Is heterosis in maize mediated through better water use?

Abstract

• Heterosis increases yield potential and improves adaptation to stress in maize (Zea mays); however, the underlying mechanisms remain elusive. • A set of tropical inbred lines and their hybrids were grown in the field for 2 yr under three different water regimes. First-year plant water use was evaluated by measuring instantaneous traits (stomatal conductance (g_s) and steady-state chlorophyll fluorescence (F_s)) in individual leaves together with time-integrative traits, which included mineral accumulation in the whole leaves of plants and oxygen isotope enrichment above source water (Δ¹⁸O) and carbon isotope discrimination (Δ¹³C) in the same pooled leaves and in mature kernels. Second-year water use was evaluated by measuring leaf temperature, g_s and relative water content (RWC). • Within each growing condition, hybrids showed higher F_s, mineral accumulation, RWC, and lower leaf temperature, Δ¹⁸O and Δ¹³C than inbred lines. Therefore, hybrids had a better water status than inbred lines, regardless of the water conditions. Differences in grain yield across growing conditions were explained by differences in water-use traits, with hybrids and inbred lines following a common pattern. Within each growing condition, most variations in grain yield, between hybrids and inbred lines, were also explained by differences in plant water-use traits. • Heterosis in tropical maize seems to be mediated by improved water use, irrespective of the water conditions during growth.