土壤管理方式对李园土壤理化性质影响研究

研究了四川大英县不同土壤管理方式下李园的土壤理化性质 ,结果表明 :不同土壤管理方式下 ,夏旱期间土壤含水量以刈割覆盖处理最高。刈割压埋、畜粪还园处理在土壤保温和降温方面的效果不如刈割覆盖处理明显 ,但优于清耕处理。各处理间土壤容重变化较大 ,0～ 2 0cm土层畜粪还园处理的土壤容重较清耕减少 0 4 5 g/cm3 。土壤养分指标值较试验前均有不同程度地提高 ,各处理土壤养分值以畜粪还园处理为最好。     

四君子汤对家兔脾虚症调整作用的实验研究

为了探讨四君子汤对脾虚症的治疗作用，根据中兽医“苦寒之药损其脾胃”的理论，利用大黄煎剂复制出家兔脾虚症模型，用四君子汤治疗，结果表明：四君子汤治疗能解除脾虚症的临床症状，使实验家兔体重增加，体温回升，血清木糖吸收率，血浆胃泌素，血浆ｃＡＭＰ和ｃＡＭＰ／ｃＧＭＰ，淋巴细胞转化率，Ｅ－玫瑰花环形成率等升高，血清胆碱酯酶活性，血浆胰高血糖素降低。说明四君子汤对脾虚症有良好的调整作用。     

高致病性PRRSV浓缩灭活疫苗的研制及免疫效果

[目的]研制高致病性PRRSV浓缩灭活疫苗。[方法]分别以病毒液、病毒浓缩液作为抗原,以甲醛、β-丙内酯为灭活剂,制成A、B、C、D 4种灭活疫苗,进行物理性状和无菌检验,安全检验合格后,与商品疫苗E进行免疫效果比较。[结果]4种疫苗均有良好的安全性。免疫后35 d,未浓缩抗原的A、C疫苗及商品疫苗E组抗体均未阳转,浓缩抗原的B、D疫苗组抗体阳转率分别达到80%和100%。[结论]浓缩病毒液制成的灭活疫苗比未浓缩病毒液制成的灭活疫苗及商品疫苗具有较好的免疫效果。     

气象条件对川中丘陵地区玉米生长和产量的影响及播期优化——以中江为例

2016、2019、2020年以四川主推玉米品种‘正红505’为试验材料,设置5个播期,研究不同播期下气象因子的差异及其对玉米生育进程和产量的影响,以期为川中丘陵地区玉米的播期优化提供理论依据。结果表明：随播期推迟,日均温升高,玉米营养生长期缩短,其间活动积温减少,气象因子对玉米全生育期的影响主要表现在营养生长阶段;相关和回归分析表明,温度是决定玉米生育期长短的主要气象因子,日均温度和活动积温对各生育时期的贡献率达83.0%,其中吐丝—成熟期达99.9%;籽粒产量同时受温度、光照和降水量的影响,其中光照条件贡献较大(贡献率35.7%~54.0%),日均温和活动积温贡献率25.2%~31.2%,降水量贡献率20.8%~33.1%;气象因子对产量构成因素的贡献率不同,对穗粒数贡献最大的是播种—吐丝阶段的温度,对千粒质量贡献最大的是吐丝–成熟阶段的光照;随播期推迟,玉米生物产量和籽粒产量均呈先增后减趋势,籽粒产量(y)与播期(x第一播期后的天数)的回归方程为y=–1.16x2+19.87x+7977.34,R2=0.47**,在4月3日左右最高。推断4月上旬是本区玉米高产的适宜播期。     

Differential host passaging alters pathogenicity and induces genomic variation in white spot syndrome virus

To understand the pathological effects of passaging WSSV through different animals, we passaged WSSV through crabs (Portunus sanguinolentus and P. pelagicus), prawn (Macrobrachium rosenbergii) and artemia (Artemia sp.). Among the three geographically distinct WSSV isolates (A166, G9 and G27) that caused over 95% mortalities in experimental infections in P. monodon, only two isolates (A166 and G9) caused mortality (5%) in M. rosenbergii. On subsequent infection of P. monodon with the passage one virus (P1V) from M. rosenbergii, only P1V of A166 caused 5% mortality while P1V of G9 failed to cause any mortality, though the infected shrimp were positive for WSSV by nested PCR. Crabs showed differential susceptibility to WSSV isolates. While passaging WSSV (G9) through P. sanguinolentus retained pathogenicity, passaging through P. pelagicus completely attenuated the two strains (A117 and G27). Passaging through M. rosenbergii changed pathogenicity of isolates (A166 and G9) from 95% to 5% cumulative mortality in experimental infections. WSSV was unable to infect Artemia and could not transmit the disease to P. monodon. WSSV (A117) passaged through P. monodon retained its virulence. An examination of tandem repeats (TR) in ORF 94 of the WSSV genome revealed variations upon passaging through different hosts. One isolate (A117), with 12 TR yielded 8 TR when passaged through P. pelagicus and 18 TR when passaged through P. monodon. Two other isolates (G9 and G27) with 9 TR, retained them when passaged through P. monodon and P. sanguinolentus but yielded 8 and 12 TR when passaged through P. pelagicus and M. rosenbergii, respectively. Thus, differences in TR number appeared to result from host selection rather than geographical isolation.     

Mortality patterns in infectious salmon anaemia virus outbreaks in New Brunswick, Canada

Mortality levels attributed to infectious salmon anaemia viral (ISAV) infections were examined at the net pen and site level in the 1996 smolt year class in three areas of New Brunswick, Canada. The year class in this region was the first known to have potential exposure to ISAV beginning at the time of seawater transfer. There was considerable variability in mortality patterns among net pen groups of fish. Net pen outbreak definitions were based on at least seven high mortality days in which there were at least 100 per 100 000 fish per day or >5% cumulative mortality for the study period. There were 106 net pen outbreaks in a study population consisting of 218 net pens. Although the number of new cases decreased as water temperature decreased, overall mortality levels at the study sites did not decrease noticeably. The median peak daily mortality rate during outbreaks was 492 per 100 000 fish per day, with 10% of cases experiencing >5200 mortalities per 100 000 fish per day. The median duration of outbreaks in net pens for which the fish were not slaughtered during the outbreak was 33 days and the median total loss in those outbreaks was 6600 per 100 000 fish.     

Change in chum salmon (Oncorhynchus keta) stomach contents associated with fluctuation of pink salmon (O. gorbuscha) abundance in the central subarctic Pacific and Bering Sea

The abundance and stomach contents of salmonids (Oncorhynchus spp.) and the biomass of prey organisms were examined in the central subarctic Pacific and Bering Sea in the summer of 1991 and 1992. Salmonids were caught by surface longline using the same level of fishing effort. Chum (O. keta) and pink (O. gorbuscha) salmon were the predominant species, representing 44% and 36% sof the total catch (n = 1275) in 1991. In 1992, chum salmon composed 85% of the total catch (n = 603), but the catch of pink salmon decreased to 1% of the total catch due to the odd/even year fluctuation of Asian pink salmon abundance in the study area. It was found that chum salmon changed their dominant diet from gelatinous zooplankton (pteropods, appendicular-ians, jellyfishes, chaetognaths, polychaetes and unidentified materials) in 1991, when pink salmon were abundant, to a diet of crustaceans (euphausiids, cope-pods, amphipods, ostracods, mysids and decapods) in 1992, when pink salmon were less abundant. Local crustacean biomass (wet weight; mg m^-3) had significant negative correlation with the CPUE (catch number per 30 hachi) of pink salmon in 1991 (r = -0.586; P = 0.026) and that of chum salmon in 1992 (r =–0.616; P = 0.014). There may be a limitation in the available prey resource for production of salmonids.     

Clinical and aetiological aspects of a summer enteritic syndrome associated with the sporulating segmented filamentous bacterium 'Candidatus Arthromitus' in farmed rainbow trout, Oncorhynchus mykiss (Walbaum)

An enteritic syndrome affecting farmed rainbow trout and occurring predominantly in summer has recently been described and related to the massive accumulation of a segmented filamentous bacterium (SFB), ‘Candidatus Arthromitus’, in the digestive tract of fish. Details of the clinical manifestations, the characteristics of the bacterium and the possible aetiology of the disease are presented in this paper. No other bacterial pathogen than ‘Candidatus Arthromitus’ was characterized in trout undergoing the enteritic syndrome. From clinical and histopathological observations, a toxin or toxic product accumulation was suspected in affected trout, and could account for the massive destruction of the intestinal mucosa. However, the origin and aetiological role of the SFB could not be clearly elucidated, although most of the filaments appeared to beviable and to produce and release strings of endospores in the lumen of the gut. The organism could not be cultured in the conditions tested, shared several morphological and structural characteristics with related bacteria described in the intestinal microflora of different vertebrate species, but no attachment structure was definitively recognized. All attempts to detect similar SFB in the fish diet orin the environment of affected fish farms were unsuccessful. It is unclear whether this organism represents a normal and not previously detected inhabitant of the intestine of trout stressed after environmental perturbation, or whether it results directly from external sources of contamination.     

The molecular detection of Taura syndrome virus emerging with White spot syndrome virus in penaeid shrimps of Thailand

This study is to investigate the outbreak of the Taura syndrome (TS) in penaeid shrimps of Thailand. Following the outbreak in 2003, the Taura syndrome virus (TSV) was detected in two closely related penaeids; the Pacific white shrimp, Penaeus vannamei, and the black tiger prawn, Penaeus monodon. Multiple viral infections were detected, we found that the TSV-infected P. vannamei also presented evidence of the White spot syndrome virus (WSSV) as evidenced by histological examination and molecular diagnostic methods. Infections of TSV and WSSV were investigated over a period of ten months between October 2003 and July 2004. TSV infection in shrimps was diagnosed by RT-PCR using the OIE recommended 9195/9992 primers. Positive shrimp gave the expected amplicon of 231 bp. We also amplified and sequenced a fragment of the vp1 gene (354 bp). The pairwise comparisons of vp1 revealed that Thai TSV was phylogenetically related to the Taiwanese strains (98.3% identity).