Spatial and temporal stolbur population structure in a cv. Chardonnay vineyard according to vmp1 gene characterization

Bois noir is a grapevine disease caused by the stolbur phytoplasma. It is widespread in all European and Mediterranean viticultural areas, and it can induce severe damage to the quality and quantity of production. The recent disease recrudescence has encouraged studies on the use of molecular markers to assess the genetic diversity of stolbur strains. The aim of this study was to evaluate the presence of Bois noir symptoms and to monitor the spatial genetic structure of the stolbur population according to vmp1 genotypes, through 2011 and 2012 in a cv. Chardonnay vineyard. In both years, there were increased vines with symptoms from July to September. The analysis of dispersal indices showed that the spatial distribution was uniform in the vineyard. However, the two‐dimensional contour maps show that Bois noir severity was higher in plants located on the borders than in the central parts of the vineyard. Stolbur population was composed of two prevalent vmp genotypes (V14, V12) across both years, along with other minor haplotypes (V3, V4, V9, V11, V15, V18, in 2011; V3, V18 in 2012). The data indicate that the vmp1 gene is an efficient marker to study the population structure of stolbur phytoplasma, to track the movement of the pathogen, and to identify the inoculum source, which will all serve in the planning of control strategies.     

‘赤霞珠’葡萄在河西走廊产区不同产地的品质分析

为明确‘赤霞珠’葡萄在河西走廊不同地区的品质差异,连续3 a在武威、张掖和嘉峪关果园采集成熟期葡萄果实进行品质测定和分析。结果表明：不同产地果实中可溶性固形物、还原糖及有机酸含量存在显著差异。张掖地区果实可溶性固形物含量最高(24.81%),武威地区果实可滴定酸含量和葡萄果实总酚含量最高(分别为1.34%和24.06 mg·g^-1),张掖地区单宁含量最低(5.57 mg·g^-1)。张掖地区果实中葡萄糖、果糖、蔗糖的总含量分别达到71.99、70.51、5.61 mg·g^-1,显著高于嘉峪关和武威地区;武威地区葡萄果实酒石酸和草酸的含量较高,分别为8.66 mg·g^-1和0.32 mg·g^-1,显著高于嘉峪关和张掖。‘赤霞珠’葡萄共检测出36种香气物质,其中包括9种醛、9种醇、4种酯、3种酮、2种酚和9种其他类化合物,各地区香气物质的类型及总量均表现为嘉峪关>张掖>武威。整体而言,张掖地区‘赤霞珠’果实品质较好,而嘉峪关地区‘赤霞珠’芳香物质积累较多。     

Temporal disease dynamics and relative importance of sexual and asexual reproduction of grape downy mildew (Plasmopara viticola) in an isolated vineyard in the North Georgia Mountains,USA

The North Georgia Mountains are the southernmost region along the United States East Coast where European wine grapes (Vitis vinifera) are grown commercially. Epidemics of downy mildew, caused by Plasmopara viticola, are frequent and severe, but little is known about the epidemiology and population biology of the pathogen in this region. Disease monitoring in an experimental vineyard from 2015 to 2017 indicated that times of disease onset and progress rates were highly variable across years and cultivars. Oospores were observed microscopically, and simulation with a process-based model indicated presence of conditions favourable for oospore germination in the spring and early summer each year. A total of 409 P. viticola isolates collected over three  years were genotyped with seven microsatellite markers, revealing very high genotypic diversity, which when combined with the observation of oospores is indicative of a sexually reproducing population. Among the 409 isolates, 225 multilocus genotypes (MLGs) were identified, of which 164 were detected only once and 61 were repeated (clonal). Eight MLGs (represented by 28 isolates) were detected across years, suggesting the possibility of asexual overwintering of P. viticola in this region. Across sampling dates, the percentage of isolates belonging to nonrepeated (unique) MLGs ranged from 27.3% to 63.2%. Even towards the end of the annual epidemic, the percentage of isolates in nonrepeated MLGs was still relatively high, around 30%. These MLGs may have originated from oospores germinating late during the growing season, although incomplete sampling at earlier dates and contribution by immigration cannot be fully excluded.     

Effect of pea plant architecture on spatiotemporal epidemic development of ascochyta blight (Mycosphaerella pinodes) in the field

The effect of pea canopy structure on epidemics of Mycosphaerella pinodes was investigated in four spring pea cultivars (Bridge, Obelisque, Solara and Athos) in two field experiments. These cultivars had similar levels of susceptibility to ascochyta blight and presented different architectural features (branching, standing ability and stem height). Stem height ranged from 77 to 95 cm in 1999 and from 72 to 92 cm in 2000, while leaf area index (LAI) ranged from 3·8 to 5·1 in 1999 and from 3·8 to 4·7 in 2000. Internode lengths varied from 4·6 to 6·0 in 1999 and from 3·8 to 4·7 in 2000. Mean distance between nodes in the canopy (MDN) ranged from 12·2 to 15·3 cm in 1999 and from 11·2 to 13·9 cm in 2000. Canopies with different architecture differed in disease progression on stipules and mainly on pods. The levels of disease on stipules and pods were strongly correlated. Moreover, if disease was considered as a function of stipule height up the stem, large differences in vertical disease distribution were observed between cultivars. Three architectural features acted on disease development: cumulative LAI above the node on which disease was assessed (LAIcum) and large MDN favouring disease development, and large internode length reducing disease severity. Modifying LAI distribution and plant organization could be one way to reduce the impact of ascochyta blight, by direct or indirect effects on environmental and dispersal conditions.     

西南地区耕地复种指数的时空格局演变及影响因素

基于复种指数和"热量-降水"定量化关系模型,分析了西南三省(四川省、贵州省、云南省)从1990—2015年间耕地复种指数的变化趋势、格局演变及其影响因素。结果表明:从1990—2015年云南、贵州和四川复种指数比分别降低27.04%、1.67%和25.83%,复种指数均值分别为147.37%、239.69%和206.05%。2006—2015年为三省粮食作物复种指数波动变化最大的时期,该期粮食作物复种指数年际变动率为四川>贵州>云南,其值分别为-41.01%、-33.55%和-29.60%。西南地区耕地复种指数总体上呈东高西低的空间分布格局,其中东部地区耕地复种指数明显高于西部地区,中部地区高于北部和南部地区。2010—2015年,中国西南地区潜力复种指数均为东部和南部地区高于中部和西北部地区,其中四川东部地区潜力复种指数最大;云南省耕地复种可提升潜力值,明显高于贵州和四川,贵州省可提升潜力地区最少。耕地复种指数年际变化受自然因素和人类活动的影响较大,其中复种指数与年均温度、≥0℃积温、人口数量和农业生产总值呈显著的正相关关系;一般而言,丘陵地区耕地复种指数低于平原地区;气...     

The significance of guttation in the secondary spread of Clavibacter michiganensis subsp. michiganensis in tomato greenhouses

Bacterial canker, caused by Clavibacter michiganensis subsp. michiganensis (Cmm), can spread in commercial tomato greenhouses causing epidemics. Results of greenhouse experiments with Cmm‐contaminated tools demonstrated disease spread for only a limited distance (<4 plants) from infected plants. However, touching symptomless infected plants bearing guttation droplets prior to touching nearby plants spread the pathogen over longer distances within rows (>22 plants). The pathogen was exuded in large numbers in the guttation fluid of infected plants; its presence in the guttation fluid was not influenced by the inoculation procedures, leaf age or the volume of the guttation droplets. Population size of Cmm and the incidence of leaflets with epiphytic bacteria were significantly higher in plants placed in a guttation‐induction chamber than in those kept in a growth chamber with high humidity, suggesting exudation through guttation contributed to the formation of epiphytic populations on leaflets. This new knowledge may provide a simple and environmentally friendly means for decreasing the spread of the disease by avoiding contact with plants during periods when they bear guttation droplets.     

Role of ascospores and conidia in the initiation and spread of South American leaf blight in a rubber tree plantation

Microcyclus ulei, the fungus causing South American leaf blight (SALB) on rubber tree leaves, produces two main types of spores: ascospores and conidia. To assess their respective epidemiological role, a field experiment was conducted in French Guiana over 3 years. Tree phenology, disease severity and climate variables were recorded while airborne spores were trapped and quantified. Ascospores were shown to play an essential role in the perpetuation of the disease outside the host's growth periods, in the resumption of epidemics, and in the spread of the disease to disease‐free zones. Conidia were trapped in visibly infected plots only, during periods of host growth. Disseminated over short distances and present only temporarily on leaves, the conidia enabled the disease to spread stepwise when the climate was conducive. Segmentation analysis revealed that the duration of high relative humidity was the climatic variable most related to ascospore trapping. Ascospore release did not require low temperatures. Considering the essential role of the ascospores in the initiation and spread of disease, artificial defoliation as a means of reducing the inoculum pressure during tree refoliation is proposed to control SALB. To check the validity of this method, a survey over several years of natural defoliation–refoliation in relation to climate and other leaf diseases is needed.     

The relationship of leaf wetness duration and disease progress of glume blotch,caused byStagonospora nodorum,in winter wheat to standard weather data

Almost 50% of the variation in leaf wetness duration can be explained by maximum and minimum temperatures, rainfall and hours with relative humidity above 90% on a daily basis. All of these parameters can be estimated from a standard weather station. If variables related to wind are added the level of explanation increases to 69–76%. Leaf wetness duration explained up to 42% of the rate of disease increase (RDI) forS. nodorum. Leaf wetness duration was accumulated over a 5-day window period and correlated with rate of disease increase after a 7-day lag period. Standard weather variables could explain 20–34% of the disease increase. The relevance of these statistical models to disease prediction is discussed.     

The proportion of viruliferous individuals in field populations of Frankliniella occidentalis: Implications for tomato spotted wilt virus epidemics in tomato

Tomato spotted wilt tospovirus (TSWV) infected plants and western flower thrips (Frankliniella occidentalis Perg., WFT) adult population densities were monitored during 1993 and 1994 in field tomatoes in Northeastern Spain. The proportion of viruliferous WFT adults in field populations was quantified. A significant association has been found between early population densities of WFT adult thrips and final TSWV incidence for early transplanted tomato crops. In contrast, for late transplanted tomato crops, whereas similar high final disease incidences of TSWV could be attained, very low WFT adult population densities were always detected. The significantly higher infectious potential of WFT populations collected during the early growth stages of late transplanted tomatoes could be relevant for the TSWV incidences attained in spite of the low thrips numbers detected.     

露地栽培番茄斑萎病毒病发生流行规律调查及TSWV重要寄主植物监测

为明确云南省昆明市露地栽培条件下番茄斑萎病毒病的发生流行特征,于2014—2015年采用病害系统调查法结合病毒ELISA及RT-PCR检测方法研究露地栽培条件下由番茄斑萎病毒(tomato spotted wilt virus,TSWV)引起的病毒病发生规律及其重要寄主种类,并研究利用防虫网隔离蓟马对番茄斑萎病毒病的防控效果。结果表明:番茄斑萎病毒病在露地番茄主要种植期3—10月普遍发生,番茄苗期和移栽初期是该病毒病防控的关键期,带毒种苗调运是该病毒病的主要传播途径;田间多种茄科和菊科植物是TSWV的重要中间寄主。在田间,菊科寄主植物油麦菜、莴苣、鬼针草、牛膝菊上TSWV的检出率均较高,在42.53%～81.63%之间;茄科寄主植物中辣椒上TSWV的检出率最高,为41.99%,其次为马铃薯,TSWV检出率为27.78%,在番茄上TSWV的检出率为19.02%,因此生产中应对这些TSWV重要中间寄主给予更多关注和防控。应用防虫网能有效隔离蓟马,使番茄斑萎病毒病发病率和病情指数较对照分别降低了6.44个百分点和5.31,可有效降低番茄苗期及定植期斑萎病毒病的发生。     

The temporal pattern of captan residues on apple leaves and fruit under field conditions in relation to weather and canopy structure

BACKGROUND: Captan is an important fungicide for controlling diseases in horticultural crops. Understanding its dissipation is important for estimating dietary risks and optimising pesticide application. Field experiments were conducted on apple leaves and fruit to investigate (1) the temporal variability of captan residues, (2) the contribution of several factors to the variability in residues and (3) the relationship between residues and climatic conditions. RESULTS: Initial captan deposits and subsequent residues on fruit and leaves were closer to a lognormal than to a normal distribution. The unit-to-unit variation contributed most to the observed variability in the initial deposit and subsequent residues. Variability due to orchards or trees or tree-zone interactions was also frequently important, but there was no discernable trend in the effects. The variability in residues did not appear to decrease over time. Canopy structure affected greatly the initial deposition but had little direct effect on subsequent captan loss. Fruit and leaves on the outside of the tree canopy received more deposit than those on the inside, but these differences gradually decreased over time. Captan loss resulted mainly from the first rainfall after an application. CONCLUSIONS: Captan loss is mainly due to rain, and the loss is negligible under dry conditions.     

Detection of Acidovorax valerianellae in corn-salad seeds, seed transmission of the pathogen and disease development in the field

Acidovorax valerianellae , the causal agent of bacterial black spot of corn salad and responsible for severe economic losses to this vegetable in France, was successfully transmitted to corn-salad plants by artificially inoculated seeds in glasshouse and field experiments. In the field experiments, climatic data recorded under plastic tunnels indicated that increasing temperature and relative humidity increased symptom development. To investigate the possible contamination of commercial seedlots of corn salad, a seed test was developed consisting of soaking batches of seeds (five batches each of 5000, 1000, 500 and 100 seeds) overnight at 4°C in distilled sterile water, followed by dilution-plating of seed extracts on TSAV (tryptic soya agar for A. valerianellae ) semiselective medium. Suspected colonies were identified by biochemical and pathogenicity tests or, within 24 h, using antibodies specific to A. valerianellae . Acidovorax valerianellae was detected in three lots. Seed infection levels ranged from 0·10 to 0·89% of contaminated seeds and a single seed carried up to 1800 A. valerianellae colony-forming units.     

Diuron mineralisation in a Mediterranean vineyard soil: impact of moisture content and temperature

BACKGROUND: The diuron‐mineralising ability of the microbiota of a Mediterranean vineyard soil exposed each year to this herbicide was measured. The impact of soil moisture and temperature on this microbial activity was assessed. RESULTS: The soil microbiota was shown to mineralise diuron. This mineralising activity was positively correlated with soil moisture content, being negligible at 5% and more than 30% at 20% soil moisture content. According to a double Gaussian model applied to fit the dataset, the optimum temperature/soil moisture conditions were 27.9 °C/19.3% for maximum mineralisation rate and 21.9 °C/18.3% for maximum percentage mineralisation. The impact of temperature and soil moisture content variations on diuron mineralisation was estimated. A simulated drought period had a suppressive effect on subsequent diuron mineralisation. This drought effect was more marked when higher temperatures were used to dry (40 °C versus 28 °C) or incubate (28 °C versus 20 °C) the soil. The diuron kinetic parameters measured after drought conditions were no longer in accordance with those estimated by the Gaussian model. CONCLUSION: Although soil microbiota can adapt to diuron mineralisation, its activity is strongly dependent on climatic conditions. It suggests that diuron is not rapidly degraded under Mediterranean climate, and that arable Mediterranean soils are likely to accumulate diuron residues. Copyright © 2010 Society of Chemical Industry     

Planococcus ficus and the spread of grapevine leafroll disease in vineyards: a 30-year-long case study in north-West Spain

European Journal of Plant Pathology - The mealybug Planococcus ficus is one of the main vectors of Grapevine leafroll associated virus-3 (GLRaV-3), which was commonly detected in cv...     

Epidemiology of a Neotropical rust (Puccinia psidii): periodical analysis of the temporal progress in a perennial host (Syzygium jambos)

The epidemiology of the Neotropical rust caused by Puccinia psidii in the Indian Myrtaceae Syzygium jambos (rose apple) was investigated in central Brazil. Disease severities recorded during a 12-month period were fitted by a Fourier curve with three cyclic components or harmonics. The first, second and third harmonics accounted for 49·6, 25·9, and 1·5% of total disease measured, respectively. A highly significant linear correlation was observed between the first harmonic and the accumulated number of days having at least 6 h wetness, or a minimum of 90% relative humidity, combined with temperatures that ranged from 18 to 20°C. No significant correlation was observed between the second and third harmonics and the weather variables evaluated. Rose apple trees showed a flush of growth with new susceptible host tissue during the evaluation period, with two major outbreaks of rust of variable intensity. Host growth was fitted by a Fourier curve with two significant harmonics. The first and second harmonics accounted for 37·5 and 22·1% of total host growth measured, respectively. A highly significant negative linear correlation was observed between the first harmonic and daily maximum and minimum temperatures, rainfall, and duration of the light period. Inoculum availability was not a limiting factor for disease progress since urediniospores were present during most of the period studied. A major peak in numbers of rust spores followed the main peak of disease severity. Thus, rust epidemics on rose apple in central Brazil were shown to depend on the duration of leaf wetness in the dark, and also on night-time temperatures during that same wetness period. This study is the first example of a periodical analysis of an epidemic in a perennial crop.     

Insecticide resistance inFrankliniella occidentalis: Corroboration of laboratory assays with field data and cross-resistance in a cypermethrin-resistant strain

Field efficacy of five insecticides to a greenhouse strain ofFrankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) of known resistance status was studied. In a greenhouse trial, the mortality of aF. occidentalis strain (Uncali) which exhibited resistance only against cypermethrin in laboratory assays, reached 56%, 68%, 82%, 94% and 99%, 24 h after application of abamectin, cypermethrin, endosulfan, malathion and methomyl, respectively. In the laboratory, for larval mortality equal to that achieved in the field, much lower doses — half of the field dose of cypermethrin and endosulfan, and one-third and one-sixth of malathion and methomyl, respectively, were required in topical application. Because of differences between laboratory and field responses ofF. occidentalis to insecticides, a sound resistance evaluation program to determine field efficacy of insecticides is needed. Resistance increased 28.0- and 139.3-fold at LC₅₀ in theF. occidentalis strain subjected to 27 and 44 cycles of cypermethrin selection, respectively. A slight cross-resistance of two- to threefold was found with endosulfan, malathion and methomyl and no cross-resistance was observed with abamectin. http://www.phytoparasitica.org posting August 4, 2008.     

Dual begomovirus infections and high Bemisia tabaci populations: two factors driving the spread of a cassava mosaic disease pandemic

A cassava mosaic disease (CMD) pandemic currently affects much of East and Central Africa. To understand the factors driving the pandemic's continued spread, complementary data sets were collected from cassava plots, planted with healthy cuttings, at eight sites along a north–south transect in southern Uganda, through the pandemic's leading edge. Data were collected on virus incidence, symptom severity, populations of the whitefly vector, Bemisia tabaci , their infectivity and ability to transmit different viruses. In 1996, 6 months after planting, CMD incidences were highest at sites 1 and 2, then decreased progressively until site 6, and remained low at sites 7 and 8. The largest B. tabaci populations also occurred at northernmost sites, 1–3. In 1997, CMD incidence increased significantly at sites 5–8 and this was associated with significant increases in the B. tabaci populations. The pandemic's spread was also associated with significant increases in the percentage of dual infections of East African cassava mosaic virus -Uganda and African cassava mosaic virus , which caused the severest symptoms and the greatest reduction in leaf area. Whitefly adults collected from within the pandemic area were infective, whereas those collected ahead of the pandemic were not. The transmission rate of African cassava mosaic virus from plants with dual infections was significantly less than that of East African cassava mosaic virus -Uganda, which may explain the latter's predominance within the pandemic. These results show that the arrival of East African cassava mosaic virus -Uganda into areas affected previously only by African cassava mosaic virus , has resulted in novel virus/vector/host–plant interactions that drive the pandemic's continued spread.     

Genetic variation and evolutionary analysis of Pepino mosaic virus in Sicily: insights into the dispersion and epidemiology

Pepino mosaic virus (PepMV) is a highly infectious potexvirus that causes a severe disease in tomato (Solanum lycopersicum) crops worldwide. In Sicily, the first outbreak was detected in a single greenhouse in 2005 and it was promptly eradicated. However, in 2008, a large number of greenhouses were simultaneously affected, and it was impossible to eradicate or control the virus. This study addressed the dispersion and the genetic diversity of PepMV isolates obtained from the outbreak in Sicily, in comparison with worldwide PepMV isolates, to gain insight into the factors determining the evolution and epidemiology of the virus. A total of 1800 samples from plants with and without symptoms were collected in the Sicilian provinces of Agrigento, Caltanissetta, Palermo, Ragusa, Siracusa and Trapani. Three isolates collected at different times were biologically characterized. The incidence of the virus increased rapidly from 13% in 2011 to 63% in 2013, and phylogenetic analysis showed that all Sicilian isolates of PepMV belonged to the CH2 strain, one of the six strains previously described. Nucleotide diversity of the Sicilian isolates was low, thus suggesting rapid spread and genetic stability.