FACTORS GOVERNING ZOOSPORE RESPONSES OF PHYTOPHTHORA MEGASPERMA VAR. SOJAE TO PLANT ROOTS

1967 ◽  
Vol 45 (11) ◽  
pp. 1983-1994 ◽  
Author(s):  
H. H. Ho ◽  
C. J. Hickman
Keyword(s):  
Root Exudate ◽  
Chemical Nature ◽  
Root Surface ◽  
Plant Roots ◽  
Root Tip ◽  
Phytophthora Megasperma ◽  
Negative Pole ◽  
New Feature ◽  
Germ Tubes ◽  
Cyst Germination

In the presence of plant roots, zoospores of Phytophthora megasperma var. sojae reacted in general as do other fungal zoospores: they were attracted to, and trapped in the immediate vicinity of the root surface, on which they encysted rapidly. Encysted zoospores formed a continuous sheath around the root, thickest just behind the root tip. Cyst germination was stimulated. Germ tubes were always initiated from the side of cysts closest to the root and grew towards it. In addition, a new feature was observed, suppression of repeated emergence of zoospores. Zoospore accumulation was nonspecific with respect to host and non-host, resistance, and susceptibility.Tests with exudates and extracts from roots of resistant and susceptible soybean varieties and a non-host, pea, confirmed the chemical nature of the stimulus inducing these responses. Zoospores observed in an electric field were not attracted towards either pole, but they were trapped and encysted rapidly around the negative pole. Cyst germination was not stimulated. Nevertheless, since encystment was more pronounced on root exudate agar mounted on the negative pole, electric charges on roots may also contribute to inducing early encystment of zoospores there.In an investigation of ions on zoospore responses, with ionic resins, all phases of zoospore response to roots, with the exception of attraction, occurred in the presence of hydrogen resin particles.

ASEXUAL REPRODUCTION AND BEHAVIOR OF ZOOSPORES OF PHYTOPHTHORA MEGASPERMA VAR. SOJAE

1967 ◽  
Vol 45 (11) ◽  
pp. 1963-1981 ◽  
Author(s):  
H. H. Ho ◽  
C. J. Hickman
Keyword(s):  
Germ Tube ◽  
Solid Surfaces ◽  
Extreme Temperatures ◽  
Phytophthora Megasperma ◽  
Frequent Contact ◽  
Ph Values ◽  
Pure Cultures ◽  
And Behavior ◽  
Germ Tubes ◽  
Cyst Germination

A method was devised to produce abundant zoospores in distilled water suspension from pure cultures of Phytophthora megasperma var. sojae. Sporangia were predominantly non-papillate, but occasionally inconspicuously or conspicuously papillate, germinating with the formation of a delicate, evanescent vesicle. Proliferation of sporangia was observed.Flagella action of freely swimming zoospores was investigated photographically. Both flagella were proved to undulate. Zoospores remained motile longest at 15 °C. Motility was markedly reduced at extreme temperatures (5 and 36 °C), at extreme pH values (below 5.2 or above 9.25), or by mechanical disturbance, dilution, and frequent contact with solid surfaces. The fate of flagella during encystment was followed. Encysted zoospores germinated by germ tubes, or by secondary zoospores, or in rare cases, the germ tube was terminated by a miniature sporangium. Repeated emergence of zoospores was favored at 15 °C whereas total cyst germination and germ tube production was best at 25 °C and in the presence of nutrients.

scholarly journals The Chemistry of Stress: Understanding the ‘Cry for Help’ of Plant Roots

Metabolites ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 357
Author(s):  
Muhammad Syamsu Rizaludin ◽  
Nejc Stopnisek ◽  
Jos M. Raaijmakers ◽  
Paolina Garbeva
Keyword(s):  
Root Exudate ◽  
Chemical Cues ◽  
Water Soluble ◽  
Plant Roots ◽  
Plant Tissues ◽  
Biotic And Abiotic Stresses ◽  
Primary And Secondary Metabolites ◽  
Cry For Help ◽  
Micro Organisms ◽  
Qualitative Changes

Plants are faced with various biotic and abiotic stresses during their life cycle. To withstand these stresses, plants have evolved adaptive strategies including the production of a wide array of primary and secondary metabolites. Some of these metabolites can have direct defensive effects, while others act as chemical cues attracting beneficial (micro)organisms for protection. Similar to aboveground plant tissues, plant roots also appear to have evolved “a cry for help” response upon exposure to stress, leading to the recruitment of beneficial microorganisms to help minimize the damage caused by the stress. Furthermore, emerging evidence indicates that microbial recruitment to the plant roots is, at least in part, mediated by quantitative and/or qualitative changes in root exudate composition. Both volatile and water-soluble compounds have been implicated as important signals for the recruitment and activation of beneficial root-associated microbes. Here we provide an overview of our current understanding of belowground chemical communication, particularly how stressed plants shape its protective root microbiome.

scholarly journals Three sympatrically occurring species of Metarhizium show plant rhizosphere specificity

Microbiology ◽  
2011 ◽  
Vol 157 (10) ◽  
pp. 2904-2911 ◽  
Author(s):  
Michael Wyrebek ◽  
Cristina Huber ◽  
Ramanpreet Kaur Sasan ◽  
Michael J. Bidochka
Keyword(s):  
Tree Species ◽  
Acer Saccharum ◽  
Panicum Virgatum ◽  
Sugar Maple ◽  
Root Exudate ◽  
Pathogenic Fungus ◽  
Plant Roots ◽  
Metarhizium Robertsii ◽  
Grass Roots

Here we tested the hypothesis that species of the soil-inhabiting insect-pathogenic fungus Metarhizium are not randomly distributed in soils but show plant-rhizosphere-specific associations. We isolated Metarhizium from plant roots at two sites in Ontario, Canada, sequenced the 5′ EF-1α gene to discern Metarhizium species, and developed an RFLP test for rapid species identification. Results indicated a non-random association of three Metarhizium species (Metarhizium robertsii, Metarhizium brunneum and Metarhizium guizhouense) with the rhizosphere of certain types of plant species (identified to species and categorized as grasses, wildflowers, shrubs and trees). M. robertsii was the only species that was found associated with grass roots, suggesting a possible exclusion of M. brunneum and M. guizhouense. Supporting this, in vitro experiments showed that M. robertsii conidia germinated significantly better in Panicum virgatum (switchgrass) root exudate than did M. brunneum or M. guizhouense. M. guizhouense and M. brunneum only associated with wildflower rhizosphere when co-occurring with M. robertsii. With the exception of these co-occurrences, M. guizhouense was found to associate exclusively with the rhizosphere of tree species, predominantly Acer saccharum (sugar maple), while M. brunneum was found to associate exclusively with the rhizosphere of shrubs and trees. These associations demonstrate that different species of Metarhizium associate with specific plant types.

STUDIES ON THE RELATIONSHIPS BETWEEN NEMATODES AND OTHER SOIL MICROORGANISMS: IV. INCIDENCE OF NEMATODE-TRAPPING FUNGI IN THE VICINITY OF PLANT ROOTS

1965 ◽  
Vol 11 (3) ◽  
pp. 491-495 ◽  
Author(s):  
E. A. Peterson ◽  
H. Katznelson
Keyword(s):  
Soil Microorganisms ◽  
Rhizosphere Soil ◽  
Red Clover ◽  
Root Surface ◽  
Plant Roots ◽  
Favorable Effect ◽  
Bacterial Isolates ◽  
Rhizosphere Effect ◽  
Root Extracts ◽  
Wheat Rhizosphere

A study was made of the occurrence of nematode-trapping fungi in the rhizosphere and on the root surface of different plants. Arthrobotrys oligospora was the predominant predaceous fungus isolated. It was almost completely absent from plant roots but occurred in varying frequency in rhizosphere soil and in root-free soil. The incidence of this fungus was consistently greater in the soybean rhizosphere and lower in the wheat rhizosphere than in corresponding soil devoid of roots, whereas for other plants, red clover, flax, etc., there was no obvious rhizosphere effect. Spore germination tests and growth of A. oligospora in root extracts of soybeans and wheat failed to account for the differences observed. However, bacterial isolates from the wheat rhizosphere were, on the whole, more antagonistic to this fungus than those from the soybean rhizosphere, whereas isolates from the latter appeared to exert a favorable effect.

Behavior of zoospores of Phytophthora megasperma var. sojae and P. drechsleri in soil

1972 ◽  
Vol 50 (11) ◽  
pp. 2125-2130 ◽  
Author(s):  
R. S. Mehrotra
Keyword(s):  
Fluorescence Microscope ◽  
Natural Soil ◽  
Moderate Degree ◽  
Percentage Germination ◽  
Phytophthora Megasperma ◽  
Potential Capacity ◽  
Perfusion Apparatus ◽  
Phytophthora Drechsleri ◽  
Germ Tubes ◽  
Modified Soil

Experiments done with the modified soil perfusion apparatus indicate the potential capacity of the zoospores and cysts of Phytophthora drechsleri and P. megasperma var. sojae as inoculum units in soil. The results indicate that although zoospores/cysts do not retain infectivity for months, those of P. drechsleri do not lose it very rapidly. Experiments done to find out the period of motility of zoospores have shown that some zoospores of P. drechsleri and P. megasperma var. sojae remained motile for up to 30 and 24 h respectively. Saprophytic behavior of the two species of Phytophthora has been studied with the help of a fluorescence microscope and using a fluorescent dye. Cysts of P. drechsleri and P. megasperma var. sojae germinate to a moderate degree in natural non-amended soil. Germination ranged from 30 to 50% in the case of P. drechsleri and 15 to 25% in P. megasperma var. sojae. Amending the soil with 0.4% glucose, 0.4% asparagine increased the percentage germination of cysts in natural soil. Germ tubes of a small percentage of cysts in the two species terminate in miniature sporangia-like structures.

scholarly journals Paenibacillus polymyxa Invades Plant Roots and Forms Biofilms

2005 ◽  
Vol 71 (11) ◽  
pp. 7292-7300 ◽  
Author(s):  
Salme Timmusk ◽  
Nina Grantcharova ◽  
E. Gerhart H. Wagner
Keyword(s):  
Plant Growth ◽  
Fluorescent Protein ◽  
Paenibacillus Polymyxa ◽  
Plant Roots ◽  
Root Tip ◽  
Broad Host Range ◽  
Plant Growth Promoting Bacteria ◽  
Soil System ◽  
Plant Growth Promoting ◽  
Growth Promoting

ABSTRACT Paenibacillus polymyxa is a plant growth-promoting rhizobacterium with a broad host range, but so far the use of this organism as a biocontrol agent has not been very efficient. In previous work we showed that this bacterium protects Arabidopsis thaliana against pathogens and abiotic stress (S. Timmusk and E. G. H. Wagner, Mol. Plant-Microbe Interact. 12:951-959, 1999; S. Timmusk, P. van West, N. A. R. Gow, and E. G. H. Wagner, p. 1-28, in Mechanism of action of the plant growth promoting bacterium Paenibacillus polymyxa, 2003). Here, we studied colonization of plant roots by a natural isolate of P. polymyxa which had been tagged with a plasmid-borne gfp gene. Fluorescence microscopy and electron scanning microscopy indicated that the bacteria colonized predominantly the root tip, where they formed biofilms. Accumulation of bacteria was observed in the intercellular spaces outside the vascular cylinder. Systemic spreading did not occur, as indicated by the absence of bacteria in aerial tissues. Studies were performed in both a gnotobiotic system and a soil system. The fact that similar observations were made in both systems suggests that colonization by this bacterium can be studied in a more defined system. Problems associated with green fluorescent protein tagging of natural isolates and deleterious effects of the plant growth-promoting bacteria are discussed.

scholarly journals Pairwise Interactions of Three Related Pseudomonas Species in Plant Roots and Inert Surfaces

2021 ◽  
Vol 12 ◽  
Author(s):  
Nesli Tovi ◽  
Tomer Orevi ◽  
Maor Grinberg ◽  
Nadav Kashtan ◽  
Yitzhak Hadar ◽  
...  
Keyword(s):  
Bacterial Colonization ◽  
Plant Roots ◽  
Microbial Consortia ◽  
Root Tip ◽  
Interaction Patterns ◽  
Interspecies Interactions ◽  
Wheat Roots ◽  
Pairwise Interactions ◽  
Inert Surfaces ◽  
External Stimuli

Bacteria are social organisms that interact extensively within and between species while responding to external stimuli from their environments. Designing synthetic microbial communities can enable efficient and beneficial microbiome implementation in many areas. However, in order to design an efficient community, one must consider the interactions between their members. Using a reductionist approach, we examined pairwise interactions of three related Pseudomonas species in various microenvironments including plant roots and inert surfaces. Our results show that the step between monoculture and co-culture is already very complex. Monoculture root colonization patterns demonstrate that each isolate occupied a particular location on wheat roots, such as root tip, distance from the tip, or scattered along the root. However, pairwise colonization outcomes on the root did not follow the bacterial behavior in monoculture, suggesting various interaction patterns. In addition, we show that interspecies interactions on a microscale on inert surface take part in co-culture colonization and that the interactions are affected by the presence of root extracts and depend on its source. The understanding of interrelationships on the root may contribute to future attempts to manipulate and improve bacterial colonization and to intervene with root microbiomes to construct and design effective synthetic microbial consortia.

scholarly journals 470 Narrow-sense Heritability Estimates for Melon Root Traits

HortScience ◽  
2000 ◽  
Vol 35 (3) ◽  
pp. 475A-475
Author(s):  
Kevin M. Crosby
Keyword(s):  
Genetic Variation ◽  
Root System ◽  
Block Design ◽  
Root Systems ◽  
Root Surface ◽  
Root Tip ◽  
Root Surface Area ◽  
Narrow Sense ◽  
Narrow Sense Heritability ◽  
Heritability Estimates

Improving melon root systems by traditional breeding is one component of the program to develop multiple-stress-resistant melons at the Texas Agricultural Experiment Station, Weslaco. Ten diverse melon lines representing four horticultural groups were intercrossed utilizing a Design II mating scheme. The male parents were: `PI 403994,' `Perlita,' `Doublon,' `Caravelle', and `PI 525106.' The female parents were: `Créme de Menthe,' `Magnum 45,' `BSK,' `PI 124111 × TDI', and `Deltex.' F1 progeny were grown in pasteurized sand in the greenhouse using a randomized complete-block design with four reps. After 4 weeks, root systems from all plants were carefully washed to remove the sand. Each root system was then placed onto a glass, plated, and scanned into the computer software Rhizo Pro 3.8 (Regent Instruments, Quebec). This software calculated root lengths of various diameter classes, root area, and root tip number. All data was input into Agrobase software for calculation of genetic variances based on Design II analysis. Significant differences of contributions by male parents to progeny variation were few. Only length of roots with 1.0- to 1.5-mm-diameter and vine length were significantly different. Differences in contributions by female parents to all traits except root tip number were highly significant. No significant interaction effects were observed for any trait. Narrow-sense heritability estimates were moderate to high for all traits. The range was from 0.56 for root tip number by males to 0.81 for both length of 0.5- to 1.0-mm-diameter roots and vine length for females. Estimates for total root length (0.76) and root surface area (0.77) were high. The lack of male by female interaction suggests very low dominance genetic variation and contributed to high heritability estimates, which represent predominantly additive gene action. Additive genetic variation allows more-efficient progress by selection, making the potential for root system improvement favorable.

scholarly journals Whole plant-environment microscopy reveals how Bacillus subtilis utilises the soil pore space to colonise plant roots

2021 ◽  
Author(s):  
Yangminghao Liu ◽  
Daniel Patko ◽  
Ilonka Engelhardt ◽  
Timothy S George ◽  
Nicola Stanley-Wall ◽  
...  
Keyword(s):  
Bacillus Subtilis ◽  
Pore Space ◽  
Light Sheet ◽  
Root Surface ◽  
Plant Roots ◽  
Soil Particles ◽  
Transparent Soil ◽  
Plant Environment ◽  
Small Pore ◽  
Soil Pore Space

AbstractPlant growth is supported by complex interactions with many biophysical elements of their environment including microorganisms, geochemicals, water and gas, all within the otherwise complex and heterogeneous soils’ physical environment. Our understanding of plant-environment interactions in soil are limited by the difficulty of observing such interactions at the microscopic scale which occur throughout the large volume of influence of the plant. Here, we present the development of 3D live microscopy approaches for resolving plant-microbe interactions across the environment of an entire seedling root growing in a transparent soil in tailor-made mesocosms, maintaining physical conditions for the culture of both plants and microorganisms. A dual-illumination light-sheet system was used to acquire scattering signals from the plant whilst fluorescence signals were captured from transparent soil particles and labelled microorganisms, allowing the generation of quantitative data on samples approximately 3600 mm3 in size with as good as 5 μm resolution at a rate of up to one scan every 30 minutes. The system can track the movement of Bacillus subtilis populations in the rhizosphere of lettuce plants in real time, revealing previously unseen patterns of activity. Motile bacteria favoured small pore spaces over the surface of soil particles, colonising the root in a pulsatile manner. Migrations appeared to be directed first towards the root cap as the point “first contact”, before subsequent colonisation of mature epidermis cells. Our findings show that microscopes dedicated to live environmental studies present an invaluable tool to understand life in soils.SignificanceBetter knowledge of microbial movement and interaction with plant roots is essential to understanding soil ecosystems. However, the lack of a suitable approach for observing biological activity in such environments severely impedes advances in this field of research. Here, we overcome this major limitation by combining the use of transparent soil with cutting edge live microscopy techniques. We performed a detailed analysis of the movements of Bacillus subtilis and revealed how the soil pore structure influences the behaviour of the bacteria, both before and during the formation of biofilms on the root surface. This work sheds light on previously unseen phenomenon, and accelerates our understanding of soil dwelling organisms which were, before now, unobserved in their native environment.

Ion uptake from soils by plant roots, subject to the Epstein-Hagen relation

Soil Research ◽  
1968 ◽  
Vol 6 (2) ◽  
pp. 159 ◽  
Author(s):  
J Kautsky ◽  
KP Barley ◽  
DK Fiddaman
Keyword(s):  
Differential Equation ◽  
Linear Approximation ◽  
Numerical Solutions ◽  
Diffusion Theory ◽  
Nonlinear Function ◽  
Solution Concentration ◽  
Root Surface ◽  
Ion Uptake ◽  
Plant Roots

Diffusion theory has been used to describe the uptake of ions from soils by single roots. Numerical solutions of the relevant differential equation are given for the case where rate of uptake is a nonlinear function of the solution concentration at the root surface. The function employed is derived from a physiological relation described by Epstein and Hagen (1962). Results are compared with those obtained using a common linear approximation.

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