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CROP PHYSIOLOGY & METABOLISM

Kernel Set in Maize Hybrids and Their Inbred Lines Exposed to Stress

Dep. of Plant Agriculture, Crop Science Building, Univ. of Guelph, Guelph, ON, Canada, N1G 2W1. Financial support, in part, from the Ontario Ministry of Agriculture and Food, Natural Science and Engineering Research Council, and Ontario Corn Producers' Association. L. Echarte was supported by a postgraduate scholarship from OAS

^* Corresponding author (lecharte{at}mdp.edu.ar)

Heterosis for grain yield in maize (Zea mays L.) has been associated with heterosis for kernel number. The objective of this study was to elucidate physiological traits underlying the superior kernel no. establishment in hybrids in comparison with that in their inbred lines, using the relationship between kernel no. plant^–1 (KN_P) and plant growth rate during the critical period of approximately 30 d bracketing silking (PGR_S). Experiments were performed at the Arkell Research Station near Guelph, ON, Canada, during 2003 and 2004. Maize was grown at three levels of water availability (100, 75, or 60% of daily transpiration) during a period bracketing silking and at two plant densities (6 and 10 plants m^–2) without nutrient limitations to generate a range of levels of resource availability plant^–1. Kernel no. plant^–1 was greater in the hybrids than in their parental inbred lines at all levels of resource availability, which was attributable mainly to a greater kernel set per unit PGR_S in the hybrids. Greater kernels set per unit PGR_S in hybrids vs. their inbred lines resulted from one or more of the following features: (i) low threshold of PGR_S for kernel set, (ii) high kernel set response to PGR_S increments at low resource availability plant^–1, and (iii) high potential kernel number. Heterosis for kernel set was associated with heterosis for ear growth rate during the critical period for kernel set bracketing silking (EGR_s) to varying degrees, and the extent of the association varied with inbred line–hybrid combination and level of resource availability plant^–1.

Abbreviations: DM, dry matter • EGR_S, ear growth rate during the critical period for kernel set bracketing silking • GDD, growing degree-day • KN_P, kernel no. plant^–1 • LAI, leaf area index • PGR_S, plant growth rate during the critical period for kernel set bracketing silking

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