Sucrose Accumulation in Sugar Beet Under Drought Stress

Drought stress may affect sucrose accumulation of sugar beet by restricting leaf development and storage root growth. The objective of this study was to identify changes occurring in the storage root of Beta beets in growth characteristics and ions and compatible solutes accumulation under drought with regard to sucrose accumulation. Two pot experiments were conducted: (1) sugar beet well supplied with water (100 % water capacity), under continuous moderate (50 %) and severe drought stress (30 %), (2) sugar beet and fodder beet well supplied with water (100 %) and under continuous severe drought stress (30 %). Under drought stress, the ratio of storage root to leaf dry matter of sugar beet decreased indicating a different partitioning of the assimilates. The sucrose concentration of the storage root was reduced. In the root, the number of cambium rings was only slightly affected, although drought stress was implemented already 6 weeks after sowing. In contrast, the distance between adjacent rings and the cell size was considerably restricted, which points to a reduced expansion of existing sink tissues. The daily rate of sucrose accumulation in the root showed a maximum between 16 and 20 weeks after sowing in well‐watered plants, but it was considerably reduced under drought stress. The concentration of compatible solutes (K, Na, amino acids, glycine betaine, glucose and fructose) decreased during growth, while it was enhanced because of drought. However, when sucrose concentration was added, a constant sum of all examined solutes was found throughout the vegetation period. It was similar in sugar beet and in fodder beet despite different concentrations of single solutes, and the total sum was not affected by water supply. A close negative relationship between the concentration of compatible solutes and sucrose occurred. It is therefore concluded that the accumulation of compatible solutes in the storage root of Beta beets under drought might be a physiological constraint limiting sucrose accumulation.     

Evaluation of the Ph‐3 gene‐specific marker developed for marker‐assisted selection of late blight‐resistant tomato

Late blight caused by Phytophthora infestans is one of the most destructive diseases of tomato (Solanum lycopersicum L.) that mainly occurs in cool and wet environments. With the spread of the A2 mating type and new clonal lineages, fewer fungicides provide effective control of the disease, which has increased its worldwide threat. Host resistance could contribute significantly to sustainable disease control. Ph‐3 is a race‐specific late blight resistance gene commonly used in commercial tomato breeding. Availability of precise and easy to use gene‐based markers would facilitate selection. In this study, a Ph‐3 on‐gene cleaved amplified polymorphic sequence (CAPS) marker, Ph3.gsm/HincII, was developed based on the published gene sequence of Ph‐3. The effectiveness of the marker was evaluated along with other published Ph‐3 markers using an F₉ recombinant inbred line (RIL) population derived from NC 23E‐2(93) × L3708. Markers Ph3.gsm/HincII and TG328/BstNI accurately genotyped the RIL population for Ph‐3. In addition, Ph3.gsm/HincII was able to differentiate variable susceptible alleles. This reliable codominant DNA marker would be very useful in marker‐assisted selection, particularly for resistance gene pyramiding.     

Genetic variation and comparative analysis of thrips resistance in glandless and glanded cotton under field conditions

Glandless cotton can be grown for cottonseed free of toxic gossypol to be used as food and feed for non-ruminant animals. However, one of the most important limiting factors preventing its commercial production is its higher insect damage than conventional glanded cotton. Thrips is the one of the most important insect pests in the early growing season that may cause yield losses. In this study, 28, 29, 26, and 2 glandless cotton lines were compared with glanded control Acala 1517-08 and other glanded lines for resistance to the Western flower thrips, Frankliniella occidentalis (Pergande) in four replicated field tests each containing 32 genotypes. In the same field, 28 glanded commercial cultivars and 78 glanded breeding lines were compared with Acala 1517-08 and Acala 1517-99 in three other tests with 32 genotypes each. The experimental layouts allowed a comprehensive comparative analysis of thrips resistance within and between glandless and glanded cotton. Overall, glandless cotton had similar or lower thrips damages than glanded cotton, indicating that the glandless trait may serve as a genetic factor for suppressing thrips damage. As compared with Acala 1517-08 which represented one of the most thrips resistant genotypes among glanded cotton tested, glandless Acala GLS and many selections from glandless germplasm were more resistant, while some were similar to Acala 1517-08, indicating that genetic factors other than the glandless trait also affect thrips resistance in cotton. The estimates for broad-sense heritability for thrips resistance were moderate, indicating that thrips resistance is selectable. This is corroborated by the identification of many thrips resistant lines from a cross between Acala 1517-08 and Acala GLS. This study has laid a foundation for a more detailed study using most resistant lines with desirable agronomic traits in multiple environments.     

Genetic variation and selection within glandless cotton germplasm

There is a renewed interest in research and use of glandless (free of gossypol) Upland cotton (Gossypium hirsutum L.) that can produce edible seeds for human food and animal feed. However, there was a lack of information on yield potential of existing glandless germplasm since intermittent breeding activities for glandless cotton were stopped in the U.S. before 2000. The objectives of the present study were to test obsolete and exotic glandless germplasm for possible production and evaluate progress in direct pedigree selection within the existing glandless germplasm in eight field tests. In multiple tests, the glandless cotton Acala GLS yielded only 65–80 % lint of the glanded control Acala 1517-08 and 46–75 % lint of commercial transgenic cultivars. Most of obsolete glandless germplasm and their selections yielded <70 % of Acala 1517-08 and only three selections yielded 82–89 % of the control. Genetic variation in yield and fiber quality traits was seen from significant differences between selections within the same glandless germplasm, indicating the existence of residual genetic variation. Most importantly, three selections from exotic glandless germplasm out-yielded Acala 1517-08 by 4–9 %, one of which had desirable fiber quality traits. These promising glandless lines with comparable yields to commercial cotton make it possible to revitalize the glandless cotton industry. More field tests will be needed to evaluate their yield potential and adaptability in the U.S. Cotton Belt.     

Soil fertility in a long‐term fertilizer trial with different tillage systems

The presented results originate from a field experiment established in 1972 on an Eutric cambisol with two main factors: soil tillage (conventional‐, reduced‐, and no‐tillage) and NPK fertilization. The test plants were maize and winter wheat in two years rotation.

The long‐term soil fertility without and with optimum fertilization, the influence of fertilization, tillage and crop sequence on grain yields, the organic carbon content (C_org) and the nitrate infiltration are discussed.

In the course of years without any NPK fertilization grain yields of maize and winter wheat decreased significantly and reached a minimum level which was modified however by the actual climatic conditions. The analogous yield level of optimum NPK fertilization at maize showed a growing tendence while at wheat it remained mostly constant.

The method of soil tillage influenced grain yield of winter wheat to a lesser extent than the yield of maize. Grain yields of maize and winter wheat were consistently lower with no‐till as compared to reduced or conventional tillage, however the differences with w. wheat were much smaller. The effect of tillage was especially high at N₀ P₀ K₀. Crop rotation had a positive effect on the yields of maize. For winter wheat at N₀ P₀ K₀ oneself was the better forecrop, while at optimum N and PK maize performed a little better. C_orgcontent of soil slightly increased in the course of 25 years not only on the fertilized plots but on the nil plots too. Increasing N‐doses showed only a little effect on the C_org. There was a little positive effect of no‐till on C_org content of soil as well as compared fall ploughing. Soil tillage did not much influence the total amount of nitrate in the soil profile. The distribution of nitrate‐N in the soil profile was more affected by the actual climatical circumstances than by the system of tillage. However big nitrate accumulations were found in the subsoil according to different soil tillage systems at some other times, as well as lack of it, which suppose the possibility of a relative quick nitrate infiltration.     

Carbon dioxide production and oxygen consumption during the early decomposition of different litter types over a range of temperatures in soil‐inoculated quartz sand

Oat straw, hay, and alfalfa litter, differing in microbial colonization and recalcitrance, were added to organic matter–free quartz sand (5 mg C [g material]^–1) and incubated in the laboratory at 5°C, 10°C, 15°C, 20°C, and 25°C. Different incubation periods were chosen so that theoretically the same amounts of CO₂ would be produced and the same amounts of O₂ would be consumed for each litter type. It was investigated whether Q₁₀ values (change in respiration rate between two temperatures) increase with decreasing temperature and how much these Q₁₀ values and also the respiratory quotient (RQ: mol CO₂/mol O₂) depend on the litter type. The sums of CO₂‐C evolved and O₂ consumed, but also the contents of microbial biomass C and microbial biomass N showed a nearly 7‐fold increase in the order oat straw < hay < alfalfa litter. In contrast, the ratio of the fungal cell‐membrane component ergosterol to microbial biomass C was highest in the oat straw (4.1‰) and lowest in the alfalfa litter (0.2‰). This ratio reached a similar level between 5°C and 15°C (1.9‰), significantly higher (p = 0.01) than the level at 20°C (0.9‰). Respiration was similar between 20°C and 25°C, with a mean Q₁₀ value of 1.9. The use of temperature rate‐modifying factors suggested by the carbon‐turnover model ROTHC revealed that the incubation period for similar respiration rates was underestimated at 5°C and overestimated at 25°C. The lignin‐poor and protein‐rich alfalfa litter showed the highest Q₁₀ values of the three litter types in the medium temperature range of 10°C to 20°C. In contrast, the lignin‐rich and protein‐poor oat straw showed significantly highest Q₁₀ values at 5°C and 25°C in comparison with the other two litter types. The RQ was significantly highest in the hay litter (1.05) and in comparison with alfalfa litter (0.97) and oat straw (0.92). Strong temperature‐dependent variations in Q₁₀ values and respiratory quotients suggest interactions between litter quality, microbial colonization of litter, and temperature, which warrants further investigation.     

Composting of Wood Containing Polycyclic Aromatic Hydrocarbons (PAHs)

The addition of various nitrogen sources, such as liquid hog manure and mineral medium, to pine wood accelerated the composting process in Dewar vessels, which was obvious from the increased decomposition temperature and the more intensive oxygen consumption and carbon dioxide production. During composting in Dewar vessels of artificially PAH-contaminated pine wood soaked with liquid manure, the PAH degradation was influenced by the inoculum used. The fastest PAH degradation was achieved by compost addition, but the most intensive carbon dioxide evolution was measured with hydrocarbon-polluted soil as an additive. After 61 days, the PAH content of the wood was reduced from each 1000 mg/kg to 26 mg/kg of phenanthrene and 83 mg/kg of pyrene. The relation between the microbial wood decay and PAH degradation shows that the detoxification at least of artificially PAH-polluted wood demands only a partial wood decay.

A pilot scale percolator was applied to composting of artificially contaminated pine wood and really polluted waste wood. After 27 days of remediation, the portion of residual PAHs was higher in the case of the really polluted material. The slower degradation in the real waste wood may be explained by the lower bioavailability of pollutants in comparison with the artificially contaminated wood. In really polluted wood, the degradation rate of PAHs depended on their degree of condensation (the higher the number of aromatic rings the smaller the degradation rate was).     

Correlation between Microcrustaceans and Environmental Variables along an Acidification Gradient in Sudbury, Canada

Multivariate methods were used to relate microcrustacean (pelagic and littoral) richness and composition (presence/absence) to water quality and other environmental variables. All acidification variables (pH, aluminium, ANC) showed significant correlation with both species richness and composition. The variation in microcrustacean richness was best explained by the combination of dissolved organic carbon (DOC), fish species richness and lake area. Of 16 variables tested, pH showed strongest correlation with the main gradient in the crustacean composition explaining between 13 and 16% of the variance in the species data (CCA). pH, elevation, lake area, average depth, DOC, conductivity and fish species richness explained 30–54% of the total variance. Stronger correlation was obtained between species composition and environmental data in analyses which included the between-year differences than analyses based on the cumulative species records. Analyses based on the pelagic species exclusively gave similarly stronger correlation than analyses based on all crustacean species. Small changes in the species composition during the three years of study may be an indication of recovery of microcrustaceans in Killarney lakes.     

Sublittoral Chironomids as Indicators of Acidity (Diptera: Chironomidae)

The sublittoral chironomid fauna of 22 lakes in Killarney Park, Ontario, Canada were examined for their response to different levels of acidification. Included in the analysis were naturally acidic lakes, lakes acidified by atmospheric deposition but now recovering, and unacidified circumneutral lakes. pH in the study lakes ranged from 4.6 to 7.7. No correlation was found between species richness and pH, nor between abundance and pH. Acid neutralizing capacity (ANC), the temperature at the sampling depth, pH, and dissolved organic carbon were the variables contributing significantly in a canonical correspondence analysis of the abundance data. ANC was the most important variable in describing the chironomid community, accounting for about 9% of the variance in the species data. This study is the first step in an effort to model the changes in the chironomid community of recovering acidified lakes and the results suggest that ANC may be an important predictor variable.     

Metal Remobilisation during Resuspension of Anoxic Contaminated Sediment: Short-Term Laboratory Study

The sediments of the Tagus estuary North Channel arecharacterised by high concentrations of trace metals andmonosulphides. During dredging operations Cd, Cu and Pb wereanalysed in water and suspended sediments collected 50 to 100 m around the dredging point. Concentrations in bothfractions fluctuated randomly: 2–3 fold for Cd and Cu and 10 for Pb. Since sampling in the dredging point reflectsintegration of rapid chemical reactions, a short-termlaboratory experiment was conducted to follow the geochemicalalterations occurring in the highest turbidity sites. Theexperiment was monitored as a function of time over a period of4 hr in short time intervals. Dissolved oxygen, pH, E_H,AVS, SO₄ ^2-, Cl^- and metals were monitored in theslurry samples. Iron, Mn, Cd, Pb and Cu were determined in thedissolved fraction (<0.45 μm), in the reactive solid phaseand in the total fraction. Resuspension resulted in asignificant release of Fe, Mn, Cd, Cu and Pb from the solids.Following the release Pb and Cu were almost totally scavengedin the 4 hr by the newly precipitated Fe oxyhydroxides, while more than 50% of the mobilised Cd remained in the dissolved fraction. The less efficient removal of Cd from solution implies a prolonged availability of this metal in the environment.