The peanut (Arachis hypogaea L.) generally is considered promiscuous since it forms symbioses with a diverse group of Bradyrhizobium. However, specific cultivar-strain combinations like Robut 33–1 and strain NC92 have resulted in significant yield increases, suggesting that host-strain combinations may be selected for superior nitrogen fixation and yield. The objectives of this study were to measure nitrogen fixation-related traits during the growing season and evaluate the interactions between host peanut genotypes and Bradyrhizobium strains under field conditions in North Carolina. A factorial experiment with four cultivars and five inoculants was conducted in two years at two locations (Clayton and Lewiston) in North Carolina. Traits measured during the growing season were nodule number and weight, root weight (1983 only), shoot weight, pod weight, nitrogenase activity and specific nitrogenase activity. In 1984, fruit yield was measured at harvest. Results indicated that cultivars and strains were different for most traits in 1983 at Clayton but significant host-strain interactions occurred only for nodule weight at 60 days after planting (DAP) and root weight at 132 DAP. In 1984, Clayton results indicated cultivar-strain interactions for all traits at 73 DAP and for several traits at 109 DAP. At Lewiston only cultivar differences were important. The Clayton fields had low populations of native Bradyrhizobium while Lewiston had a high level of the bacteria. Inoculation produced substantial yield increases at Clayton but not at Lewiston. Robut 33–1 inoculated with strain NC92 did not yield more than with other strains. Further study is needed to explain why repeated increases in yield were obtained with Robut 33–1/NC92 in tropical studies but not in North Carolina. The possibility still exists that superior cultivar-strain combinations can be identified.
1Paper No. 11666 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695–7643.