Determinants of Agricultural Intensity Index “Scores” in a Frontier Region: An Analysis of Data from Northern Guatemala

Data on farming systems in Petén, Guatemala, were used to develop an agricultural intensity index. The index can be used to assign an intensity “score” to a given farming system based on the array of practices used by the farmer, each practice’s contribution to production intensity, and the scale at which these practices are used. The scores assigned to 118 farmers in three study areas in Petén were analyzed through analysis of variance (ANOVA) to identify the factors that account for the variation in intensity levels, as measured through the index. The analyses reveal that the factors influencing agricultural intensity in Petén vary greatly from one study area to the next. This is due to differences in livelihood opportunities and strategies that, in turn, affect how agriculture fits into the local economy and how and why intensification is pursued. Variation in intensity levels can best be understood by considering the factors at the household and sub-regional scales that influence (a) whether farmers feel a need to intensify, (b) whether they see some benefit in doing so, and (c) whether they have the resources required to intensify production through particular strategies. Close attention must be paid to these factors by conservation and development organizations seeking to influence land use patterns and conserve forest in Petén. Avrum J. Shriar is an Assistant Professor at Virginia Commonwealth University where he specializes in Environmental Geography, Rural Development and Land Use, Farming Systems, and Latin America and the Caribbean. He holds a BA in Geography from Bishop’s University in Lennoxville, Quebec, a Master of Environmental Studies (MES) from Dalhousie University in Halifax, Nova Scotia; and a PhD in Geography from the University of Florida in Gainesville. Some of his recent articles have appeared in Food Policy, Geoforum, Human Ecology, Agroforestry Systems, and the Delaware Review of Latin American Studies.     

东方百合2n配子杂交后代多倍体诱导研究初报

 以东方百合栽培种为材料,诱导2n配子,通过杂交受粉,采用胚培养成功培育出73株2n配子后代。在离体培养下利用秋水仙素诱导多倍体,突变率50%. 结果突变后代不但出现四倍体而且出现一定数量的三倍体和不稳定的非整倍体。经过诱变产生的多倍体与正常二倍体比较,多倍体叶片变厚,叶色变深,叶片变大,气孔显著增大,而单位面积气孔数减少,有些材料表现出不同程度的畸变,有些表现一定的熟生性。多倍体染色体数目2n=4x=48为四倍体,2n=3x=36为三倍体,二倍体为2n=2x=24.     

根结线虫属新种——龙眼根结线虫的 描述

龙眼根结线虫（Meloidogyne dimocarpus n.sp.）采自中国福建省福州金山一龙眼园的龙眼根部。其鉴别特征为雌虫会阴花纹近圆形，线纹细密，背弓中等高而圆，尾端为经一纹的起源中心，具有一个同不规的短线纹组成的明显尾轮，由同心圆线纹包围；阴门与肛门之间有多条,连续线纹；侧区两侧为双侧线，或其中一侧为单侧线；头部正面观中唇中部显著凹陷，形成相对独立的两辰片，侧唇圆而大；口针长14.8μm，基部球横卵圆形，同杆部界线明显，雄虫头冠低，侧辰长耳状且大，两端内侧与中唇融合；口针长19.1μm，基部球圆，稍后斜，同杆部界线明显，排泄孔位于半月体前，二龄幼虫体长433μm，口针长13.3μm，尾长53.8μm，渐细、末端印圆。     

柑橘属2n花粉自然发生与沙由柚2n花粉诱导研究

果树2n配子育种较其他植物起步晚，尤其是利用2n花粉进行育种的研究在柑橘上还无先例。试验中初步观察了柑橘属部分品种的2n花粉自然发生情况，证实了柑橘属内未减数花粉的存在。同时通过秋水仙碱不同浓度与作用时间处理促进了柑橘2n花粉的发生，将长寿沙田柚2n花粉发生比例由当年的自然发生率0．87％提高到9.76％。初步观察了2n花粉离体萌发状况，其萌发率与花粉管伸长速度较为正常，但萌发启动比单倍性花粉慢。     

蛎盾蚧属一新种记述及榆蛎盾蚧地理亚种讨论(同翅目:蚧总科、盾蚧科)

本文记录本属一新种,并对榆蛎盾蚧拟定了3个地理亚种。     

入侵红火蚁生物学特性的研究

入侵红火蚁是一种杂食性害虫,它的生物学特性主要表现在它的社会性、多型性、群居地栖性、好攻击性、受惊转移和堆尸习性等,大多从卵发育为成虫需要22-38d,每个族群中有单个蚁后或多个蚁后,蚁后寿命最长可达7a,一般每天可产卵1500-5000粒,1个蚁巢可有成蚁5～50万只,盛夏和寒冬整个族群均向蚁巢下部转移,有翅繁殖蚁可四季产生,多在春末夏初飞出蚁巢在空中交配,落地后雌蚁脱翅成为蚁后,并产卵繁殖建立新的族群,主要靠人为传播和自然扩散来扩展入侵地。     

菜地土壤N_2O排放及其氮素反硝化损失

采用培养试验方法,对南京郊区 3对菜地土和水稻土的 N2O排放和氮素反硝化损失进行了研究.不加乙炔培养测定土壤 N2O排放,加乙炔( 10% V/V)培养测定反硝化损失.菜地土为相同类型水稻土改种为蔬菜约 20年的土壤.结果表明,在培养 0～ 1 d期间 ,菜地土本身 N2O排放通量 (5.15～ 218.37 ng N· g-1soil· h-1)均高于相同类型的水稻土 (2.50～ 3.94 ng N· g-1soil· h-1). 3对供试土壤中, 2个菜地土培养 21 d排放的 N2O总量与反硝化损失总量均显著高于相同类型的水稻土( P<0.05). 3对供试土壤施尿素后反硝化损失均未显著增加.施肥和不施肥处理,土壤 N2O排放累积量和反硝化损失累积量随时间 t的变化均符合修正的 Elovich方程 y=bln(t)+ a.     

太白山不同生境蚂蚁的物种多样性研究

应用 Margalef物种丰富度模型指数 Ds、Shamnon- weaver信息多样性指数 H′和 Pielou均匀度指数 Jsw,分析了太白山不同林带 (亚带 )蚁科昆虫的丰富度、多样性及均匀度 ,并根据相似系数 C,对 9个不同林带 (亚带 )进行了系统聚类分析。结果表明 ,随着太白山海拔高度及森林植被组成的变化 ,不同林带分布的蚁种组成有较大的差异 ,在海拔低、植被组成丰富的林带 (亚带 ) ,分布的蚁种多、数量大 ,丰富度和多样性指数高 ;在海拔高、植被组成相对简单的林带 (亚带 ) ,分布的蚁种少、数量小 ,多样性差 ;南坡各林带 (亚带 )蚁种的丰富度和多样性指数均大于相同海拔高度的北坡林带 (亚带 ) ;9个不同林带 (亚带 )可被分为 3类 ,并最终在相似系数 0 .1 80的水平全部聚合在一起     

Cytological Studies on Unreduced Gamete Formation of Strawberries (Fragaria)

A diploid strawberry (Fragaria vesca L. ) which can naturally produce unreduced gametes (2n pollen) and doubled-unreduced gametes (4n pollen) was used to study the cytological mechanism of 2n and 4n gamete formation. The result showed that the formation of 2n gamete was mainly due to the abnormal orientation of spindles at metaphase Ⅱ. The normal orientation of two spindles at metaphase Ⅱ was perpendicular to each other, which led to tetrad formation at the end of meiosis. Two kinds of abnormal orientation of metaphase Ⅱ spindles, i.e. parallel spindles and triangle spindles, were observed. Of the parallel spindles, the 4group chromosomes were distributed to 2 poles and formed a dyad which formed two 2n pollen grains furtheriy. Of the triangle spindles, the 4 group chromosomes were distributed to 3 poles and formed a triad which formed one 2n pollen grain and two n pollen grains. In addition, a few very big pollen grains (4n pollen)which probably due to the fusion of the tetrad were found.     

秋水仙素诱导新铁炮百合2n花粉方法的优化

以新铁炮百合种子为试材,采用正交实验设计探索利用秋水仙素处理新铁炮百合种子的诱导2n花粉方法和可能性。结果表明:种子萌发处理时间5 d、秋水仙素浓度0.05%或0.2%时新铁炮百合种子出苗的效果最好;经对大花粉率极差分析,秋水仙素处理浓度是诱导大花粉的最主要因子,秋水仙素浓度0.1%、处理时间为24 h,种子萌发处理时间7 d,种子品种富田3号是诱导新铁炮百合大花粉有效方法。