The production and utilisation of monoclonal antibodies for identification of a Frankia strain utilised as inoculum for Casuarina equisetifolia

Abstract

Monoclonal antibodies were raised against Frankia ORS020607, a strain isolated originally by H.G. Diem from nodules of Casuarina equisetifolia from Senegal. One of these antibodies, mAb8C5, was shown by ELISA to have high, but not absolute specificity for ORS020607. This antibody was employed to investigate the mobility and persistence of ORS020607 in plantations of C. equisetifolia. Seedlings were inoculated in pots of sand in a forest nursery with ORS020607, with local crushed nodule suspensions or were left uninoculated. They were planted out after 5 months in experimental plots on a moderately fertile black soil site and on a low organic, oxidised red soil site. Compared with crushed nodule inoculated seedlings or uninoculated controls, growth of seedlings at transplant was improved by inoculation with Frankia ORS020607. However, 4 years after transplant to experimental plots, the growth of trees receiving different treatments was similar. The possibility that movement of ORS 020607 between treatment plots contributed to new nodulation and enhanced growth of uninoculated trees was tested using mAb8C5 in ELISA of Frankia mycelium, extracted from the nodules of trees of the three treatments. No significant differences in reactivity were detected between nodules from uninoculated and ORS020607 inoculated trees at either the black or the red soil sites, showing that ORS020607 moved between treatment plots at both sites. However, at both sites, nodules from plots of trees that were inoculated originally with local crushed nodules gave reactions in ELISA that were significantly lower than values for ORS020607 inoculated trees, possibly due to the competitive effects for new nodulation of enhancement of the indigenous population of Frankia. Serological techniques using antibodies of high specificity against Frankia strains have value for rapid screening of field samples as a preliminary for further analysis by more discriminatory techniques based on assays of genetic polymorphisms.