Maize Kernel Development in Vitro: Sucrose Concentration, Xenia, and Maternal Effects

Abstract

Grain‐filling rates primarily determine kernel mass, an important yield component in early‐maturing maize (Zea mays L.). To learn how genes control grain‐filling rates, we studied 12 hybrids among strains divergently selected from a single genetic background. We reciprocally intercrossed three strains selected to differ for grain‐filling rates [high (HC), random (RC), and low (LC) R‐nj aleurone color] to a large‐(LG) and a small‐kernel (SM) strain. We pollinated hybrid plants with LG‐ or SM‐strain pollen to produce a (2 × 3 × 2 × 2) factorial set of kernel genotypes. After 3 d, cob pieces with a single attached ovule of each genotypo were explanted and grown in vitro with 80, 120, or 160 g L−1 sucrose. We sampled kernels and cob pieces after 7, 14, and 21 d. Kernel dry weight and water content increased while kernel moisture concentration decreased linearly during the 21 d in culture. Cob dry weight increased until 14 d in culture. Kernels cultured on a medium with 160, compared to 80, g L−1 sucrose grew 27% faster but lost moisture concentration 32% more slowly. Kernels pollinated with LG, compared to SM, pollen accumulated dry matter 27% faster and achieved 36% higher mean dry weights. Kernels explanted from LG, compared to SM, plants grew 29% faster and averaged 34% higher dry matter. Significant (P < 0.01) reciprocal differences among hybrid plants for kernel traits and xenia effects on cob piece growth in culture suggest that exogenous genes influenced development rates. Paternal and maternal genes in the kernel, and sucrose supply also influenced kernel dry matter, kernel water content, and cob dry weight in vitro.