Characterisation of different polyclonal antisera to quantify Herbaspirillum spp. in elephant grass (Pennisetum purpureum Schun.)

Immunological techniques can be applied to detect micro-organisms in different ecosystems. To follow the fate of Herbaspirillum seropedicae strain Z67 and H. rubrisubalbicans strain M4 in the rhizosphere of elephant grass, Pennisetum purpureum Schun. var. Capim Cana D'Africa, polyclonal antisera were raised against both strains. Both antisera were purified with protein-A, followed by a primary characterisation for cross-reactivity. To reduce cross-reactivity for both sera, affinity purification was used for improvement. After that, both sera could be considered as species specific. The detection limit was 10⁵ cells ml^-1 for the anti H. rubrisubalbicans serum and 10⁶ cells ml^-1 for the anti H. seropedicae serum. It was shown that two months after inoculation, both strains could be detected in the rhizoplane of elephant grass in high densities. The estimated numbers by ELISA were 10⁷ cells g^-1 fresh weight.