Abstract
Elephant grass (Pennisetum purpureum) is a perennial C4-plant with outstanding sustainable potential for bioenergy, grazing and silage, It is able to fix nitrogen in association with diazotrophic bacteria and is a high biomass producer, even in low fertility soils. This study aimed to investigate the response of two elephant grass genotypes (PCEA and PMN hybrid) to inoculation, via seed coat and leaf spray, with Azospirillum baldaniorum (Sp245) and Gluconacetobacter diazotrophicus (LP343), grown in the field. In addition, in situ colonization of field PCEA minisets with labeled mCherry strain LP343 and gfp strain Sp245 was analyzed. The results showed that the PCEA genotype produced a higher amount of biomass and total N than the PMN hybrid when inoculated with strain Sp245 on seeds and strain LP343 sprayed on leaves. The quantification of the 15N abundance (δ15N) showed no biological nitrogen fixation (BNF) contribution by either of the inoculated strains and mode of application in leaves of PCEA genotype. The microscopy confocal analysis showed internal tissue colonization of sprouted PCEA minisets by strain LP343 while detection of Sp245 was reduced during the assays. In contrast, leaf surface spot inoculation showed no internal tissue colonization by either strain although the LP343 strain remained longer on the leaf surface. The heavy miniset plant tissue colonization by LP343 (roots and leaves) could be related to its host specificity as compared to Sp245 and may therefore be responsible for the higher increase in the total N accumulated in the plant superior to N fertilization. This effect could, however, involve mechanisms other than the BNF process.
Published Version
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