Utilization of the acetylene reduction assay to screen for tolerance of symbiotic N2 fixation to limiting P nutrition in common bean uri icon

abstract

  • The limitation of symbiotic nitrogen fixation due to P deficiency restricts the development of a sustainable agriculture, particularly in Mediterranean and tropical soils. Common bean genotypes, APN18, BAT271, PVA846, POT51, G2633 and G12168, were grown in an aerated N-free nutrient solution at low (72 mu mol plant(-1) week(-1)) and control P supplies (360 mu mol plant(-1) week(-1)). Nitrogenase activity was estimated by in situ measurements of acetylene reduction activity (ARA) in a flow-through system. During the assays, maximum values of ARA (peak ARA) were reached between 20 and 30 min after exposure to C2H2, depending on P treatment and growth stage. Thereafter, a decline in C2H4 evolution was observed. This decline was most pronounced in low-P plants and there was a significant genotypic effect. ARA per plant was decreased by P deficiency, mostly because nodulation was delayed and the number and mass of nodules were reduced. The ARA decrease during pod filling was also activated by P deficiency. ARA per g dry weight nodule was increased by P deficiency in G2633 and G12168, unchanged in APN18, BAT271 and POT51 and decreased in PVA846. Except for the climbing type IV G2633, total N at harvest for all P treatments was correlated with the cumulative value of peak ARA and with peak ARA at early pod-filling which was the highest peak ARA throughout the growth cycle of type III bushy genotypes. We conclude that if phenology and growth habit are carefully considered, peak ARA is a reliable screen of genotypes for N-2 fixation tolerance to P deficiency. Selection of lines with early nodulation under P deficiency is also advisable, and the effect of P deficiency on the nodule functioning needs to be considered.

publication date

  • 1997
  • 1997