Effect of Watering Regimen on Injury to Corn and Grain Sorghum by Pratylenchus Species

The effect of simulated rainfall frequency on the pathogenicity of Pratylenchus zeae and P. brachyurus was studied in four greenhouse experiments. Corn and grain sorghum were watered at different intervals during predetermined cycles to create a gradient of water-stressed plants. Each experiment included nematode and uninoculated treatments. Growth reaction of plants to different frequencies of watering was significant but was not affected by the presence of nematodes. Pratylenchus zeae numbers differed among watering regimens on corn but not on sorghum. Numbers of P. brachyurus did not differ among watering regimens on corn or sorghum. Both lesion nematode species were harmful to corn, but sorghum increased plant growth in response to P. brachyurus. It is concluded that water stress is not the only environmental factor that influences the pathogenicity of these two species on corn and sorghum.     

Constitutive overexpression of the sucrose transporter SoSUT1 in potato plants increases arbuscular mycorrhiza fungal root colonization under high, but not under low, soil phosphorus availability

The sucrose transporter SUT1 functions in phloem loading of photoassimilates in solanaceous plant species. In the present study, wildtype and transgenic potato plants with either constitutive overexpression or antisense inhibition of SUT1 were grown under high or low phosphorus (P) fertilization levels in the presence or absence of the arbuscular mycorrhizal (AM) fungus Glomus intraradices. At a low soil P fertilization level, the extent of AM fungal root colonization was not different among the genotypes. In all plants, the AM symbiosis contributed significantly to P uptake under these conditions. In response to a high soil P fertilization level, all genotypes showed a decrease in AM fungal root colonization, indicating that the expression level of SUT1 does not constitute a major mechanism of control over AM development in response to the soil P availability. However, plants with overexpression of SUT1 showed a higher extent of AM fungal root colonization compared with the other genotypes when the soil P availability was high. Whether an increased symbiotic C supply, alterations in the phytohormonal balance, or a decreased synthesis of antimicrobial compounds was the major cause for this effect requires further investigation. In plants with impaired phloem loading, a low C status of plant sink tissues did apparently not negatively affect plant C supply to the AM symbiosis. It is possible that, at least during vegetative and early generative growth, source rather than sink tissues exert control over amounts of C supplied to AM fungi.     

Plant genotypic diversity reduces the rate of consumer resource utilization

While plant species diversity can reduce herbivore densities and herbivory, little is known regarding how plant genotypic diversity alters resource utilization by herbivores. Here, we show that an invasive folivore—the Japanese beetle (Popillia japonica)—increases 28 per cent in abundance, but consumes 24 per cent less foliage in genotypic polycultures compared with monocultures of the common evening primrose (Oenothera biennis). We found strong complementarity for reduced herbivore damage among plant genotypes growing in polycultures and a weak dominance effect of particularly resistant genotypes. Sequential feeding by P. japonica on different genotypes from polycultures resulted in reduced consumption compared with feeding on different plants of the same genotype from monocultures. Thus, diet mixing among plant genotypes reduced herbivore consumption efficiency. Despite positive complementarity driving an increase in fruit production in polycultures, we observed a trade-off between complementarity for increased plant productivity and resistance to herbivory, suggesting costs in the complementary use of resources by plant genotypes may manifest across trophic levels. These results elucidate mechanisms for how plant genotypic diversity simultaneously alters resource utilization by both producers and consumers, and show that population genotypic diversity can increase the resistance of a native plant to an invasive herbivore.     

Organ-dependent responses of Periploca sepium to repeated dehydration and rehydration

Plant responses to water deficit occur in a complex framework of organ interactions, but few studies focus on the effect of drought stress on all organs in a whole-plant. The effects of repeated dehydration and rehydration (DH) on physiological and biochemical responses in various organs of Periploca sepium Bunge (P. sepium) were investigated. The leaf relative water content decreased significantly during drought, but recovered and showed an increase when compared to well-watered control plants. The malondialdehyde (MDA) content increased in mature and old leaves, but decreased in young leaves, new stems and fine roots during drought, indicating that the young and vigorous tissues of a whole-plant are protected preferentially from the oxidative stress. Among all organs, the fine roots showed the highest levels of proline, total free amino acids (TFAA) and Na⁺, while the leaves showed the highest levels of total soluble sugars (TSS), soluble proteins (SP), Ca²⁺ and Mg²⁺. The response to DH differed in different organs, both in magnitude and in the type of solutes involved. Drought stress increased the contents of proline, TFAA, TSS, SP and K⁺ in all organs of P. sepium plants, while the accumulation amounts were obviously different among the organs. The storage starch in stems and roots plays an important role in providing carbohydrates for growth. Changes in Na⁺, Ca²⁺ and Mg²⁺ under DH presented a high degree of organ specificity. Our data indicates that response strategies are different between different organs; therefore, evidence the needs to integrate all the information in order to better understand plant tolerance mechanisms.     

Influence of Pratylenchus penetrans on Plant Growth and Water Relations in Potato

Plants of potato (Solanum tuberosum) cultivars Katahdin and Superior were inoculated with 0, 1,500, or 15,000 Pratylenchus penetrans. Transpiration, measured in the greenhouse with a porometer after 56 days of growth, was not significantly different among nematode inoculum levels or between cultivars. The rate of xylem exudation from decapitated root systems of Katahdin plants inoculated with 1,500 or 15,000 P. penetrans and Superior plants inoculated with 15,000 P. penetrans was lower than from noninoculated plants. Root weight of Katahdin and Superior was not affected by P. penetrans inoculum level. Transpiration of plants inoculated with 0, 500, 5,000 or 50,000 P. penetrans was recorded weekly from 14 to 56 days after planting. No consistent effects of nematode inoculum density on transpiration rate were observed. Root hydraulic conductivity was lower in Katahdin plants inoculated with 266 P. penetrans per plant and in Chippewa with 5,081 per plant than in noninoculated plants. Nematodes reduced leaf area of Superior, Chippewa, and Katahdin and root dry weight of Chippewa but had no effect on growth of Hudson, Onaway, or Russet Burbank plants. Assessing nematode effects on root hydraulic conductivity may provide a measure of the tolerance of potato cultivars to nematodes.     

Cluster-root formation and carboxylate release in three Lupinus species as dependent on phosphorus supply,internal phosphorus concentration and relative growth rate

Background and Aims

Some Lupinus species produce cluster roots in response to low plant phosphorus (P) status. The cause of variation in cluster-root formation among cluster-root-forming Lupinus species is unknown. The aim of this study was to investigate if cluster-root formation is, in part, dependent on different relative growth rates (RGRs) among Lupinus species when they show similar shoot P status.

Methods

Three cluster-root-forming Lupinus species, L. albus, L. pilosus and L. atlanticus, were grown in washed river sand at 0, 7·5, 15 or 40 mg P kg⁻¹ dry sand. Plants were harvested at 34, 42 or 62 d after sowing, and fresh and dry weight of leaves, stems, cluster roots and non-cluster roots of different ages were measured. The percentage of cluster roots, tissue P concentrations, root exudates and plant RGR were determined.

Key Results

Phosphorus treatments had major effects on cluster-root allocation, with a significant but incomplete suppression in L. albus and L. pilosus when P supply exceeded 15 mg P kg⁻¹ sand. Complete suppression was found in L. atlanticus at the highest P supply; this species never invested more than 20 % of its root weight in cluster roots. For L. pilosus and L. atlanticus, cluster-root formation was decreased at high internal P concentration, irrespective of RGR. For L. albus, there was a trend in the same direction, but this was not significant.

Conclusions

Cluster-root formation in all three Lupinus species was suppressed at high leaf P concentration, irrespective of RGR. Variation in cluster-root formation among the three species cannot be explained by species-specific variation in RGR or leaf P concentration.     

Ontogenetic patterns in the mechanisms of tolerance to herbivory in Plantago

Background and Aims

Herbivory and plant defence differ markedly among seedlings and juvenile and mature plants in most species. While ontogenetic patterns of chemical resistance have been the focus of much research, comparatively little is known about how tolerance to damage changes across ontogeny. Due to dramatic shifts in plant size, resource acquisition, stored reserves and growth, it was predicted that tolerance and related underlying mechanisms would differ among ontogenetic stages.

Methods

Ontogenetic patterns in the mechanisms of tolerance were investigated in Plantago lanceolata and P. major (Plantaginaceae) using the genetic sib-ship approach. Pot-grown plants were subjected to 50 % defoliation at the seedling, juvenile and mature stages and either harvested in the short-term to look at plasticity in growth and photosynthesis in response to damage or allowed to grow through seed maturation to measure phenology, shoot compensation and reproductive fitness.

Key Results

Tolerance to defoliation was high in P. lanceolata, but low in P. major, and did not vary among ontogenetic stages in either species. Mechanisms underlying tolerance did vary across ontogeny. In P. lanceolata, tolerance was significantly related to flowering (juveniles) and pre-damage shoot biomass (mature plants). In P. major, tolerance was significantly related to pre-damage root biomass (seedlings) and induction of non-photochemical quenching, a photosynthetic parameter (juveniles).

Conclusions

Biomass partitioning was very plastic in response to damage and showed associations with tolerance in both species, indicating a strong role in plant defence. In contrast, photosynthesis and phenology showed weaker responses to damage and were related to tolerance only in certain ontogenetic stages. This study highlights the pivotal role of ontogeny in plant defence and herbivory. Additional studies in more species are needed to determine how seedlings tolerate herbivory in general and whether mechanisms vary across ontogeny in consistent patterns.     

Potential but limited redundant roles of MtPIN4, MtPIN5 and MtPIN10/SLM1 in the development of Medicago truncatula

Auxin polar transport is crucial in regulating plant growth and patterning. As auxin efflux carriers, the PIN FORMED (PIN) proteins are responsible for transportation of auxin out of the cell. There are eight and ten PIN members in Arabidopsis (AtPIN) and Medicago truncatula (MtPIN), respectively. Compared with MtPIN10/SMOOTH LEAF MARGIN1 (SLM1), MtPIN4 exhibits a closer relationship with AtPIN1 based phylogenetic analysis. In addition, the gene structure and distribution of transmembrane segments of MtPIN4, MtPIN5 and MtPIN10/SLM1 are similar, implying possible redundant roles among them. However, analysis using Gene Expression Atlas revealed different expression patterns among MtPIN4, MtPIN5 and MtPIN10/SLM1. Loss of function of MtPIN10/SLM1 in M. truncatula resulted in pleiotropic phenotypes in different organs, which are similar with the defects in the pin1 mutant of Arabidopsis, suggesting that the MtPIN10/SLM1 is a putative ortholog of AtPIN1. MtPIN4, MtPIN5 and MtPIN10/SLM1 may have limited redundant functions in the development of M. truncatula. The creation of double and triple mutants will help to elucidate their potential roles in auxin transport and plant development.     

Xylem structure of four grape varieties and 12 alternative hosts to the xylem-limited bacterium Xylella fastidious

Background and Aims

The bacterium Xylella fastidiosa (Xf), responsible for Pierce''s disease (PD) of grapevine, colonizes the xylem conduits of vines, ultimately killing the plant. However, Vitis vinifera grapevine varieties differ in their susceptibility to Xf and numerous other plant species tolerate Xf populations without showing symptoms. The aim of this study was to examine the xylem structure of grapevines with different susceptibilities to Xf infection, as well as the xylem structure of non-grape plant species that support or limit movement of Xf to determine if anatomical differences might explain some of the differences in susceptibility to Xf.

Methods

Air and paint were introduced into leaves and stems to examine the connectivity between stem and leaves and the length distribution of their vessels. Leaf petiole and stem anatomies were studied to determine the basis for the free or restricted movement of Xf into the plant.

Key Results

There were no obvious differences in stem or petiole vascular anatomy among the grape varieties examined, nor among the other plant species that would explain differences in resistance to Xf. Among grape varieties, the more tolerant ‘Sylvaner’ had smaller stem vessel diameters and 20 % more parenchyma rays than the other three varieties. Alternative hosts supporting Xf movement had slightly longer open xylem conduits within leaves, and more connection between stem and leaves, when compared with alternative hosts that limit Xf movement.

Conclusions

Stem–leaf connectivity via open xylem conduits and vessel length is not responsible for differences in PD tolerance among grape varieties, or for limiting bacterial movement in the tolerant plant species. However, it was found that tolerant host plants had narrower vessels and more parenchyma rays, possibly restricting bacterial movement at the level of the vessels. The implications of xylem structure and connectivity for the means and regulation of bacterial movement are discussed.     

Perspectives of genomic diversification and molecular recombination towards R-gene evolution in plants

Plants are under strong evolutionary pressure in developing new and noble R genes to recognize pathogen avirulence (avr) determinants and bring about stable defense for generation after generations. Duplication, sequence variation by mutation, disparity in the length and structure of leucine rich repeats etc., causes tremendous variations within and among R genes in a plant thereby developing diverse recognitional specificity suitable enough for defense against new pathogens. Recent studies on genome sequencing, diversity and population genetics in different plants have thrown new insights on the molecular evolution of these genes. Tandem and segmental duplication are important factors in R gene abundance as inferred from the distribution of major nucleotide binding site-leucine rich repeats (NBS-LRRs) type R-genes in plant genomes. Likewise, R-gene evolution is also thought to be facilitated by cluster formation thereby causing recombination and sequence exchange and resulting in haplotypic diversity. Population studies have further proven that balancing selection is responsible for the maintenance of allelic diversity in R genes. In this review, we emphasize and discuss on improved perspectives towards the molecular mechanisms and selection pressure responsible for the evolution of NBS-LRR class resistance genes in plants.     

The mean and variability of a floral trait have opposing effects on fitness traits

Background and Aims Floral traits are essential for ensuring successful pollination and reproduction in flowering plants. In particular, style and anther positions are key for pollination accuracy and efficiency. Variation in these traits among individuals has been well studied, but less is known about variation within flowers and plants and its effect on pollination and reproductive success.Methods Style deflexion is responsible for herkogamy and important for pollen deposition in Passiflora incarnata. The degree of deflexion may vary among stigmas within flowers as well as among flowers. We measured the variability of style deflexion at both the flower and the plant level. The fitness consequences of the mean and variation of style deflexion were then evaluated under natural pollination by determining their relationship to pollen deposition, seed production and average seed weight using structural equation modelling. In addition, the relationship between style deflexion and self-pollen deposition was estimated in a greenhouse experiment.Key Results We found greater variation in style deflexion within flowers and plants than among plants. Variation of style deflexion at the flower and plant level was positively correlated, suggesting that variability in style deflexion may be a distinct trait in P. incarnata. Lower deflexion and reduced variation in that deflexion increased pollen deposition, which in turn increased seed number. However, lower styles also increased self-pollen deposition. In contrast, higher deflexion and greater variability of that deflexion increased variation in pollen deposition, which resulted in heavier seeds.Conclusions Variability of style deflexion and therefore stigma placement, independent from the mean, appears to be a property of individual P. incarnata plants. The mean and variability of style deflexion in P. incarnata affected seed number and seed weight in contrasting ways, through the quantity and potentially quality of pollen deposition. This antagonistic selection via different fitness components may maintain diverse style phenotypes.     

Mutation of Panax ginseng genes during long-term cultivation of ginseng cell cultures

It has previously been shown that the nucleotide sequences of the Agrobacterium rhizogenes rolC locus and the selective marker nptII developed mutations during the long-term cultivation of transgenic cell cultures of Panax ginseng. In the present report, we analyzed the nucleotide sequences of selected plant gene families in the 20-year-old P. ginseng 1c cell culture and in leaves of cultivated P. ginseng plants. We sequenced the Actin genes, which are a family of house-keeping genes; the phenylalanine ammonia-lyase (PAL) and dammarenediol synthase genes (DDS), which actively participate in the biosynthesis of ginsenosides; and the somatic embryogenesis receptor kinase (SERK) genes, which control plant development. We demonstrate that the plant genes also developed mutations during long-term cultivation. The highest level of nucleotide substitution was detected in the sequences of the SERK genes (2.00 ± 0.11 nt per 1000 nt), and the level was significantly higher when compared with the cultivated P. ginseng plant. Interestingly, while the diversity of Actin genes was similar in the P. ginseng cell culture and the cultivated plants, the diversity of the DDS and SERK genes was less in the 20-year-old cell culture than in the cultivated plants. In this work, we detail the level of nucleotide substitutions in different plant genes during the long-term culture of plant cells.     

Influence of Some Environmental Factors on Populations of Pratylenchus minyus in Wheat

The distribution and density of Pratylenchus minyus and possible relationships of several environmental components, including ammonium nitrate, were investigated in a wheat field in South Australia. Seasonal variation as measured every 2-4 weeks was eliminated from the observations by periodic regression. Correlation and regression analyses were then used to investigate the association of host plant, rainfall, temperature, and the fungus Gaeumannomyces graminis with P. minyus. Other than seasonal effects, soil moisture and G. graminis were the only components associated with P. minyus. Ammonium nitrate usually was correlated with fewer P. minyus in wheat roots. Much higher numbers of P. minyus were observed in seminal than in crown roots of wheat.     

Buzz pollination in eight bumblebee-pollinated Pedicularis species: does it involve vibration-induced triboelectric charging of pollen grains?

MethodsEight sympatric buzz-pollinated species of Pedicularis that share bumblebee pollinator species were studied, giving a rare opportunity to compare sonication behaviour of a shared pollinator on different plant species.ConclusionsSonication behaviour of B. friseanus differs among Pedicularis species, not only because worker bees assort themselves among plant species by body size, but also because bees of a given size adjust the buzz frequency to achieve a vibration velocity corresponding to the floral traits of each plant species. These findings, and the floral traits that characterize these and other buzz-pollinated species, are compatible with the hypothesis of vibration-induced triboelectric charging of pollen grains.     

Divergent selection along climatic gradients in a rare central European endemic species,Saxifraga sponhemica

Background and Aims The effects of habitat fragmentation on quantitative genetic variation in plant populations are still poorly known. Saxifraga sponhemica is a rare endemic of Central Europe with a disjunct distribution, and a stable and specialized habitat of treeless screes and cliffs. This study therefore used S. sponhemica as a model species to compare quantitative and molecular variation in order to explore (1) the relative importance of drift and selection in shaping the distribution of quantitative genetic variation along climatic gradients; (2) the relationship between plant fitness, quantitative genetic variation, molecular genetic variation and population size; and (3) the relationship between the differentiation of a trait among populations and its evolvability.Methods Genetic variation within and among 22 populations from the whole distribution area of S. sponhemica was studied using RAPD (random amplified polymorphic DNA) markers, and climatic variables were obtained for each site. Seeds were collected from each population and germinated, and seedlings were transplanted into a common garden for determination of variation in plant traits.Key Results In contrast to previous results from rare plant species, strong evidence was found for divergent selection. Most population trait means of S. sponhemica were significantly related to climate gradients, indicating adaptation. Quantitative genetic differentiation increased with geographical distance, even when neutral molecular divergence was controlled for, and Q_ST exceeded F_ST for some traits. The evolvability of traits was negatively correlated with the degree of differentiation among populations (Q_ST), i.e. traits under strong selection showed little genetic variation within populations. The evolutionary potential of a population was not related to its size, the performance of the population or its neutral genetic diversity. However, performance in the common garden was lower for plants from populations with reduced molecular genetic variation, suggesting inbreeding depression due to genetic erosion.Conclusions The findings suggest that studies of molecular and quantitative genetic variation may provide complementary insights important for the conservation of rare species. The strong differentiation of quantitative traits among populations shows that selection can be an important force for structuring variation in evolutionarily important traits even for rare endemic species restricted to very specific habitats.     

Initial determination of DNA polymorphism of some Primula veris L. populations from Kosovo and Austria

Primula veris L. (Primulaceae) is a long lived perennial and well known pharmaceutical plant, widely collected for these reasons in almost all SE Europe and particularly in Kosovo. The aim of the study is to determine molecular polymorphism of cowslip (P. veris L.) populations from Kosovo. DNA extracted from leaves were  investigated in details for presence of polymorphism. RAPD analyses were conducted using 20 different short primers. Genomic DNA amplification profiles were analyzed and processed using data labelling. Comparison between cowslip populations in genetic composition revealed that samples from Bogaj were too distinct on their own. Molecular variation was observed to be more within populations (73 %) as compared to among populations (27 %). On the other hand, genetic distance of populations revealed that the highest genetic distance is between Leqinat and Maja e Madhe. Mean values of expected heterozygosity were highest in Bogaj population, while lowest in Maja e Madhe population. The obtained results indicated that Bogaj population are more polymorphic. From the obtained data it can be concluded that RAPD markers provided a useful technique to study genetic diversity in P. veris L. populations. This technology allows identification and assessment of the genetic similarities and differences among plant populations.     

Effects of Fluctuating Temperatures and Different Host Plants on Development of Pasteuria penetrans in Meloidogyne javanica

Greenhouse and growth room experiments were conducted to investigate the effect of host plant in relation to different nematode inoculum levels, and temperature fluctuations on the development of Pasteuria penetrans. Host plant affected the development of P. penetrans indirectly through its effect on nematode development. Endospores collected from Meloidogyne javanica females reared on different hosts did not show any differences in subsequent attachment and infectivity. The numbers of endospores produced per infected female were reduced with increasing numbers of females parasitizing okra and tomato roots. Fluctuating temperatures retarded the development of P. penetrans. The life cycle of the parasite was completed faster at approximately constant temperatures close to 30 °C than when the temperature fluctuated away from 30 °C. The temperature of irrigation water did not affect the duration of life cycle of P. penetrans.     

Heritability and quantitative genetic divergence of serotiny,a fire-persistence plant trait

Background and Aims

Although it is well known that fire acts as a selective pressure shaping plant phenotypes, there are no quantitative estimates of the heritability of any trait related to plant persistence under recurrent fires, such as serotiny. In this study, the heritability of serotiny in Pinus halepensis is calculated, and an evaluation is made as to whether fire has left a selection signature on the level of serotiny among populations by comparing the genetic divergence of serotiny with the expected divergence of neutral molecular markers (Q_ST–F_ST comparison).

Methods

A common garden of P. halepensis was used, located in inland Spain and composed of 145 open-pollinated families from 29 provenances covering the entire natural range of P. halepensis in the Iberian Peninsula and Balearic Islands. Narrow-sense heritability (h²) and quantitative genetic differentiation among populations for serotiny (Q_ST) were estimated by means of an ‘animal model’ fitted by Bayesian inference. In order to determine whether genetic differentiation for serotiny is the result of differential natural selection, Q_ST estimates for serotiny were compared with F_ST estimates obtained from allozyme data. Finally, a test was made of whether levels of serotiny in the different provenances were related to different fire regimes, using summer rainfall as a proxy for fire regime in each provenance.

Key Results

Serotiny showed a significant narrow-sense heritability (h²) of 0·20 (credible interval 0·09–0·40). Quantitative genetic differentiation among provenances for serotiny (Q_ST = 0·44) was significantly higher than expected under a neutral process (F_ST = 0·12), suggesting adaptive differentiation. A significant negative relationship was found between the serotiny level of trees in the common garden and summer rainfall of their provenance sites.

Conclusions

Serotiny is a heritable trait in P. halepensis, and selection acts on it, giving rise to contrasting serotiny levels among populations depending on the fire regime, and supporting the role of fire in generating genetic divergence for adaptive traits.