3.4. Plant growth promotion potential
According to the quantitative test of the ACC deaminase and
other PGP screening results summarized in Table 3, the six most
promising ACC deaminase-producing isolates that produced the
highest level of ACC deaminase activity (above 50 mmol a-ketobutyrate
mg protein1 h1) and the new species KLBMP 1111 were
selected to investigate their plant growth promotion effects on J.
curcas L. Statistical analysis of data recorded 34 days after
endophyte inoculation is summarized in Fig 2. These strains
presented different PGP abilities and nearly all the tested strains
had considerable impact on different growth parameters of J.
curcas L. seedling compared with the negative control. The
inoculation with four Streptomyces strains KLBMP 1154, KLBMP
1179, KLBMP 1174, KLBMP 1234, and two rare actinomycete strains
KLBMP 1111 and KLBMP 1354 showed significant increase in the
seedling length and fresh weight of J. curcas L. when compared to
the control plants (Fig 2a,c). The maximum seedling fresh weight
was observed by isolate KLBMP 1111 (183% over control).
Inoculation with KLBMP 1179 caused the maximum increase in
root length (10.1 cm) which was 2.8 fold higher than the control,
followed by KLBMP 1154 and KLBMP 1234 (Fig 2b). Likewise, leaf
total area also increased significantly (P
0.05) in response to
inoculation with the isolate KLBMP 1154, isolates KLBMP 1179 and
KLBMP 1354 were next effective isolates (Fig 2d). However, strain
Streptomyces sp. KLBMP 1049, which also carries reasonable
amount of ACC deaminase, did not show significant PGP effect.