Clover Root Research Articles

Seeking Alfalfa Resistance to a Rhizophagous Pest, the Clover Root Curculio (Sitona hispidulus F.).

Simple SummaryClover root curculio (CRC) is a root feeding pest of alfalfa and clover that reduces stand life and yield. With the cancellation of soil-active insecticides in alfalfa, CRC populations and associated root damage have increased. Current CRC management practices are limited in their ability to suppress larval feeding belowground. Here, we evaluated alfalfa populations for resistance to CRC larval feeding and development belowground, and adult leaf consumption and oviposition aboveground. Divergent selection in two alfalfa cultivars in field nurseries revealed that there is genetic variability in resistance to CRC larval feeding and that significant gains in resistance from selection can occur in as few as two or three cycles of selection. While larval development was similar across the alfalfa populations tested in the lab, one alfalfa population (NY1713) displayed an overall increase in nodulation resulting in significantly lower proportions of nodules being consumed by larvae. These results provide possible candidates and soil-less method for the development and evaluation of alfalfa cultivars that may reduce the impacts of CRC root feeding and that offer an additional option for CRC management. Since the cancellation of broad-spectrum soil-active insecticides in alfalfa (Medicago sativa L.) production, clover root curculio (Sitona hispidulus F.) (CRC) larval root damage has increased. Current CRC management practices are limited in their ability to suppress larval feeding belowground. First, we field screened developmental alfalfa populations for CRC damage. Subsequently, we developed a soil-less arena to observe nodule feeding and development (head capsule width) of larvae in the lab. This method was used to evaluate five alfalfa populations (two CRC-susceptible (control) and three CRC-resistant populations) against larvae. Further, one CRC-resistant population paired with its genetically similar susceptible population were tested against adult leaf consumption and oviposition in the greenhouse. Field screening revealed that the alfalfa populations selected for little or no larval root feeding damage were more resistant to CRC larval feeding than their corresponding unselected cultivars and significantly more resistant than populations selected for susceptibility. The development of a soil-less arena provided a useful method for evaluation of root-larva interactions. Although larval development was similar across susceptible and resistant alfalfa populations, one CRC-resistant population (NY1713) displayed overall increased nodulation and, thus, had a significantly lower proportion of nodules consumed by larvae. Adult feeding and oviposition aboveground were similar across all populations tested. These results provide possible candidates and screening method for the development and evaluation of alfalfa cultivars that may reduce the impacts of larval feeding and that offer an additional option for CRC management.

Clover Root Exudates Favor Novosphingobium sp. HR1a Establishment in the Rhizosphere and Promote Phenanthrene Rhizoremediation.

ABSTRACTRhizoremediation is based on the ability of microorganisms to metabolize nutrients from plant root exudates and, thereby, to cometabolize or even mineralize toxic environmental contaminants. Novosphingobium sp. HR1a is a bacterial strain able to degrade a wide variety of polycyclic aromatic hydrocarbons (PAHs). Here, we have demonstrated that the number of CFU in microcosms vegetated with clover was almost 2 orders of magnitude higher than that in nonvegetated microcosms or microcosms vegetated with rye-grass or grass. Strain HR1a was able to eliminate 92% of the phenanthrene in the microcosms with clover after 9 days. We have studied the molecular basis of the interaction between strain HR1a and clover by phenomic, metabolomic, and transcriptomic analyses. By measuring the relative concentrations of several metabolites exudated by clover both in the presence and in the absence of the bacteria, we identified some compounds that were probably consumed in the rhizosphere; the transcriptomic analyses confirmed the expression of genes involved in the catabolism of these compounds. By using a transcriptional fusion of the green fluorescent protein (GFP) to the promoter of the gene encoding the dioxygenase involved in the degradation of PAHs, we have demonstrated that this gene is induced at higher levels in clover microcosms than in nonvegetated microcosms. Therefore, the positive interaction between clover and Novosphingobium sp. HR1a during rhizoremediation is a result of the bacterial utilization of different carbon and nitrogen sources released during seedling development and the capacity of clover exudates to induce the PAH degradation pathway.IMPORTANCE The success of an eco-friendly and cost-effective strategy for soil decontamination is conditioned by the understanding of the ecology of plant-microorganism interactions. Although many studies have been published about the bacterial metabolic capacities in the rhizosphere and about rhizoremediation of contaminants, there are fewer studies dealing with the integration of bacterial metabolic capacities in the rhizosphere during PAH bioremediation, and some aspects still remain controversial. Some authors have postulated that the presence of easily metabolizable carbon sources in root exudates might repress the expression of genes required for contaminant degradation, while others found that specific rhizosphere compounds can induce such genes. Novosphingobium sp. HR1a, which is our model organism, has two characteristics desirable in bacteria for use in remediation: its ubiquity and the capacity to degrade a wide variety of contaminants. We have demonstrated that this bacterium consumes several rhizospheric compounds without repression of the genes required for the mineralization of PAHs. In fact, some compounds even induced their expression.

Transcriptome profiling unveils the mechanism of phenylpropane biosynthesis in rhizome development of Caucasian clover.

Caucasian clover is the only perennial herb of the genus Leguminous clover with underground rhizomes. However, we know very little about its development process and mechanism. Transcriptome studies were conducted on the roots of Caucasian clover without a rhizome (NR) at the young seedling stage and the fully developed rhizome, including the root neck (R1), main root (R2), horizontal root (R3), and rhizome bud (R4), of the tissues in the mature phase. Compared with the rhizome in the mature phase, NR had 893 upregulated differentially expressed genes (DEGs), most of which were enriched in ‘phenylpropanoid biosynthesis’, ‘phenylalanine metabolism’, ‘DNA replication’ and ‘biosynthesis of amino acids’. A higher number of transcription factors (AP2/ERF, C2H2 and FAR1) were found in NR. There were highly expressed genes for R4, such as auxin response factor SAUR, galacturonosyltransferase (GAUT), and sucrose synthase (SUS). Phenylpropanoids are very important for the entire process of rhizome development. We drew a cluster heat map of genes related to the phenylpropanoid biosynthesis pathway, in which the largest number of genes belonged to COMT, and most of them were upregulated in R4.

Biological Features Of The Distribution Of Root Systems Of Perennial Legume Grasses In The Context Of Climate Change

The key factor in the choice of perennial legume grasses in the face of climate change is their drought resistance, because the development of roots directly affects this property, as well as determines their fertility. The purpose of the study was to establish what morphological and biological characteristics of grass roots ensure economic characteristics in the context of climate change. Methods of observation, comparison, and field experiment were used. The study found that the roots of alfalfa have the greatest depth in the soil, spread in the horizontal direction, the thickness of the root neck and lateral roots, which ensures plasticity, durability, and productivity of its crops. The roots of white melilot have the greatest depth in the soil, the thickness of the root neck, central root and lateral roots, their spread in the horizontal direction, which affects the drought and frost resistance of crops. The roots of birdsfoot trefoil are distinguished by the greatest number of renewal buds on the root neck, the smallest depth, and the thickness of the root neck, which affects productive longevity and the possibility of growth in poor and acidic soils. The roots of eastern galega have the greatest depth of the main plant, distribution in the horizontal direction, the thickness of the central root, which affects productive longevity and high biological plasticity. The roots of Hungarian sainfoin are distinguished by the greatest distribution in the horizontal direction and the deepest placement of the main branching, which affects high biological resistance to adverse growing conditions. It was also found out that the roots of meadow clover have the smallest spread radius in the horizontal plane, the thickness of the central and lateral roots, which determines the possibility of its cultivation in the field crop rotation. These findings would facilitate the selection of perennial legume grasses to achieve their full potential in the face of climate change

The effects of clover and nitrogen fertiliser on the presence of pasture pests in dairy pastures

A comprehensive dataset obtained from sampling four trials investigating interactions between perennial ryegrass and white clover under two levels of applied nitrogen (N) has highlighted different effects of pasture composition and N use on pasture pests.• For swards with white clover, presence of clover root weevil, whitefringed weevil and grass grub increased under low N by 36%, 11% and 5%, respectively, compared with high N treatments.• High N increased the presence of both Argentine stem weevil and root aphid by 7%.• Unexpectedly, clover reduced the presence of two grass feeders, Argentine stem weevil and black beetle, by 7% and 11% respectively.• Presence of grass grub was 17-30% lower under tetraploid ryegrasses than under diploids.• More clover and reduced N fertiliser inputs could reduce the frequency of black beetle and Argentine stem weevil with environmental benefits.

Precrop Effect of Red Clover (Trifolium pratense L.) and Alfalfa (Medicago sativa L.) on the Population Development of the Northern Root-Knot Nematode Meloidogyne hapla Chitwood, 1949 and on Succeeding Crops—A Pot Study

The northern root-knot nematode, Meloidogyne hapla, is a major pest of many crop species. The objective of the study was to determine how M. hapla population dynamics is affected by two precrops, i.e., Trifolium pratense and Medicago sativa, in three crop durations: one, two and three years of continuous cultivation. Moreover, we set ourselves the task of evaluating the effect of the legume precrop soil on the growth of the succeeding tomato plant (Solanum lycopersicum) and on the nematode population. The experiment was performed outdoors in pots with naturally infected soil. Both precrop species investigated were found to modify the J2 nematode population density in the soil. The galls and nematode females with egg masses were observed on the roots of both studied plant species at the end of each growing season. They appeared to be more abundant on the red clover roots than on those of the alfalfa. The obtained data indicate that the spring soil sampling is more appropriate for the estimation of the M. hapla population density in the red clover precrop soil. The legume precrop soil had a limiting effect on tomato growth and fruit yield. The nematode population negatively influenced tomato growth. The experiment revealed that tomato plants could be planted in alfalfa precrop soil following at least three years of continuous alfalfa cultivation. The same cannot be said of the cultivation of red clover as a precrop for tomatoes.

Effect of rosR Gene Overexpression on Biofilm Formation by Rhizobium leguminosarum

The regulatory protein encoded by the rosR gene is involved in the processes of adaptation of root nodule bacteria Rhizobium leguminosarum to changes in environmental conditions. It affects the expression of a number of genes associated with the synthesis of exopolysaccharides, which play a critical role in formation of bacterial biofilms on various surfaces. The goal of this work was to study the effect of overexpression of the rosR gene on formation of R. leguminosarum biofilms on inert surfaces and roots of heterologous plant hosts by obtaining recombinant strains with an additional copy of the rosR gene under the control of the Pm promoter. Our analysis of recombinant strains showed that additional expressed copies of the rosR gene allowed rhizobia to overcome the inhibitory effect on biofilm formation caused by low calcium concentrations in the medium, the effect of proteases and detergents, and to form biofilms more efficiently on the surface of tomato and clover roots. The results obtained open up prospects for using rosR as a tool both for increasing the efficiency of endosymbiosis of rhizobia with legumes, and for the formation of stable associative interactions with other agricultural crops.

ОЦЕНКА СОРТОВ КЛЕВЕРА ПО АГРОБИОЛОГИЧЕСКИМ И ХОЗЯЙСТВЕННО-ЦЕННЫМ ПРИЗНАКАМ

In intensifying fodder production, highly productive, high-protein and environmentally stable varieties of fodder crops are of fundamental importance. In this task, the main role is given to perennial legumes, among which clover occupies a priority. Clover is one of the leading fodder crops in many regions of Russia. In particular, in the North Caucasus, clover is of great importance in field and meadow fodder production. On hayfields and pastures of mountain slopes, this culture is used as a high-protein component in agro- and phytocenosis. The role of clover as a cheap source of protein for animals and an excellent precursor in the crop rotation link is well known. Its agrotechnical significance is also great: thanks to the nibble bacteria settling on the roots of clover, it is able to absorb atmospheric nitrogen. Clover roots penetrate deep into the ground, loosen soil layers, extracting nutrients difficult to access to other plants, enrich the soil with an organic substance, improve its structure, physical qualities, fix the arable layer and protect it from water and wind erosion. Due to the widespread use of this crop, there are increasingly high requirements for varieties cultivated in agrocenoses: increasing agrobiological and chemical-technological properties, improving soil fertility. To create highly effective pastures and hayfields, long-term and productive varieties of clover with high nutritional properties, salinity, resistance to diseases, trampling and mowing are required. The expansion of meadow clover crops is a priority area for the development of adaptive fodder production in North Ossetia, and especially in modern conditions, it is important to breed and evaluate its varieties. Meadow clover varieties are relatively resistant to adverse conditions and have high seed productivity. It is these requirements that meet the clover varieties "Dargavs," "Nart," "Mountain Saniba" and "Daryal." In order to identify clover varieties that are promising in the conditions of North Ossetia, on the basis of the North Caucasus Institute of Mining and Foothill Agriculture in the village. Mikhailovsky conducted research on their assessment of agrobiological and economic-valuable features. It was established that the variety "Mountain Saniba" stood out for the content of raw protein in dry matter, affinity, collection of dry matter per hectare. All studied varieties are adapted to the conditions of the foothill zone of North Ossetia, since they are winter straps. The growing season of the studied varieties varied on average 52-44 days by year, which is optimal for fodder harvesting in our region.

Nutritional Regime of the Soil and Growth Activity of the Apple Tree Root System in Orchards with Legume-Cereal Grass Intercropping

This work aims to study the influence of legume-cereal grasses in the inter-row spacings of the garden on the content of nutrients in the soil and the growth of apple tree roots. The amount of nitrate nitrogen was in direct proportion to the ratio of the legume component in the phytocenosis. The nitrogen content in the control option was the smallest: 19.7 mg/kg in the soil layer of 0-30 cm and 13.4 mg/kg in the layer of 30-60 cm. In the case of natural grassing-down between rows, cereal forbs prevailed. The largest amount of nitrate nitrogen was achieved when sowing the red clover and timothy grass in a ratio of 7:3. The accumulation of nitrate nitrogen is due to the activity of nodule bacteria on the roots of red clover. The accumulation of mobile phosphorus and exchangeable potassium depends on the amount of mowed mass in the inter-row spacings of the garden. The lowest content of mobile phosphorus was detected for natural grassing. In the control option, its amount was 118 mg/kg. In the 0-30 cm soil layer, the content of mobile phosphorus was 127.4-142.6 mg/kg depending on the ratio of legume-cereal grasses, and it amounted to 95.1-103.2 mg/kg in the 30-60 cm layer. For the ratio of red clover and timothy grass 3:7, the highest phosphorus content was detected. The intercropping of the garden with a legume-cereal herbal mixture also contributed to a greater accumulation of exchangeable potassium in the soil relative to natural grassing-down - 122.3-134.9 mg/kg. The optimal ratio of legume-cereal component was 3:7. A higher growth activity of the roots of the apple tree was noted in the option with sodding with a mixture of red clover and timothy grass in a ratio of 7:3.

ЭФФЕКТИВНОСТЬ ПРИМЕНЕНИЯ МИКРОУДОБРЕНИЯ И БИОПРЕПАРАТА НОВОГО ПОКОЛЕНИЯ НА ПОСЕВАХ КЛЕВЕРА ЛУГОВОГО

Feed production has been and remains one of the most important and complex problems in agriculture. The production of forage far exceeds the gross production of all other crop products. At the same time, being the most important branch of agriculture, they do not meet the needs of animal husbandry. The development of animal husbandry has recently been characterized by major organizational and technical changes. The process of specialization and concentration of its individual industries is under way at an accelerated pace. A network of large complexes for the production of livestock products on an industrial basis is being created, and farms are being comprehensively mechanized. All this led to an increase in the production of all livestock products. The successful development of animal husbandry depends, first of all, on the state of the fodder base. In recent years, fodder production has developed into one of the most important branches of agriculture. Analysis of the current state of feed production in North Ossetia shows that the supply of livestock with feed is 1.5 times lower than in some regions of the Russian Federation and has a tendency to further decline. This is due to the fact that feed production is aimed at volumetric rather than quality indicators. Therefore, all vegetable feeds of our own production are characterized by a low concentration of protein in dry matter (8.3-9.2%) and metabolizable energy (8.2-8.5 MJ). Clover is one of the leading forage crops. Its role as a cheap source of protein for animals and as an excellent precursor in crop rotation is well known. Agrotechnical significance is also great: thanks to the nodule bacteria settling on the roots of clover, it is able to assimilate atmospheric nitrogen. Clover roots penetrate deep into the ground, loosen the soil layer, extracting nutrients that are difficult for other plants to reach, enrich the soil with organic matter, improve its structure, physical properties, fix the arable layer and protect it from water and wind erosion. Get ting high and stable yields is possible with uninterrupted, harmonious, balanced supply of plants with basic nutrients in accordance with their needs throughout the growing season. The size of the yield is the most important indicator of the effectiveness of the culture under study, cultivation conditions, agricultural techniques and their combinations. It is advisable to focus on modern biological products and complex bioorganic fertilizers, because their composition is as close to optimal values as possible.

Seed treatment with cold plasma and electromagnetic field induces changes in red clover root growth dynamics, flavonoid exudation, and activates nodulation

AbstractThe effects of presowing treatment of red clover seeds with cold plasma (5 and 7 min) and electromagnetic field (10 and 15 min) on plant agronomic performance were studied. Seed treatments stimulated germination and this effect correlated with changes in the balance of seed phytohormones: a decreased amount of abscisic acid and an increased gibberellin/abscisic acid ratio. Experiments performed in rhizoboxes revealed that seed treatments stimulated root growth and root nodulation. Stressor and dose‐specific changes in the amounts of flavonoids important for communication with nitrogen‐fixing strains of rhizobacteria were detected in the root exudates. The results suggest that besides changes in plant's internal processes, the response of plants to seed treatment involves beneficial modulation of plant communication with microorganisms.

Nitrogen release from shoots and roots of crimson clover, hairy vetch, and red clover

Nitrogen (N) release from legume cover crops is a key N source for subsequent crops in rotation. In this study, chopped fresh shoots or roots (<5 mm) of crimson clover (CC), hairy vetch (HV), and red clover (RC) were incorporated into a 50:50 mixture of air-dried sandy loam soil (<2 mm) and washed builders sand at a rate of 300 mg N kg−1. The mixtures were packed in leaching tubes (four replicates), leached with 100 mL of 5 mmol L−1 CaCl2, and then incubated for 10 wk (22 °C, 0.33 bar matric potential) with weekly leaching. Total N and inorganic N (NH4+ plus NO3−) in leachate were quantified and organic N was determined as the difference between total N and inorganic N. More N was released from shoots (63.4%–70.0% of initial N) than from roots (27.3%–50.7% of initial N). Mineralized organic N and inorganic N followed the first order, single N-pool mineralization model [Nt = N0(1 – e−kt); R2 = 0.94−0.99]. Potentially mineralizable N (N0, as % of initial N) was similar for shoots (CC = 75.1%, HV = 74.2%, and RC = 71.3%), but varied for roots (CC = 36.2%, HV = 52.6%, and RC = 53.0%). The N0 pool in shoots had a half-life (t1/2 = ln 2/k) of 11.0, 9.8, and 15.1 d for CC, HV, and RC, respectively; and a half-life in roots of 23.9, 8.5, and 25.7 d, respectively. Hence, HV released its stored N in both roots and shoots faster than CC and RC. The results in this study would help farmers optimize their choice in legume cover crops and termination times to better synchronize N release with crop uptake.

Nitrogen uptake and growth of white clover inoculated with indigenous and exotic Rhizobium strains

Little information is available on investigating the effectiveness of indigenous and exotic rhizobia in enhancing nitrogen uptake and growth of white clover. This study aimed to evaluate the nitrogen fixation effectiveness of native rhizobia isolated from white clover grown in Taiwan as compared to an exotic strain, Rhizobium leguminosarum bv. trifolii BCRC 14266. Indigenous rhizobia were isolated from nodules in roots of white clover, and 16S rRNA gene sequences were used to identify their taxonomy. To compare the symbiotic effectiveness of indigenous and exotic rhizobia, white clover plants were inoculated respectively with two indigenous isolates (CHB 1120 and CHB 1121), BCRC 14266, and a non-inoculated control. Based on 16S rRNA gene sequences, CHB 1120 and CHB 1121 could be identified as Rhizobium species. Compared with the non-inoculated control and BCRC 14266, CHB 1120 and CHB 1121 significantly increased the dry weight of shoots and roots at 75 days after planting (DAP). Additionally, CHB 1120 and CHB 1121 significantly enhanced the amount of chlorophyll present in leaves estimated by SPAD readings, increasing nitrogen contents in shoots by 38.1 and 49.2%, respectively. In comparison with BCRC 14266, CHB 1120 and CHB 1121 significantly increased the nodule number and nitrogenase activity at both 45 and 75 DAP. In conclusion, the two indigenous strains significantly outperform the exotic strain and non-inoculated control in promoting nitrogen uptake and growth of white clover.

Extracellular Synthesis and Characterization of Silver Nanoparticles from Alkaliphilic Pseudomonas sp.

Bio-nanotechnology offers eco-friendly processes for the synthesis of stable nanoparticles (NPs). We hypothesized that microorganisms isolated from the root nodules of leguminous plants would biosynthesize silver (Ag) bio-nanoparticles. Clover root nodules enriched with nutrient broth (NB) produced four distinct colonies on NA plates. Microbial colonies were purified by repeated streaking and designated as SS6, SS7, SS8, and SS9 for identification using 16S rRNA sequencing. Four species of Pseudomonas were identified with a similarity score of over 99% using the EZ Taxon search engine, and tested for extracellular biosynthesis of AgNPs. Microorganism Pseudomonas taiwanensis-SS8 with alkaliphilic growth characteristics reduced the AgNO3 solution into AgNPs in the shortest time period. AgNPs were characterized using UV-Vis spectrophotometry and electron and transmission electron microscopy. A number of physical (i.e., temperature and time) and chemical (i.e., pH and growth media) parameters were optimized. An efficient polydispersal biosynthesis of AgNPs at pH 8-9 after 48 hrs in NB growth medium was observed. In addition, the AgNPs showed antimicrobial properties against 16 commonly occurring pathogenic microorganisms.

Plant Residues Decomposition and Formation of Active Organic Matter in the Soil of the Incubation Experiments

The decomposition and mineralization of various plant residues (oak and aspen leaves, pine needles, small branches and thin roots of trees, aboveground biomass and roots of meadow grasses, aboveground biomass and roots of clover, and straw and roots of barley) were investigated in the laboratory experiments by quantitative measurement of produced C–CO2. The plant residues were mixed with vermiculite or gray forest soil (Greyzemic Phaeozems Albic) and incubated under constant temperature and moisture conditions. After a year of incubation, 25–67% of Corg in plant residues were mineralized. Oak leaves, aboveground mass of meadow grasses, and aboveground mass and roots of clover were characterized by a three-pool structure of organic matter with moderate (0.1 > k1 > 0.01 day–1), slow (0.01 > k2 > 0.001 day–1), and very slow (k3 < 0.001 day–1) mineralization rates, while the other types of plant residues had only a two-pool structure with slow and very slow mineralization rates. An opposite relationship between the decomposition rate and the C : N ratio in the plant residues was found. Poorly decomposable types of plant residues were the main source for particulate organic matter (CPOM) in the soil, while highly decomposable types were the main source for microbial biomass (Cmic). The content of potentially mineralizable organic matter in the soil with plant residues correlated positively with CPOM and with Cmic.

СЕЛЕКЦИЯ ВИДОВ КЛЕВЕРА НА ИММУНИТЕТ В УСЛОВИЯХ РСО-АЛАНИИ

In the intensification of fodder production, high-yield, highprotein and environmentally sustainable varieties of fodder crops are of fundamental importance. In this task, the main role is given to legumes, the priority among which is clover. Clover is one of the leading forage crops in many regions of Russia. In particular, in the North Caucasus in the field and meadow feed production clover is of great importance. On hayfields and mountain pastures, this crop is used as a high-protein component in the agro- and phytocenosis. The role of clover as a cheap source of protein for animals and an excellent precursor in the link to crop rotation is well known. Its agrotechnical significance is also great: thanks to nodule bacteria settling on the roots of clover, it is able to assimilate atmospheric nitrogen. Clover roots penetrate deep into the earth, loosen the soil layers, removing nutrients that are difficult to reach for other plants, enrich the soil with organic matter, improve its structure, physical qualities, fix the arable layer and protect it from water and wind erosion. The article reviews the results of clover samples evaluation in vivo development in order to create varieties of clover resistant to the most harmful diseases. According to S.A. Bekuzarova, for foothill areas characterized by complex environmental conditions, we need varieties resistant to diseases. Such varieties are currently lacking, since preference in breeding was given to potential productivity [1, 2]. In order to create varieties of clover resistant to the most harmful diseases, samples were evaluated in the natural conditions of mountain phytocenoses and in the nurseries of their breeding process for such diseases as ascochitis, anthracnose, brown spot, powdery mildew, and the selection of disease-resistant samples - on an artificial infectious background . In collection nurseries, perennial meadow clover and annual species of incarnate, Alexandria, shabdar were studied. In terms of resistance to the complex of diseases, samples have been identified that allow the development of a variety with high disease-resistant characteristics, using wild-growing forms of natural phytocenoses and introduced annual clover species as the starting material.

EFFECT ON MICROBIAL PRODUCTS ON CAESIUM ELUTION BEHAVIOUR FROM CLAY MINERALS.

Some microorganisms in the environment make siderophores, which are low molecular chelators, to take up minerals from soil. Eleven bacteria were separated from the root of white clover by chlome azrol S (CAS) assay. Each bacterium was incubated in casamino acid (CAA) culture, and siderophores in CAA culture were purified. These extractions were applied to biotite or vermiculite spiked with Cs. From each clay mineral, 57.1-72.8% (5100 ppm), 55.6-63.8% (920 ppm) and 48.6-54.3% (2300 ppm), 31.6-34.4% (520 ppm) was eluted, respectively. To understand elution behaviour, Cs desorption ratio of each clay was measured every 30 min. The results indicate Cs elution was occurred quickly.

Impact of crop aerial and root biomass inputs on soil nitrifiers and cellulolytic microorganisms

In agricultural no-till systems, crop residue management has an important impact on the activity and abundance of soil microorganisms, which play a crucial role in soil health and quality. In these systems, when cover crops are included in order to increase the amount of crop residues, aerial biomass remains on the soil surface, whereas root biomass is directly incorporated into the soil. Although both aerial and root biomass may have a differential effect on the abundance and activity of nitrifiers and cellulolytic microorganisms, to our knowledge, such effects have not been individually studied in the literature. The aims of this research were to study the abundance and activity of nitrifiers and cellulolytic microorganisms, and their efficiency indexes (EIs), as affected by: i) aerial cover crop residues and roots of cover crops at two soil depths (0-0.5 and 0.05-0.2 m), and ii) soil conditions at 30, 90, and 150 days after the cover crop killing date. We conducted an experiment during two consecutive years in Paraná, Argentina (-31°50.9′S; -60°32.3′W). Treatments included two cover crop species that were added to the soil either as aerial input or as root input. Treatments were aerial input of wheat (Triticum aestivum L.) (AW) on fallowed soil, aerial input of white sweet clover (Melilotus albus Medik.) (ASC) on fallowed soil, in situ grown roots of wheat (RW), in situ grown roots of white sweet clover (RSC) and a control (C) on fallowed soil without aerial or root inputs. In each of the growing seasons, at 30, 75 and 150 days after the killing date, soil samples were collected at depths of 0-0.05 m and 0.05-0.20 m. From the soil samples, soil water content, activity and abundance of nitrifiers and cellulolytic microorganisms were determined. The average activity of nitrifiers was higher (p < 0.0001) in the topsoil layer than in the subsurface layer (0.06 vs. 0.04 mg NO3− g soil-1). However, the average cellulolytic activity did not differ among depths and treatments. The average abundance of nitrifiers was similar between soil layers (ca. 5-log g soil-1), and the abundance of cellulolytic activity ranged from 6.7 to 8.4 log g-1 soil. Our results show that in the topsoil, the microbiological variables under study had a more important effect via the source of the inputs, i.e. whether the source belongs to the aerial or roots biomass rather than the cover crop species. In addition, we detected that in the topsoil, regardless of the crop species, aerial residues promoted cellulolytic activity, whereas root inputs promoted nitrifier activity. The study allowed us to identify how the microbiological variables were affected by the source of the input at the field level.

The complete mitogenome sequence of the agricultural pest, clover root weevil: the key to its own demise?

We report the complete mitogenome of Sitona obsoletus, an agricultural pest in New Zealand and some European countries. Like other Sitona mitogenomes, the 6 tRNA gene box is ordered RNSAEF, supporting the hypothesis that this signature is common to, and potentially diagnostic, of this genus. The Trojan Female Technique (TFT) is a genetic pest control strategy that exploits mitochondrial DNA alleles that affect male, but not female fertility and fitness. The complete mitogenome is an essential first step in exploring the utility of TFT for the control of S. obsoletus.

First Report of Didymella lethalis Associated with Roots of Pea, Subterranean Clover, and Winter Vetch in Germany, Switzerland, and Italy

First Report of <i>Didymella lethalis</i> Associated with Roots of Pea, Subterranean Clover, and Winter Vetch in Germany, Switzerland, and Italy