fractions in sludge treated by lime and limestone at the end of aerobic incubation. Cadmium was found in water soluble and exchangeable fractions in small portion, even so its content in these fractions was higher than determined in slighter 0.01 mol/l CaCl₂ solution.

The effect of osmotic stress on oxidative injury, compatible solutes content and water relations was investigated in two maize cultivars (Zea mays L. cv. Ankora - drought-sensitive and cv. Nova - drought-tolerant). Relative water content in leaves of both cultivars decreased after drought treatment, leaf water loss of sensitive cv. Ankora was higher than that of cv. Nova. The 24 h water stress induced by 0.3M sorbitol (-1.4 MPa) resulted in a damage of cell membranes. Lipid peroxidation rose in all studied organs of cv. Ankora and electrolyte leakage in roots of cv. Ankora was much higher than in cv. Nova. Similarly, proline content increased significantly in all studied organs of cv. Ankora. Content of soluble sugars increased in all studied organs of both cultivars, but the mesocotyl of cv. Nova accumulated the highest amount of sugars. The electrolyte leakage was the highest in the roots of both cultivars. Osmotic stress had deep influence predominantly on the roots of both cultivars. It is apparent that stress impact on the drought-sensitive cv. Ankora was deeper than on the drought-tolerant cv. Nova.

Carbon and nitrogen transformations in soil are microbially mediated processes that are functionally related. The fate of C and N was monitored in a clay-textured soil (Typic Haplocambid) which was either unamended (control) or amended with various plant materials at the rate of 10 g residue C/kg soil. To evaluate C mineralization, soils were incubated for 46 days under aerobic conditions. Nitrogen mineralization/immobilization was evaluated at the end of eight-week incubation experiment. All CO₂ evolution data conformed well to a first-order kinetic model, C_m = C₀ (1 - e^-Kt). The product of K and C₀ (KC₀) was significantly correlated with some chemical and biochemical properties of the plant residues, including N concentration (r = 0.83, P < 0.001), C:N (r = -0.64, P < 0.05) and lignin:N (r = -0.81, P < 0.001). Among the plant residue composition characteristics, N concentration (r = 0.96, P < 0.001), C:N (r = -0.69, P < 0.01) and lignin:N (r = -0.68, P < 0.01) were significantly correlated with the net rates of N mineralization/immobilization (N_m/i).

Two high yielding wheat (Triticum aestivum L.) varieties were pollinated with seven agrarian superior varieties. F₁'s thus obtained were pollinated with diverse winter maize lines/composites and treated with a solution containing 2,4-D and GA₃. The haploid embryos were rescued 13 to 16 days post pollination on MS₁ and MS₄ media. Out of 15, only two crosses viz., (UP 2338 × HD 2285) F₁ × maize and (WH 533 × PBW 343) F₁ × maize resulted in callus development and direct germination via embryo rescue.

Ditylenchus dipsaci, the stem nematode, is a migratory endoparasite of over 500 species of angiosperms. The main method of D. dipsaci control is crop rotation, but the presence of morphologically indistinguishable host races with different host preferences makes rotation generally ineffective. Therefore, a sensitive, rapid, reliable, as well as cost effective technique is needed for identification of D. dipsaci in biological samples. This study describes the development of species-specific pairs of PCR oligonucleotides for detection and identification of the D. dipsaci stem nematode in various plant hosts. Designed DIT-2 primer pair specifically amplified a fragment of 325 bp, while DIT-5 primer pair always produced a fragment of 245 bp in all D. dipsaci isolates. Two developed SCAR primer pairs were further tested using template DNA extracted from a collection of twelve healthy plant hosts; no amplification was however observed. The developed PCR protocol has proved to be quite sensitive and able to specifically detect D. dipsaci in artificially infested plant tissues.

In 1997 and 1998 we used samples of harvested grain to verify the possibility of distinguishing 14 winter wheat genotypes and six triticale genotypes and detecting the impurity on the basis of the detection of polymorphism of prolamin kernel proteins using the methods of the PAGE ISTA. On the basis of the identity index two sister prolamin lines with different percentage of participation, which was based on the weather conditions of the year of harvest, were discovered in seven wheat genotypes (Astella, Brea, Hana, Ilona, Siria, Sofia and Šárka) and two triticale genotypes (Tornádo and KM 779). A foreign genotype was detected in the Hana and Astella varieties. The identity index of the impurity to the Astella and Hana variety (i.e. ii = 0.28 and ii = 0.20, respectively) was considerably lower. In an unknown genotype (impurity) we detected the gliadin block Gld 1B3, which is the genetic marker of rye translocation T1BL.1RS, the Sr31 gene of resistance to black rust, higher cold resistance and the marker of poor baking quality (presence of secalin genes). The results proved the potential practical application of the method of electrophoretic detection of polymorphism of prolamin proteins as markers of impurities of foreign genotypes in a seed sample.

This paper presents the results of a three-year research on the effect of perforated polyethylene foil and polypropylene fibre covering at various lengths of plant cover period (2 and 3 weeks after plant emergence) on the assimilation leaf area of early potato cultivars. In the case of plant covering for 2 weeks after emergence the assimilation leaf area and leaf area index (LAI) at the moment of cover removal were on average 2 times higher than in the cultivation without covering; at the 3-week period of plant covering they were almost 1.7 times higher. A higher favourable effect of covering was obtained in the year with the lowest air temperature in May. The use of the covers at that time increased the assimilation leaf area and LAI 2.5 times and 3 times, respectively. The research showed no significant effect of the type of cover used on the assimilation leaf area and LAI; however, the specific leaf area (SLA) was higher with the use of polypropylene fibre.