Partial resistance to Wheat dwarf virus in winter wheat cultivars

Four Hungarian winter wheat cultivars were investigated for their susceptibility to the geminivirus Wheat dwarf virus (WDV). Previously, two cultivars (Mv Regiment and Mv Emese) were assessed by breeders to exhibit virus symptoms in the field, whereas Mv Dalma and Mv Vekni showed few symptoms. Two inoculation techniques for WDV, vector transmission with the leafhopper Psammotettix alienus and agroinoculation, were used. Leafhopper transmission was more efficient than agroinoculation. However, irrespective of the technique used, no Mv Dalma or Mv Vekni plants showed clear WDV symptoms. In contrast, 3/30 Mv Emese and 4/36 Mv Regiment plants showed dwarfing and chlorosis after agroinoculation and 13/17 and 14/15 plants, respectively, had clear WDV symptoms after vector transmission. WDV‐specific PCR showed that Mv Vekni and Mv Dalma plants could be infected, especially following vector transmission (approximately 50% infection), but at significantly lower frequency than Mv Emese or Mv Regiment plants (100% infection). Furthermore, real‐time PCR showed that WDV DNA accumulated to much lower levels in infected Mv Vekni and Mv Dalma plants than in infected Mv Regiment and Mv Emese plants. The data strongly suggest that Mv Vekni and Mv Dalma are partially resistant to WDV infection. As WDV resistance has not previously been identified in wheat, and because WDV can cause significant yield losses, the resistance of Mv Vekni or Mv Dalma will provide a valuable breeding resource.     

Reducing tillage intensity affects the cumulative emergence dynamics of annual grass weeds in winter cereals

Annual grass weeds such as Apera spica‐venti and Vulpia myuros are promoted in non‐inversion tillage systems and winter cereal‐based crop rotations. Unsatisfactory weed control in these conditions is often associated with a poor understanding of the emergence pattern of these weed species. The aim of this study was to investigate, understand and model the cumulative emergence patterns of A. spica‐venti, V. myuros and Poa annua in winter cereals grown in three primary tillage regimes: (i) mouldboard ploughing, (ii) pre‐sowing tine cultivation to 8–10 cm soil depth and (iii) direct drilling. Direct drilling delayed the cumulative emergence of A. spica‐venti and V. myuros (counted together) in contrast with ploughing, while the emergence pattern of P. annua was unaffected by the type of tillage system. The total density of emerged weed seedlings varied between the tillage systems and years with a higher total emergence seen under direct drilling, followed by pre‐sowing tine cultivation and ploughing. The emergence patterns of all species were differently influenced by the tillage systems, suggesting that under direct drilling, in which these species occur simultaneously, management interventions should first and foremost consider that A. spica‐venti and V. myuros emerge over a longer period to avoid control failures.     

Investigation of wheat as a trap crop for control of Orobanche minor

Orobanche minor is a parasitic weed that attaches to the roots of red clover (Trifolium pratense) and a number of other broad‐leaved plant species in the Pacific Northwest USA. Orobanche minor seed must be stimulated by host plant exudates for germination and attachment to occur. However, plant species called false‐hosts can stimulate parasitic seed germination without attachment. These species could be utilized as trap crops to reduce the amount of parasitic seed in infested soil. Wheat (Triticum aestivum), was found to be a false‐host of O. minor; therefore, growth chamber, glasshouse and field soil experiments were conducted to evaluate the effect of six soft white winter wheats (T. aestivum), one durum wheat (Triticum turgidum), and one triticale (Triticale hexaploide) on O. minor germination. In growth chamber experiments, wheat and triticale induced 20–70% of O. minor seeds to germinate. In glasshouse studies, O. minor attachment was minimal on red clover plants grown in pots previously planted to wheat or triticale. In pots that did not receive a false‐host treatment, red clover plants averaged 4.2 O. minor attachments per plant. Red clover plants also had fewer O. minor attachments when grown in field soil taken from the plots where wheat or triticale were grown compared with plants grown in soil where no wheat or triticale were previously grown. Our results demonstrate that wheat may have the potential to be effectively integrated into an O. minor management system.     

Non-enzymatic conjugation of fenoxaprop-ethyl with glutathione and cysteine in several grass species

Laboratory studies have shown that the amounts of glutathione (GSH) and cysteine are higher in grass species that are moderately tolerant, such as wheat (Triticum aestivum L., cv. Fredrick), and moderately susceptible, such as barley (Hor deum vitlgare L., cv. Legér) and triticale (cv. OAC Trillium), to fenoxaprop-ethyl (FE) than in species that are very susceptible to the her bicide, such as oat (Avena saliva L., cv. OAC Woodstock), wild oat (Avena fatua L.), yellow foxtail (Setaria glanca (L.) Bcauv.), large crab grass (Digitaria sanguinalis (L.) Scop.) and bar nyard grass (Echinochloa crus-galli (L.) P.B.). The safener, fenchlorazole-ethyl (FCE) was found to increase and decrease, respectively, the amounts of GSH and cysteine in the moderately tolerant and moderately susceptible species but had no effect on the susceptible species. It is sug gested that in the moderately tolerant and moderately susceptible species, especially following FCE treatment, more GSH is available to detoxify the herbicide. Glutathione-S-tranferase activity (GST) for FE was found to be very low in all of the species tested. In vitro experiments at physio-logical pH. demonstrated that FE may conjugate with GSH nonenzymatically. Therefore, it is suggested that nonenzymatic conjugation of fenoxaprop-ethyl with glutathione may be an important mechanism for tolerance of some grasses to this herbicide.     

Evidence of host‐range expansion from new powdery mildew (Blumeria graminis) infections of triticale (×Triticosecale) in France

This study aimed to determine whether powdery mildew caused by Blumeria graminis is an endemic pathogen of triticale (×Triticosecale: Triticum × Secale), emerging as a result of recent changes in its pathogenicity, or whether it is a new pathogen, possibly resulting from hybridization between ff. spp. tritici and secalis. A secondary aim was to consider breeding practices that may have favoured this emergence. Phylogenetic analyses based upon six genes revealed the close relatedness of the novel entity and the ff. spp. tritici and secalis, but the IGS marker finally grouped together the isolates collected on triticale and on wheat, supporting the scenario of a recent host‐range expansion from wheat to triticale. Pathotype analyses concluded that virulence spectra of B. graminis infecting triticale were new in comparison to those observed for other reference formae speciales, and lack of fungicide resistance in triticale isolates strengthens the hypothesis of no or little genetic exchange between wheat and triticale populations of powdery mildew. This adaptation may follow the breakdown of plant resistance genes, which are probably not very diverse in current triticale cultivars since this criterion was not considered as a major one until recent years. Moreover, the complex selection and genetics of this hybrid cereal makes it difficult to predict the transmission of powdery mildew resistance genes.     

Multifunctionalised benzoxazinones in the systems Oryza sativa–Echinochloa crus‐galli and Triticum aestivum–Avena fatua as natural‐product‐based herbicide leads

BACKGROUND: Fifteen novel derivatives of D‐DIBOA, including aromatic ring modifications and the addition of side chains in positions C‐2 and N‐4, had previously been synthesised and their phytotoxicity on standard target species (STS) evaluated. This strategy combined steric, electronic, solubility and lipophilicity requirements to achieve the maximum phytotoxic activity. An evaluation of the bioactivity of these compounds on the systems Oryza sativa–Echinochloa crus‐galli and Triticum aestivum–Avena fatua is reported here. RESULTS: All compounds showed inhibition profiles on the two species Echinochloa crus‐galli (L.) Beauv. and Avena fatua L. The most marked effects were caused by 6F‐4Pr‐D‐DIBOA, 6F‐4Val‐D‐DIBOA, 6Cl‐4Pr‐D‐DIBOA and 6Cl‐4Val‐D‐DIBOA. The IC₅₀ values for the systems Echinochloa crus‐galli–Oryza sativa and Avena fatua–Triticum aestivum for all compounds were compared. The compound that showed the greatest selectivity for the system Echinochloa crus‐galli–Oryza sativa was 8Cl‐4Pr‐D‐DIBOA, which was 15 times more selective than the commercial herbicide propanil (Cotanil‐35). With regard to the system Avena fatua–Triticum aestivum, the compounds that showed the highest selectivities were 8Cl‐4Val‐D‐DIBOA and 6F‐4Pr‐D‐DIBOA. The results obtained for 6F‐4Pr‐D‐DIBOA are of great interest because of the high phytotoxicity to Avena fatua (IC₅₀ = 6 µM , r² = 0.9616). CONCLUSION: The in vitro phytotoxicity profiles and selectivities shown by the compounds described here make them candidates for higher‐level studies. 8Cl‐4Pr‐D‐DIBOA for the system Echinochloa crus‐galli‐Oryza sativa and 6F‐4Pr‐D‐DIBOA for Avena fatua‐Triticum aestivum were the most interesting compounds. Copyright © 2010 Society of Chemical Industry     

Apera spica-venti population dynamics and impact on crop yield as affected by tillage, crop rotation, location and herbicide programmes

Apera spica‐venti is a winter annual grass and, increasingly, a severe weed problem in autumn‐sown crops. Non‐inversion tillage has become more common in Denmark in recent years, but may accentuate problems with A. spica‐venti. These problems may be avoided, if selected preventive and cultural weed management practices are adopted. To this end, we conducted a 4‐year field study investigating the effects of crop rotation, tillage method, location and limited herbicide input on A. spica‐venti population dynamics and crop yield. Additionally, detailed studies were performed on the fate of A. spica‐venti seeds when incorporated to different soil depths. The location with a lighter soil texture, cooler climate and higher rainfall favoured A. spica‐venti growth and consequently crop yield loss, especially in the crop sequence comprised only of autumn‐sown crops and with non‐inversion tine tillage. Incorporating A. spica‐venti seeds in the soil improved their survival, explaining the higher A. spica‐venti proliferation seen with tine tillage as opposed to direct drilling. The rotations including an even mixture of spring‐ and autumn‐sown crops did not lead to noteworthy changes in the A. spica‐venti population, irrespective of tillage method. Thus, in many regions, management of A. spica‐venti will require rotations that balance autumn‐ and spring‐sown crops.     

Nitrogen effect on competition between winter cereals and littleseed canarygrass

Field experiments were conducted in northern Greece during 1994, 1995, and 1996 to study the effect of nitrogen fertilization on competition between littleseed canaryglass (Phalaris minor Retz.) and wheat (Triticum aestivum L.), barley (Hordeum vulgare =distichum L.) or triticale (Triticosecale). The presence of 400P. minor plants per square meter until early March did not have an adverse effect on dry weight of any crop. However, their further presence significantly reduced dry weight of wheat and triticale, but not that of barley. Grain yield of wheat and triticale was reduced 48% and 47%, respectively, by season-long competition ofP. minor, whereas the corresponding reduction for barley was only 8%. Crop yield reduction due toP. minor competition resulted mainly from reduction in ear number and less from reduction in 1000-grain weight. Nitrogen fertilization (150 kg N ha⁻¹), compared with control (0 kg N), slightly increased yield of all crops grown without weed competition. The same treatment also increased dry weight and competitive ability ofP. minor against wheat and triticale, compared with that of control (0 kg N); the split application of nitrogen (50 kg N ha⁻¹ before crop sowing and 100 kg N ha⁻¹ in early March) caused a slightly greater increase inP. minor dry weight than did 150 kg N ha⁻¹ applied once before crop sowing. Dry weight ofP. minor grown with barley was not affected by nitrogen fertilization, but it was severely reduced compared with that ofP. minor grown with wheat or triticale. http://www.phytoparasitica.org posting April 22, 2003.     

Losses in grain yield of winter crops from Lolium rigidum competition depend on crop species, cultivar and season

The competitive abilities of eight winter crops were compared against Lolium rigidum Gaud, (annual ryegrass), an important weed of southern Australia, as a potential strategy to suppress weeds and reduce dependence on herbicides. Two cultivars of each species were chosen to represent the range of competitive ability within each crop and grown in field experiments in 1992 and 1993. The order of decreasing competitive ability (with the ranges of percentage yield reduction from L. rigidum at 300 plants m^?2 in parenthesis) was as follows: oats (Avena sativa L.), 2–14%; cereal rye (Secale cereale L.), 14–20%; and triticale (×Triticosecale), 5–24%; followed by oilseed rape, (Brassica napus L.), 9–30%; spring wheat (Triticum aestivum L.), 22–40%; spring barley (Hordeum vulgare L.), 10–55%; and, lastly, field pea (Pisum sativum L.), 100%, and lupin (Lupinus angustifolius L.), 100%. Differences in competitive ability of cultivars within each species were identified, but competition was strongly influenced by seasonal conditions. Competition for nutrients (N, P and K) and light was demonstrated. L. rigidum dry matter and seed production were negatively correlated with grain yield of the weedy crops. More competitive crops offer the potential to suppress grass weeds while maintaining acceptable grain yields. Ways of improving the competitive abilities of grain legume crops are discussed.     

Deleterious activity of cultivated grasses (Poaceae) and residues on soilborne fungal,nematode and weed pests

Experiments were conducted in laboratory bioreactors and in field plots to test effects of certain cultivated members of the grass family (Poaceae = Gramineae), including wheat (Triticum aestivum cv. Yolo), barley (Hordeum vulgare cv. UC337), oats (Avena sativa cv. Montezuma), triticale (X Triticosecale), and a sorghum-sudangrass hybrid (Sorghum bicolor x S. sudanense = “sudex”, cv. Green Grazer V) for soil disinfestation potential. Soilborne pest organisms tested for effects on survival and activity included the phytopathogens Sclerotium rolfsii, Pythium ultimum and Meloidogyne incognita, and a variety of weed taxa. Following soil amendment, bioreactors were incubated for 7 days at ambient (23°C) or elevated, but sublethal (38°C day/27°C night), soil heating regimens. Addition of each of the poaceous amendments to soil at 23°C resulted in inconsistently reduced tomato root galling (49–97%) by M. incognita, or reduced recovery of S. rolfsii and P. ultimum (0–100%) fungi in soil, after 7 days’ incubation (P ≤ 0.05). When the organisms were exposed to the poaceous soil amendments at the 38^o/27^o temperature regimen, nematode galling and recovery of active fungi were consistently and significantly reduced by 98–100%. These results demonstrated feasibility of soil disinfestation (“biofumigation”) by activity of poaceous amendments, further aided by combining plant residues with soil heating (e.g. solarization). Results from three field experiments with sudex cover crops, conducted throughout the growing season, demonstrated biocidal activity on a range of weedy plants, including Amaranthus retroflexus, Calandrinia ciliata, Cerastium arvense, Digitaria sanguinalis, Echinochloa crus-galli and Poa annua. Both shoots and roots of sudex provided allelopathic weed biomass reductions of 35–100%, and for at least 106 days after shredding. Deleterious activity of shredded residues incorporated in soil was less persistent. These properties in poaceous crops can be useful for soil disinfestation; however, harmful phytotoxicity to subsequent crops may also result. In order to take full advantage of these low-input measures for controlling soilborne diseases and pests, further understanding of their properties must be gained, and user guidelines developed.     

陕西韩城严重发生的小麦矮缩病病原鉴定与原因分析

2007年在陕西韩城发现一种新的小麦病毒病害,症状表现为严重矮缩、黄化、条斑和分蘖增多等,发病面积约0.07万hm²,病田减产达50%,严重地块甚至绝收。本研究通过对采集自我国陕西韩城的7个样品进行PCR鉴定、全基因组序列测定及比较,证实陕西韩城样品确是小麦矮缩病毒(WDV)侵染所致,并对发病原因及其流行趋势进行了分析。这是小麦矮缩病在我国麦田大发生的首次报道。     

Studies on the host range of the barley strain of Wheat dwarf virus using an agroinfectious viral clone

Comparative analysis of the host ranges of the barley and wheat strains of Wheat dwarf virus (WDV; family Geminiviridae ; genus Mastrevirus ) in Europe has been severely hampered by the lack of an infectious clone of the barley strain. To remedy this situation an agroinfectious clone of a Hungarian isolate of the barley strain (WDV-Bar[HU]) was constructed and its virulence tested in barley ( Hordeum vulgare ), wheat ( Triticum aestivum ), rye ( Secale cereale ) and oat ( Avena sativa ) by agroinoculation. Although all four species could be systemically infected by the isolate, infections were asymptomatic in the rye and oat cultivars tested. WDV-Bar[HU] induced chlorosis and stunting symptoms typical of WDV in barley, while in wheat low infection rates but high mortality of infected seedlings were observed. In contrast, a much higher percentage of wheat plants agroinoculated with a wheat-strain isolate (WDV-[Enk1]) became systemically infected. WDV-[Enk1] in wheat caused symptoms similar to those caused by WDV-Bar[HU] in barley. WDV-Bar[HU] was leafhopper-transmissible to barley seedlings, in which it caused typical WDV symptoms; geminate virus particles were isolated from the infected leaves. Comparison of the genomic sequences of 11 barley strain isolates from Europe and Turkey revealed that whereas WDV-Bar[HU] represents a typical barley-strain isolate that is not detectably recombinant, the Turkish barley isolate (WDV-Bar[TR]) is probably a recombinant between a barley-strain isolate and an as-yet-undescribed WDV-like mastrevirus species.     

Pathogenic and molecular variability among isolates of Pyrenophora tritici-repentis, causal agent of tan spot of wheat in Argentina

Tan spot, caused by Pyrenophora tritici-repentis, is a common disease of wheat (Triticum aestivum) responsible for economic losses in some wheat growing areas worldwide. In this study the pathogenic and genetic diversity of 51 P. tritici-repentis isolates collected from different ecological regions of Argentina were analyzed. Virulence tests were conducted on 10 selected wheat cultivars: Buck Halcón, Chris, Gabo, Glenlea, Klein Dragón, Klein Sendero, Max, ND 495, ProInta Guazú and ProInta Imperial. Data revealed significant differences between all main factors evaluated and the interactions for 19 of the isolates analyzed. Based on the reaction type of each isolate/cultivar combination, 48 different pathogenic patterns were detected. The molecular analysis using Inter-Simple Sequence Repeats (ISSR) revealed the existence of 36 different haplotypes among 37 isolates of P. tritici-repentis originally selected for this study. These results indicate that P. tritici-repentis on wheat in Argentina is a heterogeneous fungus, implying that screening wheat germoplasm for resistance for tan spot disease requires a wide range of pathogen isolates.     

Root growth profiles of Aveneae and Poeae plants in optically active α-methylbenzyl-3-p-tolylurea media

Using a root growth inhibition assay, we studied the diverse chiral responses of plants in the tribes, Aveneae and Poeae, to the optically active compounds, R- and S- 1-α-methylbenzyl-3- p -tolylurea (MBTU). We specifically examined the responses of grasses belonging to the Poeae tribe ( Lolium , Briza , Poa , Dactylis , and Festuca ) and the Aveneae tribe ( Avena , Holcus , Agrostis , Alopecurus , Beckmannia , and Phleum ). These plants include companion weeds of wheat and barley, and turf grass. The companion weeds of cereal crops, such as Poa annua , Poa pratensis , Dactylis glomerata , Avena fatua , Avena sativa , Holcus lanatus , Agrostis stolonifera , Alopecurus myosuroides , Al. aequalis , and Beckmannia syzigachne , showed significantly inhibited root growth in response to 20 µmol L⁻¹ R- MBTU, whereas the root growth of Triticum aestivum was not inhibited at this concentration. Like Oryza sativa , almost all the Poeae and Aveneae plants tested here preferentially responded to R -MBTU, but the four grasses, Lolium multiflorum , D. glomerata , Alopecurus species, and Phleum pratense , preferentially responded to S -MBTU. Among them, the Agrostis species were highly sensitive to R -MBTU and the Alopecurus species were highly sensitive to S -MBTU. All the plants among the genera, Poa , Avena , and Alopecurus , showed a homogeneous chiral preference.     

Diversity of virulence phenotypes among annual populations of wheat leaf rust in Israel from 1993 to 2008

Leaf rust, caused by the fungus Puccinia triticina, is the most common rust disease of wheat in wheat‐producing areas worldwide. The Israeli population of wheat leaf rust has been consistently monitored since 1993. A total of 840 single urediniospore isolates from Triticum aestivum (567), T. dicoccoides (119) and T. durum (154) were analysed during 1993–2008. The structure of the pathogen population has changed to a large extent since 1993. The annual populations of P. triticina were separated into two distinct groups: 1993–1999 and 2000–2008. Differentiation among the annual pathogen populations, as well as between the overall populations of the 1990s and 2000s, could be mainly attributed to the following forces: (i) migration of leaf rust urediniospores from neighbouring regions; and (ii) selection pressure of new yellow rust‐resistant wheat cultivars that have been introduced into Israel since 1997. Genetic multiplicity of wild emmer contributes to P. triticina variability in Israel. Leaf rust populations collected from common wheat, wild emmer and durum wheat differed. The population that originated from T. durum was rather stable during the years of the survey, whereas that from T. aestivum changed significantly from the 1990s to the 2000s. Diversity within the annual populations of P. triticina was highest in 1994 when many new pathotypes and associations between virulences were observed. Single‐step derivatives of the new pathotypes became dominant after 2000. Significant changes in virulence frequency to a number of Lr genes (e.g. Lr2a, Lr15, Lr17, Lr21, Lr26) were also registered in 2000–2008.     

An isolate of Wheat streak mosaic virus from foxtail overcomes Wsm2 resistance in wheat

Wheat streak mosaic virus (WSMV) is an economically important pathogen of wheat (Triticum aestivum) causing major yield losses in regions where severe infection occurs. To detect the presence of any new virus or new WSMV isolates, green foxtail (Setaria viridis) plants exhibiting virus-like symptoms were sampled in a summer-fallowed wheat field at the Agricultural Research Center-Hays, Kansas State University, Hays, Kansas. These plants were tested serologically for four wheat viruses: WSMV, Triticum mosaic virus (TriMV), High Plains wheat mosaic virus (HPWMoV) and Foxtail mosaic virus (FoMV). Among 38 plant samples exhibiting virus-like symptoms, 29 contained WSMV as indicated by ELISA. Four isolates from samples with relatively strong reactions were transferred to healthy wheat seedlings by mechanical inoculation in a growth chamber for pathogenicity testing. Three isolates were avirulent to a wheat variety RonL, which contains Wsm2, a gene providing temperature-sensitive resistance to currently prevalent isolates of WSMV. However, one isolate, KSH294, was able to infect RonL and showed more virulence on two other varieties/lines containing Wsm2. Further sequence and phylogenetic analysis of KSH294 confirmed that this isolate displays a sequence homology with WSMV, but has sequence differences making it distinct from previously identified WSMV isolates included in the phylogenetic analysis.     

Chemical constituents of the essential oils of wild oat and crabgrass and their effects on the growth and allelochemical production of wheat

The interference of allelopathic weeds with crop plants might be mediated by volatile allelochemicals. In this study, the essential oil constituents of two weeds, wild oat (Avena fatua) and crabgrass (Digitaria sanguinalis), were investigated in relation to their effects on the growth and allelochemical production of wheat (Triticum aestivum). Subsequently, by means of gas chromatography and gas chromatography‐mass spectrometry, 52 compounds were identified from the crabgrass essential oil, particularly a signaling compound called methyl jasmonate, while 28 constituents were detected in the wild oat essential oil. Both essential oils were rich in terpenoids and inhibited the growth of wheat in air, filter paper and soil media but their inhibition varied with the growth medium and the weed species. In both the air and the filter paper media, there were not significant differences in the dry weight of wheat between the wild oat and the crabgrass essential oils. However, there was a greater reduction in the dry weight of the wheat root and plant with the wild oat essential oil than with the crabgrass essential oil in the soil medium. Furthermore, the production of the allelochemical, 2,4‐dihydroxy‐7‐methoxy‐1,4‐benzoxazin‐3‐one, in wheat was induced by the essential oils. The results suggest that allelopathic interference with wheat by wild oat and crabgrass affects not only the biomass allocation, but also the allelochemical production, of wheat.     

Residues of Mecoprop in Post-emergence-Treated Wheat and Oat

The dissipation of mecoprop in wheat (Triticum aestivum L.) and oat (Avena sativa L.) was monitored over a growing season following post-emergence application of the dimethylamine salt of mecoprop to each crop at 1·1 kg ha^?1. Residues of mecoprop, as its methyl ester, were determined gas chromatographically using electrolytic conductivity detection. Initial residues in wheat (119 (±20) mg kg^?1) and oat (95·3 (± 10·0) mg kg^?1) on the day of application (four-leaf stage of wheat and four- to five-leaf stage of oat) decreased to 0·1 to 0·2 mg kg^?1, respectively, within six weeks. Residues were non-detectable in the mature seed of both crops. Recoveries of mecoprop were in the order of 90% from the green tissue and seed of both crops fortified at 0·05 mg kg^?1.     

Observations on the host range of an isolate of Septoria nodorum from wheat

An isolate ofS. nodorum from wheat was inoculated onto grasses in the field. Re-isolates from these grasses were tested in a cross-inoculation experiment, performed in a growth chamber. The wheat isolate was pathogenic to each element of a set consisting ofElytrigia repens, Hordeum vulgare, Lolium perenne, Poa annua, andTriticum aestivum. Re-isolates from any of the elements of this set were pathogenic to all other elements. The effects of hosts and inoculum-density treatments were statistically significant. A significant isolate x host interaction suggests a form of specialization, which is possibly due to a passage effect. These observations may contribute to a better understanding of the epidemiology ofS. nodorum in the Netherlands.Samenvatting Grassen en granen te velde werden geïnoculeerd met eenS. nodorum isolaat van tarwe. Symptomen van aantasting door de schimmel werden gevonden opElytrigia repens, Hordeum vulgare, Lolium perenne, Poa annua enTriticum aestivum. Van deze vijf waardplanten werden her-isolaten gewonnen, die vervolgens in een klimaatkamer geinoculeerd werden op ieder van de vijf waardplanten. Aldus ontstond een kruisinoculatiematrix van bladaantastingspercentages (Tabel 2), die aan een variantieanalyse (Tabel 3) kon worden onderworpen. De volgende effecten waren significant: waardplanten, inoculumdichtheden, interactie herisolaat x waardplant, en interactie herisolaat x waardplant x inoculumdichtheid. De interacties suggereren beïnvloeding door de waardplant, dus een passage-effect. Bij passage over een waardplant zou enige mate van fysiologische specialisatie kunnen optreden. Dit wordt bevestigd door gegevens van Weber (Tabel 5). Deze waarnemingen over de waardplantreeks kunnen van belang zijn voor een beter begrip van de epidemiologie vanS. nodorum in Nederland.     

Selective regulation of germination and growth of annual weeds by crop residues

Residues from mature, harvested crops of sorghum (Sorghum bicolor Moench.), sunflower (Helianthus annuus L.), oilseed rape (Brassica napus L.), wheat (Triticum aestivum L.) and field pea (Pisum sativum L.), exhibited selective effects on weed germination and growth under field conditions. Weed species in the study included Avena fatua L., Avena sterilis ssp. ludoviciana (Durieu) Nyman, Echinochloa crus-galli (L.) Beauv., Phalaris aquatica L., Phalaris paradoxa L., Lolium perenne L., Vulpia myuros (L.) Gmel., Hibiscus trionum L., Polygonum aviculare L., Bilderdykia convolvulus (L.) Dumort. and Lamium amplexicaule L. All crop residues tested, and in particular wheat and pea residues, promoted the germination and growth of A. fatua and A sterilis ssp. ludoviciana. Other grass weeds, however, were inhibited by the presence of crop residue, the extent of inhibition being dependent on residue type. Germination response of dicotyledonous weed species was also a function of residue type, H. trionum numbers were significantly higher in plots where oilseed rape, sorghum or sunflower residue had been incorporated, while L. amplexicaule was inhibited by these residue types and stimulated by pea and wheat residues.