Kernel Set of Temperate and Tropical Maize Hybrids Expose to Heat Stress around Flowering.

Maize grain yield is affected by the occurrence of heat stress around flowering due to negative effects on final kernel numbers (KN), but there is no information on the effects of this abiotic constraint on potential number of florets, silking dynamics, and kernel set (i.e. kernels per floret). Knowledge on the genotypic variation for these traits among temperate (Te) and tropical (Tr) hybrids is also lacking. In this work we analyzed the dynamics of silking among plants and silk emission among apical ears, potential floret numbers, kernel set and final KN for three F1 hybrids of contrasting genetic background (Te, Tr, and Te x Tr), cropped in the field (Exp1: 2008-2009, Exp2: 2009-2010) under two temperature regimes (unheated control and heated) applied during 15 days before (S1: V15-R1) or along silking (S2: R1-R2). Heating always had a negative effect (P<0.05) on observed traits. Largest reductions in KN were registered for S2 (-69.5% in Exp1 and -78.9% in Exp2) and for the temperate hybrid (>-77%). These reductions were mostly due to a decrease in kernel set (-31% in Exp1; -67.2% in Exp2), and to a less extent to a decrease in the number of silking plants (-10%), potential floret numbers (-10 to -15%, only in S1) and number of exposed silks per apical ear (-20%).