Remobilization of nitrogen from senescing leaves of pigeonpea (Cajanus cajan (L.) Millsp.):: Genotypic differences across maturity groups?

Remobilization of leaf nitrogen during the seed filling stage was investigated in relation to patterns of leaf abscission with three pigeonpea genotypes (Cajanus cajan L.) of different maturity duration [extra-short (ESD), short (SD), and medium (MD)]. Leaflet abscission (trifoliate leaf) started from the bottom of the plants. The life span of defined leaf layers in the canopy differed among the genotypes and tended to be longer toward the top of the plants. At harvest, the leaf layer close to the pod-bearing top of the plant had a survival rate of 75% and 31% in ESD and SD pigeonpea, respectively, indicating that a large number of leaves in ESD was not entirely exploited for nutrient redistribution to the seed. Net remobilization of nitrogen from leaves during the reproductive stage was obtained from an above-ground plant budget for N and amounted to 35%, 47%, and 37% of the pod's requirement for N in ESD, SD, and MD, respectively. The amount of nitrogen in the defined leaf layers decreased exponentially with time, and the rate of N loss was calculated from the regressions in terms of half-life. For most of the layers half-life was longest in ESD pigeonpea indicating slower abscission and remobilization compared to both other genotypes. The present study compares two pigeonpea hybrids (ESD and SD) with a conventional genotype (MD). The results imply (1) that the efficiency to remobilize leaf nitrogen for seed development is related to the pattern of leaf abscission in pigeonpea, and (2) that SD pigeonpea remobilizes leaf N more efficiently than ESD and MD.