Non-symbiotic bacterial diazotrophs in crop-farming systems: can their potential for plant growth promotion be better exploited?

Biological N₂ fixation (BNF) by associative diazotrophic bacteria is a spontaneous process where soil N is limited and adequate C sources are available. Yet the ability of these bacteria to contribute to yields in crops is only partly a result of BNF. A range of diazotrophic plant growth-promoting rhizobacteria participate in interactions with C₃ and C₄ crop plants (e.g. rice, wheat, maize, sugarcane and cotton), significantly increasing their vegetative growth and grain yield. We review the potential of these bacteria to contribute to yield increases in a range of field crops and outline possible strategies to obtain such yield increases more reliably. The mechanisms involved have a significant plant growth-promoting potential, retaining more soil organic-N and other nutrients in the plant-soil system, thus reducing the need for fertiliser N and P. Economic and environmental benefits can include increased income from high yields, reduced fertiliser costs and reduced emission of the greenhouse gas, N₂O (with more than 300 times the global warming effect of CO₂), as well as reduced leaching of NO₃⁻-N to ground water. Obtaining maximum benefits on farms from diazotrophic, plant growth promoting biofertilisers will require a systematic strategy designed to fully utilise all these beneficial factors, allowing crop yields to be maintained or even increased while fertiliser applications are reduced.     

Effect of sewage sludge on suppressiveness to soil-borne plant pathogens

The objective of this study was to evaluate the effect of sewage sludge on soil suppressiveness to the pathogens Fusarium oxysporum f. sp. lycopersici on tomato, Sclerotium rolfsii on bean, Sclerotinia sclerotiorum on tomato, Rhizoctonia solani on radish, Pythium spp. on cucumber, and Ralstonia solanacearum on tomato. Soil samples were collected from an experimental corn field in which sewage sludge had been incorporated once a year, since 1999. Sludge from two sewage treatment stations in Brazil (Franca and Barueri, SP) were applied at the rates of one (1N), two (2N), four (4N) and eight (8N) times the N recommended doses for the corn crop. Soil suppressiveness was evaluated by methods using indicator host plants, baits and mycelial growth. There was no effect of sewage sludge on soil suppressiveness to Fusarium oxysporum f. sp. lycopersici in tomato plants. For S. rolfsii, reduction of the disease in bean was inversely proportional to the dose of Franca sludge. The incidence of dead plants, caused by S. sclerotiorum, was directly proportional to sludge doses applied. For R. solani and R. solanacearum, there was a linear trend with reduction in plant death in soils treated with increasing amounts of sludge from Franca. There was an increase in the pathogen community of Pythium spp., proportional to the amounts of sewage applied. The effects of sewage sludge varied depending on the pathogen, methodology applied and on the time interval between the sewage sludge incorporation and soil sampling.     

Relationship between total nodulation and nodulation at the root crown of peanut, soybean and common bean plants

The objective of this study was to simplify the procedure for evaluation of legume nodulation, by examining if there is a relationship between the nodulation of the whole root system and at the crown region. Roots of peanut, soybean and common bean plants growing in soils were split in two parts (crown and bottom) and assessed for nodulation (nodule number and dry weight). In general, most nodules were concentrated at the crown, and crown nodulation was generally positively correlated with total nodulation of all three legume crops. The results are highly applicable in studies such as strain selection for inoculants and assessment of inoculation technologies, among others, and is an important contribution to help reduce the time and labor required for the evaluation of nodulation parameters.     

Growth promoting effects of corn (Zea mays) bacterial isolates under greenhouse and field conditions

Fertilizer costs are a major component of corn production. The use of biofertilizers may be one way of reducing production costs. In this study we present isolation and identification of three plant growth promoting bacteria that were identified as Enterobacter cloacae (CR1), Pseudomonas putida (CR7) and Stenotrophomonas maltophilia (CR3). All bacterial strains produced IAA in the presence of 100 mg l⁻¹ of tryptophan and antifungal metabolites to several soilborne pathogens. S. maltophilia and E. cloacae had broad spectrum activity against most Fusarium species. The only strain that was positive for nitrogen fixation was E. cloacae and it, and P. putida, were also positive for phosphate solubilization. These bacteria and the corn isolate Sphingobacterium canadense CR11, and known plant growth promoting bacterium Burkholderia phytofirmans E24 were used to inoculate corn seed to examine growth promotion of two lines of corn, varieties 39D82 and 39M27 under greenhouse conditions. When grown in sterilized sand varieties 39M27 and 39D82 showed significant increases in total dry weights of root and shoot of 10-20% and 13-28% and 17-32% and 21-31% respectively. Plants of the two varieties grown in soil collected from a corn field had respective increases in dry weights of root and shoot of 10-30% and 12-35% and 11-19% and 10-18%. In sand, a bacterial mixture was highly effective whereas in soil individual bacteria namely P. putida CR7 and E. cloacae CR1 gave the best results with 39M27 and 39D82 respectively. These isolates and another corn isolate, Azospirillum zeae N7, were tested in a sandy soil with a 55 and 110 kg ha⁻¹ of nitrogen fertility at the Delhi research Station of Agriculture and Agri-Food Canada over two years. Although out of seven bacterial treatments, no treatment provided a statistically significant yield increase over control plots but S. canadense CR11 and A. zeae N7 provided statistically significant yield increase as compared to other bacteria. The 110 kg rate of nitrogen provided significant yield increase compared to the 55 kg rate in both years.     

An empirical evaluation of the area and isolation paradigm of metapopulation dynamics

Much of metapopulation theory assumes that the persistence of individual populations in a metapopulation, and persistence of the metapopulation as a whole, is best modeled by the area of habitat patches and their isolation. Estimates of isolation typically include a measure of geographic distance and a measure of either population size or patch area. This “area and isolation paradigm” assumes a functional relationship between the area of a patch and its extinction probability, and between isolation of a patch and its colonization probability. Although these assumptions are fundamental to use of incidence function models of metapopulation dynamics, the assumptions have been validated in only a small number of studies. We tested the ability of area and isolation to predict extinction and colonization patterns using multiple-year occupancy data for 10 species from three taxonomic groups (butterflies, amphibians, and birds). We examined 13 potential models of metapopulation dynamics. All models included four basic parameters: occupancy during the first year of the survey, probability of extinction, probability of colonization, and single-visit detection probability. In eight models, each parameter was either constant or time-dependent. Five models included a patch-level covariate of extinction probability (patch area or population size), colonization probability (connectivity, the inverse of isolation), or both. Extinction patterns generally were predicted more effectively as a function of local population size than as a function of patch area, a constant probability of extinction, or a time-dependent probability of extinction. In most cases, inclusion of connectivity as a patch-level covariate did not improve predictions of colonization patterns. We estimated single-visit detection probabilities for all species in our analyses, thus providing evidence-based guidelines for the refinement of future monitoring protocols.     

Seasonal variation in trehalose contents of roots and nodules of leguminous trees in a tropical deciduous forest in Mexico

Seasonal variations of trehalose contents in roots and root-nodules of five legumes in a tropical deciduous forest in Jalisco, México, were determined. The tree species were: Lonchocarpus eriocarinalis and Erythrina lanata (sub-family Papilionoideae) and Piptadenia constricta, Albizia occidentalis and Lysiloma microphylum (sub-family Mimosoideae). Trehalose accumulation in nodules and roots varied seasonally and among species. For example, the Papilionoid-species retained nodules longer than those in the Mimosoideae (5 and 4 months, respectively), and accumulated the highest amounts of trehalose (average values of 178 vs. 2.88 mg g⁻¹ nodule (d. wt), respectively). Generally, maximum trehalose contents in nodules and roots were observed in November, at the beginning of the dry season.     

The effect of habitat fragmentation on communities of mutualists: Amazonian ants and their host plants

The consequences of fragmentation for communities of mutualist partners are for the most part unknown; moreover, most studies addressing this issue have been conducted on plant-pollinator communities. We evaluated how the experimental fragmentation of lowland Amazonian rain forest influenced a community of ant-plant mutualists. We inventoried a total of 1057 myrmecophytes in four fragments and four continuous forest sites; the twelve plant species recorded were occupied by 33 ant morphospecies, of which 11 were obligate plant inhabitants. Neither plant species richness, ant species richness, nor total ant-plant density were significantly lower in forest fragments. However, eight of the plant species, including three of the four most common, had higher mean densities in continuous forest than fragments. Of these four species, only one (Cordia nodosa) had significantly different colonization rates between habitat types, with higher colonization rates of plants in fragments. This may be because the Azteca species it is associated with increases in abundance in forest isolates. Although our results suggest that communities of ant-plant mutualists are likely to persist in fragmented tropical landscapes 25 years after fragment isolation, most species are rare and populations sizes in fragments are extremely low. Environmental and demographic stochasticity could therefore limit long-term population viability. We suggest future studies focus on evaluating how fragmentation has altered herbivore pressure and the dispersal of ants and plants to fragments, since the interaction of these factors is likely to have the greatest impact on long-term patterns of population persistence.     

Organic acid exudation by mycorrhizal Andropogon virginicus L. (broomsedge) roots in response to aluminum

Elevated aluminum (Al) availability limits plant growth on acidic soils. Although this element is found naturally in soils, acidic conditions create an environment where Al solubility increases and toxic forms of Al impact plant function. Plant resistance to Al is often attributed to organic acid exudation from plant roots and the chelation of cationic Al in the rhizosphere. The association of arbuscular mycorrhizal (AM) fungi with the roots of plants may alleviate Al toxicity by altering soil Al availability or plant exposure through the binding of Al to fungal structures or through the influence of fungi on exudation from roots. Diverse communities of AM fungi are found in soil ecosystems and research suggests that AM fungi exhibit functional diversity that may influence plant performance under varying edaphic environments. In the present study, we evaluated acidic isolates of six AM species in their responses to Al. Andropogon virginicus (broomsedge), a warm-season grass that commonly grows in a range of stressful environments including acidic soils, was used as a plant host for Acaulospora morrowiae, Glomus claroideum, Glomus clarum, Glomus etunicatum, Paraglomus brasilianum, and Scutellospora heterogama. Fungal spores were germinated and exposed to 0 or 100 μM Al on filter paper in sand culture or were grown and exposed to Al in sand culture in association with A. virginicus. Short- and long-term responses to Al were evaluated using direct measurements of fungal spore germination, hyphal elongation, and measurements of A. virginicus colonization and plant growth as a phytometer of AM function in symbio. Spore germination and hyphal elongation varied among AM species in response to Al, but patterns were not consistent with the influences of these AM species on A. virginicus under Al exposure. Exposure to Al did not influence colonization of roots, although large differences existed in colonization among fungal species. Plants colonized by G. clarum and S. heterogama exhibited the least reduction in growth when exposed to Al, produced the highest concentrations of Al-chelating organic acids, and had the lowest concentrations of free Al in their root zones. This pattern provides evidence that variation among AM fungi in Al resistance conferred to their plant hosts is associated with the exudation of Al-binding organic acids from roots and highlights the role that AM fungal diversity may play in plant performance in acidic soil environments.     

Control of one invasive plant species allows exotic grasses to become dominant in northern Great Plains grasslands

Decline of leafy spurge (Euphorbia esula) in the northern Great Plains of the US is generally viewed as a success story for biological control, but quality of the vegetation that survived the infestation is key to recovery of ecosystem function. In addition, effects of other invasive species, notably cool-season exotic grasses, must be taken into account. Objectives of this study were (1) to evaluate direction and significance of changes in biomass of native and exotic grasses, forbs, and leafy spurge and in plant species composition following control of leafy spurge by flea beetles and (2) to evaluate the relative effects of leafy spurge and exotic grasses on biomass of native grasses, biomass of forbs, and richness of native species. We monitored species composition (1998-2003 and 2008) and biomass (2000, 2002, 2003 and 2008) of these groups on spurge-infested and noninfested permanent plots at three sites with unbroken prairie sod in North Dakota, USA. We found little evidence, in terms of species richness or biomass of native grasses or forbs, that leafy spurge was being replaced by desirable native species, although desirable as well as weedy and exotic species were characteristic of 2008 vegetation at all three sites. Structural equation models revealed that leafy spurge had temporally intermittent negative effects on forb biomass and species richness, but no effects on native grasses. In contrast, exotic grass had consistently strong, negative effects on native grass biomass, as well as stronger negative effects than leafy spurge on native species richness. Although substantial native plant diversity remains at these sites, exotic grasses pose an important threat to these crucial building blocks of native prairie ecosystems.     

Changes in mineral nitrogen, phosphorus availability and salt-extractable aluminium following the application of green manure residues in two weathered soils of South Vietnam

Phosphorus deficiency and aluminium toxicity in weathered soils can be amended by applying organic residues. Nitrogen mineralization, changes in P-availability and changes in salt-extractable Al following the incorporation of residues of various green manures (Flemingia congesta, Mucuna pruriens, Pueraria phaseoloides, Tithonia diversifolia) were quantified in a field core incubation experiment. Dried residues were added at an application rate of 45 kg P ha⁻¹ to two soils representative for the main soil groups of the South Vietnamese uplands, set up in incubation cores in an experimental field near Ho Chi Minh City, Vietnam.Decomposition of the residues proceeded at high rates. Mineralized nitrogen from the residues was recovered mainly as ammonium during the first 2 weeks of incubation. Nitrogen release from Tithonia residues with the highest lignin content and lignin:N ratio occurred more gradually compared to the three legumes. Resin-extractable P was significantly increased by residue treatments. Largest and sustained increases in resin-extractable P (0.67 and 2.06 mg P kg⁻¹ in the two soils) were observed in samples amended with Tithonia, which was related to the large P-content (0.37%) and small C:P ratio (110) of the residues. The P-concentration in the residues, rather than the total amount of P applied through the residues, affected the increase in P-availability. The increase in resin-extractable P was correlated to the P-content (R=0.64) and C:P ratio (R=−0.65) of the residues. Salt-extractable Al-concentrations were considerably reduced by the organic amendments, up to 70 and 50% in the two soils. At the rate of 45 kg P ha⁻¹, no significant differences between the residue treatments to reduce soil acidity were observed.As such, the application of high quality residues that are rich in P, in particular T. diversifolia, may enhance crop production by creating favourable soil conditions during the initial stages of plant development of the main crop.     

The nematode-trapping fungus Arthrobotrys oligospora in soilof the Bodega marine reserve: distribution and dependenceon nematode-parasitized moth larvae

Of the 13 nematode-trapping fungi previously detected at the Bodega Marine Reserve (BMR, Sonoma County, CA, USA), Arthrobotrys oligospora is by far the most abundant. Why A. oligospora is so abundant is unclear, but the answer may involve bush lupines (Lupinus arboreus), ghost moth larvae (Hepialus californicus), and insect-parasitic nematodes (Heterorhabditis marelatus). Previous research documented a dramatic increase of A. oligospora in BMR soil with the addition of an H. marelatus-parasitized moth larva. The current study tested two predictions based on the hypothesis that the H. marelatus-parasitized ghost moth larva is a unique and important resource for A. oligospora at BMR. First, because ghost moth larvae are concentrated in soil under bush lupines, we predicted that A. oligospora numbers would be greater under lupines than away from lupines. Second, we predicted that A. oligospora would be enhanced more by moth larvae containing living H. marelatus than by moth larvae containing dead H. marelatus or no H. marelatus or by nematodes alone. The first prediction was supported by data from a field study (A. oligospora population density was greater beneath lupines than in grasses 2 m away), but the difference was small. The second prediction was not supported by data from a laboratory experiment (dead moth larvae caused dramatic increases in A. oligospora numbers whether or not the dead moth larvae contained living nematodes). While H. marelatus are clearly unnecessary for the large increase in A. oligospora numbers, the importance of nematodes in general remains unclear because addition of dead moth larvae always resulted in large increases in bacterivorous nematodes and because addition of nematodes alone enhanced A. oligospora in one trial but not in two others.     

Restoring forest herb communities through landscape-level deer herd reductions: Is recovery limited by legacy effects?

White-tailed deer (Odocoileus virginianus) overbrowsing has altered plant species diversity throughout deciduous forest understories in eastern North America. Here we report on a landscape-level (306 km²) project in Pennsylvania, USA that tracked the herbaceous community response to deer herd reductions. From 2001 to 2007, we estimated deer densities, browse impact on woody seedlings, and censused the herbaceous flora in permanent plots throughout the area. We assessed herb layer species richness, abundance, and dominance and measured three known phytoindicators of deer impact: Trillium spp., Maianthemum canadense, and Medeola virginiana. We predicted that browse-sensitive taxa would increase in abundance, size, and flowering as would overall species diversity following deer culls and browse impact that declined by an order of magnitude by 2007. Following intensified deer harvests, we observed a limited recovery of the herbaceous community. Trillium spp. abundance, height, and flowering; M. canadense cover; and M. virginiana height all increased following herd reductions. Similarly, forb and shrub cover increased by 130% and 300%, respectively. Nevertheless, species diversity (i.e., richness and dominance) did not vary. Our work demonstrates that reducing deer densities can provide rapid morphological and population-level benefits to palatable species without a concomitant recovery in diversity. We suggest that decreasing deer populations alone may not promote plant diversity in overbrowsed, depauperate forests without additional restoration strategies to mitigate a browse-legacy layer dominated by browse-resistant species.     

Herbicides have negligible effects on ants and springtails in an Australian wheat field

The effects of herbicides applied to a direct drilled and traditionally tilled wheat field on trap catches of the abundant Collembola and Formicidae were examined. Significantly higher abundances of Collembola and species richness of ants were found on the direct-drilled plots. A significant effect of the herbicides, bromoxynil (C₇H₃Br₂NO) and hoegrass (diclofop-methyl), on the activity of two of the fourteen species of surface-dwelling Collembola was detected but no effect was observed on surface-active Formicidae. Jeannenotia stachi numbers were significantly more reduced on the direct-drilled compared to the traditionally tilled plot after herbicide treatment possibly because of higher predator abundance on the latter. In the short term, herbicides have a minimal effect on most species of surface-active arthropods although Collembola were more adversely affected than Formicidae.     

Population responses of oribatids and enchytraeids to ectomycorrhizal and saprotrophic fungi in plant-soil microcosms

The oribatid mites Oppiella nova, Tectocepheus velatus and Nothrus silvestris and the enchytraeid worm Cognettia sphagnetorum are four common animal species in boreal forest soils. According to the literature, they respond differently to clear-cutting of forest stands. O. nova responds with population decreases, T. velatus and N. silvestris with small changes and C. sphagnetorum with population increases. We hypothesised that the presence/absence of ectomycorrhizal (EM) fungi is a major factor in explaining these reactions. The population responses of these soil animals to inoculation of five species of EM fungi growing in symbiosis with their host tree (Pinus sylvestris L.) and one saprotrophic fungus, Hypholoma capnoides, growing on wood were tested in pot microcosms with artificial soil (peat and vermiculite) for 70-84 days. Additionally, plants without inoculation of EM fungi, plants growing in forest soil (FS) and plant-free peat and vermiculite (PV) were included. O. nova increased significantly in abundance in the treatments with the EM fungi Suillus variegatus and Paxillus involutus, but not in the other treatments. T. velatus increased significantly in abundance in FS, but declined in most of the other treatments, and N. silvestris showed a similar, albeit not significant, response. C. sphagnetorum did not increase in abundance in any of the treatments with EM fungi but increased its abundance four times in both FS and PV. The results show that the fungivore O. nova preferentially feeds on certain EM fungi, especially S. variegatus, whereas the EM fungus Piloderma fallax and the saprotrophic H. capnoides are not preferred. In contrast, C. sphagnetorum is restricted in its population growth by the EM fungi studied, and this dominant microbi-detritivore is clearly favoured by the absence of EM fungi.     

Suppressiveness of 18 composts against 7 pathosystems: Variability in pathogen response

Compost is often reported as a substrate that is able to suppress soilborne plant pathogens, but suppression varies according to the type of compost and pathosystem. Reports often deal with a single pathogen while in reality crops are attacked by multiple plant pathogens. The goal of the present study was to evaluate the disease suppression ability of a wide range of composts for a range of plant pathogens. This study was conducted by a consortium of researchers from several European countries. Composts originated from different countries and source materials including green and yard waste, straw, bark, biowaste and municipal sewage. Suppressiveness of compost-amended (20% vol./vol.) peat-based potting soil was determined against Verticillium dahliae on eggplant, Rhizoctonia solani on cauliflower, Phytophthora nicotianae on tomato, Phytophthora cinnamomi on lupin and Cylindrocladium spathiphylli on Spathiphyllum sp., and of compost-amended loamy soil (20% vol./vol.) against R. solani on Pinus sylvestris and Fusarium oxysporum f. sp. lini on flax. From the 120 bioassays involving 18 composts and 7 pathosystems, significant disease suppression was found in 54% of the cases while only 3% of the cases showed significant disease enhancement. Pathogens were affected differently by the composts. In general, prediction of disease suppression was better when parameters derived from the compost mixes were used rather than those derived from the pure composts. Regression analyses of disease suppression of the individual pathogens with parameters of compost-amended peat-based mixes revealed the following groupings: (1) competition-sensitive: F. oxysporum and R. solani/cauliflower; (2) rhizosphere-affected: V. dahliae; (3) pH-related: P. nicotianae; and (4) specific/unknown: R. solani/pine, P. cinnamomi and C. spathiphylli. It was concluded that application of compost has in general a positive or no effect on disease suppression, and only rarely a disease stimulating effect.     

Road crossing structures for amphibians and reptiles: Informing design through behavioral analysis

Road traffic causes significant amphibian and reptile mortality, which could be mitigated through the installation of road crossing structures that facilitate safe passage, but only if reptiles and amphibians are willing to use them. Through a series of behavioral choice experiments with frogs and turtles, we examined how aperture diameter, substrate type, length, and light permeability influenced individuals’ preferences for specific attributes of crossing structures, and how individuals responded to various heights of barrier fences. Snapping turtles (Chelydra serpentina), green frogs (Rana clamitans), and leopard frogs (Rana pipiens) preferred larger diameter tunnels (>0.5 m) whereas painted turtles (Chrysemys picta) preferred tunnels of intermediate (0.5-0.6 m) diameter. Green frogs preferred soil- and gravel-lined tunnels to concrete- and PVC-lined tunnels. Painted turtles showed non-random choice of different lengths of tunnel, possibly indicating some avoidance of the longest tunnel (9.1 m); although no species preferred to exit via the longest tunnels (9.1 m), members of all four species used such tunnels. Green frogs preferred tunnels with the greatest light permeability. Fences 0.6 m in height were effective barriers to green frogs, leopard frogs, and snapping turtles, whereas 0.3 m fences excluded painted turtles. We conclude that tunnels > 0.5 m in diameter lined with soil or gravel and accompanied by 0.6-0.9 m high guide fencing would best facilitate road crossing for these and likely other frog and turtle species.     

Strong bottom-up and weak top-down effects in soil: nematode-parasitized insects and nematode-trapping fungi

The soils of the Bodega Marine Reserve (BMR, Sonoma County, California) contain many nematode-trapping fungi and many ghost moth larvae parasitized by entomopathogenic nematodes. The current study determined whether these nematode-parasitized moth larvae, which can produce very large numbers of nematodes, enhanced the population densities of nematode-trapping fungi and whether the fungi trapped substantial numbers of nematodes emerging and dispersing from moths. Wax moths were used in place of ghost moths because the former are easier to obtain. When nematode-parasitized moth larvae were added to laboratory microcosms containing BMR field soil, the population densities of four nematode-trapping fungi increased substantially. The greatest increase in population density was by Arthrobotrys oligospora, which uses adhesive networks to capture nematodes. A. oligospora population density increased about 10 times when the added moth larvae were parasitized by the nematode Heterorhabditis marelatus and about 100 times when added moth larvae were parasitized by the nematode Steinernema glaseri. Other trapping fungi endemic to the soil and enhanced by nematode-parasitized moth larvae included Myzocytium glutinosporum, Drechslerella brochopaga, and Gamsylella gephyropaga, which produce adhesive spores, constricting rings, and adhesive branches, respectively. The data suggest that the previously documented abundance and diversity of nematode-trapping fungi in BMR soil can be explained, at least in part, by nematode-parasitized insects, although that inference requires further studies with ghost moths. The strong bottom-up enhancement of nematode-trapping fungi was not matched by a strong top-down suppression of nematodes, i.e. the fungi trapped fewer than 30% of dispersing nematodes.     

Nematode suppression with brassicaceous amendments: application based upon glucosinolate profiles

Glucosinolate profiles differ among plant species and their isothiocyanate (ITC) derivatives differ in toxicity to nematodes. Successful management of plant-parasitic nematodes by ITCs requires the incorporation of appropriate amounts of glucosinolate-containing biomass. Plant materials, containing glucosinolate-precursors of the ITCs most toxic to nematodes, were selected and applied to soil based upon ITC lethal concentration (LC) values. This provided a reliable and repeatable basis for application rates for suppression of Meloidogyne javanica and Tylenchulus semipenetrans by Brassica hirta and M. javanica by B. juncea. Sufficient biomass of B. hirta to potentially yield 0.03-0.12 μmol ml⁻¹ of glucotropeolin reduced nematode survival compared to similar amounts of broccoli (Brassica oleraceae var. botrytis). At biomass levels providing >0.37 μmol ml⁻¹ of glucotropeolin, mortality of M. javanica was 100% with B. hirta. Biomass of B. juncea potentially yielding 2.82 μmol ml⁻¹ of sinigrin reduced M. javanica survival 65% below that obtained by a similar amount of broccoli. Rates of B. juncea to yield lethal levels of allyl ITC to reduce T. semipenetrans survival underestimated the glucosinolate application rates for this amendment. Application of plant biomass to soil >2.9% w/w reduced M. javanica survival regardless of the glucosinolate concentration of the amendment material. Application of brassicaceous amendments to soil initiates complex and dynamic biological and chemical processes. Despite the inherent complexity, we find that brassicaceous amendments can be applied to achieve consistent and repeatable nematode suppression when based upon the chemistry of the incorporated material.     

Development and reproduction of Sancassania polyphyllae (Acari: Acaridae) feeding on entomopathogenic nematodes and tissues of insect larvae

We studied the effect of different food sources, infective juveniles of the entomopathogenic nematodes, Steinernema feltiae and Heterorhabditis bacteriophora (Rhabditida: Steinernematidae, Heterorhabditidae), and tissues from the insect larva, Polyphylla fullo (Coleoptera: Scarabaeidae) or Galleria mellonella (Lepidoptera: Pyralidae), on the development, reproduction and longevity of Sancassania polyphyllae (Acari: Acaridae). We showed that the immature mite stages - protonymph and tritonymph - could develop to the next developmental stage on living or sonicated (i.e., ruptured) S. feltiae or H. bacteriophora. However, the mite larval stage could only develop to the next developmental stage on sonicated infective juveniles of the nematodes. Subsequently, we demonstrated that S. polyphyllae completed development from protonymph to adult on live S. feltiae or H. bacteriophora, whereas all immature stages of S. polyphyllae completed their development from larva to adult on insect tissues. The total developmental period of S. polyphyllae that fed on insect tissues was significantly shorter than those that fed on live infective juveniles. The pre-oviposition, oviposition, and post-oviposition periods and female longevity were not significantly different among the food sources. The total and daily fecundity of S. polyphyllae feeding on P. fullo and G. mellonella was significantly higher than those feeding on S. feltiae and H. bacteriophora, although there was no significant difference observed between P. fullo and G. mellonella or between S. feltiae and H. bacteriophora. The net reproductive rate (R₀) was highest (588.3♀/♀) when S. polyphyllae fed on P. fullo. The longest mean generation time (T₀) occurred on H. bacteriophora (12.6 days) and the shortest occurred on P. fullo (10.5 days). S. polyphyllae, which fed on P. fullo (r_m=0.61) and G. mellonella (r_m=0.55) had the highest intrinsic rate of increase (r_m) compared to mites that fed on S .feltiae (r_m=0.45) and H. bacteriophora (r_m=0.41).     

Phytase and phosphatase producing fungi in arid and semi-arid soils and their efficiency in hydrolyzing different organic P compounds

Seven most efficient phytase and phosphatases producing fungi were isolated from the soils of arid and semi-arid regions of India and tested for their efficiency on hydrolysis of two important organic P compounds: phytin and glycerophosphate. The native soil organic P may be exploited after using these organisms as seed inoculants, to help attain higher P nutrition of plants. The identified organisms belong to the three genera: Aspergillus, Emmericella and Penicillium. Penicillium rubrum released the most acid into the medium during growth. Aspergillus niger isolates were found to accumulate biomass the fastest. A significant negative correlation (r=−0.593,n=21, p<0.01) was observed between the development of fungal mat and pH of the media. The extracellular (E) phosphatases released by different fungi were less than their intracellular (I) counterpart, but the trend was reversed in case of phytase production. The E:I ratio of different fungi ranged from 0.39 to 0.86 for acid phosphatase, 0.29 to 0.41 for alkaline phosphatases and 9.4 to 19.9 for phytase. The efficiency of hydrolysis of different organic P compounds of different fungi varied from 2.12-4.85 μg min⁻¹ g⁻¹ for glycerophosphate to 0.92-2.10 μg min⁻¹ g⁻¹ for phytin. The trend of efficiency was as follows: Aspergillus sp.>Emmericella sp.>Penicillium sp. The results indicated that the identified fungi have enough potential to exploit native organic phosphorus to benefit plant nutrition.