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 inve stigated in relation to patterns of leaf abscission with three pigeonp ea genotypes (Cajanus cajan L.) of different maturity duration [extra- short (ESD), short (SD), and medium (MD)]. Leaflet abscission (trifoli ate leaf) started from the bottom of the plants. The life span of defi ned 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% a nd 31% in ESD and SD pigeonpea, respectively, indicating that a large number of leaves in ESD was not entirely exploited for nutrient redist ribution 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 defi ned leaf layers decreased exponentially with time, and the rate of N l oss was calculated from the regressions in terms of half-life. For mos t of the layers half-life was longest in ESD pigeonpea indicating slow er abscission and remobilization compared to both other genotypes. The present study compares two pigeonpea hybrids (ESD and SD) with a conv entional genotype (MD). The results imply (1) that the efficiency to r emobilize leaf nitrogen for seed development is related to the pattern of leaf abscission in pigeonpea, and (2) that SD pigeonpea remobilize s leaf N more efficiently than ESD and MD.