Proportion Of Infected Plants Research Articles

A comparative study of viral infectivity, accumulation and symptoms induced by broad bean wilt virus 1 isolates

Broad bean wilt virus 1 (BBWV-1, genus Fabavirus, family Secoviridae) is a bipartite positive-sense single-stranded RNA virus distributed worldwide infecting many herbaceous species. Until now, scarce information regarding biological properties of BBWV-1 isolates is available. This work shows a comparative study on virus infectivity (proportion of infected plants over inoculated plants), virus accumulation and symptoms induced by four genetically different BBWV-1 isolates (Ben, B41/99, NSRV and PV0548) which were mechanically inoculated on several herbaceous hosts. The four BBWV-1 isolates infected broad bean, tomato, pepper and Nicotiana benthamiana plants, whereas none of them infected cucumber, common bean and melon. Infectivity ranged from 40 to 60% in tomato and from 75% to 95% in pepper, whereas it was 100% in broad bean and N. benthamiana for the four BBWV-1 isolates. Symptoms showed differences depending on the host plant, the viral isolate and the infection time. Virus accumulation was determined in broad bean and pepper plants and showed differences among host species and BBWV-1 isolates. No association between plant symptom manifestation and viral titre was observed.

On a combinatorial problem in botanical epidemiology

In botanical epidemiology, one of the major problems is to study the spread of diseases within crops. Several approaches to study the patterns and temporal evolution of diseases have been discussed in the literature, e.g., statistical techniques or variogram analysis. Recently, AlSharawi, Burstein, Deadman and Umar determined the total number of ways to have ℓ isolated infected individuals among m infected plants in a row of n plants. They discussed this in a straightforward combinatorial fashion and considered several associated points, like expectation value and variance of the number of isolated infected plants. In the present paper, we derive their results with the help of generating function techniques and use this method to extend the discussion to plants arranged in a circle as well as in two rows. The dependence of the expected number of isolated infected plants on the proportion of infected plants is considered for large n in all these cases as well as in the case of an arbitrary number of rows and a simple asymptotic behavior is found. Connections to several combinatorial sequences are established.

Crotalaria spectabilis and Raphanus sativus as Previous Crops Show Promise for the Control of Bacterial Wilt of Tomato Without Reducing Bacterial Populations

AbstractRalstonia solanacearum is responsible for bacterial wilt affecting many crops worldwide. The emergent population of R. solanacearum (phylotype IIB/4NPB) wilts previously resistant varieties and has rapidly spread throughout Martinique. No conventional method is known to control it. In this study, previous crops used as sanitizing crops were investigated as an environmentally safe alternative method of control. The ability of the emergent population of R. solanacearum to persist in planta and in the rhizosphere of Brassicaceae, Asteraceae and Fabaceae grown as previous crops was evaluated in controlled conditions, and the incidence of bacterial wilt was assessed in the following tomato crop. Results showed that all species carried R. solanacearum latently. Among Brassicaceae and Asteraceae, the highest density of R. solanacearum was found in planta and in the rhizosphere of Tagetes erecta. The density of the R. solanacearum population in the rhizosphere of Raphanus sativus cv. Karacter was significantly higher than that in Raphanus sativus cv. Melody. In Fabaceae, the density of R. solanacearum population in planta was statistically similar in all species. The density of the R. solanacearum population in the rhizosphere of Crotalaria juncea was significantly higher than that in Crotalaria spectabilis. This study showed for the first time that Crotalaria spectabilis and Raphanus sativus cv. Melody grown as previous crops improve the performance of the following tomato with similar effects on R. solanacearum populations in the soil as bare soil. The incidence of the disease in tomato decreased by 86% and 60%, after R. sativus cv. Melody and C. spectabilis, respectively, and the proportion of infected plants also decreased. These results suggest that C. spectabilis and R. sativus cv. Melody can be used as previous crops to help bacterial wilt control in ecological management strategies without drastic suppression of R. solanacearum population in stem tissues and in the rhizosphere.

The effect of temperature and rainfall on participation of the pathogens causing root and stem rot in spring barley (Hordeum vulgare L.)

Field experiments conducted in the years 1990-1995 were localized at the Plaiit Cultivation Station, Ulhówek to repeat the cultivation of spring barley cultivars Roland and Lot. In conditions of monoculture, Bipolaris sorokiniana and Fusarium culmorum were of the foremost importance in causing root and stem rot. The proportion of infected plants did not increase with time. Depending on the period of vegetation and the cultivar, the percentage of seedlings with necrosis symptoms ranged from 6% to 53,5% and that of stem base rot from 14% to 59%. In the case of both cultivars. root and stem rot was especially intensive in the third successive season of vegetation, i, e,. in 1992. That season was characterized by warm and wet weather conditions. favourable for the infection of seedlings by <em>B.sorokiniane</em> during the period of six weeks after the sowing of grain. Bipolaris sorokiniana always had the greatest proportion in the infction of spring barley but not in the seasons distinguished by hot and dry weather conditions. On the other hand, during dry and hot weather conditions the only or the dominating fungus obtained from the infcted stem base after the heading of spring barley was F. culmorum. In conditions of monoculture, favourable for root and stem rot of spring barley, the temperature and rainfalls clearly distinguished the proportion of B. sorokiniana and F. culmorum in plant infection.

Brassica green manure rotation crops reduce potato stem rot caused by Sclerotinia sclerotium

This study was conducted to evaluate the potential of biofumigation in three Brassica crops including Brassica napus, Brassica juncea and Brassica campestris against potato stem rot caused by Sclerotinia sclerotiorum in field tests. Results from field trials carried out in three naturally infected potato fields during three cropping seasons of 2008–2010 showed that the Brassica crops used as green manure cover crops were able to significantly reduce disease incidence and mean percentage of dead plants (as a proportion of infected plants). Although results varied somewhat by field site and year, B. juncea generally provided the highest level of control, averaging greater than 55.6 % reduction in disease incidence over all fields and years, compared to average disease reductions of 31.6 and 45.8 % for the B. napus and B. campestris crop treatments, respectively. Furthermore reduction of dead plants averaged 61.6, 39.2 and 32.1 % for B. juncea, B. napus, and B. campestris, respectively. In this study, Brassica crops showed various significant inhibitory effects in different fields and years indicating that disease development is affected by other factors including environmental conditions.

Activity of benzothiadiazole on chrysanthemum yellows phytoplasma (‘ Candidatus Phytoplasma asteris’) infection in daisy plants

A commercial preparation of the plant resistance elicitor benzothiadiazole (BTH) (Bion, Syngenta Crop Protection) was tested for its capacity to induce systemic resistance against chrysanthemum yellow phytoplasma (CYP) infection in the Chrysanthemum carinatum plant. Following one 2.4 mM BTH application, plants were exposed to CYP-infective Macrosteles quadripunctulatus leafhoppers. Symptom development and phytoplasma multiplication in the test plants were measured over time. BTH application delayed symptom development and phytoplasma multiplication in treated plants compared with the control ones. CYP titre and symptom severity were significantly lower for the first two weeks post-inoculation in treated plants compared with the control ones, suggesting that systemic acquired resistance (SAR) induced by BTH in C. carinatum is temporary. Higher concentrations of BTH resulted in phytotoxic effects involving the whitening of apical leaves. BTH application was ineffective in reducing the transmission efficiency of CYP by its leafhopper vector. Actually, in both single and group transmission tests, the proportion of infected plants was similar among BTH-treated and untreated plants. The survival of M. quadripunctulatus was unaffected by feeding on BTH-treated daisy plants. Moreover, when leafhoppers were allowed to choose between treated and untreated plants, they showed no preference. We conclude that SAR induced in daisy plants by BTH has no detrimental effects on the vector leafhopper. If the activity of BTH against phytoplasmas is confirmed also on other phytoplasma/host–plant associations, BTH applications might be included in new, more environmentally friendly, integrated management strategies of phytoplasmoses.

Long‐term changes of aphid vectors of Barley yellow dwarf viruses in north‐eastern Italy (Friuli‐Venezia Giulia)

AbstractMigrations of aphid vectors of Barley yellow dwarf viruses (BYDV) were monitored using a Rothamsted Insect Survey suction trap in Friuli‐Venezia Giulia (north‐eastern Italy). Catches from 1983 to 2002 were studied for trends, correlations of total catches of each year with those of previous years, correlations between the autumn and the spring + summer catches of the same year and between spring + summer catches of one year with catches of the previous autumn. Infectivity of autumn alates was studied using biological tests, and infectivity indexes were calculated for all vector species and for Rhopalosiphum padi alone. Colonisation of barley and proportion of infected plants were checked in a field close to the suction trap from 1992 to 2002 and related to trap catches. Catches were also correlated to acreage dedicated to cereal and fodder crops in the region. During the 20 years, 15 BYDV vector species were caught in the trap, but only five species were found consistently colonising barley plants during autumn. R. padi was the most numerous species in catches, while Sitobion avenae was the predominant colonising species in the barley field. Relatively to R. padi, S. avenae colonies were about six times more numerous than expected from catches. The yearly abundance of catches of most species did not change significantly during the 20 years, with a few exceptions, significantly correlated to changes in the acreage dedicated to cereal and fodder crops. There was a significant decrease of the autumn catches of both R. padi and the total of BYDV vectors.

MIXED INFECTION OF PEACH TREES WITH PEACH LATENT MOSAIC VIROID AND HOP STUNT VIROID IN THE CZECH REPUBLIC

Peach latent mosaic viroid (PLMVd) and Hop stunt viroid (HSVd) are the only viroids known to naturally infect stone fruit trees. During a field validation of detection methods developed for plant certification, several peach trees from the experimental orchard of the Czech University of Agriculture in Prague were tested for the presence of both viroids. Leaves from apparently symptomless trees of several varieties were collected in late summer 2002. Five of the 66 tested trees were infected by PLMVd only, 46 resulted infected by both PLMVd and HSVd, whereas 15 did not contain any of the tested viroids. Although such a high proportion of infected plants can probably be attributed to the experimental and teaching practices in the orchard, these results have prompted us to carry out a survey for the PLMVd and HSVd occurrence on peach trees in the Czech Republic.

Density-dependent parasitism of Delphacodes kuscheli eggs by Anagrus flaveolus: Influence of egg patchiness and density

Many herbivorous insects display a marked tendency to aggregate and previous work has shown that the parasitoids likely to be more effective for pest control programs are those that concentrate their attacks on denser host patches. However, as herbivore density changes different spatial patterns usually emerge in their distribution. In Tucumán province, Argentina the mymarid Anagrus flaveolus is a native egg parasitoid of Delphacodes kuscheli, which oviposits endophitic eggs and is the only demonstrated vector of the MRCV virus that seriously affects maize (Zea mays). Winter is the critical period for maize colonization from oat (Avena sativa) crops where D. kuscheli overwinters. We analyzed, under field conditions and during the winter critical period, percentage parasitism by A. flaveolus when host patch density increases following two different patterns: an increase in the batch size, and an increase in the number of infested plants with similar mean batch size. In order to generate a heterogeneous egg patchiness, 144 oat plants were arranged in 36 groups of four plants each, and four types of groups were created by placing one, two, three or four infested plants per group. Each group was characterized by the number of infested plants as well as by the number of eggs. If one, two, three or all four plants were infested, the group was denominated G1, G2, G3 or G4, respectively. Considering only G1, the number of eggs per group increased only if the batch size increased. On the other hand, considering all G1, G2, G3 and G4 groups, the increase in patch density from G1 to G4, was essentially due to an increase in the number of infested plants. The groups were symmetrically distributed in the field in a homogeneous 200-m2 area (the position of each group was randomly assigned), and allowed for oviposition for 48 h since A. flaveolus only attacks eggs that have three or less days of development. We found that almost all infected plants were parasitized by A. flaveolus but parasitism never surpassed 64% of the available eggs, suggesting that the parasitoid selectively attacks eggs inserted in particular places of the oat plant, and/or never saturates a batch. We also found that parasitism was spatially direct density dependent when only G1 was considered, as well as when G1, G2, G3 and G4 were considered together. In the first case, an increase in the number of eggs in a group of four plants represents an increase in the batch size, and higher batch size received higher parasitism. In the second case, it represents an increase in the number of infested plants, and higher patch density received higher parasitism. Although the proportion of infected plants parasitized was similar, infected plants with similar number of eggs received higher parasitism when placed in denser groups (G3 and G4) than when placed in the less dense groups (G1 and G2). Behavioral mechanisms leading to a restriction on re-dispersal, like an area-restricted search behavior, as well as supernormal stimulus of contiguous host egg batches in certain places that may require a higher threshold before mutual interference has an effect, could be explained these results.

The prevalence and spatial distribution of viruses in natural populations of Brassica oleracea.

We report a survey of four viruses (beet western yellows luteovirus (BWYV), cauliflower mosaic caulimovirus (CaMV), turnip mosaic potyvirus (TuMV), turnip yellow mosaic tymovirus (TYMV)) in five natural populations of Brassica oleracea in Dorset (UK). All four viruses were common; 43% of plants were infected with BWYV, 60% with CaMV, 43% with TuMV and 18% with TYMV. For each virus there were significant differences in the proportion of infected plants among populations, which were not completely explained by differences in the age of plants. Multiple virus infections were prevalent, with 54% of plants having two or more virus types. There were statistically significant associations between pairs of viruses. The CaMV was positively associated with the other three viruses, and BWYV was also positively associated with TuMV. There was no detectable association between BWYV and TYMV, whereas TuMV and TYMV were negatively associated. We suggest these associations result from BWYV, CaMV and TuMV having aphid vectors in common, as aphids are attracted to plants that already have a virus infection. Infected plants were distributed randomly or were very weakly aggregated within populations. The implications of widespread multiple virus infections in natural plant populations are discussed with respect to the release of transgenic plants expressing virus-derived genes.

Stabilization effects of spatial aggregation of vectors in plant disease systems

AbstractStabilization effects of spatial aggregation of vectors were examined in insect‐borne plant disease systems by constructing a model that describes the yearly dynamics of rice stripe virus disease transmitted by the small brown planthopper Laodelphax striatellus (Fallén). Two transmission paths between vectors were considered: vertical transmission from parents through eggs, and horizontal transmission from infected plants by acquisition feeding. In this model, a paddy field was divided into quadrats and horizontal transmission was assumed to occur within each quadrat. A negative binomial distribution was used to describe the frequency distribution of vectors per quadrat. The parameters of the model were estimated using field data collected in Ibaraki Prefecture, Japan. The model showed that (1) the disease cannot invade into an epidemiological system if the mean crowding of vectors is less than a critical value, (2) the proportion of infected vectors is maintained at about 30% irrespective of the vector density if vectors are highly aggregated, and (3) the proportion of infected plants is maintained at a low level irrespective of the vector density if vectors are highly aggregated. It was also shown that these stabilization effects of aggregation in this epidemiological system come from a mechanism that is common to other systems such as single‐species systems and competition systems.

Changes in the incidence of African cassava mosaic virus disease and the abundance of its whitefly vector along south–north transects in Uganda

Abstract: Surveys of the incidence of African cassava mosaic disease (ACMD) and its whitefly vector, Bemisia tabaci, were made at three‐month intervals in 1992 and 1993 along two south–north transects. One was in central and the other in eastern Uganda. ACMD incidence was high within the northern localities of each transect and low towards the south. Incidence increased over the period at localities on the ACMD epidemic ‘front’ which was the interface between high incidence areas to the north and low incidence areas to the south. Combining data for both transects, the relationship between ‘infective potential’ (the product of whitefly number and the incidence of ACMD attributed to the use of infected cuttings, ‘x’) and the increase in proportion of infected plants caused by whiteflies (‘y’, as transformed to account for multiple infection) was described by the straight line regression: y = 47.8x + 9.2 (F ratio = 63.0, r2 = 0.78). This emphasises the importance for control of reducing ACMD incidence by phytosanitation and/or use of resistant varieties since reduction of whitefly numbers is not easily achieved. Possible mechanisms for the expansion of the ACMD epidemic and implications of the study findings for control of ACMD are discussed.

Inoculation of containerized Pseudotsuga menziesii and Pinus pinaster seedlings with spores of five species of ectomycorrhizal fungi

Container-grown Pseudotsuga menziesii and Pinus pinaster seedlings were inoculated with water suspensions of spores of five ectomycorrhizal fungi commonly found in northeastern Spain. Pseudotsuga menziesii seedlings were inoculated with basidiospores of Melanogaster ambiguus, or Rhizopogon subareolatus, or with ascospores of Tuber maculatum. Pinus pinaster seedlings were inoculated with basidiospores of Melanogaster ambiguus, Rhizopogon roseolus or Scleroderma citrinum. The spore concentrations were 102–107 spores per seedling for Melanogaster ambiguus (in Pseu dotsuga menziesii) and Rhizopogon subareolatus, 103–107 for Melanogaster ambiguus (in Pinus pinaster), Rhizopogon roseolus, and Scleroderma citrinum, and 102–104 for Tuber maculatum. Melanogaster ambiguus colonized more short roots in a larger proportion of plants at 107 spores per seedling than at any other rate. The highest colonization by Rhizopogon subareolatus was obtained at 104 spores per seedling and higher, and all inoculated plants became infected at 106 spores per seedling and higher. Tuber maculatum colonized a high percentage of short roots at all rates tested; the proportion of infected plants was over 80% at 103–104 spores per plant, decreasing to 50% at 102 spores per plant. Rhizopogon roseolus colonized the highest number of short roots on nearly all the inoculated plants when applied at 105 spores per seedling and higher. Scleroderma citrinum colonized a high percentage of short roots on all inoculated plants when applied at 105 spores per seedling and higher. The abundance of sporocarps of Melanogaster ambiguus, Rhizopogon subareolatus, R hizopogon roseolus and Scleroderma citrinum and their colonization ability at relatively low rates allows these spores to be used as ectomycorrhizal inocula on a large scale.

Productivity and persistence of prairie grass (Bromus willdenowii Kunth)

AbstractA field trial measured effects of the head smut fungus Ustilago bullata Berk, on forage productivity of prairie grass (Bromus willdenowii Kunth). Simulated swards containing different proportions of U. bullata infected and non infected plants were established in the autumn, and sward and plant parameters were measured over the following 15 months. Total herbage produced from swards containing only non‐infected plants was 27.3 t ha−1, while that from totally infected swards was 14.6 t ha−1. Infected plants produced fewer and lighter tillers than non‐infected plants when both were growing together in swards. Almost all the U. bullata infected plants died during an epidemic of bacterial wilt disease (caused by Xanthomonas campestris pv. graminis (Egli, Goto and Schmidt) Dye), while most of the‘non‐infected plants survived. The deleterious effects of U. bullata on individual plant productivity affected sward productivity only when the proportion of infected plants in swards was greater than 50%. Plants not infected with U. bullata compensated for low productivity and death of infected plants by producing large numbers of tillers.

Spread of barley yellow dwarf virus and relative importance of local aphid vectors in central Washington

SUMMARYData from bioassays of field collected aphids, barley indicator plants exposed to natural conditions, and various types of aphid traps were used to describe the spread of barley yellow dwarf virus (BYDV) in wheat and barley near Prosser, Washington. Bioassays were also used to assess the relative importance of local vector species.Of alate aphids collected from grain in the 1982 and 1983 fall migration seasons, 3.4–14–5% transmitted BYDV. Data from concurrent and post‐migration assays of resident aphids (apterae and nymphs) reflected an increase in the proportion of infected plants in the field. Maximum increase in the percentage of viruliferous aphids occurred in late November and December of 1982 and November of 1983. The 1982 increase occurred after aphid flights had ceased for the year, suggesting active secondary spread. Collections in pitfall traps and infected trap plants from November to February confirmed aphid activity and virus spread. Rhopalosiphum padi was the most important vector in central Washington in 1982 and 1983 because of its abundance and relative BYDV transmission efficiency. Metopolophium dirhodum was more winter‐hardy than R. padi and equal to R. padi in its efficiency as a vector; however, it was not as abundant as R. padi except during the mild winter of 1982–83, when it was a major contributor to secondary spread. Sitobion avenae may be important in years when it is abundant, but it was only a quarter as efficient as R. padi. Rhopalosiphum maidis was a much less efficient vector than R. padi and it only reached high populations in late autumn barley.

Cross protection of glasshouse tomatoes against tobacco mosaic virus

Abstract A mild strain of tobacco mosaic virus (TMV) was used to cross protect the TMV-susceptible tomato cultivars ‘Potentate’ and ‘V548’ in a commercial glasshouse trial. Plants infected with the mild strain (MII-16) showed increased fruit set and approximately 25% greater yields than those infected with a severe strain of TMV. The number of flowers formed was not affected by infection with either strain. The mild strain did not affect crop growth and infected plants remained symptomless throughout the trial. Application of the mild strain by hand inoculation resulted in a greater proportion of infected plants than inoculation by the airbrush method. Efficiency of the airbrush method was greatly influenced by the stage of plant development at the time of inoculation. Plants became protected from severe strain TMV infection 8 days after the mild strain inoculation.

Estimation of the Proportion of Vectors in a Natural Population of Insects

A procedure is investigated for estimating the proportion of vectors capable of transmitting aster-yellows virus in a natural population of Macrosteles fascifrons (Stal), the six-spotted leafhopper. A straightforward method and one used in practice is to collect random samples of the population and cage insects individually with previously unexposed aster test plants. If a plant exhibits aster-yellows symptoms in a given time interval, the insect is classified as a vector, and the proportion of infected plants is an estimator of the proportion of vectors in the population. When large numbers of insects are available, this procedure requires a considerable overhead in plants and cages, and it is desirable to use several insects on each plant. If k insects are caged with each plant, the outcome is still binomial, for the experimenter can distinguish only two types of test plants; infected and non-infected. If p is the probability that a randomly selected insect is a vector, the probability that a plant is non-infected is equal to (1 p)k. Some properties of the maximum likelihood estimator of p when such a procedure is used are investigated in this paper, and a method for determining the optimum number of insects per plant for certain cost considerations is given. In general, it will be seen that the experimenter should choose k small and n large, commensurate with costs, to insure against the risk of a dangerously inefficient experiment when little or no information is available regarding p. A closely related problem is the estimation of the frequency or density ,u of a population of microorganisms when a binomial classification only of each sample is possible or desirable, but where the distribution of the number of individuals in a diluted sample is Poisson. This dilution procedure was developed by R. A. Fisher [1921], Fisher et. al. [1922], and is discussed at length by Fisher and Yates [1948], Cochran [1950], and D. J. Finney [1952]. If the population density is ,u, the samples are usually diluted or concentrated by a factor z > 0 such that the density

THE RELATION BETWEEN THE SIZE OF PLANT AND THE SPREAD OF SYSTEMIC DISEASES: I. A DISCUSSION OF IDEAL CASES AND A NEW APPROACH TO PROBLEMS OF CONTROL

it is implicit in the concept of systemic disease that there should be a connexion between the size of the plant and the spread of infection.a first, general theorem, thought to be universally valid, is: the spread of an infectious systemic disease increases with the size of the plants, size being appropriately determined and other factors being constant.a second theorem for infections which enter a crop from without (e.g. from the soil or from another field) is: when a systemic disease enters a crop from some uniform outside source, the logarithm of the proportion of healthy plants is directly proportional to the size of the plants, other factors being constant; as an approximation, the proportion of infected plants is directly proportional to their size, provided that the proportion is small. a corollary to this theorem is that if the proportion of infected plants is small and if the size is inversely proportional to the density of planting, the number of infected plants per unit area will be approximately constant, factors other than size and number being constant.a third theorem for the spread of infection within a crop is: when a systemic disease spreads within a crop, the rate of infection is proportional to the size of the healthy plants, other factors being constant. if factors other than size, time and the proportion of infected plants are constant, the expression for the rate takes one of the three forms: dx/dt=ks (i‐x), (i) dx/dt=ks (i‐x)x, (ii)or dx/dt=ks (i‐x) f (s, t, x), (iii)in which x and 1‐x are, respectively, the proportions of infected and healthy plants, s is the size, and k is a constant. the second part of this theorem is tentative.in these theorems we take by definition a disease to be systemic if a single effective transmission suffices to bring about maximum infection of the plant. size refers to that part of the plant which can receive infection. this definition, with the size of the receiving part having its colloquial meaning, serves for the first, general theorem. for quantitative relations, the guise but not the substance of the definition is changed: size is proportional to the probability that the plant receives infection at any instant from a uniform source in appropriate circumstances. both for general and quantitative relations there is a special case when disease is introduced into a crop by insects or other vectors. size, then, is the catchment zone of the plant for the insects. this accords with the meaning assigned to size in other circumstances; size is here a convenient fiction, the use of which gives precisely the same results as the use of numbers, which are a reality.reduction of size is discussed as a measure of control peculiar to systemic diseases.