覆盖方式对旱地小麦花后旗叶抗氧化生理及粒重形成的影响

于2017—2018年和2018—2019年,在西北中部旱作雨养农业区以冬小麦‘康庄974’为试验材料,设秸秆带状覆盖(SM)、地膜覆盖(PM)和无覆盖对照(CK)共3个栽培处理,分析不同覆盖方式对小麦灌浆期土壤水分和温度及抗氧化能力的影响,探讨花后干物质积累量和粒重形成的关系。结果表明,随生育期推进,花后旗叶相对含水量(RWC)逐渐降低,丙二醛(MDA)含量逐渐升高,且PM较SM降、升幅度明显。与CK相比,覆盖显著提高花后旗叶抗氧化酶活性,增加渗透调节物质含量;开花时间越长,SM抗氧化酶活性升高的幅度越大,而PM主要提高花后7 d旗叶抗氧化能力。SM和PM的粒重分别较CK增加14.3%和19.1%(P<0.05)。相关分析表明,土壤水分(SW)是影响旗叶生理活性的关键因子,提高SW,有利于增加RWC(r=0.84^**),从而提高旗叶抗氧化能力,其中RWC和抗坏血酸酶(ASA)活性呈极显著正相关关系(r=0.82^**);ASA活性和脯氨酸(Pro)含量呈极显著正相关关系(r=0.94^**),和MDA含量呈极显著负相...     

6种牧草苗期耐旱性综合评价

为筛选苗期抗旱性较强的牧草,用于干旱半干旱地区的人工草地建植。采用盆栽法对6种牧草进行模拟干旱试验,测定其株高（PH）、地上干重（SDW）、地下干重（RDW）、根冠比（RSR）、叶片相对含水量（RWC）、脯氨酸含量（Pro）、可溶性蛋白含量（SP）、抗氧化酶活性等指标,计算单项指标抗旱系数,运用相关分析、主成分分析、隶属函数法等方法对6种牧草进行抗旱性综合评价。结果表明：干旱胁迫对6种供试材料的生长和生理指标均有显著影响。相关分析表明,PH、GR、RDW等12项指标之间呈正相关关系,但这12项指标均与丙二醛（MDA）含量呈负相关关系。主成分分析表明,4个主成分贡献率可达98.40%,可代表6种供试材料绝大部分数据信息。结合隶属函数法及权重,计算出6种供试材料的抗旱性综合评价值（D值）,得到供试材料的抗旱性能力顺序为：长穗偃麦草>披碱草>沙打旺>无芒雀麦>紫花苜蓿>扁穗冰草。D值与PH(0.984^**)、RDW(0.948^**)、Pro(0.971^**)和SP(0.959^**     

白菜型冬油菜抗倒伏性评价及其与株型性状的相关分析

于2018—2019年以44份不同抗倒性的白菜型冬油品系(种)为试材,依据改良倒伏系数(ILC)法对其抗倒伏性进行聚类分析和评价,探讨白菜型冬油菜株型、茎秆力学特性、干物质积累量等对其倒伏性的影响。结果表明:依据ILC可将白菜型冬油菜参试材料聚为3类:Ⅰ类为强抗倒性材料,包含2个品系(种);Ⅱ类为中等抗倒性材料,包含15个品系(种);Ⅲ类材料抗倒性最弱,包含27个品系(种)。聚类结果与田间倒伏分级结果基本吻合,两者呈极显著正相关(r=0.452~(**)),表明利用ILC评价白菜型冬油菜的抗倒伏性具有可靠性。与Ⅱ类、Ⅲ类材料相比,抗倒性强的Ⅰ类材料株高显著变矮,重心高度显著降低,其平均株高和重心高度比倒伏Ⅲ类材料分别降低19.8 cm和17.8 cm。白菜型冬油菜茎秆抗折力在三类材料间均存在显著差异,抗倒伏Ⅰ类参试材料平均茎秆抗折力是Ⅲ类材料的2.59倍。白菜型冬油菜倒伏系数与株高(r=0.346~*)、地上部鲜质量(r=0.344~*)、重心高度(r=0.579~*)呈显著正相关,与茎秆抗折力(r=-0.518~*)呈显著负相关。与Ⅱ类、Ⅲ类材料相比,Ⅰ类参试材料根长增长38%～41%,根鲜质量增大71%～102%,分枝部位降低32%～44%,一次分枝数增加10%左右、单株角果数增加30%～38%、角果长度增长1%左右、每角粒数增加11%～14%,千粒重增加21%～23%。白菜型冬油菜参试材料抗倒伏性存在显著差异,植株高度、重心高度、地上部鲜质量、茎秆抗折力等是影响其抗倒伏性的关键因素,株高较小、重心高度较低、茎秆抗折力大的白菜型冬油菜品种更高产抗倒伏。     

灌溉条件下燕麦不同品种的产量差异及与农艺性状的关系

燕麦是传统旱地作物,产量低而不稳,在灌溉条件下会出现倒伏等问题。为了探讨灌溉条件下高产燕麦品种对农艺性状的特殊要求,对12个燕麦品种进行了产量差异及与主要农艺性状的相关性和通径分析。结果表明,各品种的产量及基本苗、成穗数、穗粒数、千粒重、主穗长、旗叶长等农艺性状均存在显著差异,生育期、株高差异不显著,产量在3 706.20～5 106.30 kg·hm~(-2)之间,变异系数CV=10.07%,燕麦品种MF9521-281产量最高;相关性分析显示,产量与成穗数(r=0.9557)、基本苗(r=0.6761)、千粒重(r=0.5186)、株高(r=0.2634)、生育期(r=0.0964)呈正相关,与穗粒数(r=-0.4452)、主穗长(r=-0.5977)、旗叶长(r=-0.9376)呈负相关;各性状对产量的直接通径系数大小顺序为:成穗数千粒重穗粒数生育期旗叶长基本苗株高主穗长。综合分析表明,灌溉条件下燕麦获得高产的理想模型是:较高的成穗数(508.05～552.75×10~4·hm~(-2)),适宜的基本苗(420.00～422.55×10~4·hm~(-2))、千粒重(22.27～25.25 g)、株高(113.85～118.80 cm)、生育期(85 d),较小的穗粒数(46.75～50.18粒)、主穗长(18.90～19.95 cm)、旗叶长(16.50～17.60 cm)。     

解淀粉芽胞杆菌PHODG36菌剂的研制及其对马铃薯黄萎病的防病增产效果

解淀粉芽胞杆菌Bacillus amyloliquefaciens PHODG36是一株具有抑菌和促生作用的多功能菌株。本研究以菌株PHODG36原粉为有效成分、滑石粉为填料研制了不同芽胞浓度的微生物菌剂，通过盆栽试验研究了菌剂拌种处理马铃薯种薯后对其出苗的影响，在冀北和冀南地区开展田间小区试验研究了该菌剂对马铃薯黄萎病的防治效果及对马铃薯产量的影响。结果表明，制备的PHODG36菌剂外观为浅黄色粉末，无团块。该菌剂平均粒径D₅₀为（38.25±0.46）μm，pH为（6.65±0.15），贮藏后未出现结块和发粘现象，浓度介于1.5×10⁹～2.0×10¹⁰ CFU/g。与空白对照和化学药剂相比，不同浓度菌剂拌种处理后校正出苗率之间差异不显著，而菌剂随着浓度的增加，校正出苗率呈下降趋势。不同地区的田间试验表明，PHODG36菌剂在1.5×10⁹～1.0×10¹⁰ CFU/g对感病品种黄萎病的病情指数防效为43.08%～58.46%，增产率为8.29%～30.37%；对抗病品种主要表现为增产作用，增产率介于1.85%～9.0%。综合分析表明，菌剂使用浓度为1.5×10⁹～1.0×10¹⁰ CFU/g能够有效降低黄萎病的发生，节约投入成本，且增产作用明显。研究结果为黄萎病的防控提供绿色产品，并为该菌剂进一步的大面积推广示范应用奠定了基础。     

西伯利亚落叶松树轮稳定碳同位素对气候的响应

利用采自阿尔泰山南坡东段正格采点的西伯利亚落叶松树轮样本,建立树轮宽度年表,对比宽度年表,按照树轮稳定碳同位素研究步骤,提取树轮稳定碳同位素序列（δ¹³C）和去趋势序列（DS）。分析表明：阿尔泰山南坡东部近160 a西伯利亚落叶松树轮δ¹³C变化于-22.8‰～-25.4‰,平均值为-24.0‰,变差系数-0.017。相关分析表明：正格采点树轮宽度序列对各气候要素相关不显著;树轮去趋势序列（DS）对前期气候因子的响应也不敏感;在生长季内（5~9月）,树轮去趋势序列（DS）与富蕴气象站平均气温、平均最高气温和平均相对湿度有较好的相关性,树木生长季内的平均气温、平均最高气温与树轮去趋势序列（DS）显著正相关,6~7月平均最高气温与去趋势序列（DS）相关达到0.611（P<0.000 001);与生长季内平均相对湿度呈负相关关系,其中6~7月相对湿度与去趋势序列（DS）相关最高(r=-0.493, P<0.001),与7月降水量呈负相关关系(r=-0.459, P<0.01)。生长季内的平均最高气温和相对湿度对阿尔泰山西伯利亚落叶松树轮δ¹³C的响应最为敏感,阿尔泰山西伯利亚落叶松树木碳同位素分馏的主要控制因子为6~7月的平均最高气温,降水对树轮稳定碳同位素影响不大,相对湿度对树轮稳定碳同位素没有直接影响。     

土地利用变化对土壤水补给来源影响研究

为探究不同植被类型深剖面土壤水补给来源,以黄土区长武塬为研究区,采集两种土地利用方式(农地、18 a苹果园、26 a苹果园)下20 m深土壤剖面,测定土壤水及其稳定性和放射性同位素含量,基于同位素方法对不同土地利用类型下不同深度土壤水来源进行溯源分析。研究表明：(1)苹果园土壤水含量明显低于农地,说明果园耗水强度更大,对深层土壤水影响更为显著。(2)农地、18 a和26 a苹果园下降水偏移量分别为-22‰、-20‰和-6‰,说明降水补给土壤水后受到蒸发作用影响,且农地土壤水比果园受到的蒸发效应更强。(3)该区土壤水补给主要以活塞流为主;对于补给不同深度土壤的可能水源,6 m以下补给水的同位素组成(δ²H=-83.8‰,δ¹⁸O=-12.1‰)较0～6 m (δ²H=-68.8‰,δ¹⁸O=-10.1‰)更为贫化,且6 m以下补给水的氢氧稳定同位素组成与日降水量≥50 mm·d^-1的降水更相似。与农地(δ²H=-70.6‰,δ¹⁸O=-...     

有机-无机复合肥在水稻上应用研究

本文应用不同品种有机-无机复合肥在同一水稻品种上施用不同量的产量和收益表现,为发展通城县粮食生产提供理论及实践依据。结果表明：在生产上,施用30%宜施壮有机-无机复合肥和施用30%祥云有机-无机复合肥80 kg/667m²,产量可达到700 kg/667m²以上,比习惯施肥产量要高,且差异达显著水平;而施用30%祥云有机-无机复合肥40 kg/667m²、60 kg/667m²的平均产量和施用30%宜施壮有机-无机复合肥20 kg/667m²、40 kg/667m²、60 kg/667m²的平均产量与习惯施肥(施用40%中化复合肥60 kg/667m²)的平均产量差异并不显著,但在施肥各处理中,以施用30%宜施壮有机-无机复合肥20 kg/667m²净收益最好,达到956.8元/667m²,因此从稳产减肥增效考虑,建议生产上大量推广30%宜施壮有机-无机复合肥20 kg...     

褐藻胶-富里酸改性石膏对玉米根系形态及植株生长的影响

为探究褐藻胶-富里酸改性石膏(AFG)对玉米(Zea mays L.)根系形态和植株生长的调控作用,评估AFG在玉米生产上的应用价值,于2022年设置6个AFG施用量：0(T0)、20(T20)、40(T40)、60(T60)、80(T80)、100 kg·hm^-2(T100),分析施用AFG对玉米根系形态性状和产量的影响。结果表明：施用AFG处理较不施用处理显著提高了土壤有效硫含量;施用AFG对根系形态性状具有明显调控作用,与T0相比,根总长度、根表面积、根平均直径、根尖数、根体积和根干质量的提高幅度分别为7.6%～18.2%、14.0%～31.2%、5.1%～11.0%、11.6%～17.9%、20.9%～45.7%和7.8%～18.7%。与其他处理相比,T40处理的根系形态性状最优,进一步提高AFG施用量则调控效果有降低趋势。施用AFG处理的玉米单株籽粒产量较不施用处理增加2.6%～8.9%,并以T40处理的单株籽粒产量最高。根尖数、根表面积、根系体积、根总长度、根冠比、根干质量和根平均直径与单株籽粒产量呈显著相关,对单株籽粒产量影响最强的根系性状为根干质量...     

水分胁迫对不同品种春小麦的水分利用率及生理指标的影响

通过生育期充足供水(T1)、孕穗期胁迫(T2)和抽穗期胁迫(T3)3种处理,研究了旱地类型(DE)、中间类型(IE)、水地类型(WE)春小麦不同品种水分利用效率(WUE)和生态生理指标的差异.结果表明:水分胁迫明显降低籽粒产量、WUE、光合速率(Pn)、气孔导度(Cd)和蒸腾速率(Tr).T2处理下3种类型的相对产量是DE(70.76%)＞IE(69.59%)＞WE(59.88%),而T3处理3种类型接近(81.00%～88.21%).相对于DE,IE,WE在各处理中均具有较高产量.各处理下,籽粒产量与WUE正相关极显著(r=0.860**～0.965**),与Pn,Cd 和Tr 负相关显著或极显著(r=-0.612*～-0.830**).复水后WE表现出较强的补偿效应.     

Epidemiology and simulation of population development of Sitobion avenae in winter wheat

The epidemiology ofSitobion avenae and its natural enemies in winter wheat was studied in 1975, 1976 and 1977. Immigration was important until the end of flowering. The alate immigrants had apterous offspring. These became the driving force in population growth. Their offspring were mostly alatae which usually left the field. A model of the epidemic was developed. Quantitative relations between the aphids and their environment were obtained from literature or established in laboratory trials. The model simulated population development and population composition from the beginning of June till the population peak at the end of June or early in July. Because quantitative data on relations between aphids and their natural enemies and pathogens are scarce, and since the knowledge on wing formation is still limited, the population collapse could not be predicted. In the future, prognosis over a period of three weeks seems possible.Samenvatting De toenemende betekenis van graanbladluizen (vooralSitobion avenae) gepaard gaande met een sterke toename van het gebruik van insecticiden op granen maakte verbetering van de prognose over het schadelijk optreden wenselijk. Door gedetailleerde tellingen in het veld (Fig. 1–7) werden gegevens verkregen over het verloop van de epidemie en het optreden van natuurlijke vijanden in 1975, 1976 en 1977.Een immigratieperiode tot in de bloei kon worden vastgesteld. Daarna lijkt de aantrekkelijkheid van het gewas voor alate luizen te verminderen. De alate immigranten krijgen aptere nakomelingen. Deze vormen de stuwende kracht van de populatiegroei. De nakomelingen van apteren zijn merendeels alaat. Zij verlaten het gewas.Een model van de populatieontwikkeling gedurende de epidemie werd opgesteld. De relatiediagrammen Fig. 9 en 10 laten groei en ontwikkeling vanS. avenae en een predator (Syrphus corollae) zien. Kwantificering van de betrekkingen werd mogelijk door literatuurgegevens en laboratoriumexperimenten.Met het model kon de populatieontwikkeling vanS. avenae vanaf begin juni tot aan de populatiepiek in 1975, 1976 en 1977 vrij goed worden gesimuleerd (Fig. 12). Ook de populatieopbouw kon worden gesimuleerd (Fig. 14). De teruggang van de populatiedichtheid blijkt moeilijker te voorspellen door het ontbreken van gegevens over natuurlijke vijanden.Het lijkt waarschijnlijk dat in de toekomst met het model een prognose over de piek van de bladluispopulatie circa 3 weken tevoren mogelijk zal zijn.     

Tumours of Begonia and some other ornamentals,induced by Corynebacterium fascians

In 1975 many tumours were observed in plants ofBegonia Schwabenland grown in Aalsmeer. Submersion of the roots ofNicotiana megalosiphon seedlings in a homogenate of tumorous tissue, induced tumours after two weeks. Short periods of submergence yielded results similar to those obtained after longer periods. Tumour homogenates lost their infectivity after ten min at 50°C. Aphids transmitted the infectious agent.Treatment with propylene oxide did not inhibit infectivity completely. Filtration through a 450 nm filter removed the infectious agent.Tobacco tumor virus or a viroid could not be isolated. Cultures ofCorynebacterium fascians, isolated from tumours ofN. megalosiphon were highly infectious and induced tumours in healthyN. megalosiphon andBegonia. Tumorous tissue homogenates ofPelargonium zonale, Dahlia sp.,Gladiolus sp., andLilium sp. also caused tumours inN. megalosiphon, from whichC. fascians was isolated. It was not possible to produce tumours inN. megalosiphon with homogenates from roses with symptoms of bud proliferation.Samenvatting In 1975 werden vele tumoren waargenomen inBegonia Schwabenland op Aalsmeerse bedrijven (Fig. 1). De infectiositeit van tumorweefsel kon goed en snel worden vastgesteld door de wortels van zaailingen vanNicotiana megalosiphon in een homogenaat van tumorweefsel te dompelen. Tumoren ontstonden na twee weken, de eindbeoordeling geschiedde na een maand (Fig. 2). Ook verschillende andereNicotiana spp.,Melilotus officinalis (Fig. 3) enPisum odoratum (Fig. 4) werden aangetast.Bij de infectiositeitstoets gaven zeer korte dompeltijden even goede resultaten als langere (Tabel 1). Infectieus sap verloor zijn infectievermogen na 10 min verhitting bij 50°C. Bladluizen brachten de smetstof over. Propyleenoxide verminderde de infectiositeit wel, doch onderdrukte deze niet totaal. Bij filtratie door een 450 nm filter bleef het infectieuse agens op het filter achter. Het tumor-inducerende agens was ook aanwezig in die delen van planten met tumoren welke gezond leken en het ging voor een gering deel over met zaad (Tabel 2).Uit tumoren konden wij geen tabakstumorvirus of een viroïde isoleren. Culturen vanCorynebacterium fascians, geïsoleerd uit tumoren vanN. megalosiphon bleken zeer infectieus en veroorzaakten tumoren inN. megalosiphon enBegonia. Homogenaten van tumorweefsel vanPelargonium zonale, dahlia (Fig. 5), gladiool (Fig. 6) enLilium Mid Century Hybrid Enchantment (Fig. 7) veroorzaakten ook tumoren opN. megalosiphon, waaruitC. fascians werd geïsoleerd. Met sap van kroeskopzieke rozen konden wijN. megalosiphon niet besmetten.     

Survey of Bacterial and Fungal Seedborne Diseases in Imported and Domestic Potato Seed Tubers

Potato seed tubers are imported to Israel from northern Europe and planted in spring; tubers harvested early from the spring crop are used as seed for the autumn crop. Although only seed lots registered as certified are imported, a previous survey (1984–1994) indicated that most imported lots were affected by latent or active infections caused byErwinia carotovora,Streptomyces scabies, Rhizoctonia solani, Fusarium spp. andSpongospora subterranae. The survey was extended until 1998, and included additional pathogens:Ralstonia solanacearum,Helminthosporium solani, Colletotrichum coccodes andVerticillium dahliae. Most of these pathogens were also monitored in domestic seed tubers, and are reported for the first time. Brown rot was not observed in any of the imported lots. Blackleg and soft rot caused byErwinia spp. were detected in most of the imported lots; however, less than 7% of the lots were contaminated at high levels, while approximately 65% were contaminated at moderate levels. Common scab was detected in most of the imported lots; 51% of the imported lots were contaminated at moderate or high levels, whereas only 6.5% of the domestic seed lots were contaminated at these levels. Black scurf was detected in most of the imported lots; on average, 47.3%, 44.2% and 1.4% of the lots were contaminated at low, moderate and high levels, respectively, and only 7.1% were disease-free. In contrast, most of the domestic lots were either disease-free (45.4%) or had a low disease incidence (37.3%). Only 16.7% of the lots were moderately infected and 0.2% were highly contaminated. Silver scurf was observed in most of the imported lots during all years of the survey, with no differences among the producing countries; on average, 22.7%, 66.1% and 7.5% of the lots were contaminated at low, moderate and high levels, respectively, and only 3.7% were disease-free. Most of the domestic lots (76%) were disease-free and only 6.6% were infected at moderate or high levels. Black dot was observed in a considerable portion of the shipments from Holland during all years of the survey, particularly in 1998, when 34% of the lots were infected. The shipments from France and Germany were infected at low levels, except in 1998, when 19% and 11% of the lots, respectively, arrived infected. In shipments from Scotland and Ireland low incidences of the disease were observed in 1994 and 1995. In the domestic lots, black dot incidence was low (<2.4%) except in 1996, when 11% of the lots were infected.V. dahliae was monitored only in domestic seed tubers. The incidence of disease-free lots was 56–64%, whereas in 20–30% of the lots the level of infection was <5%, and in 6–16% of the lots the level was >5%. The survey findings demonstrate transmission of seedborne pathogens; most of these pathogens can become established in the soil and eventually cause severe outbreaks of disease in potatoes grown in Israel. http://www.phytoparasitica.org posting May 16, 1999.     

Identification and pathogenicity of Pythium species causing damping-off of kidney bean

Five Pythium species (Pythium irregulare, P. mamillatum, P. myriotylum, P. spinosum and P. ultimum var. ultimum) were isolated from the hypocotyls and roots of kidney bean plants with damping-off from a commercial field and from experimental plots that have undergone either continuous cropping with kidney bean or rotational cropping with arable crops. In inoculation tests, all five Pythium species were pathogenic to kidney bean. This is the first report of damping-off of kidney bean caused by Pythium species; we named this disease damping-off of kidney bean. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under accession numbers AB291811, AB291944 and AB291945.     

Spatial pattern of Cercospora leaf spot of sugar beet in fields in long- and recently-established areas

Spatial disease pattern of Cercospora beticola was characterised during natural epidemics of Cercospora leaf spot (CLS) in sugar beet. We applied linear regression and geostatistical analyses to characterise CLS spatial patterns in three field trials, in long-established and recently-established CLS-areas, during two consecutive years. Linear regression showed a positive influence of average disease severity of within-row neighbouring plants (0.38 < < 0.88). Semi-variograms modelled the spatial dependence of disease severity for two directions per week in both years. Disease severity displayed strong spatial dependence over time. The within-row spatial dependence was the largest, but across-row dependence was irregular and weaker. Both long- and recently established areas showed strong spatial dependence of disease severity within row, decrease in variability between years and within the second trial year and a relation between and the relative nugget. Observed differences were more field than area specific. These spatial and temporal analyses indicated that disease severities of adjacent plants were dependent; hence, we concluded that C. beticola is dispersed mainly over short distances from plant to plant.     

Bacterial induction of the accumulation of phaseollin,pisatin and rishitin and their antibacterial activity

Bean hypocotyls, pea pods and tomato fruits were tested for phaseollin, pisatin and rishitin production when challenged with the phytopathogenic bacteriaErwinia carotovora, Pseudomonas phaseolicola, P. pisi andP. solanacearum, and their isolated extracellular polysaccharides. All bacteria induced phytoalexin accumulation, whereas only phaseollin and pisatin, but not rishitin, were elicited by EPS. The inhibitory effect of these three phytoalexins on bacterial growth was studied in liquid medium; whereas phaseollin and pisatin strongly inhibited growth, only a slight inhibitory effect resulted from the presence of rishitin in the medium.Samenvatting Bonehypocotylen, erwtepeulen en tomatevruchten werden onderzocht op hun vermogen tot vorming van respectievelijk faseolline, pisatine en rishitine, na inoculatie met de fytopathogene bacteriënErwinia carotovora, Pseudomonas phaseolicola, P. pisi enP. solanacearum en na behandeling met oplossingen van hun extracellulaire polysacchariden (EPS). Alle bacteriesoorten induceerden fytoalexinevorming, terwijl hun EPS wel faseolline- en pisatine-, maar geen rishitinevorming induceerden. Faseolline en pisatine remden de groei van de bacteriën in vloeibaar medium sterk; rishitine daarentegen had slechts een geringe groeiremming tengevolge.     

Identification and Characterisation of Bacteria Causing Soft-rot in Agave tequilana

Agave tequilana is the raw material for the production of the alcoholic beverage tequila. A bacterial disease has affected the A. tequilana crop in recent years. Previous reports based on colony and cell morphology, Gram stain and potato rot indicated that Erwinia sp. is the main pathogen. We isolated a several bacterial isolates capable of producing soft-rot symptoms in greenhouse pathogenicity assays. An extensive characterisation involving pathogenicity tests, fatty acid profile, metabolic and physiological properties, ribosomal DNA sequence and intergenic transcribed spacer amplification (ITS-PCR) and restriction banding pattern (ITS-RFLP) was made of each isolate. Three different species: Erwinia cacticida, Pantoea agglomerans and Pseudomonas sp. were identified. Fatty acid and metabolic profiles gave low similarity values of identification but 16S rDNA sequence, ITS-PCR and ITS-RFLP confirmed the identification of E. cacticida. In the phylogenetic tree, E. cacticida from blue agave was grouped neither with E. cacticida type strains nor with Erwinia carotovora. This is the first report that associates E. cacticida with A. tequilana soft-rot symptoms.     

Effects of the saprophytic leaf mycoflora on growth and productivity of winter wheat

The effects of the saprophytic mycoflora and its interference with cereal aphids on growth and yield of winter and spring wheat was studied in field experiments in 1980, 1981 and 1982.Yields varied between 5000 and 8000 kg dry matter of kernels per ha. The effect of the saprophytic mycoflora on yield was determined in different treatments: A) no control measures against cereal aphids and saprophytic and necrotrophic fungi, B) no control of cereal aphids, control of saprophytic and necrotrophic fungi, C) control of cereal aphids and control of saprophytic and necrotrophic fungi, D) control of cereal aphids and stimulation of saprophytic mycoflora and E) control of cereal aphids, no control of saprophytic and necrotrophic fungi nor stimulation of saprophytic mycoflora.Considerable differences in top densities of saprophytic mycoflora (10 times as large in A and D as in B and C) were determined. The consequences of these differences for the growth and productivity of wheat were minor. A negative effect of saprophytic mycoflora on the yield could not be detected in 1981 and 1982, whereas a small positive significant effect was found in 1980. This stimulation may have been due to competition between necrotrophic fungal pathogens and saprophytic mycoflora. As a result of favourable weather conditions necrotrophic fungal pathogens were very numerous in 1980 and could form an important yield reducing factor. Yield levels may effect the importance of the necrotrophic and saprophytic mycoflora as yield reducing factors. Additionally, in the presence of aphid honeydew captafol was found to be relatively ineffective against saprophytic fungi.     

Evaluation of Natural Chemical Compounds Against Root-lesion and Root-knot Nematodes and Side-effects on the Infectivity of Arbuscular Mycorrhizal Fungi

The survival of two species of plant parasitic nematodes: the root-lesion nematode Pratylenchus brachyurus, and the root-knot nematode Meloidogyne javanica, was evaluated in saturated atmospheres of 12 natural chemical compounds. The infectivity of two isolates of arbuscular mycorrhizal fungi: Glomus mosseae and Glomus intraradices, under identical experimental conditions, was also determined. All the compounds tested exerted a highly significant control against M. javanica and among them, benzaldehyde, salicilaldehyde, borneol, p-anisaldehyde and cinnamaldehyde caused a mortality rate above 50% over P. brachyurus. The infectivity of G. intraradices was inhibited by cinnamaldehyde, salicilaldehyde, thymol, carvacrol, p-anisaldehyde, and benzaldehyde, while only cinnamaldehyde and thymol significantly inhibited mycorrhizal colonization by G. mosseae.     

Biocontrol agents in combination with Moringa oleifera extract for integrated control of Sclerotium-caused cowpea damping-off and stem rot

Damping-off and stem rot disease-causing Sclerotium rolfsii has been reported as a destructive soil-borne pathogen of numerous crops, especially in the tropics and subtropics. Trials were conducted to test the efficacy of biocontrol agents alone or combined with Moringa oleifera leaf extracts for the control of the disease. In the laboratory, PDA was amended with Moringa leaf extract, and mycelial growth of S. rolfsii was measured. In the greenhouse and field, Trichoderma Kd 63, Trichoderma IITA 508 and Bacillus subtilis were evaluated as seed treatments, soil drench or sprinkle, separately or combined with Moringa leaf extracts. Percentage disease incidence, severity and control were recorded. In the laboratory, the higher the extract concentration the less the mycelial growth and no mycelial growth occurred on extract at 15 or 20 g leaves 10 ml⁻¹ water. In the greenhouse, the highest disease control was observed at a Moringa extract concentration of 15 kg leaves 10 l⁻¹ water (w/v). Seed treatments using Trichoderma Kd 63, and soil sprinkle using Trichoderma IITA 508 had a significantly (P = 0.05) higher effect on a disease incidence than Bacillus. Disease severity followed the same pattern. Moringa seed treatment combined with Trichoderma soil sprinkle resulted in significantly more than 94% and 70% disease control in the greenhouse and field, respectively, with significant yield increase in the field. This is the first report of Moringa leaf extract combined with Trichoderma as an integrated control for Sclerotium damping-off and stem rot of cowpea in the field.