The rangelands of Pakistan are deficient in P, as soils are calcareous and alkaline and dominated by mica mineralogy. Phosphorus deficiency has been observed in 90% of the soils of the Pakistan (Rashid and Qayyum, 1990; Memon et al., 1992). Phosphorus use efficiency, therefore, is very low in rangelands and it need to be increased to a considerable extent for boosting forage production.
Vesicular arbuscular mycorrhizae (VAM) occur widely under various environmental conditions and are found in associations of forage crops. The beneficial effect of mycorrhizal fungi in phosphate nutrition of crop plants in soils low in phosphorus have been reported by different workers (Mackay and Barber, 1985a, 1985b).
Due to the presence of native endophytes and other soil microorgnisms, mycorrhizal inoculation has proved better and beneficial in some unsterile soils than in sterile soils (Manjunath et al., 1983; Mosse, 1981). In addition, plant hormones which are produced by soil bacteria have been reported to stimulate mycorrhizal formation (Azcon et al., 1978).
The present report deals with the results of pot experiments to assess the
effects of inoculation of seed of Avena sativa with a VAM fungus in the
absence and presence of 25 kg P2O5 ha-1 on
yield, dry mater production by plants under sterile soil conditions.
|Effect of mycorrhizal inoculation on growth of plants.
||Effect of fertilizer application especially that of phosphorus on growth
of plants with and without mycorrhizal inoculation.
Materials and Methods
Pots experiments were conducted during 1996-1998 at Quaid-I-Azam University, Islamabad and University of Arid Agriculture, Rawalpindi, Pakistan. Inoculation of Gigaspora rosea, Glomus intraradices + Gigaspora rosea, Glomus etunicatums + Glomus intraradices and one control were used to conduct the following experiment in order to study the effect of mycorhizae inoculation and P2O5 on growth of Avena sativa.
Autoclaved and analyzed soil with the following composition was used in 16 cm diameter earthen pots, Moisture 32%, total organic Carbon 0.6%, total nitrogen (mg kg-1) 16, phosphorus (mg kg-1) 5.3, potassium (mg kg-1) 140 and pH 7.4.
The seeds of Avena sativa were obtained from the National Agricultural Research Centre, Islamabad. All experiments were arranged in open air under natural field conditions using Completely Randomized Design.
Avena sativa fodder seeds and three VAM species and one control were
used with three replications. Twelve pots were filled with autoclaved soil.
Inoculation with VAM was done by layering method (Jackson, 1972). Pots were
kept in open air under natural field conditions. Four plants were grown in each
pot. Plants were harvested just after seed formation.
Additional twelve pots of Avena sativa were inoculated with given
mycorrhizae species at 25 kg P2O5 ha-1.
The data regarding different plant characteristics under study were subjected
to analysis of variance technique to determine significance of mean among the
treatments by Steel and Torrie (1980) and comparisons of treatment means accomplished
by least significant difference (LSD) test at 0.05 level of significance.
Results and Discussion
Table 1 shows that the shoot dry weight under control without mycorrhizae at 0 kg P2O5 ha-1 was 27.38 g whereas shoot dry weight increased from 29.50 to 33.35 g and 38.45 g in plant inoculated by Gigaspora rosea, Glomus intraradices + Gigaspora and Glomus etunicatum + Glomus intraradices, respectively. As compared to 31.11 g shoot dry weight under control without inoculation at 25 kg P2O5 ha-1, the shoot dry weight increased from 37.14 g to 42.18 g and 45.22 g at 25 kg P2O5 ha-1 in plants inoculated by Gigaspora rosea, Glomus intraradices + Gigaspora and Glomus etunicatum + Glomus intraradices, respectively.
This may be noted that shoot dry weight in the last two figures 33.35, 38.45 g at 0 kg P2O5 ha-1 and 42.18, 45.22 g at 25 kg P2O5 ha-1, were particularly higher due to co-inoculations. These results are supported by Bagyaraj and Manjunath (1980). They reported that the crop benefited due to inoculation of Glomus fasciculatum alone, even in the presence of additional phosphorus at the rate of 60 kg P2O5 ha-1. The results also highlighted due to the dual inoculation of VAM fungi with Azospirillum brasilense in increasing the yield of different genotypes of wheat. Bethlenfalvay (1983) reported that in general the application of 30 kg P2O5 ha-1 was found to be the best in increasing dry matter production of root, shoot and grain yield. This may be because of the beneficial response from mycorrhizal inoculation at moderate fertility.
The root dry weight (Table 2) under control without mycorrhizae
at 0 kg P2O5 ha-1 was 13.61 g whereas root
weight increased from 14.75 to 16.84 to 19.13 g in plant inoculated by Gigaspora
rosea, Glomus intraradices + Gigaspora and Glomus etunicatum + Glomus
intraradices. As compared to 15.45 g root dry weight under control, without
inoculation at 25 kg P2O5 ha-1, the root weight
increased 18.69 to 21.09 to 22.50 g at 25 kg P2O5 ha-1
in plant inoculated by Gigaspora rosea, Glomus intraradices + Gigaspora
and Glomus etunicatum + Glomus intraradices, respectively.
This may be noted again that root dry weight in the last two figures 16.84,
19.13 g at 0 kg P2O5 ha-1 and 21.09 to 22.50
g at 25 kg P2O5 ha-1, were particularly higher
due to dual inoculation. This estimate compares favourable with similar data
reported by Singh and Subba Rao (1987) who reported that Glomus fasciculatum
inoculation significantly increased the yield of root and shoot of wheat crop.
||Effect of inoculation with mycorrhizae at varying level of
P2O5 on the shoot dry weight (g) of Avena sativa
||Effect of inoculation with mycorrhizae at varying level of
P2O5 on the root dry weight (g) of Avena sativa
Such increases were pronounced due to inoculation G. fasciculatum, both
in absence and presence of different level of phosphorus (0, 60 kg P2O5
ha-1), respectively. Fay et al. (1996) investigated the effects
of arbuscular mycorrhizal infection by Glomus mosseae on growth and photosynthesis
of barley (Hordeum vulgare L. cv. Manitou) in sand culture at 5 levels
of calcium phosphate. Mycorrhizal infection was low and varied with P supply.
It was at the lowest P supply that VAM plants had higher rates of photosynthesis
and greater P and N efficiency.