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An experiment was conducted at the College of Horticulture,
Vellanikkara on the "effect of Azospirillum and V A mycorrhiza on the growth of
cocoa seedlings and incidence of seedling blight disease", during 1998-2000. The
experiment was conducted using native isolates and commercial cultures of
Azospirillum and V A mycorrhiza. The objective of the experiment was to find out
whether there is any synergistic effect for the combined inoculation of
Azospirillum and V A mycorrhiza in improving the growth and establishment of
cocoa seedlings and to find out the efficacy of the inoculants in imparting
resistance to seedling blight disease.
The first experiment showed that there was a positive influence for both
V A mycorrhiza and Azospirillum in improving the growth parameters. The height
and number of leaves were maximum in native Azospirillum inoculated plants.
Native mycorrhizal inoculation recorded maximum height of plant while the
number of leaves was maximum in plants inoculated with commercial V A
mycorrhiza inoculant. Combined inoculation of native Azospirillum and V A
mycorrhiza ranked only second but it was on par with the best treatment
combination. The native isolates of both the inoculants and their combination was
found to increase the height to the maximum. Maximum number of leaves was
noted in plants inoculated with commercial V A mycorrhiza. V A mycorrhizal
inoculation did not influence the number of leaves. The results on the leaf length

breadth ratio revealed that Azospirillum inoculation could influence the shape of
leaves. It could be presumed that the linear nature of leaves is an indication on the
efficiency of inoculated A zospirillum. Eventhough commercial Azospirillum was
effective in improving the collar girth, the efficiency was slightly reduced when it
was combined with native V A mycorrhiza. Commercial Azospirillum inoculation
and the combination of native Azospirillum and native V A mycorrhiza were
equally effective in improving the collar girth of cocoa seedlings to the maximum.
The different treatments and their combinations affected the dry matter of the plant
differently. VA mycorrhizal application was found to reduce the moisture content
of the plant and make the plant more sturdy than succulent. This may be a factor
that contributes to disease resistance of mycorrhizal plants. Due to the various
treatments the moisture content of roots did not vary much.
Native mycorrhiza was found better in improving nitrogen content of
the plant compared to commercial mycorrhiza. But commercial Azospirillum was
better than native Azospirillum in improving the nitrogen content of the plant.
Absorption of phosphorus was maximum (0.16%) in native VA mycorrhizal
inoculated plants. Both the mycorrhizal inoculants were found to increase the
phosphorus content of the plants. Azospirillum inoculation did not affect the
phosphorus content of the plants. Dual inoculation of commercial cultures of both
the organisms was found equally effective with native Azospirillum application
alone in potassium absorption. V AM infection percentage was also maximum in





native V A mycorrhizal inoculated plants. Combined inoculation of native isolates
of both the organisms influenced the mycorrhizal infection positively.
Out of the ten parameters observed, the native Azospirillum isolate Al
ranked first in nine of the parameters. Similarly native mycorrhizal isolate MI
showed superiority in seven of the parameters tested proving the superiority of
native isolates over commercial inoculants.
In controlling the seedling blight disease of cocoa, it was found that dual
inoculated plants showed a reduction in disease index by 0.77. In VA mycorrhiza
treated plants reduction in disease index was 0.26. In Azospirillum treated plants
there was a slight increase in disease index by 0.33. The disease reduction by dual
inoculation was higher than that was achieved by the application of the fungicide
potassium phosphonate. Among fungicides tested application of potassium
phosphonate 0.3 per cent was better in controlling the seedling blight disease.