Colonization dynamics of arbuscular mycorrhizal fungi (AMF) in Ilex paraguariensis crops: Seasonality and influence of management practices

The yerba mate (Ilex paraguariensis St. Hill.) is a native species from subtropical regions of Argentina, Brazil, Paraguay and Uruguay. Arbuscular mycorrhizal fungi (AMF) are symbiotically associated with 82% of the vegetable species including crops of economic importance. The aim of the present study was to determine the association of yerba mate with AMF growing in natural and crop conditions, and to evaluate the influence of tillage practices and seasonality on root colonization. We selected five situations ranging from old systems to recent implementations with different agricultural managements and intensity of tillage, as reference native trees were analyzed. Root samples of yerba mate were extracted in winter and summer during the years 2013–2014. The percentage of root colonization was determined. Significantly higher values of colonization were found in native trees. Regarding seasonality, significantly higher values on the total mycorrhizal colonization were observed in winter. Organic matter and nitrogen were the soil factors that showed significant correlation with the percentage of colonization. This work confirms the association of I. paraguariensis with AMF, showing that yerba mate is a host species under both crop and natural conditions. Even though crop management of yerba mate is compatible with the symbiosis, it affects the colonization negatively.Fil: Velázquez, María Silvana. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Botánica Spegazzini; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Juan Carlos, Fabisik. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Abarca, Camila Lucía. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Botánica Spegazzini; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Allegrucci, Natalia. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Botánica Spegazzini; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Cabello, Marta Noemí. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Botánica Spegazzini; Argentin

Pythium species from rice roots differ in virulence, host colonization and nutritional profile

Background: Progressive yield decline in Philippine aerobic rice fields has been recently associated with three closely related Pythium spp., P. arrhenomanes, P. graminicola and P. inflatum. To understand their differential virulence towards rice seedlings, we conducted a comparative survey in which three isolates each of P. arrhenomanes, P. graminicola and P. inflatum were selected to investigate host colonization, host responses and carbon utilization profiles using histopathological analyses, phenoarrays, DNA quantifications and gene expression studies. Results: The isolate of the most virulent species, P. arrhenomanes, quickly colonized the outer and inner root tissues of rice seedlings, including the xylem, by which it possibly blocked the water transport and induced severe stunting, wilting and seedling death. The lower virulence of the tested P. graminicola and P. inflatum isolates seemed to be reflected in slower colonization processes, limited invasion of the vascular stele and less systemic spread, in which cell wall fortification appeared to play a role. Progressive hyphal invasions triggered the production of reactive oxygen species (ROS) and phenolic compounds, which was the strongest for the P. arrhenomanes isolate and was delayed or much weaker upon inoculation with the P. inflatum isolate. The necrosis marker OsJamyb seemed faster and stronger induced by the most virulent isolates. Although the isolate of P. inflatum was nutritionally the most versatile, the most virulent Pythium isolate appeared physiologically more adapted to its host, evidenced by its broad amino acid utilization profile, including D-amino acids, L-threonine and hydroxyl-L-proline. The latter two compounds have been implicated in plant defense and their use by P. arrhenomanes could therefore represent a part of its virulence strategy. Conclusions: This study illustrates that the differential virulence of rice-pathogenic P. arrhenomanes, P. graminicola and P. inflatum isolates is related to their root colonization capacity, the intensity of induced root responses and their ability to utilize amino acids in their colonization niche. Accordingly, this paper presents important knowledge concerning rice root infections by oomycetes, which could be helpful to further disentangle virulence tactics of soil-borne pathogens

Suitability of Mycorrhiza-Defective Rice and Its Progenitor for Studies on the Control of Nitrogen Loss in Paddy Fields via Arbuscular Mycorrhiza

Employing mycorrhiza-defective mutants and their progenitors does not require inoculation or elimination of the resident microbial community in the experimental study of mycorrhizal soil ecology. We aimed to examine the suitability of mycorrhiza-defective rice (non-mycorrhizal, Oryza sativa L., cv. Nipponbare) and its progenitor (mycorrhizal) to evaluate nitrogen (N) loss control from paddy fields via arbuscular mycorrhizal (AM) fungi. We grew the two rice lines in soils with the full community of AM fungi and investigated root AM colonization. In the absence of AM fungi, we estimated rice N content, soil N concentration and microbial community on the basis of phospholipid fatty acids; we also quantified N loss via NH3 volatilization, N2O emission, runoff and leaching. In the presence of AM fungi, we did not find any evidence of AM colonization for non-mycorrhizal rice while mycorrhizal rice was colonized and percentage of root colonization was 17–24%. In the absence of AM fungi, the two rice lines had similar N content, soil N concentration and microbial community. Importantly, there was no significant difference in N loss via all the four pathways between mycorrhizal and non-mycorrhizal systems. This mycorrhizal/non-mycorrhizal rice pair is suitable for further research on the role of AM fungi in the control of soil N loss in paddy fields

Striga seed-germination activity of root exudates and compounds present in stems of Striga host and nonhost (trap crop) plants is reduced due to root colonization by arbuscular mycorrhizal fungi.

Root colonization by arbuscular mycorrhizal (AM) fungi reduces stimulation of seed germination of the plant parasite Striga (Orobanchaceae). This reduction can affect not only host plants for Striga, resulting in a lower parasite incidence, but also false hosts or trap crops, which induce suicidal Striga seed germination, thereby diminishing their effectiveness. In order to better understand these AM-induced effects, we tested the influence of root colonization by different AM fungi on the seed-germination activity of root exudates of the Striga hermonthica nonhost plants cowpea and cotton on S. hermonthica. We also tested the effect of AM fungi on the seed-germination activity of the Striga gesnerioides host plant cowpea on S. gesnerioides. Moreover, we studied whether mycorrhization affects the transport of seed-germination activity to above-ground plant parts. Mycorrhization not only resulted in a lower seed germination of S. gesnerioides in the presence of root exudates of the S. gesnerioides host cowpea but also seed germination of S. hermonthica was also lower in the presence of root exudates of the S. hermonthica nonhosts cowpea and cotton. Downregulation of the Striga seed-germination activity occurs not only in root exudates upon root colonization by different AM fungi but also in the compounds produced by stems. The lowered seed-germination activity does not appear to depend on the presence of seed germination inhibitors in the root exudates of mycorrhizal plants. The implication for Striga control in the field is discusse

Arbuscular mycorrhizal fungal symbiosis with Sorbus torminalis does not vary with soil nutrients and enzyme activities across different sites

Effects of soil chemical properties on arbuscular mycorrhizal fungal (AMF) symbiosis with wild service tree (Sorbus torminalis L. Crantz) were examined for study the rates of root colonization at three forest sites: Kheiroud, Lalis, and Takrin in northern Iran. Soil characteristics including pH, available phosphorus (P), potassium (K), organic matter, total nitrogen, acid and alkaline phosphatase activities, CaCO3, spore density (SD) and AMF colonization of soil and root samples were analyzed. The study sites were investigated in spring and autumn to highlight the effects of soil chemical properties on AMF statues for better nurseries and reforestation management of this rare tree species in forests. Changes in soil pH, P, K, organic matter, total nitrogen, acid and alkaline phosphatase, CaCO3, SD, and AMF colonization of soil and root samples were analyzed at the study sites. K, pH, root colonization, SD and acid phosphatase activity showed no significant differences among sites in spring and autumn, while total nitrogen, P, organic matter and alkaline phosphatase activities showed significant differences among sites and seasons. AMF colonization rates were more than 51% and 32% of roots in spring and autumn, respectively. No correlation between root colonization and soil chemical parameters in spring and autumn were detected. There was no correlation between percentage of AM root colonization and SD nor other soil parameters in spring and autumn. SD and CaCO3 were significantly negatively correlated in spring and autumn. Despite differences in soil characteristics, the results showed that SD and root colonization were not significantly different among the sites. They also showed that wild service trees had strong symbiosis with AMF, while soil properties might not have a significant effect on this symbiosis. Therefore, colonized seedlings can be considered as an appropriated method for reforestation and conservation of this rare tree species

Plant host selectivity for multiplication of Glomus mosseae spore

The study aimed to select plant host for multiplication of Glomus mosseae spores. Five plant species were used [(corn, (Zea mays) sorghum, (Sorghum bicolor) lentil, (Lens culinaris), barley, (Hordeum vulgare) and green bean, (Phaseolus vulgaris)]. Plants were inoculated with Glomus mosseae and grown for 75 days under glasshouse conditions. Mycorrhizal sporulation and colonization of all plant hosts were assessed at different sampling periods. At 75 days of growth the highest number of Glomus mosseae spores was found in mycorrhizosphere of corn plant (167 spore/10 g soil), while the lowest in the mycorrhizosphere of barley (35 spore/10 g soil). The highest percentage of root colonization was in corn (76%), while the lowest colonization was found in green bean (24%). Corn was the most suitable host for spore production of Glomus mosseae and to extensive root colonization. It was recorded that plants having more colonization percentage were able to produce more Glomus mosseae spores. The study indicated that different plant species significantly influenced the root spore production and root colonization percentage of Glomus mosseae

Role of edaphic factors on VAM fungal colonization and Spore populations in certain tropical wild legumes

Four nodulating annual tropical wild legumes, viz., Alysicarpus monilifer, Desmodium triflorum, Indigofera linnaei and Tephrosia purpurea from three different regions in the Western Ghats ecosystem were investigated to assess their mycorrhizal status. The response ofvesicular-arbuscular mycorrhizal (VAM) root colonization and spore number to edaphicfactors such as soil moisture, pH and available Nand P was analysed. Though the spore number varied significantly both within and between sites, a uniformly high degree ofroot colonization was observed for all the plants in the present study. The spore number recorded was high, rangingfrom 15 to 165 spores gl soil. Spores of sixteen VAM fungal species belonging to Acaulospora, Glomus and Scutellospora were isolated from the rhizosphere soils. Soil moisture generally had a positive influence on VAM colonization and sporulation except in I. linnaei. The pH correlated negatively with root infection in I. linnaei and T. purpurea, but had no influence in the other two species. The effect of 2-pH on sporulation varied with host species and sites. No general correlation existed between available soil nutrients, root colonization and spore number but the influence ofNand P was counteractive on VAM infection. The present study indicates that the response of root colonization and spore number to edaphic factors is a localised rather than a generalised phenomenon

Tripartite symbiosis of Lentil (Lense culinaris L.), Mycorrhiza and Azospirillum brasilense under Rainfed Condition

A field experiment was conducted aiming to determine the possibility of improving the lentil performance when co-inoculated with Vesicular Arbuscular Mycorrhiza (VAM) fungi and Azospirillum under natural rain-fed conditions, in Iran. Results showed the substantial impact of VAM fungi on grain protein, root colonization and shoot dry weight. Highest value for shoot dry weight recorded in plants which inoculated with G. intraradices and highest values for root colonization and grain protein content was observed in plants which inoculated with G. mosseae. Also, Azospirillum had a significant effect on shoot dry weight and root colonization. A significant differences on grain protein content observed when combination of both microorganisms have been used

Tamarind (Tamarindus indica L.) parkland mycorrhizal potential within three agro-ecological zones of Senegal

Introduction. Tamarind (Tamarindus indica L.) belongs to the Fabaceae family; it is a multipurpose tree with slow growth. In order to help improve its growth and development, we assessed mycorrhizal diversity of tamarind parklands in Senegal. Materials and methods. Three sites of tamarind populations were sampled for each agro-ecological zone in Senegal: the Sahelian zone (i), Sahelo-Sudan zone (ii) and Sudan zone (iii). Soil and root samples were collected in each site and used for arbuscular mycorrhizal (AM) spore isolation and root colonization assessment. We identified the mycorrhizal fungi from spore collections and evaluated the root mycorrhization rate, defined as percentage of roots colonized according to agro-ecological zones. Results and discussion. The results did not reveal a specific AM fungal strain associated with tamarind plants. Three arbuscular mycorrhizal fungi (AMF) were identified from spores on the genus level: Glomus, Scutellospora and Acaulospora. Tamarind sites with sandy soil texture (70-90%) and located in dry areas (Sahel and Sudano-Sahel zones) were shown to be rich in mycorrhizal propagules. High densities of soil AM propagules evaluated with the Most Probable Number method (MPN) were found in Niokhoul (1100 propagules per 50 g of soil), Sakal (790 propagules per 50 g of soil) and Mbassis (780 propagules per 50 g of soil). However, higher mycorrhizal colonization (11%) was observed in the Sahel agro-ecological zone compared with the Sudano-Sahelian and Sahelian zones (3%) of Senegal. Conclusion. Our study explored natural AMF diversity as a starting point to develop inocula to be used in commercial nursery production of tamarinds

Colonization Ability of Biological Control Agent Tricoderma Spp on Cocoa Pod and Seedling

Some of Trichoderma species as antagonistic fungi are usually considered soil microorganism, They colonize plant roots, some- times forming a symbiotic relationship. Three species of Trichoderma (T. virens, T. harzianum and T. asperellum) have been inoculated on cacao seedling and cocoa pod. Trichoderma species can be re-isolated from surface sterilized cacao seedling, including the stem and leaf, root, and pod then observed their colonization ability. Fungal hyphae were observed under the microscope emerging from the leaf, steam, root of seedling and pod as soon as 1 day after their isolation from surface sterilized cacao seedling and pod. All Trichoderma species were able to enter and make colonization. The highest percentage of colonization occurred in the T. harzianum by 73.3% (leaves), 46.7% (trunk) and 86.7% (roots). While colonization on the skin cocoa pod (epidermis) also has a different percentage, the highest percentage indicated in the treatment of T. harzianum by 63.3%. We conclude that T. harzianum better biological control agent base on their ability to colonize all part of seedling and pod. Trichoderma species into the cacao stem, leaf, root and pod allowing systemic colonization of this tissue