Young Plants (young + plant)

Distribution by Scientific Domains
Distribution within Life Sciences

Selected Abstracts

Resistance to Leveillula taurica in the genus Capsicum

V. L. De Souza
One hundred and sixty-two Capsicum genotypes were evaluated for powdery mildew (Leveillula taurica) resistance, following inoculations with a suspension of 5 × 104 conidia mL,1 on 10-leaved to 12-leaved plants. Genotypes were graded into five resistance classes, based on the areas under the disease progress curves calculated from disease incidence (percentage infected leaves per plant) and severity (total number of colonies per plant). Results revealed a continuum from resistance to susceptibility, with the majority (70%) of C. annuum materials being classified as moderately to highly susceptible to L. taurica. Conversely, C. baccatum, C. chinense and C. frutescens were most often resistant, indicating that resistance to L. taurica among Capsicum species is found mainly outside the C. annuum taxon. Nevertheless, some resistant C. annuum material was identified that may be useful for resistance breeding. Eight genotypes were identified as immune to the pathogen: H-V-12 and 4638 (previously reported), and CNPH 36, 38, 50, 52, 279 and 288. Only H-V-12 and 4638 are C. annuum, while all others belong to the C. baccatum taxon. Latent period of disease on a set of commercial sweet pepper genotypes varied, indicating diverse levels of polygenic resistance. The latent period progressively reduced with plant maturity, from 14·3 days in plants at the mid-vegetative stage to 8·6 days in plants at the fruiting stage. Young plants of all commercial genotypes tested at the early vegetative stage were immune, irrespective of the reaction of the genotype at later stages, demonstrating widespread juvenile resistance to L. taurica in the Capsicum germplasm. Inoculation of plants of different botanical taxa with a local isolate indicated a wide host range. Some hosts, including tomato (Lycopersicon esculentum), artichoke (Cynara scolymus) and poinsettia (Euphorbia pulcherrima), produced large amounts of secondary inoculum. Other hosts included okra (Abelmoschus esculentus), eggplant (Solanum melongena), cucumber (Cucumis sativus), Solanum gilo, Chenopodium ambrosioides and Nicandra physaloides. [source]

Ontogenetic switches from plant resistance to tolerance: minimizing costs with age?

Karina Boege
Abstract Changes in herbivory and resource availability during a plant's development should promote ontogenetic shifts in resistance and tolerance, if the costs and benefits of these basic strategies also change as plants develop. We proposed and tested a general model to detect the expression of ontogenetic tradeoffs for these two alternative anti-herbivory strategies in Raphanus sativus. We found that ontogenetic trajectories occur in both resistance and tolerance but in opposite directions. The juvenile stage was more resistant but less tolerant than the reproductive stage. The ontogenetic switch from resistance to tolerance was consistent with the greater vulnerability of young plants to leaf damage and with the costs of resistance and tolerance found at each stage. We posit that the ontogenetic perspective presented here will be helpful in resolving the current debate on the existence and detection of a general resistance,tolerance tradeoff. [source]

Different portions of the maize root system host Burkholderia cepacia populations with different degrees of genetic polymorphism

Luigi Chiarini
In order to acquire a better understanding of the spatial and temporal variations of genetic diversity of Burkholderia cepacia populations in the rhizosphere of Zea mays, 161 strains were isolated from three portions of the maize root system at different soil depths and at three distinct plant growth stages. The genetic diversity among B. cepacia isolates was analysed by means of the random amplified polymorphic DNA (RAPD) technique. A number of diversity indices (richness, Shannon diversity, evenness and mean genetic distance) were calculated for each bacterial population isolated from the different root system portions. Moreover, the analysis of molecular variance ( amova) method was applied to estimate the genetic differences among the various bacterial populations. Our results showed that, in young plants, B. cepacia colonized preferentially the upper part of the root system, whereas in mature plants, B. cepacia was mostly recovered from the terminal part of the root system. This uneven distribution of B. cepacia cells among different root system portions partially reflected marked genetic differences among the B. cepacia populations isolated along maize roots on three distinct sampling occasions. In fact, all the diversity indices calculated indicated that genetic diversity increased during plant development and that the highest diversity values were found in mature maize plants, in particular in the middle and terminal portions of the root system. Moreover, the analysis of RAPD patterns by means of the amova method revealed highly significant divergences in the degree of genetic polymorphism among the various B. cepacia populations. [source]

Population structure and establishment of the threatened long-lived perennial Scorzonera humilis in relation to environment

Guy Colling
Summary 1The intensification of agriculture has resulted in the decline of many plant species of nutrient-poor wet grasslands. At some sites local populations of long-lived characteristic species have persisted and might benefit from recent extensification schemes. However, little is known about the population biology of these plants, and the prospects for the populations are uncertain. 2We studied the population structure and establishment of the long-lived Scorzonera humilis in 23 populations in Luxembourg and neighbouring Belgium. Two types of populations could be distinguished according to their population structure: regenerating populations, with a high proportion of plants with only one or a few rosettes, and aged populations, with a low proportion of small, young plants but a high proportion of individuals with many rosettes. The total density of Scorzonera individuals was higher in regenerating than in aged populations. 3Within sites, S. humilis was restricted to more open and nutrient-poor patches. The composition of the vegetation in plots where S. humilis was present was significantly different from that of plots without the species, indicating that S. humilis is restricted to particular microhabitats. 4In multiple regression analyses, environmental variables explained a large part of the variation in the total density of genets, the density of genets of different size and the density of rosettes. The main variables of influence were site productivity and soil moisture. With increasing productivity and decreasing soil moisture the proportion of small genets decreased and that of large genets increased. Increased productivity had contrasting effects at the genet and ramet (rosette) levels. While genet density decreased, ramet density increased, indicating that if a site is fertilized, recruitment of new genets and survival of genets is reduced, but growth of surviving genets is increased. 5The results of a sowing experiment indicated that an aged population structure was due to a lack of recruitment. The number of seeds that germinated and the proportion of seedlings that survived until the next summer were positively correlated with soil moisture and negatively with productivity. Germination rate and establishment success were significantly higher in Molinion grassland than in the Calthion grasslands. 6The results suggest that for long-lived species the size and number of populations may not be good indicators of the status of a species. In S. humilis large populations (> 1000 genets) still exist, but all are of the aged type. In order to preserve existing populations of S. humilis, management should aim to reduce productivity and increase soil moisture. [source]

Age-related changes in defensive traits of Acacia tortilis Hayne

Juan H. Gowda
Abstract The theory of plant defences proposes that investments in physical and chemical defences are driven by the risk of herbivore damage, and limited by the cost of producing the particular defensive trait in terms of resources that could be directed to other sinks, such as growth and reproduction. We sampled twigs of 18 mature Acacia tortilis trees and their cohort of juveniles to test some predictions of this hypothesis. We expected a higher allocation of defensive traits to leaves and twigs in the young plants than in the mature ones as a result of a higher risk of damage by ungulates at the juvenile stage. Our results show that the juvenile plants produce more spines along their twigs, but have lower concentrations of phenolic compounds in their leaves than in the mature ones. We also expected a negative relation between the concentration of foliar nutrients and phenolic compounds, as predicted by the carbon/nutrient hypothesis. Only mature plants showed this pattern. Reproduction (in mature plants) and water stress (in juvenile plants) did not relate to allocation to secondary compounds as predicted by current hypotheses of plant defence. Résumé La théorie sur la défense des plantes propose que les investissements dans des défenses physiques et chimiques sont suscités par le risque de dommages dus aux herbivores, et limités par le coût de la production d'un caractère défensif particulier, exprimé en terme de ressources qui auraient pu être affectées à une autre destination, telle que la croissance ou la reproduction. Nous avons récolté des rameaux de 18 Acacia tortilis mâtures et de leurs cohortes de juvéniles pour tester diverses prédictions de cette théorie. Nous nous attendions à une plus forte attribution de caractères défensifs dans les feuilles et les rameaux des jeunes plants que dans ceux des arbres mâtures puisque le risque de dommages dus aux ongulés est plus grand au stade juvénile. Nos résultats montrent que les plants juvéniles produisent plus d'épines le long des branches mais que leurs feuilles ont une concentration moindre en composés phénoliques que celles des arbres mâtures. Nous nous attendions aussi à une relation négative entre la concentration des nutriments foliaires et les composés phénoliques, selon l'hypothèse carbone/nutriment. Seuls les plants mâtures reproduisaient ce schéma. La reproduction (chez les plants mâtures) et le stress hydrique (chez les plants juvéniles) n'avaient pas de relation avec l'attribution aux composés secondaires, comme le prédisaient les hypothèses actuelles sur la défense des plantes. [source]

Host-race formation: promoted by phenology, constrained by heritability

Abstract Host-race formation is promoted by genetic trade-offs in the ability of herbivores to use alternate hosts, including trade-offs due to differential timing of host-plant availability. We examined the role of phenology in limiting host-plant use in the goldenrod gall fly (Eurosta solidaginis) by determining: (1) whether phenology limits alternate host use, leading to a trade-off that could cause divergent selection on Eurosta emergence time and (2) whether Eurosta has the genetic capacity to respond to such selection in the face of existing environmental variation. Experiments demonstrated that oviposition and gall induction on the alternate host, Solidago canadensis, were the highest on young plants, whereas the highest levels of gall induction on the normal host, Solidago gigantea, occurred on intermediate-age plants. These findings indicate a phenological trade-off for host-plant use that sets up the possibility of divergent selection on emergence time. Heritability, estimated by parent,offspring regression, indicated that host-race formation is impeded by the amount of genetic variation, relative to environmental, for emergence time. [source]

Effect of fallows on population dynamics of Cosmopolites sordidus: toward integrated management of banana fields with pheromone mass trapping

Béatrice Rhino
1The banana weevil Cosmopolites sordidus Germar (Coleoptera: Curculionidae) is the most serious pest of banana and plantain in most production areas, including the West Indies. 2During a period of 2 years, we assessed the efficacy of a pheromone mass-trapping control strategy of C. sordidus in field conditions in Guadeloupe at different cropping stages, both in sanitation fallows and in different ratoon banana crops. 3In the fallows, catches peaked 3 months after beginning trapping and then decreased to zero after 9 months. By contrast, for the new plantations, the catches of C. sordidus increased after the 11th month and, in the older banana fields, there was no decrease in C. sordidus catches. The C. sordidus catches increased in the neighbouring banana plots, whereas they decreased in the fallows, and these catches decreased with the distance from fallow. 4In conclusion, mass trapping with synergized pheromone traps within fallows should allow better sanitation of banana plantations. Yet, within the farms, fallows must not be located next to new plantations to avoid massive damage to the young plants. More generally, the present study emphasizes that the control of this insect should be managed at the farm scale and not at the field scale, with special attention being paid to the location of fallows. [source]

Uncoupling nitrogen requirements for spring growth from root uptake in a young evergreen shrub (Rhododendron ferrugineum)

T. Lamaze
Abstract , , Internal cycling of nitrogen (N) was investigated in a subalpine field population of the evergreen shrub Rhododendron ferrugineum during spring growth. , , The foliar nitrogen of 5-yr-old-plants was directly labeled with 15N and subsequently traced to all plant compartments. In addition, 15N-ammonium uptake was estimated in glasshouse experiments. , , Before shoot growth, redistribution of 15N occurred in the plant without net N transfer. During spring development, the decreases in both leaf 15N and total N were almost identical in terms of percentage, and most of the 15N withdrawn from the leaf compartments was recovered in the growing shoots. Net changes in the N contents of the various leaf and woody compartments indicate that internal remobilization (especially from 1-yr-old leaves) could have met most of the N needs of new shoot growth. Simultaneously, the rate of mineral N uptake was very low. , , Thus, leaves in young plants provide N for new shoots (by contrast with old individuals) and allow, with woody tissues, almost complete uncoupling of N requirement for spring growth from root uptake. [source]

Calystegines in Calystegia sepium do not Inhibit Fungal Growth and Invertase Activity but Interact with Plant Invertase

PLANT BIOLOGY, Issue 2 2004
D. Höke
Abstract: Calystegines are alkaloidal glycosidase inhibitors. They accumulate predominantly in young and meristemic parts of Calystegia sepium (Convolvulaceae). C. sepium, bindweed, infests meadows and cereal fields and is difficult to control chemically. Fungal pathogens against C. sepium are established as mycoherbicides. Stagonospora convolvuli LA39 attacks C. sepium and does not affect crop plants, but young plants of C. sepium are less susceptible to the fungus. The interaction of Stagonospora convolvuli with calystegines was investigated. Further, endophytic fungi of several classes were isolated from wild-grown Calystegia sepium leaves, and selected strains were tested for interaction with calystegines. Fungal growth on agar containing calystegines was not affected considerably. Plants in climate chambers were infected with an endophyte, Phomopsis, and with the fungal pathogen, Stagonospora convolvuli. Calystegine levels were measured in infected and non-infected plant tissues. Accumulation depended on developmental stage of the plant tissue and was not influenced by infection. Acid invertase was measured from fungal mycelia and from infected and non-infected plant tissues. Fungal acid invertase activity was not inhibited by 10 mM calystegine B2, while invertase from C. sepium leaves was inhibited. It is concluded that calystegines do not inhibit fungal development and sucrose consumption under the conditions of the present investigation, but may act by redirection of plant carbohydrate metabolism. [source]

Root-selective expression of AtCAX4 and AtCAX2 results in reduced lamina cadmium in field-grown Nicotiana tabacum L.

Victor Korenkov
Summary To assess the impact of enhanced root vacuole cadmium (Cd) sequestration on leaf Cd accumulation under a low Cd dose, as generally occurs in agriculture, leaf Cd accumulation was examined in field-grown tobacco plants expressing genes encoding the high-capacity-Cd, tonoplast-localized, divalent cation/H antiporters AtCAX4 and AtCAX2 (AtCAX, Arabidopsis cation exchanger). It has been shown previously that root tonoplast vesicles isolated from plants expressing these genes, directed by root-selective promoters, show enhanced Cd transport activity, and young plants show enhanced root Cd accumulation when grown in solution culture containing 0.02 µm Cd, a moderate Cd dose. In this article, we present results which show that the lower leaves of mature plants expressing AtCAX2 or AtCAX4, under the control of two different root-selective promoters, accumulate 15%,25% less lamina Cd than control plants when grown in the field (3 years, three different collection methods). Reciprocal grafting experiments of AtCAX2 shoots onto control roots (and vice versa), grown in solution culture with 0.005 µm Cd, indicated that the root controls Cd translocation and accumulation in the shoot in control and AtCAX2 and AtCAX4 tobacco plants exposed to low Cd concentration. The results are consistent with a model in which supplementation of Cd/H antiporter activity in root cell tonoplasts enhances root Cd sequestration, resulting in decreased translocation of Cd to the shoot of field-grown plants. These results suggest that human Cd intake from food and tobacco use could be reduced via the enhancement of root vacuolar sequestration of this pollutant. [source]

Phytophthora pinifolia sp. nov. associated with a serious needle disease of Pinus radiata in Chile

A. Durán
During the course of the past three years, a new disease of Pinus radiata, referred to as ,Daño Foliar del Pino' (DFP) has appeared in the Arauco province of Chile and subsequently spread to other areas. The disease is typified by needle infections, exudation of resin at the bases of the needle brachyblasts and, in younger trees, necrotic lesions in the cambium, which eventually girdle the branches. The disease causes the death of young seedlings and mature trees can also succumb after a few years of successive infection, probably hastened by opportunistic fungi such as Diplodia pinea. Isolations on selective medium for Phytophthora spp. led to the consistent isolation of a Phytophthora sp. from needle tissue. DNA sequence comparisons for the ITS rDNA and cox II gene regions, and morphological observation showed that this oomycete represents a previously undescribed species for which the name Phytophthora pinifolia sp. nov. is provided. This new species is characterized by unbranched sporangiophores, and non-papillate, sub-globose to ovoid sporangia that are occasionally free from the sporangiophore with medium length pedicels. Despite using a number of oospore inducing techniques, oogonia/antheridia were not observed in isolates of P. pinifolia. Pathogenicity trials with P. pinifolia showed that it is pathogenic to P. radiata and causes rapid death of the succulent apical parts of young plants. Phytophthora pinifolia is the first Phytophthora known to be associated with needles and shoots of a Pinus sp. and its aerial habit is well matched with the occurrence and symptoms of DFP in Chile. [source]

Effectiveness of resistance genes to the large raspberry aphid, Amphorophora idaei Börner, in different raspberry (Rubus idaeus L.) genotypes and under different environmental conditions

Summary The introduction into commerce of raspberry cultivars with major gene resistance to the large raspberry aphid, Amphorophora idaei, an important pest and virus vector on red raspberry in Europe, has been very effective both in decreasing pest numbers and greatly restricting infection with the viruses it transmits. However, biotypes of the aphid able to overcome these genes have developed in the field in recent years. Additionally, in field and laboratory tests, the response to aphid biotypes and recognised aphid strains of certain raspberry cultivars, such as Glen Prosen and Delight, differ markedly despite the fact that they are reputed to contain the same A. idaei -resistance gene, A1. In attempts to understand the reasons for this difference in response, analysis was made of the segregation of progeny seedlings from crosses between A. idaei -resistant and -susceptible cultivars to two recognised strains of the aphid. These studies showed that, as expected, cv. Autumn Bliss contained the A. idaei -resistance gene, A10, and cvs Delight and Glen Prosen each contained the A. idaei -resistance gene, A1. When progeny seedlings were assayed in a heated glasshouse as young plants and in an unheated Tygan house as 1 m tall plants, the segregation ratios for resistance and susceptibility to A. idaei were largely unchanged. However, when the resistance of individual progeny plants was assessed, c. 37% of the putative gene A1 -containing progeny and 9,23% of the putative gene A10 -containing progeny, behaved differently in these two environments. Experiments involving an A. idaei -resistant and -susceptible parent cultivar showed that shading plants increased their susceptibility to A. idaei colonisation. Whilst this shading effect has implications for experimentally detecting A. idaei -resistant progeny in segregating raspberry seedlings, it does not explain the difference in field resistance to A. idaei of cvs Delight and Glen Prosen. Such differences in the field seem best explained by the presence in these cultivars of ,minor' genes for A. idaei resistance and/or susceptibility that influences the effectiveness of gene A1. [source]