我国蔬菜根结线虫发生、致害和绿色防控研究进展

根结线虫是威胁我国蔬菜生产的最重要病原物类群之一,寄主达3 000多种,每年造成的蔬菜损失价值高达5亿美元,目前缺乏安全高效的防治方法。近年来,随着保护地蔬菜种植面积的增加,根结线虫病对我国蔬菜生产的危害逐年加重,因此必须加强对蔬菜根结线虫病发生、致害和防治的深入研究。该文对近10来年我国根结线虫的发生分布和危害、主要种类、鉴定和快速诊断方法、成灾规律、与植物的互作及机理、绿色防控等方面的研究进展进行综述,并展望我国根结线虫的研究趋势。     

剂型、灌水量和土壤疏松度对甲维盐在土壤中分布及防治根结线虫效果的影响

为明确剂型、灌水量等对杀线虫剂防治根结线虫效果的影响,采用土壤薄层层析和高效液相色谱法分析了乳油和微囊悬浮剂型及不同灌水量对甲维盐在不同疏松度土壤中的分布特点,并以番茄为材料进行了根结线虫田间防治试验。结果表明,微囊悬浮剂型甲维盐随水迁移能力较乳油剂型强。药量相同、单株灌水量为1 600 m L时,2种剂型在疏松土壤中分布较为均匀,其次是800m L;200 m L和400 m L时,乳油剂型的分布均匀度明显大于微囊悬浮剂型。单株灌水量800 m L时2种剂型在致密土壤中分布的均匀度显著低于疏松土壤,乳油剂型略高于微囊悬浮剂型。番茄定植后单株甲维盐有效成分为10 mg、灌水量为800 m L和1 600 m L时,乳油剂型防效分别为67.90%和79.62%,微囊悬浮剂型分别为65.00%和77.50%,差异不显著。表明田间使用甲维盐乳油或微囊悬浮剂型防治蔬菜根结线虫时应尽量在移栽后随水冲施,且单株灌水量不低于800 m L。     

Powdered neem seed and cake for management of the banana weevil,cosmopolites sordidus, and parasitic nematodes

Field trials were conducted in Kenya with ‘Nakyetengu’, an East African highland banana cultivar (AAA-EA), highly susceptible to banana pests. Regardless of soil fertility levels, incorporation around the plant base of powdered neem(Azadirachta indica A. Juss.) seed or cake at 60-100 g/mat at 4-month intervals, gave better control of the banana weevil,Cosmopolites sordidus (Germar), and of parasitic nematodes, than that achieved with soil application of Furadan 5G (carbofuran) at 60 g/mat at 6-month intervals. Compared with untreated control, fruit yield in most of the neem treatments was significantly higher, particularly during the second cycle of crop production. Neem application conferred a net economic gain, whereas Furadan application proved uneconomical. Application of powdered neem seed or cake at higher rates (200–400 g/mat) at 6-month intervals caused phytotoxicity, resulting in drying up of banana plants before fruiting, or in ‘chokethroat’,i.e., inflorescence emergence failure.     

The influence of cyst nematodes and drought on potato growth. 3. Effects on carbon isotope fractionation

A good agreement was found between drought induced water-use efficiencies and carbon isotope fractionation of potato plants of the same age. Discrimination of¹³Carbon isotope increased with plant age and with the rank order of the distinguished plant organs. In young plants, nematode infection (contrary to drought) reduced¹³C discrimination but also reduced the water-use efficiency, leading to the conclusion that nematode infection, by slowing down the plant metabolism may have reduced the extrusion of¹³C. Towards senescence both nematode infection and drought reduced¹³C discrimination and increased water-use efficiencies indicating that then nematode caused water stress in the plants.     

烯效唑在棉花及土壤中的残留及消解动态

建立了烯效唑在棉花叶片、棉籽和土壤中残留的高效液相色谱-串联质谱（HPLC-MS/MS）检测方法,并运用该方法对烯效唑在棉花叶片和土壤中的残留消解规律进行了研究。样品用乙腈-水提取,经Cleanert NH2固相萃取柱净化,电喷雾正离子多反应监测模式HPLC-MS/MS检测,外标法定量。结果表明:烯效唑在棉花叶片、棉籽和土壤中的平均添加回收率在74%~101%之间,相对标准偏差（RSD）在1.2%~10%之间（n=5）。烯效唑在3种基质中的检出限（LOD）均为0.01 ng,定量限（LOQ）均为0.01 mg/kg。该方法准确、灵敏、简单,适用于棉花样品中烯效唑残留的检测。田间试验结果表明:烯效唑在棉花叶片和土壤中的消解半衰期分别为4.2~5.0 d及15.8~19.7 d;于收获期采样,烯效唑在棉籽和土壤中的最终残留量分别为0.01 mg/kg和0.022 mg/kg。     

玫瑰黄链霉菌片剂对根结线虫病的防治作用及对土壤微生物区系的影响

玫瑰黄链霉菌Men-myco-93-63是从马铃薯疮痂病自然衰退土壤中筛选到的对多种重要植物病原菌具有较强抑制作用的拮抗链霉菌,其发酵液对根结线虫具有较好的防治作用。为明确Men-myco-93-63活菌片剂在蔬菜根结线虫防治中的应用前景,采用温室盆栽法和稀释平板法研究了Men-myco-93-63活菌片剂对黄瓜根结线虫病的防治效果及对土壤微生物区系的影响。结果表明:Men-myco-93-63片剂对黄瓜根结线虫病具有较好的防效,1.0和1.5 g/株用量下防效分别为51.85%和55.56%,而对照药剂淡紫拟青霉颗粒剂1.5 g/株及M en-myco-93-63固体发酵物(发酵物与病土体积比为1∶200)的防效分别为54.17%和50.00%;施药60d后,该片剂对植株根际土壤中微生物区系影响较大,1.0 g/株用量下,细菌和放线菌数量分别比空白对照增加了225.45%和75.45%,真菌数量降低了66.43%,3种可培养微生物的总量比空白对照增加了195.35%,表明M en-myco-93-63片剂的施用可明显改善根际土壤中的微生物结构。     

Evaluation of entomopathogenic nematodes for biocontrol of the european corn borer,Ostrinia nubilalis, on sweet corn in Israel

The potential of entomopathogenic nematodes for biological control of the European corn borer (ECB),Ostrinia nubilalis (Hübner), was evaluated under laboratory, screenhouse and field conditions. The ‘All’ and ‘Mexican’ strains ofSteinernema carpocapsae (Weiser) and the ‘HP88’ strain ofHeterorhabditis bacteriophora Poinar were compared in both dose response assays (5, 50 and 500 infective juveniles [IJ] per petri dish containing five 5th-instar ECB eggs; 72 h of incubation) and exposure time assays (3, 6 and 9 h of incubation). In the dose response assays the highest rates of ECB killing resulted from infestation with the Mexican strain ofS. carpocapsae. In the exposure time assays there were no significant differences between the killing rates of the three nematode strains. Sweet corn plants(Zea mays var.saccharata) grown in a screenhouse, were infested with ECB neonates and 4 days later sprayed with a suspension of the Mexican strain ofS. carpocapsae (50,000 IJ per plant). The number of ECB larvae found on treated corn plants after one week was significantly (P=0.05) lower (3- to 5-fold) than the number found on untreated plants. Similar treatment in the field significantly reduced the rate of economic ear damage from 20% to 5%. Contribution from the Agricultural Research Organization. No. 2260-E, 1997 series     

氟吡菌酰胺不同施药方式对水稻拟禾本科根结线虫的防治效果

为评价41.7%氟吡菌酰胺悬浮剂防治水稻拟禾本科根结线虫Meloidogyne graminicola的应用潜力,将氟吡菌酰胺与吡虫啉种衣剂混合后采用种子包衣法及喷洒法研究其对水稻拟禾本科根结线虫的田间防效,并测定了不同施药方法对水稻生长和产量的影响。结果表明,氟吡菌酰胺4.2、8.3、12.5 g（a.i.）/kg种子与吡虫啉18.0 g（a.i.）/kg种子混合包衣处理,播种后35 d其根结抑制率和防效分别为41.0%~51.8%和47.4%~58.6%,土壤中2龄幼虫减退率为38.6%~40.4%,显著高于单施吡虫啉18.0 g（a.i.）/kg种子处理。水稻播种后连续3次以氟吡菌酰胺250.2、375.3、500.4 g（a.i.）/hm²进行土壤喷洒,最后1次施药后7 d,其根结抑制率和防效分别为81.0%~89.9%和65.9%~74.3%,土壤中2龄幼虫减退率为65.4%~73.4%,均显著高于对照药剂克百威1 800.0 g（a.i.）/hm²处理。氟吡菌酰胺各处理对水稻苗期生长均有较好的保护作用,能显著提高千粒重和有效穗数,产量比空白对照增加50.0%~61.2%,保产效果显著。水稻播种后35 d采用氟吡菌酰胺对稻田进行1次喷洒,对水稻具有一定的保护作用,保产效果不明显。表明采用氟吡菌酰胺与吡虫啉混合包衣种子处理及在水稻苗期进行喷洒处理对水稻拟禾本科根结线虫防效显著,具有显著的保产效果。     

The potential of combining <Emphasis Type="Italic">Pasteuria penetrans</Emphasis> and neem (<Emphasis Type="Italic">Azadirachta indica</Emphasis>) formulations as a management system for root-knot nematodes on tomato

Initial applications of 10⁴ spores g⁻¹ of Pasteuria penetrans, and dried neem cake and leaves at 3 and 2% w:w, respectively, were applied to soil in pots. Juveniles of Meloidogyne javanica were added immediately to the pots (500, 5,000 or 10,000) before planting 6-week-old tomato seedlings. The tomatoes were sampled after 64 days; subsequently a second crop was grown for 59 days and a third crop for 67 days without further applications of P. penetrans and neem. There was significantly less root-galling in the P. penetrans combined with neem cake treatment at the end of the third crop and this treatment also had the greatest effect on the growth of the tomato plants. At the end of the third crop, 30% of the females were infected with P. penetrans in those treatments where spores had been applied at the start of the experiment. The effects of neem leaves and neem cake on the nematode population did not persist through the crop sequences but the potential for combining the amendments with a biological control agent such as P. penetrans is worthy of further evaluation.     

Evaluation of biocontrol preparations and plant extracts for the control of <Emphasis Type="Italic">Phytophthora infestans</Emphasis> on potato leaves

The potential of biocontrol products and plant extracts for control of late blight on potato plants, caused by Phytophthora infestans was evaluated in detached leaf assays and on potted plants. Based on an initial screening of 22 preparations and plant extracts, the 10 most active treatments were selected for further investigation. In the detached leaf assays the commercial preparations Elot-Vis, Serenade and Trichodex, and plant extracts of Rheum rhabarbarum and Solidago canadensis showed a significant effect on the level of infestation by P. infestans. However, none of the treatments was as effective as copper. In the case of Serenade, the metabolites produced by its active micro-organism, Bacillus subtilis, were demonstrated to be the effective component of the formulation, and not the micro-organism itself. In order to take curative and protective modes of action into account, the test substances were applied 24 h before, or 90 min after inoculation with P. infestans. Generally, better effects were obtained when the applications were made 24 h before inoculation. For defining the optimum time of application, potted plants were treated 72 or 24 h before, and 1 and 24 h after inoculation with P. infestans. In these tests, Trichodex showed no activity, while Elot-Vis gave best results when applied 1 day before inoculation. Serenade and the extracts of R. rhabarbarum and S. canadensis (all at 5% concentration) however, were effective when applied up to 3 days before and just after inoculation with P. infestans. The results of the experiments on potted plants indicated direct effects on the pathogen for all agents except the extract of S. canadensis, but other mode of actions, e.g. induced resistance, could not be ruled out. None of the treatments had a curative effect.     

Comparative effects of temperature and humidity on the activity of three potential antagonists of rose powdery mildew

Three reported antagonists of cucumber powdery mildew,Stephanoascus flocculosus, Stephanoascus rugulosus, andTilletiopsis washingtonensis, were tested and compared under different environmental conditions for their potential for controlling rose powdery mildew, caused bySphaerotheca pannosa var.rosae. Under controlled conditions in vitro, all three fungi induced a rapid collapse of conidia, conidiophores and hyphae ofS. pannosa var.rosae on detached leaflets of miniature roses within 48 h following their application, as observed under a SEM. Both temperature and relative humidity (r.h.) affected the activity of the antagonists differently. The colonization of powdery mildew was maximal at 26 °C, especially forSt. rugulosus andT. washingtonensis. Maximal colonization was achieved at the highest r.h. tested (90%) for all three antagonists but onlySt. flocculosus maintained a colonization of 80% or better under lower r.h. These observations stress the importance of considering environmental conditions when assessing the activity of antagonistic microorganisms.     

The role ofPseudomonas spp. and competition for carbon,nitrogen and iron in the enhancement of appressorium formation byColletotrichum coccodes on velvetleaf

Colletotrichum coccodes is currently being investigated as a mycoherbicide against the weed velvetleaf (Abutilon theophrasti). Two isolates ofPseudomonas spp. (Ps2 and Ps5) reduced the percentage of germ tubes and increased appressorial formation ofC. coccodes on detached leaves of velvetleaf. A study was conducted to see whether this effect could be attributed to competition for nutrients or iron betweenC. coccodes andPseudomonas spp. Ps2 and Ps5 had no effect on early spore germination, but reduced the percentage of germ tubes at 24 and 30 h, compared to the nontreated control. This reduction was diminished by the addition of nutrients but not Fe³⁺. Ps2 and Ps5 stimulated the formation of dark-coloured appressoria without germ tubes (AWGT), but this stimulation was diminished by the addition of nutrients or Fe³⁺. Germ tube branching at 30 h was also inhibited by the bacteria, but was not diminished by the addition of nutrients or iron. EDTA stimulated conidial germination at 10 h, which was reduced by the addition of Fe³⁺. However, EDTA did not stimulate the formation of appressoria (AWGT). These results suggest that the reduction in the percentage of germ tubes and the increase in the percentage of appressoria induced by the bacteria may be due to the competition for carbon or nitrogen. Iron competition may also be involved in the stimulation of appressorial formation, but not in the reduction in germ tube percentage and branching. Phylloplane bacteria may compete for carbon, nitrogen and iron, limiting the saprophytic phase of the pathogen on the phylloplane and accelerating the development of the parasitic phase. This may enhance the field efficacy ofC. coccodes as a biocontrol agent against velvetleaf.     

四种拟除虫菊酯类杀虫剂对枸杞蚜虫的毒力及对三磷酸腺苷酶和谷胱甘肽S-转移酶活性的影响

为寻找防治枸杞蚜虫的适用药剂,采用玻璃管药膜法,测定了4种拟除虫菊酯类杀虫剂对枸杞蚜虫的毒力及对其三磷酸腺苷酶(ATPase)和谷胱甘肽S-转移酶(GSTs)活性的影响。结果表明:枸杞蚜虫对联苯菊酯最敏感,LC50值为4.34 mg/L;氯菊酯、高效氯氰菊酯和甲氰菊酯的LC50值分别为17.08、40.50和184.84 mg/L。4种杀虫剂对枸杞蚜虫两种ATPase活性均有抑制作用,药剂浓度为1×10-4mol/L时,4种药剂对Na+-K+-ATPase活性的抑制率均高于对Ca2+-M g2+-ATPase的抑制率,其中对Na+-K+-ATPase活性的抑制率从高到低依次为:联苯菊酯高效氯氰菊酯氯菊酯甲氰菊酯,而对Ca2+-M g2+-ATPase的抑制率则是联苯菊酯最高(46.41%),高效氯氰菊酯最低(33.04%)。4种药剂对枸杞蚜虫GSTs活性的影响差异较大:联苯菊酯在低浓度时对GSTs具有诱导作用,高浓度时则表现为一定的抑制作用;不同浓度高效氯氰菊酯和氯菊酯对GSTs活性均表现为抑制作用,抑制率最高达85.02%;而甲氰菊酯处理后GSTs的活性则升高了193.07%~249.96%。     

西兰花轮作及其残体还田对土壤中病原菌微菌核数量、黄萎病发生及马铃薯产量的影响

为明确西兰花轮作及其残体还田对土壤中病原菌大丽轮枝菌Verticillium dahliae微菌核数量、马铃薯黄萎病发生以及马铃薯产量的影响,分别于2017-2018年和2018-2019年在内蒙古自治区乌兰察布市凉城县岱海镇元山子农场人工病圃和锡林郭勒盟正蓝旗上都镇菜园村自然病圃开展田间试验,利用NP-10培养基测定不同处理土壤中的大丽轮枝菌微菌核数量,并对马铃薯地上叶片和地下块茎上黄萎病的发病率、病情指数以及马铃薯总产量和商品薯产量进行调查。结果显示,以马铃薯连作方式为对照,西兰花轮作及其残体还田后土壤中大丽轮枝菌微菌核的数量明显减少,其中在人工病圃于7、8和9月调查时分别降低了8.46%、36.41%和36.27%,在自然病圃于7、8和9月调查时则分别降低了7.22%、38.06%和48.84%;马铃薯地上叶片和地下块茎上黄萎病的发病率和病情指数均显著降低,在人工病圃对黄萎病的防效为32.91%和54.82%,在自然病圃对黄萎病的防效为46.72%和34.78%;马铃薯总产量和商品薯产量均有所提高,在人工病圃分别增产27.74%和40.08%,在自然病圃分别增产7.12%和8.77%。表明西兰花作为理想的轮作作物可应用于马铃薯黄萎病的有效防控。     

Ecological Studies on the Larger Grain Borer, Prostephanus truncatus (Horn) (Col.: Bostrichidae) and their Implications for Integrated Pest Management

In this article, we review studies of the ecology of the larger grain borer, Protephanus truncatus, both outside and within the maize storage systems. Laboratory studies have shown that P. truncatus can breed on a wide range of woody substrates (branches, roots, and seeds). Pheromone trap catches in different habitats strongly suggest that P. truncatus is well-established in certain non-agricultural environments, presumably breeding in dead or dying wood. In Meso-America, West and East Africa, P. truncatus reproduction in the field has been documented in branches ring-barked by cerambycid beetles. Within a maize store, P. truncatus densities can increase from very small initial colonies of probably less than 200 individuals to densities in excess of 1000 beetles per kg after about 4–6 months of storage. Insect parasitoids are very often found in smallholders' grain stores attacked by P. truncatus, but they do not contribute significantly to population regulation. Declines in maize store population levels in Benin from 1993 to 1996, and in adult abundance in pheromone traps in the natural environment in Kenya, have been attributed to predation by the introduced predator, Teretrius nigrescens, but in recent years pheromone trap catches in West Africa suggest that the situation may be complex. Several environmental factors, notably temperature, humidity, and daylength, and their interactions, have been correlated with P. truncatus flight activity, as well as, in West Africa, the emptying of maize stores. Laboratory experiments have shown food quality also affects flight activity. Factors terminating dispersal and flight are most likely attraction to the male-released aggregation pheromone. Short range attraction to plant volatiles has also been recorded. In Africa the highest densities of P. truncatus tend to occur in humid lowlands, which contrasts with the situation in meso-America where P. truncatus tend to occur in greatest numbers in cooler upland regions. Pheromone trap catches can be significant predictors of the risk of stores becoming infested. Coupled with the development of a rule-based model of flight activity, these studies may offer the prospect of predicting the risk of store infestation based upon temperature and humidity measurements.     

Studies on the origin,spread, and evolution of an important group ofPuccinia recondita f. sp.tritici pathotypes in Australasia

Wheat brown rust pathotype (pt) 104-2,3,(6),(7), 11 was first detected in Australasia in Victoria during 1984. Although it appeared similar to a pre-existing pathotype, 104-2,3,6,(7), detailed greenhouse test revealed nine pathogenic differences between the two rusts. Six differences involved contrasting virulence/avirulence for the resistance genes/specificitiesLr12, Lr27+Lr31 andLr16, and three uncharacterised genes, present in the wheat cultivars Gaza and Harrier, and in triticale cultivar Lasko. Differences in partial virulence between the pathotypes were found for the genesLr2a, Lr13 andLr26. A comparison of the phenotypes for 13 isozyme systems in the two pathotypes revealed two differences, including aPgm2 allele in pt 104-2,3,(6),(7),11 not found in other contemporary AustralasianPuccinia recondita f. sp.tritici pathotypes. On the basis of these differences, it was concluded that pt 104-2,3,(6),(7),11 was introduced into the Australasian region before or during 1984.Seven variants of pt 104-2,3,(6),(7),11, that differed by single virulences, were detected during 1984–1992. Pt 104-2,3,(6),(7),11 and a derivative pathotype with virulence forLr20 underwent rapid increases in frequency, largely displacing pathotypes which predominated before 1984. Although first detected in eastern Australia, both pathotypes spread to New Zealand, and the derivative pathotype appeared in Western Australia. The rapid spread and increase of these pathotypes could not be explained by host selection. Pt 104-2,3,(6),(7),11 and derivatives may therefore be more aggressive than other contemporary Australasian pathotypes.Abbreviations NSW New South Wales - Prt Puccinia recondita f. sp.tritici - Qld Queensland - SA South Australia - WA Western Australia     

Influence of soil type and pH on the colonisation of sugar beet seedlings by antagonistic Pseudomonas and Bacillus strains,and on their control of Pythium damping-off

In five different soils originating from Scotland (Craibstone and Cruden Bay), Germany (Magdeburg and Uelzen) and Greece (Tymbaki), Pseudomonas fluorescens B5 reached higher population sizes (4.7–5.7logCFU/plant) on 12-day-old sugar beet seedlings than Bacillus subtilis MBI 600 (4.1–4.8logCFU/plant). Total population size per plant was not affected by soil type. In all five soils, the antagonists reached highest population densities in the hypocotyl and the upper 2cm root section (P. fluorescensB5: 5.2–6.8log₁₀CFU/g plant fresh weight, Bacillus subtilisMBI 600: 5.2–6.1log₁₀CFU/g plant fresh weight) and declined to 0–3log₁₀CFU below 4cm root depth. Colonisation by P. fluorescens B5 down the root was slightly increased in the soils from Craibstone, Magdeburg, and Uelzen compared to the sandy clay loam from Tymbaki. In lux-marked P. fluorescens B5, population density was positively correlated with light emission in all soils; the light emission indicated physiological activity of the strains. However, P. fluorescens B5 reduced Pythium damping-off (measurement after 14 days plant growth) only in three of the five soils (Craibstone, Cruden Bay and Magdeburg). Co-inoculation of B. subtilis MBI 600 increased downward colonisation of the root by P. fluorescens B5, but not the total population ofP. fluorescens B5 per plant. Bacillus subtilisMBI 600 did not reduce Pythium damping-off in any of the soils nor did it influence the efficiency of co-inoculated P. fluorescens B5; its population consisted mainly of physiologically inactive spores. In Craibstone soil, pH did not affect population density, distribution along the root or biocontrol activity against P. ultimum of P. fluorescens B5 or B. subtilis MBI 600.     

Evaluation of the API 50CH and API ZYM systems for rapid characterization of Clavibacter michiganensis subsp. sepedonicus, causal agent of potato ring rot

API 50CH and API ZYM systems were used to characterize fifty-three strains of Clavibacter michiganensis subsp. sepedonicus from different geographic locations and several reference strains of the same and different species, including other potato pathogens. Clavibacter michiganensis subsp. sepedonicus strains displayed a high level of homogeneity, both in carbohydrate utilization and in enzymatic activity. Using API 50CH and API ZYM it was possible to differentiate C. michiganensis subsp. sepedonicus strains from the remaining taxa analysed in this study, which included representative strains of the other subspecies of C. michiganensis as well as other bacterial pathogens affecting potatoes. Therefore, these systems could be used as an effective method to characterize C. michiganensis subsp. sepedonicus. Such a procedure would constitute an alternative system to the conventional nutritional and physiological identification tests currently included in the official methods employed in the European Union to detect and identify this bacterium. The results obtained with the API systems agreed with the current taxonomic classification of C. michiganensis, clearly separating sepedonicus from the other subspecies belonging to this species.     

Production of phytotoxic metabolites by five species of Botryosphaeriaceae causing decline on grapevines, with special interest in the species Neofusicoccum luteum and N. parvum

In recent years an increasing number of species of Botryosphaeriaceae have been associated with grapevine decline worldwide. Five species isolated from declining grapevines in Spain (Botryosphaeria dothidea, Diplodia seriata, Dothiorella viticola, Neofusicoccum luteum and N. parvum) were checked for toxin production in liquid cultures. Cultural conditions for all fungi were adjusted to obtain optimal production of phytotoxic culture filtrates, by growing the fungi in steady liquid cultures of Czapek–Dox broth for different time intervals. Phytotoxicity of D. seriata and N. parvum reached a maximum after 14 days while the remaining species showed the highest phytotoxicity levels after 21 days in culture. All fungi produced hydrophilic high-molecular weight compounds with phytotoxic properties. In addition, N. luteum and N. parvum produced lipophilic low-molecular weight phytotoxins, not detected consistently among the remaining species. This led to a more exhaustive study on the phytotoxicity of N. luteum and N. parvum. Culture filtrates and corresponding extracts of both species were consistently highly phytotoxic in different assays. The gas-chromatography analysis of the acetylated O-methyl glycosides of the phytotoxic exopolysaccharides produced by N. parvum showed these substances to be composed mainly of glucose, mannose and galactose. Results suggest that phytotoxic metabolites could be involved in the virulence of both species in planta.     

Impacts of atmospheric CO<Subscript>2</Subscript> concentrations and soil water on the population dynamics,fecundity and development of the bird cherry-oat aphid<Emphasis Type="Italic">Rhopalosiphum padi</Emphasis>

The impacts of elevated CO₂ and soil water on the population dynamics, adult fecundity and nymphal period of the bird cherry-oat aphidRhopalsiphum padi (Linnaeus) were evaluated in three experiments: (i)Combined effects of CO ₂ and soil water on aphid populations. Spring wheat was grown in pots at three CO₂ concentrations (350, 550 and 700 ppm) and three soil water levels (40%, 60% and 80% of field water capacity, FWC) in field open-top chambers (OTC) and infested with the bird cherry-oat aphid. Aphid population dynamics were recorded throughout the growing season; at the same time, adult fecundity and duration of the nymphal period were recorded. Chemical composition of spring wheat leaves was also analyzed. (ii)Indirect effects of CO ₂ concentrations and soil water on aphid adult fecundity and nymphal period. The experiment was conducted with the leaf discs method in the laboratory. Aphids were reared on leaf discs excised from the treated wheat in OTC with different CO₂ and soil water levels. (iii)Direct effects of CO ₂ concentrations on aphid adult fecundity and nymphal period. Aphids were reared on leaf discs excised from the wheat grown under natural conditions. The experiment was conducted with the leaf disc method in OTC with the three CO₂ concentrations. It was found that the direct effect of CO₂ concentration on aphid population parameters was minor. CO₂ and soil water affected aphid population indirectly through their effects on wheat characteristics. The aphid population under 550 ppm CO₂ was far larger than the one under 350 ppm CO₂, whereas the population under 700 ppm CO₂ was slightly higher than that under 550 ppm CO₂. The largest aphid population was obtained with the 60% soil water treatment, regardless of CO₂ treatment. The effects of CO₂ concentration on aphid population were, however, not significantly correlated with soil water level. Adult fecundity increased with CO₂ concentration, the highest fecundity being achieved under 60% FWC treatments. The nymphal period was not affected by CO₂ concentration. The shortest period occurred under 60% FWC. Atmospheric CO₂ and soil water had significant effects on the chemical composition of the wheat leaves. Aphid population size was positively correlated with leaf water content, concentrations of soluble proteins, soluble carbohydrates and starch, and negatively correlated with DIMBOA and tannins concentrations. http://www.phytoparasitica.org posting Oct. 20, 2003.