Infection of wheat seminal roots by varieties of Phialophora radicicola and Gaeumannomyces graminis

The growth of isolates of Phialophora radicicola var. radicicola, P. radicicola var. graminicola, Gaeumannomyces graminis var. graminis, G. graminis var. tritici and Leptosphaeria narmari was compared on the coleoptiles and roots of wheat seedlings. Fungal growth was measured as the extent and density of dark runner hyphae. All except P. radicicola var. graminicola grew on coleoptiles and all grew on roots although only G. graminis var. tritici extensively colonized the root stele. Growth rate on roots was positively correlated with that on agar, P. radicicola var. graminicola and L. narmari growing at about half the rate of the other fungi; hyphal density was high for P. radicicola var. graminicola but relatively low for the other fungi. For P. radicicola var. radicicola, P. radicicola var. graminicola and G. graminis var. tritici growing from buried inocula, the extent and density of hyphae up roots towards the seed was similar to that down, but G. graminis var. tritici caused chocolate-brown stelar discoloration up roots only.Root invasion by P. radicicola var. radicicola, P. radicicola var. graminicola and G. graminis var. tritici was described from sections. Each gave a different pattern of hyphae and host response within an inoculum layer, and progressive changes occurred away from the inoculum. Studies of the rate of penetration by each fungus and the rate and pattern of death of cortical cells explained the differences between fungi. G. graminis var. tritici penetrated living cells in advance of other soil micro-organisms, and hence by hyaline hyphae inducing much lignituber formation as a host resistance reaction. P. radicicola var. graminicola penetrated only senescent or dead cells in association with other soil microorganisms, and hence by dark hyphae, inducing little lignituber formation. P. radicicola var. radicicola was intermediate in all these respects. The high hyphal density of P. radicicola var. graminicola was due to the colonization of cortical cells and spaces by dark, clearly visible, rather than hyaline hyphae, which are invisible in unstained roots. Cell death in the outer cortex explained the observed progressive restriction of growth by all fungi to the inner cortex with increasing distance from the inoculum. Spread by G. graminis var. tritici up roots was ectotrophic relative to the stele but down roots hyphae spread rapidly within the stele. Stelar reactions suggested as resistance mechanisms occurred up roots only. Their absence down roots is attributed to infection disrupting stelar transport.     

Antagonistic activity of the rhizosphere mycoflora against Gaeumannomyces graminis under conventional and zero-tillage

The effect of individual constituents of the rhizosphere mycoflora on Gaeumannomyces graminis was studied in conjunction with studies that were concerned with the general effects of conventional and zero-tillage on the mycoflora of the rhizosphere, rhizoplane and roots of winter wheat. Material for the isolation of micromycetes was sampled from plots that had been subjected to two extremes of tillage i.e., ploughing and zero-tillage. These plots were part of a long-term field experiment on the monoculture of cereals at Hrušovany u Brna, and they were situated in a corn-producing region.The occurrence of micromycetes was increased in the rhizosphere under direct drilling. The antagonistic activity of individual representatives of the mycoflora was evaluated in vitro, using the biotic-effect method. The total biotic effect of the rhizosphere was calculated from both the frequency and activity against Gaeumannomyces graminis of individual species (isolates) of micromycetes. The more pronounced antagonistic activity of the rhizosphere found under zero-tillage, fully agreed with the lower frequency of infested plants, ascertained by visually evaluating the health status of plants from the respective stands.     

Dynamics of root colonization by the take-all fungus, Gaeumannomyces graminis

The progressive colonization of wheat seminal roots by Gaeumannomyces graminis var. tritici was monitored following inoculation by single inoculum units. G. graminis grew equally well above and below inoculation sites prior to blockage of the stele but after this growth was favoured up roots, above inoculation sites, rather than down, resulting in an asymmetrical pattern of root colonization. This asymmetrical pattern was common to superficial and cortical runner hyphae. It is suggested that cessation of host assimilate supply to the distal portion of infected roots inhibited further extensive growth of G. graminis. This hypothesis was tested by comparing extents of colonization by G. graminis on seminal roots of wheat with normal, enhanced and diminished assimilate supplies. A diminished assimilate supply to infected roots retarded the extent of pathogen colonization.     

Pathozones of genetic subtypes of Gaeumannomyces graminis in cereals

The extent of damage to the host plant caused by Gaeumannomyces graminis var. tritici (Ggt) and var. graminis (Ggg) is a result of a net effect of host susceptibility and mycelium infectivity. The disease severity on cereal roots caused by G. graminis (Gg) fungi varies considerably depending on the genetic subtypes. Results of our rhizobox placement experiments additionally showed a subtype-specific effect of the spatial distance between host and fungus on the infection. The highest pathogenicity of each subtype was found in different zones of the root system: pathozones of different subtypes alternated along the root. The extent of the pathozone profiles did not depend on the infectivity of the inoculum and plant age. However, disease severity was shown to be affected by defence reactions of the host plant. An attack of a fungal subtype that is easily recognized by the host plant leads to defence reactions like increased root growth, thus minimizing the damage to the shoot. Detailed analysis showed that a Ggt subtype had a high potential for colonizing root laterals. It formed concentric zones of high colonization efficiency at a distance of ca. 5 cm around the shoot.     

Nitrogen metabolism in Nicotian a rustica L. grown with molybdenum. I. vegetative development

Abstract

The effect of 1 ppm of molybdenum on nitrate reductase (EC 1.6.6.1.3) and nitrite reductase (EC 1.7.7.1) activity, and the nitrate, nitrite, ammonium, total nitrogen, total protein content on vegetative development of Nicotiana rustica L. was studied. This molybdenum supply increased the ammonium and nitrite content in leaves and the protein content in the root. Variations in enzymatic activity was not observed. The vegetative stage was shorter in the plants grown with this molybdenum supply.     

Alleviation of salinity stress in rice plant by encapsulated salt tolerant plant growth promoting bacteria Pantoea agglomerans strain KL and its root colonization ability

ABSTRACT

The present investigation indicates the effects of 0 to 8% NaCl stress on plant growth promoting traits such as ACC (1-aminocyclopropane-1-carboxylate) deaminase, phosphate solubilization, IAA (indole acetic acid), ammonia and exopolysaccharide production of Pantoea agglomerans strain KL isolated from salt-stressed soil of Kolhapur, Maharashtra, India. We have studied the effect of encapsulated inoculum (EI) and free inoculum (FI) of P. agglomerans strain KL on the alleviation of salinity stress (100 mM NaCl) and promotion of rice plant growth in the pot experiment. The present study showed significant improvement in plant growth supplemented with EI in terms of increased length, biomass, photosynthetic pigment and decreased level of proline, malondialdehyde. Furthermore, EI supplemented plant exhibited decreased sodium and increased calcium and potassium uptake. Root colonization study revealed the survival of encapsulated organism which was less after 10 days. However, a significant number of colony forming unit were noted after 20 and 30 days. In addition, the scanning electron microscopic analysis of salt-stressed plant root showed tremendous root colonization by EI. Hence, the present study demonstrates the potency of P. agglomerans strain KL in the expression of plant growth promoting traits and amelioration of salt stress by EI.     

The influence of use of different rates of mycorrhizal inoculum on root infection,plant growth,and phosphorus uptake

Abstract

Sorghum and leek plants were used as hosts in order to test the effectiveness and infectiveness of four mycorrhizal species on spore production, plant growth and phosphorus (P) uptake. When sorghum was used as a test plant, Glomus mosseae, Glomus etunicatum, and Glomus caledonium, respectively, gave the highest number of spores, while on leek, G. etunicatum, G. mosseae, and G. caledonium, respectively, resulted in higher spore production. Glomus intraradices produced the least amount of inoculum among the four species. Based on relative spore production and root infection, G. mosseae and G. etunicatum were determined to be the two best fungi as sources of inoculum for further use in the experiment. It is very important to know the minimum amount of inoculum in order to reach the maximum percentage of infection. Thus different amounts of inoculum were applied to determine optimum rates of inoculation. Sorghum and leek plants were infected with 0, 6, 12, 18, and 24 g G. mosseae and G. etunicatum of mycorrhizal inoculum per pot in a low P content and natural soil. As the inoculum rate increased, plant parameters and the percent of infection gradually increased with increasing rate to 18 g. Higher inoculum rates did not stimulate growth on infection percentage.     

A new growth medium for the study of siderophore-mediated interactions

Summary A microbial growth medium, RSM, was developed to study the role of siderophores (microbial Fe-transport compounds) in the inhibition of the take-all pathogen, Gaeumannomyces graminis var. tritici, by Pseudomonas putida strain B10. The inorganic constituents of the medium were designed to mimic the rhizosphere while the organic composition was designed to promote rapid growth and siderophore production. The antibiosis experiments were highly reproducible and the antagonism appeared to be due to production of pseudobactin, the siderophore of B10. On plates amended with chrome azurol S, G. graminis did not produce siderophores while other fungi did. The growth of G. graminis on plates prepared with Fe chelate buffers was inhibited at a free ferric ion concentration of 10^–24.6 M, although three other fungi were not inhibited, even at 10^–25.5 M, presumably due to their greater production of siderophores. In liquid medium amended with Fe chelate buffers, both the doubling time and the lag phase of P. putida increased as the free ferric ion concentration was reduced. A wide variety of fungi and bacteria were found to grow on this medium. Because the inorganic composition of RSM is based on that of the rhizosphere, the development of this medium may be a first step towards the study of the chemistry and biology of the rhizosphere under well defined conditions.     

小麦/蚕豆间作条件下小麦的氮、钾营养对小麦白粉病的影响

通过小麦/蚕豆间作盆栽试验,研究比较了单作和间作条件下不同氮、钾营养水平对小麦氮、钾养分吸收和小麦白粉病发生的影响。结果表明:小麦蚕豆间作提高小麦子粒产量74.7%～133.9%,低氮条件下,间作提高小麦氮吸收量14.7%～169%;在高氮条件下,间作提高氮吸收量的优势降低;间作提高小麦钾吸收量32%～69%,增施钾肥提高小麦钾吸收量25.5%～57.3%。小麦间作蚕豆能明显减轻小麦白粉病的发生,间作平均防效达42.1%～83.1%;小麦白粉病的发生与小麦茎叶的氮吸收量呈显著正相关关系,r=0.623*～0.702*.*。     

Light integral as an indicator of water use in commercial greenhouse nurseries

Abstract

Irrigation strategies in pot plants of Kalanchoë blossfeldiana were studied in two commercial greenhouse nurseries by continuous weighing of plants on a high-precision balance. The objectives were to study actual irrigation strategies implemented by growers and to evaluate the method of continuous weighing as a potential tool for future irrigation management. Mean values of temperature, relative humidity, light, and weight were recorded every five minutes using data loggers. The change in weight over time was estimated and related to the calculated total canopy surface area of the studied plants. The rate of weight change was then statistically tested in relation to the recorded external factors. The factor with the strongest effect on total water-consumption rate over time was the light integral. As expected, water consumption was also affected by temperature and humidity, as well as the time of day. Although the growers indicated clear irrigation strategies, the study showed that these were not implemented in a true sense or correlated to the information available in greenhouse climate computers. The study also indicated that a high-precision weighing balance might be an important tool for future control of plant growth and plant architecture through irrigation in the pot plant industry.     

Effects of defoliation on carbohydrate status,nodules and spring growth in white clover in a sub-arctic climate

Abstract

In order to improve the basis for utilizing white clover (Trifolium repens L) in northern agriculture, we studied the effects of defoliation intensity on spring growth in a sub-arctic climate in relation to carbohydrate and nodule status. White clover plants (cv Snowy) were studied in a pot experiment in the field on the coast of northern Norway from spring 2001 until spring 2002. The experiment was repeated with some modifications from spring 2002 until spring 2003. During the growing season from summer to autumn, the plants were totally stripped of leaves down to the stolon, cut at four or seven cm height or left undisturbed. The plants were sampled destructively in autumn, early spring and late spring and sorted into leaves, stolons and roots. The plant material was weighed and analysed for carbohydrate reserves and nodule number. Defoliation during the growing season resulted in reduced concentration of reserve carbohydrates in autumn and reduced winter survival of the stolons. The most severe defoliation treatment reduced the herbage growth in spring. In contrast, the two milder defoliation treatments had no effect on herbage growth during spring or on total plant dry matter and nodule status in late spring. In conclusion, moderate defoliation during the growing season had no effect on herbage growth the following spring nor on carbohydrate, nodule or dry matter status of the plant in late spring. Moderate defoliation increased spring growth and thereby also the nitrogen demand of the plants. This probably enhanced nodule formation and development of inactive to active nodules.     

Soils suppressive to Gaeumannomyces graminis var. tritici: Effects on other fungi

The effect of soils suppressive to Gaumannomyces graminis var. tritici (Ggt) on the severity of root and crown rots caused by Rhizoctonia solani, Gibberella zeae, Pythium irregulare, Cochliobolus sativus and Fusarium culmorum was tested in pot bioassays. An induced suppressive soil was obtained from the rhizosphere of wheat plants grown at 15°C for 28 days in fumigated soil inoculated with live inoculum (colonized oat grain) of Ggt.Root rot caused by R. solani was significantly less in soil amended with either induced or naturally suppressive soil. Disease caused by the other pathogens was also reduced by the induced suppressive soil, with the least reduction occurring with F. culmorum.Colonization of the surfaces of seminal roots of wheat plants by Gaeumannomyces graminis var. graminis (Ggg) and a Phialophora-like fungus (Plf 119) was also studied using the line-intercept method. In non-suppressive soil the maximum area of the primary seminal root colonized by Ggg was 7.4 per cent and by Plf 119 was 3.3 per cent. Colonization of roots by Ggg and Plf 119 was reduced substantially by the addition of induced suppressive soil.     

Sensitivity of Cirsium arvense to simulated tillage and competition

Abstract

Single and combined effects were studied of root length, burial depth, cutting and competition from a seasonal green manure crop on the growth and development of C. arvense from roots found in the upper soil layer. The experiment was performed under field conditions and partly repeated in a green house. The green manure consisted of a mixture of phacelia, common vetch, red clover and Italian ryegrass. Root fragments of 5 and 10 cm length were buried at 5 and 15 cm soil depth, simulating soil tillage. Use of green manure alone reduced growth of C. arvense more than any other single factor (81–99%), while root length and burial depth were more variable in their effect (0–96% reduction). Combined treatments involving both green manure, deep root burial (15 cm) and short root length (5 cm) reduced growth of C. arvense consistently by 95–100%. At the minimum regenerative capacity of C. arvense the number of leaves was 3–7 in plots with no green manure, at which time cutting had the greatest effect on regrowth the following year. The level for minimum regenerative capacity was not possible to decide for C. arvense growing in competition with green manure. Combined multiple treatments in spring, including use of green manure and mechanical operations in the upper soil layers, appear to be a potential means of reducing C. arvense infestations.     

Influence of earthworm culture on fertilization potential and biological activities of vermicomposts prepared from different plant wastes

The present investigation was aimed to analyze influence of earthworm culture on nutritive status, microbial population, and enzymatic activities of composts prepared by utilizing different plant wastes. Vermicomposts were prepared from different types of leaves litter of horticulture and forest plant species by modified vermicomposting process at a farm unit. Initial thermophilic decomposition of waste load using cow‐dung slurry was done in the separate beds. The culture of Eisenia fetida was used for vermicomposting in specially designed vermibeds at the farm unit. The physico‐chemical characteristics, enzyme activities (oxido‐reductases and hydrolases), and microbial population (bacteria, fungi, free‐living nitrogen‐fixing bacteria, actinomycetes, Bacillus, Pseudomonas, phosphate‐solubilizing bacteria and fungi) of vermicomposts were found significantly higher (p < 0.05) than those of control (without earthworm inoculum). The study quantified significant contributions of earthworm culture to physico‐chemical, enzymatic, and microbiological properties of vermicompost and confirmed superior fertilization potential of vermicompost for organic farming. The agronomic utility of vermicompost was assessed on yellow mustard plant in a pot experiment. Pot soil was amended with different ratios (5%, 10%, 20%) of vermicompost and normal compost (without earthworm inoculum). Effects of these amendments on the growth of Brassica comprestis L. were studied. The significant differences (p < 0.05) in the growth of plant were observed among vermicompost‐, compost‐amended soil, and control. Vermicompost increased the root and shoot lengths, numbers of branches and leaves per plant, fresh and dry weights per plant, numbers of pods and flowers, and biochemical properties of plant leaf significantly, especially in 20% amendment. These results proved better fertilization potential of vermicompost over non‐earthworm‐inoculated compost.     

The role of macronutrients in cabbage-head formation

Abstract

Cabbage plants were grown at graded levels of nitrogen supply and light intensity, and the combined effects on cabbage-head development were studied during the spring and autumn seasons.

The cabbage-head yield (i.e. dry weight of inner head leaves) was the highest at 50 ppm N in the nutrient solution, followed by 500 and 5 ppm N at full light intensity, and decreased with decrease in the, light intensity by shading. The decrease in cabbage-head yield caused by the shading was greater at high nitrogen levels during the autumn (low solar energy) season than during the spring (high solar energy) season. As the nitrogen supply increased or the light intensity decreased during both the spring and autumn seasons, nitrogen, especially soluble N, accumulated and the carbohydrate (sugar and starch) content decreased in the plants. Cabbage-head development occurred efficiently when the total N content in the outer leaves remained at about 2–3% and the carbohydrate production was large at full light intensity.     

Effect of certain herbicides on soil microbial populations and their influence on saprophytic growth in soil and pathogenicity of take-all fungus

Summary The application of diquat + paraquat, glyphosate and trifluralin to unsterilized field soil increased take-all caused by the fungus, Gaeumannomyces graminis var. tritici Walker by 13.0% 16.6% and 10.8% respectively, while no effect on disease was recorded in sterilized soil treated with the same herbicides. The herbicides tested had no effect on the saprophytic growth of the pathogen with the exception of glyphosate, which increased its growth in unsterilized soil. The application of diquat + paraquat and glyphosate to unsterile soil had no effect on the numbers of actinomycetes. The diquat + paraquat treatment, however, increased populations of fungi while the glyphosate decreased the numbers of bacteria. The proportion of soil fungi antagonistic to the pathogen was reduced in glyphosate-treated soil. The frequency of occurrence of Eupenicillium euglaucum (v. Beyma) Stolk & Samson (strain B), and Penicillium verruculosum Peyr. (strain B), which were strong and low level antagonists of Ggt on agar, were reduced in their occurrence in soil by 7.7% and 2.5% respectively, following glyphosate treatment. Moreover, the numbers of Aspergillus viridinutans Ducker & Thrower, which showed moderate antagonism to the pathogen, was decreased by 1.9% and 4.1% in diquat + paraquat and glyphosate treatments respectively. The proportion of antagonists rather than total numbers of fungi appears to be related to the treatment effect observed on the soil growth and pathogenicity of G. graminis var. tritici in our investigation. The increase in disease of wheat in certain herbicide-treated soils may be due to the shift in soil microbial populations away from those which are antagonistic to the pathogen.     

Interactions between Onychiurus armatus and Trichoderma harzianum in take-all disease suppression in a simple experimental system

In a simple experimental system with wheat plants, interactions between the collembolan Onychiurus armatus and Trichoderma harzianum, a soil-borne fungus parasite of several plant pathogenic fungi, were studied in the presence of Gaeumannomyces graminis var. tritici, one of the most important foot and root fungal pathogens of cereals world-wide. Trichoderma harzianum was used according to two different modalities: fungal inoculum applied to seed or mixed with substrate. The isolate of T. harzianum proved to be ineffective against the pathogenic fungus, independent of the application modality, as shown in the experiments where this fungus was used alone, whereas Collembola used alone significantly reduced disease severity. However, the mode by which T. harzianum was applied significantly influenced the disease control ability of Collembola. In fact, only when T. harzianum was coated to seed were springtails able to reduce the disease caused by G. graminis var. tritici.     

Influence of pre‐storage drying conditions and duration of storage on the effectiveness of root inoculum of Glomus aggregation

A greenhouse experiment was undertaken to evaluate the influence of pre‐storage drying treatments and duration of storage on the effectiveness of root inoculum of Glomus aggregatum. Conditions under which roots were dried prior to storage had little or no effect on the level of arbuscular mycorrhizal (AM) effectiveness measured in terms of pinnule phosphorus (P) content of Leucaena leucocephala leaves after the first 14 days of storage. As duration of storage was further prolonged the time required by root inocula for initiating AM effectiveness and attaining peak levels of effectiveness was progressively prolonged relative to that required by the crude inoculum. However, the two sources of inoculum had similar peak AM effectiveness in many instances. Roots dried in the greenhouse or in the oven at 40°C were significantly inferior to that dried at 60°C. Root inocula stimulated growth of the indicator plant to the same extent as the crude inoculum after 14 days of storage. However, the effectiveness of root inocula in stimulating growth declined with further increase in duration of storage. Among root inocula tested, that dried at 60°C prior to storage was relatively more effective than that dried in the greenhouse or in the oven at 40°C. The overall inferiority of root inocula to that of the crude inoculum appears to be related to loss of viability of root inocula with increase in duration of storage.     

Dry Weight and Nitrogen Content of Chickpea and Winter Wheat Grown in Pots for Three Rotations

ABSTRACT

Chickpea [Cicer arietinum (L.)] cultivars ‘ICCV-2’ and ‘Sarah’ were studied along with a control, multistrain, TAL 1148, and TAL 480 Bradyrhizobium strains to determine the effect(s) of cultivar and inoculum on dry weight (DW) and nitrogen (N) content of the legume, as well as soil mineral N, DW, and N content of wheat [Triticum aestivum (L.) emend. Thell.] in a continuous wheat-legume rotation. Chickpeas were planted during the summer and harvested in the fall of 1992, 1993, and 1994. Vegetative growth from chickpeas was incorporated into the soil prior to wheat planting, and soil cores were taken at 35 to 48 d after chickpea harvests. Additional summer fallow treatments for the winter wheat part of the experiment received 0, 45, and 90 kg N ha^?1 each year. Wheat plants were removed the following spring and stubble was incorporated into the soil before planting chickpeas in the summer. ‘Sarah’ chickpeas accumulated about the same or more shoot DW and shoot N compared to ‘ICCV-2’; whereas ‘ICCV-2’ generally produced more pod DW and pod N compared to ‘Sarah.’ Inoculum had no significant effect on chickpea DW or N content. Wheat DW and N following legumes increased marginally after growing ‘Sarah’ chickpeas, as evidenced by higher values of some treatments. Only the multistrain or absence of inoculum in ‘Sarah’ chickpeas resulted in significantly greater wheat DW or N content compared to the fallow wheat receiving no added N fertilizer. The contributions from ‘ICCV-2’ chickpeas to wheat DW and N content were not significant. Soil mineral N, as well as wheat DW and N content, fluctuated or increased during this three-year study, which demonstrated some benefit from incorporation of chickpeas into a wheat-legume cropping system.     

The decomposition of turfgrass clippings is fast at high air humidity and moderate temperature

Abstract

In grassland areas where herbage production has no economic value, the cut grass is often left on the sward surface where its decomposition is influenced by weather conditions. Although the influence of temperature and humidity on decomposition has been investigated under controlled lab conditions, experimentation has generally been under ideal moisture conditions that have not tested the combinations of climatic limitations that might occur in the field. The decomposition of mown turfgrass clippings deposited at different times of vegetation period was studied in situ using nylon bags during the first 8 weeks after deposition to investigate the effect of weather conditions (the air temperature, relative humidity, precipitation) on decomposition. Decomposition is the highest in the case of high air humidity and temperature of 10°C. Limiting factors for decomposition at temperatures above 10°C is the air humidity and below 10°C the air temperature. The general tendency was that the rate of decomposition increased with increasing air temperature up to 10°C, but with further increases of air temperature the decomposition rate slowed down. Relative air humidity had a variable impact (at the beginning of the decomposition process (weeks 1–2) the influence was negative, during weeks 3–8 of the decomposition process the effect was positive), and hence had no generalized relationship with decomposition over the studied decomposition period (weeks 1–8). The most significant influence of weather conditions on the decomposition rate was recorded directly after cutting. If the cutting was done during hot weather conditions, the material was drying fast and therefore decomposed slowly. Our results indicate that for fast decomposition of clippings it is important to maintain the freshness of material. Lower decomposition rates occurred during conditions of hot and dry weather, and also cooler (temperature near to 0°C) weather, and can be compensated as soon as favourable weather arrives.