Perumalsamy Priyadharsini

Interactions Between Arbuscular Mycorrhizal Fungi and Potassium-Solubilizing Microorganisms on Agricultural Productivity

Microbial interaction is a key determinant of soil fertility, plant health, and crop productivity. Arbuscular mycorrhizal fungi (AMF) belonging to the phylum Glomeromycota are a ubiquitous component of most natural and agroecosystems. These fungi associate with most of the plant species and provide several benefits including better nutrition and increased tolerance to various biotic and abiotic stresses. Mycorrhizal symbiosis can affect the microbial population and their activity in the rhizosphere both qualitatively and quantitatively including mineral solubilization by microorganisms. These changes are mediated through the so-called mycorrhizosphere effect resulting from direct or indirect changes in root exudation (composition and quantity) patterns or through fungal exudates. In most instances, the interaction between AMF and nutrient-solubilizing microorganisms is synergistic resulting in stimulation of plant growth through improved nutrient acquisition and inhibition of plant pathogens. The ecological impact of AMF interactions with microorganisms involved in potassium solubilization is not well resolved compared to those involved in phosphate solubilization. Although direct studies on the interactions between AMF and potassium-solubilizing microorganisms (KSMs) on plant growth are limited, studies on plant growth-promoting microorganisms (PGPMs) and AMF do involve organisms with K-solubilizing capabilities. Evidence does exist on the influence of KSMs on mycorrhizal formation and function. Interactions between AMF and KSMs are vital in sustainable low-input crop production systems that rely on biological processes to achieve improved plant growth and yield in addition to maintaining soil fertility. This article examines the interactions between AMF and KSMs on plant growth, development, and crop productivity.

Role of Arbuscular Mycorrhizal Fungi in Alleviation of Acidity Stress on Plant Growth

Soil acidity is a major constraint for crop production worldwide as nearly half of the potential arable lands are acidic. Plant productivity in acid soils is limited by toxic levels of aluminum (Al), manganese (Mn), and iron (Fe) as well as deficiencies of plant available nutrients, especially phosphorus (P). Plants have developed several morphological, biochemical, and physiological adaptations against acidity stress. Among these, symbiosis with arbuscular mycorrhizal (AM) fungi is a strategy plants have evolved to survive and thrive in acid soils. The AM symbiosis increases plant growth in acid soils through enhanced uptake of nutrients. A reduction in Al and Mn phytotoxicities also occurs in response to AM symbiosis through a number of mechanisms such as binding of the toxic ions by the fungal hyphae, vesicles or auxiliary cells, exudation of organic acids, phosphatases, and production of glomalin. However, like plants, AM fungal species and ecotypes also vary to a great extent in their tolerance and ability to impart plant growth benefits in acid soils. It is, therefore, essential to identify suitable AM fungi that could confer tolerance and render maximum benefits to crops in acid soils.

Arbuscular mycorrhizal and dark septate fungal associations in shallot (Allium cepa L. var. aggregatum) under conventional agriculture

Arbuscular mycorrhizal and dark septate fungal associations in shallot (Allium cepa L. var. aggregatum) under conventional agriculture We examined roots of the shallot (Allium cepa L. var. aggregatum), one of the most popular cultivated crops of the family Aliaceae, cultivated under conventional agriculture for arbuscular mycorrhizal fungal (AMF) and dark septate fungal endophyte (DSE) associations. All the plants had dual colonization of both AMF and DSE associations. The intermediate-type AMF morphology in the shallot is the first report of this AMF type for the family Aliaceae. The extents of total AMF and DSE colonization ranged from 20.7 to 67.3% and 3.6 to 35.3% respectively and varied significantly among fields. Though no significant relationship existed between total AMF and DSE variables, they were correlated to the soil variables. Significant correlations existed between soil P and microscelerotia and also between soils N and K and AMF spore numbers. A total of six AMF spore morphotype belonging to Glomus and Scutellospora were identified. Scutellospora calospora was the most dominant morphotype in the studied fields.

Arbuscular Mycorrhizal (AM) and Dark Septate Endophyte (DSE) Fungal Association in Lycophytes and Ferns of the Kolli Hills, Eastern Ghats, Southern India

Abstract We examined the extent and type of arbuscular mycorrhizal (AM) and dark septate endophyte (DSE) fungal associations in three lycophyte and 44 fern species collected from three different sites in the Kolli Hills, Eastern Ghats, southern India. Of the 47 plant taxa (belonging to 21 families and 33 genera) examined, 46 had AM fungal and 33 had DSE fungal associations. But, fungal structures were absent in the aquatic fern Azolla pinnata (Azollaceae). This is the first report of AM and DSE fungal status for 16 and 28 species, respectively. Among terrestrial lycophytes and ferns, 26 species had dual association of both AM and DSE fungi, whereas 11 species had only AM fungal association. Vittaria elongata from epiphytic habitats had dual association of AM and DSE fungi. Likewise, Cheilanthes tenuifolia (saxicolous or terrestrial), Cheilanthes opposita, Lepisorus nudus, Pyrrosia lanceolata (terrestrial or epiphytic), and Asplenium lanceolatum (saxicolous or epiphytic) examined from different sites or habitats also had dual association of AM and DSE fungi. Seventy two percent of the mycorrhizal lycophytes and ferns had intermediate-type AM and 15 percent had both Paris- and intermediate-types at different sites. Significant variations in AM fungal structures were evident in 16 ferns occurring in two or more sites. Nine AM fungal spore morphotypes belonging to Acaulospora, Funneliformis, Glomus, Gigaspora, and Sclerocystis were found to be associated with lycophytes and ferns.

In vitro asymbiotic seed germination, mycorrhization and seedling development of Acampae praemorsa (Roxb.) Blatt. & Mc Cann, a common south Indian orchid

Abstract Objective To develope a conservation strategies for orchid species. Methods Seeds of Acampae praemorsa (Roxb.) Blatt. Mc Cann ( A. praemorsa ) were obtained from mature pods collected from Velliangiri hills and germinated on Murashige and Skoog (MS) medium supplemented with various concentration of Benzylaminopurine (BAP). Results Maximum seed germination (85%) was observed on MS media supplemented with 2 mg/L BAP. Seed germination percentage increased with increasing concentrations of BAP (0.5 mg/L to 2 mg/L), but 3 mg/L of BAP inhibited seed germination. Variations observed were significantly ( P ex vitro conditions. Conclusions In present study all the mycorrhizal seedlings survived, because orchid mycorrhizal fungi enhance growth of orchid plantlets and present study gives an effective protocol for seed germination and plantlet regeneration from immature seeds which can be used for establishing A. praemorsa populations in Velliangiri Hills and elsewhere.

A new species of Malaxis (Orchidaceae: Epidendroideae) from the Southern Western Ghats, India

A new species, Malaxis nilgiriensis, is described and illustrated based on the material collected from the Nilgiris of Western Ghats, southern India. It superficially resembles Malaxis versicolor but differs by the presence of a pseudobulb and stolon, a short inflorescence, and a lip slightly bilobed with four retuse teeth. The taxonomic phenology of the new species as well as its etymology, conservation status, and diagnostic features are discussed.

Occurrence of Foliicolous Parasitic Alga Cephaleuros Virescens on Cultivated Ornamental Plants in Southern India

Abstract The algal leaf spot, caused by Cephaleuros virescens Kunze, has been reported in a wide range of plant species from the tropical and subtropical areas worldwide. Investigations on the presence of algal infection mostly involved wild plants and plantation crops of economic interest. Nevertheless, limited studies have examined cultivated ornamental plants for the presence of C. virescens. During the summer and monsoon seasons of 2011 we examined ten leaves of five plants belonging to 86 ornamental plant taxa in 38 families growing in home gardens in Coimbatore, Tamil Nadu, India for the algal presence. Nine of the 86 plant taxa were found to host the algae C. virescens. Although majority of the investigated species are considered as typical hosts of C. vi-rescens, its infection was found only in nine plant species. Although the incidence of the algal leaf spot disease was in general low, there was significant variation in the frequency of occurrence of the algal lesions and the lesion size among the investigated plant taxa and seasons. On plants of five species (Alpinia purpurata, Ficus benjamina, Ficus elastica “Variegata”, Michelia champaca, Polyalthia longifolia), C. virescens was found during both seasons, while infections on the remaining four species (Aglaonema commutatum, Dieffenbachia maculata, Eucalyptus globulus, Syngonium podophyllum) were observed only during the monsoon. The susceptibility of different plant species in a genus and varieties of a species varied suggesting the host influence on the development of infections in addition to variation attributed to the local environmental conditions.

Arbuscular Mycorrhizal Fungal Strains and Soil Type Influence Growth, Nodulation, and Nutrient Uptake of Casuarina equisetifolia

The effects of arbuscular mycorrhizal (AM) fungal species and strains on seedling growth and uptake of nutrients were determined for Casuarina equisetifolia under nursery conditions. Seedlings of C. equisetifolia were inoculated individually with four strains each of Acaulospora scrobiculata and Glomus aggregatum in two soil types (alfisol and vertisol). Seedling height, root collar diameter, nodulation, dry weights, nutrient contents, nutrient uptake efficiencies, mycorrhizal inoculation effect (MIE), and seedling quality were determined at harvest. Seedlings inoculated with different AM fungal strains invariably had significantly higher plant growth, and nutrient parameters measured. Nevertheless, the response was higher for seedlings inoculated with strains of G. aggregatum compared to those inoculated with strains of A. scrobiculata. The mycorrhizal response as measured by MIE was significantly affected by soil types. These results suggest the importance of selecting a specific AM fungal strain suited for a soil type in forest nurseries for the production of high-quality seedlings.