Effect of arbuscular mycorrhizal inoculation on nutrient uptake, growth and productivity of cowpea (Vigna unguiculata) varieties

The objective of the present study is to find out the effect of Arbuscular mycorrhiza (AM) fungal inoculation on growth, productivity and nutrient uptake in two cowpea (Vigna unguiculata) varieties. The AM inoculated plants out performed than non-inoculated plants (control) in terms of growth, productivity parameters and nutrient uptake. AM fungal inoculation had a significant effect on productivity of cowpea attributed to growth, plant height, number of nodules, mycorrhizal dependency and number of flowers per plant.


INTRODUCTION
Arbuscular mycorrhiza (AM) is widespread symbiotic associations that are commonly described as the result of co-evolution events between fungi and plants where both partners benefit from the reciprocal nutrient exchange (Sharma, 2003;Bonfante and Genre, 2008).AM is the most common type of mycorrhizal association, occurring in 2/3 of land plants (Hodge, 2000).Mycorrhizal fungi have been reported in roots of chickpea plants, improving the growth and yield of these plants, especially in phosphorus deficient soils (Zaidi et al., 2003).
In the present investigation, Vigna unguiculata varieties with and without mycorrhiza were grown in the phosphorus deficient soil.The objective of this study is to determine the response of these legumes to VAM inoculation.

MATERIALS AND METHODS
This study was conducted during winter at the Department of Botany, University of Peshawar.The site lies from 33°27˝ to 34°27˝N.In the experimental work, rhizospheric soil from wheat field having 145/100 gm of different Arbuscular mycorrhizal fungi (AMF) species Glomus fasciculatum, Glomus mosseae and Glomus aggregatum and roots of wheat and maize infected with arbuscular mycorrhiza were used as rhizobase inoculum.These root pieces along with soil base inoculum (rhizospheric soil) were spread uniformly in layers at a depth of 3 and 6 cm before sowing.Inoculums for each pot consisted of 160 gm of mycorrhizal infected roots and adhering soil.
The experiment was laid out in a random block design (RCBD) with two treatments (control and uncontrolled), each treatment was replicated five times with five plants in each pot (Two treatments × 2 varieties of cowpea × 5 replicates).The following parameters were recorded: Agronomic and yield parameters including plant height, number of flowers/plant, no. of nodules/plant and nutrient uptake of micro-nutrient, macro-nutrients as known.Mycorrhizal dependency (MD) value of selected legumes was calculated by the formula given by Plenchette et al., (1983).
At each harvest, dry weights of roots and shoots were determined by drying samples at 70°C for 72 h.Shoot and roots were grinded homogenously and ashing was done at 400°C for 1 h, ash samples were analyzed for mineral including K, Ca, Mg, P, Al, Fe, S, and Si; chemical analysis were done by energy-dispersive x-ray analysis (EDXA) according the standard methods (Haq et al., 2003).Experimental data was statistically analyzed by applying the analysis of variance (ANOVA) test; the means were subjected to least significant difference (LSD) test.
Plate 2. Effect of AM inoculation of plant height of cowpea variety (V2).

Effect of AM on plant growth and productivity in cowpea
Results of AM fungi inoculation on plant growth and productivity are given in Table 2. ANOVA and LSD are given in Table (3a Khan (1994) who also reported that, mycorrhizal plants reduce cropping time due to earlier flowering and fruiting.Pods per plant are an important yield-determining factor.

Mycorrhizal dependency (M.D)
Cowpea results showed that V2 (china variety) is more dependent than V1 (Watni variety), 38 and 29%, respecttively (Figure 1).Our results correlate with the findings of Singh et al. (2004) who reported that, dry matter accumulation per plant increased with the advancement in age of the crop up to harvest in all treatments.The   with the findings of Khalil et al. (1994) who studied the mycorrhizal dependency of soybean and corn.Soybean had a higher mycorrhizal dependency than maize.When mycorrhizal and non-mycorrhizal plants were compared, the N, P, K, Ca and Mg uptake were significantly increased in mycorrhizal plants.It is widely accepted that plants with highly branched root system (Gramineae) are less mycotrophic (less dependent on the fungi for normal growth) than those with coarser roots (e.g.cassava, onion).Root branching determines plant dependence on the symbiosis (Smith and Read, 1997;Barakh and Heggo, 1998).Zadeh and Rastin (1997) reported that; vesicular-arbuscular mycorrhizal fungi (VAMF) in soybean plants increased dry matter.The results are in accordance with our results that in V2 (China variety) and V1 (Watni variety), dry matter increased by AMF.The results showed that, all varieties were found to differ in their mycorrhizal dependency as also shown by Menge et al. (1978), Azcon and Ocampo (1981), Hall (1988), Bethlenfalvay et al. (1989) and Xavier and Germida (1998).Our results confirmed the findings of other workers who observed that plant species and even cultivars of same species differ in their mycorrhizal dependency.This difference is generally related with soil type, root geometry, plant growth rates, mycorrhizal species and soil phosphorus (Hall, 1975;Plenchette et al., 1983;Menge, 1983;Hatrick et al., 1992;Hatrick et al., 1993).
The mycorrhizal plants under observation showed root and shoot dry weight.As we know that due to VAM inoculum, the total biomass is a gain factor of plant height, leaves and root, which commonly resulted to more dry weight.These results are in line with the observations of Thompson and Wildermuth, (1987), Hatrick et al. (1992), Tarafdar and Marschner (1994) and Tarafdar and Marschner (1995), Shivana (1994) and Bai et al. (2008) who stated that, dry matter differences between mycorrhizal and non-mycorrhizal plants are due to benefits derived by plants from mycorrhizal association.

Nutrient uptake by mycorrhizal and non-mycorrhizal plants
Nutrients (Ca, K, Mg, P, Fe and Si S and Si) uptakes of cowpea (V.unguiculata) varieties are shown in Figure 2. It showed that varieties and the effect of treatments were significantly different.Maximum uptake of nutrient was attained in mycorrhizal plants.Our results are supported by the Singh et al. (2004), Sharma (2004) and Ghazala (2005) who reported that nutrient uptake of mycorrhizal plants was higher when compared with non-mycorrhizal one.One of the most dramatic effects of mycorrhizal infection on the host plant is the increase in phosphorus  (P) uptake (Veierhiling et al., 2000;Rohyadi et al., 2004;Bai et al., 2008) that are mainly due to the capacity of the mycorrhizal fungi to absorb phosphate from soil and transfer it to the host roots (Asimi et al., 1980).Our results was supported by the following state-ment, AMF have been shown to improve immobile nutrients uptake such as P, Zn and Cu (George 2000;Liu et al., 2002).Mycorrhizal fungi can also improve absorp-tion of phosphorus (Kalipada and Singh, 2003) potassium (Liu et al., 2002), magnesium (Liu et al., 2002), copper (George, 2000), zinc (Jamal et al., 2002;Habte and Osorio, 2002;Chen et al., 2003) and calcium (Liu et al., 2002).
, b and c) showing varieties, interaction between varieties and treatments and the effect of treatments that were significantly increased regarding growth and yield.Our results agree with the Mathew and Hameed (2002), Niranjan et al. (2002), Lukiwat and Simanungkalit (2002), Zaidi et al. (2003), Rohyadi et al. (2004), Singh et al. (2004), Jalaluddin (2005) Satyawati et al. (2005), Rajasekaran and Nagarajan (2005) and Deshmukh et al. (2007).Avis et al. (2008) studied the effect of G. mossae on the growth and productivity of legumes.They observed that arburcular mycorrhiza was significantly affected when compared with nonmycorrhizal plants.Mycorrhizal plants performed better than non-mycorrhizal plants.Maximum flowers were produced at mycorrhizal treatments.The process of flowering and fruiting was first appeared in the mycorrhizal plants.The results are in good agreement with that of

Table 1 .
Soil content analysis.

Table 2 .
Effect of VAM inoculation on growth and yield of cowpea varieties.
Numerical values are the of 5 replicates.

Table 3a .
ANOVA for plant height.

Table 3b .
ANOVA for no. of flower per plant.

Table 3c .
ANOVA for nodules per plant.