快速城镇化地区土地利用演变及驱动机制——以巢湖流域为例

[目的]探究巢湖流域土地利用演变特征规律及驱动机制,为实现区域土地资源的优化配置和社会经济的可持续发展提供理论依据。[方法]收集巢湖流域及区县1996—2014年土地利用变更调查及社会经济统计年鉴,运用土地利用数量、程度及空间差异计量模型,以及主成分分析法,采用数据统计软件,模拟巢湖流域土地利用变化演化规律及其驱动因素。[结果]近20a来巢湖流域各土地利用类型均发生变化,但不同土地利用类型变化的总量、变化幅度和变化速度却存在明显差异,耕地、园地、草地减少较为突出,林地略有增加,其他农用地减少将近1/2;建设用地总量增长幅度更大,特别是城镇工矿用地及交通基础设施用地增长迅猛,农村居民点用地略有减少;巢湖全域土地利用程度自2004年之后呈现逐年上升趋势,合肥市辖区及周边县域土地利用开发程度较高,其他区域相对较低;耕地减少率金安区、瑶海区、肥西县、含山县居前,城镇用地增加率肥西县、长丰县、巢湖市位于前列;投资拉动、经济发展、工业推进、人口增加及城镇化是巢湖流域特别是近10a多土地利用变化的主要驱动因素。[结论]巢湖流域加快建设长三角世界级城市群副中心城市及生态文明先行示范区,需进一步优化土地利用空间格局,盘活建设用地存量,提高建设用地效率,走资源节约型与环境友好型的土地利用模式。     

东江流域2001-2013年土地利用/覆被类型变化的时空特征及成因

[目的]区分人类活动和自然环境变化对东江流域土地利用/覆被类型变化的贡献率,为优化流域土地利用方式、保护流域生态环境和支持粤港澳大湾区建设提供有益的信息和科技支撑。[方法]基于时间序列的遥感影像土地利用/覆被类型栅格数据,结合区域经济发展、土地利用评价指标体系和灰色关联分析,量化东江流域2001-2013年间土地利用/覆被类型变化的时空特征和成因。[结果]①随着时间推移,东江流域土地利用/覆被类型格局由常绿阔叶林、草地和耕地共同主导型转变为常绿阔叶林主导型;②研究期内不同土地利用/覆被类型变化差异明显,灌丛、混合林、常绿阔叶林和草地变化剧烈且相互之间转化频繁,水域、耕地和城镇用地面积变化相对平缓;③非城镇用地转化空间差异显著,耕地的转化程度表现为：下游 > 上游 > 中游;④人口增加、城市建设、技术革新和经济增长是推动东江流域土地利用/覆被类型发生变化的主要原因。[结论]总体来说,最近10 a多东江流域的土地利用/覆被类型变化有利于流域生态环境和水资源的保护,进而有助于粤港澳大湾区的建设。     

生态脆弱区土地利用变化及驱动力——以河北省张北县为例

[目的]研究河北省张北县的土地利用变化及其驱动因素,为该区域土地管理决策和土地资源可持续利用供科学依据。[方法]以1989,1995,2000,2010年TM遥感影像为数据源,运用遥感、地理信息系统、数理统计分析等技术与方法,系统分析了张北县土地利用变化的时空特征,剖析了土地利用变化的驱动因素。[结果]张北县主要地类为耕地、林地和草地,1989—2010年土地利用数量变化主要表现为耕地和草地面积的减少,林地和建设用地面积的增加,其中2000—2010年土地利用变化更为剧烈;地类转换主要表现为耕地、草地向林地转变以及耕地、草地向建设用地的转变;空间变化主要表现为东部坝头地区林地增加明显,中部平原地区建设用地扩张明显。[结论]近20年来张北县土地利用变化明显,主要受自然及社会经济因素综合影响。此外政策因素也是该区域土地利用变化的主要驱动因素。     

基于GEE数据平台的北洛河流域1970-2019年土地利用结构变化特征

[目的] 探究北洛河流域土地利用时空变化及其驱动力,为该区土地资源优化、环境质量改善和水沙生态要素变化分析等提供科学依据。[方法] 基于GEE平台整理和处理北洛河流域1970—2019年间6期遥感影像数据,从时间变化、动态度、转移方向和空间分布等角度分析流域土地利用变化特征,并对其驱动因素进行探讨。[结果] 研究时段内,北洛河流域土地利用类型以耕地、林地和草地为主,数量结构从2000年前的1：1.1：0.6变化到2000年后的1：2.7：0.7。1970—2019年研究区耕地、草地和水域的减少率分别为16.6%,6.7%和0.1%,林地和建设用地的面积增加率为19.9%和1.3%。流域耕地和草地斑块趋于分散且简单化,林地斑块趋于聚集和复杂化。土地利用转移主要以耕地转林地、耕地转建设用地和草地转林地为主。流域土地利用综合动态度先增后减,2000—2010年间达最大。流域中,上游丘陵沟壑区土地利用结构变化最为显著,其次为中游的甘泉、宜君、华池、合水等县。[结论] 国家政策的演变、社会经济发展和人口增长决定了土地利用变化的方向和程度,自然因素为长期辅助影响因素。     

海河上游清水河流域土地利用变化特征

[目的]海河上游清水河流域处于半湿润向半干旱过渡的生态环境脆弱区,研究该地区土地利用时空变化规律,旨在为当地生态环境建设提供一定的决策依据。[方法]基于清水河流域1990—2018年4期Landsat遥感影像解译的土地利用数据,在优选的最佳空间尺度下通过Logistic-CA-Markov模型对清水河流域土地利用变化进行分析和预测。[结果]①近30 a来清水河流域土地结构主要以耕地、林地、草地为主,三者面积之和比例超过总量的96%;其中,建设用地面积持续增加且变化程度最剧烈。②通过对受试者工作特征(ROC)曲线进行拟合优度评价,在100 m×100 m空间尺度下,各个地类ROC值达到最优水平。③2018—2027年间,草地和水域面积预计分别减少42.44,5.43 km~2,耕地、林地和建设用地面积分别增加16.51,16.89,14.67 km~2。[结论]①100 m×100 m是针对具有典型小流域特征的清水河流域进行预测模拟研究的最合适尺度;②因2022冬奥会的筹备促使建设用地的开发力度加大将成为未来清水河流域土地格局变化的主要因素。     

吉林省1990-2018年土地利用空间分布及其变化

[目的] 对吉林省土地利用空间分异变化特征及其驱动因素进行分析，为省域土地利用的可持续发展及其生态环境建设提供科学依据。[方法] 以吉林省1990年和2018年两期土地利用数据为基础，计算土地利用的区位指数、多样化指数、信息熵与均衡度，结合莫兰指数进行空间自相关的探索，综合分析吉林省土地利用空间分异特征。[结果] ①吉林省1990-2018年土地利用保持以林地和耕地双优势为主的特征；西部和中部耕地双优势相对增加，西部林草用地双优势增强、水域双优势消失，中部长春市区呈现耕地双优势的发展趋势。②土地利用多样化指数、信息熵与均衡度指数保持西高东低的特征，除长春主城区提高外，其他地区均呈现总体下降的态势。多样化指数及信息熵均呈正的全局自相关，二者的高-高聚集区在吉林省西部地区，聚集面积均有所收缩；低-低的聚集区在东部地区，两期数据相比略有波动，总体基本稳定。③自然环境因素（气温、降水）对土地利用空间分异的影响相对显著。[结论] 吉林省的土地利用变化有着明显的空间分异特征，自然环境因素社会经济因素是其主要驱动因素。     

陕西省2000-2018年土地利用时空演变及驱动因素

[目的] 分析陕西省土地利用变化及驱动因素,为促进该省土地资源综合优化配置和社会经济可持续发展提供科学依据。[方法] 基于2000,2010和2018年陕西省的土地利用遥感监测数据,通过土地利用动态度、土地利用转移矩阵、空间自相关等方法定量分析陕西省土地利用的时空演变特征,并利用主成分分析法对其土地利用变化的驱动力进行分析。[结果] 各土地利用类型面积均有不同程度的变化。其中,耕地面积下降最多,工矿建设用地面积增速最快,水域面积变化最小。土地利用类型受自然条件的影响,空间差异性显著。农村居民用地、未利用地、耕地、林地、草地的空间聚集性强,水域、城镇居民用地和工矿生产用地的空间集聚性性相对较弱,草地、工矿建设用地形成新的集聚区。陕北高原和关中平原土地利用转移相对频繁,陕南山区土地利用转换相对较小。榆林市和延安市主要表现为耕地向林地和草地转移以及未利用地和草地向工矿建设用地转移,西安市主要表现为耕地和农村居民用地向城镇居民用地转移。土地利用变化的主要因素是城市化发展过程中社会经济的发展以及产业结构的调整。[结论] 陕西省土地利用变化区域差异较大,应因地制宜制定土地利用规划,促进人口—经济—生态之间的协调发展。     

1990-2014年甘肃省白龙江流域土地利用变化对人类活动响应

[目的]综合分析1990-2014年甘肃省白龙江流域土地利用变化及其对人类活动的响应,以期为该区未来的土地利用优化提供参考.[方法]基于1990年,2002年,2014年3期遥感影像解译获取的土地利用数据,计算土地利用变化速度、土地利用转移矩阵和土地利用程度.[结果] 1990-2014年流域的综合土地利用动态度从10.24％增长到17.59％;1990-2014年流域的土地利用类型变化以草地、耕地和林地的转换为主;1990-2002年流域内各县(区)的土地利用程度综合变化指数介于1.38～6.65,而2002-2014年流域内各县(区)的土地利用程度综合变化指数介于一15.43～0.17.[结论]1990-2014年流域人类活动对土地的利用由简单索取开发型转变为保护与生态建设型,从破坏性、粗放式和低利用效率向保护性、集约式和高利用效率发展.     

珠峰北麓朋曲流域土地覆被变化及未来情景模拟

[目的] 模拟未来短、中远期珠峰北麓朋曲流域土地利用变化，为该流域的土地利用规划提供科学参考。 [方法] 基于朋曲流域(珠峰北麓)2010-2020年的土地覆被数据，综合考虑人为和自然两大要素12项驱动因子，采用Markov-FLUS模型，对朋曲流域自由发展、耕地保护和生态保护3种未来情景下的土地覆被变化进行了模拟。 [结果] ①2020年朋曲流域土地覆被实际情况与Markov-FLUS模型模拟情况的总体精度(OA)为90%，kappa系数为0.82，精确度较高，模型可用于该区未来情景模拟； ②2010-2020年朋曲流域5种土地覆被类型发生变化，其中，林地和草地的面积变化最为明显，林地面积增加778.16 km²，草地面积减少726.89 km²； ③朋曲流域未来情景的模拟结果显示：在自由发展、耕地保护、生态保护3种不同情景下，短期内草地和其他用地类型面积变化较大，中远期除草地、其他用地类型面积变化较大以外，林地面积变化开始增大；无论是短期还是中远期来看，耕地保护情景下耕地面积均呈持续减少趋势。 [结论] 维持朋曲流域的可持续发展，必须强化落实耕地保护政策、注重耕地永续利用；生态保护情景下自然保护区内的植被类型相互转换受到限制，生物多样性得到有序协调发展。     

秦淮河流域1980-2010年土地利用变化及驱动机制

[目的]研究近30a来秦淮河流域不同时期土地利用/覆被变化特征及驱动力,为秦淮河流域的生态经济系统可持续发展和流域管理提供科学依据。[方法]利用GIS功能对秦淮河地区1980,1995,2000,2005,2008,2010年土地利用现状图进行叠加转换,建立土地利用变化转移矩阵,在此基础上分析秦淮河地区近30a来的土地利用变化特征,并结合相应的社会统计资料分析土地利用变化的驱动力。[结果]流域内耕地面积逐年减少,建设用地面积逐年增加,林草覆盖面积略有减少;土地利用程度变化存在明显的时间差异性,2005—2008期间变化最大;建设用地的增加主要源于耕地的转入,其次是林地、水域;经济发展、人口增长和人民生活水平的提高是该区土地利用/覆被变化的主要驱动力。[结论]城市化发展要素是推动该区建设用地增加、耕地面积减少这一现象的主要驱动力。     

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.     

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.     

Einfluss der düngungsmethoden auf die entwicklung von zuckerrübenkrankheiten

Während neunjähriger (1994-2002) Untersuchungen in der Versuchsanstalt Ba?cyny (Fahlerde, Fall-Gleyboden, ausgebildet aus leichtem Lehmboden) wurde der Befall mit Krankheiten an der Zuckerrübe in Abhängigkeit von der Düngungsmethode bewertet. Folgende Methoden wurden angewendet: A - Mineraldünger, B - Stalldung und Mineraldünger, C - Stroh-, Gründung und Mineraldünger, D - Kompostdünger und Biopräparate (ökologische Düngung). Auf den Objekten A, B, C wurden bei konstanter Phosphor-Kalium-Düngung die Stickstoffgaben von 0 bis 180 kg.ha^?1 differenziert. Auf dem ökologischen Objekt D ohne Mineraldünger wurden statt Stickstoff die Biopräparate P₅₀₀ und P₅₀₁ verabreicht. Der geringste Befall von Krankheiten wurde an der Zuckerrübe auf jenem Objekt festgestellt, das mit Kompost und den Biopräparaten gedüngt worden war. Im Rahmen der konventionellen Düngungsmethoden wurde allgemein die höchste Intensität der Krankheiten an der mit Stroh, Gründung und Mineraldünger gedüngten Zuckerrübe beobachtet. Ausnahmen von dieser Regel bildete das Vorkommen von echtem Mehltau und Keimlingsfäule. Auf den Objekten A, B, C nahm die Intensität der Krankheiten mit der Steigerung der Stickstoffgabe zu. Auch die auf Objekt D verabreichten Biopräparate stimulierten die Entwicklung der Krankheiten. The effect of various fertilization methods on the diseases of sugar beet was estimated on the basis of nine-year studies (1994-2002) conducted in the Experimental Production Farm in Ba?cyny on loess-based, sedimentary-gley, light-clay soil. The following fertilization methods were applied: A - mineral fertilization, B - mineral and manure fertilization, C - straw, green manure and mineral fertilization, D - ecological compost and biodynamic preparations fertilization. In the objects A, B and C fertilized with phosphorus and potassium, various doses of nitrogen ranging from 0 to 180 kg/ha^?1 were used. In the ecological object D, where mineral fertilization was not used, biodynamic preparations P₅₀₀ and P₅₀₁ were applied instead of nitrogen. The lowest ratio of the diseases of sugar beet was observed in the object fertilized with the compost and biodynamic preparations. In view of the conventional fertilization methods, generally the highest incidence of diseases was noted in the sugar beet fertilized with straw, green manure and mineral fertilizers. The exception was the occurrence of powdery mildew and the black leg. In objects A, B and C the incidence of the diseases increased with the increase in nitrogen doses. The applied biodynamical preparations in the object D stimulated the development of diseases too.     

Prospects for control of Pythium damping-off of lettuce with Trichoderma,Gliocladium and Enterobacter spp.

Summary Damping-off of lettuce (Lactuca sativa) caused by Pythium ultimum was studied in pots containing a non-sterile potting mix in the glasshouse. Fifty P. ultimum sporangia g^-1 compost reduced the plant stand to 15% and shoot dry weight to 18%, but this reduction was totally prevented by applying Trichoderma harzianum at 2×10⁵ viable propagules g^-1 potting mix. Gliocladium virens and Enterobacter cloacae also alleviated the damping-off. E. cloacae did not adversely affect the action of the fungal antagonists. The co-existence of the bacterial and fungal antagonists was revealed on the root surface and inner surface of the testa by scanning electron microscopy, indicating the compatibility of the biocontrol agents.     

细菌、真菌及植物氮营养信号研究进展

氮素吸收代谢是所有生物生命活动的核心部分,因此,各种生物对氮的吸收与同化过程都有精细的调节。这种调节依赖于生物对体内氮素状况信号及体外（生长介质中）氮素信号的感受。过去几十年中,在细菌、真菌中已经对氮素营养信号有了较好的研究,而植物中则相对缓慢,但也有了一定的认识。本文重点比较细菌、真菌及植物中氮信号系统的组成,以期为进一步认识植物中的氮信号接受与转导系统提供启示。     

Aircraft operations near concentrations of birds in Antarctica: The development of practical guidelines

Aircraft operations have the potential to disturb and to impact negatively on bird life. A gradient of increasing behavioural response is evident in birds when exposed to increasing aircraft stimulus. The most major disturbance is likely to lead to impacts on the health, breeding performance and survival of individual birds, and perhaps bird colonies. A process of revision to policies on aircraft operations contained in management plans for a number of specially protected areas in Antarctica by the United Kingdom, accompanied by consultations made within the scientific community through the Scientific Committee on Antarctic Research (SCAR) and with operational interests through the Council of Managers of National Antarctic Programmes (COMNAP) resulted in new guidelines being adopted by the Antarctic Treaty Consultative Parties in June 2004. The principal recommendations of the guidelines are that bird colonies should not be overflown below 2000 ft (∼610 m) above ground level and landings within 1/2 nautical mile (∼930 m) of bird colonies should be avoided wherever possible. These guidelines are less stringent and less specific than those that were recommended by the SCAR specialist group on birds, and represent a compromise to accommodate operational needs. While the adoption of clear and consistent guidelines for the operation of aircraft in Antarctica is welcome in that this provides practical advice that is likely to reduce incidences of close aircraft/bird encounters, there remains insufficient knowledge of the interactions between aircraft and birds in Antarctica, and the consequent impacts on individual birds and on bird populations. It is important, therefore, that the guidelines adopted are considered interim, and should be kept under scrutiny with revisions made as new and improved research results appear.     

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.