Interaction between VA mycorrhiza and bradyrhizobium in cowpea
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Date
1999
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Department of Plant Pathology, College of Horticulture, Vellanikkara
Abstract
An investigation . I. on Interaction
between VA mycorrhiza and Bradyrhizobium in cowpea was carried out at the College of Horticulture,
Vellanikkara during the period 1994-97. The main objectives of the study were to
explore the beneficial effects of dual. inoculation of VA mycorrhiza and
Bradyrhizobium in enhancing the uptake of nitrogen and phosphorus and to evolve
specific recommendation on the use of these inoculants together in reducing the use
of nitrogenous and phosphatic fertilizers.
The results of this investigation revealed the following conclusions. The
survey on the natural occurrence of VAM in cowpea showed a fairly good VAM
colonisation in all the plant samples collected from the five locations. VAM
colonisation was found more in lateral roots than in tap root. The VAM colonisation
and spore count were more during rainy season compared to summer. The
predominant spores present in all the survey locations were identical to that of
Glomus sp.
After the screening of V AM, the local isolate from farmer's field at
Nadathara was selected for further studies based on its performance.
Observation of cowpea plants at 10 days after sowing showed the
presence of nodules and VAM colonisation in the roots of inoculated plants. Both
the nodulation and VAM colonisation were found to reach a peak at 40th day after
sowing. Dual inoculation was found to have a synergistic effect in nodulation and
VAM colonisation.
Light microscopy of VAM infected roots showed both 'H' and 'V'
shaped branching of hyphae, arbuscules and vesicles of VAM fungus.
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Electron microscopy revealed two types of fungal penetrations into the
roots. It also showed the terminal attachment of oval shaped vesicles and highly
branched arbuscules with short twisted branches with bulged tips in the root cortex.
Electron microscopic study of nodules revealed that the nodule surface
was free of V AM hypha, but the inner tissues of nodules had the hyphal presence.
The pot culture experiment recorded synergistic effect in dual inoculation
with VAM and Bradyrhizobium in enhancing five biometric characters, viz. number
of leaves, fresh and dry weights of plant, number of nodules and fresh weight of
nodules.
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Among the inoculant-fertilizer interactions, eventhough all observations
except fresh weight of plant recorded non significance between treatments, those in
I which VAM was a partner, recorded the maximum values for all the observations
except root length.
Dual inoculation with VAM and Bradyrhizobium improved the level of
six nutrients, viz. nitrogen, phosphorus, magnesium, calcium, zinc and manganese
in cowpea.
The result of interaction with microsymbionts and fertilizer levels
recorded inconsistent values. Treatment with VAM + B + 1/4 N + P + K recorded
maximum nitrogen, VAM + ½ N + P + K and N + ½ P + K alone recorded
maximum phosphorus and dual inoculation along with ½ N+P+K recorded
maximum magnesium and calcium content of plant.
Inoculation of VAM + Bradyrhizobium along with ½ N + P + K ranked
top III increasing the soil nitrogen to the maximum. There were no significant
differences among treatments and its combinations in influencing the phosphorus J status of soil. The application of either VAM or Bradyrhizobium or its combinations
reduced the potassium content of soil.
The results of the field experiment revealed that the treatment T 10
(VAM+B+ ½ N+ ½ P+K) out perform other treatments in five characters, viz. plant
height, fresh and dry weights of plant, nodule number and fresh weight of nodules at
50 per cent flowering. At harvest this treatment recorded the maximum values in
fresh and dry weights of plant, nodule number and fresh and dry weights of nodules.
Treatment T 10 increased nodulation to 180 per cent over Bradyrhizobium
inoculation alone.
Bradyrhizobium+ ½ N+P+K was found to be the best treatment in
improving the nitrogen content of plant, whereas VAM+B+ ½ N+ ½ P+K was the best
for improving the phosphorus, potassium, magnesium and zinc content of plant.
Another finding was that the different treatments involving
microsymbionts and different fertilizer doses were not able to influence the nitrogen,
phosphorus and potassium content of soil to a significant level.
The percentage of V AM colonisation was not significantly affected by
dual inoculation and also by the application of different levels of fertilizers.
Dual inoculation had no influence on the spore count of V AM. 'The high
level of phosphorus in soil had some negative influence on the spore count.
Treatment B+ ½ N+ P+K was the best in increasing the yield to the
maximum, which was on par with T 10.
The overall results showed that T10 (VAM+B+ ½ N+ ½ P+K) where dual
inoculation was done and nitrogen and phosphorus fertilizers were reduced to half of the recommended dose, was the best treatment in improving the biometric
characters and nutrient status and yield of cowpea. Thus a judicious treatment
would be VAM+B+ ½ N+ ½ P+K to get the best performance of cowpea.
The percentage of V AM colonisation recorded a significant positive
correlation with nodule number and fresh and dry weights of nodule.
There was a significant positive correlation between nodule number and
plant dry weight and also with yield. The percentage of VAM colonisation had a
significant positive correlation with calcium content and significant negative
correlation with manganese content of plant.
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Citation
171451