Genetic diversity of Botrytis in New Zealand vineyards and the significance of its seasonal and regional variation

Species‐ and population‐specific differences in fungicide resistance and aggressiveness within Botrytis makes basic data on genetic diversity important for understanding disease caused by this fungus. Genetic diversity of Botrytis was surveyed between 2008 and 2012 from grapes from five New Zealand wine‐growing regions. A total of 1226 isolates were gathered from symptomless flower buds at the start of the growing season and 1331 isolates from diseased fruit at harvest. Two species were found, B. cinerea and B. pseudocinerea. Botrytis pseudocinerea was common in both Auckland vineyards sampled, and infrequent elsewhere. However, even in Auckland, it was rarely isolated from diseased fruit. The presence of the Boty and Flipper transposons was assessed. Isolates with all four transposon states (Boty only, Flipper only, both Boty and Flipper, no transposons) were found for both species. Both vineyards in the Auckland region had high numbers of Flipper‐only isolates at flowering; both vineyards from the Waipara region had high numbers of Boty‐only isolates at flowering. Most isolates from diseased fruit at harvest contained both transposons. These observations suggest that B. pseudocinerea, and isolates with one or both of the transposons missing, may be less aggressive than B. cinerea, or than isolates with both transposons present. Two clades were resolved within B. pseudocinerea, only one of which has been reported from European vineyards. Phylogenetic diversity within B. cinerea in New Zealand was similar to that known from Europe, including isolates that appear to match Botrytis ‘Group S’. The taxonomic implications of this genetic diversity are discussed.     

Experimental and molecular evidence of Reptalus panzeri as a natural vector of bois noir

Bois noir (BN) is an economically important grapevine yellows disease induced by the stolbur phytoplasma and principally vectored by the cixiid Hyalesthes obsoletus. This study addresses the involvement of other planthoppers and/or leafhoppers in BN epidemics in the South Banat district of northeastern Serbia, by performing transmission experiments and multilocus typing of stolbur phytoplasma isolates to determine the vector‐related characteristics of the disease. Transmission trials were conducted with adults of two cixiid congeners, Reptalus panzeri and R. quinquecostatus, which were found to harbour stolbur phytoplasma in the vineyards under study. A molecular characterization of stolbur phytoplasma isolates was performed by sequence analysis and/or RFLP typing of the two housekeeping genes tuf and secY and the two membrane proteins stamp and vmp1. Transmission trials with naturally infected R. panzeri adults from either the BN‐infected vineyards or maize redness (MR)‐affected maize fields revealed a high stolbur phytoplasma transmission efficiency to grapevines. In contrast, experiments conducted with stolbur‐positive R. quinquecostatus originating from BN‐infected vineyards, provided no evidence for a vector role of this species. Seven stolbur phytoplasma genotypes, all of which were tuf‐b types, were detected among the grapevine‐ and insect‐associated field samples according to the tuf/secY/vmp1/stamp typing. STOLg was the genotype most frequently found in naturally infected grapevine (42%), as well as R. panzeri originating from the vineyards (85%) and maize fields (98%). The same genotype was found in all experimental plants inoculated by R. panzeri, confirming its vectorship of the disease.     

Detection of botryosphaeriaceous species in environmental samples using a multi‐species primer pair

Botryosphaeriaceous species are significant grapevine trunk pathogens worldwide, which can be difficult to identify to species level using conventional morphological methods. This study developed and optimized a quick, reliable molecular identification method that could facilitate investigations into the epidemiology of these diseases in vineyards. The multi‐species primers, BOT100F and BOT472R, amplified a 371–372 bp portion of the rRNA gene region from the six botryosphaeriaceous species commonly found in New Zealand vineyards. In silico analysis indicated that they would amplify DNA from six of the 12 lineages of the Botryosphaeriaceae, including all of the main species pathogenic to grapevines. A detection sensitivity of 1 and 0·1 pg DNA in standard and nested PCR, respectively, was achieved and this was calculated as equivalent to 2·5 conidia. Validation of the primers for environmental samples showed that their specificity was not compromized by the presence of competing DNA templates extracted from wood and soil. Single stranded conformational polymorphism (SSCP) analysis of the amplicons could resolve Neofusicoccum australe, N. luteum, Diplodia mutila and D. seriata, but did not differentiate between N. parvum and N. ribis. The optimized PCR‐SSCP was used to identify botryosphaeriaceous species present in rainwater traps collected over 1 year in a vineyard known to contain infected vines. It could detect multiple species in individual samples and demonstrated differences in the dispersal patterns of conidia from different species. Given the specificity and sensitivity of this method it could prove useful in epidemiology studies involving the numerous botryosphaeriaceous species that infect a wide range of host species.     

Aetiology of anthracnose on grapevine shoots in Brazil

Anthracnose is an important disease in vineyards in south and southeast Brazil, the main grape‐producing regions in the country. This study aimed to identify the causal agents of grapevine anthracnose in Brazil through multilocus phylogenetic analyses, morphological characterization and pathogenicity tests. Thirty‐nine Elsinoë ampelina and 13 Colletotrichum spp. isolates were obtained from leaves, stems and berries with anthracnose symptoms collected in 38 vineyards in southern and southeastern Brazil. For E. ampelina isolates, the internal transcribed spacer (ITS), histone H3 (HIS3) and elongation factor 1‐α (TEF) sequences were analysed. HIS3 was the most informative region with 55 polymorphic sites including deletions and substitutions of bases, enabling the grouping of isolates into five haplotypes. Colonies of E. ampelina showed slow growth, variable colouration and a wrinkled texture on potato dextrose agar. Conidia were cylindrical to oblong with rounded ends, hyaline, aseptate, (3.57–) 5.64 (?6.95) μm long and (2.03–) 2.65 (?3.40) μm wide. Seven species of Colletotrichum were identified: C. siamense, C. gloeosporioides, C. fructicola, C. viniferum, C. nymphaeae, C. truncatum and C. cliviae, with a wide variation in colony and conidium morphology. Only E. ampelina caused anthracnose symptoms on leaves, tendrils and stems of Vitis vinifera and V. labrusca. High disease severity and a negative correlation between disease severity and shoot dry weight were observed only when relative humidity was above 95%. In this study, only E. ampelina caused anthracnose symptoms on grapevine shoots in Brazil.     

Molecular tracing of the transmission routes of bois noir in Mediterranean vineyards of Montenegro and experimental evidence for the epidemiological role of Vitex agnus‐castus (Lamiaceae) and associated Hyalesthes obsoletus (Cixiidae)

Epidemiological aspects and transmission routes of bois noir (BN), a grapevine yellows disease induced by ‘Candidatus Phytoplasma solani’, have been exhaustively studied in the affected vineyards of continental Europe but not in the Mediterranean coastal zone. Because ‘Ca. Phytoplasma solani’ and its principal vector Hyalesthes obsoletus presumably originate from the Mediterranean, gaining knowledge of the epidemiological peculiarities of the disease in this area is essential for understanding its global spread and diversification, as well as for designing local management strategies. In this study, molecular epidemiology was applied to trace transmission pathways of ‘Ca. Phytoplasma solani’ in the Mediterranean vineyards of Montenegro, using multilocus sequence typing of tuf, vmp1 and stamp genes of the isolates associated with various hosts. Thus, ‘Ca. Phytoplasma solani’ was tracked from a tentative reservoir plant (inoculum source) through an associated vector population to the infected grapevine. Three pathways of transmission were documented, originating from Urtica dioica, Convolvulus arvensis and Vitex agnus‐castus; however, only the route originating from U. dioica was direct, whereas the latter two were overlapping and could be intermixed. Vitex agnus‐castus is a natural source of ‘Ca. Phytoplasma solani’, representing an important link in disease epidemiology in the Mediterranean and a possible origin of several genotypes occurring in central Europe. Experimental confirmation of the role of Vitex‐associated H. obsoletus in BN transmission in Montenegrin vineyards indicates its tentative role as a vector in the wide area of the Mediterranean, where some of the major wine‐producing regions are located.     

Monitoring of QoI fungicide resistance in Plasmopara viticola populations in Japan

BACKGROUND: The increasing occurrence of QoI fungicide resistance in Plasmopara viticola (Berk. & MA Curtis) Berl. & DeToni populations is becoming a serious problem in the control of grapevine downy mildew. In Japan, the existence of QoI‐fungicide‐resistant P. viticola was reported in 2009. RESULTS: The QoI fungicide resistance in P. viticola samples collected from vineyards in Japan in 2008 and 2009 was monitored. Resistant P. viticola were detected in the regions where QoI fungicides have been introduced in accordance with the pest management programme, whereas in Hokkaido vineyards, where QoI fungicides have not yet been introduced, QoI‐fungicide‐resistant P. viticola were not found. CONCLUSION: Japan comprises thousands of islands and is physically isolated from other countries by the sea. Monitoring the emergence, incidence and distribution of QoI fungicide resistance in P. viticola populations in Japan is necessary to improve pest management strategies for downy mildew disease in Japanese vineyards. Copyright © 2010 Society of Chemical Industry     

High genetic and virulence diversity detected in Neofusicoccum luteum and N. australe populations in New Zealand vineyards

Genotypic and virulence diversity of Neofusicoccum luteum and N. australe isolates recovered from grapevines displaying symptoms of dieback and decline in New Zealand were investigated. The universally primed PCR (UP‐PCR) method was used to investigate the genetic diversity of 40 isolates of N. luteum and 33 isolates of N. australe. Five UP‐PCR primers produced a total of 51 loci from N. luteum and 57 from N. australe with a greater number of polymorphic loci produced in N. australe (86%) compared with N. luteum (69%). Analysis of UP‐PCR data showed both species found in New Zealand vineyards were genetically diverse at both the inter‐ and intra‐vineyard levels with only a single pair of clonal isolates in N. luteum. Cluster analysis of UP‐PCR data produced four genetic groups in N. luteum and 10 in N. australe (P < 0.05). For both species, there was no relationship between the genetic groups and the origin of isolates. The mean genetic diversity (H) of N. luteum was less than for N. australe, being 0.1791 and 0.2417, respectively. Pathogenicity assays of both species using isolates from either the same or different genetic groups inoculated onto either green shoots or grapevine trunks, showed virulence diversity within the population; however, no correlation was identified between genetic groups and virulence.     

Phylogeny,distribution and pathogenicity of Lasiodiplodia species associated with dieback of table grape in the main Brazilian exporting region

Botryosphaeria dieback is an important disease of table grape in the São Francisco Valley, the main Brazilian exporting region. The objectives of this study were to identify species of Lasiodiplodia associated with botryosphaeria dieback of table grapes in the São Francisco Valley, investigate the prevalence and distribution of the species in the region, and evaluate their pathogenicity and virulence in green shoots of table grape. A total of 112 Lasiodiplodia isolates were obtained from 14 vineyards, located in Casa Nova, Juazeiro and Petrolina. Fungal identifications were made using phylogenetic analysis based on partial sequences of translation elongation factor 1‐α (EF1‐α) and internal transcribed spacer (ITS) sequences, in combination with morphometric characteristics of conidia. Eight species of Lasiodiplodia were identified: L. brasiliense, L. crassispora, L. egyptiacae, L. euphorbicola, L. hormozganensis, L. jatrophicola, L. pseudotheobromae and L. theobromae. Except for L. crassispora, L. pseudotheobromae and L. theobromae, all the other species are reported for the first time on grapevine worldwide. The distribution of Lasiodiplodia species differed between the three table grape populations of São Francisco Valley. All Lasiodiplodia species isolated in this study were present in the population of Casa Nova and Lasiodiplodia theobromae was the most prevalent. All species of Lasiodiplodia were pathogenic on detached green shoots of grapevine, with L. brasiliense being the most virulent.     

Host suitability of Vitis rootstocks to root‐knot nematodes (Meloidogyne spp.) and the dagger nematode Xiphinema index,and plant damage caused by infections

The host suitability of commercial Vitis rootstocks commonly used in Spain (161‐49C, 41B, 1103P, 110R, 140Ru and SO4) to root‐knot nematodes (Meloidogyne arenaria, M. incognita, M. javanica) and Xiphinema index, and damage caused by nematode infection were determined under controlled conditions. The three root‐knot nematodes reproduced with a rate higher than one in all rootstocks, indicating that they are suitable hosts for these nematodes. Growth of rootstocks infected with the root‐knot nematodes was less vigorous than that of nematode‐uninfected controls in the majority of the rootstocks studied. Root infection resulted in moderate to severe root galling in all rootstocks. The shoot and main stem diameters appeared to be the most sensitive variables of damage caused by infection by Meloidogyne spp., with reduction rates from 36% and 53% in 161‐49C to 57% and 66% in 140Ru, respectively. The shoot height was not significantly affected by the root‐knot nematodes and the root fresh weight generally increased as a consequence of intensive galling. The nematode X. index caused significant root damage with a reproduction factor higher than one in all rootstocks. However, reproduction factor was significantly influenced by the rootstock and significantly decreased by about 12‐fold (5·7 to 18·1‐fold) with the increase in inoculum density from 100 to 1000 nematodes per plant. The root dry weight was reduced by X. index infections, and was the plant growth variable most affected by the nematode infection in all rootstocks at both inoculum densities. Meloidogyne arenaria, M. incognita, M. javanica and X. index, prevalent in many world vineyards, are all shown to have a damaging effect on the six tested rootstocks.     

Evolution and spread of glyphosate resistance in Conyza bonariensis in California and a comparison with closely related Conyza canadensis

Glyphosate‐resistant weeds are an increasing problem in perennial cropping systems in the Central Valley of California, USA. To elucidate the evolutionary origins and spatial spread of resistance, we investigated the geographical distribution of glyphosate resistance and the population genetic diversity and structure of Conyza bonariensis and compared the results with previously studied C. canadensis. Thirty‐five populations from orchards and vineyards across the Central Valley were sampled. Population genetic structure was assessed using microsatellite markers. Population‐level resistance was assessed in glasshouse screening of plants grown from field‐collected seed. Bayesian clustering and analyses of multilocus genotypes indicated multiple origins of resistance, as observed in C. canadensis. Pairwise F_ST analysis detected spatial spread of resistance in the south of the Central Valley, also similar to C. canadensis. The results strongly indicate that the southern valley was an environment markedly more suitable than the northern valley for resistance spread and that spread in Conyza species was driven by increased uniformity of strong selection in the southern valley, due to recent regulation on herbicides other than glyphosate. Accordingly, resistant C. canadensis individuals occurred at high frequencies only in the southern valley, but interestingly resistant C. bonariensis occurred at high frequencies throughout the valley. Expression of resistance showed varying degrees of plasticity in C. bonariensis. The lower selfing rate and substantially greater genotypic diversity in C. bonariensis, relative to C. canadensis, indicate greater evolutionary potential over shorter time periods. Interspecific hybridisation was detected, but its role in resistance evolution remains unclear.     

Esca in young and mature vineyards,and molecular diagnosis of the associated fungi

Esca is one of the most important grapevine trunk diseases, and it can induce severe decline. In the past, the disease occurred mostly on mature vines, but today it is also present in young vineyards. The aim of this study was to investigate the incidence of esca in young (< 7 years old) and mature (> 11 years old) vineyards on cvs Montepulciano, Sangiovese, Verdicchio and Passerina located in the main viticultural areas of the Marche Region, central-eastern Italy. The average incidence of diseased plants was higher in mature (32.6%) than young (5.2%) vineyards, and Verdicchio and Passerina appeared to be the most sensitive among the cultivars considered, followed by Sangiovese and Montepulciano. The analysis of the spatial spread of esca carried out in two mature vineyards on cv. Verdicchio and a young vineyard on cv. Sangiovese showed a fluctuation in the numbers of infected plants over the three years of observation. The fungi associated with symptomatic plants were detected by classical and molecular tools. Isolation on agar media yielded colonies of Phaeomoniella chlamydospora (Pch), Botryosphaeria spp. (Bot), Fomitiporia mediterranea (Fomed) and, sporadically, Phaeoacremonium aleophilum (Pal). In samples from young plants, Bot and Pch were recurrent, while Pch and Fomed were found in mature vines and old rootstocks. Molecular detection with specific primer pairs for Pch, Pal, Fomed, and B. dothidea confirmed the data obtained using classical tools, and in some cases it was more sensitive. This study thus provides a further contribution to the association between causal agents and esca symptoms, and it confirms the importance of molecular tools for a sensitive detection of associated pathogens, which can also be present in propagative materials.     

Site-specific field resistance of grapevine to <Emphasis Type="Italic">Plasmopara viticola</Emphasis> correlates to altered gene expression and was not modulated by the application of organic amendments

The influence of site on resistance of grapevine (cv. Chasselas) to Plasmopara viticola was evaluated. Grapevine leaves from three vineyards in the region of Lake Neuchatel (Switzerland) were tested for their susceptibility to P. viticola in the lab in five successive years (2004–2008), and the expression levels of four selected defence-related genes (Glucanase, Lipoxygenase 9, 9-cis epoxycarotenoid dioxygenase, Stilbene synthase) were studied in 1 year. In all 5 years of examination, differences between sites were substantial. In four out of 5 years, plants from site Hauvernier were much less susceptible to P. viticola than plants from site Auvernier. In another year, differences were less pronounced but still significant for one leaf age. Susceptibility of plants from a third site (Concise) varied from year to year. Differences in the genetic background were excluded by microsatellite analysis. Differences in susceptibility were mirrored in the constitutive expression pattern of four defence-related genes, with samples from the Hauterive site clearly separated from samples of the other two sites in redundancy analysis. Furthermore, it was evaluated whether site-specific resistance can be modulated by agronomic practices such as the application of organic amendments. In two commercial vineyards (cv. Pinot noir), soils had either not (control) or yearly (compost) been amended with a compost for the last 9 years. Leaves from plants grown in any of the two treatments did not differ in their susceptibility to P. viticola in both years of examination. Additionally, under controlled conditions, none of 19 different composts amended to the substrate of grapevine seedlings or cuttings affected their susceptibility to P. viticola, but 8 out of 19 composts reduced severity in the control bioassay Arabidopsis thaliana—Hyaloperonospora arabidopsidis, indicating that a modulation of site-specific susceptibility of grapevine plants by organic amendments is at the very least, difficult.     

Understanding the effects of multiple sources of seasonality on the risk of pathogen spread to vineyards: vector pressure,natural infectivity,and host recovery

Seasonality plays an important role in the dynamics of infectious disease. For vector‐borne pathogens, the effects of seasonality may be manifested in the variability in vector abundance, vector infectiousness, and host‐infection dynamics over the year. The relative importance of multiple sources of seasonality on the spread of a plant pathogen, Xylella fastidiosa, into vineyards was explored. Observed seasonal population densities of the primary leafhopper vector, Graphocephala atropunctata, from 8 years of surveys in northern California were incorporated into a model of primary spread to estimate the risk of pathogen infection under different scenarios regarding seasonality in vector natural infectivity (i.e. constant or increasing over the season) and grapevine recovery from infection (i.e. none or seasonal recovery). The extent to which local climatic conditions affect risk estimates via differences in vector abundance was investigated. Seasonal natural infectivity, seasonal recovery, and especially the combination, reduced (up to 8‐fold on average) within‐season and cumulative yearly estimates of pathogen spread. Estimated risk of infection also differed greatly among years due to large differences in vector abundance, with wet and moderate winter and spring conditions favouring higher G. atropunctata abundance. Seasonal variation of the pathogen–vector interaction may play an important role in the dynamics of disease in vineyards, reducing the potential prevalence from what it could be in their absence. Moreover, climate, by affecting sharpshooter leafhopper abundance or activity, may influence Pierce’s disease dynamics.     

A model for the development of Erysiphe necator chasmothecia in vineyards

A temperature‐driven, mechanistic model predicting the development of Erysiphe necator chasmothecia in vineyards was developed and validated in 38 vineyards in the Po Valley (northern Italy), Baden‐Württemberg (Germany), and South Australia between 2005 and 2011. The model, which begins operating when the first ascocarp initials are formed, predicts on a daily basis the proportions of chasmothecia at the yellow, brown and black maturity stage. The initialization date was estimated with an iterative procedure that minimized the residuals of predicted versus observed values. In all vineyards, a drop to more favourable temperatures for ascocarp production over 2–4 days in the week or in the 2 weeks before the model initialization date probably triggered chasmothecia production. Model predictions provided a good fit of observed data (coefficients of determination, model accuracy, efficacy and efficiency were all ≥0·90), with some overestimation. When predicted production of black chasmothecia (on leaves) was compared with observed dispersal of chasmothecia from vines, lack of splashing rain was probably the main cause of overestimation. When observed numbers of yellow, brown or black chasmothecia on leaves were compared with model predictions, removal of the developing chasmothecia by rainfall was probably the main cause of overestimation. Inclusion of the effect of rainfall on the removal of immature and mature chasmothecia from the powdery mildew colonies could improve the model. The model could be used to time the application of fungicides or biocontrol agents for reducing ascocarp formation and reducing primary inoculum in the following season.     

Soil application of neonicotinoid insecticides for control of insect pests in wine grape vineyards

BACKGROUND: Soil application of systemic neonicotinoid insecticides can provide opportunities for long‐term control of insect pests in vineyards, with minimal risk of pesticide drift or worker exposure. This study compared the effectiveness of neonicotinoid insecticides applied via irrigation injection on key early‐season and mid‐season insect pests of vineyards in the eastern United States. RESULTS: On vines trained to grow on drip irrigation, early‐season application of imidacloprid, clothianidin, thiamethoxam and dinotefuran provided high levels of control against the potato leafhopper, Empoasca fabae. Protection of vines against Japanese beetle, Popillia japonica, and grape berry moth, Paralobesia viteana, was also observed after mid‐season applications. Efficacy was poor in commercial vineyards when treatments were applied to the soil before irrigation or rain, indicating that vines must be grown with an irrigation system for efficient uptake of the insecticide. CONCLUSIONS: In drip‐irrigated vineyards, soil‐applied neonicotinoids can be used to provide long residual control of either early‐season or mid‐ to late‐season foliage pests of vineyards. This approach can reduce the dependence on foliar‐applied insecticides, with associated benefits for non‐target exposure to workers and natural enemies. Copyright © 2012 Society of Chemical Industry     

Distribution and genetic diversity of root‐knot nematodes (Meloidogyne spp.) in potatoes from South Africa

A molecular‐based assay was employed to analyse and accurately identify various root‐knot nematodes (Meloidogyne spp.) parasitizing potatoes (Solanum tuberosum) in South Africa. Using the intergenic region (IGS) and the 28S D2–D3 expansion segments within the ribosomal DNA (rDNA), together with the region between the cytochrome oxidase subunit II (COII) and the 16S rRNA gene of the mtDNA, 78 composite potato tubers collected from seven major potato growing provinces were analysed and all Meloidogyne species present were identified. During this study, M. incognita, M. arenaria, M. javanica, M. hapla, M. chitwoodi and M. enterolobii were identified. The three tropical species M. javanica, M. incognita and M. arenaria were identified as the most prevalent species, occurring in almost every region sampled. Meloidogyne hapla and M. enterolobii occurred in Mpumalanga and KwaZulu‐Natal, respectively, while M. chitwoodi was isolated from two growers located within the Free State. Results presented here form part of the first comprehensive surveillance study of root‐knot nematodes to be carried out on potatoes in South Africa using a molecular‐based approach. The three genes were able to distinguish various Meloidogyne populations from one another, providing a reliable and robust method for future use in diagnostics within the potato industry for these phytoparasites.     

Overwintering grapevine debris as an important source of Botrytis cinerea inoculum

Production of Botrytis cinerea conidia from infected grapevine debris (trash) left on the ground and in the canopy in the season following harvest was studied in vineyards in Marlborough, New Zealand. When subsamples were incubated under high relative humidity in the laboratory, rachides had the greatest sporulation potential (P < 0·05), followed by tendrils, cane lengths and petioles. Trash remaining on the ground under the canopy had higher rates of sporulation (P < 0·05) than that in the inter‐row. The sporulation potential of rachides at different times during the growing season was assessed by placing them in vine canopies or on the inter‐row soil in three vineyards in late spring. Subsamples were removed on five occasions between flowering (capfall) and harvest, and incubated under high relative humidity in the laboratory. Mean numbers of conidia produced from the canopy rachides diminished from 3·5 × 10⁵ per rachis at capfall to 2·6 × 10⁴ at harvest, and from 3·9 × 10⁵ to 2·7 × 10³, respectively, from the ground rachides. The greater loss in sporulation capacity of ground rachides was considered to be associated with their earlier spontaneous sporulation and greater degradation in the moist inter‐row sward, where they lost 29% of their weight (P < 0·001) and 23% of their pedicels (P < 0·001), compared to the canopy rachides which lost 0% of their weight and 3% of their pedicels from capfall to harvest. This study has shown that necrotic, overwintering grapevine debris can produce B. cinerea conidia throughout the following growing season, so may contribute to the subsequent risk of bunch rot.     

Genetic diversity within and between sulfonylurea‐resistant and susceptible populations of Schoenoplectus juncoides in Japan

To reveal the effects of herbicide selection on genetic diversity in the outcrossing weed species Schoenoplectus juncoides, six sulfonylurea‐resistant (SU‐R) and eight sulfonylurea‐susceptible (SU‐S) populations were analysed using 40 polymorphic inter‐simple sequence repeat loci. The plants were collected from three widely separated regions: the Tohoku, Kanto and Kyushu districts of Japan. Genetic diversity values (Nei's gene diversity, h) within each SU‐S population ranged from h = 0.125 to h = 0.235. The average genetic diversity within the SU‐S populations was H_S = 0.161, and the total genetic diversity was H_T = 0.271. Although the H_S of the SU‐R populations (0.051) was lower than that of the SU‐S populations, the H_T of the SU‐R populations (0.202) was comparable with that of the SU‐S populations. Most of the genetic variation was found within the region for both the SU‐S and SU‐R populations (88% of the genetic variation respectively). Two of the SU‐R populations showed relatively high genetic diversity (h = 0.117 and 0.161), which were comparable with those of the SU‐S populations. In contrast, the genetic diversity within four SU‐R populations was much lower (from h = 0 to 0.018) than in the SU‐S populations. The results suggest that selection by sulfonylurea herbicides has decreased genetic diversity within some SU‐R populations of S. juncoides. The different level of genetic diversity in the SU‐R populations is most likely due to different levels of inbreeding in the populations.     

Occurrence of Grapevine Pinot gris virus in Friuli Venezia Giulia (Italy): field monitoring and virus quantification by real‐time RT‐PCR

Since 2003 the presence of a new syndrome characterized by symptoms of stunting, chlorotic mottling, leaf deformation, reduced yields and quality has been reported in some white berry varieties of Vitis vinifera in Trentino‐Alto Adige and Friuli Venezia Giulia vineyards. The identification of a new virus, provisionally called Grapevine Pinot gris virus (GPGV), in a cv. Pinot gris vine suggested an association between this new syndrome and the virus presence (Giampetruzzi et al., 2012), however the contemporary presence of GPGV in both symptomatic and asymptomatic plants has still to be explained. In this work, a large‐scale monitoring over a 3‐year period (2012–14) of Friuli Venezia Giulia vineyards and nurseries has shown a widespread presence of GPGV in symptomatic plants and also in asymptomatic vines, even if at a slightly lower percentage. Quantitative analyses of the virus titer revealed a great variability in the viral content of both symptomatic and asymptomatic plants but the mean GPGV quantity in symptomatic vines was significantly higher than in asymptomatic plants.     

Characterization of Neofabraea vagabunda isolates causing apple bull's eye rot in Italy (Emilia‐Romagna region)

Neofabraea vagabunda is the prevalent cause of bull's eye rot, one of the main postharvest diseases of apple, in many producing areas, but its biology has not been studied in detail. The molecular identification, by DNA sequencing of the β‐tubulin region, of 41 isolates collected from apples showing bull's eye rot in the Emilia‐Romagna region confirmed N. vagabunda as the main species in Italy. A biological and morphological characterization of N. vagabunda isolates was performed in vitro. Assays at temperatures ranging from 0 to 30 °C carried out on 10 isolates demonstrated: (i) a marked influence of temperature on colony morphology, conidial production, conidial size and mycelial growth, showing the cold‐tolerant character of N. vagabunda; and (ii) that culture at 15 °C on tomato agar (TA) for 14 days is a rapid and reliable method to favour pathogen conidial production. Trials performed on 38 isolates using these incubation conditions recorded the presence of two N. vagabunda morphotypes, differing for colony morphology, conidial size, conidiomata formation and temperature requirement. The alkalizing ability of the pathogen during growth on TA was also demonstrated for the first time. The pathogenicity of 25 N. vagabunda isolates was proved in vivo on artificially infected Cripps Pink apples. A pH increase was also recorded in apple tissue infected by N. vagabunda isolates (on average 0.2 and 0.3 units of pH after 60 and 120 days of incubation, respectively), suggesting that the N. vagabunda transition from quiescence to necrotrophic colonization in apples could involve the secretion of alkalizing compounds.