品种和播期对华北春玉米产量及水分利用效率的影响

华北平原冬小麦夏玉米一年两作种植制度主要受水资源的约束,发展休耕轮作是实现该区域农业可持续发展的途径之一。春玉米高效生产是提升休耕轮作产能的关键因素,如何利用品种特性进行播期调整以适应区域生产特点提高产量是该区春玉米生产中面临的主要问题。为此,于2016年5—9月在中国科学院南皮生态农业试验站以5个玉米品种(‘华农887’、‘胡新338’、‘郑单958’、‘华农866’和‘联创1号’)为材料,比较分析了3个播期(5月1日、5月15日和5月30日)下春玉米生育时期、产量及产量要素、耗水和水分利用效率的变化情况,并结合气象因子分析探讨了春玉米产量及其构成要素与环境因子的关系。结果表明:随着播期推迟,不同春玉米品种的生育期总天数均呈显著减少趋势(P0.05),生育期总天数的减少主要是播种到抽雄天数减少所致。不同春玉米品种的生育期总天数也存在较大差异,在各播期处理下均相差5~7 d。在产量方面,5月1日和5月15日播种的5个玉米品种间平均产量没有显著差异,5月30日播种的平均产量显著高于前2个播期,其产量提升主要是百粒重增加所致。随着播期的推迟,春玉米的耗水量变化不大,水分利用效率呈增加趋势,这主要与降水的分布有关。通过气象因子分析,不同播期下百粒重与抽雄前后的积温和降水呈显著相关(P0.05)。综合产量、耗水和水分利用效率分析,在该区域推荐5月30日左右为春玉米的适宜播种日期,‘华农866’和‘华农887’是适宜该区生产的潜力品种。     

气候变化背景下华北平原夏玉米花期高温热害特征及适宜播期分析

利用华北平原夏玉米种植区55个气象站点1981−2017年逐日地面观测资料,以日最高气温≥35℃持续3、4、5d,且相对湿度≤70%为一次轻、中、重度高温热害,从年代际尺度、年尺度、旬尺度分析37a来华北平原不同播期下夏玉米花期高温热害的时空变化特征;以开花期避开中度高温热害为标准,推算夏玉米花期规避高温的适宜播期。结果表明:6月上旬播种,夏玉米花期遭遇高温热害的频率最大,河南省南部的信阳、固始等地区遭遇高温热害频率超过20%;6月中旬播种,夏玉米花期遭受高温热害频率为9%~12%。2011年以来华北平原夏玉米花期高温热害加重,发生频率高于P1−P3时段(1981−2010年)。华北平原早熟玉米平均适宜播种期在6月15日−7月5日,中熟玉米平均适宜播种期在6月15−27日,晚熟玉米平均适宜播种期在6月15−20日。在各适宜播种期范围内,华北平原南部应适当晚播,北部则应适当早播。     

安徽沿江地区露地鲜食玉米适宜播期确定

以鲜食玉米“彩甜糯100”为材料，设置4月1、16日，5月1、16、31日，6月15、30日，7月15、30日和8月14日共10个播期，研究不同播期鲜食玉米的生育期、产量和产值及其与气象因子的关系，以明确安徽省沿江地区露地播种条件下鲜食玉米的适宜播期。结果表明：(1)随播期推迟，鲜食玉米生育期呈长-短-长变化趋势，株高、秸秆鲜重及产量表现为高-低-高，穗粒数呈多-少-多变化趋势。4月1日-5月1日和7月30日播期的鲜食玉米平均产量为20026.56kg·hm^-2，显著高于其他播期处理(P<0.05);7月30日播期处理直接销售鲜穗产值为70245.00元·hm^-2，较其他处理显著增加68.66%～123.50%(P<0.05)。(2)5月31日-7月15日播种鲜食玉米，生育期内≥32℃日数占全生育期日数的56.25%～60.26%，高温积热较4月1日-5月1日和7月30日播期处理高47.78%～54.46%;5月31日-7月15日播种鲜食玉米生育进程加快，株高降低，物质积累减少，产量降低。8月14日播种鲜食玉米，受灌浆期低温影响，...     

基于气温资料的黑龙江省玉米播种期分析

利用1961-2010年黑龙江省70个地面气象站逐日平均气温资料,应用气候倾向率统计方法,结合ArcGIS软件,对黑龙江省玉米播种开始日期及其气候倾向率的空间差异、现有推广品种及救灾品种最迟播种日期的空间分布进行分析。结果表明:黑龙江省大部玉米始播期在4月下旬-5月上旬,松嫩平原大部在4月22日-5月5日,三江平原大部及牡丹江地区局部在4月26日-5月5日,其它地区在5月6-20日。50a中,黑龙江省部分地区玉米始播期呈显著提前趋势(P0.05),全省平均变化趋势不显著。各地玉米始播期提前幅度不同,黑河大部、齐齐哈尔大部提前幅度最大。现有推广品种的最迟播期中晚熟品种在5月中旬;松嫩平原中熟品种大部在5月下旬初;三江平原和牡丹江地区中熟品种最迟播期在5月下旬末,早熟和早中熟品种在5月下旬初。救灾品种的最迟播期自北向南呈延迟趋势,在6月1-23日,大部地区集中在6月11-15日。研究结果可为黑龙江省玉米作物应对气候变化及有效防御玉米早播的潜在风险提供科学依据。     

黄淮海北部地区夏玉米稳产高产的播期优选

全球气候变暖背景下，农业气象灾害的加剧已经严重威胁农业稳产高产。科学地调整播期是农业生产趋利避害的主要措施。该研究分析了黄淮海北部地区主栽夏玉米品种郑单958和登海605不同播期（6月5日、6月10日、6月15日、6月20日和6月25日）下生育期气候资源、主要农业气象灾害及产量的变化特征。结果表明：1）随播期推迟，夏玉米生育期内总活动积温和总辐射呈减少趋势，花期降水逐渐增多；降水分布受播期和年型的影响变化显著。2）播期6月15日时主要农业气象灾害（花期高温热害和花期连阴雨）发生频率最低。3）夏玉米产量在播期6月10日和15日时较高，且与花后≥15 ℃活动积温呈显著的二次相关关系（P<0.05）。试验结果表明，6月15日是黄淮海北部地区夏玉米的适宜播期。研究结果为作物应对气候变化的播期调整提供了方法借鉴，也为黄淮海北部地区夏玉米稳产高产提供了播期依据。     

气象因子变化对华北平原夏玉米产量的影响

利用统计分析方法对中国科学院栾城农业生态试验站11a玉米产量数据和影响夏玉米气象产量变化的主要气象因子进行了分析。结果表明：该区域夏玉米生长期间的日照时数有明显的下降趋势,6、7、9月的日平均温度有逐渐升高的趋势,8月的日平均温度有降低的趋势;该区夏玉米产量的增加,气象因子占有比较重要的位置,占到31．45％;6月下旬的平均气温、8月下旬-9月上旬的日较温差、7月中旬和9月上旬的日照时数是影响夏玉米产量波动的关键气象因子。     

气候变化背景下华北平原夏玉米各生育期水热时空变化特征

气候变化背景下,华北平原气候资源也发生了相应变化。研究作物生长季各生育期的水热时空变化特征,对适应气候变化技术与政策的制定有重要意义。本文基于华北平原49个气象站点的逐日气象数据和27个农业气象试验站的物候期数据,分析了1961—2010年在夏玉米营养生长期、并进期、生殖生长期和全生育期的生长度日(GDD)、高温度日(HDD)、降水量及气候倾向率的时空分布。结果显示,华北平原夏玉米各生育期GDD、HDD均呈东北-西南走向的递增趋势,降水量呈东南-西北递减趋势。华北平原夏玉米在全生育期GDD倾向率、HDD倾向率、降水量倾向率分别为8.14℃·d·10a-1、-2.45℃·d·10a-1、-10.75 mm·10a-1。华北北部GDD在营养生长期呈递减趋势,在并进期、生殖生长期以及全生育期呈递增趋势,而华北南部GDD变化趋势与之相反;HDD在各生育期均呈现北部递增,南部递减趋势。降水量在各生育期均表现为北部降低,南部增加趋势。因此,河北省北部、北京市和天津市等华北北部地区夏玉米生产高温风险与干旱风险呈增加趋势,而河南省大部、山东省南部等华北南部地区高温风险与干旱风险呈降低趋势。     

播期对春玉米生长发育与产量形成的影响

以"郑单958"和"鲁单984"为材料,比较研究了两个播期(4月24日和5月15日)条件下春玉米的生长发育和产量形成,探讨了春玉米生长发育与气候条件的关系.结果表明,不同播期的春玉米生长发育和产量都存在显著差异.与4月24日播期相比,5月15日播期的春玉米产量(干重)提高2 157 kg·hm-(郑单958)和1 137 kg·hm-2(鲁单984).粒重在播期间,品种间及播期与品种互作问差异均不显著.穗粒数在品种问不显著,但在播期间差异达显著水平,第2个播期穗粒数提高幅度达37.8%(郑单958)和11.2%(鲁单984).通过对不同播期间气象因子的分析发现,降雨是影响华北平原春玉米生长发育和产量形成的最重要气象因子.降雨主要通过对穗粒数的调节来影响产量.开花期降雨过多所带来的低温寡照影响玉米的受精授粉与结实:拔节至大喇叭口期降雨通过调节叶面积大小影响作物干物质积累,进而影响籽粒的发育情况.本试验中,5月15日是春玉米获得高产的最佳播期.合理安排播期,重视降雨对春玉米生长发育及产量形成的影响,是华北平原春玉米获得高产的重要措施.     

浙江地区甬优15直播稻的最佳播期分析

以“甬优15”水稻为材料,于2017年在浙江龙游农业气象试验站进行5个播期的分期播种试验（A1：5月5日,A2：5月15日,A3：5月25日,A4：6月4日,A5：6月14日）,分析播期对直播稻叶面积指数（LAI）、光合生产、群体干物质积累和转移以及产量的影响。结果表明：适宜播期（A2,5月15日）下,直播稻LAI、群体光合势、群体生长率高,群体干物质积累多,地上部干物质的输出量和转化率大,A2地上部营养器官干物质输出量和转换率分别比A1、A3、A4、A5高7.87%、15.29%、49.43%、56.43%和5.59%、13.18%、28.60%和39.83%。与当地常年单季晚稻适宜播种日期（5月25日）相比,适当早播（5月15日）可增加直播稻的有效穗数、结实率及穗粒数,提高水稻产量,其中A2产量最高（为8879.70kg·hm-2）,分别比A1、A3、A4和A5高392.10、610.20、1445.85和2085.15kg·hm-2。由此可见,甬优15在浙江龙游最佳直播期为5月中旬,偏早或偏迟（5月上旬或5月下旬）播种均将导致减产,而过迟播种（6月及以后）将导致产量严重降低。     

春玉米干物质积累和产量对播期调控下水热变化的响应

为探究春玉米(Zea mays L.)干物质积累和产量对播期调控下水热变化的响应,在河北科技师范学院试验基地,于2017—2020 年进行了4年的播期试验,以京农科728和MC812为材料,分析了播期(5月1日、5月10日、5月20日、5月30日)引起的春玉米干物质积累量、产量构成因素、产量以及水分利用率的变化。结果表明,受温度与降水影响,春玉米干物质积累量在生育前、中期随播期的推迟而下降,而灌浆后期至成熟期以5月30日播种春玉米干物质积累量最多。春玉米干物质积累动态符合Logistic模型,5月30日播种春玉米干物质积累的总持续时间和快增期持续时间均最长。有效穗数、穗粗、轴粗、穗行数和出籽率不受温度与降水的影响,但穗粒数、千粒重、穗长、行粒数受其影响显著,各指标随播期延迟先下降再上升,并以5月20日播种的春玉米最低。产量与千粒重呈显著正相关,5月30日播种的春玉米产量最高。另外,随播期的推迟,总耗水量减少,水分利用效率提高。综上可知,合理安排播期,重视降雨对春玉米生长发育及产量形成的影响,是冀东地区春玉米获得高产的重要措施。本研究为冀东地区春玉米播期选择提供了理论依据和技术支持。     

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.