不同条件育秧提高水稻秧苗抗逆性的研究

稻麦轮作系统中,麦秸还田腐解产生的有毒有害物质可对下茬水稻幼苗产生不利影响,有效减缓或避免其负面影响对于水稻生产尤为重要,而筛选能够提高水稻秧苗抗性的育秧技术不失为重要途径。通过采用5种不同育秧条件对水稻秧苗进行抗性锻炼,以期提高水稻秧苗对麦秸还田条件的抗逆性和适应性,并在移栽后采取相同的栽培措施(氮素和水肥管理)对其进行评估。试验结果表明,干旱及低营养条件下育秧均降低了水稻株高、生物量以及叶绿素含量,且增加了水稻植株丙二醛含量和脯氨酸含量,使水稻的生长发育受到抑制;而施用秸秆、浇施秸秆腐解液以及酚酸混合液进行育秧的处理均增加了水稻株高、地上部鲜重、叶绿素含量、总根长、根表面积、根体积、根尖数、根分枝数和平均根直径,且均降低了水稻植株丙二醛含量和脯氨酸含量,提高了水稻秧苗对麦秸腐解产生负面影响的抗逆性和适应性。通过在水稻育秧期添加适量麦秸、麦秸腐解液或酚酸混合液均可有效提高水稻秧苗对麦秸还田条件的适应性。     

添加水稻秸秆对油菜(Brassica napusL.)幼苗生长的影响

近几年,水稻秸秆直接还田对油菜幼苗生长的负效应受到关注。有许多研究在水稻残体或腐解物中检测出了酚酸等被广泛证实具有化感作用的物质,因此在水稻秸秆产生的负效应中,化感抑制作用不容忽视。本研究以酚酸为目标化感物质,以湖北省油菜主栽品种"中双11号"为受体,采用4种采自典型稻油轮作系统中的土壤进行盆栽试验,研究水稻秸秆对油菜幼苗生长的影响。结果表明:(1)整体看来,添加秸秆对油菜幼苗总生物量的主效应在进贤土为正,在汉川土为负,在阳逻和麻城土为无明显影响;(2)功能叶片光合色素含量在全部土壤下的显著降低均出现在播种后33 d之内,与水稻秸秆腐解速率最大值的出现与存在时间上的重叠。秸秆处理对油菜幼苗的负效应在早期强于后期;(3)土壤水溶态酚酸含量为3.3~49.0μg·g-1soil。添加秸秆虽导致土壤中水溶态酚酸浓度增加,但其明显增加主要发生在试验后期,且增量与幼苗生物量化感效应指数呈正相关关系。因此酚酸含量的变化不能解释水稻秸秆的负效应,为揭示秸秆处理的负效应机制,需要转换目标化感物质。     

农作物秸秆浸提液对丛枝菌根真菌侵染番茄幼苗的影响研究

本研究采用水稻、小麦、玉米、大豆和番薯5种农作物秸秆,制成水浸提液与AM真菌结合施用,研究秸秆浸提液对AM真菌作用效果的影响,同时分析了5种秸秆浸提液的化学组分。结果表明,水稻、小麦、玉米和番薯秸秆浸提液显著提高了AM真菌对番茄根系的侵染,其中水稻秸秆浸提液处理的番茄生物量及地上部磷含量都有显著增加。经过GC-MS测定得到的各秸秆浸提液化学组分主要为酚酸类物质,这些物质可能对AM的调节发挥重要作用。     

棉秆腐解液对棉花种子萌发及幼苗生长的影响

针对新疆棉区长期连作与棉花秸秆还田的普遍现象,采用生物测定的方法,研究了棉秆腐解液对棉花自身的化感作用。结果表明,棉秆腐解液对棉花种子萌发及幼苗生长的影响表现出“低促高抑”,抑制作用随腐解液浓度增大而增强。2.5、5 g·L^-1的腐解液能提高棉花种子萌发率,促进胚根生长,而10、20、30 g·L^-1的浓度则产生抑制作用。5 g·L^-1处理棉花幼苗的根长、株高等指标显著高于对照。过高的腐解液浓度（〉10 g·L^-1）使棉苗根系活力减弱,抑制棉花幼苗根的生长发育,使植株叶片叶绿素含量降低,从而导致根重、根长、株高等下降,20、30 g·L^-1两处理根鲜重与根长均显著低于对照。在5、10 g·L^-1的浓度范围内,棉花幼苗体内SOD、POD活性分别增高,超过以上浓度则酶活性开始下降,20 g·L^-1以上浓度使MDA含量急剧增高。     

柠条锦鸡儿茎叶水浸提液对4种农作物幼苗生理特性的影响

采用改进的水浸提液法制得浸提母液,土培法对玉米、小麦、糜子和荞麦进行幼苗生长试验,研究不同浓度柠条锦鸡儿茎叶水浸提液对4种牧草幼苗的影响.结果表明:25.0 mg/ml的柠条茎叶水浸提液使4种农作物幼苗丙二醛(MDA)含量增加,但根系活力却明显降低,而叶片细胞膜透性显著增加;4种农作物幼苗叶绿素含量分别下降了45.00％,29.00％,46.67％和35.71％.当柠条茎叶水浸提液浓度为25.0 mg/ml时,4种农作物幼苗体内超氧化物歧化酶(SOD)活性仅糜子表现出显著的促进作用;糜子、荞麦和小麦幼苗体内过氧化氢酶(CAT)活性显著增高;过氧化物酶(POD)活性均表现出显著增加;当浓度为100.0 mg/ml时,4种农作物幼苗体内SOD、CAT和POD的活性均有显著抑制.从化感综合效应指数来看,柠条茎叶水浸提液对4种农作物幼苗生理特性的化感抑制效应大小为糜子＞荞麦＞小麦＞玉米.     

玉米秸秆腐解液对苗期根际土壤酶活性及根系活力的影响

玉米连作现象在黑龙江省农田生态系统中较为普遍,秸秆焚烧既浪费资源又污染环境,研究玉米秸秆还田后的化感效应尤显重要,但秸秆还田后的效应尚不清楚。本研究以玉米(郑单958)为受体,采用盆栽试验,分析不同腐解时间(0.25、60、120、180d)、不同腐解浓度(0、0.125、0.25、0.5 g·m L-1DW)玉米秸秆腐解液对苗期根际土壤酶活性及根系活力的影响,试图从土壤酶学和根系活力变化的角度初步阐明连作状态下秸秆还田对苗期玉米生长的影响,以期为大田生产中应用秸秆还田技术提供相关科学依据。结果表明:玉米幼苗四叶、五叶、六叶期,土壤蔗糖酶、脲酶活性均在60d腐解天数,0.5 g·m L-1DW浓度处理下达到最高。土壤酸性磷酸酶活性均在120d腐解腐解天数,0.5 g·m L-1DW处理下达到最高。土壤过氧化物酶活性在幼苗四叶、五叶期,腐解60d,0.5 g·m L-1DW浓度处理下达到最高,六叶期酶活与对照相比差异均不显著。玉米幼苗根际土壤蔗糖酶、脲酶、酸性磷酸酶、过氧化物酶的活性随腐解液浓度的增加而增加;随着玉米秸秆腐解天数的增加,呈现先升高后降低的趋势;随叶龄增加,腐解液对根际土壤酶活性的影响逐渐减弱。玉米幼苗根系活力随着秸秆腐解液浓度的增大先升高后降低;低(0.125 g·m L-1DW)、中(0.25 g·m L-1DW)浓度下对根系活力的促进作用也随叶龄增加逐渐减弱。     

半夏植株腐解液对8种作物的化感作用及化感物质成分分析

为探究半夏植株腐解液(PTDL)化感作用与连作障碍的关系以及半夏合理种植制度的建立,采用生物测试法研究半夏植株腐解液对8种作物种子萌发和幼苗生长的影响,并结合气质联用(GC-MS)技术对潜在的化感物质进行定性分析。结果表明,在物种水平,半夏植株腐解液对8种受试材料均有化感抑制作用,作用强度依次为生菜莴笋小麦玉米高粱油菜决明子半夏。半夏植株腐解液的自毒作用呈低促高抑的浓度效应,0.01 g·m L-1是半夏植株腐解液产生显著自毒作用的临界浓度;半夏植株腐解液对生菜等7种作物的抑制作用强度与浓度呈正相关。乙醚萃取半夏植株腐解液所得活性组分中鉴定到30种化合物,其中2,6-二叔丁基对甲酚、芥酸酰胺和2,2'‐亚甲基双(4甲基-6-叔丁基苯酚)的相对含量合计占总体的60.35%,为化感物质,由此推测这是导致半夏连作障碍发生的重要原因之一。本研究为缓解和消除半夏连作障碍提供了理论依据。     

蚯蚓堆肥浸提液对幼苗生长的影响

蚯蚓堆肥浸提液的育苗试验结果表明，不同浓度蚯蚓堆肥浸提液理化性质呈梯度变化，对幼苗生长发育的影响不同。与纯无机营养液体系相比，蚯蚓堆肥浸提液对番茄、小白菜及水稻幼苗的地上部生长、根系生长和活力、壮苗指数、叶绿素含量、抗氧化酶活性等指标均有不同程度提高。其中，添加浓度为 7.5%蚯蚓堆肥浸提液的应用效果最佳；随着浸提液浓度的增加，盐分浓度相应增加，则抑制了育苗生长。综上，在无机营养液中添加浓度 7.5%的蚯蚓堆肥浸提液能够不同程度促进幼苗的生长，具有良好的壮苗效果，为蚯蚓堆肥浸提液的应用奠定了一定的理论基础。     

不同生长环境下黄顶菊浸提液对多年生黑麦草萌发与生长的影响

为阐明黄顶菊入侵机制,本文在调查不同生境下黄顶菊居群特征的基础上,进一步采用植株浸提液生物测试的方法研究了不同生境、生长密度及替代植被下黄顶菊对多年生黑麦草的化感潜力。结果表明:黄顶菊的化感作用强弱与其入侵能力存在一定相关性,黄顶菊浸提液的化感潜力随浓度升高而增强;不同植株组织浸提液的化感潜力存在显著差异,表现为地下部分明显低于地上部分;不同生境下黄顶菊浸提液的化感潜力顺序为水边>果园>路边,50 g.L 1茎叶浸提液对多年生黑麦草发芽率化感效应敏感指数分别为2.83(水边)、1.31(果园)和0.71(路边);不同密度黄顶菊的茎叶化感潜力顺序为高、中密度区显著大于低密度区,50g.L 1浓度浸提液对多年生黑麦草发芽率化感效应敏感指数分别为3.91(高密度)、4.89(中密度)和0.29(低密度);根部浸提液的化感潜力顺序则相反。不同替代植被下茎叶浸提液的化感效应为混种>单种,而根系浸提液的化感效应敏感指数则差别不大。因此,黄顶菊不同组织器官化感活性物质分配不同,同时其化感效力能够适应环境条件而发生变化,这可能是造成黄顶菊在不同环境中入侵效果差异的原因之一。     

解淀粉芽孢杆菌Lx-11的促水稻生长作用及促生长物质分析

生防菌Lx-11是一株对水稻细菌性条斑病具有较好防治效果的解淀粉芽孢杆菌,为明确其对水稻的促生作用,本研究以感病品种金刚30为试验材料,通过比较不同稀释倍数的生防菌Lx-11无菌上清滤液对水稻种子萌发和幼苗的生长的影响,测定其对水稻芽长、根长和株高,以及叶绿素a、叶绿素b和总叶绿素含量和根系活力的影响,运用液质联用仪检测无菌上清滤液中与促生相关的物质赤霉素、脱落酸、生长素和亚精胺的含量。结果表明,生防菌Lx-11无菌上清滤液稀释后对水稻种子和幼苗均有一定的促生作用,且随着菌液稀释倍数的增加,促生作用呈先增加后减少变化,稀释倍数为100倍时,对水稻种子和幼苗的形态和生理指标的影响最为显著;当稀释倍数达到200倍以上,其对水稻的促生效果下降。不同浓度无菌上清液处理水稻幼苗时,水稻植株的叶绿素a、叶绿素b、总叶绿素含量和根系活力均有不同程度的增加,其中以100倍稀释液增加最大,分别为45.97%、49.62%、46.95%和225.43%。生防菌Lx-11无菌上清滤液中生长素、赤霉素、脱落酸和亚精胺的含量分别为1 200、75.5、3 130和811ng·mL~(-1)。综上,生防菌Lx-11对水稻植株的生长具有明显的促进作用,且促生长物质主要存在于发酵上清液中。本研究为解淀粉芽孢杆菌Lx-11在微生物农药领域的田间高效应用提供了理论依据。     

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.     

“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.     

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.     

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     

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.