N-FIXATION ASSOCIATIVE

PROJECT CONSISTS OF CONTRACT WITH UNIVERSITY OF FLORIDA TO DETERMINE THE FEASIBILITY OF BIOLOGICAL NITROGEN FIXATION (BNF) BY BACTERIA ASSOCIATED WTITH THE ROOTS OF GRASSES, INCLUDING CEREAL GRAINS. THE USAID PROJECT OFFICER EVALUATED THE PROJECT ON SITE. PROJECT IS ON SCHEDULE WITH SATISFACTORY PROGRESS. THE DIFFICULTIES ENCOUNTERED IN OBTAINING A SYSTEM IN WHICH GRASS BENEFITS SIGNIFICANTLY FROM BNF ARE GREATER THAN EXPECTED AND THE RESEARCH NEEDED TO DEVELOP SUCH A SYSTEM MAY BE RELATIVELY LONG-TERM. SYSTEMS INVESTIGATED INCLUDE (1) AXENIC CULTURES OF GRASS PLANTS AND SPECIFIC CULTURES OF BACTERIA IN LABORATORY/GREENHOUSE CONDITIONS, (2) GREENHOUSE PLANTINGS WITH AND WITHOUT ADDED BACTERIA, AND (3) FIELD EXPERIMENTS WITH AND WITHOUT ADDED BACTERIA. MEASUREMENTS INCLUDE ACETYLENE REDUCTION ASSAY (ARA) OF THE ACTIVITY OF ANY NITROGENASE ENZYME PRESENT, TOTAL DRY MATTER, AND TOTAL NITROGEN. FIELD PLOTS IN 6/79 WERE GROWING WELL AND HAD BEEN HARVESTED AT LEAST ONCE. POORLY DRAINED SANDY SOILS WERE CHOSEN AS THE TWO SITES. HUSBANDRY WAS EXCELLENT BUT DIFFERENCES IN YIELD DUE TO INOCULATION WERE SMALL. N-UPTAKE FROM 15 N-LABELED EXPERIMENTS ARE PLANNED TO MORE PRECISELY MEASURE ANY DIFFERENCES IN DI-NITROGEN FIXED. IN THE GREENHOUSE, GRASS SEEDLINGS OFTEN SHOWED INCREASED GROWTH WHEN INOCULATED WITH BACTERIA BUT THE EFFECT SEEMED TO BE DUE TO PLANT HORMONES RATHER THAN DI-NITROGEN FIXATION. IN TISSUE CULTURE, SUGAR CANECALLUS COULD BE MAINTAINED FOR LONG PERIODS WHEN AZOSPIRILLUM WAS PRESENT. THE CALLUS DIED WHEN NO BACTERIA, OR SOME OTHER SPECIES, WERE PRESENT, AZOSPIRILLUM REISOLATED FROM THE CALLUS HAD MUCH GREATER NITROGENASE ACTIVITY WHEN MEASURED BY ARA. THE SURVIVAL OF INOCULATED BACTERIA INTO SOILS HAS BEEN POOR, AND STUDIES TO OBTAIN GREATER PERSISTENCE ARE UNDER WAY. THE WORK ON BNF IN GRASSES CONTINUES TO SHOW PROMISE BUT IS STILL PLAGUED BY LACK OF CONSISTENT EFFECTS. THE GOAL OF PRACTICAL DOMESTICATION OF BNF IN GRASSES IS STILL ELUSIVE AND MORE STUDIES ARE NEEDED TO CLARIFY THE SITUATION.