Plant symbiotic mutants as a tool to analyse nitrogen nutrition and yield relationship in field-growth peas (Pisum sativum L.)

Abstract

Pisum sativum L. is known for high seed and protein yields but also for.yield instability. Because legumes utilize two sources of nitrogen (atmospheric N2 fixed in nodules and assimilation of soil mineral N), studies on their nitrogen nutrition is more complex than in other plants. In this work, pea symbiotic mutants (with no nodules at all ([Nod-]), with inefficient nodules ([Nod+Fix-]) or showing an hypernodulating and a ‘nitrate-tolerant symbiosis’ character ([Nod++Nts]), their semi-leafless isogenic homologues and the parental control line cv Frisson were fertilized with three levels of mineral nitrogen (0, 25 or 50 g N m-2) to generate a range of mineral nitrogen regimes in the same genetic background. Impact of the source and level of nitrogen nutrition was measured on reproductive development, growth, nitrogen accumulation and seed yield. It was shown that a N deficiency induced flowering termination. It also led to a large decrease in the number of seeds produced and the amount of N accumulated in forage and in seeds, when little effect was observed on the progression rates of reproductive stages along the stem. The single seed weight and the amount of dry matter accumulated in forage neither responded strongly to N deficiency. The source of nitrogen was shown to be of little importance to yield but the application of about 50 g N m-2 was necessary to reach the yield of the control cv Frisson when exclusive assimilation was ensuring the N requirements of the plant. Despite the fact that the nitrate-tolerant and hypernodulating mutant P64 used in this study did not yield as well as the parent cv Frisson, it is proposed that [Nod++Nts] characters could act as a yield regulating factor.