Involvement of a vascular hypersensitive response in quantitative resistance to Ralstonia solanacearum on tomato rootstock cultivar LS‐89

Ralstonia solanacearum causes bacterial wilt disease in Solanaceae spp. Expression of the Phytophthora inhibitor protease 1 (PIP1) gene, which encodes a papain‐like extracellular cysteine protease, is induced in R. solanacearum‐inoculated stem tissues of quantitatively resistant tomato cultivar LS‐89, but not in susceptible cultivar Ponderosa. Phytophthora inhibitor protease 1 is closely related to Rcr3, which is required for the Cf‐2‐mediated hypersensitive response (HR) to the leaf mould fungus Cladosporium fulvum and manifestation of HR cell death. However, up‐regulation of PIP1 in R. solanacearum‐inoculated LS‐89 stems was not accompanied by visible HR cell death. Nevertheless, upon electron microscopic examination of inoculated stem tissues of resistant cultivar LS‐89, several aggregated materials associated with HR cell death were observed in xylem parenchyma and pith cells surrounding xylem vessels. In addition, the accumulation of electron‐dense substances was observed within the xylem vessel lumen of inoculated stems. Moreover, when the leaves of LS‐89 or Ponderosa were infiltrated with 10⁶ cells mL^?1 R. solanacearum, cell death appeared in LS‐89 at 18 and 24 h after infiltration. The proliferation of bacteria in the infiltrated leaf tissues of LS‐89 was suppressed to approximately 10–30% of that in Ponderosa, and expression of the defence‐related gene PR‐2 and HR marker gene hsr203J was induced in the infiltrated tissues. These results indicated that the response of LS‐89 is a true HR, and induction of vascular HR in xylem parenchyma and pith cells surrounding xylem vessels seems to be associated with quantitative resistance of LS‐89 to R. solanacearum.     

Antifungal effect and reduction of <Emphasis Type="Italic">Ulmus minor</Emphasis> symptoms to <Emphasis Type="Italic">Ophiostoma novo-ulmi</Emphasis> by carvacrol and salicylic acid

There are still no effective means to control Dutch elm disease (DED), caused by the vascular fungi Ophiostoma ulmi and O. novo-ulmi. Plant phenolics may provide a new strategy for DED control, given their known antifungal activity against pathogens and their involvement in plant defence mechanisms. The in vitro antifungal activity of salicylic acid, carvacrol, thymol, phenol, o-cresol, m-cresol, p-cresol, and 2,5-xylenol against the DED pathogens was tested. Also, the protective effect of watering Ulmus minor seedlings with these compounds was tested against O. novo-ulmi. Salicylic acid, carvacrol, and thymol showed the strongest antifungal in vitro activity, while carvacrol and salicylic acid provided the strongest in vivo protection against O. novo-ulmi (63 and 46% reduction of leaf wilting symptoms with respect to controls, respectively). The effect of the treatments on tree phenology was low, and a significant negative relation was observed between the number of days to bud burst and the leaf wilting symptoms after inoculation, probably determined by genetic differences among the elm tree progenies used. The treatments with salicylic acid, carvacrol and thymol induced the highest shift in phenolic metabolite profile with respect to control trees. The protective effect of carvacrol and salicylic acid is discussed in terms of their combined activity as antifungal compounds and as inductors of tree defence responses.     

Dutch elm disease in New Zealand: impacts from eradication and management programmes

Ophiostoma novo‐ulmi, the cause of the current pandemic of Dutch elm disease, is considered one of the 20 worst pests to have been introduced to New Zealand. An attempt to eradicate the pathogen came close to success, but was eventually stopped and replaced by management programmes. These programmes are slowing the spread of the pathogen. If left uncontrolled it is likely that New Zealand will lose 90% of its elm trees. Although elms are exotic trees in New Zealand, the loss of such a large number of popular amenity trees is likely to have numerous social, cultural, environmental and economic effects. It is estimated that this disease could cost public and councils over NZD $350 million in tree removal and replacement costs. Control of O. novo‐ulmi is limited, but biological control using d‐factor viruses has been proposed. Although O. novo‐ulmi was not eradicated from New Zealand, the eradication programme had many successes; in particular, the effective interaction of good management and science in the early years of the campaign. Also highlighted in this review are several tactics and steps that could be applied to eradication attempts for other species.     

Is there evidence for post-epidemic attenuation in the Dutch elm disease pathogen Ophiostoma novo-ulmi?

The first pandemic of Dutch elm disease (DED) in Europe and North America caused by the introduced Ophiostoma ulmi began in the early 1900s but declined unexpectedly in Europe from the 1930s onwards after killing 30–40% of the elms. Later a second pandemic caused by the much more aggressive Ophiostoma novo-ulmi spread across the same areas and by 1990 most of Britain's c. 30 million mature elms had died. During the second pandemic, O. novo-ulmi acquired debilitating viruses and changed from being largely clonal to highly heterogeneous through horizontal transfer of novel, sometimes deleterious, genes from O. ulmi. In the post-epidemic period a new disease dynamic has emerged, with millions of small recruitment elms repeatedly attacked by sequential cycles of disease. This study investigated the possibility of pathogenic attenuation in O. novo-ulmi as the epidemic has progressed. Isolates collected from the three original outbreak areas in Britain in 1982–3 (early post-epidemic period) and 2011 (advanced post-epidemic) were compared for two fitness components: pathogenic aggressiveness and in vitro growth rate. Mean aggressiveness of the 2011 isolates to clonal English elm (Ulmus procera) proved not to differ significantly from that of the 1982 isolates, either overall or within each outbreak area. Similarly, the mean growth rates of the 1982 and 2011 samples showed no differences. The implications of these findings are discussed in relation to the future of the current DED pandemic in Europe, the decline of the first pandemic, and the difficulty of drawing parallels between different tree–pathogen systems.     

Length and diameter of xylem vessels as factors in resistance of elms to Ceratocystis ulmi

Conductivity of the vascular system of 2-year-old shoots as regards air and water was higher in susceptible than in resistant elms. The xylem vessels of resistant elms were relatively shorter and the percentage of short vessels was greater than in susceptible elms. The percentage of vessels with a large diameter was smaller in resistant elms than in susceptible ones. These results might explain the limited spreading of the spores in the new annual ring of resistant elms.Samenvatting Tweejarige scheuten van resistente iepen bleken lucht en water minder snel door te laten dan vergelijkbare scheuten van vatbare iepen. De vaten bij resistente iepen waren relatief kort en het percentage korte vaten was groter dan bij vatbare iepen. Het percentage grote vaten was kleiner bij resistante iepen dan bij vatbare. Dit zou een verklaring kunnen zijn voor de relatief geringe verspreiding van de sporen in de nieuwe jaarring van de resistente iepen.     

Analysis of Spanish populations of Ophiostoma ulmi and O. novo-ulmi using phenotypic characteristics and RAPD markers

One hundred and six isolates of the Dutch elm disease (DED) fungi Ophiostoma ulmi and Ophiostoma novo-ulmi were collected from elm trees with symptoms in 15 regions of Spain. Isolates were compared with eight reference strains belonging to O. ulmi and the two subspecies of O. novo-ulmi. The purpose of this study was to assign Spanish isolates to species and subspecies of the DED fungi and to analyse the genetic variability within the Spanish populations of these pathogens. Isolates were examined for their growth rates, colony morphologies and fertility responses and by using random amplified polymorphic DNA (RAPD) markers. Six isolates were identified as O. ulmi , 16 as O. novo-ulmi ssp. novo-ulmi and 78 as O. novo-ulmi ssp. americana . Nei's and Shannon's diversity indices and the upgma dendrogram from RAPD profiles indicated a high level of variation among isolates, probably reflecting post-epidemic status of DED in Spain. Although most isolates were separated into three major clusters representing the three taxa of DED fungi in the RAPD analysis, two isolates from central Spain clustered between O. novo-ulmi ssp. americana and O. novo-ulmi ssp. novo-ulmi , and four isolates from Mallorca clustered between O. ulmi and the group representing O. novo-ulmi ssp. novo-ulmi . Mating tests conducted with these isolates revealed a variety of fertility responses. The novel combinations between molecular profile and fertility reaction suggest that three isolates from Mallorca may be interspecific hybrids of the DED fungi.     

Vulnerability to drought-induced cavitation in shoots of two typical shrubs in the southern Mu Us Sandy Land,China

Salix psammophila and Caragana korshinskii are two typical shrubs in the southern Mu Us Sandy Land of China which are threatened by increasing water deficits related to climate change and large-scale human activities(e.g. coal mining and oil exploitation). In this study, we assessed their vulnerability to xylem embolism and the related anatomical traits in two-year-old regenerated shoots of these two shrubs to understand how they cope with drought environment. We also evaluated the in situ hydraulic safety margins to hydraulic failure from measurements of annual predawn and midday leaf water potentials. The results showed that S. psammophila stems had a higher water transport capacity than C. korshinskii stems. The stem xylem water potentials at 12%, 50% and 88% loss of conductivity were –1.11, –1.63 and –2.15 MPa in S. psammophila, respectively, and –1.37, –2.64 and –3.91 MPa in C. korshinskii, respectively. This suggested that C. korshinskii was more resistant to cavitation than S. psammophila. Compared with S. psammophila, C. korshinskii had shorter maximum vessel length, lower vessel density, smaller conductive area and higher wood density, which may contribute to its more resistant xylem. The in situ hydraulic safety margins indicated that even during the driest periods, both shrubs lived well above the most critical embolism thresholds, and the hydraulic safety margin was wider in C. korshinskii than in S. psammophila, suggesting that the regenerated shoots of both shrubs could function normally and C. korshinskii had greater hydraulic protection. These results provide the basis for an in-depth understanding of the survival, growth and functional behavior of these two shrubs under harsh and dry desert environments.     

A rapid virulence assay for the Dutch elm disease fungus Ophiostoma novo‐ulmi by inoculation of apple (Malus × domestica ‘Golden Delicious’) fruits

Large‐scale virulence tests using trees or saplings are expensive, time‐consuming and require a considerable amount of space. The suitability of using ‘Golden Delicious’ apples as a rapid screen for identifying Ophiostoma novo‐ulmi transformants with reduced virulence was thus evaluated. When a collection of O. novo‐ulmi field isolates belonging to subspecies novo‐ulmi or americana was inoculated to apples, members of subsp. novo‐ulmi induced, on average, larger necrotic lesions than subsp. americana isolates. The size of the lesions on apples was not correlated with mycelial growth rate of isolates on nutrient agar. Insertional mutants from O. novo‐ulmi subsp. novo‐ulmi isolate H327 were inoculated to ‘Golden Delicious’ apples and Ulmus parvifolia × U. americana saplings in parallel experiments. Results clearly indicated that the O. novo‐ulmi transformants included several exhibiting significantly altered levels of virulence. Variability among replicates within a treatment was reduced in apple inoculation data compared to elm sapling data. Overall, the ‘Golden Delicious’ apple assay was found to be an excellent means for rapidly assessing the virulence level of O. novo‐ulmi isolates.     

RNA silencing of PEX6 gene causes decrease in pigmentation,sporulation and pathogenicity of Fusarium oxysporum

Peroxisomes are single membrane‐bound organelles that play a pivotal role in various developmental processes in all eukaryotic cells. This study targeted the PEX6 gene, which encodes for peroxisomal biogenesis factor 6, by RNA interference (RNAi) in Fusarium oxysporum f. sp. lycopersici. Fusarium oxysporum is a soilborne filamentous, hemibiotrophic fungus that invades tomato roots and colonizes the xylem vessels, thereby causing complete wilting of infected tomato plants. The expression of FoPEX6 in F. oxysporum was found to be higher during early stages of growth and development. The FoPEX6 gene was isolated and a hairpin RNAi construct was prepared and introduced into F. oxysporum 4471 through glass‐bead transformation. The fungal transformation status, i.e. integration, expression and presence of the intended small interfering RNAs (siRNAs), was confirmed by PCR, qPCR and stem‐loop PCR, respectively. The silenced fungal transformants exhibited reduced pigmentation and a significant reduction in sporulation as compared to the wild type. They also showed dramatic reduction in pathogenicity (virulence) on tomato, based on root infection and fruit invasion assays. These results suggest that PEX6 has a central role in pigmentation, sporulation and pathogenicity in F. oxysporum.     

Anatomical factors in resistance to Dutch elm disease

The localizing of pathogen (Ceratocystis ulmi) establishment in Dutch elm disease-resistant hosts is hypothesized as the major mechanism of resistance to this disease. Four factors are proposed that, singly or in all possible combinations, could regulate this general mechanism. We tested one of these factors, vessel size and number of contiguous vessels in the functional xylem at the point of natural inoculation. Using 23 selections from the Ulmaceae, we examined a constant area of second-year xylem of 2-year-old twigs. These anatomical data indicate that a correlation exists between increasing disease susceptibility and increasing vessel group size (the product of average vessel diameter and average number of contiguous vessels). Other evidence suggests that lateral pathogen movement is at first confined to the vessel group or groups of initial inoculation. Therefore, in a given limited time period, tylosis production could more effectively block vertical pathogen movement in vessel groups of small size. Relationships between vessel group size and the extent of sapwood discoloration are discussed. Vessel size and arrangement also is discussed in relationship to the resistance reported for young, greenhouse-grown trees. The use of vessel group size is suggested in screening programs for disease resistance. Recent research on oak suggests chemical modification of xylem tissue to lessen elm susceptibility.Samenvatting Als hypothese wordt gesteld, dat resistentie tegen de iepeziekte in de eerste plaats berust op het vermogen van resistente gastheren om de uitbreiding van de ziekteverwekker (Ceratocystis ulmi) te beperken. Er worden vier factoren genoemd die (alleen of in combinatie) dit vermogen zouden bepalen. Een van de vier werd getoetst, en wel afmeting van vaten en aantal aaneengrenzende vaten in de buitenste jaarring op de plaats waar natuurlijke infecties plaatsvinden. Er werden 22 iepeselecties en één andere Ulmacee gebruikt, waarin de vaten gemeten en geteld werden in een constant oppervlak van de dwarsdoorsnee van het tweede-jaars-hout van twee jaar oude twijgen. Deze anatomische gegevens tonen een correlatie tussen toenemende vatbaarheid voor de ziekte en toenemende vaatgroepgrootte, die hier gedefinieerd is als het produkt van de gemiddelde vatdiameter en het gemiddelde aantal aaneengrenzende vaten (zie Tabel 4). Uitbreiding van de schimmel in dwarsrichting van de boom is om te beginnen beperkt tot die vaatgroepen die oorspronkelijk geïnfecteerd waren. Daarom zal de uitbreiding van de schimmel in de lengterichting met meer effekt door thyllen geblokkeerd kunnen worden in vaatgroepen van geringere grootte.De verhouding tussen vaatgroepgrootte en mate van houtverkleuring na infectie wordt besproken. Grootte en rangschikking van vaten wordt ook genoemd in verband met een zekere mate van resistentie van jonge, in de kas opgekweekte bomen. Het gebruik van vaatgroepgrootte wordt voorgesteld als een maatstaf bij het selecteren van resistente individuen uit grote populaties. Recent onderzoek over het effect van de stof TCPA op de anatomie van eiken suggereert dat het mogelijk is met chemicaliën de opbouw van het houtweefsel van iep te wijzigen en zodoende zijn vatbaarheid voor de iepeziekte te verkleinen.Journal Paper No. J-6392 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 1706. Appears also as Mededeling 106 of the Forest Research Station De Dorschkamp.     

Fire blight. Why do views on host invasion by Erwinia amylovora differ?

The fire blight pathogen, Erwinia amylovora, commonly infects flowers and shoots of certain rosaceous hosts and systemic (whole‐tree) invasion sometimes follows. The bacterium may be found in the parenchyma of bark tissue and/or in mature xylem vessels of stem tissue. Views differ on initial sites of multiplication and the optimal route for systemic migration. This article presents the evidence on which the different views are based. There are limited observations on orchard pear and apple trees; in most experimental studies, young apple shoots on potted plants were used. Tissue maturity at the site of shoot inoculation is of prime importance. If xylem vessels are damaged, inoculum may be sucked into the vessels and the bacteria will multiply there. In younger tissue, there is less suction pressure. The critical stem entry site for the invasion of cortical parenchyma seems to be near or above the most recently unfolded leaf. No one has suggested that migration in bark tissue cannot be a major route. If the xylem route is followed, the pathogen needs a means of escape into bark tissue, where typical symptoms develop; means of escape from mature xylem vessels have not been demonstrated and remain a matter for speculation. Published evidence does not seem to support the idea that fire blight is a vascular wilt disease, nor that the extracellular polysaccharide produced by E. amylovora is a toxin and responsible for the wilting symptom seen in the early stages of the disease.     

Multiple resistance of Papaver rhoeas L. to 2,4‐D and acetolactate synthase inhibitors in four European countries

The issue of cross‐ or multiple resistance to acetolactate synthase (ALS) inhibitors and the auxinic herbicide 2,4‐D was investigated in Papaver rhoeas L., a common and troublesome weed in winter cereals, in a broad‐scale study across four European countries. A combination of herbicide sensitivity bioassays and molecular assays targeting mutations involved in resistance was conducted on 27 populations of P. rhoeas originating from Greece (9), Italy (5), France (10) and Spain (3). Plants resistant to the field rate of 2,4‐D were observed in 25 of the 27 populations assayed, in frequencies ranging from 5% to 85%. Plants resistant to ALS‐inhibiting herbicides (sulfonylureas) were present in 24 of the 27 populations, in frequencies ranging from 4% to 100%. Plants resistant to 2,4‐D co‐occurred with plants resistant to sulfonylureas in 23 populations. In four of these, the probability of presence of plants with cross‐ or multiple resistance to 2,4‐D and sulfonylureas was higher than 0.5. ALS genotyping of plants from the field populations or of their progenies, identified ALS alleles carrying a mutation at codon Pro197 or Trp574 in 2,4‐D‐sensitive and in 2,4‐D‐resistant plants. The latter case confirmed multiple resistance to 2,4‐D and ALS inhibitors at the level of individual plants in all four countries investigated. This study is the first to identify individual plants with multiple resistance in P. rhoeas, an attribute rarely assessed in other weed species, but one with significant implications in designing chemical control strategies.     

Differences in the responses of melon accessions to fusarium root and stem rot and their colonization by Fusarium oxysporum f. sp. radicis‐cucumerinum

Fusarium root and stem rot caused by the fungus Fusarium oxysporum f. sp. radicis‐cucumerinum is a major disease in greenhouse cucumbers. Over the past decade, the disease has been documented in melon greenhouses in Greece, and recently it has been sporadically recorded in greenhouse melons in Israel. Variations in disease response were found among 41 melon accessions artificially inoculated with the pathogen: 10 accessions were highly susceptible (90–100% mortality), 23 exhibited an intermediate response (20–86%) and eight were resistant (0–4%). Two melon accessions – HEM (highly resistant) and TAD (partially resistant) – were crossed with the susceptible accession DUL. The responses of the three accessions and F₁ crosses between the resistant and susceptible parents were evaluated. HEM contributed higher resistance to the F₁ hybrid than TAD. Roots of susceptible and resistant accessions were 100 and 79% colonized, respectively, following artificial inoculation. However, only susceptible plants showed colonization of the upper plant tissues. Microscopic evaluation of cross sections taken from the crown region of the susceptible DUL revealed profuse fungal growth in the intercellular spaces of the parenchyma and in xylem vessels. In the resistant cultivar HEM, very little fungal growth was detected in the intercellular spaces of the parenchyma, and none in the xylem or any other vascular tissue. Finding resistant accessions may create an opportunity to study the genetics of resistance inheritance and to develop molecular markers that will facilitate breeding resistant melon cultivars.     

新疆榆树黄萎病病原菌鉴定

2013年以来,在石河子大学农学院试验站榆树苗上,出现了一种病害,可导致叶片褪绿,变黄,萎蔫,甚至枯死,剖茎检查可见维管束变成褐色。采用常规组织分离法对病茎组织进行分离、纯化获得单孢纯培养菌株;通过常规纸钵撕底蘸根法对其进行致病性测定;用形态学和rDNA-ITS序列分析方法对病原菌进行鉴定。结果表明,分离菌株的菌落形态、分生孢子梗和分生孢子的形态都与大丽轮枝菌(Verticillium dahliae)一致;经分子生物学鉴定,该菌的rDNA-ITS序列与中国棉花黄萎病菌(V.dahliae)的ITS序列(登录号EU 835817.1)相似性达99.0%,故将引起新疆榆树黄萎病的病原菌鉴定为大丽轮枝菌(V.dahliae)。     

Assessment of Pierce's disease susceptibility in Vitis vinifera cultivars with different pedigrees

Pierce's disease (PD) of grapevine is caused by the bacterium Xylella fastidiosa. In this study, an integrated approach was applied to assess PD susceptibility among different Vitis vinifera cultivars that incorporated disease severity, bacterial pathogen abundance and loss of stem xylem hydraulic conductivity. It was hypothesized that levels of PD susceptibility in V. vinifera can be attributed in part to the host anatomical features that are shaped by its pedigree background. Two popular wine grape cultivars were initially selected from the occidentalis group, Merlot and Cabernet Sauvignon, and one from the orientalis group, Thompson Seedless. The more recently bred table grape cultivar Scarlet Royal, that has mixed pedigree parentage, was also included. PD susceptibility was compared to the known PD resistant b43-17 V. arizonica/candicans wild grape species from North America. The data indicated that Thompson Seedless was ranked as the most susceptible to PD because it significantly exhibited the most severe disease symptoms at 12 weeks post-inoculation and hosted the highest X. fastidiosa titre of the cultivars, and lost over 90% of its stem hydraulic conductivity. In contrast, the other three cultivars displayed less susceptibility to PD. The way in which the xylem anatomy could impact PD susceptibility in V. vinifera cultivars is discussed, together with how grape pedigrees and their cognate centre of domestication may have influenced xylem anatomical features. This work provides a reference framework to further test the hypothesis that V. vinifera cultivars with wide xylem vessels may be more prone to PD decline.     

Field response of near‐isogenic brown midrib sorghum lines to fusarium stalk rot,and response of wildtype lines to controlled water deficit

To increase digestibility for ruminant livestock and for lignocellulosic ethanol conversion efficiency in sorghum (Sorghum bicolor), brown midrib (bmr) lines carrying bmr6 or bmr12 and the double mutant (bmr6 bmr12) in two backgrounds (RTx430 and Wheatland) were developed, resulting in lines with significantly reduced lignin, as compared with the near‐isogenic wildtype. Under greenhouse conditions, these lines had previously demonstrated no increased susceptibility, and some lines were more resistant to the highly virulent stalk rot pathogen, Fusarium thapsinum, compared to the wildtype. Fusarium stalk rot of sorghum is a destructive disease that under high temperatures or drought conditions may lead to lodging. To determine if greenhouse observations could be extended to field environments, bmr and near‐isogenic wildtype lines were inoculated with F. thapsinum at field locations, Mead (irrigated) and Havelock (dryland) in Nebraska, USA. Analysis of mean lesion lengths showed those of most bmr lines were statistically similar to the wildtype. Across both genetic backgrounds, bmr6 and bmr6 bmr12 double mutant plants grown at Mead had significantly smaller mean lesion lengths than the corresponding wildtype (P ≤ 0.05). To assess responses of the two genetic backgrounds to controlled (greenhouse) water stress, wildtype RTx430 and Wheatland plants were inoculated with F. thapsinum under well‐watered and water stress conditions. Mean lesion lengths resulting on water deficit plants were significantly larger than those on well‐watered plants (P = 0.01). These results indicate that this bioassay can be used to screen sorghum lines in the greenhouse for increased resistance or tolerance to both drought and fusarium stalk rot.     

Significant in vitro antagonism of the laurel wilt pathogen by endophytic fungi from the xylem of avocado does not predict their ability to control the disease

The ascomycete Raffaelea lauricola causes laurel wilt, a lethal vascular disease of avocado, Persea americana, and other members of the Lauraceae plant family. Few effective control measures for laurel wilt exist and new measures are needed. In this study, biological control of the disease with endophytic fungi from avocado was examined. Thirty‐two endophytes (24 operational taxonomic units or OTUs) isolated from the xylem of healthy trees (the infection court of R. lauricola) were evaluated against R. lauricola with in vitro dual‐culture assays. Nine OTUs that showed strong in vitro antagonism of the pathogen were tested in planta against laurel wilt. In three greenhouse experiments, grafted avocado plants of Simmonds or Russell cultivars, which are both susceptible to laurel wilt, were inoculated with endophytes and, after 10–16 days, inoculated with the same isolate of R. lauricola that was used in the in vitro assays. Within 14 days of inoculation with R. lauricola, laurel wilt developed in plants that were not treated with endophytes (positive controls) but also developed in endophyte‐treated plants to the extent observed in the positive controls (P = 0.05). The pathogen colonized plants rapidly and systemically, but endophytes generally did not colonize xylem more than 2 cm above the point at which plants were inoculated. Although the tested endophytes strongly antagonized the pathogen in vitro, this did not translate to an ability to reduce development of laurel wilt. The management of laurel wilt and other plant diseases with fungal endophytes is discussed.     

Sanitation campaign against Ceratocystis ulmi in The Netherlands1

The introduction and rapid spread of the aggressive strain of Ceratocystis ulmi in The Netherlands led to development of a 100% subsidised nationwide felling campaign. Since 1978, all elms have been assessed twice a year for health and viability, and diseased trees have been destroyed within a month. This limited losses to 1% of the important elm clones planted along roads, but at high annual cost (6 million F1) because of the need also to destroy diseased field elms. In future, long-term costs will be reduced by destruction of the less important field elms in the west of the country. In the east, the campaign has been abandoned (with some exceptions round cities).