Shipra Singh

Diversity of arbuscular mycorrhizal fungi associated with the rhizosphere of tea growing in ‘natural’ and ‘cultivated’ ecosites

The colonization and diversity of arbuscular mycorrhizal fungi (AMF) associated with the rhizosphere of tea [Camellia sinensis (L.) O. Kuntze] growing under ‘natural’ as well as ‘cultivated’ conditions in the Kumaun region of Uttaranchal Himalaya (India), during the periods of active growth and dormancy were investigated. Root and rhizosphere soil samples, collected from both the ecosites (natural and cultivated), were monitored for root colonization. While the percent root colonization was quite high (77.66 ± 4.40 and 86.40 ± 3.02%, in the natural and cultivated tea, respectively) during the period of active growth in both the ecosites, relatively higher colonization (97.33 ± 0.78 and 98.13 ± 0.80%, in the natural and cultivated tea, respectively) was recorded during the period of dormancy. The rhizosphere of cultivated tea bushes was found to be dominated by Glomus morhpotypes (88.89% of the total isolates) along with three morphotypes of Acaulospora; occurrence of 35 morphotypes belonging to four genera viz. Acaulospora (11.43%), Gigaspora (11.43%), Glomus (68.57%) and Scutellospora (8.57%) was recorded in the rhizosphere of tea plants from the natural ecosite. A total of 51 AMF morphotypes were detected. Shannon–Weaver index of diversity was higher (1.80 ± 0.13 and 2.05 ± 0.10 during periods of active growth and dormancy, respectively) at the species level for the natural ecosite over its counterparts from the cultivated ecosite. Values for the diversity indices of natural and cultivated ecosites did not show much variation in the period of dormancy. These data suggest that collectively, various cultural practices negatively affect AMF diversity at the genus level in tea plantations of the colder regions.

General microflora, arbuscular mycorrhizal colonization and occurrence of endophytes in the rhizosphere of two age groups of Ginkgo biloba L.of Indian Central Himalaya

The populations of the general microflora (bacteria, actinomycetes and fungi) in the rhizosphere and their corresponding non-rhizosphere soil samples of Ginkgo biloba L. of two age groups (Group A, <25 years-young trees; Group B, >60 years-old trees) growing under a temperate location of Indian Himalayan Region (IHR) have been determined. Observations were also made for the diversity, distribution and colonization of arbuscular mycorrhizal (AM) fungi and occurrence of endophytes in roots of G. biloba. The population of general microflora was found to be higher in the rhizosphere of Group B trees, more clearly reflected in terms of rhizosphere: soil (R:S) ratios. Contrary to this, per cent colonization and spore densities of AM fungi were higher in the rhizosphere of Group A trees as compared to the rhizosphere of Group B. AM fungal colonization was observed mostly in form of loose coils. All the spores detected, belonged to the genus Glomus with five different types. Presence of endophytes (both bacteria and fungi) was observed in the cortical cells of G. biloba roots, more profound in case of Group B trees. Data suggest that, while the species of Glomus dominated the rhizosphere of G. biloba, an inverse correlation exist between the colonization of general microflora and the colonization of AM fungi including endophytes.

Tripartite Association Among Plant, Arbuscular Mycorrhizal Fungi and Bacteria

Most plant roots are colonized by arbuscular mycorrhizal (AM) fungi and their presence, generally, stimulates plant growth. In addition, AM fungi can interact with different bacterial species establishing a tripartite association and represent a vital component in the plant ecosystem. These interactions may range from loose to endosymbiotic association. In context of AM fungi, interaction with host plant is long been studied, however, information is little on the mechanisms controlling interaction of bacteria with AM fungi and host plant in the mycorrhizosphere. Understanding the interaction between AM fungi and bacteria is essential for describing the soil-plant interface. Although there are several studies concerning interactions between AM fungi and bacteria, the underlying mechanisms behind these associations are in general not very well understood, and their functional properties still require experimental confirmation. Modern tools of molecular biology and genome sequencing have solved the questions about the identity and role of bacteria associated with AM fungi. In this chapter, different aspects of tripartite association among plant, AM fungi and bacteria are discussed with greater emphasis on associated bacterial component.

Dendrocalamus strictus ((Roxb.) Nees): A Suitable Host for the Maintenance and Propagation of AM Fungi under Temperate Conditions

Dendrocalamus strictus ((Roxb.) Nees) was tested as a perennial host plant for propagation of an arbuscular mycorrhizal (AM) fungal consortium, initially isolated from rhizosphere of tea plants growing in the colder regions. The host performance in terms of colonization and spore production was compared with two annual hosts. The mycorrhizal dependency and growth enhancement potential were analyzed to test the suitability of D. strictus as a host plant. After 90 days of growth, 77.2% roots of D. strictus were found to be colonized by AM fungi with a spore count of 7 per g soil. AM fungal colonization and spore density values were lower in case of the host plants tested. Growth of D. strictus plants was found to be enhanced, in terms of all studied parameters; significant increases were recorded in shoot length as well as fresh and dry weight of shoots, a part of commercial importance. Similarly, P content, protein concentration, chlorophyll a and chlorophyll b contents were found to increase significantly. These data suggest that D. strictus can be used for the multiplication of AM fungi, isolated originally from the rhizosphere of tea; simultaneously, higher shoot biomass can provide additional economic benefit, using this environment friendly technology.