Harvest index stability of Argentinean maize hybrids released between 1965 and 1993

Harvest index (HI) and its stability are key determinants of crop yield. HI of Argentinean maize hybrids released at different decades was compared using as a framework the relationship between yield and final shoot biomass on a per plant basis (Y-P and S-P, respectively). The objectives of this work were (i) to determine differences among hybrids in the parameters of the Y-P-S-P relationship and in HI stability and (ii) to explain these differences by studying the response of yield components (i.e. kernel number per ear and weight per kernel) to resource availability. Two experiments were carried out at Balcarce, Argentina (37degrees45'S, 58degrees18'W; elevation 130 m) during two growing seasons, 1998-1999 and 1999-2000. A wide range of Y-P and S-P was generated by manipulation of plant density. Shoot dry matter per plant, grain yield per plant and its components were measured at physiological maturity. Hybrids differed in their Y-P response to resource per plant availability and in HI stability. The greater HI stability of non-prolific plants of modem hybrids was associated with lower biomass thresholds for yield at low S-P and with greater reproductive plasticity at high SF, Prolificacy contributed to HI stability in all hybrids to a similar extent. All yield components contributed to explain yield and HI responses to variation in S-P, At low S-P, Y-P increments were mainly related to KNP increments. At intermediate S-P, increases in Y-P were related to both yield components to a similar extent. However, a plateau for KW was found in the two oldest hybrids. At large S-P, Y-P response to S-P was related to prolificacy. (C) 2003 Elsevier Science B.V. All rights reserved.