干旱胁迫及复水对豌豆苗期保护酶活性及膜脂过氧化的影响

采用盆栽控水试验法,研究了干旱胁迫及复水对豌豆苗期叶片超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)活性及丙二醛(MDA)含量、质膜相对透性(RC)的影响,对豌豆苗期抗氧化能力进行了综合评价。结果表明:干旱胁迫降低了SOD活性,随胁迫程度加重和历时延长降幅增大。轻度干旱胁迫10 d或重度干旱胁迫提高了POD和CAT活性,随胁迫程度加重和历时延长增幅加大。复水5 d对CAT、SOD活性产生部分补偿效应,对POD活性产生等量补偿效应。复水10 d对SOD活性产生等量补偿效应,对CAT、POD活性产生等量或超补偿效应;干旱胁迫增加了MDA含量,随胁迫程度加重增幅加大、胁迫历时延长增幅减少。复水5 d、10 d对干旱胁迫5 d豌豆叶片MDA含量分别产生部分和等量补偿效应。干旱胁迫导致膜脂透性增大,随胁迫程度加重和历时延长增幅加大。复水5 d、10 d可分别产生部分和等量补偿效应。     

干旱胁迫对玉米叶片光响应及叶绿素荧光特性的影响

利用大型移动防雨棚开展玉米干旱胁迫及复水试验,通过分析玉米叶片光响应曲线和叶绿素荧光参数,揭示不同生育期干旱胁迫对玉米光合作用和叶绿素荧光的影响程度.结果表明:1)干旱胁迫后玉米净光合速率(Pn)显著降低;当光合有效辐射(PAR)过高时受到强光抑制作用Pn略低,干旱胁迫后受光抑制影响较对照明显;干旱胁迫对玉米光合能力的影响表现为:拔节期＞乳熟期＞苗期;复水10d后光合作用略有恢复,但恢复较缓慢.2)不同发育期受到干旱胁迫后均表现为实际光化学效率(ΦPSⅡ)、光化学淬灭系数(qP)下降,非光化学淬灭系数(qN)升高的趋势,但拔节期叶绿素荧光参数对土壤干旱胁迫的响应比苗期、乳熟期更加敏感,下降和升高幅度更大;复水后,叶绿素荧光参数虽略有恢复,但短期内难以达到正常水平.     

干旱胁迫对豌豆根系形态及产量的影响

采用盆栽方法,研究了55%的土壤相对含水量在分枝期、孕蕾期、花荚期进行15 d历时的干旱胁迫对豌豆干物质累积、根系生长及产量的影响。结果表明,与全生育期正常供水(75%)相比,三种干旱胁迫处理均降低了豌豆的干物质累积量,胁迫时期越早,复水对豌豆地上部干物质累积的补偿效果越好,分枝期干旱胁迫在成熟期达到了等量补偿;干旱胁迫均显著抑制了根系的生长,分枝期干旱胁迫对根系生长的抑制具有滞后效应,胁迫结束时与对照间差异不显著,在花荚盛期显著低于对照,孕蕾期干旱胁迫根系的复水补偿生长作用较好,各根系形态指标在成熟期均达到了超越补偿;三种胁迫方式均抑制了根瘤的形成及其生长,且复水后均产生了不足补偿,胁迫时期越早,补偿效果越差;花荚初期干旱胁迫对豌豆产量的抑制作用最大,比对照低20.41%,其次为孕蕾期,比对照低6.63%,分枝期干旱胁迫不影响子粒产量。     

干旱复水对棉花苗期抗氧化系统及光合荧光参数的影响

为研究水分胁迫对棉花光合作用及相关生理指标的影响,揭示水分胁迫与棉花生理指标及光合作用之间的关系,采用盆栽称重控水法对新陆早19号进行干旱胁迫0、2、4、6、8 d及复水2 d处理,测定棉花叶片MDA、H_2O_2含量,SOD、POD、CAT等指标以及光合参数和叶绿素荧光参数的变化。结果显示:随着干旱胁迫的加强,棉花叶片活性氧含量、电导率和MDA含量增加,复水后除H_2O_2含量外,其它均降到对照值;在活性氧含量最高时,抗氧化酶CAT和SOD的活性最高,以清除棉花叶片内过量的活性氧;棉花功能叶片的光合作用、气孔导度、蒸腾速率随着干旱胁迫强度的增加逐渐下降,在干旱第8天达到最低,复水后恢复;光化学猝灭系数(qP)和光量子产量(Yield)随着干旱胁迫的加强而降低,复水后不能恢复。说明水分胁迫下棉花可通过提高抗氧化酶活性清除过量活性氧,通过调节气孔导度抑制棉花的光合作用,降低蒸腾速率。     

干旱和复水对两种葡萄砧木叶片光合和叶绿素荧光特性的影响

采用盆栽称重控水法，干旱胁迫处理1103P和101-14M两种砧木，处理21 d后复水，分别测定干旱处理0、7、14、21 d及复水第7、14 天，葡萄砧木叶片光合和叶绿素荧光参数。结果显示：干旱胁迫后，1103P和101-14M的净光合速率(Pn)均逐渐降低，101-14M的Pn降幅大于1103P，短时间干旱胁迫引起两种砧木Pn降低的主要因素是气孔限制，而长时间干旱胁迫后Pn降低主要是非气孔限制。随着干旱胁迫的持续，1103P和101-14M的初始荧光产量(Fo)呈增加趋势，但101-14M的增幅大于1103P，说明干旱胁迫后101-14M的光反应中心受损害程度大于1103P;复水后1103P和101-14M两种砧木的Pn值逐渐增加，复水第7天，二者分别为对照的83.20%和66.31%,复水第14天，分别为对照的107.30%和88.43%; 复水后1103P和101-14M两种砧木的Fo值呈现逐渐降低趋势，复水后第7天，1103P和101-14M 的Fo值为对照的102.95%和109.60%，复水后第14天，1103P和101-14M Fo为对照的101.56%和101.81%，说明复水后1103P和101-14M两种砧木受损的光合反应中心得到了修复，光合速率也逐渐恢复，1103P复水后恢复生长的能力高于101-14M。     

高温干旱跨代效应对小麦芽期耐旱性和耐盐性的影响

选用生长于新疆吐鲁番地区高温胁迫(HT)、石河子地区花后干旱胁迫(DT)以及正常灌溉(NW)环境下收获的‘SDWW-7’、‘津农6号’和‘金石农1号’小麦种子,分别用不同浓度的PEG-6000和NaCl溶液模拟干旱胁迫和盐胁迫,研究来自3种环境条件下收获种子的耐旱性和耐盐性。结果表明：(1)高温干旱胁迫导致父代小麦籽粒千粒重降低,下降幅度为23.55%～46.15%;高温干旱胁迫对‘SDWW-7’和‘金石农1号’的淀粉含量影响存在显著差异(P<0.05)。(2)子代小麦材料在遭受干旱胁迫时,经过高温锻炼后的‘SDWW-7’、‘津农6号’及经过干旱锻炼后的‘金石农1号’长势更好,其相对盐害率的均值仅为1.24%～2.72%。(3)子代小麦材料在遭受盐胁迫时,通过发芽势、发芽率、相对盐害率等筛选指标发现‘SDWW-7’、‘津农6号’、‘金石农1号’在经历高温锻炼后的子代表现最优;两种锻炼方式对子代小麦耐盐性的影响程度表现为‘SDWW-7’>‘津农6号’>‘金石农1号’。(4)子代小麦抗旱性综合评价表明在15%PEG-6000(D1)、20%PEG-6000(D2)干旱胁迫...     

3个新疆狗牙根品种对土壤干旱及复水的响应

通过分析土壤干旱及复水对3个新疆狗牙根品种生理生化指标(相对电导度、丙二醛、过氧化氢酶、过氧化物酶、超氧化物歧化酶、游离脯氨酸、可溶性蛋白、可溶性糖)的影响。结果表明:随着胁迫程度的加强,相对电导度均呈增大趋势。干旱胁迫60d时,均出现重度胁迫,其中喀什狗牙根叶片相对电导度的变化幅度最小(29.67%),细胞膜受伤害率也最小。过氧化产物丙二醛(MDA)缓慢上升,且与相对电导度呈正相关,喀什狗牙根叶片MDA含量变化幅度最小(7.91μmol/g),膜脂过氧化程度不严重;游离脯氨酸(Pro)含量增加,且随胁迫时间的延长,Pro含量增加幅度增大,新农2号狗牙根Pro积累量最大,其次为新农1号狗牙根、喀什狗牙根。可溶性糖含量有升有降,但变化幅度不大,说明狗牙根对可溶性糖的渗透调节作用的效果是短期的;蛋白质含量变化趋势不同,喀什狗牙根叶片蛋白质含量变化幅度最小,新农2号狗牙根叶片蛋白质含量变化幅度最大;SOD和CAT活性在干旱处理60d时达到最大值,POD活性在干旱处理30d时达到最大值。综合以上指标得出,喀什狗牙根抗旱性比新农1号狗牙根和新农2号狗牙根强。     

夏玉米苗期对不同时长干旱-复水的生理响应机制

为探究干旱-复水环境下夏玉米苗期的生理调节机制，采用桶栽的方式，设置3个水分处理：正常处理(CK) :75%~85%θ_f（田间持水量），轻度胁迫(W₁) :60%~70%θ_f，中度胁迫(W₂) :50%~60%θ_f；设置3个胁迫时长，7 d(T₁)、10 d(T₂)、13 d(T₃)；于胁迫与复水期间测定夏玉米苗期叶片的渗透调节物质、抗氧化酶及光合指标。结果表明：在轻度和中度胁迫下，脯氨酸(Pro)含量呈先增大后减小趋势，第3天达到峰值，相较于CK分别提高32.7%、44.1%；复水后，胁迫10 d处理的Pro累积量高于胁迫7 d的处理，而胁迫13 d无明显累积效应。超氧化物歧化酶(SOD)活性在胁迫期间呈先增大后减小趋势，第3天达到峰值，相较于CK分别提高22.0%、12.4%；复水后活性增强，且胁迫13 d处理的SOD活性高于胁迫10 d和胁迫7 d处理。过氧化物酶(POD)活性在轻度胁迫处理下呈先增大后减少趋势，在第3天达到峰值，相较于CK提高28.5%，而在中度胁迫处理下POD活性呈减小趋势，且低于CK；复水后酶活性均恢复至正常处理水平。丙二醛(MDA)含量在胁迫期间呈增高趋势，且胁迫时长越长，增幅越大，在胁迫13 d处理下，中度和轻度胁迫下的MDA含量相较于CK分别提高140%和281%；复水后胁迫缓解，所有处理组的MDA含量均恢复至正常处理水平。在轻度和中度胁迫下，夏玉米的净光合速率、气孔导度以及蒸腾速率分别为CK的92.5%和77.7%、93.9%和74.3%、87.9%和74.5%，光合作用受到限制；复水后，中度胁迫处理表现出光合补偿效应，光合指标值均高于其他处理。研究表明，持续10 d维持土壤50%~60%θ_f较利于夏玉米生长，其复水后出现显著的光合补偿效应。     

干旱胁迫下春小麦干物质积累和分配及其模拟

为探究干旱胁迫下春小麦干物质积累和分配规律,明确其干旱致灾和受灾阈值,建立定量的模拟模型,对半干旱区春小麦进行小区水分控制试验,设置充足灌水(CK)和持续干旱(GH)2组处理,分析干旱胁迫对干物质积累和分配的影响。结果表明:干旱胁迫13 d后,茎、叶、地上部干物质重开始明显减少,胁迫23 d后,穗干物质重开始明显减少,分别较CK组减少40.80%、22.03%、31.29%、32.90%,对应的干旱致灾阈值为土壤含水量减至10.40%[田间持水量(CF)的37.4%]和8.56%的(30.8%CF),受灾阈值为茎、叶、穗、地上部干物质积累百分率达到80.39%、92.75%、16.87%、47.18%。干旱胁迫不影响各器官分配指数的排序,但会改变排序的变化时间节点和持续时间。胁迫17 d后,各器官分配指数开始发生明显变化,茎平均相对减少12.50%,叶平均相对增加8.14%,穗平均相对增加15.04%,对应的干旱致灾阈值为土壤含水量减至9.54%(34.3%CF)。地上部干物重、叶的分配指数受光合速率的影响最大,茎、穗的分配指数受叶片含水率的影响最大。干旱胁迫促使穗的分配指数增加。建立的地上部干物重、叶和穗的分配指数最优模型可有效模拟干旱胁迫下春小麦的干物质积累和分配。该结果可为春小麦干旱致灾过程机理研究提供理论参考。     

干旱胁迫对藜叶片干旱诱导蛋白的影响

采用SDS-PA GE(十二烷基硫酸钠-聚丙烯酰胺)凝胶电泳法进行蛋白质的分离,研究干旱胁迫对藜叶片干旱诱导蛋白的影响.结果表明:干旱胁迫10 d,中度干旱藜的叶片110.3 KD和103.9 KD及24.8 KD,22.7KD,21.0 KD蛋白谱带明显加强,重度干旱胁迫下22.7 KD,21.0 KD蛋白谱带增强,但弱于中度干旱胁迫;干旱胁迫15 d,中度干旱胁迫下蛋白谱带与第10 d中度干旱胁迫下的蛋白谱带相比,26.4 KD和19.2 KD蛋白谱带增强.这说明干旱诱导了藜一些适应水分胁迫相关基因的表达,或使一些基因的表达量增强,导致一些新蛋白质的出现或某些蛋白质量的增加而增强其对干旱胁迫的抵抗能力.     

Identification of two serological flagellar types (H1 and H2) inPseudomonas syringae pathovars

Flagellar antigen specificity was studied for the speciesPseudomonas syringae, P. viridiflava andP. cichorii. After checking their motility, bacteria were reacted against six polyclonal antisera containing anti-O (LPS) and anti-H (flagellar) antibodies by indirect immunofluorescent staining. Two distinct flagellar serotypes (H1 and H2) were described. The distribution of H1 and H2 serotypes was then determined for a collection of 88 phytopathogenicPseudomonas strains. Serotype H1 was possessed byP. syringae pv.aptata (12 strains),P. s. pv.helianthi (2),P. s. pv.pisi (11), andP. s. pv.syringae (13). Serotype H2 was possessed byP. cichorii (2),P. s. pv.delphinii (1),P. s. pv.glycinea (4),P. s. pv.lacrymans (1),P. s. pv.mori (1),P. s. pv.morsprunorum (10),P. s. pv.persicae (1),P. s. pv.phaseolicola (8),P. s. pv.tabaci (10) andP. s. pv.tomato (1).P. viridiflava (5) revealed HI, H2 and untyped flagella. The following isolates were untypable by the H1/H2 system:P. corrugata (3),P. fluorescens (2),P. tolaasii (1). H1/H2 serotypes distribution is not linked toP. syringae O-serogroups. On the other hand, H1/H2 distribution seems remarkably linked to the new genospecies of theP. syringae group.Abbreviations CFBP French Collection of Phytopathogenic Bacteria, Angers, France - ICMP International Collection of Micro-organisms from Plants, Auckland, New-Zealand - NCPPB National Collection of Plant Pathogenic Bacteria, Harpenden, Great Britain     

Gel detection of Allium porrum polygalacturonase-inhibiting protein reveals a high number of isoforms

Polygalacturonase inhibiting proteins (PGIPs) are leucine-rich repeat glycoproteins, localized in the cell wall of most plant species, capable of countering the activity of endo-polygalacturonases (endo-PGs) produced by phytopathogenic fungi. The PGIP from Allium porrum leaves was analysed to ascertain the presence of different molecular forms of PGIP. Leek PGIP was separated into two fractions: a soluble and an ionically wall-bound PGIP, each of which was then purified by cation-exchange chromatography. Two and three peaks of PGIP activity were obtained, respectively. PGIP isoforms contained in each peak were separated by isoelectrofocusing (IEF) on a polyacrylamide gel. Following the separation, the gel was first overlaid with sodium polygalacturonate and then treated with the endo-PG from either Sclerotinia sclerotiorum, Fusarium moniliforme or Botrytis aclada. The endo-PG(s) hydrolyse the overlaid substrate except where active inhibitors are present. The presence of PGIPs is revealed by ruthenium red staining of the nonhydrolysed substrate. Each PGIP peak following IEF separation revealed several PGIP isoforms with pIs between 5.0 and 7.0. More than 20 isoforms were detected in total, with considerable differences in their inhibitory activity. While similar PGIP isoform patterns were obtained by developing the IEF gels with the endo-PGs of S. sclerotiorum and B. aclada, less intense PGIP bands were observed with the endo-PG from B. aclada, consistent with inhibition assays performed in solution. The endo-PG from F. moniliforme, which is not inhibited at all by leek PGIP in solution, consistently showed no PGIP band on the gel assay.     

Epidemiology of Fusarium Diseases and their Mycotoxins in Maize Ears

Fusarium species cause two distinct diseases on ears of maize, Fusarium ear rot (or pink ear rot) and Gibberella ear rot (or red ear rot), both of which can result in mycotoxin contamination of maize grain. The primary causal agent for Fusarium ear rot is Fusarium verticillioides, but F. subglutinans and F. proliferatum are also important. Gibberella ear rot is caused primarily by F. graminearum, but F. culmorum can also be important, especially in Europe. Aspects of the epidemiology of both diseases have been studied for decades, but only recently have efforts been made to synthesize this information into comprehensive models of disease development. Much of the work on F. graminearum has focused on Fusarium head blight of small-grain crops, but some of the results obtained are also relevant to maize. The primary mycotoxins produced by these fungi, fumonisins and deoxynivalenol, have differing roles in the disease-cycle, and these roles are not completely understood, especially in the case of fumonisins. Progress is being made toward accurate models for risk assessment of both diseases, but key challenges remain in terms of integrating models of pre- and post-infection events, quantifying the roles of insects in these diseases, and characterizing interactions among competing fungi and the environment.     

Benomyl-resistant Fusarium-isolates in ecological studies on the biological control of fusarium wilt in carnation

Ecological properties and stability of benomyl resistance of three benomyl-resistant mutants of nonpathogenicFusarium-isolates antagonistic to fusarium wilt in carnation, and three benomyl-resistant mutants of a pathogenic isolate ofFusarium oxysporum f.sp.dianthi were evaluatedin vitro and in glasshouse experiments. The benomyl resistance of the nonpathogenic mutants was stable under all conditions tested, also after a 1000-fold increase of the population in sterilized soil. Mutants of the pathogen were stable during allin vitro tests, but after proliferation in carnation stems only part of the population was benomyl resistant.Compared to the wild type, mutants of the pathogen were less pathogenic, also if thein vitro propeties were similar. Colonization of carnation by benomyl-resistant nonpathogenicFusarium in the presence of the pathogen showed that the antagonistic effect correlated with the presence of the nonpathogenic isolates within the carnation stem. The wild types and two of the mutant nonpathogenicFusarium-isolates controlled fusarium wilt in the susceptible cultivar Lena for 50% or more.UV-induced benomyl resistance appeared to be a valuable marker to distinguish between differentFusarium isolates and to study the population dynamics, but intensive screening of the mutants is a prerequisite since alterations in antagonism and pathogenicity can occur.     

DNA sequence analysis of ribosomal ITS region 1 of Phytophthora vignae f. sp. adzukicola, the pathogen that causes stem rot of adzuki bean

Sequences of the internal transcribed spacer (ITS) region 1 were used to examine the phylogenetic relationships among races of 19 isolates of Phytophthora vignae f. sp. adzukicola and between this forma specialis and three isolates of the closely related P. vignae f. sp. vignae. The ITS 1 sequences were highly conserved (> 98.7% similarity) among representatives of both formae speciales groups. The results of this study indicate that P. vignae is a monophyletic group. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under the accession nos. AB120062–AB120080 and AB120122     

Reliable detection of the fungal pathogenfusarium oxysporum f.sp.albedinis, causal agent of bayoud disease of date palm, using molecular techniques

Bayoud, caused by the soilborne fungusFusarium oxysporum f.sp.albedinis (FOA), is the most serious disease of date palm. Since the disease is located in the North African countries of Morocco and Algeria, and advancing steadily eastwards, the ultimate goal is to prevent spread of the pathogen to other date-growing areas in the region and farther afield. Molecular diagnostic techniques have been developed for detection of FOA. In view of the fact that the fungus does not exist in Israel, DNA of FOA was obtained to determine the reliability of these methods for diagnostic purposes. Random amplified polymorphic DNA was not reliable enough for differentiation between FOA and various pathogenic and saprophyticFusarium isolates. However, the polymerase chain reaction utilizing FOA-specific primers was accurate and enabled amplification of a unique band specific to FOA DNA alone, and not that of the other tested pathogenic and saprophyticFusaria. The availability of a rapid and reliable diagnostic tool for detection of FOA will enable the Plant Protection and Inspection Services of the Israel Ministry of Agriculture to test date palm tissue for the presence of the pathogen. Contribution no. 513/00 from the Inst. of Plant Protection, ARO, The Volcani Center, Bet Dagan, Israel.     

Components of Partial Resistance to Powdery Mildew in Wheat Mutants

Components of resistance to powdery mildew (latent period, pustule density and conidium production) were analysed on glasshouse-grown artificially inoculated plants of wheat mutants (n = 11) derived from either induced mutagenesis or adventitious regeneration of cv. Guardian. These mutants had previously been shown to be partially resistant to the disease in the field over a two-year period. Analyses were carried out at three stages of development: seedling, tillering and heading. None of the mutants exhibited a latent period significantly different from that of the susceptible parent Guardian at any stage of development tested. With respect to pustule density, one mutant (M61) was significantly more resistant than Guardian at all stages of development, two mutants (M19 and SC100) were more resistant at tillering and heading, and two (M156 and SC267) were more resistant only at heading. Significantly reduced conidium production per pustule (as a measure of pustule size) over a 24h period was observed on three mutants (M61, SC100 and SC231) at tillering and heading, while mutant SC68 exhibited this trait at heading only. On the basis of resistance components and relative grain yield in the presence of mildew, the eleven mutants were categorised into five categories. Tests for associations between field resistance score and components of resistance measured in the glasshouse, both measured at heading, revealed a significant positive correlation only between pustule density and field score. To assess the effects of combining different components (i.e. pyramiding different partial resistance genes), mutants were crossed. Transgressive segregation for at least one component was observed in the F₂ generation in crosses between mutants with complementary modes of action (i.e. involving different components of partial resistance), but not in cases where the parents exhibited the same component of resistance.     

Relationship between the incidence of latent infections caused by <Emphasis Type="Italic">Monilinia</Emphasis> spp<Emphasis Type="Italic">.</Emphasis> and the incidence of brown rot of peach fruit: factors affecting latent infection

Five field experiments were performed in commercial orchards located in Lleida (Spain) over three growing seasons, 2000–2002, in order to estimate the relationship between the incidence of latent infection caused by Monilinia spp. in peaches and the incidence of post-harvest brown rot. No latent infection was recorded at popcorn and the maximum incidence occurred pre-harvest; in some orchards a second peak was detected during the pit hardening period. Monilinia laxa is the most prevalent species isolated from peaches with brown rot. There was a positive correlation between the incidence of latent infection and that of post-harvest brown rot. The average incidence of latent infection during the crop season explained 55% of the total variation in the incidence of post-harvest brown rot. The effect of temperature (T) and duration of wetness (W) on the incidence of latent infection in peach and nectarine orchards was analysed using multiple regression. The regression analysis indicated that T and W jointly explained 83% of the total variation in the incidence of latent infection. The model predicts no latent infections when T < 8°C, and >22 h wetness are required when T = 8°C but only 5 h at 25°C are necessary for latent infection to occur. The incidence of brown rot and latent infection of peaches caused by M. laxa under controlled experimental conditions were also affected by T and W, as well as by fruit maturity and inoculum concentration. Latent infections were produced in fruit when T was not suitable for the development of brown rot symptoms. In these experiments more than 4–5 h of daily wetness were required after embryo growth in fruit sprayed to run-off with an inoculum concentration higher than 10⁴ conidia ml⁻¹ of M. laxa for brown rot and latent infections to develop. The fitted model obtained from the field data was able to predict the observed data obtained under controlled environmental conditions.     

Genetic variation among <Emphasis Type="Italic">Fusarium</Emphasis> isolates from onion,and resistance to <Emphasis Type="Italic">Fusarium</Emphasis> basal rot in related <Emphasis Type="Italic">Allium</Emphasis> species

The aim of this research was to study levels of resistance to Fusarium basal rot in onion cultivars and related Allium species, by using genetically different Fusarium isolates. In order to select genetically different isolates for disease testing, a collection of 61 Fusarium isolates, 43 of them from onion (Allium cepa), was analysed using amplified fragment length polymorphism (AFLP) markers. Onion isolates were collected in The Netherlands (15 isolates) and Uruguay (9 isolates), and received from other countries and fungal collections (19 isolates). From these isolates, 29 were identified as F. oxysporum, 10 as F. proliferatum, whereas the remaining four isolates belonged to F. avenaceum and F. culmorum. The taxonomic status of the species was confirmed by morphological examination, by DNA sequencing of the elongation factor 1-α gene, and by the use of species-specific primers for Fusarium oxysporum, F. proliferatum, and F. culmorum. Within F. oxysporum, isolates clustered in two clades suggesting different origins of F. oxysporum forms pathogenic to onion. These clades were present in each sampled region. Onion and six related Allium species were screened for resistance to Fusarium basal rot using one F. oxysporum isolate from each clade, and one F. proliferatum isolate. High levels of resistance to each isolate were found in Allium fistulosum and A. schoenoprasum accessions, whereas A. pskemense, A. roylei and A. galanthum showed intermediate levels of resistance. Among five A. cepa cultivars, ‘Rossa Savonese’ was also intermediately resistant. Regarding the current feasibility for introgression, A. fistulosum, A. roylei and A. galanthum were identified as potential sources for the transfer of resistance to Fusarium into onion.     

Germination and appressorium formation of wheat leaf rust on susceptible,partially resistant and resistant wheat seedlings and on seedlings of other Gramineae

Germination and appressorium formation of wheat leaf rust urediospores were studied in two experiments. No consistent differences could be detected between 11 genotypes of wheat (Triticum aestivum), two of barley, one ofTriticum dicoccum, one ofT. dicoccoides, one ofT. boeoticum and one ofAegilops squarrosa. Host genotypes and non-hosts gave similar results, suggesting that the phases before penetration of the host leaf are not affected by the resistance mechanisms operating in hosts and non-host genotypes.Samenvatting Kieming en de vorming van appressoria is bestudeerd in twee experimenten. Er zijn geen systematische verschillen waargenomen tussen 11 genotypen van tarwe, twee van gerst, een vanTriticum dicoccum, een vanT. dicoccoides, een vanT. boeoticum en een vanAegilops squarrosa. Waard en niet-waard genotypen gaven overeenkomstige resultaten, dit suggereert dat de fasen voor penetratie van het gastheerblad niet beïnvloed worden door de resistentiemechanismen werkzaam in waard en niet-waard.