Effect of Temperature During Grain Filling On the Amylose/Starch Ratio in Maize Hybrids With Different Kernel Hardness.

Dry milling industry demands hard maize kernels to maximize flaking grits yield during the milling process. Kernel hardness is an intrinsic property but modified by the environment. It depends on the linkage between the protein matrix and starch granules. High amylose endosperms would be more compressible and become harder than endosperms with high amylopectin content. It has been reported that starch percentage varied little in kernels from different locations but amylose/starch ratio did, showing late sowing dates less amylose content than earlier ones. Moreover, increases in temperature has been reported to decrease total activity of SBE enzyme, reducing starch α-1,6 bonds and thus increasing amylose/starch ratio. The aim of this work was to evaluate the effect of temperature during grain filling on the kernel amylose/starch ratio in three maize hybrids differing in kernel characteristics (i.e, flint, semi-flint and semi-dent hybrid). The Experiments were carried out in two years, three locations and two sowing dates per location to obtain a wide range of thermal conditions during grain filling. Positive and lineal relationships between mean temperature during grain filling and amylose/starch ratio were detected for the semi-flint and the semi-dent hybrids (R2 ≥ 0.37; p≤0.035; n ≥ 11). A single regression model accounted for the variability of amylose/starch ration of both hybrids (R2 = 0.44; p<0.0006; n = 23). Accordingly, as location latitude was increased or sowing date was delayed the amylose/starch ratio was reduced, what is in accordance with the cooler condition during the grain filling period for these environments. These findings would have a relevant utility in maize production since they help us to choose the appropriated management practices and locations to increase kernel hardness for dry milling industry.