Rooting of micro seed pieces by combined use of humic substances and endophytic diazotrophic bacteria in sugar cane.

摘要

The purpose of this study was to evaluate the effect of the combined use of humic acid (HA) and Herbaspirillum seropedicae, an endophytic nitrogen-fixing bacteria, on the root growth of seed pieces - heat-treated or not - of the sugarcane variety RB 72 454. After hot water treatment, the cane cuttings were immersed for 12 h as follows: in water (control plant), in HA solution (20 mg/litre of C) from vermicompost, in bacterial inoculant of H. seropedicae, strain HRC54 (108 cells/mL), and in a combination of bacteria and HA. Root growth was improved by 60 to 118% in length and from 33 to 233% in surface area on sugarcane plant treatments compared to control, with more pronounced effect in plants under heat treatment. Likewise, the positive effect of the combined treatment (bacteria inoculation and humic acid) on shoot and root biomass was significant compared to the control with heat-treated cuts. For non-heated seed pieces, bacteria inoculation did not result in a positive plant growth effect, but only in the presence of humic acid. The combined or isolated use of both HA and bacteria did not significantly modify the bacteria population in the root tissue of heat-untreated sugarcane. For heat-treated cuts, bacteria inoculation, combined or not with HA, increased the size of diazotrophic bacteria population on roots. The results highlight the importance of thermotherapy to increase the positive effect of the selected bacteria strain of H. seropedicae. In the case of HA application, plant growth stimulation was not related to thermotherapy. The plant root growth promoting effect induced by both HA and the inoculation of selected nitrogen-fixing bacteria strain could represent an innovative approach to a sustainable sugarcane crop production.