Occurrence and distribution of Arbuscular Mycorrhizal Fungi in agricultural fields of Mysore.

Transcription

1 World Journal of Science and Technology 2012, 2(2):01-07 ISSN: Available Online: Occurrence and distribution of Arbuscular Mycorrhizal Fungi in agricultural fields of Mysore. Sunil kumar C.P., Seema H.S and Rajkumar H. Garampalli * Department of Studies in Botany, University of Mysore, Manasagangotri, Mysore , Karnataka, India. Abstract Occurrence and abundance of arbuscular mycorrhizal fungi in the agricultural fields in and around Mysore district was studied. Almost all the sampling sites belong to semi-arid region. Most of the crops growing in this region were sampled. AMF percent colonization and spore density and species richness was assessed. Soil samples exhibit varied physico-chemical parameters which correlates with AMF percent colonization and spore count. Four AMF genera namely Glomus, Acaulospora, Gigaspora and Scutellospora were identified by spore morphological characteristics. A total of about 45 AMF morphotypes were observed. Among 45 species 6 species were could not able to identify. Genus Glomus was found to be very dominant by exhibiting 19 species followed by Acaulospora of about 10 species. Spore count and species richness was found higher in host plants like maize and sorghum. Higher percent colonization, spore density and species richness were found in samples like YLDR, KRN and HNSR which were collected from irrigated agricultural fields. Keywords: AM fungi, Diversity, Semi-arid region, Soil parameters. INTRODUCTION The Arbuscular Mycorrhizal fungal (AMF) symbiosis is the most widespread symbiosis between a plant and fungi (Smith & Read 1997). In this symbiosis, the host plant provides the fungus with soluble carbon sources, at the same time the fungus enhances the uptake by plants of certain nutrients, particularly phosphate (Jayachandran & Shetty 2003), increase resistance against soil pathogens (Newsham et al. 1995; Lingua et al., 2002), stabilize of soil aggregates (Miller & Jastrow1990) by producing the glycoprotein Glomalin (Wright and Upadhyaya1998), alleviate abiotic (Goicoechea et al. 1997) and biotic stress (Jaizme-Vega et al. 1997), and modify root morphology (Berta et al. 1990a). AMF are among the most ecologically significant organisms on the planet (Fitter etal.2011) since they act as a living connection between soil and plants, influencing soil fertility and plant nutrition, diversity and productivity (Smith and Read 2008; van der Heijden et al. 1998a). By forming an extended intricate hyphal network, AMF can efficiently absorb mineral nutrients from soil and deliver them to their host plants in exchange for carbohydrates. AMF can also enhance tolerance of abiotic stresses such as drought and metal toxicity (Meharg & Cairney 2000). Therefore it is evident that AMF are an important associate for crop plants in sustainable agriculture. Influence of arbuscular mycorrhizal fungi on agro-ecosystems and crop plants have been observed and acknowledged by many researchers. Enhanced uptake of P (phosphate) is generally regarded as the most important benefit that AMF provide to their host Received: Dec 15, 2011; Revised: Jan19, 2012; Accepted: Feb 18, *Corresponding Author Rajkumar H. Garampalli Department of Studies in Botany, University of Mysore, Manasagangotri, MYSORE , Karnataka, India. Tel: ; Fax: rajkumarhg@yahoo.co.in plant, and plant P status is often the main controlling factor in the plant fungal relationship (Thompson 1987; Graham 2001), AMF may also enhance plant uptake of N from organic sources (Hodge et al. 2001), this may be associated with increased growth and yield of host plants (van derheijden 1998b; Earanna et al. 2002; Rajan et al. 2004; Nisha & Rajeshkumar 2010). It is also observed that, if colonization by AMF is disrupted, uptake of P, growth and in some cases yield can be significantly reduced (Thompson 1994).Also there is considerable evidence to suggest that AMF are able to increase the host plant s tolerance to water stress (Davies et al.2002; Auge et al. 2004) including that caused by high salinity (Al-Karaki et al. 2001). Therefore the above aspects suggested that the diversity and community structure of AMF were important both in sustaining the stability of the plant community and reestablishing vegetation in disturbed arid and semi-arid ecosystems. But the major factors affecting the diversity, abundance and distribution of Arbuscular Mycorrhizal Fungi in agricultural fields are soil ph, higher content of Phosphorous, Nitrogen, Organic matter, Water stress etc. Among them water deficit and soil nutrients imbalance are the most common stresses affecting the diversity, abundance of AM fungi in arid and semi-arid regions. These factors could also affect the crop production in different in agro ecosystems (Porras-Soriano et al. 2009). Agricultural practices like tillage (Anderson et al. 1987) and irrigation also had impact on AMF diversity. Arbuscular mycorrhizal fungal diversity was found quite low in fields of green gram in South India, which may be attributed to conventional tillage (Vasalkumar et al. 2007). Water availability has been recognized as the most critical determinant of crop productivity in agro ecosystems (Abbott & Robson 1991). However, seasonal variations could also affect the species richness of AM fungi. Karthikeyan & Selvarajan (2009) reported that species richness was highest during summer and late summer seasons and they were significantly correlated with soil ph, soil calcium, phosphorous and percent root colonization. Similarly the highest number of AMF spores was found in rainy season while moderate in winter and least in summer (Nisha et al. 2010). Similar

2 2 observations reported by Khade & Rodrigues (2008) where colonization of AM fungi in Carica papaya exhibiting variations depending on edaphic factors and seasonal patterns in the weather. From all these aspects it is apparent that AMF diversity in agricultural ecosystems was under risk of annihilation. Therefore it is essential to evaluate the occurrence of AMF in agro ecosystems and the viable effects of different agro climatic circumstances on their diversity pattern. So there is need to develop AMF management strategies applicable for sustainable low input but reasonably productive and sound agriculture, as they are fundamental for the functioning of terrestrial ecosystems, plant health and performance. In the present work we undertook a survey to evaluate the diversity of AM fungi from agricultural fields in and around Mysore district of the Karnataka state in India. MATERIALS AND METHODS Study site The study site lies in southern part of Karnataka state. Mysore is at 770m above sea level and 140kms from Bangalore. It has an area of 6,268 sq kms, geographically lies 11 30' N to 12 50' N latitudes and 75 45' E to 77 45' E longitudes. Average rainfall annually is around 86 centimeters. Most of the Mysore area is semiarid region. Majority of the agricultural systems depend on monsoon, except few regions are well facilitated with river water and tube well irrigation. As the region identified as semi-arid, the major food crops Sunil Kumar CP et al., of this region are Paddy,, Sorghum, Ragi, Tobacco and few other vegetable crops. Collection of Soil and Root samples The rhizospheric soil and root samples were collected from crop plants in and around Mysore district, South Karnataka in the month of February- March Totally 9 sampling sites are noted (Table 1). Approximately 500 g of rhizosphere soil from each site were collected. The samples were taken from a particular plant block covering an area of 100m 2 were collected randomly from a depth of 10-30cm from different plants. Soil particles adhered to fine roots were removed by generous shaking and roots connected to each sampled plant were also collected to quantify their arbuscular mycorrhizal status and were stored in std. FAA solution to assess percent colonization. The soil samples were combined to make the composite samples, which were air dried and stored at 4 0 c. Analysis of Soil chemical properties Collected soil samples were divided into two subsamples for chemical analysis and spore isolation. Subsamples were air-dried for 2 weeks and stored at 4 C. Examination of soil physico-chemical properties were done at CSRTI (Central Sericultural Research and Training Institute) Mysore. Analysis results were shown in Table 1. Table 1. Sampling sites, host plants and Soil analysis report of samples collected from Mysore district. Sl. No. Sample Name Standing crop at the time of sampling 1 MYS (Mysore) (Zea mays L.) 2 HNSR Capsicum (Hunsur) (Capsicum annum L.) 3 PRPT (Piriyapattana) (Zea maysl.) 4 KRN Tomato (K.R.Nagar) (Solanum lycopersicum L.) 5 GPT Sorghum (Gundlupet) (Sorghum bicolor L.) 6 BGR Pigeon pea (Begur) (Cajanus cajan(l.) Millsp.) 7 CHN (Chamarajanagar) (Zea mays L.) 8 YLDR (Yelandur) (Zea mays L.) 9 NJD Sorghum (Nanjangudu) (Sorghum bicolor L.) Assessment of AM fungal colonization ph EC Mmhos/cm OC (%) Available P (kg/ha) Available K (kg/ha) Isolation and Identification of AM fungal spores Percent colonization of AM fungi in crop plants was determined according to the procedure described by Phillips & Hayman (1970). The roots were boiled in 10% KOH for 1hour, acidified with 5N HCL and stained overnight with 0.5% trypan blue. Excess stains of the roots were destained with lactophenol. The assessment of mycorrhizal infection was done by the slide method; root segments were selected randomly from the stained samples and observed for the presence or absence of functional structures (Mycelium, Arbuscules and Vesicles) of AM fungi. A minimum of 100 root segments were used for this enumeration and the colonization by AM fungi was calculated using the following formula; Spores of AM fungi spores were isolated by following wet sieving and decanting method (Gerdemann & Nicolson 1963). 100gms of soil was suspended in tap water and allowed to settle for few minutes and the supernatant was decanted through stacked sieves. The sieve sizes ranged from µm. Spores from bottom sieve and middle were collected on Petri dish and counted under stereozoom microscope (Labomed-CZM6). Spores were then mounted on clean glass slide in PVLG (polyvinyl alcohol + Lactic acid + Glycerol), for identification of AM fungal species. Spores were photographed and identified up to species level by consulting suitable keys (Schenck & Perez 1990) and also by visiting the INVAM website which provides photographs and species description (

3 World Journal of Science and Technology 2012, 2(2): Statistical analysis Ecological measures of diversity used to describe the structure of AMF communities included spore density, species richness, relative abundance, isolation frequency, Shannon Wienerindex of diversity, evenness, Simpson s index of diversity and Sorenson s coefficient (Zhao & Zhao 2007) (Table 1). The value of this index also ranges between 0 and 1, but now, the greater the value, the greater the sample diversity. Spore density reflected the biomass of AMF species, at least to some extent. The Pearson correlation coefficient was employed to determine the relationships between spore density, species richness and percent colonization. This was determined by using SPSS software (Version16.0). Table 2. Percent colonization, Spore density, Species richness, Shannon Wiener index and Simpson s index of diversity of AMF in collected samples. Sample name % colonization Spore density/ 100gm of dry soil Species richness Shannon Wiener index Simpson's index of diversity MYS HNSR PRPT KRN GPT BGR CHN YLDR NJD Fig 1. AMF Percent colonization and Spore density/100 gm of soil Table 3. Pearson s Correlation coefficient (Two tailed) between Percent colonization, Spore density (SD) and Species richness (SR). %Colonization SD SR %Colonization (0.124) (0.131) SD 0.551(0.124) (0.310) SR (0.131) (0.310) 1 RESULTS Soil chemical analysis Physio-chemical parameters of collected soil samples were given in Table 1. Diverse range of ph was observed as higher in MYS and NJD (8.11 and 8.10 respectively), which is considerably alkaline. Lowest ph was recorded in BGR and GPT (6.08 and 6.11 respectively), which is acidic in terms of significance. Apart from these other samples possessed normal or average range of ph. Highest electrical conductivity (EC) was observed only in samples of MYS. Highest organic carbon (OC) was observed in PRPT i.e kg/ha, lowest OC recorded in NJD and GPT samples. Highest available Phosphorous was found in samples of MYS and CHN (73.63 and kg/ha respectively). Potassium content was also found very high in MYS sample (1837 kg/ha) followed by CHN (762 kg/ha)(table1). Percent colonization, Spore density and Species richness Rate of percent colonization of AMF in roots of host plants was assessed. Of all the nine root samples, highest AMF percent colonization was observed in samples of YLDR (99%), KRN (95%), GPT and NJD both about 90% (Fig 1). Lowest root colonization was detected in BGR (70%), in pigeon pea host plant. Almost all the samples exhibit higher spore density/100 gm of soil. Among nine samples highest spores were recovered from KRN sample (824 spores/100gm of dry soil), followed by CHN (802 spores) and HNSR (716). Lowest spores were procured from BGR sample (479 spores) where pigeon pea is the host plant (Table 2). There were about 45 AMF spore types recovered from all nine samples, among that 6 species were designated as unidentified species. Among 39 identified AMF taxa 19 species were belonged to genus Glomus, ten species belonged to genus Acaulospora, five species were belonged to Gigaspora and five species belonged to genus Scutellospora (Table 4). Species richness was highest in the YLDR (28 sps) where maize is the host plant, followed by HNSR (23sps) tomato host plant

4 4 and NJD (20sps) where sorghum was the host plant (Table 2). Isolation frequency [IF], Relative abundance [RA] and Diversity of AMF communities. Among identified 39 species Acaulospora leavis and Glomus fasciculatum were widely distributed with highest rate of IF i.e. 88.8%, followed by A. bireticulata, A. myriocarpa, A. scrobiculata and G. clarum, G. mossae occurred in most of the samples i.e. 77.7% (Table 4). Whereas some other species were exhibited noteworthy relative abundance among AMF species, which reveals their sporulation capability. Glomus mossae (93.85) and G. fasciculatum (94.12) were the only two species which were shown highest relative abundance >80%. Species like G. microcarpum (57.16), A. myriocarpa (56.14) and G. aggregatum (53.66) are the other AMF species shown highest rate of sporulation among samples (Table 4).Shannon wiener diversity index of all the nine samples shows variability, where highest diversity index observed in YLDR followed by HNSR and NJD. Similarly, higher value of Simpson s index observed in NJD, YLDR, CHN and HNSR (Table 2). Correlation between Percent colonization, spore density and species richness Sunil Kumar CP et al., reveals positive correlation results, but no significant correlation was observed (Table 3). DISCUSSION Diversity of AMF communities present in the rhizospheric region of food crops was assessed. The sampling sites were differed in their agro climatic properties, mainly irrigation condition. The results of the current study indicate that AMF abundance, species richness, and species diversity were varied among different sampling sites, as some of the sites were irrigated and some were nonirrigated. First, variability in the root percent colonization was recorded among all the samples, where almost all the root samples shows healthier colonization except BGR (70%) and MYS (78%), here spore density also comparatively low (Table 2) (Fig 1). It is also important to observe the fact that in soil ph, P and K contents are much higher in this sample (Table 1). Therefore the above mentioned reasons would be responsible for the inferior spore abundance and colonization. It is well documented that rapid changes in soil nutrients may affect percent association and spore number of AM fungi (Abbott & Robson 1991). Table 4. Species Diversity, occurrence, isolation frequency and relative abundance Species MYS HNSR PRPT KRN GPT BGR CHN YLDR NJD IF (%) RA (%) Acaulospora sps 1 - X X - X X - X X Acaulospora capsicula Blaszkowski - X Acaulospora bireticulata Rothwell & Trappe X X - - X X X X X Acaulospora denticulata Sieverding & Toro - X - X - X - - X Acaulospora foveata Trappe & Janos X X X X X - X X X Acaulospora spinosa Walker & Trappe X Acaulospora rehmii Sieverding & Toro X X Acaulospora scrobiculata Trappe X X X - X - X X X Acaulospora myriocarpa Spain, Sieverding & Schenck - X X X X X - X X Acaulospora mellea Spain & Schenck - X X Glomus sps 1 X X - X X - X X X Glomus sps X - X Glomus sps 3 - X - - X - - X X Glomus aggregatum Schenck & Smith - - X - - X X Glomus ambisporum Smith & Schenck - X - X - X - X X Glomus badium Oehl, Redecker & Sieverd. - - X - X - X X Glomus clarum Nicol. & Schenck X - - X X X X X X Glomus etunicatum Becker & Gerdemann X X - - X X X X Glomus coronatum Giovannetti X - X - X X Glomus intraradices Schenck & Smith - X X - - X X X Glomus deserticola Trappe, Bloss &Menge X X - X Glomus drummondii Blaszk. & C. Renker X Glomus fasciculatum (Thaxter) Gerd. & Trappe emend. X X X X X - X X X Walker &Koske Glomus geosporum (Nicol. &Gerd.) Walker X - - X - - X X X Glomus lacteum Rose & Trappe - X - X X Glomus macrocarpum Tulasne &Tulasne X - X - X X X Glomus microcarpum Tulasne &Tulasne X X X - X - - X X Glomus mossae (Nicol. &Gerd.) Gerd. & Trappe - X X X X X X - X Glomus tortuosum Schenck& Smith - X X Gigasporasps1 - - X X Gigasporasps2 X X Gigaspora dicepens Hall & Abbott - X X X Gigaspora margarita Spain, Sieverding & Schenck X - X GigasporaroseaNicol. &Schenck X - - X Scutellospora sps1 - - X X Scutellospora sps X X Scutellospora sps 3 X X X Scutellospora cerradensis Spain & Miranda - X X X Scutellospora biornata Spain, Sieverding & Toro X X

5 World Journal of Science and Technology 2012, 2(2): U S 1 X X X U S 2 - X X U S 3 X X U S X U S X U S 6 - X - - X - - X SD = 5905 SR (* Species presence indicated by X and absence as -, SD- spore density, SR- species richness) It is well established that AM symbiosis improves phosphorus nutrition, but since the work of Sanders & Tinker (1973) and numerous experiments have also shown that increasing phosphate availability decreases the mycorrhization level, suggesting that AMF might play a minor role in natural ecosystems or agriculture fields with high P availability (Ryan & Graham 2002). Similarly CHN and BGR samples also possessed higher P content, where BGR shows most lower percent colonization, species richness and spore density among all the nine samples (Table 2), whereas, spore density and percent colonization does not seems to be affected in the sample of CHN. The standing crop of the BGR sample was pigeon pea and the sampling site was completely nonirrigated and the soil in the sampling site contains small sized rocks and silica well mixed with the soil. Highest spore density was observed in KRN sample where percent colonization is also superior, but the species richness was low compared to other samples. Here all the soil chemical parameters were normal except ph, which is slightly acidic (6.18). Sampling site is well connected with irrigation systems and host plant (tomato) was shown to sustain higher SD and PC. Maximum number of AMF species were recovered from the sample of YLDR, here percent colonization and SD was also higher than any other samples. All the soil chemical parameters of this sample were found to be normal. It is also important to note that sampling site is well irrigated site and host plant is. Several researchers have acknowledged the capability of monocots and other crop plants in the mass production of AMF inoculum and their host specificity (Douds et al. 2005; Chaurasia & Khare 2005; Bagyaraj & Manjunath 1980). They produce enormous root biomass in short period of time compared to plants grown in natural conditions, and also the production of root exudates is very less. Therefore we could assume that maize plant soil and root samples harbored large AMF population due to the above reasons. In our survey, among nine samples four samples were derived from maize host plants, because is the important crop plant in this region. Among four maize sampling sites YLDR, CHN and MYS possessed good number of spore density and root colonization. HNSR sample was also showed higher species richness (23sps) after YLDR and also a good colonization and spore density, where capsicum was the host plant. Here also all the soil chemical parameters were found to be normal. Among 45 AMF spore types, 39 were identified and in general genus Glomus was found to be dominant which accounts 19 species. Among 19 species Glomus mossae, G. clarum, G. microcarpum and G. fasciculatum are the most frequently occurred species in almost all the sample with highest rate of IF and RA (Table 4). After Glomus, genus Acaulospora occupied second place by exhibiting ten species. Further, Acaulospora bireticulata, A. foveata, A. scrobiculata and A. myriocarpa were the dominant species among genus Acaulospora with highest RA and IF in almost all the samples. By procuring highest isolation frequency and relative abundance it is evident that the above mentioned species were widely distributed in almost all the samples and better sporulation capability in their host plant. Some AM species like Acaulospora capsicula, A. spinosa, A. rehmii, A. mellea, Glomus drummondii, Glomus lacteum, Scutellospora sps. 2, S. biornata, S. cerradiensis, US2 and US5 were observed only in samples of irrigated agricultural sites. While Glomus coronatum, Gigaspora sps2 and US4 were found to occur only in non-irrigated field samples (Table 4).It is also observed that there are considerable differences between spore density and mycorrhization rate within a sample and among all the samples. Similar observations were made by Lopez-Sanchez & Honrubia (1992) suggesting that the diversity of the spores in the soil does not correlate with the mycorrhization rate. Therefore we believe that agroclimatic conditions, especially irrigation factor and soil chemical parameters have influenced the diversity of AMF in agricultural fields, which is very significant and crucial in the view of ecological and agronomical aspects, as the plant health and survival is primarily depends on these symbionts. However, soil organisms, especially fungi, have received little attention in the field of conservation biology, although they have a crucial role in producing fundamental ecosystem services such as soil fertility, formation and maintenance, nutrient cycling and plant community dynamics (Gianinazzi et al. 2010; Pringle et al. 2011; van der Heijden & Horton 2009; Wall et al. 2010).Moreover AMF contribute to the formation and maintenance of soil structure by the enmeshing action of extraradical hyphae and by the production of a protein, glomalin, which improves soil aggregates stability (Bedini et al. 2009;Gadkar et al. 2006; Wright & Upadhyaya1998). The diversity of AMF observed in this assessment was greater than that of other research findings where survey of AMF were carried out in agricultural fields and medicinal plants of India (Vasalkumar et al. 2007; Muthukumar & Udaiyan 2000; Khade & Rodrigues 2002; Karthikeyan & Selvarajan 2009; Ragupathy & Mahadevan1993). In conclusion, the observed high richness of Glomeromycota in the two types of agricultural ecosystems indicates the need to obtain comparable descriptive soil fungal community data from a more diverse range of agricultural ecosystems. This unique richness of AMF could be speculatively attributed to the agro-climatic conditions and or type of host species. REFERENCES [1] Abbott L.K., and A.D. Robson., Factors influencing the occurrence of Vesicular Arbuscular Mycorrhiza. Agriculture Ecosystem and Environment. 35: [2] Al-Karaki G.N., R. Hammad, and M. Rusan., 2001.Response of two tomato cultivars differing in salt tolerance to inoculation with mycorrhizal fungi under salt stress. Mycorrhiza. 11: [3] Anderson E.L., P.D. Millner, and H.M. Kunishi., root length, density and mycorrhizal inferction as influenced by

6 6 tillage and soil phosphorus. Journal of Plant Nutrition.10: [4] Augé R.M., D.M. Sylvia, and S. Park., Partitioning mycorrhizal influence on water relations of Phaseolus vulgaris into soil and plant components. Canadian Journal of Botany.82: [5] Bagyaraj D.J., and A. Manjunath., 1980.Selection of suitable host for mass production of VA-mycorrhizal inoculum.plant Soil. 55: [6] Berta G., A. Fusconi, A. Trotta, and S. Scannerini., 1990a. Morphogenetic modifications induced by the mycorrhizal fungus Glomus strain E3 in the root system of Allium porrum L. New Phytologist.114: [7] Bedini S., E. Pellegrino, L. Avio, S. Pellegrini, P. Bazzoffi, E. Argese, and M. Giovannetti., Changes in soil aggregation and glomalin related soil protein content as affected by the arbuscular mycorrhizal fungal species Glomus mossae and Glomus intraradices. Soil Biology and Biochemistry. 41: [8] Chaurasia B., and P.K. Khare., Hordeum vulgare: a suitable host for mass production of arbuscular mycorrhizal fungi from natural soil. Applied ecology and environmental research. 4(1): [9] Davies F.T., V. Olalde-Portugal, L. Aguilera-Gomez, M.J. Alvarado, R.C. Ferrera-Cerrato, and T.W. Boutton., Alleviation of drought stress of Chile ancho pepper (Capsicum annuum L. cv. San Luis) with arbuscular mycorrhiza indigenous to Mexico. Scientia Horticulturae. 92: [10] Douds Jr. D.D., G. Nagahashi, P.E. Pfeffer, W.M. Kayser, and C. Reider., On-farm production and utilization of arbuscular mycorrhizal fungus inoculum.canadian Journal of Plant Science. 85(1): [11] Earanna N., B.P. Tanuja, D.J. Bagyaraj, and C.K. Suresh., 2002.Vesicular arbuscular mycorrhizal selection for increasing the growth of Rauvolfia tetraphylla. Journal of Medicinal and aromatic plant sciences. 24: [12] Fitter A.H., T. Helgason, and B. Hodge., Nutritional exchanges in the arbuscular mycorrhizal symbiosis: implications for sustainable agriculture. Fungal Biology Reviews. 25: [13] Gadkar V., J.D. Driver, and M.C. Rillig., A novel in vitro cultivation system to produce and isolate soluble factors released from hyphae of arbuscular mycorrhizal fungi. Biotechnology Letters.28: [14] Gerdemann J.W., and T.H. Nicolson., Spores of mycorrhiza, Endogonespecies extracted from soil by wet sieving and decanting. Mycological society. 46: [15] Gianinazzi S., A. Gollotte, M.N. BinetN, D. van Tuinen, D. Redecker, and D. Wipf., 2010.Agroecology: the key role of arbuscular mycorrhizas in ecosystem services. Mycorrhiza. 20: [16] Goicoechea N., M.C. Antolín, and M. Sánchez-Díaz., Influence of arbuscular mycorrhizae and Rhizobium on nutrient content and water relations in drought stressed alfalfa. Plant Soil. 192: Sunil Kumar CP et al., [17] Graham J.H., What do root pathogens see in mycorrhizas? New Phytologist.149: [18] Hodge A., C.D. Campbell, and A.H. Fitter., An arbuscular mycorrhizal fungus accelerates decomposition and acquires nitrogen directly from organic material. Nature.413: [19] Jaizme-Vega M.C., P. Tenoury, J. Pinochet, and M. Jaumot., 1997.Interactions between the root-knot nematode Meloidogyne incognita and Glomus mosseae in banana. Plant Soil. 196: [20] Jayachandran K., and K.G. Shetty., Growth response and phosphorus uptake by arbuscular mycorrhizae of wet prairie sawgrass. Aquatic Botany. 76: [21] Karthikeyan C., and T. Selvaraj., Diversity of Arbuscular Mycorrhizal Fungi on the coastalsaline soils of the West coast of kerala, Southern India. World Journal of Agricultural sciences. 5(S): [22] Khade S.W., and B.F. Rodrigues., Ecology of arbuscular mycorrhizal fungi associated with Carica papaya L. in agrobased ecosystem of Goa, India. Tropical and Subtropical Agroecosystems.8: [23] Khade S.W., and B.F. Rodrigues., Arbuscular mycorrhizal fungi associated with some pteridophytes from western ghat region of Goa. Tropical Ecology. 43(2): [24] Lopez-Sanchez M.E., and M. Honrubia., Seasonal variation vesicular-arbuscular mycorrhizae in eroded soils from southern Spain. Mycorrhiza. 2: [25] Meharg A.A., and J.W.G. Cairney., Co-evolution of mycorrhizal symbionts and their hosts to metal contaminated environments. Advances in Ecological Research. 30: [26] Miller R.M., and J.D. Jastrow., Hierarchy of root and mycorrhizal fungal interactions with soil aggregation. Soil Biology and Biochemistry.22: [27] Muthukumar T., and K. Udaiyan., Arbuscular mycorrhizas of plants growing in the Western Ghats region, Southern India. Mycorrhiza. 9: [28] Newsham K.K., A.H. Fitter, and A.R. Watkinson., Arbuscular mycorrhiza protect an annual grass from root pathogenic fungi in the field. Journal of Ecology. 83: [29] Nisha M.C., and S. Rajeshkumar., Effect of arbuscular mycorrhizal fungi on growth and nutrition of Wediliachinensis (Osbeck) Merril. Indian Journal of Science and Technology. 3(6). [30] Nisha M.C., M.S. Subramaniam, and S. Rajeshkumar., Diversity of Arbuscular Mycorrhizal Fungi.Associated with Plants having Tubers from Anaimalai Hills. Journal for Bloomers Research. 2: [31] Philips J.M., and D.S. Hayman., Improved procedures for clearing and staining parasitic and vesicular-arbuscular mycorrhizal fungi for rapid assessment of infection. Transactions of the British Mycological Society. 55: [32] Porras-Soriano A., M.L. Sorano-Marintin, A. Porras-Piedra, and P. Azcon., Arbuscular mycorrhizal fungi increased growth, nutrient uptake and tolerance to salinity in olive trees

7 World Journal of Science and Technology 2012, 2(2): under nursery conditions. Journal of Plant Physiology. 166: [33] Pringle A., E. Barron, K. Sartor and J. Wares., Fungi and the Anthropocene: biodiversity discovery in an epoch of loss. Fungal Ecology. 4: [34] Rajan S.K., D.J. Bagyaraj and J. Arpana., Selection of efficient arbuscular mycorrhizal fungi for inoculating Acacia holosericea. Journal of Soil Biology and Ecology. 24: [35] Ragupathy S., and A. Mahadevan., 1993.Distribution of vesicular-arbuscular mycorrhizae in the plants and rhizosphere soils of the tropical plains, Tamil Nadu, India. Mycorrhiza. 3(3): [36] Ryan M.H., and J.H. Graham., Is there a role of Arbuscular mycorrhizal fungi in production agriculture? Plant soil.244: [37] Sanders F.E., and P.B. Tinker.,1973. Phosphate flow into mycorrhizal roots. Pesticide Science. 4: [38] Schenck N.C., and Y. Perez., 1990.Manual for the identification of VA Mycorrhizal fungi. Synergistic publications. Gainesville. Florida. USA. [39] Smith S.E., and D.J. Read., Mycorrhizal symbiosis. 2nd edition.academic Press. London. U.K. [40] Smith S.E., and D.J. Read., Mycorrhizal Symbiosis. 3rd edition.academic Press. London. U.K. [41] Thompson J.P.,1987. Decline of vesicular-arbuscular mycorrhizae in Long Fallow Disorder of field crops and its expression in phosphorus deficiency of sunflower. Australian Journal of Agricultural Research.38: [42] Thompson J.P., Inoculation with vesicular-arbuscular mycorrhizal fungi from cropped soil overcomes long-fallow disorder of linseed LinumusitatissimumL. by improving P and Zn uptake. Soil Biology and Biochemistry.26: [43] Van der Heijden M.G.A., T. Boller, A. Wiemken, and I.R. Sanders.,1998a. Different arbuscular mycorrhizal fungal species are potential determinants of plant community structure. Ecology.79: [44] Van der Heijden M.G.A., J.N. Klironomos, and M. Ursic., 1998b. Mycorrhizal fungal diversity determines plant biodiversity, ecosystem variability and productivity. Nature.396: [45] Van der Heijden M.G.A., and T.R. Horton., Socialism in soil? The importance of mycorrhizal fungal networks for facilitation in natural ecosystems. Journal of Ecology. 97: [46] Vasalkumar N., J.G. Ray, and V.P. Potty., Arbuscular Mycorrhizal Fungi Associated with Green Gram in South India. Agronomy Journal. 99: [47] Wall D.H., R.D. Bardgett, and E.F. Kelly., Biodiversity in the dark. Nature Geoscience. 3: [48] Wright S.F., and A. Upadhyaya., 1998.A survey of soils for aggregate stability and glomalin, a glycoprotein produced by hyphae of arbuscular mycorrhizal fungi. Plant and Soil.198: [49] Zhao D., and Z. Zhao., Biodiversity of arbuscular mycorrhizal fungi in the hot-dry valley of the Jinsha River, southwest China. Applied Soil Ecology.37: