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Abstract

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 (YP and SP, respectively). The objectives of this work were (i) to determine differences among hybrids in the parameters of the YP–SP 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 (37°45′S, 58°18′W; elevation 130 m) during two growing seasons, 1998–1999 and 1999–2000. A wide range of YP and SP 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 YP response to resource per plant availability and in HI stability. The greater HI stability of non-prolific plants of modern hybrids was associated with lower biomass thresholds for yield at low SP and with greater reproductive plasticity at high SP. 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 SP. At low SP, YP increments were mainly related to KNP increments. At intermediate SP, increases in YP were related to both yield components to a similar extent. However, a plateau for KW was found in the two oldest hybrids. At large SP, YP response to SP was related to prolificacy.