Heat Stress in Maize: Response of Grain Yield Components in Hybrids of Contrasting Genetic Background.

Heat stress is an important source of yield reduction in maize (Zea mays L) and its effects depend upon the growth stage when it takes place. The objective of this study was to evaluate the effect of two temperature regimes (control and heated) on grain yield determination of three corn hybrids of contrasting genetic background: (i) temperate (Te), (ii) tropical (Tr), and (iii) temperate x tropical (TeTr). Three different 15-d periods were tested, which started at: (i) V15 (GS1), (ii) R1 (GS2), or (iii) R2 (GS3). Several traits were evaluated: plant and ear growth during the critical period for kernel set, flowering dynamics (anthesis and silking evolution), kernel number per plant (KNP), individual kernel weight (KW) and grain filling evolution, plant grain yield (PGY), postsilking leaf senescence and plant nitrogen status by SPAD evolution. A significant (p=0.01) STAGE*HYB*TEMP interaction was detected for PGY. Maximum PGY (106.6 g plant^-1 ± 12.6) corresponded to control plots and heated plots of TeTr-GS3 and Tr-GS1. Heated plots of Te-GS2 had the lowest PGY (5.6 g plant^-1). There was a significant (p=0.0069) STAGE*HYB*TEMP interaction for KNP. This grain yield component was severely affected by heat stress at (i) GS2 for Te (22 kernels plant^-1), and (ii) GS1 for Te and TeTr. There was a HYB*TEMP interaction (p=0.016) and a STAGE*TEMP interaction (p=0.10) for KW. Hybrid Te was the most affected by heat stress (34% decrease as compared to control). Heat stress at GS3 and GS2 reduced KW (228.1 mg y 229.3 mg, respectively) respect to GS1 (296.8 mg). Grain filling rate and duration of grain filling did not different between hybrids at confidence interval of 0.99. These physiological determinants of grain filling were also similar between GS1 and GS2. Grain filling duration of Te and grain filling rate of Tr were reduced by heating at GS3.