Maize (Zea mays L.) kernel mass is a primary grain yield component controlled by genes from both the pollen and the maternal plant. We studied the contribution of genes attributable to kernel weight difference when inherited through the pollen versus the plant. We measured grain-filling characteristics, kernel moisture concentration, rate of moisture ross, and mature kernel dry weight for apical, mid-ear, and basal kernels of field-grown plants. We produced 12 hybrid strains by reciprocally intercrossing three strains that differ for grain-filling rates [high (tiC), random (RC), and low (LC) R-nj color expression] with two kernel-weight strains [large .(LG) and small (SM)]. Plants of each hybrid strain were pollinated with either LG or SM pollen in Fargo, ND, in 1990, 1991, and 1992. Multivariate analyses of variance showed that LG and SM pollen effects differed for rate of grain filling, lag phase duration, and kernel dry weight. Kernels from LG pollen had 0.4% shorter lag phases, grew 5.2% faster, and were 3.9% heavier at maturity than kernels from SM pollen. Developmental similarities among apical, mid-ear, and basal kernels suggested that a common assimilate supply controlled their growth. Kernels from LG plants had 2.6% higher grain-filling rates, 5.9% longer effective filling periods, 0.7% shorter lag phases, 7.6% heavier mature kernds, and 23 g kg-t
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-i 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-i 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.
Kernel mass is a primary yield component in maize (Zea mays L.) governed by both xenia and maternal effects. Because kernel growth depends on assimilate supply, we wanted to learn if kernel-weight genes also affect plant size and agronomic characters. We reciprocally crossed three strains known to differ for rates of grain filling [high (HC), random (RC), and low (LC) R-nj color] with two kernel-weight strains [large (LG), and small (SM)] to produce 12 hybrid strains. For 2 yr at two locations, we grew plants of each hybrid at 24 000, 48 000, and 72 000 plants ha-~ in plots arranged so that wind pollinated silks with either LG or SM pollen. Leaf number, leaf width, leaf length, and time to silk were measured to compute leaf area and average leaf expansion rate (ALER). We also measured grain yield and grain moisture concentration at harvest. In one of four environments, " hybrids pollinated by the LG strain had 34% higher yields and 24 g kg-~ lower harvest moisture than hybrids pollinated by the SM strain. Increasing plant density delayed silking, increased leaves per plant, and decreased leaf width. Hybrid plants from the LG strain yielded 10% more than hybrid plants from the SM strain. They also had 12% higher grain moisture at harvest, 11% greater leaf surface area (mainly from more and wider leaves), and silked 0.6 d later than SM plants. Hybrid plants from the HC strain produced higher grain yields and greater leaf surface areas than plants from the RC or the LC strains. Leaf surface area was correlated (r = 0.80, P < 0.01) with grain yield. Kernel growth genes influenced yield via xenia effects but mainly by genes in the plant. Although R-nj color genes only increased yields of specific reciprocal hybrids, in properly planned hybrids these genes may complement genes that increase yield via larger kernels.
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