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.
The objectives of this study were to assess phenotypic diversity of Bambara groundnut germplasm from Côte d'Ivoire using qualitative traits and to understand the genetic diversity at different levels. Hundred and one accessions collected from four agro-ecological zones (central, eastern, northern, western) were characterized in a randomised complete block design with three replications. Thirteen qualitative traits were recorded from seedling emergence to physiological maturity of the crop species. All recorded traits were found to be polymorphic with three or four phenotypic classes. The results revealed a considerable amount of phenotypic variation in the germplasm studied. The phenotypic variation was expressed in color, shape, texture, flexibility, growth habit, pilosity and hardness in both the aerial organs and the underground pods. Cluster analysis grouped together accessions into six genetically distinct groups independently to their geographical origin, suggesting seeds exchanges between growing-zones. The chi-square analysis highlighted the presence of phenotypic variability within and between accessions from each agro-climatic zone for most of the traits evaluated indicating some adaptive forms related to the four zones. Estimates of Shanon-Weaver diversity index (H') for all agro-climatic zones ranged from 0.32 to 0.66 with a mean of 0.46. The northern zone appeared phenotypically more diversified (H' = 0.66) than the others. These results are useful to ensure efficient germplasm collection, conservation and management strategies.
We analysed the genetic diversity of nine populations of two subspecies of Sarotherodon melanotheron using allozymes in relation to the existence of environmental pressures. The genetic variability of Sarotherodon melanotheron melanotheron in the Ivorian ecosystem (A = 1.23, He = 0.04 and P (95%) = 11.11) was lower than that of Sarotherodon melanotheron heudelotii of the estuaries in Gambia and Saloum (A = 1.68, He = 0.08 and P (95%) = 22.23). The analysis of allelic diversity revealed that the individuals of S. m. melanotheron subspecies from a much polluted environment (lagoon of Grand-Lahou or Ebrié) presented a relatively higher frequency of allele GPI-2 * 80 than those of a less polluted environment (Aby lagoon and Ayamé lake). The allele IDH-2 * 90 was expressed only in the specimens of S. m. heudelotii found in the Saloum estuary, a very saline environment compared to the estuary of Gambia. A deficit of heterozygosis was observed with the tilapia Sarotherodon melanotheron. This study confirmed the possibility of using allozymes as biomarkers and bioindicators of environmental disturbances.
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