Chemistry Reference
In-Depth Information
Grain Yield Determination and Resource
Use Efficiency in Maize Hybrids Released
in Different Decades
Laura Echarte, Lujan Nagore, Javier Di Matteo, Matías Cambareri,
Mariana Robles and Aída Della Maggiora
Additional information is available at the end of the chapter
http://dx.doi.org/10.5772/55287
1. Introduction
Maize (Zea mays L.) grain yield have increased during the last decades. A recent review [1]
indicated genetic grain yield gains of 74 to 123 kg ha
-1
year
-1
for different time periods
between 1930 and 2001, in the US corn belt, Argentina and Brazil [2-6]. Current reviews on
the physiological processes associated with those yield increments have been focused on US
corn belt hybrids and maize hybrids of Ontario, Canada [e.g. 1; 7; 8]. As such, grain yield
increments were associated mainly with an increased kernel number, a consistently
improved stay green, and a longer period of grain fill. Those reviews agreed on that harvest
index (HI; i.e. the relationship between grain yield and final shoot biomass) did not
consistently change over time; in contrast, HI of Argentinean maize hybrids have increased
during the 1960-1990 period [9; 10]. This review will be focused on the ecophysiological
mechanisms contributing to the greater yield in modern than in older maize hybrids; with
particular interest in Argentinean maize hybrids because they have shown a distinctive trait
change over the years (i.e. HI increment).
Grain yield
Grain yield can be expressed as the product between shoot biomass and harvest index. In
Argentina, harvest index was increased while shoot biomass was not consistently increased
over the years during the period 1965-1993 [11]. As such, HI increased from 0.41 to 0.52 in
maize crops growing under optimal conditions [9]. The increased harvest index was
associated mainly to a greater increase in grain yield numerical components (i.e. kernel
number and/or kernel weight) than in shoot biomass. On the contrary, shoot biomass has
increased while harvest index have remained constant in maize hybrids released in Canada
