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M Meenakshisundaram & K Santhaguru / Int J Cur Sci Res. 2011; 1(2): 23 - 30.
4.Discussion
Nitrogen and Phosphorus are the major inputs for the production
of cereals. However, the escalating cost of chemical fertilizers forced
us to exploit alternate source of fertilizers- biofertilizers. The
endophytic diazotrophs proliferate inside roots, stem and leaves
and fix N efficiently exploiting on environment where there is little
competition for nutrients and low oxygen prevailed [27]. In this
study Saccharum officinarum plant species from Madurai districts
of Tamil Nadu were chosen for isolation of Gluconacetobacter
diazotrophicus .
Arbuscular Mycorrhizal fungal spores were isolated from
rhizosphere of S.bicolor grown in different localities of southern
Tamil nadu using wet sieving and decanting technique and
identified as Entrophosphora infrequens, Gigaspora albida, Glomus
albida, Glomus dimorphicum, Glomus tubaeformis, Glomus
fasciculatum, Glomus mosseae, Glomus macrocarpum, Scutellospora
heterogamma and Sclerocystis pachycaulis. Although there is no
strict host specificity [28] , individual sp. of AM fungi vary in their
potential to promote plant growth [29] . Both inter and
intraspecific differences in the efficiency of AM fungi in terms of
plant growth have been reported in many instances [30,31,32 ]
Among the ten species of AM fungi were colonized on plant roots
and produced vesicular infection and not produced arbuscular
infection. The notable absence of arbuscules may be due to the short
study period, since arbuscules generally degenerate within 14 days.
Also, it has been shown that colonization of non-host roots with
intercellular development of hyphae, often form vesicles but not
arbuscules [33]. The wide variation in per cent AM infection
reported here clearly indicates that G.fasciculatum forms a
preferential association with S.bicolor. Similar preferential
association has also been reported in Trifoliate organ [34].The
increase of AM infection observed when AM fungi were
coinoculated with G.diazotrophicus varied for each of the tested
fungus. A similar trend was observed with enhancement of
mycorrhizal root colonization in dual inoculated sweet potato,
sugarcane and sweet sorghum plants was reported [14] when
G.diazotrophicus was coinoculated with the acid-tolerant AM
fungus Glomus clarum [35] .
Significant increase in fresh and dry matter yield was observed in
dual inoculated plants over other treatments viz uninoculated
control, G.diazotrophicus inoculated and G.fasciculatum inoculated
plants. Similar increase in plant growth was observed in S.bicolor
inoculated with G.diazotrophicus + G.fasciculatum [36] . Production
of growth hormones by diazotrophs [37, 38] plays a vital role in
enhancing the growth of grasses. It has also been shown that
G.diazotrophicus is beneficial to sugarcane through production of
growth promoting factors [39]. Early study from this laboratory has
also shown that IAA production by G.diazotrophicus correlated well
with the induction of plant growth [40] .
The nitrogen content of S.bicolor increased considerably upon
inoculation with G.diazotrophicus. The N15 incorporation studies in
sugarcane have also demonstrated the potential for nitrogen
fixation in G.diazotrophicus-sugarcane interaction [41]. Maximum
N content observed in plants inoculated with G.fasciculatum +
G.diazotrophicus, could be the result of better nitrogen fixation and
uptake of N from the soil. The enhanced level of P in dual inoculated
plants reported here could be the result of uptake of P from soil. The
increase in plant biomass in S.bicolor upon dual inoculation was
associated with increased nitrogen and phosphorus content.
Investigations have shown that the growth and yield increase of
legumes inoculated with AM fungi and rhizobia is due to enhanced
N and P uptake [42,43,,44 ,45].
The chlorophyll content increased significantly in G.fasciculatum
+ G.diazotrophicus inoculated plants. This increase bears a positive
correlation with the increase in soluble sugars. The promotion of
chlorophyll formation in dual inoculated plants may presumably
reflect more photosynthesis to meet the carbon requirements of AM
fungi and G.diazotrophicus, since both the microsymbionts depend
on the host plant for their carbon source [46, 47]
5.Conclusion
The present study revealed that G.diazotrophicus +
G.fasciculatum form a preferential association with S.bicolor. Our
results suggested the need for screening microbial compatibility
and efficiency prior to field application.
Acknowledgements
The authors thank to Dr. J.Dobereiner, Embrapa, Brazil for
providing the type strain of G. diazotrophicus PAL5, and The
president, Nehru Memorial College, Trichy, Putanampatti, for moral
support and encouragement.
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