107 inoculants in the internal parts of wheat roots (Baldani et al. 1986). Their results
(Baldani et al. 1986 and 1987) suggest that the Azospirillum could penetrate to the
inside of epidermal tissues, although it also could reside as free-living bacteria in the
soil and rhizosphere of many crops. Baldani et al. (1986, 1987) suggested that the
Azospirillum could colonize inside epidermal tissues although these bacteria could
exist as free-living bacteria in the soil and rhizosphere of many crops. Obligate
endophytes such as Gluconacetobacter diazotrophicus and Herbaspirillum spp.
could be a very promising group for nitrogen fixation in sugarcane compared to
Azospirillum. Azospirillum isolates can colonize perhaps endophytically with sugarcane (Tejera et al. 2004). However, obligate endophytes of G. diazotrophicus were
not detected in the apoplastic fluid of the stems (Tejera et al. 2004).
Field experimental results in India have shown that application of
A. diazotrophicus by inoculating setts (cuttings) increased sugarcane yield for four
varieties significantly when the microbe was applied in association with vesicular
arbuscular mycorrhiza (Muthukumarasamy et al. 1999a, b). Those authors claimed
that this practice completely substituted for the recommended dose of 275 kg ureaN ha
À1
. This is an ambitious claim, but the result could involve a PGPR effect.
20.3.3.3 Acetobacter
Acetobacter as gram negative produce carbon dioxide and water from lactate and
acetate called acetic acid bacteria (Cleenwerck et al. 2002). Of this genus,
Gluconacetobacter diazotrophicus has a rod-like shape and circular ends (Eskin
et al. 2014) and is well known obligate endophyte which grows best on sucrose-rich
medium (James et al. 1994) such as sugarcane sap. This bacterium also produces
much IAA, and this is related to its endosymbiosis. They do not survive in the
surface of root of sugarcane. Boddey et al. (1991) conducted a
15 N dilution/N
balance study, confirming that up to 60–80% of sugarcane plant N (equivalent to
over 200 kg N ha
À1 yr.
À1 ) was derived from BNF, and A. diazotrophicus apparently
played a role for much of this BNF (Boddey et al. 1991). Many scientists now apply
Acetobacter-sugarcane system as an effective experimental model for BNF study.
Treating seedlings with this bacterium results in greater growth rates while nif
À
mutants of this genus are significantly less effective in increasing plant growth,
indicating that the diazotrophic character (nif
+
) is important for this system (Lee et al.
2002).
A field study of co-inoculation of A. diazotrophicus with vesicular arbuscular
mycorrhiza has shown increased sugarcane yield for four varieties of sugarcane
(Muthukumarasamy et al. 1999a, b). Those researchers insisted that this practice
should completely substituted for the recommended dose of 275 kg urea-N ha
À1
(Muthukumarasamy et al. 1999a, b).
20 The Diazotroph as an Endophyte and How a Diazotroph Interacts with Its. . .
409
(Baldani et al. 1986 and 1987) suggest that the Azospirillum could penetrate to the
inside of epidermal tissues, although it also could reside as free-living bacteria in the
soil and rhizosphere of many crops. Baldani et al. (1986, 1987) suggested that the
Azospirillum could colonize inside epidermal tissues although these bacteria could
exist as free-living bacteria in the soil and rhizosphere of many crops. Obligate
endophytes such as Gluconacetobacter diazotrophicus and Herbaspirillum spp.
could be a very promising group for nitrogen fixation in sugarcane compared to
Azospirillum. Azospirillum isolates can colonize perhaps endophytically with sugarcane (Tejera et al. 2004). However, obligate endophytes of G. diazotrophicus were
not detected in the apoplastic fluid of the stems (Tejera et al. 2004).
Field experimental results in India have shown that application of
A. diazotrophicus by inoculating setts (cuttings) increased sugarcane yield for four
varieties significantly when the microbe was applied in association with vesicular
arbuscular mycorrhiza (Muthukumarasamy et al. 1999a, b). Those authors claimed
that this practice completely substituted for the recommended dose of 275 kg ureaN ha
À1
. This is an ambitious claim, but the result could involve a PGPR effect.
20.3.3.3 Acetobacter
Acetobacter as gram negative produce carbon dioxide and water from lactate and
acetate called acetic acid bacteria (Cleenwerck et al. 2002). Of this genus,
Gluconacetobacter diazotrophicus has a rod-like shape and circular ends (Eskin
et al. 2014) and is well known obligate endophyte which grows best on sucrose-rich
medium (James et al. 1994) such as sugarcane sap. This bacterium also produces
much IAA, and this is related to its endosymbiosis. They do not survive in the
surface of root of sugarcane. Boddey et al. (1991) conducted a
15 N dilution/N
balance study, confirming that up to 60–80% of sugarcane plant N (equivalent to
over 200 kg N ha
À1 yr.
À1 ) was derived from BNF, and A. diazotrophicus apparently
played a role for much of this BNF (Boddey et al. 1991). Many scientists now apply
Acetobacter-sugarcane system as an effective experimental model for BNF study.
Treating seedlings with this bacterium results in greater growth rates while nif
À
mutants of this genus are significantly less effective in increasing plant growth,
indicating that the diazotrophic character (nif
+
) is important for this system (Lee et al.
2002).
A field study of co-inoculation of A. diazotrophicus with vesicular arbuscular
mycorrhiza has shown increased sugarcane yield for four varieties of sugarcane
(Muthukumarasamy et al. 1999a, b). Those researchers insisted that this practice
should completely substituted for the recommended dose of 275 kg urea-N ha
À1
(Muthukumarasamy et al. 1999a, b).
20 The Diazotroph as an Endophyte and How a Diazotroph Interacts with Its. . .
409