Screening and selection of pearl millet for root associated bacterial nitrogen fixation

Abstract

There are several reports of genotypic variability in grass species for their ability to achieve associations with N 2-fixing soil bacteria. These findings imply that plant breeding may be useful in enhancing these associations and thereby making available plant germplasms needed for agronomic and physiological studies of associative N 2-fixation in grasses. When the N 2-fixing bacterium Azospirillum brasilense (strain JM 125) was used as inoculum, differences were found among selfed lines of pearl millet ( Pennisetum americanum (L.) K. Shum.) for an ability to support bacterial acetylene reduction activity (ARA) when assayed in enclosed seedling agar tubes. These lines were selfed again or hybridized. Although line to line discrepancies were seen, the ARA of these lines and hybrids when categorized into high or low groups matched the activity of their original parental lines. Also, the selfed and hybrid groups obtained from high ARA lines supported higher numbers of bacteria and lost greater quantities of 14C from their roots than did those groups obtained from low ARA lines. Two of these lines, one having high ARA and one having low ARA, were grown in soil in the greenhouse and were found to differ in their respective ability to support ARA by the soil N 2-fixing microbes. However, overall ARA of the high line was quite low unless analyzed in a hydroponic culture system at low O 2 tensions.