沙棘木蠹蛾幼虫病原真菌——球孢白僵菌的分离与鉴定

在对沙棘木蠹蛾危害情况进行调查时,从死亡的沙棘树干内发现了罹病致死的沙棘木蠹蛾,通过对虫尸体内病原真菌的分离与鉴定,确定为球孢白僵菌(Beauveria bassiana)。经室内致病力测定,接种浓度4亿/mL、8亿/mL、12亿/mL,54 d的感病率分别是72.22%、83.33%、100%,证明球孢白僵菌是沙棘木蠹蛾的病原菌。同时表明浓度越高感病率越高。     

Functional resilience of microbial communities from perturbed upland grassland soils to further persistent or transient stresses

The microbial functioning of soils following perturbation was assessed at a temperate upland grassland site, maintained by the Soil Biodiversity and Ecosystem Function Programme at Sourhope Research Station, Scotland. Published results indicated that the soil microbial communities were resilient to these initial perturbations; in this paper we tested whether they were equally resilient to a subsequent perturbation. Soil samples were taken from field plots receiving treatments that represented different forms of perturbation, viz. reseeding, application of sewage-sludge, biocide or nitrogen plus lime, and a non-perturbed control. Functional resilience following further perturbation comprising a transient heat or persistent copper perturbation was assessed over 28 days, by monitoring the short-term decomposition of added plant residues. Bacterial community structure was assessed by DGGE separation of eubacterial 16S rDNA PCR products. PCR-DGGE did not distinguish any significant difference (P>0.05) between the bacterial communities of soils under different treatments, showing differences only between treated soils and the untreated, control soils.Two days after the application of stresses, functional capability differed in soils under different treatments. Soil samples from all the treated plots were less resilient to heat stress than soil from control plots. The initial reduction in decomposition following the addition of copper differed between treatments, but function had not recovered in any of the Cu-amended soils within 28 days. Soil resilience varied according to the type and duration of stress applied, microbial activity, soil characteristics and treatment regimes. The initial resistance of function to stress was not predictive of recovery of function over time.     

Dough Strain Hardening Properties as Indicators of Baking Performance

Bread loaf volume is an important economic criterion. Breeders, millers, and bakers need measurements allowing them to evaluate dough performance during processing. Strain hardening is an important dough property. It describes the stability of the gas cell walls and the ability of cells to expand further; therefore, the higher the strain hardening index (n), the better the baking performance. Dough exhibits strain hardening during uniaxial extensibility tests. However, obtaining n from an extensibility test is time consuming. The objectives of this study were to identify the extensibility parameters that contribute to n. Three parameters were retained in the model (R² = 0.90): dough strength (R_max), extensional delay (E_Diff), and initial slope of the curve (E_i). R_max was the largest contributor and was proportional to the dough strain hardening properties. E_Diff and E_i had a detrimental effect on n. The appropriateness of the model was validated with two sample sets (19 genotypes, 12 environments). Significant correlations were found between loaf volume and n (r = 0.52–0.64) for 7 of the 12 environments. The strain hardening index was found to be a good predictor for baking performance as judged by loaf volume.     

Response of weed emergence to rate of Vicia villosa Roth and Secale cereale L. residue

Vicia villosa Roth (hairy vetch) or Secale cereale L. (rye) residue at 2 to 4 times the natural field rate reduced seedling emergence of a wide variety of weed species. However, the natural rate of residue was insufficient for control of most weed species. The form of the response of weed emergence to increasing rates of residue varied among species: emergence of some species showed a monotonic decline in response to increasing rates of residue whereas emergence of others increased at low rates before declining at higher rates. In addition to reducing number of seedlings, high rates of residue delayed the date of emergence. Seed size was generally not a good indicator of a species' ability to emerge through residue, although one very large seeded weed, Abutilon theophrasti. was especially insensitive to residue. V. villosa and 5. cereale did not differ greatly in their effect on weeds early in the growing season, but V. villosa decomposed more rapidly and allowed greater emergence later in the season. Effet de résidus de Vicia villosa Roth et de Secale cereale L. sur la levée des mauvaises herbes Des résidus de Vicia villosa Roth (Vesce velue) et de Secale cereale L. (seigle) à 2–4 fois la quan-tité normale réduisaient la levée d'un large spectre de mauvaises herbes. Cependant la quantité normale de résidus était insuffisante pour lutter contre la plupart d'entre elles. La réponse de la levée des mauvaises herbes à des quantités crois-santes de rVsidus différait selon les espèces. Pour certaines, la levée subissait un déclin monotone; pour d'autres, elle augmentait en présence de faible quantités de reésidus puis décroissait pour des quantités plus importantes. Ces dernières réduisaient la levée et la retardaient également. La taille des graines n'était généralement pas un bon indicateur de la capacité des espèces à lever au travers des résidus, bien qu'une trèAs grosse grains, Abutilon theophrasti Medic., était particu-lièrement insensible aux résidus. V. villosa et 5. cereale ne différaient pas beaucoup dans leur effet sur les mauvaises herbes en début de saison, mais V. villosa se décomposait plus rapidement et permettait des levees plus importantes en fin de saison. Wirkung von Emterückständen von Vicia villosa Roth und Secale cereale L. aufdie Keimung von Unkräutern Durch 2- bis 4 fache Ernteräckstände der Be-haarten Wicke (Vicia villosa) und des Roggens (Secale cereale) wurde die Keimung einer großen Zahl von Unkrautarten herabgesetzt. Normale Ernterückstandsmengen behinderten jedoch die Keimung nur unzureichen. Die Art und Weise der Reaktion der Keimung auf höhere Riick-stände war von Art zu Art verschieden: Die Keimung einiger Arten nahm mit zunehmender Menge an Ernterückständen gleichmäßig ab, während sie bei anderen bei niedrigen Mengen anstieg, urn dann bei höheren Mengen abzunehmen. Zusätzlich zur Verringerung der Keimpflanzendichte wurde bei hohen Rück-standsmengen die Keimung verzögert. Die Samengröße war im allgemeinen kein guter Indikator für die Fähigkeit einer Art, durch das Rückstandsmaterial zu keimen, obwohl eine Art mit großen Samen, Abutilon theophrasti, gegenüber diesen Rückständen besonders unempfindlich war. Die Rückstände der beiden Kulturpflanzen zeigten zu Beginn der Vegetationsperiode keine großen Wirkungsunterschiede, aber die Rückstände von Vicia villosa zerfielen schneller und ließen später eine stärkere Keimung zu.     

Nitrogen fertilization and plant development of cotton as determined by nodes above white flower 1

Early maturation is very beneficial in successfully harvesting a high‐quality, high‐yielding cotton (Gossypium hirstum L.) crop. If harvest is delayed until inclement weather patterns are established, both yield and fiber quality may be lost. The objective of these studies was to determine the maturity differences that occur in cotton differentially fertilized with nitrogen (N). Field experiments with irrigated cotton were conducted in 1990 and 1991 in three locations to study the effects of soil applied N rates on cotton maturity as estimated by nodes above white flower (NAWF) measurements. The test sites and soils were a production field near Manila, AR, on a Dundee sandy loam (fine‐silty, mixed, thermic Aeric Ochraqualfs), the Southeast Branch Experiment Station (SEBES) near Rohwer, AR, on an Hebert silt loam (fine‐silty, mixed, thermic Aeric Ochraqualfs), and the Northeast Research and Extension Center (NEREC) near Keiser, AR, on a Sharkey silty clay (very fine, montmorillonitic, nonacid, thermic Vertic Haplaquepts). Criteria used as indicators of crop maturity and earliness in these studies were the time in days after planting (DAP) and the accumulated heat units (HU) for the crop to reach NAWF=5. Increasing N rates delayed maturity at SEBES both years and at Manila in 1991 but not at NEREC either year. Differences in maturity between N treatments of 168 and 224 kg N/ha were minimal at all locations both years. Smaller differences in time for the plants to achieve NAWF=5 were observed in the cotton grown at Manila in 1990 and at NEREC both years. The smaller differences at Manila are assumed to be due to high levels of residual N from previous crops. Early‐season vegetative growth was indicated by NAWF extrapolated to first flower (60 DAP or 945 HU). A trend of higher NAWF at the extrapolated first flower stage with increasing N rate was observed, but generally differences were minimal. The NAWF values at DAP=60 were lower in 1991 than in 1990 for all locations.     

Vegetation response to intensity of herbaceous weed control in a newly planted loblolly pine plantation

Growth of loblolly pine (Pinus taeda L.) seedlings through three growing seasons after planting increased with intensity of herbaceous weed control using herbicides. Weed control had no effect on pine survival. Two years of complete herbaceous weed control (CHC, control throughout the first two growing seasons after planting) and operational herbaceous weed control (OHC, sulfometuron at 0.42 kg ai/ha at the beginning of the first growing season), resulted in lower biomass of weeds plus trees than with no herbaceous weed control (NHC) during the first growing season. Differences in total biomass during the first year were due to differences in biomass of herbaceous weeds. Total biomass on CHC and OHC plots was at least as great as NHC the second year, and greater by the third year, as pines assumed dominance as a result of increased growth from reduction of herbaceous weeds. The operational herbicide treatment had no significant impact on overall herbaceous weed biomass and cover, and little effect on species composition compared to no herbaceous weed control two and three growing seasons after treatment. The CHC treatment significantly reduced herbaceous weed biomass, cover and composition through three growing seasons.     

Classification of Single‐ and Double‐Mutant Corn Endosperm Genotypes by Near‐Infrared Transmittance Spectroscopy

A total of 1,176 grain samples representing 10 different single‐ and double‐mutant genotypic classes of specialty starch corn were used for developing various classification models based on near‐infrared transmittance spectra. The genotypes used included amylose‐extender (ae), dull (du), sugary‐2 (su2), waxy (wx), ae wx, ae du, ae su2, du wx and du su2. Two‐class classification models (only two genotypes compared) were developed using partial least squares analysis (PLS) while three‐way and multiclass models were examined using principal component analysis (PCA). The effectiveness of the calibrations was evaluated by examining the percentage of unknown grain samples incorrectly classified. In general, two‐class models performed better than multiclass models. However, they did not show improvement when discriminating among genotypes with overlapping amylose contents such ae du vs. ae and ae su2 vs. ae. Three‐way models including double‐mutants and their corresponding single‐mutant counterparts had misclassification percentages typically <5% using 14 PCA factors but again, with the exception of models including genotypes with overlapping amylose contents such as ae du vs. ae vs. du. The best multiclass model using all 10 genotypic classes simultaneously revealed only two classes (ae su2 and du) with misclassification rates >10% based on 16 PCA factors. This study demonstrates that, depending on the material to be considered, near‐infrared transmittance spectroscopy could be useful when segregation of specialty starch hybrids grain from other grain types is necessary.     

Whole Grain Amylose Analysis in Maize Using Near-Infrared Transmittance Spectroscopy

The development of genetically modified starches has relied on the use of maize (Zea mays L.) endosperm mutant alleles that alter starch structural and physical properties. A rapid method for predicting amylose content would benefit breeders and commercial handlers of specialty starch corn. For this reason, a study was conducted to investigate the use of near-infrared transmittance spectroscopy (NITS) as a rapid and nondestructive technique for predicting grain amylose content (GAC) in maize. Many single- and double-mutant inbreds and hybrids were used to create a calibration set for the development of a predictive model using partial least squares analysis. A validation set composed of similar genetic material was used to test the prediction model. A coefficient of correlation (r) of 0.94 was observed between GAC values determined colorimetrically and those predicted by NITS; however, the predicted values were associated with a large standard error of prediction (SEP = 3.5). Overall, NITS discriminated well among high amylose and waxy genotypes. The NITS calibration was used to determine levels of contamination by normal kernels in waxy and high-amylose (Amy VII) grain samples intended for wet milling. In both cases, a 5% contaminated sample could be detected from pure samples according to predicted NITS values.     

Precambrian sponges with cellular structures

Sponge remains have been identified in the Early Vendian Doushantuo phosphate deposit in central Guizhou (South China), which has an age of approximately 580 million years ago. Their skeletons consist of siliceous, monaxonal spicules. All are referred to as the Porifera, class Demospongiae. Preserved soft tissues include the epidermis, porocytes, amoebocytes, sclerocytes, and spongocoel. Among thousands of metazoan embryos is a parenchymella-type of sponge larvae having a shoe-shaped morphology and dense peripheral flagella. The presence of possible amphiblastula larva suggests that the calcareous sponges may have an extended history in the Late Precambrian. The fauna indicates that animals lived 40 to 50 million years before the Cambrian Explosion.