Seasonal progression of leaf rust in ‘Niagara Rosada’ grapevine in a biannual crop system in Brazil

The soil-borne fungus Fusarium oxysporum can cause both Fusarium yellows and Fusarium root rot diseases with severe yield losses in cultivated sugar beet. These two diseases cause similar foliar symptoms but different root response and have been proposed to be caused by two distinct F. oxysporum formae speciales. Fusarium yellows, caused by F. oxysporum f. sp. betae, presents vascular discoloration, whereas Fusarium root rot, due to F. oxysporum f. sp. radicis-betae, appears as black rot visible on the root surface. The aim of this work was to study the host-pathogen interaction between sugar beet lines and isolates originally characterized as Fusarium oxysporum f. sp. betae. Eight susceptible sugar beet lines, selected by the USDA-ARS (US) and UNIPD (University of Padova, Italy) breeding programs, were inoculated with three different isolates of F. oxysporum f. sp. betae, the causal agent of Fusarium yellows, representing different genetic groups. All inoculated lines developed symptoms, but severity, expressed as area under the disease progress curve (AUDPC), differed significantly (P < 0.05) among lines. Two lines from UNIPD, 6 and 9, were the most susceptible to the disease, whereas the other lines showed similar levels. The three isolates of F. oxysporum f. sp. betae differed significantly (P < 0.05) in disease severity. Five weeks after inoculation the plants were harvested and roots examined. Surprisingly, severe root rot was observed in the susceptible UNIPD lines when inoculated with all three isolates, while this symptom was never observed in the USDA germplasm. The development of this disease symptom obviously depends on the plant genotype.     

Ophraella communa,the ragweed leaf beetle,has successfully landed in Europe: fortunate coincidence or threat?

We report the occurrence of the North American ragweed leaf beetle Ophraella communa in Europe. During our surveys to monitor populations of the invasive alien plant Ambrosia artemisiifolia in Europe, we found the beetle south of the Alps, in more than 130 sites in southern Switzerland (Ticino) and northern Italy (Lombardia, Piemonte and Emilia‐Romagna). At sites where O. communa was present, up to 100% of the plants were attacked with damage levels high enough to completely defoliate and prevent flowering and seed set of most ragweed plants. That in its first year of discovery, O. communa was already found over a large area of c. 20 000 km² and in all habitat types occupied by A. artemisiifolia reflects its great dispersal potential and wide habitat suitability. This oligophagous beetle is a successful biological control agent against A. artemisiifolia in China, but despite extensive host specificity tests, the risk of attack and the level of damage of sunflower under field conditions remain unclear. The recently launched COST Action on ‘Sustainable management of Ambrosia artemisiifolia in Europe (SMARTER)’ offers an ideal framework to respond quickly to the recent establishment of O. communa in Europe and to collect data that can help determine whether this event should be considered a troublesome introduction or whether it is likely to become the first case of a successful biological control of an invasive weed in continental Europe.     

Responses of leaf water potential and gas exchange to the precipitation manipulation in two shrubs on the Chinese Loess Plateau

Regulation of leaf gas exchange plays an important role in the survival of trees and shrubs under future climate change. However, the responses of leaf water potential and gas exchange of shrubs in semi-arid areas to the precipitation alteration are not clear. Here, we conducted a manipulated experiment with three levels of precipitation, i.e., a control with ambient precipitation, 50% above ambient precipitation(irrigation treatment), and 50% below ambient precipitation(drought treatment), with two common shrubs, Salix psammophila C. Wang & C. Y. Yang(isohydric plant, maintaining a constant leaf water potential by stomatal regulation) and Caragana korshinskii Kom.(anisohydric plant, having more variable leaf water potential), on the Chinese Loess Plateau in 2014 and 2015. We measured the seasonal variations of predawn and midday leaf water potential(Ψpd and Ψmd), two parameters of gas exchange, i.e., light-saturated assimilation(An) and stomatal conductance(gs), and other foliar and canopy traits. The isohydric S. psammophila had a similar An and a higher gs than the anisohydric C. korshinskii under drought treatment in 2015, inconsistent with the view that photosynthetic capacity of anisohydric plants is higher than isohydric plants under severe drought. The two shrubs differently responded to precipitation manipulation. Ψpd, An and gs were higher under irrigation treatment than control for S. psammophila, and these three variables and Ψmd were significantly higher under irrigation treatment and lower under drought treatment than control for C. korshinskii. Leaf water potential and gas exchange responded to manipulated precipitation more strongly for C. korshinskii than for S. psammophila. However, precipitation manipulation did not alter the sensitivity of leaf gas exchange to vapor-pressure deficit and soil moisture in these two shrubs. Acclimation to long-term changes in soil moisture in these two shrubs was primarily attributed to the changes in leaf or canopy structure rather than leaf gas exchange. These findings will be useful for modeling canopy water-carbon exchange and elucidating the adaptive strategies of these two shrubs to future changes in precipitation.     

Interactions in the Brassica napus–Pyrenopeziza brassicae pathosystem and sources of resistance to P. brassicae (light leaf spot)

Pyrenopeziza brassicae, cause of light leaf spot (LLS), is an important pathogen of oilseed rape and vegetable brassicas and has a wide geographic distribution. Exploitation of host resistance remains the most sustainable and economically viable solution for disease management. This study evaluated 18 oilseed rape cultivars or breeding lines for host resistance against P. brassicae in glasshouse experiments. Selected cultivars/lines were inoculated with eight single-spore isolates of the pathogen obtained from three different regions in England. Analysis of P. brassicae infection-related changes on host plants identified leaf deformation as a characteristic feature associated with P. brassicae infection, this showed poor correlation to LLS severity measured as the amount of pathogen sporulation on infected plants. Resistant host phenotypes were identified by limitation of P. brassicae sporulation, with or without the presence of a necrotic response (black flecking phenotype). Investigation of this pathosystem revealed significant differences between cultivars/lines, between isolates, and significant cultivar/line-by-isolate interactions. In total, 37 resistant and 16 moderately resistant interactions were identified from 144 cultivar/line-by-isolate interactions using statistical methods. Most of the resistant/moderately resistant interactions identified in this study appeared to be nonspecific towards the isolates tested. Our results suggested the presence of isolate-specific resistant interactions for some cultivars. Several sources of resistance have been identified that are valuable for oilseed rape breeding programmes.     

Comment on ‘In Turkish wheat cultivars the resistance allele of LR34 is ineffective against leaf rust’

Journal of Plant Diseases and Protection -     

‘Candidatus Phytoplasma australiense’ is the phytoplasma associated with Australian grapevine yellows, papaya dieback and Phormium yellow leaf diseases

Sequence comparisons and phylogenetic analysis of the 16S rRNA genes and the 16S/23S spacer regions of the phytoplasmas associated with Australian grapevine yellows, papaya dieback and Phormium yellow leaf diseases revealed minimal nucleotide differences between them resulting in the formation of a monophyletic group. Therefore, along with Australian grapevine yellows, the phytoplasmas associated with Phormium yellow leaf and papaya dieback should also be considered as Candidatus Phytoplasma australiense.     

Effects of short-term low temperatures on photosystem Ⅱ function of samara and leaf of Siberian maple (Acer ginnala) and subsequent recovery

Samara is the reproductive organ (seed) for many tree species in arid land in northwestern China. It is ecologically important in population development due to its dispersal function. However, information on its photosynthesis and effect of environmental stresses on its photosynthesis is still very limited. In the present study, responses of photosystem II (PSII) activity in samara and leaf of Siberian maple to short-term chilling/freezing and subsequent recovery potential were comparatively investigated by using polyphasic fluorescence test. The samara had more efficient photosynthesis (Fv/Fm and PIABS) and more efficient electron transport (φEo) but lower energy dissipation (DIo/RC) than leaf. Generally, the PSII performance and the electron transport for both samara and leaf were inhibited under low temperature stress, accompanied by an increase of energy dissipation in PSII reaction centers (RCs). PSII of both samara and leaf was not markedly affected by chilling and could acclimate to chilling stress. Short-term freezing could completely inhibit PSII activity in both samara and leaf, indicated by the drop of values of Fv/Fm, PIABS, φEo to zero. PSII functional parameters of short-term dark frozen samara could be largely recovered whereas those of frozen leaf could not be recovered. The higher tolerance of samara to short-term low temperature stress than leaf is of great ecological significance for seed development, population establishment of Siberian maple.     

Epidemiology of flavescence dorée in vineyards in northwestern Italy

ABSTRACT A serious outbreak of flavescence dorée (FD) was reported in Piemonte, northwestern Italy, in 1998, and since then, the disease has compromised the economy of this traditional wine-growing area, even following the application of compulsory insecticide treatments to control Scaphoideus titanus, the vector of the causal phytoplasma. Affected vines show severe symptoms, varying according to the cultivar, and are rogued to reduce disease spread. Following winter and pruning, a previously affected vine may appear symptomless and free of phytoplasmas in its aerial as well as its root system, even by nested-polymerase chain reaction assays. Such plants are considered to be "recovered". Since 1998 homogenous data on the incidence of newly infected, healthy, or recovered plants productivity, presence of vectors, and treatment schedules have been collected in seven severely affected vineyards of southern Piemonte for 5 years (1999 to 2003). Infectivity and recovery rates were also calculated each year. From 1999 to 2003, the average number of healthy plants decreased and the numbers of recovered plants and those with symptoms increased. Productivity of recovered vines, although lower than that of healthy ones, was always higher than that of vines with symptoms and was not influenced by the time elapsed from date of recovery. The relationships between the ln-transformed number of vectors trapped in the vineyards the previous year and the infection and the recovery rates were fitted by an exponential (R(2) = 0.95) and an asymptotic (R(2) = 0.93) model, respectively.     

Can the extract of Aristolochia argentina Griseb affect the foraging decisions of the leaf cutting ant Acromyrmex lundi (Guérin)? Preliminary assays

ABSTRACT

The aim of this study was to evaluate whether foraging decisions of Acromyrmex lundi in the field are affected by the extract of Aristolochia argentina. A free choice test was performed using Rosa x hybrida leaves treated with the extract and control with acetone. Two leaves (treated and control) were presented on either side of a foraging trail. The percentage of removed material was recorded for 90 minutes of observation on two consecutive days. Dry weight and repellency index were calculated. Ant activity, the percentage of carried leaves and weight data were analyzed using a “t”-test for paired data, and a General Linear Mixed Model test was used to evaluate the different variables and their interactions. A. argentina extract (1%) did not affect the foraging activity of A. lundi, whereas the 5% dose caused significant differences in foraging activity as well as between the factors and the interactions. A repellency index of above 95% was obtained at the 5% dose. The extract of A. argentina could be considered for future management of this insect.     

Specific characters of 16S rRNA gene and 16S–23S rRNA internal transcribed spacer sequences of Xylella fastidiosa pear leaf scorch strains

Pear leaf scorch, the only Xylella fastidiosa-induced disease reported from Taiwan, was found in area where the variety Hengshan (Pyrus pyrifolia) was grown. Strains of pear leaf scorch Xyl. fastidiosa (XF-PLS) shared similarities to strains of other host origins in the requirement of complex medium and the exhibition of rippled cell walls, however, recent serological and molecular biology studies showed difference among them. Five strains of XF-PLS were compared with 20 other strains originally isolated from almond, oleander, pecan, plum, peach, mulberry, grapes, citrus, coffee, and sycamore by sequence analyses of the 16S rRNA gene and 16S–23S rRNA internal transcribed spacer region (ITS). When sequences of 16S rRNA gene based on fragment size of 1,537–1,540 bp were compared, the similarity index among 5 XF-PLS strains was 99.3–99.8%, whereas it was 97.8–98.6% between XF-PLS strains and strains from other hosts. When sequences of 16S–23S rRNA ITS based on fragment size of 510–540 bp were compared, the similarity index among 5 XF-PLS strains was 99.0–100%, whereas it was 80.7–82% between XF-PLS strains and strains from other hosts. Multiple sequence alignments led to the identification of 5 polymorphic nucleotides in the 16S rRNA gene among the 25 Xyl. fastidiosa strains, and there were considerable variations in the nucleotide sequences of 16S–23S rRNA ITS between XF-PLS and the other 20 Xyl. fastidiosa strains. The phylogenetic trees revealed that XF-PLS strains were separated from strains of other hosts. Strains of other hosts were divided into four subgroups: strains from (1) oleander, (2) grape, almond M23 and mulberry, (3) citrus and coffee, and (4) pecan, peach, plum, sycamore and almond M12. Results indicate that XF-PLS strains were not closely related to the above-mentioned strains from other hosts and could possibly belong to a new subspecies of Xyl. fastidiosa.     

Detection of <Emphasis Type="Italic">Ageratum enation virus</Emphasis> from cat’s whiskers (<Emphasis Type="Italic">Cleome gynandra</Emphasis> L.) with leaf curl symptoms in India

An association of a begomovirus with leaf curl symptoms on Cleome gynandra was detected using a polymerase chain reaction (PCR) with begomovirus-specific primers. Further, the complete DNA-A of the begomovirus was cloned and sequenced. BLAST analysis of the sequence data revealed 92–99% identities and close relationships with several isolates of Ageratum enation virus (AgEV); therefore, we identified the virus associated with leaf curl symptoms of C. gynandra as an isolate of AgEV. This report is the first on the detection of AgEV in plants of C. gynandra with leaf curl in India.     

Effect of Cotton leaf curl virus infected plants on the biology of the whitefly,Bemisia tabaci (Hemiptera: Aleyrodidae): Vector–virus mutualism

Cotton leaf curl virus (CLCuV) (Geminiviridae : Begomovirus), the causative agent of leaf curl disease in cotton plants (Gossypium hirsutum), is exclusively transmitted by whitefly species Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). CLCuV transmission occurs in Sriganganagar (Rajasthan), an area endemic with cotton leaf curl disease. The relationships between plant viruses, their herbivore vectors and host plants can be beneficial, neutral, or antagonistic, depending on the species involved. To further understand these relationships, fecundity and life history parameters of an indigenous non- b (Asia II genetic group) biotype whitefly, B. tabaci, were compared on 10, 25, and 40 days post-inoculation (DPI), in CLCuV-infected and healthy cotton plants to determine the effect of virus on its vector. The development time of the immature stages of whiteflies was significantly reduced on CLCuV-infected plants. The development time of the immature stages did not change with severity of symptoms at 25 and 40 DPI (45- and 60-d-old plants). Cotton leaf curl virus infection increased percent egg viability of B. tabaci. Whiteflies deposited significantly fewer eggs on virus-infected plants than on healthy plants. Whiteflies had better egg viability on younger plants than older plants, whereas plant age did not affect the fecundity. Male and female whiteflies had shorter longevity on CLCuV-infected plants than on healthy plants.     

Versuche mit Herbiziden in Waid Isatis tinctoria L. in Thüringen

Between 2002 and 2006 seven experiments with different herbicides were carried out in woad in two Thuringian experimental stations. The objective of these tests was to get the required data for the approval procedure according to the regulations of §§?18?a and?b PflSchG. The tests showed the applicability of some herbicides for the weed control in woad. Because of the possible use of woad for pharmaceutical purposes in the future investigations with dried leaves and roots of woad were carried out with the objective of getting data of the residues of active compounds in the plant materials. The results of the tests have shown that the maximum residue level for some active compounds can be exceeded. At the current situation of woad cultivation further herbicide tests in this crop are not intended.     

Versuche mit Herbiziden in Zitronenmelisse Melissa officinalis L. in Thüringen

Between 1996 and 2008 19 experiments with 33 herbicides were carried out in lemon balm in experimental stations and on lemon balm fields of Thuringian farms. The main objective of the tests was to get the necessary data for the authorization procedure according to the regulations of §?18a PflSchG. Lemon balm plants are very susceptible against some herbicides like Bacara, Bandur, Centium 36?CS, Goltix 700?SC, Husar, Sumimax. Other herbicides like Boxer, Stomp?SC and other Pendimethalin-herbicides can cause severe damages on peppermint if they are applied to the false stage of development of the plant and/or unfavourable climatic conditions. The use oft the herbicides Basagran, Boxer, Fusilade MAX, Lentagran WP and Stomp SC, Stomp Aqua, Stomp Raps is authorized for the application in lemon balm according the regulations of §?18a PflSchG. The herbicides Goltix 700?SC, Lontrel?100 und CLIOPHAR?100, Roundup UltraMAX and Targa Super can be used in lemon balm according the regulations of §?18b PflSchG. Further experiments with herbicides in lemon balm are intended to the authorization to more herbicides and to unsolved problems with the weed control in this crop like for example the often insufficient effects of the recently authorized herbicides against Solanum spec., Galinsoga spec., Polygonum spec. and other weeds.     

Versuche mit Herbiziden in Baldrian Valeriana officinalis L. in Thüringen

Between 1998 and 2008 12 experiments with 25 herbicides were carried out in valerian in experimental stations and on valerian fields of Thuringian farms. The main objective of the tests was to get the necessary data for the authorization procedure according to the regulations of § 18 a PflSchG. The use oft the herbicides Devrinol FL, Lentagran WP, Stomp Aqua and Stomp Raps is authorized for the application in valerian according the regulations of § 18 a PflSchG. The herbicides Basagran, Boxer, Roundup UltraMAX and Targa Super can be used in valerian according the regulations of § 18 b PflSchG. Further experiments with herbicides in valerian are intended to the authorization to more herbicides and to unsolved problems with the weed control in this crop like for example the often insufficient effects of the recently authorized herbicides against Solanum spec., Galinsoga spec., Polygonum spec. and other weeds.     

Virusnachweis in Blattläusen

Potato virus Y (PVY) causes great economic losses in potato production world-wide. Concerning important it has replaced Potato leafroll virus (PLRV). Virus is transmitted by different aphid species in a non-persistent manner. During last years the developing of new effective methods for PVY monitoring, forecasting and detection in aphids is of increasing interest. Sensitive, rapid detection of virus in its natural vectors is of a great need to investigate the relationship between aphid migration and the spread of PVY. Simple diagnostic protocol for the detection of non-persistent Plum pox virus and semipersistent Citrus tristeza virus in aphids, proposed by Olmos et al. (2005) was probed to validate and estimate the efficiency of its applying for the detection of PVY in different aphid species too.     

A selective barrier in the midgut epithelial cell membrane of the nonvector whitefly <Emphasis Type="Italic">Trialeurodes vaporariorum</Emphasis> to <Emphasis Type="Italic">Tomato yellow leaf curl virus</Emphasis> uptake

We studied the presence of a potential transmission barrier that blocks Tomato yellow leaf curl virus in the nonvector greenhouse whitefly, Trialeurodes vaporariorum. Because T. vaporariorum can ingest and retain the virus after acquisition feeding on an infected plant, comparable to the vector whitefly Bemisia tabaci, circumstance evidence suggested that a transmission barrier presents at location(s) where the virus moves from the digestive tract lumen to the hemolymph. To provide direct evidence for the site of a transmission barrier in the nonvector insect, we compared the accumulation levels and localization of the virus between the two species of whiteflies. Quantitative real-time and conventional PCR analysis showed that accumulation of the virus during acquisition feeding and retention after a short acquisition period were indistinguishable between the two species, but the circulation of the virus within the whiteflies differed significantly between the species. In an immunofluorescence analysis using an antibody specific to the coat protein of the virus, the virus was restricted to the luminal surface of the midgut epithelial cells and did not enter their cytoplasm or that of the salivary glands in T. vaporariorum. In contrast, the virus was localized within the cytoplasm of the midgut epithelial cells and in the paired salivary glands of B. tabaci adults. This direct evidence shows that a selective transmission barrier at the luminal membrane surface of midgut epithelial cells in the nonvector whitefly blocks entrance of the virus into the midgut epithelial cells, resulting in incompetence as a vector of the virus.     

A model system for plant-virus interaction—infectivity and seed transmission of <Emphasis Type="Italic">Cherry leaf roll virus</Emphasis> (CLRV) in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

The wide natural incidence of Cherry leaf roll virus (CLRV) in deciduous forest trees and nurseries in northern Europe is believed to have occurred, apart from occasional mechanical spread and transmission through grafting, mainly by seed transmission. The mode of the vertical transmission and its role in the epidemiology of the virus has not been investigated, basically due to the inconvenient host-pathogen combinations studied to date. With the aim of obtaining an appropriate system for identification of viral genes and products participating in infection processes and seed transmission of CLRV, we performed infection and seed transmissibility tests with CLRV in Arabidopsis thaliana plants. Two phylogenetically and serologically different CLRV isolates were tested. Both of them were found able to infect A. thaliana plants, exhibited clear symptoms of the infection and spread systemically in the plants. Infection of the seeds and of a remarkable number of seedlings generated from infected seeds was possible for two consecutive generations. These results, for first time, report seed transmission of CLRV in the model plant A. thaliana and allow the assumption to be made of embryo invasion during seed transmission. Furthermore, first indications are given that genetically diverse CLRV isolates exhibit different abilities for vertical transmission in A. thaliana. The CLRV-A. thaliana model system is suitable for investigating viral invasion of developing plant organs and meristematic tissue, a prerequisite for successful virus dissemination via vertical transmission through seed.