Influence of edaphic and climatic factors on dynamics of root colonization and spore density of vesicular-arbuscular mycorrhizal fungi in Acacia farnesiana Willd. and A. planifrons W.et.A.

 A study was conducted to assess the dynamics of vesicular-arbuscular mycorrhizal (VAM) fungi associated with Acacia farnesiana and A. planifrons in moderately fertile alkaline soils. The intensity of root colonization by VAM fungi and the distribution of VAM fungal structures varied with host species over a period of time. The occurrence of vesicles with varied morphology in the mycorrhizal roots indicates infection by different VAM fungal species. This was further confirmed from the presence of spores belonging to different VAM fungal species in the rhizosphere soils. Root colonization and spore number ranged from 56% – 72% and 5 – 14 g^{–  1}soil in A. farnesiana and from 60% – 73% and 5 – 15 g^{–  1} soil in A. planifrons. Per cent root colonization and VAM spore number in the rhizosphere soil were inversely related to each other in both the Acacia species. However, patterns of the occurrence of VAM fungal structures were erratic. Spores of Acaulospora foveata, Gigaspora albida, Glomus fasciculatum, G. geosporum and Sclerocystis sinuosa were isolated from the rhizosphere of A. farnesiana whereas A. scrobiculata, G. pustulatum, G. fasciculatum, G. geosporum and G. microcarpum were isolated from that of A. planifrons. The response of VAM status to fluctuating edaphic factors varied with host species. In A. farnesiana though soil nitrogen (N) was positively correlated with root colonization, soil moisture, potassium and air temperature were negatively correlated to both root colonization and spore number. Per cent root colonization and spore number in A. planifrons were negatively related to each other. Further, in A. planifrons as the soil phosphorus and N were negatively correlated with the density of VAM fungal spores, the same edaphic factors along with soil moisture negatively influenced root colonization. Received: 16 May 1995 / Accepted: 7 February 1996     

Statistical treatment of VAM infection data

Summary The amount of vesicular-arbuscular mycorrhizal (VAM) infection, when expressed as length of infected roots, is commonly quite variable among replicate pots within an experimental treatment. In this paper we show that frequency distributions of VAM infection parameters are often non-normal in form and may follow the negative binomial, a distribution commonly associated with aggregated organisms in nature. The lack of normality means that statistical procedures should either be non-parametric or should include data transformations.     

Genotype dependent variation in mycorrhizal colonization and response to inoculation of pearl millet

Summary Genotypes of pearl millet (Pennisetum americanum L. Leeke) were examined for differences in vesicular-arbuscular mycorrhizal (VAM) colonization and response to inoculation. For thirty genotypes tested across three field locations there was a range of mycorrhizal colonization intensity between 25 and 56%. In another experiment with two male-sterile lines, restorer lines and their derived crosses, grown in pots filled with non-sterilized soil there were significant differences between genotypes for colonization by mycorrhiza. This showed hostgenotype dependence for mycorrhizal colonization.Root growth rates, mycorrhizal root length, percentage root colonization and plant growth and P uptake were studied in ten genotypes. A set of 3 genotypes with similar root lengths varied significantly with regard to mycorrhizal root length and the percentage colonization. This supports the suggestion that VAM colonization and spread is dependent on the host genotype. The growth responses differed significantly between the genotypes and they also differed in their responses to P uptake and VAM inoculation. The utility of host-genotype dependent differences in VAM symbiosis in plant breeding is discussed.Journal Article No. 453     

Mycorrhizal status of some plants of the Araucaria forest and the Atlantic rainforest in Santa Catarina, Brazil

 In Brazil, the Araucaria forest and the Atlantic rainforest are two threatened ecosystems, with 10% or less of their original areas presently existing. To assess the mycorrhizal status in these forests, roots of 29 native species, belonging to 19 families, were collected throughout the year from different regions of Santa Catarina, Brazil. Roots were washed, and then cut in a cryo-microtome to seek ectomycorrhizal colonization. Other roots were stained before being examined for vesicular-arbuscular mycorrhizas (VAM). Patterns of colonization were identified and photographed. All plants presented evidence of vesicular-arbuscular mycorrhizal colonization. No evidence of ectomycorrhizal colonization was found. Vesicular-arbuscular mycorrhizal colonization patterns varied from single intracellular aseptate hyphae, coils, and/or appressoria, to vesicles and/or arbuscules. Results confirmed that VAM hosts are predominant in South American forests while ectomycorrhizas are extremely rare even among genera known as ectomycorrhizal in other regions of the humid tropics. Accepted: 27 August 2000     

Use of sucrose-agar globule with root exudates for mass production of vesicular arbuscular mycorrhizal fungi

A sucrose-agar globule (SAG) was newly introduced to increase production of the vesicular arbuscular mycorrhizal (VAM) fungal spores, Gigaspora gigantea and Glomus fasciculatum. An SAG inoculum and a sucrose-agar globule with root exudates (SAGE) inoculum were prepared, and their spore productions were compared with a soil inoculum. When the SAGE was used as the inoculum on sucrose-agar medium plates the number of spores was increased (35% more than the soil inoculum). After the soil inoculum and SAGE were inoculated on an experimental plant, Zingiber officinale, the percentage root colonization, number of VAM spores, and dry matter content were analyzed. It was observed that the SAGE showed a higher percentage of root colonization (about 10% more), and increases in the number of spores (about 26%) and dry matter (more than 13%) for the two VAM fungal spores than the soil inoculum. The results of this study suggested that the SAGE inoculum may be useful for the mass production of VAM fungi and also for the large scale production of VAM fungal fertilizer.     

Occurrence of vesicular-arbuscular mycorrhizae in Pseudotsuga menziesii and Tsuga heterophylla seedlings grown in Oregon Coast Range soils

 Vesicular-arbuscular mycorrhizae (VAM) were common in seedlings of Pseudotsuga menziesii and Tsuga heterophylla grown in a greenhouse soil bioassay in soils collected from the Oregon Coast Range. Although root samples were heavily colonized by ectomycorrhizal fungi (EM), VAM colonization was observed in the cortical cells of both secondary and feeder roots. Vesicles, arbuscules, and hyphae typical of VAM occurred in 48% of 61 P. menziesii and 25% of 57 T. heterophylla seedlings. The ecological significance of VAM presence in the Pinaceae, as well as interactions among VAM, EM, and the plant host, deserve future investigation. Accepted: 16 August 1995     

Delta-9-tetrahydrocannabinol and human spermatozoa

Thein vitro effect of δ⁹-tetrahydrocannabinol on adenosine triphosphatase and phosphodiesterase activities as well as on the cyclic-AMP content of human spermatozoa has been studied. At a concentration of 1.0 ▪g, sperm metabolism may be increased as shown by increased cyclic AMP and adenosine-triphosphatase activity while at a higher concentration (10 ▪g tetrahydrocannabinol), it may be reversed.     

Transpiration of detached leaves from mycorrhizal and nonmycorrhizal cowpea and rose plants given varying abscisic acid, pH, calcium, and phosphorus

 Vesicular-arbuscular mycorrhizal (VAM) colonization can alter transpiration of host leaves, but scientists remain unclear about the mechanisms involved. We tested whether intact root systems were required to observe effects of root colonization by Glomus intraradices on leaf transpiration, or whether some VAM influence resided in leaves even after they were detached from root systems. We measured the transpiration of detached leaves of VAM and nonmycorrhizal plants exposed to different levels of several substances known to influence stomata locally or act in whole-plant regulation of transpiration: abscisic acid, calcium, phosphorus, and hydrogen ions. In rose, some VAM influence on transpiration resided in leaves, even after they had been separated from their root systems. However, removing leaves from their root systems eliminated the VAM influence on stomatal behavior of cowpeas. Accepted: 22 June 1998     

Residual toxicity of soil-applied chlorothalonil on mycorrhizal symbiosis in Leucaena leucocephala

The residual effect of the fungicide chlorothalonil on the vesicular-arbuscular mycorrhizal (VAM) symbiosis was evaluated in a greenhouse experiment. The soil used was an oxisol (Tropeptic Eutrustox) treated with P to obtain target levels near-optimal for VAM activity or sufficient for nonmycorrhizal host growth. In the uninoculated soil treated with the former P level, the fungicide reduced VAM colonization of roots and completely suppressed symbiotic effectiveness measured in terms of pinnule P content. When this soil was inoculated with Glomus aggregatum, symbiotic effectiveness was significantly reduced but not eliminated by 50 mg of the fungicide kg⁻¹. At higher chlorothalonil levels, VAM effectiveness but not VAM colonization was completely suppressed in the inoculated soil. The pattern with which chlorothalonil influenced tissue P content and dry matter yield at the time of harvest closely paralleled its effect on VAM effectiveness. In the soil treated with P level sufficient for nonmycorrhizal host growth, the adverse effect of the fungicide on the above variables was appreciably milder than when the host relied on VAM fungi for its P supply. The toxic effect of the fungicide, therefore, was partly offset by P fertilization, suggesting that VAM fungi were more sensitive to chlorothalonil than the host. Our results demonstrate that although the toxic effect of chlorothalonil declined as a function of time, a significant level of toxicity persisted 12.5 weeks after the chemical was applied to soil. Contribution from Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No. 3625. Contribution from Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No. 3625.     

Chain binomial models and binomial autoregressive processes

Summary We establish a connection between a class of chain‐binomial models of use in ecology and epidemiology and binomial autoregressive (AR) processes. New results are obtained for the latter, including expressions for the lag‐ conditional distribution and related quantities. We focus on two types of chain‐binomial model, extinction–colonization and colonization–extinction models, and present two approaches to parameter estimation. The asymptotic distributions of the resulting estimators are studied, as well as their finite‐sample performance, and we give an application to real data. A connection is made with standard AR models, which also has implications for parameter estimation.     

Growth and nutrient status of citrus plants as influenced by mycorrhiza and phosphorus application

To test the hypothesis that high levels of soluble phosphate applied in combination with VAM fungi, to citrus plants, can cause growth depression even in the absence of other limiting factors, and also to test if rock phosphate, under these conditions, may be a satisfactory P source, a greenhouse experiment was conducted using sterilized soil with four levels of phosphate (0, 50, 100 and 200 ppm P) supplied either as soluble P or as rock phosphate. Citrus seedlings were either inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus etunicatum or left uninoculated. Six months after the start of the experiment, the plants were harvested and shoot dry weight, P and K uptake, root colonization and the number of spores in 50 cm³ of soil were determined. Significant increases were found in dry matter yields and in P and K contents, due to VAM fungus inoculation, at the zero and 50 ppm soluble P levels and at all rock phosphate levels. At 100 ppm soluble P, the development of VAM plants was equilvalent to that of non-VAM plants, and at 200 ppm, growth was significantly less than that of non-VAM plants. Root colonization and sporulation were reduced at higher P levels. The absolute growth depression of VAM plants at the higher P level was likely due to P toxicity. In addition, high leaf P and K concentrations may have interfered with carbohydrate distribution and utilization in these symbioses. Rock phosphate may be used with VAM citrus to substitute for medium amounts of soluble phosphate.     

ASPECTS OF THE MYCORRHIZAL ECOLOGY OF PRAIRIE DROPSEED,SPOROBOLUS HETEROLEPIS (POACEAE)

Vesicular-arbuscular mycorrhizal (VAM) fungal colonization of prairie dropseed and rhizosphere spore abundance were sampled seasonally at two sites in Illinois. At Goose Lake Prairie (GLP), Gaussian ordination of 49 vegetation stands, using plant cover data for 40 species, assigned stands x-vector values and ordered them along a soil moisture-nutrient gradient. Prairie dropseed cover data plotted over ordered stands yielded a significant Gaussian curve across a relatively narrow gradient segment. In contrast, colonization and spore abundance had significant negative linear correlations with stand x-vector values that decreased from the drier, low-nutrient portion of the gradient to the wetter, high-nutrient sector. Variation in spore abundance suggested that no VAM fungal species responded to environmental gradient conditions in a manner similar to that of prairie dropseed. The differential responses of host and VAM mycobionts across the gradient suggest that their respective success may be partially independently determined or limited by different parameters. Also, the generally ubiquitous VAM fungal distributions suggest that the host may be more sensitive to gradient conditions than its mycobiont associates. Colonization and spore abundance at GLP were significantly negatively correlated with available Ca and Mg, and pH. Spore abundance was significantly positively correlated with available K. Neither colonization nor spore abundance were significantly correlated with available P, total N, or organic matter. Seasonally, patterns of VAM colonization and rhizosphere spore abundance varied, having significant positive correlations at GLP and Weston Cemetery Prairie (WCP) in some seasons but not others. In general, colonization levels were highest in fall 1983 for GLP and fall 1984 for WCP. For 1984, increasing colonization was observed from spring (WCP) or summer (GLP) to fall.     

Oviposition pattern of phytophagous insects: on the importance of host population heterogeneity

Frequency distributions of insect immatures per host are often fitted to contagious distributions, such as the negative binomial, to deduce oviposition pattern. However, different mechanisms can be involved for each theoretical distribution and additional biological information is needed to correctly interpret the fits. We chose the chestnut weevil Curculio elephas, a pest of the European chestnut Castanea sativa, as a model to illustrate the difficulties of inferring oviposition pattern from fits to theoretical distributions and from the variance/mean ratio. From field studies over 13–16 years, we show that 20 out of the 31 yearly distributions available fit a negative binomial and 25 a zero-inflated Poisson (ZIP). No distribution fits a Poisson distribution. The ZIP distribution assumes heterogeneity within the fruit population. There are two categories of host: the first comprises chestnuts unsuitable for weevil oviposition or in excess relative to the number of weevil females, and the second comprises suitable fruits in which oviposition behavior is random. Our results confirm this host heterogeneity. According to the ZIP distribution, the first category of hosts includes on average 74% of the chestnuts. A negative binomial distribution may be generated by either true or false contagion. We show that neither interference between weevil females, nor spatial variation in the infestation rate exist. Consequently, the observed distributions of immatures are not the result of false contagion. Nevertheless, we cannot totally exlude true contagion of immatures. In this paper we discuss the difficulty of testing true contagion in natural conditions. These results show that we cannot systematically conclude in favour of contagion when fitting a distribution such as the negative binomial or when a variance/mean ratio is higher than unity. Received: 22 September 1997 / Accepted: 15 December 1997     

Influence of temperature on colonization of spring barleys by vesicular arbuscular mycorrhizal fungi

The effects of three soil temperatures on growth of spring barleys (Hordeum vulgare L.) and on their root colonization by vesicular arbuscular mycorrhizal (VAM) fungi from agricultural soils in Montana (USA) or Syria at different inoculum concentrations were tested in soil incubators in the greenhouse. The number of mycorrhizal plants as well as the proportion and intensity of roots colonized increased with higher soil temperatures. VAM fungi from Montana, primarily Glomus macrocarpum, were cold tolerant at 11°C while those from Syria, primarily G. hoi, were heat tolerant at 26°C. Inoculum potential of Montana VAM fungi was higher than Syrian VAM fungi in cool soils. Harmal, selected from Syrian barley land races, had the highest colonization by mycorrhizal fungi of the cultivars tested.Journal Series Paper: J-2532 Montana Agricultural Experiment Station.     

The mycorrhizal status of vascular epiphytes in Bale Mountains National Park,Ethiopia

Roots of 28 species of epiphytic vascular plants were collected on tree trunks and branches at six afromontane forest sites between 1700 and 3300 m above sea level in Bale Mountains National Park, Ethiopia. Seven of the 28 epiphyte species were colonized by vesicular-arbuscular mycorrhizal fungi (VAM). Mycorrhizal colonization only occurred at two of the six sites examined, at 2900 m and 3300 m, but more than one type of VAM endophyte was present in each case. Three facultative epiphytic species were all highly colonized by VAM on the forest floor, whereas roots from epiphytic habitats were weakly colonized. No correlations were found between VAM colonization, fine root diameter and root hair length, but VAM colonization and root hair abundance were negatively correlated. The lack of VAM colonization of potential, epiphytic host species at the majority of the sites examined points to the dispersal of VAM propagules as the factor limiting mycorrhizal colonization of epiphytic habitats. It is suggested that root systems of hemiepiphytic tree species serve as corridors between forest floor and tree trunks through which VAM may spread via hyphal growth.     

Effects of vesicular-arbuscular mycorrhizal inoculation at different soil P availabilities on growth and nutrient uptake of in vitro propagated coffee (Coffea arabica L.) plants

 In a pot experiment, the growth and the nutrient status of in vitro propagated coffee (Coffea arabica L.) microcuttings were investigated for 5 months following vesicular-arbuscular mycorrhizal (VAM) inoculation with either Acaulospora melleae or Glomus clarum at four soil P availabilities. Control plants remained P-deficient even at the highest soil P availability while mycorrhizal plants were P-sufficient at all soil P availabilities. Growth of control plants was only improved at the highest soil P availability. In P-deficient soil, neither of the two VAM species improved plant growth. Plant growth increased by 50% following inoculation with either A. melleae or G. clarum when P availability went from deficient to low. No further plant growth improvement was induced by either VAM species at intermediate and high soil P levels. Nevertheless, growth of plants inoculated with G. clarum was still significantly greater than that of non-mycorrhizal plants at the highest soil P availability. Root colonization by G. clarum increased with increasing soil P availability while root colonization by A. mellea decreased with soil P level increasing above low P availability. Soil P availability also affected Zn nutrition through its influence on VAM symbiosis. With increasing soil P availability, foliar Zn status increased with G. clarum or decreased with A. mellea in parallel to root colonization by VAM. This study demonstrates the beneficial effects of VAM inoculation on in vitro propagated Arabica coffee microcuttings, as shown previously for seedlings. This study also demonstrates differences in tolerance to soil P availability between VAM species, most likely resulting from their differing abilities to enhance coffee foliar P status. Accepted: 14 November 1996     

Interactions of arbuscular mycorrhizae,Meloidogyne arenaria,and phosphorus fertilization on peanut

 The individual and combined effects of two arbuscular mycorrhizal fungi (AMF), Meloidogyne arenaria, and phosphorus (P) fertilization, (0, 25, 75, and 125 μg/g soil) on peanut plant growth and pod yield were determined in greenhouse studies. Best growth and yield usually occurred at 75 or 125 μg P regardless of inoculation treatment. Peanut growth and yield were generally stimulated by AMF development, and growth alone was suppressed by M. arenaria at 0 and 25 μg P. In challenge inoculations, VAM increased peanut plant tolerance to the nematode and offset the growth reductions caused by M. arenaria at the two lower P levels. However, VAM and added P increased galling and M. arenaria egg production/g root, thereby increasing peanut susceptibility to nematode attack. M. arenaria had only a minimal effect on root colonization by AMF and sporulation by the fungi. Accepted: 9 June 1995     

Seasonality of vesicular-arbuscular mycorrhizae in sedges in a semi-arid tropical grassland

Vesicular-arbuscular mycorrhizal (VAM) colonization and spore numbers in the rhizosphere of Cyperus iria L. and C. rotundus L., growing in a semi-arid tropical grassland, was studied during the 1993 and 1994 monsoons. In addition, climatic and chemical properties of the soils were determined in order to investigate their influence on mycorrhizal variables. VAM fungal association in the sedges was confirmed by plant- and root-trap culture techniques. The soil nutrients exhibited seasonal variations, but were highly variable between years. Intercellular hyphae and vesicles with occasional intraradical spores characterized mycorrhizal association in sedges. Dark septate fungi also colonized roots of sedges. Temporal variations in mycorrhizal colonization and spore numbers occurred, indicating seasonality. However, the patterns of mycorrhizal colonization and spore numbers were different during both the years. The VAM fungal structures observed were intercellular hyphae and vesicles. Changes in the proportion of root length with VAM structures, total colonization levels and spore numbers were related to climatic and edaphic factors. However, the intensity of influence of climatic and soil factors on VAM tended to vary with sedge species.     

Ectomycorrhizal, vesicular-arbuscular and dark septate fungal colonization of bishop pine (Pinus muricata) seedlings in the first 5 months of growth after wildfire

 We followed the colonization frequency of ectomycorrhizal (EM), vesicular-arbuscular mycorrhizal (VAM), and dark septate (DS) fungi in 1- to 5-month-old bishop pine seedlings reestablishing after a wildfire. Seedlings were collected on a monthly basis at either a VAM-dominated chaparral scrub site or an EM-dominated forest site, both of which were burned. In both vegetation types, fully developed EM were observed from the third month after germination. EM fungi observed on the seedlings from the scrub site were limited to Rhizopogon subcaerulescens, R. ochraceorubens and Suillus pungens. Seedlings from the forest were colonized by a greater variety of EM fungi including Amanita spp., Russula brevipes and a member of the Cantharellaceae. VAM structures (vesicles, arbuscules or hyphal coils) were observed in the seedling root systems beginning 1 month after germination at the scrub site and 3 months after germination at the forest site. Seedlings from the scrub site consistently had more frequent VAM fungal colonization than those from the forest site through the fifth month after germination. DS fungi were observed in most seedlings from both the scrub and forest sites beginning in the first month post-germination. We propose that these fungi survived as a resident inoculum in the soils and did not disperse into the sites after the fire. Accepted: 14 February 1998     

I σ-Index,a measure of dispersion of individuals

Conclusion and summary As theI _σ-index is neither affected by the mean per sample unit except for regular distribution nor standing on the assumption of any definite type of contagious distribution, it may have the most wide range of application among the ones hitherto deviced for measuring the dispersion of individuals in a population. The relations of theI _σ-index to ,k of negative binomial distribution andN of binomial distribution as well as the new dispersion index,I _B , given in this paper may serve, if necessary, for the analysis of data in the ecological works. Aided by the Scientific Research Fund from the Ministry of Education.