Efficacy of AM fungi and its Interaction with Rhizobium in Winged bean (Psophocarpus tetragonolobus (L) D.C)

Pot experiments were conducted under greenhouse conditions to investigate the effect of three arbuscular mycorrhizal (AM) fungi (Glomus fasciculatum, Glomus mossae and Acaulospora leavis) individually and its interaction with rhizobium in a mixture, on the growth and mineral nutrition of Winged bean (Psophocarpus tetragonolobus). Inoculation of AM fungi along with rhizobium in different combinations of single and triple inoculation gave different results in growth parameters like plant height, dry weight of shoot and root, per cent root colonization, nodule number, spore number, P and N uptake. In conclusion, it was found that Glomus fasciculatum was found to be efficient AM fungi for winged bean and inoculation of all the three AM fungi and rhizobium resulted in highest growth parameters. Efficacy of AM fungi and its Interaction with Rhizobium in Winged bean (Psophocarpus tetragonolobus (L) D.C) INTRODUCTION Arbuscular mycorrhizal fungi (AMF) are known to improve the nutritional status, growth and development of plants, protect plants against root pathogens and also offer resistance to drought and salinity (Jeffries, 1987; Lakshman, 2009). Use of AM fungi in increasing the plant growth is well documented. In the last three decades, there were lot of reports regarding the use of AM fungi to increase the plant growth and yield of agricultural crops, horticultural crops and forestry species. All AM fungi are obligate biotrophs that benefit the plant in several ways, for example by increasing nutrient capture, drought resistance, pathogen protection beneficial alterations of plant growth regulators and synergistic interactions with beneficial rhizosphere microorganisms (Bagyaraj, 1991). Legumes are plants that bear seeds in pods. They markedly differ from non-legume crops because much of the nitrogen they require is produced through fixation of atmospheric nitrogen by bacteria inhabiting nodules borne on their roots. The AM fungi associated with legumes are responsible for adequate P nutrition. Increased P assimilation influence positively nitrogenase activity that in turn promotes root and mycorrhizal growth. The conducive effect of dual inoculation of roots with AM fungi and Rhizobium on growth, nutrient uptake and N2 fixation in soybean (Bethlenfalvay et al., 1990), cowpea (Islam et al., 1990), and pea (Xavier and Germida, 2003) has been established. Olivera et al., (2004) reported that P application increased leaf area, plant dry biomass, nodule biomass, and shoot and root P content in common bean plants. Winged bean (Psophocarpus tetragonolobus) is a tropical crop that is listed as one of the under exploited legumes. Winged beans have exceptionally high protein content and have been suggested as a potential food source for the tropics. It is unique among leguminous crops in that, several parts of the plant leaves, pods, seeds and tubers is edible and rich in protein. Mycorrhizal studies on this plant have not been reported so far. Therefore, the present study was undertaken. MATERIALS AND METHODS The rhizospheric soil samples were collected from legume growing areas of different localities of Dharwad. AM fungal spores isolated were mass multiplied by using Sorghum vulgarae L. as a host plant in separate earthen pots. Pots measured 30 cm diameter and contained sterilized soil: sand mixture in the ratio of 3:1. Single or multiple AM fungal inoculum containing soil, hyphae, spores (215-250/ 50 g soil) and root bits was mixed with the soil in each experimental pot. Rhizobium inoculation was done by treating the seeds with a peat based culture before sowing. AMF inoculum used for each treatment is as follows. 1. Control 2. AM fungi (Glomus fasciculatum) 3. AM fungi (Acaulospora leavis) 4. AM fungi (Glomus mossae) 5. Rhizobium 6. GF+AL+Rh 7. GF+GM+Rh 8. AL+GM+Rh 9. GF+AL+GM+Rh Surface sterilized (seeds dipped in 1% mercuric chloride for three minute) seeds of Winged bean (Psophocarpus tetragonolobus) were sown in each pot above the soil inoculum and pots were arranged in random block design. Each treatment was maintained in triplicate. The spores were isolated from rhizospheric soil of Winged bean (Psophocarpus tetragonolobus) and spore count was recorded by wet sieving and decanting method (Gerdemann and Nicholson, 1963) . The growth parameters of Winged bean (Psophocarpus tetragonolobus) such as plant height, dry weight of shoot and root, number of nodules spore number per cent root colonization, P and N uptake was determined. Phosphorus content in shoot was determined calorimetrically by the vanadomolybdate/phosphoric-yellow colour method outlined by Jackson (1973). Total nitrogen content was determined by the Microkjeldahl method (Bremmer, 1960). Percentage mycorrhizal infection of the roots was determined by the root slide technique (Nicolson, 1960) after clearing the roots with 10% KOH and stained with 0.05% trypan blue (Phillips and Hayman, 1970). Number of colonized segments Root colonization = --------------------------------------X 100 Total number of segments examined The data was statistically analyzed by using analysis of variance with the help of SPSS software. The mean values were compared by Duncun’s multiple range tests at 0.05 level of significance RESULTS AND DISCUSSION In the present investigation, different AM fungi were inoculated to know the effect of single and multiple inoculation on winged bean. Table 1 revealed that inoculation of different AM fungi along with Rhizobium resulted increase in all growth parameters such as plant height, dry weight of shoot and root, root colonization, nodule number, spore number, P and N uptake than the control plants. But different AM fungi such as Glomus fasciculatum, Glomus mossae and Acaulospora leavis in combination with Rhizobium responded variedly in multiple combinations. After 45 days highest growth parameters were observed in plants inoculated in combination of all the three AM fungi (Glomus fasciculatum, Glomus mossae and Acaulospora leavis). In case of triple inoculation, the combination of Glomus fasciculatum + Glomus mossae+ Rhizobium showed highest growth in (48.0 cms) plant height when compared with the combination of Glomus mossae+ Acaulospora leavis+ Rhizobium (37.6cms)