Enchytraeids and nematophagous fungi in tomato fields and vineyards

ABSTRACT I tested the hypothesis that exclusion of enchytraeids and microarthropods in agricultural fields improves establishment of two nematophagous fungi. Soil was collected from three tomato fields and two vineyards and either heat-treated (2 h at 60 degrees C) or not. Alginate pellets containing hyphae of the fungi Hirsutella rhossiliensis or Monacrosporium gephyropagum were added to the soil, which was packed into cages (PVC pipe, 80-cm(3) volume) sealed with fine (20 mum) or coarse (480 mum) mesh. Cages were buried 22 cm deep in the same fields from which the soil had been collected. After 7 to 50 days, the cages were recovered and fungi and fauna quantified. Fine mesh largely excluded enchytraeids, collembolans, and mites but rarely affected fungus numbers. In contrast, heat treatment of soil rarely affected enchytraeids, collembolans, or mites but frequently increased fungus numbers, regardless of mesh size. The data are inconsistent with the initial hypothesis but are consistent with the idea that organisms narrower than 20 mum interfere with fungal growth from the pellets.     

Prevalence, polyphasic identification, and molecular phylogeny of dagger and needle nematodes infesting vineyards in southern Spain

The occurrence and geographic distribution of longidorid nematode species inhabiting the rhizosphere of grapevine plants in southern Spain were investigated. Nematode surveys were conducted on 77 vineyards during the spring seasons of 2006, 2007 and 2008 in the main Andalusian grapevine-growing areas, including the provinces of Cádiz, Córdoba, and Huelva. Morphological and morphometrical studies identified two Longidorus and nine Xiphinema species, viz.: Longidorus alvegus, L. magnus, Xiphinema adenohystherum, X. hispidum, X. index, X. italiae, X. lupini, X. nuragicum, X. pachtaicum, X. rivesi, and X. turcicum. Overall, frequencies of infestation were, in decreasing order: X. pachtaicum 90.8%, X. index 30.3%, X. italiae 13.2%, L. magnus 11.8%, X. hispidum 7.9%, X. lupini 3.9%, L. alvegus and X. rivesi 2.6%, and X. adenohystherum, X. nuragicum and X. turcicum 1.3%. Xiphinema hispidum, X. lupini, L. alvegus and L. magnus were compared with nematode type specimens and are reported for the first time in Spain. Furthermore, the male of L. alvegus is described for the first time in the literature. Molecular characterisation of these species using D2–D3 expansion regions of 28S rRNA, 18S rRNA and ITS1-rRNA was carried out and maximum likelihood and Bayesian inference analysis were used to reconstruct phylogenetic relationships among these species and with other longidorids. The monophily of the genera Xiphinema and Longidorus was accepted and the genera Paralongidorus and Xiphidorus were rejected by the Shimodaira-Hasegawa test based on tree topologies.     

Distribution of grapevine leafroll associated virus-3 variants in South African vineyards

Three genetic variants of Grapevine leafroll-associated virus 3 (GLRaV-3) were identified from vineyards of the Western Cape, South Africa. In a previous study, three full genome sequences of isolates representing each of the variant groups were determined. The three variant groups were represented by accessions 621, 623 and PL-20, of variant groups I, II and III respectively. A specific single strand conformation polymorphism (SSCP) profile was assigned to each variant which was used as a quick, reliable detection and differentiation method. In this study we analysed the occurrence of these three GLRaV-3 variants in mother blocks in different cultivars and from different vine growing regions using SSCP. The majority of the plants studied, were infected with the group II variant, similar to isolates 623 and GP18. The distribution of three GLRaV-3 variants within a spatio-temporally recorded cluster of diseased plants was studied by means of SSCP profile analysis of ORF5 amplified PCR products. We showed that different GLRaV-3 variants are transmitted to adjacent plants in an infection cluster. Results showed that, in some leafroll disease clusters, the variant that was present in the original GLRaV-3 infected plant of a cluster was transmitted to adjacent plants in a row and across rows.     

Insights into the epidemiology of Pierce's disease in vineyards of Mallorca,Spain

Xylella fastidiosa (Xf), the causal agent of Pierce's disease (PD), has long been considered a major threat to prosperous European viticulture. In May of 2017, PD was officially detected on a grapevine in Mallorca. To better understand the epidemiology of the first established outbreak of PD in Europe, the disease incidence and severity were assessed, vector transmission experiments were performed, and cultivar responses to Xf infections both in the field and in inoculation experiments were monitored. The genetic structure of Xf local populations was also investigated by multilocus sequence typing analysis, and their whole genome sequences and phylogenetic positions compared with respect to PD strains worldwide. Disease incidence was moderately low (0.07) and highly variable, ranging from 0.0 to 0.99. Its economic impact on wine production was considered low. Vineyards managed under conventional viticulture were significantly less infected than organic farming. Under greenhouse conditions, the insect Philaenus spumarius efficiently transmitted the pathogen from infected to healthy grapevines. In the inoculation experiments, Xf infected, to some degree, 29 of the 30 cultivar × rootstock combinations (n = 239). Cultivars Viura, Gorgollasa and Sauvignon Blanc were the most susceptible ones. All Xf isolates from grapevines belonged to sequence type ST1; they phylogenetically clustered within the Californian ST1 clade, with which they shared a 99.94% identity and the same plasmid. In addition, ST1 caused almond leaf scorch disease, where notably its incidence (0.78) and severity was much higher than PD. The likely reasons for these wide differences are discussed in the context of a 20-year Xf introduction scenario.     

Impact of molecular phylogenetics on the taxonomy and diagnostics of fungi*

Most phytosanitary inspections rely on a visual ‘disease‐free’ inspection, and the question is raised whether this is sufficient, given the fact that plant pathogenic fungi may enter countries as endophytes, or latent pathogens in apparently healthy tissue. Inspectors mostly deal with lists of names of fungal species, but many pathogens are in fact species complexes, and pest lists rarely remain up to date with respect to new systematic treatments. Pathogens may also introduce new genetic diversity or mating types, which could be as devastating as the introduction of a new pathogen. It is therefore proposed that an international initiative should be funded to ensure that systematic support, accurate nomenclature, genetic material and genomic data are available to assist NPPOs in their task.     

High genotypic and virulence diversity in Ilyonectria liriodendri isolates associated with black foot disease in New Zealand vineyards

A total of 57 Ilyonectria liriodendri isolates were identified by a combination of species‐specific PCR and DNA sequencing from a collection of 174 Ilyonectria‐like isolates recovered from 101 diseased grapevine samples. These samples were representative of the national vineyard, comprising material contributed by 49 grape growers across seven grape growing areas. This species was predominant, representing 33% of the recovered isolates, and has been reported as a major pathogen of grapevines in other countries. The genetic diversity of the 57 New Zealand isolates was compared to that of isolates from Australia and South Africa using universally primed polymerase chain reaction (UP‐PCR). A total of 66 informative loci distinguished 52 genotypes, of which five contained up to four clonal isolates. Four main clades were identified in a neighbour‐joining (NJ) tree. The international isolates (Australia and South Africa) were placed in a clade that did not include New Zealand isolates. There was a high level of intra‐ and inter‐vineyard genetic variation indicating the free movement of isolates between regions. A subset of nine isolates from different branches of the NJ tree produced two vegetative compatibility groups and hyphal fusion was observed between non‐self pairings. Pathogenicity tests using isolates from different genetic groups inoculated onto either detached roots or 1‐year‐old potted vines showed variability in virulence; however, no correlations were detected.     

Isolation and identification of hyperparasitic fungi associated with Erysiphaceae

In the vicinity of Bonn a limited survey was conducted on the occurrence of hyperparasites on powdery mildew species on some Papilionaceae. Eight parasitic fungi were isolated among whichDissoconium aciculare, a hitherto unknown deuteromycete.Samenvatting In de omgeving van Bonn (Bondsrepubliek Duitsland) werd een onderzoek verricht naar het voorkomen van hyperparasieten van soorten van echte meeldauw. Acht parasitaire schimmelsoorten werden geïsoleerd, waaronderDissoconium aciculare, een tot nu toe nog niet beschreven deuteromyceet.     

Cryptic diversity,multilocus phylogeny,and pathogenicity of cercosporoid fungi associated with common bean and cowpea

In recent years, common bean (Phaseolus vulgaris) and cowpea (Vigna unguiculata) plants in the north of Iran have exhibited symptoms resembling Cercospora leaf spot (CLS) disease. This study was initiated to elucidate the taxonomy and pathogenicity of cercosporoid taxa associated with leaf spot diseases of these two legume crops in Iran. A total of 138 samples with CLS symptoms were collected from cultivated common bean and cowpea species in northern Iran and subjected to microscopic examination, resulting in identification of 98 Cercospora and 59 Pseudocercospora samples. A six-locus phylogenetic analysis (ITS, actA, tef1, gapdh, his3, and cmdA) coupled with examination of the morphology of 42 representative isolates from these samples confirmed that several cercosporoid fungi occur on common bean and cowpea in Iran. Five Cercospora species (C. iranica, C. cf. flagellaris, Cercospora sp. G, Cercospora sp. T, and C. vignigena) and two Pseudocercospora species (P. griseola f. griseola and P. cf. cruenta) were found; of these, C. cf. flagellaris was the dominant species, occurring on both common bean and cowpea. Pathogenicity tests confirmed that all seven species could infect leaves of common bean and/or cowpea. This is the first report of C. iranica, Cercospora sp. G, and Cercospora sp. T associated with common bean and/or cowpea in the world. In addition, C. vignigena was recorded for the first time in Iran. Results achieved in this study will assist strategies for the management of CLS disease of common bean and cowpea.     

Agrometeorology,modelling and forecasting within IPM in horticultural crops and vineyards1

This summary presents the real possibilities for the use of agrometeorology in achieving IPM in horticultural crops and vineyards, and also the problems. Some examples of the practical application of forecasting models for fungal and insect pests are used to document the usefulness of this recently improved approach to modern phytotherapy, which aims to increase the effectiveness of treatments while simultaneously reducing their number. In this way one can obtain a reduced impact of chemical pollution on man and the environment. However, the practical requirements of IPM programmes must be emphasized and these set the standard for the type, quantity and quality of the meteorological data input. The contribution of biotic factors is compared with that of abiotic ones. Finally, the present needs of agrometorology in IPM are focused, with an outline of its future perspectives.     

Colonization of Vitis spp. wood by sGFP-transformed Phaeomoniella chlamydospora, a tracheomycotic fungus involved in Esca disease

To evaluate wood colonization and interactions with Vitis spp. of Phaeomoniella chlamydospora, a fungal agent involved in Esca disease, isolate CBS 229.95 was transformed using a pCT74 construct which contained the genetic markers for synthetic green fluorescent protein (sGFP) and hygromycin B phosphotransferase. Nine stable P. chlamydospora fungal transformants (Pch-sGFP lines) were obtained using polyethylene-glycol-mediated transformation of protoplasts. These were characterized for sgfp and hygromycin B phosphotransferase (hph) genome insertions and for sGFP fluorescence emission, using quantitative polymerase chain reaction and fluorimetric systems, respectively. No correlation was observed between sgfp copy number genome insertion and sGFP fluorescence expression. Cuttings of Vitis vinifera 'Montepulciano', 'Verdicchio', 'Sangiovese', 'Biancame', and 'Cabernet Sauvignon'; and the grapevine rootstocks 'Kober 5BB', 'SO4', '420A', '1103P', and V. rupestris were inoculated by immersion in a conidial suspension of the selected fungal Pch-sGFP71 line and incubated at 4 ± 1 and 25 ± 1°C. Wood colonization was estimated through epifluorescence microscopy and was affected by incubation temperature. After 6 months at 4 ± 1°C, the fungal growth was completely inhibited. At 25 ± 1°C, the highest extent of wood colonization was recorded in Montepulciano and Verdicchio, with the lowest in the rootstocks SO4 and V. rupestris. The expression of the Pch-sGFP71 transformed line was localized in the xylem area, primarily around the vessels. The use of sGFP-transformed P. chlamydospora helped to clarify different aspects associated with the location of this pathogen in grapevine tissue, before disease symptom expression.     

Pathogenic fungi of planthoppers associated with rice crops in Argentina

We conducted a survey of pathogenic fungi of planthoppers associated with rice crops in Los Hornos, Buenos Aires, Argentina, and a study of the seasonality and prevalence of these pathogens. Samples were taken in rice for two consecutive years. The plants sampled included rice Oryza sativa L. (Poaceae) and its surrounding weeds. The planthopper Oliarus dimidiatus Berg. (Hemiptera: Fulgoromorpha: Cixiidae) was the most abundant species associated with rice. Two species of entomophthoralean and one species of hypocrealean fungi infected and killed adults of O. dimidiatus in the rice agroecosystem. The fungi were identified as: Pandora sp. (Entomophthorales: Entomophthoraceae), Conidiobolus coronatus (Costantin) Batko (Entomophthorales: Ancylistaceae), and Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Hypocreales: Clavicipitaceae). Pandora sp. was the most predominant pathogen collected. It was recorded from the middle of February to the middle of April 2005, and not found again until the end of March 2006. The report of Pandora sp., C. coronatus and B. bassiana represents the first records of these fungi as pathogens of hoppers associated with rice crops in Argentina.     

Micrometeorology of vineyards and phytopathological models1

In intensive viticulture, the distribution of the principal meteorological elements depends principally on aspect, slope and altitude. The present research aims to examine microclimate modelling in vineyards, by connecting local atmospheric conditions with macroscale meteorological conditions as reported by the standard meteorological networks. To study the effect of topography on crop microclimate, vineyard temperature has been measured with an infrared thermometer, and phenological, allometrical and yield measurements have been made in vineyards located close to the Chianti Classico hills (IT). The climatic and pathological data has been used to verify mathematical models simulating microclimatic conditions and to protect grapevines from downy mildew (Plasmopara viticola). The models allow a reduction in the number of treatments against the disease, lightening at the same time the damage to the ecosystem and the cost for the farmer.     

Pathogenicity of fungi associated with winter loss and injury in white lupin

Fungi isolated from diseased white lupin plants were tested for pathogenicity in standardized glasshouse tests to assess their potential as causes of plant death in winter in autumn-sown crops. Pleiochaeta setosa and, to a slightly lesser extent, Fusarium avenaceum caused lesions or plant death when inoculated onto hypocotyls of lupin seedlings. Disease was more severe when the hypocotyls were wounded before inoculation. F. avenaceum also caused injury when inoculated onto roots; wounding the roots had no effect. Some isolates of F. solani also caused injury, especially after root inoculation, but isolates of F. oxysporum and Cylindrocarpon destructans were only slightly or non-pathogenic. Isolates of Fusarium and C. destructans , but not of P. setosa , differed in pathogenicity. There were differences in susceptibility to disease among three lupin cultivars.     

Identification,pathogenicity and community dynamics of fungi and oomycetes associated with pea root rot in northern France

The pea root rot complex is a major concern for green pea production worldwide. This study aimed at characterizing its composition and dynamics throughout a cropping season in northern France. To this end, fungi and oomycetes were isolated from green pea plant roots with symptoms sampled at the flowering stage in 22 fields in 2017, and at the pea emergence, elongation and flowering stages in two fields in 2018. Out of 646 isolates collected, 317 were identified using molecular markers. Fusarium oxysporum, F. solani and F. redolens were highly predominant. Pathogenicity tests separated the isolates into four aggressiveness groups. F. solani isolates were the most aggressive. Phylogenetic analysis of their TEF1 sequences showed that they mainly belonged to the F. pisi lineage, and that F. oxysporum isolates were genetically close to isolates from the UK that did not belong to the forma specialis pisi. In addition, several Clonostachys rhizophaga isolates are reported for the first time to cause pea root rot. The oomycetes were rarely found and were represented by a few Pythium spp. isolates. Lastly, this study shows that the fungal and oomycete communities associated with pea root rot change during the cropping season. The level of dissimilarity of the root-rot-associated communities decreased throughout the cropping season towards a more similar composition at the flowering stage, dominated by F. solani, F. oxysporum and F. redolens. The proportion of nonpathogenic to weakly pathogenic isolates decreased progressively during the growing season in favour of moderately to highly pathogenic isolates.     

Identification and community dynamics of fungi associated with root,crown, and foot rot of field pea in western Canada

Fungal and oomycete communities in symptomatic roots, crowns and lower stem tissues of field pea plants from sites across the Canadian prairies were characterized using plate culture and sequence-based identification. Symptomatic plants were sampled at the mid-flowering stage from a total of 21 fields in 2014 and 2015. Fungi and oomycete species were isolated on agar medium and grouped into operational taxonomic groups (OTU) based on their morphology. From the OTUs, 40 fungal and oomycete species were identified according to translation elongation factor-1 alpha or ITS sequences. Fusarium spp. accounted for more than 60 % of total isolations. The fungal communities were similar in roots and crowns, but differed from communities in lower stems. In 2014, the most prevalent fungi isolated from roots were F. avenaceum, F. solani and F. redolens, but F. solani was dominant in 2015. In crown tissues, F. avenaceum was most prevalent in 2014 but F. solani was more prevalent in 2015. Stem tissues were primarily colonized by Peyronellaea spp. (= Ascochyta / Phoma spp.) and Alternaria spp. in 2014, but there was a drastic decrease in Peyronellaea spp. in 2015. This study indicated that climate, primarily precipitation levels, and local edaphic characteristics may play a profound role in the structure of phytopathogen communities associated with the root and foot rot diseases complex of field pea on the Canadian prairies.     

Survey of fungi associated with subterranean clover leaves and petioles in Western Australia

A wide range of fungi was recorded from leaves and petioles of subterranean clover ( Trifolium subterraneum L.), with and without symptoms of disease, in Western Australia. Leptosphaerulina trifolii (Rostrup) Petrak and Phoma medicaginis Malb. & Roum. were the two most frequently isolated fungi. Ascochyta caulicola Lamb., Colletotrichum truncatum (Schw.) Andus & Moore, Curvularia trifolii (Kauffm.) Boedijn., Fusarium avenaceum (FR.) Sacc, Myrothecium verrucaria (Fr.) Sacc, Phoma medicaginis , and Stemphylium globuliferum (Vestergr.) Simmons were new records on subterranean clover foliage in Western Australia. Phoma medicaginis was demonstrated to be pathogenic and this is the first record as a pathogen on subterranean clover foliage in Western Australia, M. verrucaria and F. avenaceum caused leaf spotting or more extensive lesions as a consequence of undetermined phytotoxic products produced on agar plate cultures.     

Anthracnose of capsicum in Papua New Guinea; varietal reaction and associated fungi

Abstract

Twenty‐three varieties of Capsicum annuum (L.) were assessed for levels of natural anthracnose infection. Infection rates ranged from 0.0 to 17.2% with sweet bell varieties being generally more susceptible than long pungent varieties. The primary pathogen appears to be Colletotrichum capsici (Syd.) Butler & Bisby but Curvularia Iunata (Wakker) Boedjin was also frequently associated with the disease.     

落叶松枯梢病分子检测初步研究

本研究对小兴安岭、长白山和完达山3个区域的落叶松枯梢病病原菌Botryosphaeria laricina(K.Sawada)的ITS序列进行了PCR扩增、序列测定和亲缘关系比对分析.并通过对落叶松梢栖真菌ITS序列的分析,设计出特异引物ITSA1与ITSB1.该特异引物可以将落叶松枯梢病病原菌与其它9种(属)落叶松梢栖真菌分别开,具有较好的特异性和较高的灵敏度,初步建立了落叶松枯梢病的分子检测方法.     

Incidence and distribution of botryosphaeriaceous species in New Zealand vineyards

The aim of this study was to determine the identification, incidence and distribution of botryosphaeriaceous species in New Zealand vineyards. A field study of 43 vineyards across six wine growing regions was conducted. A total of 336 isolates of botryosphaeriaceous species were isolated from 238 diseased grapevine samples. Morphological identification and phylogenetic analysis of the ribosomal RNA gene region, partial sequence of the translation elongation factor 1-alpha gene (EF1-α) and the β-tubulin gene identified nine botryosphaeriaceous species: N. parvum, N. luteum, N. australe, N. ribis, D. mutila, D. seriata, B. dothidea, Do. iberica and Do. sarmentorum. These species have been reported in other grape growing regions worldwide. Eighty eight percent of vineyards and 68% of symptomatic vines sampled were positive for botryosphaeriaceous species. Incidence and distribution of the botryosphaeriaceous species populations varied between the North and South Islands with N. parvum being the predominant species. The variability in incidence and distribution of the botryosphaeriaceous species may be influenced by climatic conditions and different sources of inoculum in the regions sampled. The results of this research clearly identified botryosphaeriaceous species as the target pathogens for development of management strategies for grapevine decline in New Zealand.