Preharvest seed infection byAspergillus flavus group fungi and subsequent aflatoxin contamination in groundnuts in relation to soil types

Preharvest seed infection byAspergillus flavus and aflatoxin contamination in selected groundnut genotypes (fourA. flavus-resistant and fourA. flavus-susceptible) were examined in different soil types at several locations in India in 1985–1990. Undamaged mature pods were sampled at harvest and seed examined forA. flavus infection and aflatoxin content in two or more trials at ICRISAT Center on light sandy soils and red sandy loam soils (Alfisols), and on Vertisols, at Anantapur on light sandy soils, and at Dharwad and Parbhani on Vertisols. Rainy season trials (1985–1989) were all rainfed. Post-rainy season trials were irrigated; late-season drought stress (90 days after sowing (DAS) until harvest at 125 DAS) was imposed in the 1987/88 and 1989/90 seasons.A. flavus infection and aflatoxin contamination levels were much lower in seed of all genotypes from Vertisols than in seed from Alfisols across locations and seasons. Vertisols also had significantly lower populations ofA. flavus than Alfisols. There were no marked differences between light sandy soils and red sandy loam soils (Alfisols) in respect of seed infection byA. flavus and aflatoxin contamination. Significant interactions between genotypes and soil types were evident, especially in theA. flavus-susceptible genotypes. Irrespective of soil types,A. flavus-resistant genotypes showed lower levels of seed infection byA. flavus and other fungi than didA. flavus-susceptible genotypes. The significance of the low preharvest aflatoxin risk in groundnuts grown on Vertisols is highlighted.ICRISAT Journal Article No. JA 1122     

Oil Cakes as Media for Growing Catenaria anguillulae Sorokin, a Facultative Endoparasite of Nematodes

Summary Growth, morphology, visibility of sporangia and colony colour of 10 isolates of Catenaria anguillulae were compared on six media: linseed oil-cake agar, mustard oil-cake agar, neem oil-cake agar, beef extract agar, Emerson agar and YPSS agar with a view to selecting the best growth medium. In general, maximum radial growth of most of the isolates was recorded on linseed oil-cake agar medium, whereas neem oil-cake agar medium supported least growth of all the isolates of C. anguillulae. Linseed oil-cake agar medium also maintained the typical characters of the fungus and clear visibility of morphological details.     

Soil temperature, digging behaviour, and the adaptive value of nest depth in South American species of Acromyrmex leaf-cutting ants

In leaf-cutting ants, workers are expected to excavate the nest at a soil depth that provides suitable temperatures, since the symbiotic fungus cultivated inside nest chambers is highly dependent on temperature for proper growth. We hypothesize that the different nesting habits observed in Acromyrmex leaf-cutting ants in the South American continent, i.e. superficial and subterranean nests, depend on the occurrence, across the soil profile, of the temperature range preferred by workers for digging. To test this hypothesis, we first explored whether the nesting habits in the genus Acromyrmex are correlated with the prevailing soil temperature regimes at the reported nest locations. Second, we experimentally investigated whether Acromyrmex workers engaged in digging use soil temperature as a cue to decide where to excavate the nest. A bibliographic survey of nesting habits of 21 South American Acromyrmex species indicated that nesting habits are correlated with the soil temperature regimes: the warmer the soil at the nesting site, the higher the number of species inhabiting subterranean nests, as compared to superficial nests. For those species showing nesting plasticity, subterranean nests occurred in hot soils, and superficial nests in cold ones. Experimental results indicated that Acromyrmex lundi workers use soil temperature as an orientation cue to decide where to start digging, and respond to rising and falling soil temperatures by moving to alternative digging places, or by stopping digging, respectively. The soil temperature range preferred for digging, between 20°C and maximally 30.6°C, matched the range at which colony growth would be maximized. It is suggested that temperature-sensitive digging guides digging workers towards their preferred range of soil temperature. Workers’ thermopreferences lead to a concentration of digging activity at the soil layers where the preferred range occurs, and therefore, to the construction of superficial nests in cold soils, and subterranean ones in hot soils. The adaptive value of the temperature-related nesting habits, and the temperature-sensitive digging, is further discussed.     

Soil calcium and plant disease in serpentine ecosystems: a test of the pathogen refuge hypothesis

Ecologists have long sought mechanistic explanations for the patterns of plant distribution and endemism associated with serpentine soils. We conducted the first empirical test of the serpentine pathogen refuge hypothesis, which posits that the low levels of calcium found in serpentine soils provide associated plants with a refuge from attack by pathogens. We measured the range of soil calcium concentrations experienced by 16 wild population of California dwarf flax (Hesperolinon californicum) and experimentally recreated part of this range in the greenhouse by soaking serpentine soils in calcium chloride solutions of varying molarity. When flax plants grown in these soils were inoculated with spores of the rust fungus Melampsora lini we found a significant negative relationship between infection rates and soil calcium concentrations. This result refutes the pathogen refuge hypothesis and suggests that serpentine plants, by virtue of their association with low calcium soils, may be highly vulnerable to attack by pathogens. This interaction between plant nutrition and disease may in part explain demographic patterns associated with serpentine plant populations and suggests scenarios for the evolution of life history traits and the distribution of genetic resistance to infection in serpentine plant communities.     

Distribution of soil fractions and location of soil bacteria in a vertisol under cultivation and perennial grass

Effects of soil management on soil characteristics were investigated on the rhizosphere (RPP) and the nonrhizosphere (NRPP) soil of a re-grass vertisol underDigitaria decumbens and in the soil under continuous cultivation (CC). A low energy technique allowed to separate eight size and density fractions, including macro- and micro-aggregates while preserving soil bacteria. Organic C and N, microbial biomass C and the number of total bacteria (AODC) and ofAzospirillum brasilense and their distribution were determined in soil fractions isolated from the CC, NRPP and RPP soils. Soil macroaggregates (>2000 m) were similarly predominant in the NRPP and RPP soils when the dispersible clay size fraction (<2 m) respresented more than 25% of the CC soil mass. The main increase of C content in RPP originated from the macroaggregates (> 2000 m) and from the root fraction, not from the finer separates. The proportion of organic C as microbial biomass C revealed the low turnover of microbial C in the PP situations, especially in the clay size fraction of the NRPP soil. A common shift of AODC toward the finer separates from planted soils (CC and RPP) revealed the influence of living plants on the distribution of soil bacteria. The relative abundance ofA. brasilense showed the presence of the active roots ofDigitaria in the macroaggregates and their contact with the dispersible clay size fraction of the rhizosphere soil.     

Influence of mound construction by red and hybrid imported fire ants on soil chemical properties and turfgrass in a sod production agroecosystem

Mound construction by imported fire ants (Solenopsis spp.) actively modify the biogeochemical and physical properties of soil; however, their influence on nutrient levels in surrounding vegetation is poorly understood. Aside from the reported persistence of elevated available P and K levels in clay-rich soils one year after mound abandonment, the relative stability of nutrient concentrations from one season to the next is largely unknown. Nutrient concentrations were concurrently analysed from ant mounds and undisturbed soils as well as plant samples collected from warm-season turfgrass in a commercial sod production agroecosystem. Initial collection of soil and turfgrass samples coincided with peak annual biomass (September 2006); the second soil sample collection occurred over twelve weeks later during turfgrass dormancy and ant brood minimum (December 2006). Total C, C/N ratios, organic matter (OM), and Zn²⁺ concentrations as well as pH of ant mound soils were significantly higher than control plot soils; these trends persisted across seasons. Turfgrass harvested from ant mound perimeters in September exhibited elevated N, P, Ca²⁺, S, Cu²⁺, Fe²⁺, and Na⁺ concentrations. Evaluation of the relative stability of soil parameters across seasons revealed a significant drop in ant nest pH from September to December 2006. Total N of mound soils was distinctively greater than control soil counterparts during September only. Soil P, K⁺, Ca²⁺, Mg²⁺ and S (all macronutrients), as well as Na⁺ concentrations from ant mound soils were substantially elevated during the late Autumn to Winter transition compared to control soil locations, whereas Fe²⁺ and Mn²⁺ levels (both micronutrients) were significantly lower in ant mound soils versus control soil environments. Continuous pedoturbation by imported fire ants as well as seasonal shifts in mound soil chemistry resulting from changes in assimilation/dissimilation among mound biota may influence the site-specific effectiveness of microfaunal pathogens (e.g., Thelohania solenopsae) or parasites (e.g., Orasema spp.) identified as classical biological control agents of non-native Solenopsis spp. Therefore, further study of the intrinsic complexities of soil ecosystem dynamics of imported fire ant mounds across several seasons is warranted. Received 10 September 2007; revised 23 April 2008; accepted 1 May 2008.     

Intermittent wetting of soils at high temperature reduces survival of the take-all fungus

Two pot experiments using naturally infested soil and a range of watering regimes were conducted to study the possible effect of level and frequency of wetting of hot soil (to simulate the period between growing seasons in Western Australia) on inoculum of the take-all fungus (Gaeumannomyces graminis var.tritici). In combination with the high soil temperatures, all watering regimes reduced infectivity and propagule number of the take-all fungus, this reduction being absent in dry soils.     

Geobotanical studies on zinc deposit areas of Zawar mines,Udaipur

This study reveals disjunct distribution patterns of certain plant species on zinc-rich soils in the Zawar mines region near Udaipur. Ten plant species have high constancy and fidelity values on zinc-rich soils in comparison to normal soil. The plant community composed of these species has been named Impatiens balsamina-Triumfetta pentandra association. As Impatients balsamina is the most characteristic species on metal dumps, it can be considered as a local indicator for the metal zinc.Acknowledgements: The authors are grateful to the University Grants Commission of India, New Delhi for substantial financial assistance.     

Catenaria anguillulae in the mermithid nematode Romanomermis culicivorax

Disease epizootics in laboratory cultures of the mermithid nematode Romanomermis culicivorax were caused by a chytridiomycetous fungal parasite, Catenaria anguillulae. Techniques used for mass rearing the nematode provided ideal conditions for dispersal of zoospores and multiplication of the fungus; up to 90% of the postparasites of R. culicivorax were parasitized. The fungus was isolated and grown on yeast extract-soluble starch agar, and the effects of different temperature and pH regimes on the fungus were investigated as possible methods for prevention or control. A temperature suitable for mass rearing the nematodes but unsuitable for the fungus could not be found, as C. anguillulae had a broad temperature range. Adjustment of pH or a short period of chilling (0°C) were more promising control measures. At acid pH (<5), zoospore motility and germination and infection of postparasites were suppressed. The disease was controlled by rearing nematodes in water adjusted to a pH of 4.5.     

Fusarium nygamai, a potential bioherbicide for Striga hermonthica control in sorghum

Glasshouse trials were performed to investigate the control of the parasitic weed Striga hermonthica by Fusarium nygamai and the performance of the host plant sorghum (Sorghum bicolor) using different inoculum substrates and inoculum amounts of the fungus. Optimal constant and alternating temperatures for the growth of the fungus were 25°C and 30/20°C, respectively. Striga incidence was decreased up to 100% when the fungus was incorporated into the soil preplanting. Emerged Striga plants at different stages of growth up to the flowering stage were killed by the fungus when the fungus was applied postemergent. In root-chamber trials none of the Striga seeds germinated when 10 ml inoculum suspension of 8 × 10⁶ spores/ml of F. nygamai was applied on seeds of the parasitic weed sprinkled on the surface of filter paper. F. nygamai has potential as a bioherbicide for Striga control. Further studies regarding its performance under field conditions and its safety to the environment and humans should be assessed.     

Isolation and characterization of Arthrobacter sp. strain MCM B-436, an atrazine-degrading bacterium, from rhizospheric soil

Atrazine is one of the most environmentally prevalent s-triazine-ring herbicides. The widespread use of atrazine and its toxicity necessitates search for remediation technology. As atrazine is still used in India as a major herbicide, exploration of atrazine-degrading bacterial community is of immense importance. Considering lack of reports on well characterized atrazine-degrading bacterial cultures from India and wide diversity and density of microorganisms in rhizosphere, soil sample from rhizosphere of atrazine-resistant plant was studied. Arthrobacter sp. strain isolated in this investigation utilizes atrazine as the sole nitrogen source. In addition, the bacterium degrades other triazines such as ametryn, cyanizine, propazine and simazine. PCR analysis confirms the presence of atzBCD and triazine hydrolase (trzN) genes on chromosomal DNA. Sequencing of the trzN gene reveals high sequence similarity with trzN from Nocardioides sp. C190. An inducible and intracellular atrazine chlorohydrolase enzyme was isolated and partially purified from this isolate. This study confirms the presence of atrazine-degrading microbial population in Indian soils and could be used efficiently for remediation of contaminated soils. Presence of trzN gene indicates possible presence of bacterial community with more efficient and novel enzymatic capabilities. Comparison of enzyme and gene structure of this isolate with other geographically distinct atrazine-degrading strains will help us in the better understanding of gene transfer and evolution.     

Distribution of soil invertase in relation to the root systems ofPicea sitchensis (Bong.) Carr. andAcer pseudoplatanus L. during development of young plants

A method is described for sampling rhizosphere soil under newly establishedPicea sitchensis andAcer pseudoplatanus. The technique involves taking soil samples to a depth of 150 mm at 100 mm intervals along transects, each 45° from its neighbour, radiating from the base of the stem. Invertase activities were measured in the soil samples and compared to their activities in fallow and rhizosphere soils. When the field soil was dry, the tree root systems were carefully excavated to retain as many fine roots as possible. The distribution of the soil invertase was matched to the spatial distribution of the roots showing the precise position of the rhizosphere relative to the initial blind soil sampling. Statistics were applied to derive equations for calculating the percentage enzyme activity relative to that found in rhizosphere soil at various locations radiating from the base of the stem. This information was subsequently applied to soil sampled under trees of the same age as those excavated to give a non-destructive method for sampling rhizosphere soil routinely from under a large number of trees.     

<Emphasis Type="Italic">Catenaria anguillulae</Emphasis> Sorokin: a Natural Biocontrol Agent of <Emphasis Type="Italic">Meloidogyne graminicola</Emphasis> Causing Root Knot Disease of Rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Summary Catenaria anguillulae parasitized and killed the eggs and second stage juveniles (J₂) of Meloidogyne graminicola under natural conditions. The percentage of infection in eggs was higher than J₂ of M.␣graminicola, which ranged between 0–50.3% and 0–18.9% in 2004 and 0–46.6% and 0–21.7% in 2005, respectively. The higher parasitism of eggs and J₂ was recorded from those fields in which plants were severely infected with M. graminicola. The degree of parasitism of eggs and J₂ by C. anguillulae varied with severity of root knot disease. The fields with a higher root gall index recorded a higher percentage of infection in eggs and J₂ of M. graminicola. In general, old galls when teased and incubated, recorded higher parasitism of eggs and juveniles than young galls.     

Identification of a mycorrhizal fungus in Epipogium roseum (Orchidaceae) from morphological characteristics of basidiomata

A mycorrhizal fungus, ME1-1, isolated from an achlorophyllous orchid, Epipogium roseum, was identified as Coprinellus disseminatus (≡ Coprinus disseminatus) based on characteristics of basidiomata that were artificially induced. Spawn of ME1-1 cultivated on a medium that consisted of sawdust and wheat, sandwiched between two mats of volcanic soils, which was incubated at 20.0° ± 0.5°C in 80.0% ± 0.5% relative humidity in the dark. The basidiomata were formed on the soil after 2 months. Morphological and anatomical characteristics of the basidioma mostly accorded with those of Coprinellus disseminatus. We therefore concluded that C. disseminatus is one of the mycobionts of E. roseum.     

A new species of Gigaspora from desert soils of Rajasthan,India

A new species of the endogonaceous fungus Gigaspora, isolated from the Indian semi-arid region, is described. The fungus, named G. tuberculata, produces rusty-brown azygospores with septate subtending hypha. The azygospores bear warts all over the outer wall. The shape, size and general appearance of these spores resemble those of Scutellospora persica.Neeraj and A.K. Varma are with the Microbiology Unit, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India; K.G. Mukerji is with the Applied Mycology Laboratory, Botany Department, University of Delhi, Delhi 110 006, India. B.C. Sharma is with the Department of Textile Engineering, Indian Institute of Technology, New Delhi 110 016, India.     

广西珍珠湾三种红树林林分土壤碳氮储量的研究

为了探讨不同红树林林分土壤有机碳(soil organic carbon,SOC)和全氮(total nitrogen,TN)储量空间的分布特征以及与C/N的相关性,该研究以广西防城珍珠湾红树林湿地为对象,通过样地调查取样和实验室分析,测定了SOC和TN的含量以及土壤碳储量的计量,揭示了广西北仑河珍珠湾秋茄、木榄和混交林三种红树林林分SOC和TN储量空间的分布特征以及C/N与SOC和TN的相关性。结果表明:(1)秋茄、木榄和混交林的SOC储量分别为140.73、124.94、144.71 t·hm~(-2),三者无显著性差异(P0.05);木榄和混交林垂直分布特征表现为20～40 cm0～20 cm40～60 cm,秋茄表现为随着土层深度的增加而递减。(2)秋茄、木榄和混交林的TN储量分别为6.49、5.01、5.87 t·hm~(-2),表现为随着土层深度的增加而减少的趋势。(3)秋茄、木榄和混交林的SOC与TN储量之间的相关性极显著(P0.01),相关系数分别为0.924、0.971和0.844,说明SOC与TN之间存在一定的耦合效应。(4)三种林分的C/N比值范围为16.77～24.39,表明有机质主要来源于陆地,木榄和混交林土壤的C/N值与SOC储量有显著的相关性(P0.05),三种林分的C/N比值与TN储量相关性均不显著。(5)三种红树林林分的土壤碳储量均高于我国森林土壤碳储量的平均值,且SOC与TN储量之间的相关性极显著。     

Effects of rhizosphere remediation and bioaugmentation on carbofuran removal from soil

Rhizosphere soil contains important sources of nutrients for microorganisms resulting in high number of microorganisms capable of degrading various types of chemicals in the soil. Thus, this study investigated a carbofuran dissipation in rhizosphere soils of 6 weeds namely, umbrella sedge (Cyperus iria L.), fuzzy flatsedge (C. pilosus V.), small flower umbrella plant (C. difformis L.), tall-fringe-rush hoorah grass (Fimbristylis miliacea V.), cover fern (Marsilea crenata P.), and water primrose (Jussiaea linifolia V.). Rhizosphere soil of fuzzy flatsedge showed the shortest half-life (t_1/2) of carbofuran (15 days) among other soils. So, it was selected to be used in the bioaugmentation experiment using carbofuran degrader namely Burkholderia cepacia, PCL3, as inoculum in order to examine whether they would improve carbofuran degradation in soil. The results showed that the addition of PCL3 into rhizosphere soil did not improve carbofuran degradation suggesting that microorganisms in rhizosphere soil might be capable enough to remove carbofuran from soil. The number of carbofuran degraders in the rhizosphere soils was greater than in bulk soil 10–100 times which might be responsible to a rapid degradation of carbofuran in rhizosphere soils without the addition of PCL3. The ability of PCL3 to degrade carbofuran was evident in bulk soil (t_1/2 of 12 days) and autoclaved soils (t_1/2 13–14 days) when compared to soils without an inoculation (t_1/2 of 58 days) indicated that the addition of a degrader was useful in improving carbofuran degradation in soil.     

Effect of Crotalaria juncea Amendment on Squash Infected with Meloidogyne incognita

Two greenhouse experiments were conducted to examine the effect of Crotalaria juncea amendment on Meloidogyne incognita population levels and growth of yellow squash (Cucurbita pepo). In the first experiment, four soils with a long history of receiving yard waste compost (YWC+), no-yard-waste compost (YWC-), conventional tillage, or no-tillage treatments were used; in the second experiment, only one recently cultivated soil was used. Half of the amount of each soil received air-dried residues of C. juncea as amendment before planting squash, whereas the other half did not. Crotalaria juncea amendment increased squash shoot and root weights in all soils tested, except in YWC+ soil where the organic matter content was high without the amendment. The amendment suppressed the numbers of M. incognita if the inoculum level was low, and when the soil contained relatively abundant nematode-antagonistic fungi. Microwaved soil resulted in greater numbers of M. incognita and free-living nematodes than frozen or untreated soil, indicating nematode-antagonistic microorganisms played a role in nematode suppression. The effects of C. juncea amendment on nutrient cycling were complex. Amendment with C. juncea increased the abundance of free-living nematodes and Harposporium anguillulae, a fungus antagonistic to them in the second experiment but not in the first experiment. Soil histories, especially long-term yard waste compost treatments that increased soil organic matter, can affect the performance of C. juncea amendment.     

Cultural characteristics, morphology, and variation within Claviceps africana and C. sorghi from India

Sorghum ergot in India is caused by Claviceps africana and C. sorghi. The distributions of these two species in India is not known. Eighty-nine sorghum ergot isolates were cultured from young sphacelia obtained from male sterile sorghum plants artificially inoculated using inoculum collected in the field. Based on cultural characteristics, the isolates were separated into two groups which differed distinctly in the morphology of their sphacelia, conidia, and sclerotia. Marked differences also were observed in rates of secondary conidial production and disease spread between the groups. In combination with molecular evidence, our results confirm that the isolates placed in Group I represent C. africana and Group II isolates represent C. sorghi. C. africana was found to be widely distributed in all sorghum growing areas of India. The species first described as occuring in India, C. sorghi, appears to be restricted to a few locations in the states of Maharashtra, Andhra Pradesh, and Karnataka.     

Epidemiology and molecular typing of Candida isolates from burn patients

This study, spread over a span of 2 years describes Candida infections in burn patients of an Indian hospital. A total of 220 burn patients were monitored and Candida could be isolated from 138 patients. A total of 228 different Candida species were obtained from various body locations of these patients. Species identification revealed that Candida albicans was the most predominant (45) followed by Candida tropicalis(33), Candida glabrata (13.5), C. parapsilosis (4), C. krusei (2.75) and C. kefyr (1.75). DNA fingerprinting of all C. albicans isolates was done by using CARE-2 probe. Fingerprinting analyses of all the C. albicans strains revealed that strains collected from different patients were different. It is noteworthy that patients with disseminated candidiasis had a similar, but unique strain isolated from all body locations, suggesting a possibility that commensal isolates might be turning pathogenic. Taken together, this is probably the first ever detailed survey of Candidainfections in burn patients in India and is expected to lead to better clinical management of this group of patients.