Spatial patterns of the Citrus leprosis virus and its associated mite vector in systems without intervention

Leprosis is caused by the Citrus leprosis virus cytoplasmic type and is vectored by the mite Brevipalpus yothersi. Miticide applications, which cost $54 million annually, are based on inspection for the presence of mites. The aim of the present study was to characterize the spatial patterns of B. yothersi-infested trees and trees with leprosis symptoms for further improvement in sampling and disease control. The presence of mites and the occurrence of leprosis were assessed over two years in 1160 Valencia trees and 720 Natal trees in a commercial sweet orange grove in Sao Paulo State, Brazil. To assess the natural growth and dispersal of mites and leprosis, mite populations were not controlled during the experimental period. Maps of mite-infested trees and trees with leprosis symptoms were analysed at three different levels of spatial hierarchy using complementary methods, i.e. among adjacent trees within and across rows, within quadrats, and the strength and orientation of aggregation among quadrats. The study showed that the spatial patterns of virus-infected and mite-infested trees were different, with a strong aggregation pattern of trees with leprosis symptoms that increased over time. Conversely, the spatial pattern of B. yothersi showed randomness or weak aggregation at all three spatial hierarchical levels. Disease incidence increased steadily in plots of both cultivars, unlike in mite-infested trees where incidence fluctuated over time. These results have important implications for the development of better management strategies for leprosis. Sampling methods and action thresholds for mite control should consider primary disease inoculum in addition to the incidence of mites.     

A comparison of popular approaches to optimize landscape resistance surfaces

Landscape Ecology - Landscape resistance surfaces are often used to address questions related to movement, dispersal, or population connectivity. However, modeling landscape resistance is...     

紫花苜蓿耗水规律及灌溉制度优化研究

为研究河套灌区紫花苜蓿的耗水规律,同时对现有灌溉制度进行优化,在田间试验的基础上,设置不同灌水水平对前两茬苜蓿进行了研究。结果表明:现蕾期和开花期是紫花苜蓿耗水的旺盛阶段,该阶段土壤水分亏缺会直接影响苜蓿产量的形成。通过多元线性回归的方法求解得到了两茬紫花苜蓿各生育期的敏感性系数,分别在0.103~0.731和0.041~0.375之间,且以现蕾期和开花期为最大,说明这两个生育阶段为苜蓿生长的关键阶段。以Jensen模型为基础,采用最小二乘法初步优化了两茬紫花苜蓿生育期内的灌溉制度,第1茬灌溉定额以1 400 m3/hm~2为宜,第2茬以2 300 m3/hm~2为宜,两茬灌水次数分别以4次和5次为最优。     

土壤容许流失量研究的进展与趋势

概述了国内外土壤容许流失量（Ｔ值）研究的历史、目前研究的现状和未来的发展趋势,对Ｔ值研究的主要内容如成土速度、土壤养分流失、泥沙淤积损失、土壤流失与土地生产力的关系、保护沟道侵蚀的重要性等做了讲述。介绍了Ｔ值的数学表达和不同国家的Ｔ值标准,阐述了进行Ｔ值双值性研究的必要性,并对Ｔ值研究中存在的问题进行了分析。     

Synthesis and herbicidal activity of 2alpha, 4alpha-dimethyl-8-oxabicyclo[3.2.1]oct-6-en-3-one derivatives.

The catalytic oxidation of 2alpha,4alpha-dimethyl-8-oxabicyclo[3.2. 1]oct-6-en-3-one with osmium tetraoxide and excess hydrogen peroxide resulted in the formation of 2alpha,4alpha-dimethyl-6, 7-exo-isopropylidenedioxy-8-oxabicyclo[3.2.1]octan-3-one (2), with 91% yield. Addition of aryllithium reagents to this compound resulted in the formation of the aromatic alcohols (6a-h) with 48-76% yield. These alcohols were treated with thionyl chloride in pyridine, and the corresponding alkenes (7a-h) were obtained with 46-80% yield. The effect of compounds 6a-h and 7a-h on the root growth of Sorghum bicolor was evaluated at a concentration of 6.6 microg g(-)(1). The alcohols 6a-h caused an inhibitory effect (8-100%) on the S. bicolor radicle growth. The three most active compounds were 6e (aryl = p-methylphenyl), 6g (aryl = p-chlorophenyl), and 6h (aryl = p-fluorophenyl) and caused 100% inhibition. The effect of alkenes 7a-h was less pronounced and varied from 15% to 46% inhibition. Another experiment was carried out in a greenhouse to evaluate the effect of alcohols 6e, 6g, and 6h, at a 6.6 microg g(-)(1) dose, against Cucumis sativus, S. bicolor and the weeds Bidens pilosa, Desmodiumtortuosum, and Pennisetum setosum. All three compounds showed an inhibitory effect on the development of the aerial parts (26-73%) and roots (13-79%) of the weeds and crops.     

典型黑土pH值变化对营养元素有效态含量的影响研究

采用室内培养实验的方法,控制典型黑土样品的酸碱度值,探讨典型黑土中Cu、Zn、Mn、P和Fe等营养元素有效态含量与pH值的关系。结果表明:pH值变化0.5个单位左右,有效态铜含量变化约0.5～1倍;有效态锰含量变化约3～5倍;有效态锌含量变化9～15倍之多;有效态磷含量变化约1.5～2倍;有效态铁含量变化约3～4倍。说明精确掌握土壤的酸碱度值对于土壤诊断、合理施肥、提高作物产量和实现土地的可持续利用都具有重要的理论与实践意义。     

Phenolic profile of quince fruit (Cydonia oblonga Miller) (pulp and peel)

Qualitative and quantitative analyses of phenolic compounds were carried out on quince fruit samples from seven different geographical origins in Portugal. For each origin, both pulp and peel were analyzed by reversed-phase HPLC-DAD and HPLC-DAD/MS.The results revealed differences between the phenolic profiles of pulps and peels in all studied cases. The pulps contained mainly caffeoylquinic acids (3-, 4-, and 5-O-caffeoylquinic acids and 3,5-dicaffeoylquinic acid) and one quercetin glycoside, rutin (in low amount). The peels presented the same caffeoylquinic acids and several flavonol glycosides: quercetin 3-galactoside, kaempferol 3-glucoside, kaempferol 3-rutinoside, and several unidentified compounds (probably kaempferol glycoside and quercetin and kaempferol glycosides acylated with p-coumaric acid). The highest content of phenolics was found in peels.