塑性土壤破碎方法的比较

用改装的三轴剪切仪对拉伸、扭转、弯曲、直剪、切割和纯切割等基本加载方式进行了详细研究。结果表明,弯曲加载是需要最小力及最少能耗使塑性土壤破碎的一种有效的加载方式。     

Economic Impact of Double‐Crested Cormorant,Phalacrocorax auritus,Depredation on Channel Catfish,Ictalurus punctatus,Aquaculture in Mississippi,USA

The Yazoo River Basin of Mississippi, USA, supports the largest concentration of hectares devoted to channel catfish, Ictalurus punctatus, aquaculture production in North America. The Yazoo Basin also supports large numbers of resident, wintering and migrating fish‐eating birds, with the Double‐crested Cormorant, Phalacrocorax auritus, implicated as the most serious depredating species. We used data from aerial surveys of numbers and distribution of cormorants in the Yazoo Basin and on commercial catfish ponds during winters (November–April) 2000–2001 and 2003–2004 to refine estimates of regional economic losses due to cormorant depredation. In both periods, the greatest monthly estimates of cormorant foraging occurred from 1 January to 31 March. Losses in terms of biomass, number, and dollar value were greater for foodfish ponds than fingerling ponds. Monthly weighted estimates of catfish consumed were 1775.3 and 1346.6 m.t. over winters 2000–2001 and 2003–2004, respectively. Total estimated losses for foodfish and fingerling ponds in 2000–2001 were $11.56 and $0.48 million, respectively, and in 2003–2004 were $5.22 and $0.40 million, respectively. Maximum dollar loss occurred during March in 2000–2001 and during February in 2003–2004. In this study, the volatility in variable production costs and nominal sales price, and distribution of cormorants on pond types and regionally were key factors in resulting economic loss estimates.     

Environmental Manipulation of Growth and Sexual Maturation in Yellow Perch, Perca flavescens

Yellow perch, Perca flavescens, exhibit sexually dimorphic growth detected as the fish enter puberty. The purpose of this study was to evaluate the differential influences of photoperiod and temperature on the sexual maturation and dimorphic growth pattern of yellow perch. Four combinations of constant (CP) or natural (NP) photoperiod with constant (CT) or natural (NT) temperature were evaluated (CPCT, CPNT, NPCT, NPNT). Following 6 months of growth, results indicate that (1) CT is the strongest promoter of overall growth regardless of photoperiod. Perch reared under CT were 26.4 ± 8.1 g heavier than perch reared under NT (P < 0.0001). (2) CP also promotes overall growth regardless of temperature. CP perch outgrew NP perch by 7.0 ± 8.1 g (P < 0.0872). (3) NP (decreasing) initiates maturation in yellow perch regardless of temperature. (4) NT is required for late maturational processes. While both NP groups initiated maturation, only NPNT females were able to recruit oocytes to a vitellogenic stage. Only NPNT males were able to sustain spermiation to the end of the study. (5) CPCT confer the best overall growth performance, fully inhibit maturation in both genders, and suppress a sexually dimorphic growth pattern up to 53 g average weight. These results indicate that using a CPCT regime during intensive fingerling production will produce a larger, more uniform fish population that could alleviate losses as a result of cannibalism. Perch that remained immature did not exhibit a dimorphic growth pattern.     

农杆菌介导转化为目的的水稻组培体系的建立

高效可靠的组培再生体系是水稻农杆菌遗传转化的基础。该试验通过对培养基类型、光照条件和水稻基因型的研究,发现富含脯氨酸的N6D培养基能明显促进愈伤组织的生长,光照条件也可显著改善其生长。Calrose76和合系41号被证实为易于组培高效再生的粳稻品种,该高效组培体系的为云南栽培良种合系41号的进一步农杆菌转化体系的建立铺平了道路。     

Forms and distribution of potassium in particle size fractions on talc overburden soils in Nigeria

The potassium status of soils developed over talc overburden in a southern Guinea savanna of Nigeria was evaluated using exchangeable, acid extractable, total and residual potassium values in particle-size fractions. Soil samples collected from genetic horizons of six profile pits at Kampe Forest Reserve were separated into sand, silt and clay fractions. Exchangeable K, acid-extractable K, total K and residual K were determined in these fractions. Reserved K values were similar to those of mobile K, but lower than total and residual K, whereas exchangeable K showed the lowest values. Total K was >25 cmol kg^?1 in all the profiles; reserved K ranged from 9.26 to 24.45 cmol kg^?1 and mobile K ranged from 5.12 to 29.57 cmol kg^?1. Exchangeable K accounted for <1% of total K and ranged from 0.20 to 0.50 cmol kg^?1. In most cases, the clay fraction of the soils had the highest values for all potassium forms, followed by the silt fraction, while the sand fraction had the lowest values for these forms of potassium.     

Characterization of anti-channel catfish MHC class IIbeta monoclonal antibodies

This study characterizes four monoclonal antibodies (mAb) developed against the major histocompatibility complex (MHC) class II beta chain of the channel catfish, Ictalurus punctatus. Immunoprecipitations using catfish clonal B cells revealed that each of these mAbs immunoselected proteins of approximately 32 and 36 kD, which are of the appropriate sizes for MHC class II alpha and beta chains, respectively. Cell distribution studies using a fluorescence-activated cell sorter (FACS) combined with RT-PCR analyses demonstrated that MHC class II beta is expressed at a high density on catfish clonal macrophage, B and T cell lines, on alloantigen stimulated leukocytes, and on lipopolysaccharide-induced B-cell blasts. Collectively, these results demonstrate the potential importance of these antibodies as reagents in future studies dealing with the functional role of MHC class II molecules in immune recognition of self from non-self.     

Review: The strobilurin fungicides

The original article to which this Correction refers was published in Pest Management Science 58 (7): 649–662 (2002).Copyright © 2004 Society of Chemical Industry     

Vavilov wheat accessions provide useful sources of resistance to tan spot (syn. yellow spot) of wheat

Host genetic resistance is the most effective and sustainable means of managing tan spot or yellow spot of wheat. The disease is becoming increasingly problematic due to the adoption of minimum tillage practices, evolution of effector‐mediated pathogenicity, and widespread cultivation of susceptible cultivars from a narrow genetic base. This highlights the importance of broadening the diversity of resistance factors in modern breeding germplasm. This study explored 300 genetically diverse wheat accessions, originally sourced from the N. I. Vavilov Institute of Plant Genetic Resources (VIR), St Petersburg, Russia. The collection was screened for resistance to tan spot at seedling and adult stage under controlled conditions, and in the field across 2 years. The phenotypic datasets, coupled with ToxA bioassay screening, identified a number of accessions with useful sources of resistance. Seedling disease response corresponded well with ToxA sensitivity (r = 0.49, P < 0.000), but not adult responses (r = ?0.02 to ?0.19, P < 0.002), and overall reactions to ToxA appeared to show poor correspondence with disease response at the adult stage. ToxA‐insensitive accessions were generally found resistant across different growth stages (all‐stage resistance, ASR) in all experiments (seedling and adult stage under controlled conditions and field). ToxA‐sensitive accessions that were susceptible at seedling stage, but resistant at both adult‐plant stages, were deemed to carry adult‐plant resistance (APR). This study provides detailed information on the degree of tan spot resistance in the Vavilov wheat collection and discusses strategies to harness these sources to boost the diversity of resistance factors in modern wheat breeding germplasm.     

Crop and soil response to subsoil loosening, deep incorporation of phosphorus and potassium fertilizer and subsequent soil management on a range of soil types.: Part 2: Soil structural conditions

Abstract. In a series of experiments on 16 sites both a power-driven rotary-tine Wye Double Digger and a rigid tine winged subsoiler produced significant subsoil loosening and fissuring. The Double Digger consistently produced the greatest clod breakdown together with the least soil bulk densities and cone penetration resistances. Management strategies after loosening had an important influence on the longevity of the loosening effect. The rate of recompaction was least with controlled traffic and bed systems and increased with random traffic and with the growing of root crops. No significant differences in crop response were monitored between the two loosening treatments, yield response depending largely on the extent of moisture stress experienced by the crop. Loosening on silty soils reduced yields in wet seasons and this was associated with soil structural instability. Visual soil profile examination is necessary to support bulk density and cone penetration resistance measurements when assessing soil compaction.