不同有机物料与化肥配施对土壤真菌群落结构和生态功能的影响

为减少土壤土传病害,保障农田土壤健康,指导有机物料合理利用,在有机物料用量和化肥用量一致的基础上,设置单施化肥（CK）、羊粪+化肥（A）、木薯渣+化肥（P）、木本泥炭+化肥（M）、味精废浆料+化肥（I）5个处理,以玉米为供试作物进行了有机物料与化肥配施试验,观察了不同处理下土壤真菌群落结构的变化。结果表明：施用有机物料降低了土壤真菌群落多样性,但提高了真菌群落丰富度,其中味精废浆料配施化肥处理的真菌群落丰富度最高,各处理土壤中优势真菌门类均为子囊菌门、担子菌门和被孢菌门。施用有机物料后,木薯渣、木本泥炭和味精废浆料处理的子囊菌门的相对丰度均增加,担子菌门的相对丰度均降低;而羊粪处理表现出相反趋势,子囊菌门的相对丰度降低,担子菌门的相对丰度增加。冗余分析结果表明,土壤pH是影响真菌群落的主要环境因子,其次为有机质、电导率和速效钾,而碱解氮和有效磷的影响较小。另外,有机物料与化肥配施可以提高腐生营养型和共生营养型真菌的比例,减少病原菌的数量,其中以木本泥炭与化肥配施的效果更显著,这有利于维持土壤生态系统的稳定,为作物生产提供健康的土壤条件。     

硒砂瓜连作对土壤真菌群落结构的影响

硒砂瓜是宁夏地区重要的经济作物,其连作严重影响硒砂瓜产量和品质。目前硒砂瓜连作对土壤真菌群落结构的影响尚不清楚。本研究采用Illumina MiSeq高通量测序技术,探讨硒砂瓜连作对土壤真菌群落结构的影响。研究发现,硒砂瓜连作土壤中真菌群落多样性指数和丰富度指数随连作年限的增加先上升后下降。供试土壤样本中共检测到真菌8门、25纲、244属,其中子囊菌门（Ascomycota）、接合菌门（Zygomycota）是优势菌门,占90%以上。与对照相比,连作30年土壤中子囊菌门丰度下降32.51%,接合菌门丰度上升29.89%。供试土壤中真菌主要的优势属为被孢霉属（Mortierella）、绿僵菌属（Metarhiziun）、假霉样真菌属（Pseudallescheria）、镰刀菌属（Fusarium）和青霉属（Penicillium）。与对照相比,连作5年土壤中假霉样真菌属丰度增加45.81%,连作10年土壤中镰刀菌属丰度增加26.74%,连作15年土壤中绿僵菌属下降26.83%,连作20年土壤中青霉属增加29.68%,连作25年土壤中绿僵菌属减少18.30%,连作30年土壤中被孢霉属丰度上升29.89%。土壤理化性质与硒砂瓜连作年限间无显著相关性,而与土壤真菌群落结构存在显著的相关性。土壤全磷、碱解氮、有效磷含量是影响土壤真菌群落最主要的因素。研究结果表明,导致硒砂瓜连作障碍的主要原因不是土壤理化性质变化,而是土壤真菌群落结构的改变。研究结果可为硒砂瓜土传病害的生物防治提供参考依据。     

不同有机物料强还原处理对植烟土壤微生物群落的影响

  目的  本文探究了在厌氧强还原条件下,豆渣、甘蔗渣单施及其等比例混合物施用后,不同处理间土壤理化性质与微生物群落变化的相关关系。  方法  应用Tax4Fun及FUNGuild分别对细菌和真菌群落进行功能预测,采用Vegan和pheatmap等R语言软件包完成统计分析和绘图,利用生物信息学方法分析不同样本中微生物群落结构和多样性变化,确定微生物与RSD技术之间的相关性。  结果  结单一用蔗渣和豆渣的RSD处理都提高了真菌群落丰富度。在门的水平上,放线菌（Actinobacteria）、厚壁菌门（Firmicutes）、酸菌门（Acidobacteria）、子囊菌门（Ascomycota）和担子菌门（Basidiomycota）的相对丰度发生变化,揭示了处理间群落结构存在显著差异。此外,RSD还有效降低了镰刀菌属（Fusarium）、链格孢属（Alternaria）等土传病原菌的丰度。斯皮尔曼相关性分析说明全氮、全磷、碱解氮、速效钾、pH和有机质是造成群落结构差异的主要影响因子。功能注释结果显示RSD技术能提高土壤中细菌群落萜类和多酮类化合物代谢的功能活性及腐生真菌的丰度。  结论  单独施用豆渣的RSD处理可以通过促进土壤肥力的提升及土壤健康群落重构来缓解植烟土壤连作障碍,是一种优良的控制土传病害的技术手段。     

生物炭连续还田对苏打盐碱水稻土养分及真菌群落结构的影响

以苏打盐碱土为供试土壤，设置0，3.0，7.5，12.0，16.5 t/hm² 5个梯度生物炭还田量，通过盆栽试验研究不同量生物炭连续多年还田对苏打盐碱水稻土养分及真菌群落结构的影响。结果表明：（1）不同量生物炭还田后，提高了土壤pH、有机质、速效钾、有效磷和全磷含量，土壤全氮和全钾含量呈现先增加后降低的趋势，对盐碱土起到了改良的效果。（2） Illumina MiSeq测序结果表明，还田量为7.5 t/hm²时，Aphelidiomycota、担子菌门以及链格孢属的相对丰度显著高于对照；还田量为12.0 t/hm²时，子囊菌门、毛霉亚门以及被孢霉属的相对丰度显著高于对照，相关分析显示土壤理化特性与菌门和菌属的相对丰度关系密切，表明生物炭通过调节土壤的理化特性，从而影响真菌的相对丰度。（3）生物炭还田处理对土壤真菌α多样性影响不显著，对土壤真菌群落结构产生一定的影响，其中高生物炭还田量处理对其影响更为显著。进一步利用冗余分析（RDA）研究影响群落结构变化的环境因子表明，全钾含量对群落结构影响最大。     

长期有机无机肥配施对东北黑土真菌群落结构的影响

【目的】分析长期有机无机肥配施对土壤真菌丰度、多样性及其群落特征的影响,探讨东北黑土真菌群落变化与施肥的相关性,为进一步调节土壤微生物结构,改善其生态功能提供参考依据。【方法】依托黑龙江省农业科学院36年长期定位试验站,选取4个不同施肥处理:不施肥处理（CK）、有机肥处理（M）、氮磷钾无机肥处理（NPK）和有机肥配施无机肥处理（MNPK）的耕作层土壤为研究对象,以真菌ITS基因为分子标靶借助qPCR技术和Illumina Miseq高通量测序平台,研究不同施肥处理对黑土中真菌群落丰度、多样性和组成的影响,并与土壤化学性质进行偶联分析,揭示群落与施肥的相关性。【结果】长期施用无机肥显著降低土壤pH,而有机无机配施可以有效缓解土壤酸化。NPK处理的ITS基因丰度显著高于MNPK;MNPK处理的细菌/真菌比值（26.91104）显著大于NPK,各处理比值由高到低为MNPK M CK NPK。细菌/真菌比值与土壤pH正相关;MNPK处理的真菌多样性指数值略大于NPK。Ascomycota和Zygomycota为土壤中主要真菌门,不同施肥处理之间真菌组成的相对丰度存在显著差异,对照处理Ascomycota的相对丰度为45.35%,MNPK和NPK处理分别为50.93%和56.16%。有机肥有利于降低病原真菌相对丰度,具有高度侵染性的Cochliobolus在MNPK（0.41%）和M（0.39%）中的相对丰度显著小于CK（3.25%）和NPK（2.08%）。CCA分析表明,土壤理化性质共解释土壤真菌群落结构变化的73.3%,有效磷（贡献量为32.4%,P=0.002）、铵态氮（贡献量为14.8%,P=0.01）和硝态氮（贡献量为16.2%,P=0.048）是3个重要的影响因子。【结论】不同施肥条件下土壤真菌丰度、多样性,以及菌群组成特征不同。与无机肥相比,有机肥无机肥配施能够有效改善真菌群落结构,降低真菌的丰度,增加真菌多样性,并提高土壤pH,减缓土壤酸化。土壤有效磷、铵态氮和硝态氮含量是影响黑土土壤真菌群落结构变化重要因素。     

稻田土壤真菌群落结构与功能对化肥 减量配施紫云英还田的响应

为探明长期化肥减量与紫云英还田配施对稻田土壤真菌群落组成结构及功能特性的影响,以豫南稻区紫云英- 水稻田间定位试验为研究对象,选取了空白对照(CK)、单施化肥(F100)、80% 化肥和22.5 t/hm² 紫云英还田量配施(MV1F80)、80% 化肥和45 t/hm² 紫云英还田量配施(MV2F80)、60% 化肥和22.5 t/hm² 紫云英还田量配施(MV1F60)、60% 化肥和45 t/hm² 紫云英还田量配施(MV2F60)6 个处理。通过采用高通量测序方法比较不同施肥处理对土壤真菌群落多样性、组成和结构特性的影响;采用FUNGuild 功能预测的方法分析不同施肥处理间功能类群的丰度差异。结果表明,化肥减量与紫云英还田配施较CK 处理显著提高了Shannon 指数和Shannoneven指数,且Shannon 指数和Shannoneven 指数均与全氮呈显著正相关。门分类水平上,化肥减量与紫云英还田配施较CK 显著降低了子囊菌门(Ascomycota)相对丰度,增加了担子菌门(Basidiomycota)相对丰度;属分类水平上,化肥减量与紫云英还田配施处理的翅孢壳属(Emericellopsis)和无色穗孢属(Achroiostachys)相对丰度显著低于CK,镰刀菌属(Fusarium)相对丰度显著低于F100 处理。此外,冗余分析(RDA)发现,影响土壤真菌群落结构和组成的主要环境因子为土壤容重、有机碳、全氮、全磷和全钾。从真菌功能预测分析来看,化肥减量与紫云英还田配施较F100 处理显著降低了动物病原菌- 内生菌- 地衣寄生菌- 植物病原菌- 土壤腐生菌- 木质腐生真菌功能类群丰度。由此可见,化肥减量与紫云英还田配施通过改善土壤肥力属性,改变了稻田土壤真菌群落组成、结构、多样性及功能特性,在一定程度上降低了土壤潜在致病菌丰度,有助于豫南稻区土壤健康和可持续发展。     

不同有机肥对植烟红壤真菌群落结构及功能的影响

  【目的】  研究植烟土壤中与养分循环相关的真菌群落结构和功能类群对不同有机肥施用的响应，为指导烤烟合理施肥、减缓连作障碍和土传病害提供科学依据。  【方法】  选择烤烟品种‘云烟87’为供试作物，以当地农业废弃物为原料堆制有机肥，设置6个处理:单施化肥 (CK)、鸡粪有机肥 (T1)、芝麻饼肥 (T2)、菜籽饼肥 (T3)、牛粪 (T4)、稻草 (T5)，所有处理氮磷钾总量和比例用化肥调整为一致。随机区组田间试验，每个处理3次重复。采用高通量测序结合FUNGuild分析方法，测定分析烟草不同生长阶段各处理的土壤真菌群落结构、多样性、组成及群落功能。  【结果】  结合UPGMA聚类分析和主坐标分析 (PCoA) 发现，相比T2和T3处理，T5、T4和T1处理在烟草旺长期对土壤真菌群落结构的影响较大；成熟期T2与T3处理对土壤真菌群落结构的影响逐渐增大，且超过T4和T5处理。相比CK，T2、T3及T5处理中腐生营养型真菌比例分别显著提高了262.0%、64.0%和198.0%。其中T5处理土壤中腐生营养型真菌所占比例超过病理营养型真菌，成为其主要优势菌群；T1、T2及T4处理的土壤共生营养型真菌分别显著增加了80.0%、320.0%和85.71%。T1、T2和T4处理分别提高了土壤中植物病原菌Monographella (408.98%)、Microidium (93.63%)、Gibberella (559.22%) 的相对丰度。  【结论】  相比单施化肥处理，有机肥会导致土壤真菌群落结构发生变化，且不同有机肥的影响程度和时期均不同，其主要是增加了土壤腐生营养型真菌的比例，更有利于土壤生态系统的稳定和健康。5种供试有机肥处理中，稻草配施化肥最有利于降低长期烟稻轮作的土传病害风险，提高土壤肥力，鸡粪和菜籽饼次之；芝麻饼和牛粪在提高腐生营养型和共生营养型真菌比例的同时，也会增加烟稻轮作体系中水稻赤霉病及烟草根腐病风险。     

不同程度重金属污染对稻田土壤真菌群落结构的影响

为了研究土壤真菌群落结构在不同程度重金属污染中的变化,本文用Illumina Hi Seq高通量测序技术分析了苏南地区某金属冶炼厂和加工产业区的重金属污染水稻土的真菌群落结构,发现不同程度重金属污染对水稻季土壤真菌丰度和群落结构均有显著影响。经过真菌主成分分析发现,PC1影响因素对样品处理差异的贡献率是35.96%,PC2影响因素对样品处理差异的贡献率是21.48%;通过真菌冗余度分析发现,重金属Pb和Cu污染对土壤真菌群落结构的影响显著;通过对真菌属水平的相对丰度分析表明,重金属污染会显著降低敏感真菌的丰度,如被孢霉属相对丰度最高降低了87.50%、木霉属最高降低了99.46%、离壳菌属和菇属最高降低了100.00%,同时耐性真菌的相对丰度会提高,如类球囊霉属的相对丰度最高增加了98倍、四枝孢霉属最高增加了56倍、根囊壶菌属最高增加了2.62倍。综上所述,不同程度重金属污染对稻田土壤真菌群落结构有显著影响,且随着污染程度的增加,抗逆真菌相对数量和种类显著增加,敏感真菌的相对数量急剧减少,真菌群落结构随着重金属污染程度增加进一步分化。     

长期连作及强还原土壤灭菌处理对烤烟根际土壤真菌群落的影响

烤烟是重要的经济作物,连作障碍已成为限制其产业发展的主要原因之一,研究长期连作及强还原土壤灭菌处理(RSD)对烤烟根际土壤真菌群落的影响,为缓解烤烟连作障碍提供理论基础。选取烤烟连作 3、5和 7年根际土壤分析理化性质和真菌群落演替规律。选取烤烟连作 3年样地实施强还原土壤灭菌处理(RSD),与未处理(3年)对比,以此评价 RSD修复效果。结果表明:(1)连作处理显著降低烤烟根际土壤 pH及总碳和总氮的含量,RSD处理较未处理(3年)显著提升土壤总碳和总氮的含量。(2)测序结果表明,连作处理显著促进真菌群落 Alpha多样性,主坐标轴分析和聚类分析表明连作处理显著改变真菌群落结构,真菌群落相对丰度的变化及 FUNGuild数据库比对结果表明,连作处理促使病原菌丰度增加。(3)与未处理(3年)相比,RSD处理显著降低真菌群落多样性和病原菌丰度。(4)相关性热图分析表明病原菌相对丰度与 pH、总碳和总氮含量呈显著负相关。因此,长期连作烤烟导致根际土壤质量退化,造成病原菌增多;RSD处理对连作土壤的质量和真菌群落具有良好的修复效果。     

木霉P3.9菌株对枇杷根际真菌多样性及其群落组成的影响

枇杷根际土壤用木霉P3.9菌株孢子悬浮液灌根,Illumina平台高通量测序,分析引入木霉P3.9菌株对枇杷根际真菌多样性及其群落组成的影响。结果表明,镰刀菌属Fusarium、短柄镰刀菌Fusarium brachygibbosum是枇杷根际土壤真菌优势种群。添加木霉P3.9菌株没有改变枇杷根际真菌群落多样性,而改变了根际真菌群落组成。添加木霉P3.9菌株10～30 d之间,枇杷根际真菌群落几乎未发生改变。40～90 d之间,枇杷根际真菌群落组成发生改变。添加木霉P3.9菌株90 d之内导致根际真菌数量减少2种。一方面,优势属Mortierella、Trichoderma和非优势属Cladophialophora显著增加,优势种Mortierella alpina和M. exigua也显著增加。另一方面,优势属Phoma、Aspergillus、Lectera和9个非优势属显著降低。优势种Phoma omnivirens、Podospora communis和10个非优势种也显著降低。说明枇杷根际添加木霉P3.9菌株对其根际真菌多样性无不良影响,反而可以改善有益真菌群落物种丰度,减少有害真菌群落物种丰度,对枇杷连作根际土壤有潜在修复作用及肥力提升作用。     

“绿色革命”以来大气CO2浓度升高对C3作物营养品质的影响

自20世纪60年代"绿色革命"以来,育种技术和农耕技术的发展促进了农作物产量的大幅提升,然而作物的营养品质出现下降趋势。在相似的遗传背景下,大气CO_2浓度升高会使单位体积农作物产品的营养元素含量下降,因此"绿色革命"至今,农作物产品的营养元素下降可能受大气CO_2浓度升高影响。通过植物生长箱模拟"绿色革命"初期和目前的大气CO_2浓度水平(310μmol/mol和400μmol/mol),针对主要C_3作物水稻、小麦和大豆,研究"绿色革命"以来大气CO_2浓度升高对其籽粒的C、N、Fe、Zn元素含量的影响,结果表明:CO_2浓度升高对3种作物籽粒的C元素含量几乎没有影响,变化幅度在±1.5%之间;籽粒的N、Fe、Zn元素含量普遍呈现下降趋势,但均未达到显著水平。     

Potential of wild species for genetic enhancement of some semi-arid food crops

Discovery and incorporation of genes from wild species provide means to sustain crop improvement, particularly when levels of resistance in the cultigens are low and virulent strains of pests and pathogens overcome the host plant resistance. The extent of utilization and the potential of the wild genepool for genetic enhancement were reviewed in five important food crops viz. sorghum, pearl millet, chickpea, pigeonpea and groundnut grown in the semi-arid tropics. Introgression from compatible wild germplasm in the primary gene pool resulted in transfer of new cytoplasmic male sterility systems in pearl millet and pigeonpea, development of high protein, cleistogamous flower and dwarf pigeonpea lines and foliar disease resistant groundnut cultivars. Utilization of wild species in secondary and tertiary gene pools has been generally limited due to sterility, restricted recombination or cross incompatibility. Nevertheless, these species are extremely important as they contain high levels of resistance to several important biotic and abiotic stresses. Several of them, like those belonging to the Parasorghum section and the rhizomatous Arachis species are sources of multiple resistances and hold great promise to sustain crop productivity.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Collection and preliminary evaluation of native turfgrass accessions in Italy

Despite a raising interest on turfs in Italy, all theavailable varieties of this kind in the Country are of foreign origin, and areoften poorly adapted to the prevailing climatic conditions. This prompted tobegin a collection activity of indigenous turfgrass species, with the ultimategoal of identifying promising materials for future breeding based on localgenetic resources. The collection was carried out in three areas of Italy, viz.the northern Po Plain, the coastal region of Liguria, and the island of Sardiniathat are characterised, respectively, by subcontinental, warm temperate, andtypical Mediterranean climate. Altogether, 141 sites were visited, yielding 226accessions belonging to eight species of potential interest for turfs:Poa pratensis, Poa trivialis,Festuca rubra, Festuca arundinacea,Lolium perenne, Agrostis stolonifera,Agrostis tenuis, and Cynodon dactylon,this last being a warm-season grass. Poa pratensis andCynodon dactylon were mostly collected in northern Italyand Sardinia, respectively, whereas Festuca arundinacea andLolium perenne were rather ubiquitous. The collection sitesranged from 0 to 1040 m asl, but sites over 750 m wereonly visited in the inner part of Sardinia. All the accessions, collected aswhole plants, were transplanted at Lodi, northern Italy, where they are beingevaluated. Their preliminary evaluation for traits of importance for turf use,such as sward colour and overall quality, highlighted the great variation andthe occurrence of interesting accessions in all species. Other characters wererecorded, bearing specific importance in individual species, and in all casespromising accessions were identified. The germplasm of Festucarubra, Festuca arundinacea, and Loliumperenne proved highly infected by endophytic (symbiotic) fungi of thegenus Neotyphodium.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Effect of some fungicide seed treatments on the survival of Bradyrhizobium japonicum and on the nodulation and yield of soybean [Glycine max. (L) Merr.]

Several commercial fungicide seed treatments were evaluated for their possible effect on the survival of Bradyrhizobium japonicum on seeds and on the nodulation and yield of soybeans in a greenhouse and a field experiment. quinolate Pro (carbendazim and oxine copper), Vitavax 200FF (carboxin and thiram), and Monceren (pencycuron) had a small effect or no effect on the survival of B. japonicum and on the nodulation and yield of soybeans. They can thus be considered compatible with soybean seed inoculation. Germipro UFB (carbendazim and iprodione), Apron 35J (metalaxyl), and Tachigaren (hymexazol) decreased B. japonicum survival and the nodulation and yield of soybeans and thus cannot be considered compatible with soybean seed inoculation.     

Leaf position and genotype differences for mineral element concentrations in sorghum grown on tropical acid soil 1

Mineral element deficiencies and toxicities are common problems associated with sorghum [Sorghum bicolor (L.) Moench] production on acid soils. To better understand some of the mineral element problems and the analysis of plant tissue of sorghum plants grown on acid soils, four sorghum genotypes were grown on an acid Oxisol at Carimagua, Colombia limed with dolomite at 2 and 6 Mg ha^‐1.

Samples for mineral element analyses were obtained from leaves at different positions on the four genotypes. Concentrations of P and Mg were highest in the flag leaf (Leaf No. 1) and decreased as the position on the plant declined from the top of the plant for plants grown at 2 Mg lime ha^‐1. Similar decreases in P, Mg, K, and Zn concentrations occurred in plants grown with 6 Mg lime ha^‐1. Concentrations of Ca, S, Si, Mn, Fe, Cu, and Al increased as leaf position declined from the flag leaf for plants grown at 2 and 6 Mg lime ha^‐1. The higher lime supply enhanced Ca and reduced Mn and Fe concentrations in leaves. Differences in mineral element concentrations for the four genotypes used were fairly extensive. The elements to show the greatest range among genotypes were Al and Si and the elements to show the least range among genotypes were P, K, and S. Care should be used in collecting leaf samples for plant analysis and genotypic differences for accumulation of mineral elements should be considered in interpretation of results.