We evaluated combinations of two strains of plant growth-promoting rhizobacteria (PGPR) formulated with the carrier chitosan for the ability to induce growth promotion of tomato plants and resistance to infection by Cucumber mosaic virus (CMV). Each PGPR combination included GB03 (Bacillus subtilis) and one of the following PGPR strains: SE34 (B. pumilus), IN937a (B. amyloliquefaciens), IN937b (B. subtilis), INR7 (B. pumilus), or T4 (B. pumilus). The PGPR combinations formulated with chitosan are referred to as biopreparations. Tomato plants treated with each of the biopreparations appeared phenotypically and developmentally similar to nonbacterized control plants that were 10 days older (referred to as the older control). When plants were challenged with CMV, all plants in the biopreparation treatments and the older control treatment had significantly greater height, fresh weight, and flower and fruit numbers than that of plants in the CMV-inoculated same age control treatment. CMV disease severity ratings were significantly lower for biopreparation-treated and older control tomato plants than for that of same age control plants at 14 and 28 days postinoculation (dpi). CMV accumulation in young noninoculated leaves was significantly less for all biopreparation-treated plants and those in the older control than for the same age control plants at 14 dpi and for four of the five biopreparation treatments at 28 dpi. In those tomato plants shown to be infected, the amount of CMV in noninoculated leaves was significantly lower for three of the biopreparation treatments and the older control treatment at 14 dpi and biopreparation G/INR7 treatment at 28 dpi when compared with the control treatment. These data show that treatment of tomato plants with biopreparations results in significant enhancement of growth and protection against infection by CMV.

Rhizobacteria-Mediated Growth Promotion of Tomato Leads to Protection Against Cucumber mosaic virus

Navas M-L (2012). Trait-based approaches to unravelling the assembly of weed communities and their impact on agro-ecosystem functioning. Weed Research52, 479–488.

Summary
The trait-based approach to plant functional ecology has gained considerable attention over the last two decades, allowing ecologists to address questions relating to species distribution, community assembly and ecosystem functioning. We show here how this approach can be used to address these issues for weed ecology in a new way, allowing research to shift from purely weed control issues to a more global understanding of the impact of weed communities on the agro-ecosystem. We review how weed species are sorted by environmental factors and management according to the value of traits and the role thereof in the assembly of weed communities. How weed trait values and their distribution within communities affect agro-ecosystem processes is discussed in relation to loss of crop production. We also introduce the question of the impact of weed functional structure on ecosystem services and suggest some directions for research at species, community and agro-ecosystem levels.

Trait-based approaches to unravelling the assembly of weed communities and their impact on agro-ecosystem functioning

Plants encounter numerous pests and pathogens in the natural environment. An appropriate response to attack by such organisms can lead to tolerance or resistance mechanisms that enable the plant to survive. Many studies concentrate on the signalling pathways that enable plants to recognize and respond to attack, and measure the downstream effect in either biochemical or molecular terms. At the whole plant level, ecologists examine the fitness costs of attack not only for the plant but also over a range of trophic levels. The links between these differing levels of study are beginning to be addressed by the adoption of molecular approaches in more ecologically relevant settings. This review will describe the different approaches used by ecologists and cell biologists in this field and will try to address the question of how we can explore the response to, and consequences, of attack by multiple enemies.

Crosstalk between plant responses to pathogens and herbivores: a view from the outside in

C 4 and CAM photosynthesis have repeatedly evolved in plants over the past 30 million years. Because both repurpose the same set of enzymes but differ in their spatial and temporal deployment, they have long been considered as distinct and incompatible adaptations. Portulaca contains multiple C 4 species that perform CAM when droughted. Spatially explicit analyses of gene expression reveal that C 4 and CAM systems are completely integrated in Portulaca oleracea , with CAM and C 4 carbon fixation occurring in the same cells and CAM-generated metabolites likely incorporated directly into the C 4 cycle. Flux balance analysis corroborates the gene expression findings and predicts an integrated C 4 +CAM system under drought. This first spatially explicit description of a C 4 +CAM photosynthetic metabolism presents a potential new blueprint for crop improvement. 

Spatial resolution of an integrated C 4 +CAM photosynthetic metabolism

This paper reports Portulaca grandiflora as a new host of a Candidatus phytoplasma and demonstrates its association with the little leaf disease on P. grandiflora. Plants exhibited typical visual symptoms of a phytoplasma, with reduced leaf size. Pleomorphic bodies, observed by transmission electron microscopy, were restricted to the phloem of symptomatic tissue. However, no bacteria, fungi or viruses were observed under transmission electron microscopy. Products of the expected size were amplified by PCR using nested, phytoplasma-specific primer pairs. In addition, plants temporarily showed amelioration of phytoplasma symptoms following treatment with the antibiotic tetracycline.

/pdf/first-record-of-a-candidatus-phytoplasma-associated-with-4faur8cenv.pdf

First record of a Candidatus phytoplasma associated with little leaf disease of Portulaca grandiflora

The study characterized the influence of cucumber mosaic virus (CMV) on the growth response of two annual weeds to nitrogen. Plants were grown individually along a N gradient from 4 to 32 mmol l−1 and data were interpreted using growth analysis. Plant biomass increased with N concentration and was significantly higher for healthy than infected plants at the two highest N concentrations. Healthy plants of Portulaca oleracea L. were characterized by lower biomass allocation to leaves and higher biomass allocation to roots than infected plants; no change in biomass allocation was recorded for Stellaria media Vill. Relative growth rate (rgr), net assimilation rate (nar) and specific leaf area (sla) of plants increased with increasing N concentration. Healthy plants of P. oleracea were characterized by a higher rgr and nar and a lower sla than infected plants, whereas healthy S. media had a higher rgr but a similar nar and sla or leaf weight ratio (lwr) compared with infected plants. The consequences of these results on the population dynamics of weeds and virus spread are discussed.

Influence of cucumber mosaic virus infection on the growth response of Portulaca oleracea (purslane) and Stellaria media (chickweed) to nitrogen availability

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Influence of cucumber mosaic virus infection on the growth response of Portulaca oleracea (purslane) and Stellaria media (chickweed) to nitrogen availability