Selective involvement of members of the eukaryotic initiation factor 4E family in the infection of Arabidopsis thaliana by potyviruses

Arabidopsis thaliana plants with mutations in the genes encoding eukaryotic initiation factor (eIF4E) or isoform of eIF4E (eIF(iso)4E) were tested for susceptibility to Clover yellow vein virus (ClYVV), a member of the genus Potyvirus. ClYVV accumulated in both inoculated and upper uninoculated leaves of mutant plants lacking eIF(iso)4E, but not in mutant plants lacking eIF4E. In contrast, Turnip mosaic virus (TuMV), another member of the genus Potyvirus, multiplied in mutant plants lacking eIF4E but not in mutant plants lacking eIF(iso)4E. These results suggest the selective involvement of members of the eIF4E family in infection by potyviruses.     

Growth, development and consumption by four syrphid species associated with the lettuce aphid, Nasonovia ribisnigri, in California

The lettuce aphid, Nasonovia ribisnigri Mosley, was accidentally introduced into California from Europe during the late 1990s and soon became an economic pest of Romaine lettuce along California’s central coast region. Indigenous syrphid larvae attack the lettuce aphid and are believed to be effective in the management of this invasive pest, although there have been no studies on the capacity of the syrphid larvae to kill and consume lettuce aphids. We focused on four syrphid species commonly found in central coast lettuce fields: Allograpta obliqua (Say), Eupeodes fumipennis (Thomson), Sphaerophoria sulphuripes (Thomson), and Toxomerus marginatus (Say). Laboratory feeding experiments were conducted to estimate the development times of all juvenile stages, the daily growth rate of larvae, the number of third instar aphids killed, the aphid biomass killed, and the aphid biomass consumed as measures of predator performance. Results show that during larval development E. fumipennis killed the most third-instar aphids (507 aphids, 88 mg biomass killed) and reached the largest size, followed by A. obliqua (228 aphids, 39 mg killed), S. sulphuripes (194 aphids, 31 mg killed) and T. marginatus (132 aphids, 20 mg killed). Body size alone did not account for species differences in per-capita larval consumption rates. This information is discussed in relation to the predation potential of syrphids through the short cropping cycle of lettuce, and the choice of plant species to use for floral resource provisioning to enhance the activity of syrphids needed for effective management of lettuce aphids in California’s central coast fields.     

IAA Producing Enterobacter sp. I-3 as a Potent Bio-herbicide Candidate for Weed Control: A Special Reference with Lettuce Growth Inhibition

Development of bio-herbicides is an emerging method to weed management in agricultural field. Very few studies were conducted on identification of microbial bio-herbicides to weed control. The present study was aimed to isolate and identify the effective bio-herbicide potential bacterium from soil and assess their role on plant growth inhibition. Three-hundred and one rhizobacteria were isolated from agriculture field soil samples collected from various parts of Republic of Korea. Two bacterial strains, I-4-5 and I-3 were significantly reduced the seedling growth of radish when compared to their controls. The highest rate of seedling growth inhibition was observed in I-3 bacterial isolate treatment in lettuce and radish. The mechanism of an effective bio-herbicide I-3 to plant growth inhibition was determined by analyzing IAA in their culture medium. IAA biosynthesis pathway of Enterobacter sp. I-3 was identified as tryptophan-dependent pathway and its production was increased due to addition of tryptophan in culture medium as quantified by using GC–MS SIM. In an in vitro study revealed that I-3 bacterial culture exudate combined with tryptophan significantly decreased leaf length, leaf width, root length and increased the number of lateral roots of lettuce. Indeed, the genomic DNA of I-3 bacterium was isolated and 16S rDNA was sequenced to find out the name of the bacterium. Based on phylogenetic analysis, I-3 isolate was identified and named into Enterobacter sp. I-3. The results of this study suggest that the utilization of Enterobacter sp. I-3 to crop field can be act as a potential bio-herbicide against weed growth.

Electronic supplementary material

The online version of this article (doi:10.1007/s12088-015-0515-y) contains supplementary material, which is available to authorized users.     

Allelopathic potential of two invasive alien Ludwigia spp.

The allelopathic potential of two invasive alien Ludwigia [Onagraceae: L. peploides (Kunth) Raven and L. grandiflora (Michaux) Greuter and Burdet], that have developed quasi-monotypic stands in many aquatic ecosystems in France, was investigated. Since allelopathy involves the release of compounds into the environment, the water of monospecific experimental cultures was directly tested against two target species: Lactuca sativa L., the standard cultivar for bioassays, and Nasturtium officinale R. Brown, a resistant and widespread native hydrophyte. The treatment was carried out at the three main phases of development of both Ludwigia in February, May and August. For each experiment, the germination, mortality and culture yield percentages, the seedling growth (radicle and hypocotyl elongation) and the health of 15-day-old-seedlings were measured. The water of each Ludwigia tank induced: (1) a decrease in germination for watercress in August (control: 68.6%, L. peploides: 48.6%, L. grandiflora: 61.1%); (2) an increase in mortality in May only for watercress (control: 3.4%, L. peploides: 13.5%, L. grandiflora: 12%) and in August for both target species (up to 22.3% vs. 3% for lettuce and 27% vs. 12.5% for watercress); (3) a disturbance of seedling elongation for lettuce in all seasons; and (4) a seedling chlorosis of both target species, particularly in May and August. This study showed that L. peploides and L. grandiflora possess an allelopathic activity that influences the water quality throughout the year. Combined with the various competitive attributes, allelopathy may contribute to the great success of these two invasive Ludwigia in Europe. In threatened wetland communities of the Mediterranean area, in particular, allelopathy might have an important impact by diminishing the seedling survival of the most vulnerable species.     

Calcium changes during megasporogenesis and megaspore degeneration in lettuce (<Emphasis Type="Italic">Lactuca sativa</Emphasis> L.)

Potassium pyroantimonate was used to localize loosely-bound calcium in young ovules of lettuce (Lactuca sativa L.) during megasporogenesis to investigate the relationship between ionically available calcium and megaspore degeneration. At the megasporocyte (megaspore mother cell) stage, few calcium precipitates were located in the ovule. Following meiosis in the megasporocyte, a linear tetrad of four megaspores is formed, with three of the four megaspores degenerating from the micropylar end inward. Only the chalazal-most megaspore continues to develop, becoming the functional megaspore. A decrease in amount of calcium precipitates in the megaspore, particularly in the nucleus, precedes the breakdown of the micropylar megaspores, which subsequently undergo structural disintegration and loss of recognizable cellular features. A partial recovery of calcium precipitates occurs during later degeneration. The functional megaspore retains a consistently higher concentration of calcium precipitates during development, which is retained in the developing embryo sac. This, to our knowledge, is the first report related to calcium dynamics during megaspore degeneration, and may facilitate future research aimed at elucidating the mechanisms of megasporogenesis.     

Relevant Effects of Ethylene and Ga2+ on Germination of Lettuce Seeds

Relevant effects of ethylene and Ca2+ on germination of lettuce (lactuce sative L.) seeds were investigated. It was shown previously that lettuce seeds were highly sensitive ro temperatures. More than 70% of seeds germinated at 22℃, but they ceased to germinate at 25℃. 40%–50% of seeds could be induced to germinate after imbibition with 400 ppm exogenous ethylene for 3 days at 25℃. The amounts of endogenous ethylene liberated at 22℃ were much greater than those at 25℃. Ethyleneglycol bis NN tetraacetic acid(EGTA, Ca2+ specified chelating regent) La3+, Co2+ and chlorpromazin(CPZ, calmodulin antagonist) could be used ant only to inhibit germination at 22℃, but also to inhibit germination induced by ethylene at 25℃. Although La3+ and CPZ inhibited seed germination, they could not repress the production of ethylene at 22℃. It was suggested that Ca2+ and CaM affected the induction response of ethylene to lettuce seed germination, but had no effect on ethylene liberation. Co2+ could be applied to inhibit the action as well as its production of ethylene.     

Expression of a chimeric nitrate reductase gene in transgenic lettuce reduces nitrate in leaves

 Transgenic plants of four glasshouse-grown lettuce cultivars ('Cortina', 'Evola', 'Flora' and 'Luxor') were obtained by co-cultivating excised cotyledons with Agrobacterium tumefaciens. The Agrobacterium strain LBA4404 contained the binary vector pBCSL16, which carried a nitrate reductase (nia) cDNA linked to CaMV promoter and terminator sequences, and the neomycin phosphotransferase II (nptII) gene. Transformed shoots were selected by their ability to root on medium containing kanamycin sulphate, by a positive NPTII assay and by PCR analysis. The presence of the nia cDNA in transgenic lettuce was confirmed by nitrate reductase (NR) enzymatic assay, a reduction in the nitrate content of leaves and by Southern hybridisation. PCR analysis of cDNA fragments from transgenic plants confirmed that both nia and nptII genes were expressed in first seed-generation (T1) lettuce plants. The commercial importance of reduced nitrate concentrations in lettuce is discussed. Received: 7 January 1998 / Revision received: 24 February 1998 / Accepted: 22 March 1999     

Sources and genetic structure of a cluster of genes for resistance to three pathogens in lettuce

The second largest cluster of resistance genes in lettuce contains at least two downy mildew resistance specificities, Dm5/8 and Dm10, as well as Tu, providing resistance against turnip mosaic virus, and plr, a recessive gene conferring resistance against Plasmopara lactucae-radicis, a root infecting downy mildew. In the present paper four additional genetic markers have been added to this cluster, three RAPD markers and one RFLP marker, CL1795. CL1795 is a member of a multigene family related to triose phosphate isomerase; other members of this family map to the other two major clusters of resistance genes in lettuce. Seven RAPD markers in the region were converted into sequence characterized amplified regions (SCARs) and used in the further analysis of the region and the mapping of Dm10. Three different segregating populations were used to map the four resistance genes relative to molecular markers. There were no significant differences in gene order or rate of recombination between the three crosses. This cluster of resistance genes spans 6.4 cM, with Dm10 1.2 cM from Dm8. Marker analysis of 20 cultivars confirmed multiple origins for Dm5/8 specificity. Two different Lactuca serriola origins for the Du5/8 specificity had previously been described and originally designated as either Dm5 or Dm8. Some ancient cultivars also had the same specificity. Previously, due to lack of recombination in genetic analyses and the same resistance specificities, it was assumed that Dm5 and Dm8 were determined by the same gene. However, molecular marker analysis clearly identified genotypes characteristic of each source. Therefore, Dm5/8 specificity is either ancient and widespread in L. serriola and some L. sativa, or else has arisen on multiple occasions as alleles at the same locus or at linked loci.     

Taxonomy and pathogenicity of Olpidium brassicae and its allied species

The classification and physiology of the zoosporic plant-pathogen Olpidium brassicae and its relationships with the closely-related species are often confusing. This review focuses on these species and intends to differentiate them based on the literatures published since the discovery and establishment of the species by Woronin in 1878 under the name of Chytridium brassicae to current molecular era. The goal of this review is to help researchers better understand the taxonomy, the host range, and the potential role in plant health of O. brassicae-related species. To reach the goal, we reviewed the rationales behind the creation or reduction in synonymy of the different names for O. brassicae and its allied species in order to elucidate the evolution of the species concept on them based on the traditional morphological studies. Furthermore, the studies by molecular biology methods improve our knowledge and perspectives on O. brassicae and its host specificity. In particular, we clarify the differences between O. brassicae and Olpidium virulentus, and propose potential new research avenues. We therefore hope that this review will give a better perspective on Olpidium spp. and their potential role in the root microbiome of plants in natural environments and in agricultural settings.     

The Response of Lettuce Cultivars against Two Lettuce mosaic virus isolates,One Able to Systemically Infect the Resistant Cultivar Salinas 88

The response of seven lettuce cultivars to two geographically different Lettuce mosaic virus (LMV) isolates (LMV‐A, LMV‐T) was statistically evaluated based on infection rate, virus accumulation and symptom severity in different time trials. LMV‐A is characterized by the ability to systemically infect cv. Salinas 88 (mo1²‐carrying resistant cultivar), and inducing mild mosaic symptoms. Among lettuce cultivars, Varamin (a native cultivar) similar to cv. Salinas showed the most susceptibility to both LMV isolates, whereas another native cultivar, Varesh, was tolerant to the virus with minimal viral accumulation and symptom scores, significantly different from other cultivars at P < 0.05. LMV‐A systemically infects all susceptible lettuce cultivars more rapidly and at a higher rate than LMV‐T. This isolate accumulated in lettuce cultivars at a significantly higher level, determined by semiquantitative ELISA and induced more severe symptoms than LMV‐T isolate at 21 dpi. This is the first evidence for a LMV isolate with ability to systemically infect mo1²‐carrying resistant cultivar of lettuce from Iran. In this study, accumulation level of LMV showed statistically meaningful positive correlation with symptom severity on lettuce plants. Based on the results, three evaluated parameters differed considerably by lettuce cultivar and virus isolate.