Maize resistance to northern corn leaf blight is potentiated by nickel

Northern corn leaf blight (NCLB), caused by Exserohilum turcicum, is one of the most devastating diseases affecting maize yield worldwide. A foliar spray of nickel (Ni) to potentiate maize resistance against NCLB was investigated by examining alterations in the photosynthetic apparatus (leaf gas exchange and chlorophyll [Chl] a fluorescence parameters), production of ethylene and reactive oxygen species as well as activities of defence and antioxidant enzymes. Mycelial growth of E. turcicum was inhibited by Ni in vitro. Inoculated plants sprayed with Ni exhibited higher foliar Ni concentration, reduced NCLB symptoms, and lower concentrations of malondialdehyde and hydrogen peroxide. In inoculated leaves of plants not sprayed with Ni, concentrations of Chl a, Chl b, and carotenoids were lower and the photosynthetic apparatus was impaired at the biochemical level due to high NCLB severity. The activities of antioxidant enzymes were not affected by Ni, except an increase in glutathione reductase activity for noninoculated plants sprayed with Ni. High lipoxygenase and polyphenoloxidase activities, lower ethylene production, as well as elevated production of phenolics and lignin helped decrease NCLB severity in the leaves of Ni-sprayed plants.     

Isolation of culturable phosphobacteria with both phytate-mineralization and phosphate-solubilization activity from the rhizosphere of plants grown in a volcanic soil

Chilean volcanic soils contain large amounts of total and organic phosphorus, but P availability is low. Phosphobacteria [phytate-mineralizing bacteria (PMB) and phosphate-solubilizing bacteria (PSB)] were isolated from the rhizosphere of perennial ryegrass (Lolium perenne), white clover (Trifolium repens), wheat (Triticum aestivum), oat (Avena sativa), and yellow lupin (Lupinus luteus) growing in volcanic soil. Six phosphobacteria were selected, based on their capacity to utilize both Na-phytate and Ca-phosphate on agar media (denoted as PMPSB), and characterized. The capacity of selected PMPSB to release inorganic P (Pi) from Na-phytate in broth was also assayed. The results showed that from 300 colonies randomly chosen on Luria–Bertani agar, phosphobacteria represented from 44% to 54% in perennial ryegrass, white clover, oat, and wheat rhizospheres. In contrast, phosphobacteria represented only 17% of colonies chosen from yellow lupin rhizosphere. This study also revealed that pasture plants (perennial ryegrass and white clover) have predominantly PMB in their rhizosphere, whereas PSB dominated in the rhizosphere of crops (oat and wheat). Selected PMPSB were genetically characterized as Pseudomonas, Enterobacter, and Pantoea; all showed the production of phosphoric hydrolases (alkaline phosphatase, acid phosphatase, and naphthol phosphohydrolase). Assays with PMPSB resulted in a higher Pi liberation compared with uninoculated controls and revealed also that the addition of glucose influenced the Pi-liberation capacity of some of the PMPSB assayed.     

Therapy-induced acute recruitment of circulating endothelial progenitor cells to tumors

The contribution of bone marrow-derived circulating endothelial progenitor cells (CEPs) to tumor angiogenesis has been controversial, primarily because of their low numbers in blood vessels of untreated tumors. We show that treatment of tumor-bearing mice with vascular disrupting agents (VDAs) leads to an acute mobilization of CEPs, which home to the viable tumor rim that characteristically remains after such therapy. Disruption of this CEP spike by antiangiogenic drugs or by genetic manipulation resulted in marked reductions in tumor rim size and blood flow as well as enhanced VDA antitumor activity. These findings also provide a mechanistic rationale for the enhanced efficacy of VDAs when combined with antiangiogenic drugs.     

Quantitative trait loci associated with trichomes in the <Emphasis Type="Italic">Solanum galapagense</Emphasis> accession LA1401

Pest resistance in Solanum galapagense has been associated with the presence of type IV glandular trichomes and allelochemicals. Knowledge of the genetic factors involved in determining the presence and type of trichomes may assist in the process of gene introgression for development of pest resistant tomato cultivars. In this study, we sought to identify QTLs associated with the presence of type IV trichomes in an F₂ population derived from the interspecific cross of Solanum lycopersicum TOM-684?×?S. galapagense accession LA1401. Two QTLs contributing to type IV trichome occurrence and density were detected, one major QTL (gal.IV-2), responsible for 35.22% of phenotypic variation, was located on chromosome 2. The other QTL (gal.IV-3) was located on chromosome 3, and explained 23.35% of the phenotypic variation in the F₂ population. These QTLs were responsible for 26.44 and 3.37% of the variation observed in a progeny derived from a backcross to TOM-684. The same QTLs were also associated with type II?+?III non-glandular trichomes, whose densities were negatively correlated to those of type IV trichomes, suggesting that the loci found may have pleiotropic effects for high type IV/low type II?+?III trichome densities. Our results indicate that the inheritance for type IV trichomes can be explained by a few genetic factors affecting the presence of a gland and the density of trichomes. These results further suggest a revision to trichome classification used for tomato may be appropriate.     

Characterization of <Emphasis Type="Italic">Fusarium</Emphasis> species associated with tobacco diseases in Northwestern Argentina

Phenotypic traits are regularly used to diagnose the development of Fusarium head blight (FHB) in the field, whereas mycotoxin accumulation in wheat grains can only be accurately evaluated through costly methods, such as high–performance liquid chromatography (HPLC). The aim of this study was to determine whether: (i) the results provided by existing commercial decision support tools could be anticipated using phenotypic measurements, including a novel technique of computer–assisted image analysis of spikes; and (ii) these measurements could avoid using HPLC. We monitored the FHB development during two consecutive years in highly contaminated plots in the Burgundy region (France). Contamination by crop residues was simulated through a field inoculation with barley grains artificially colonized by Fusarium graminearum. The development of the disease on spikes and harvested grains was assessed on one tolerant and two susceptible wheat varieties. The accumulated amounts of mycotoxins were measured in harvested grains using HPLC. As expected, the measured traits revealed that the inoculum responsible for infection on spikes mainly came from residues left on the soil surface, and the susceptible varieties were more diseased than the tolerant variety. Weather conditions had a strong effect on disease development. The novel computer–assisted image analysis technique had a better prediction power of deoxynivalenol accumulation, was more objective and time–saving than classical visual symptom assessments. This assessment method could be suitable to supplement the use of existing prediction tools and might avoid systematic and costly mycotoxin measurements in likely infected plots.     

The role of rhizobacteria in rice plants: Growth and mitigation of toxicity

Allelopathic compounds reduce the growth and productivity of upland rice plants, especially in consecutive plantations. The rhizobacteria Pseudomonas fluorescens BRM-32111 and Burkholderia pyrrocinia BRM-32113 have been recorded as growth promoters in rice. This study was developed to understand the effect of the application of rhizobacteria on upland rice plants in consecutive plantations. Experiments were conducted in a completely randomized design with four replications of four treatments: rice seed inoculated with P. fluorescens BRM-32111, rice seed inoculated with B. pyrrocinia BRM-32113 (both sown on soil with rice residue), non-inoculated plants sown on soil with rice residue (control with residue (WR)), and non-inoculated plants on soil with no residue (NR). Roots and seedling growth were adversely affected by allelopathic compounds in control WR plants. Plants inoculated with rhizobacteria P. fluorescens BRM-32111 or B. pyrrocinia BRM-32113 induced an increase of 88% in biomass, 3% in the leaf area, 40% in length, 67% in root biomass, 21% in chlorophyll a, 53% in chlorophyll (a+b), 50% in rate of carbon assimilation (A), 227% in A/rubisco carboxylation efficiency (C_i) and 63% in water use efficiency (WUE) compared to control WR plants. These results indicate that rhizobacteria P. fluorescens BRM-32111 and B. pyrrocinia BRM-32113 increase the tolerance of rice plants to stress from allelochemicals. There are possible practical agricultural applications of these results for mitigating the effects of environmental allelochemistry on upland rice.