Natural diversity of inflorescence architecture traces cryptic domestication genes in barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.)

Many-grained mutants occurring spontaneously among their less well-endowed field mates may have appeared to early farmers as fortunate twists of fate foreboding wealth and abundance. In domesticated barley, the number of kernel rows in spike can be tripled by recessive mutant alleles at the Six-rowed spike 1 (vrs1) locus that abolish the suppression of lateral spikelet fertility. In another barley row-type, so called intermedium-spike (int), lateral floret size is often intermediate between six-and two-rowed types. Phenotypic and sequence analyses of our intermedium-spike collection revealed that other genes can increase the size of florets and even stimulate occasional grain setting in lateral spikelets. Here, we show that a complete six-rowed phenotype occurs in a diverse panel of intermedium-spike barley carrying wildtype Vrs1 in the presence of the Int-c.a allele of the intermedium spike-c (int-c) gene, previously considered only as a modifier of lateral spikelet fertility. Int-c.a-type alleles had arisen before domestication and are associated with the enlargement of lateral florets in wild barley, suggesting that natural selection/evolution acts towards reduced lateral floret size. Since Int-c.a cannot overcome the suppression of lateral florets in the genomic background of wild barleys, we infer the existence of other gene loci, at which novel alleles or allelic combinations were selected for after domestication, to increase grain number of barley independently of Vrs1.     

Diversity and differentiation of <Emphasis Type="Italic">Oryza sativa</Emphasis> and <Emphasis Type="Italic">O. rufipogon</Emphasis> in Indonesia

Analysis of the genetic structure of Indonesian Oryza sativa and O. rufipogon using neighbour-joining trees based on single nucleotide polymorphism (SNP) and simple sequence repeat (SSR) markers revealed that O. sativa in Indonesia is separated from O. rufipogon. Accessions of O. sativa in this study were differentiated into two major groups, indica and tropical japonica, excluding some varieties. SSR and SNP markers revealed the high value of differentiation (F _ST) and genetic distance (D) between indica and tropical japonica and we discovered four loci by SNP markers and one locus by SSR markers that play a role in differentiation between indica and tropical japonica. Interestingly, genetic diversity (H) in O. rufipogon was lower than that in O. sativa, however H in O. rufipogon was the highest and H in tropical japonica was the lowest when O. sativa was divided into two groups. Inbreeding coefficient (Fst) showed evidences that gene flow (Nm) between species and within species might be one of the mechanisms related to the diversification and differentiation of Indonesian rice germplasm by asymmetric pattern between species and within O. sativa as revealed by SSR and SNP markers. In addition, we found evidences on stabilizing selection in Indonesian rice germplasm and they might be the reasons why Indonesian rice germplasm did not differentiate due to source location of landrace. However, we found a weak relation between SSR and SNP markers probably due to highly polymorphic in SSR and the different properties of both markers.     

Polymorphism of <Emphasis Type="Italic">Got2</Emphasis> DNA sequences sheds light on <Emphasis Type="Italic">Aegilops tauschii</Emphasis> Coss. intraspecies divergence and origin of <Emphasis Type="Italic">Triticum aestivum</Emphasis> L.

DNA sequences of nuclear gene Got2 was studied in 60 accessions of Aegilops tauschii, 29 of subsp. tauschii and 31 of subsp. strangulata. It was found that Got2 allozyme polymorphism in Ae. tauschii is due to a single, unique, mutation which led to replacement of glutamic acid by isoleucine in residue 256 of the enzyme molecule, encoded by Got2. As revealed by Got2 DNA sequences variation, initially in its history Ae. tauschii was presented by subsp. strangulata, and among phylogenetic lineages of subsp. strangulata, the lineage “t-9¹s” (TauL3) is the most ancient, a relict one. Subspecies tauschii is relatively “young”. Initially it was presented by the lineage marked by combination of allozyme alleles Got2 ¹⁰⁵ and Acph1 ¹⁰⁰. In the past it inhabited the Continental area from Caucasia to Pakistan, but later on it was forced out by newly originated, now—a major lineage of subsp. tauschii, marked by Got2 ¹⁰⁰. This lineage extended the Continental area of the species up to Kirgizstan, but actually failed to penetrate into pre-Caspian area, occupied by subsp. strangulata. These results essentially differ from those obtained previously, using chloroplast DNA (cpDNA) sequences polymorphism. As revealed by cpDNA, the major, “usual”, subsp. strangulata (TauL2) is “younger” than subsp. tauschii, which resided on phylogenetic tree between relict lineage “t-9¹s”of subsp. strangulata—and major subsp. strangulata. But both cpDNA and Got2 DNA sequences indicate that the level of genetic variation in subsp. tauschii is much lower than in subsp. strangulata. According to Got2 DNA sequences variation, it was Ae. tauschii subsp. strangulata lineage “k-109″ which donated genome D to Triticum aestivum L. This lineage includes accessions: k-109 from South-Eastern Precaspian Azerbaijan; KU-2105, KU-2159 from Western Precaspian Iran; KU-2080 from Eastern Precaspian Iran.     

<Emphasis Type="Italic">Trichoderma</Emphasis> improves the growth of <Emphasis Type="Italic">Leymus chinensis</Emphasis>

Bio-fertilizer application has been proposed as a strategy for enhancing soil fertility, regulating soil microflora composition, and improving crop yields, and it has been widely applied in the agricultural yields. However, the application of bio-fertilizer in grassland has been poorly studied. We conducted in situ and pot experiments to investigate the practical effects of different fertilization regimes on Leymus chinensis growth, with a focus on the potential microecological mechanisms underlying the responses of soil microbial composition. L. chinensis biomass was significantly (P?<?0.05) increased by treatment with 6000 kg ha^?1 of Trichoderma bio-fertilizer compared with other treatments. We found a positive (R² =?0.6274, P <?0.001) correlation between bacterial alpha diversity and L. chinensis biomass. Hierarchical cluster analysis and nonmetric multidimensional scaling (NMDS) revealed that soil bacterial and fungal community compositions were all separated according to the fertilization regime used. The relative abundance of the most beneficial genera in bio-fertilizer (BOF) (6000 kg ha^?1Trichoderma bio-fertilizer) was significantly higher than in organic fertilizer (OF) (6000 kg ha^?1 organic fertilizer) or in CK (non-amend fertilizer), there the potential pathogenic genera were reduced. There were significant negative (P?<?0.05) correlations between L. chinensis biomass and the relative abundance of several potential pathogenic genera. However, the relative abundance of most beneficial genera were significantly (P?<?0.05) positively correlated with L. chinensis biomass. Soil properties had different effects on these beneficial and on these pathogenic genera, further influencing L. chinensis biomass.     

Relationship between spike morphology and habitat of four <Emphasis Type="Italic">Aegilops</Emphasis> species of section Sitopsis

This study examines the relationship between spike morphology and natural habitat for 84 accessions of four Aegilops species, belongs to section Sitopsis, Ae. bicornis, Ae. longissima, Ae. searsii, and Ae. sharonensis in genus Aegilops, section Sitopsis, wild relatives of Triticum aestivum L. These species are considered valuable genetic resources for future cultivation and breeding of domesticated wheat. The goals of the study were to: (1) document variation in spike morphology among these four species; (2) examine the relationship between spike morphology and native habitat; (3) document geographical distribution of distinct spike morphology; and (4) examine the relationship between spike morphology and heading time and value for these four species. The results reveal significant differences in spike morphology among species of section Sitopsis. The most noteworthy variation involved the absence/presence of lateral awn, such that species with lateral awn were restricted in coastal, though species without lateral awn were mainly distributed in inland. This suggests that local climate may be a determinant of variation in lateral awn, and that this trait may be subject to convergent evolution. Differences in heading time in sympatric area were also observed. The differences may enhance species divergence and could represent a lead speciation event. The results of this study will facilitate identification of populations or accessions of wild wheat with favorable traits and/or novel adaptive genes.     

Origin of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) domestication genes

A number of genes that contribute to the domestication traits of cultivated rice have been identified. These include Sh4, Rc, PROG1 and LABA1, which are associated with non-shattering rachis, white pericarp, erect growth and barbless awns, respectively. The mutations giving rise to the “domestication alleles” of these genes are either invariable in cultivated rice, or have variability that is strictly associated with the phenotypic trait. This observation forms the basis to those current rice domestication models that envisage a single origin for the domesticated phenotype. Such models assume that the domestication alleles are absent or rare in wild rice, emerged under cultivation and spread across all rice groups by introgressive hybridization. We examined whole-genome sequencing datasets for wild and cultivated rice to test the former two assumptions. We found that the rc and laba1 alleles occur in wild rice with broad geographical distribution, and reach frequencies as high as 13 and 15%, respectively. These results are in agreement with previous observations of the prog1 and sh4 domestication alleles in wild populations. We also show that the diversity of the genomic regions surrounding the rc, laba1, prog1 and sh4 alleles in wild accessions is greater than that in cultivated rice, suggesting that these alleles emerged prior to domestication. Our findings indicate that the possibility that independent rice groups obtained identical domestication alleles directly from the wild population needs to be considered.     

Study Potential of Indigenous <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> and <Emphasis Type="Italic">Bacillus subtilis</Emphasis> in Bioremediation of Diesel-Contaminated Water

Petroleum products which are used in a wide variety of industries as energy sources and raw materials have become a major concern in pollution of terrestrial and marine environments. The purpose of this study was to assess the potential of indigenous microbial isolates for degradation of diesel fuel. Two most proficient bacterial strains among five isolated strains from polluted soil of an industrial refinery were studied. The isolates then were identified as Pseudomonas aeruginosa and Bacillus subtilis using biochemical tests and 16S rRNA gene sequence analyses. P. aeruginosa showed higher biodegradation efficiency than B. subtilis in shaking flask containing diesel-contaminated water. P. aeruginosa and B. subtilis degraded about 87 and 75% of total hydrocarbons, respectively, in flasks containing 2% diesel and 98% water. The biodegradation efficiency of the isolates decreased as diesel contamination increased from 2 to 5%. The isolates showed significantly higher efficiency on degradation of short-chain hydrocarbons in 20 days, i.e., by using P. aeruginosa, removal efficiency of C₁₀ hydrocarbons was near 90%, while about 69% of C₂₀₊ hydrocarbons and 47% of aromatic hydrocarbons were removed. Therefore, the isolates showed high capability in biodegradation of diesel contamination of the refinery.     

Effects of ectomycorrhizal fungus <Emphasis Type="Italic">Boletus edulis</Emphasis> and mycorrhiza helper <Emphasis Type="Italic">Bacillus cereus</Emphasis> on the growth and nutrient uptake by <Emphasis Type="Italic">Pinus thunbergii</Emphasis>

The present greenhouse study was undertaken to evaluate the effects of co-inoculating the ectomycorrhizal (ECM) fungus Boletus edulis with the mycorrhiza helper bacterium Bacillus cereus HB12 or HB59 on the growth and nutrient uptake of Pinus thunbergii. The inoculation with mycorrhiza helper bacterium significantly (P?≤?0.05) increased the ectomycorrhizal colonization. Treatments with dual inoculum (the mycorrhiza helper bacterium plus mycorrhiza) significantly (P?≤?0.05) increased the P. thunbergii growth. Bacteria–mycorrhizae interactions resulted in a great utilization of phosphate and potassium. The single inoculation resulted in a higher root activity than the control while the co-inoculation led to the highest root activity. The 6-CFDA staining assay showed that B. cereus enhanced fungal activity in ectomycorrhizal symbiosis. The results conclusively suggest that B. cereus isolated from the rhizosphere of P. thunbergii can potentially be used as individual inoculant or co-inoculated with ECM fungi to increase the production in sustainable ecological systems. These results support the potential use of B. cereus (HB12 or HB59) and B. edulis as mixed inoculants stimulating growth of P. thunbergii.     

Diversity of <Emphasis Type="Italic">Citrus</Emphasis><Emphasis Type="Italic">depressa</Emphasis> Hayata (Shiikuwasha) revealed by DNA analysis

Citrus depressa Hayata is an indigenous mandarin species on the Ryukyu Islands located in the subtropical region of Japan. We deduced its phylogenetic relationships by evaluating accessions grown on various Ryukyu Islands via cleaved amplified polymorphic sequence analysis of cpDNA and sequence-related amplified polymorphism (SRAP). The cpDNA results indicated that C. depressa could be classified into two types. SRAP revealed patterns of diversity within C. depressa consistent with our cpDNA results. These results indicate that maternal origin may influence or is correlated with the constitution of the nuclear genome of C. depressa. Another Japanese mandarin species, Citrus tachibana (Makino) Tanaka was distinguished from C. depressa by SRAP markers. Moreover, both C. depressa and C. tachibana could be distinguished from other Citrus species. Our results suggest that Japanese mandarin possesses a characteristic genome with the genus Citrus.     

Identification of new sources of resistance to <Emphasis Type="Italic">Striga gesnerioides</Emphasis> in cowpea <Emphasis Type="Italic">Vigna unguiculata</Emphasis> accessions

The parasitic weed, Striga gesnerioides, is a major threat to cowpea productivity throughout the savannas of West and Central Africa. The identification of sources of S. gesnerioides resistance and their incorporation into breeding programs would be a beneficial strategy to combat the devastation caused by the parasite in cowpea fields. In this study we examined one hundred and ninety-four (194) accessions, four commercial varieties and two controls collected from a mini core collection of cowpea held at the International Institute of Tropical Agriculture genebank for resistance to S. gesnerioides race 3 (SG3), the most prevalent race in Nigeria, using phenotypic screening and molecular marker analysis. Our studies identified two cowpea accessions, Tvu-1272 and Tvu-16514, that are resistant to S. gesnerioides SG3. Resistance in these lines is associated with the molecular marker SSR1, known to segregate with the gene conferring resistance to SG3 in the cultivar B301. Phenotypically, resistance in Tvu-1272 and Tvu-16514 is expressed as a hypersensitive response at the site of infection on the roots. Allelism tests indicated that the gene that conferring SG3 resistance in Tvu-1272 is independent of that conferring resistance in B301. Tvu-1272 and Tvu-16514 will provide additional new sources of resistance to Striga and races prevalent in Nigeria.     

Characterization of a world collection of <Emphasis Type="Italic">Agropyron cristatum</Emphasis> accessions

The genetic diversity was studied of 115 Agropyron cristatum accessions from 17 countries. Tetraploids were the most common (74.8%), followed by diploid (16.3%) and hexaploid (6.9%). We observed a relation between geographic distribution and ploidy level. The tetraploids, the most widespread, were found from Europe through Russia to East Asia. The diploids appeared over the same general range, except in Turkey, Iran and Georgia where no diploid accessions were found. Hexaploid accessions mainly came from a region comprising the east of Turkey, the north of Iran and Georgia. A selection of 71 accessions, including all three ploidy levels, were analyzed by capillary electrophoresis using six wheat simple sequence repeat (SSR) markers. All markers presented high levels of polymorphism, generating 166 different alleles ranging in size between 84 and 256 bp. Based on polymorphic information content values obtained (0.579–0.968), all the SSRs were classified as informative markers (values?>?0.5). According to the dendrogram generated, all the A. cristatum accessions were distinctly classified. Diploid, tetraploid and hexaploid accessions are not clearly differentiated from each other on the basis of SSR markers. A field experiment was conducted to morphologically characterize 18 accessions including the three ploidy levels. Significant differences were found between the accessions in spike length, spike width and number of spikelets per spike. All the cytological, molecular, and morphological data demonstrate the high genetic diversity present in A. cristatum, making it a valuable resource for future breeding programs.     

Remarks on genetic diversity and relationship of <Emphasis Type="Italic">Punica protopunica</Emphasis> and <Emphasis Type="Italic">P. granatum</Emphasis> assessed by molecular analyses

Here, two Punica species, viz., P. protopunica Balf. fil., reported as native to Socotra, and P. granatum L., were compared for the first time. Analysis of one P. protopunica and eleven P. granatum accessions was performed using three molecular markers, i.e., sequence related amplified polymorphism (SRAP), target region amplification polymorphism (TRAP), and intron targeted amplified polymorphism (ITAP), along with analysis of pgWD40 sequences, a gene involved in anthocyanin biosynthesis. All markers revealed the relationship between the two species and placed them at 33% similarity. SRAP, TRAP, and ITAP generated a total of 299, 260, and 160 bands, respectively. Of these, 78, 74, and 41 bands were specific for P. protopunica, and 92, 85, and 57 bands, respectively, were shared between both species. Sequence analysis of pgWD40~870 bp amplicons exhibited 100% identity among P. granatum accessions and 98% identity to that of P. protopunica. Phylogenetic analysis of WD40 sequences from monocot and dicot species, including both Punica species confirmed the relation between P. protopunica and P. granatum, supporting earlier reports that P. protopunica could be an ancestral species of P. granatum. Furthermore, the genetic diversity among and within P. granatum accessions from Egypt (3), Mexico (5), and Yemen (3) was assessed. Molecular marker-based relationships among region-bulked accessions was approximately the same (~90% similarity), whereas the degree of genetic variation was altered within each region. Specific bands (alleles) for accessions of each region along with those shared among them were identified. Thus, these bands could be used for pomegranate genotyping and breeding programs.     

Compositions of <Emphasis Type="Italic">n</Emphasis>-Alkanes and <Emphasis Type="Italic">n</Emphasis>-Methyl Ketones in Soils of the Forest-Park Zone of Moscow

The seasonal changes in the contents and compositions of n-alkanes and n-methyl ketones have been studied in typical soddy-podzolic soils (Albic Retisols (Ochric)) under lime forests in the Losiny Ostrov National Park, Moscow. In the humus horizons, the reserves (about 370 mg/m²) of odd n-alkanes with the chain length of C₂₅–C₃₅—the biomarkers of terrestrial vegetation—are 4–5 times below their amount entering with the leaf falloff in autumn. A noticeable contribution of microbial biomass hydrocarbons to the lipid fraction in the AY and AYel horizons manifests itself in the increased fraction of odd and medium-chain (<C₂₅) homologues (OEP = 4–6, LSR = 5–7) in the spectrum of n-alkanes. The lowest content of methyl ketones and odd n-alkanes was observed immediately after the winter period (OEP = 22, A/K = 21–170). In the EL and BT horizons, the n-alkane fraction of organic matter and the relative content of high molecularweight n-alkanes more resistant to microbial destruction (C₃₃, C₃₅) increases by 3–4 times in comparison with that in the abovelying horizons, and the type of distribution of n-alkanes by the carbon chain length changes: the dominance of odd homologues is absent; in the EL horizon, OEP = 1.     

C-banded karyotype of <Emphasis Type="Italic">Thinopyrum bessarabicum</Emphasis> and identification of its chromosomes in wheat background

C-banded pattern in two accessions of Thinopyrum bessarabicum (Save ex Rayss) A. Löve (2n = 2x = 14, E^bE^b) and their idiogram was established. C-banding analysis was further used to identify the chromosomes of Tritipyrum amphiploid (2n = 6x = 42, AABBE^bE^b) and a BC₁F₂ genotype from wheat and Tritipyrum. Two 18S-26S rDNA loci were detected on Th. bessarabicum chromosomes by in situ hybridization using an 18S-26S rDNA probe. E^b chromosomes in Tritipyrum generally were identified by their distinctive C-banding patterns which reflected heterochromatin regions. C-banding procedure resulted in sharp and distinct bands in one or both ends of E^b chromosomes without interval bands. Observed C-bands in E^b genome mainly reflected the telomeric and subtelomeric sequences which also showed more strong signals in genomic in situ hybridization. Results showed the importance of the C-banding technique as a screening tool in identification of addition and substitution lines in the progenies of wheat and Tritipyrum crosses during segregating generations.     

Putative Role of <Emphasis Type="Italic">Flavobacterium</Emphasis>, <Emphasis Type="Italic">Dokdonella</Emphasis> and <Emphasis Type="Italic">Methylophilus</Emphasis> Strains in Paracetamol Biodegradation

Paracetamol, the most widely and globally used analgesic and antipyretic, is easily accumulated in aquatic environments. In the present study, the biodegradation of paracetamol in different media (one for general growth, one specific for sulfate reducing bacteria, a mineral salts medium and municipal wastewater) inoculated with two types of sludge (from anaerobic lagoon and from oxidation ditch) under different oxygenic conditions (anoxic; moderate oxygenation in open flasks and high oxygenation by aeration) was investigated. In addition, bacteria with relative abundances increasing simultaneously with paracetamol degradation, when this drug was the only carbon source, thus with a putative role in its degradation, were identified using 16S rRNA gene sequences. The results show that aerobic microorganisms had a major role in the degradation of paracetamol, with 50 mg/L totally removed from municipal wastewater after 2 days incubation with aeration, and that the metabolites 4-aminophenol and hydroquinone plus one compound not identified in this work were produced in the process. The identification of bacteria with a role in the degradation of paracetamol revealed a strain from genus Pseudomonas with the highest final relative abundance of 21.2%, confirming previous works reporting strains of this genus as paracetamol decomposers. Besides, genera Flavobacterium, Dokdonella and Methylophilus were also in evidence, with initial relative abundances of 1.66%, 1.48 and 0.00% (not detected) in the inoculum and 6.91%, 3.80 and 3.83% after incubation, respectively. Therefore, a putative role of these genera in paracetamol biodegradation is suggested for the first time.

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Graphical Abstract ?

     

Microbial and Physico-chemical Characteristics Associated with the Incidence of <Emphasis Type="Italic">Legionella</Emphasis> spp. and <Emphasis Type="Italic">Acanthamoeba</Emphasis> spp. in Rainwater Harvested from Different Roofing Materials

The incidence of Legionella and Acanthamoeba spp. was correlated to microbial indicator analysis and physico-chemical characteristics of rainwater harvested from catchment areas constructed from galvanized zinc, Chromadek®, and asbestos, respectively. Quantitative PCR (qPCR) analysis indicated that no significant difference (p?>?0.05) in copy numbers of Legionella spp. and Acanthamoeba spp. was recorded in tank water samples collected from the respective roofing materials. However, significant positive Spearman (ρ) correlations were recorded between the occurrences of Legionella spp. gene copies vs. nitrites and nitrates (p?=?0.05) in all tank water samples. Significant positive correlations were also established between Acanthamoeba spp. vs. barium (p?=?0.03), magnesium (p?=?0.02), sodium (p?=?0.02), silicon (p?=?0.05), arsenic (p?=?0.03), and phosphate (p?=?0.01), respectively. Additionally, while no significant correlations were observed between Legionella spp. vs. the indicator bacteria (p?>?0.05), positive correlations were observed between Acanthamoeba spp. vs. total coliforms (p?=?0.01) and Acanthamoeba spp. vs. Escherichia coli (p?=?0.02), respectively. Results obtained in the current study thus indicate that the incidence of Acanthamoeba and Legionella spp. in harvested rainwater was not influenced by the roofing material utilized. Moreover, it is essential that the microbial quality of rainwater be assessed before this water source is implemented for potable and domestic uses as untreated harvested rainwater may lead to legionellosis and amoebae infections.     

The foliar spray of <Emphasis Type="Italic">Rhodopseudomonas palustris</Emphasis> grown under <Emphasis Type="Italic">Stevia</Emphasis> residue extract promotes plant growth via changing soil microbial community

Purpose

The extract of Stevia residue is an ideal substitute for cultivation of the purple nonsulfur bacterium, like Rhodopseudomonas palustris (R. palustris). But the influence of R. palustris grown under residue extract on its downstream application is still not well-characterized. The objective of this study was to assess the effect of foliar spray of R. palustris grown under Stevia residue extract on the plant growth and soil microbial properties.

Materials and methods

A pot experiment was carried out under the greenhouse condition, consisting of four treatments varying in the sprayed substances: sterilized water (control), R. palustris grown under the chemical medium supplemented with L-tryptophan (SyT), R. palustris grown under Stevia residue extract supplemented with L-tryptophan (ExT), and R. palustris grown under Stevia residue extract supplemented with NH₄Cl (ExT). The net photosynthesis rate of the uppermost leaves was measured with a portable photosynthesis system. Soil microbial activity was analyzed by microcalorimetry. Soil bacterial community components were determined by real-time quantitative PCR (qPCR) and high-throughput sequencing techniques.

Results and discussion

Compared with SyT, the R. palustris grown under Stevia residue extract not only improved the plant biomass and the net photosynthetic rate to a large extent, but also increased soil microbial metabolic activity and altered community compositions as well. The treatments receiving R. palustris, especially ExT and ExN, increased the relative abundances of some functional guilds involved in C turnover and nutrient cycling in soil, including Acidobacteria, Actinobacteria, Proteobacteria, Gemmatimonadaetes, Nitrospirae, and Planctomycetes.

Conclusions

R. palustris grown under the Stevia residue extract showed advantages over that under the chemical medium on both plant growth and soil microbial properties. One of the possible reasons could result from the increases in microbial activity and several bacterial keystone guilds involved into C and nutrient cycling, both of which potentially contribute to the improved plant growth. The results would be conducive to the downstream application of R. palustris in an economical way.

     

Effect of <Emphasis Type="Italic">Bacillus subtilis</Emphasis> QST713 and <Emphasis Type="Italic">Trichoderma asperellum</Emphasis> T34 on P uptake by wheat and how it is modulated by soil properties

Purpose

The effect on P uptake by plants after inoculation with P-mobilizing microorganisms may be modulated by soil properties, including natural microbiota. However, to put this theory into practical use, research is needed to shed new light on the soil factors which affect the capability of improving P nutrition in plants. The aim of this study was to assess how two P-mobilizing microorganisms, Trichoderma asperellum T34 and Bacillus subtilis QST713, influence P uptake by wheat plants in different soils; this will allow us to identify the soil properties which affect the efficiency of P nutrition in plants.

Materials and methods

In a completely randomized experiment, wheat was grown in pots in a growing chamber in soils with Olsen P values ranging from 4.8 to 8.7 mg kg^?1. The plants were inoculated with three treatments: T34, B. subtilis, and a non-inoculated control.

Results and discussion

Overall, B. subtilis was more effective in increasing plant P uptake and in mobilizing soil P (measured as Olsen P values) than T34. In some soils, B. subtilis was the only treatment which increased Olsen P in the rhizosphere after cultivation. However, the effect of both microorganisms differed depending on the soil. For B. subtilis, phytase hydrolysable P, Olsen P, carbonates, the Fe_ca/Fe_cbd ratio, and citrate-soluble P accounted for 92% of the variation in P uptake in inoculated plants (compared with the non-inoculated control). Most of these soil properties also accounted for 87% of the variation in the levels of shoot dry matter (DM) in B. subtilis-inoculated plants compared with shoot DM in the control plants. In addition, Olsen P, the Fe_ca/Fe_cbd ratio, and phytase hydrolysable P in the NaOH extracts accounted for 82 and 74% of the variation in the effect of T34 on P uptake and shoot DM, respectively. Overall, the lower the initial Olsen P in the soil, the higher the P uptake caused by microorganisms.

Conclusions

The initial availability of P and organic P in soil, in addition to other properties affecting P dynamics in the soil, may explain the triggering and efficiency of the P-mobilizing mechanisms in microorganisms. These are crucial in explaining the potential benefits to crops and, as a result, their practical use as a bio-fertilizer.

     

Evaluation of genetic resources in the genus <Emphasis Type="Italic">Asparagus</Emphasis> for resistance to <Emphasis Type="Italic">Asparagus virus 1</Emphasis> (AV-1)

Forty-four Asparagus officinalis cultivars, gene bank accessions and breeding lines as well as thirty-four accessions of wild relatives of Asparagus were evaluated for resistance to Asparagus virus 1. Three different test strategies were developed for the assessment of individual plants: (1) natural infection under field conditions, or two vector-mediated infection assays using the green peach aphid Myzus persicae (2) in an insect-proof gauze cage or (3) in a climate chamber. The AV-1 infections were verified by DAS-ELISA and RT-PCR approaches. All tested 660 individual plants of A. officinalis germplasm were susceptible to AV-1 infection. In contrast, in 276 plants of 29 Asparagus wild accessions no virus infection could be detected. These resistant accessions comprised of nineteen diploid, tetraploid and hexaploid species of both the Eurasian clade and the African clade of the asparagus germplasm. Data of the AV-1 resistance evaluation are discussed in relation to the genetic distance of the resistance carrier and potential application in breeding.