Agronomic Traits In Maize Research Articles

Xenia and Maternal Effects on Maize Agronomic Traits at Three Plant Densities

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−1 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−1 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.

Hybrid Performance among Maize Populations Selected for Resistance to Insects

Improvement of resistance to insects while maintaining other desirable agronomic traits in maize (Zea mays L.) populations has been an elusive goal for breeders. This study was conducted to evaluate crosses among II insect‐resistant breeding populations to identify paired populations for selection or extraction of inbreds. A complete diallel was evaluated for lodging, plant height, ear height, yield, ear damage by insects, and maturity in a complete‐block experiment with five replicates at two locations. Locations were combined because errors were homogeneous and the crosses × locations interaction was nonsignificant. General combining ability (GCA) effects were significant (P ≤ 0.01) for all traits, specific combining ability (SCA) effects were significant (P ≤ 0.01) for all traits except yield and maturity, reciprocal effects were significant (P ≤ 0.01) for all traits except yield, and maternal effects were significant (P ≤ 0.05) for all traits except yield and damage by insects. Hybrid checks were earlier, Shorter, higher yielding, and less prone to lodging but also less resistant to insects than were population crosses. Paired crosses resistant to corn earworm (Helicoverpa zea Boddie) and maize weevil (Sitophilus zeamais Motschulsky) that performed well for other traits are available fdr selection and inbred extraction. Paired crosses with resistance to fall armyworm (Spodoptera frugiperda J.E. Smith) were not identified. The information on GCA, SCA, reciprocal, and maternal effects will assist in identifying critical population crosses.

Dosage effects of y gene on grain yield and other agronomic traits in maize

White-endosperm (y y y) maize (Zea mays L.) is vital to the maize dry-milling industry. However, a substantially greater acreage in the U.S.A. is planted to yellow (Y Y Y) than white maize. Data on comparative performance of yellow and white maize is scanty, and results are inconclusive. This field study was conducted to provide information on dosage effects of y gene on grain yield, 500-kernel (K) weight, shelling percentage, plant and ear height, and cob weight. Yellow x yellow, yellow x white, and white x white endosperm crosses were made among five yellow and five white endosperm lines of Mo14W × Oh7B parentage.

Association of Restriction Fragment Length Polymorphisms among Maize Inbreds with Agronomic Performance of Their Crosses

Restriction fragment length polymorphisms (RFLPs) have been suggested as molecular markers to facilitate improvement of agronomic traits in maize (Zea mays L.). The objective of this study was to evaluate the utility of RFLP data in elucidating heterotic patterns among maize lines. Eight maize inbred lines and their 28 singlecross hybrids werevaluated for grain yield at two Iowa locations in each of 2 yr in a randomized‐complete block design. The diallel mating design permitted estimation of general and specific combining ability effects. Restriction fragment length polymorphism analysis of inbred lines included five restriction enzymes and five eDNA and 28 genomic clones distributed over the maize genome. Restriction fragment length polymorphism patterns of crosses were predicted from analysis of the inbred parents. Genetic distances between inbred lines were estimated as modified Rogers' distance (MRD). Grain yield and specific combining ability were significantly correlated with MRD for six of the 10 chromosomes. Dispersion of inbred lines and hybrids for RFLP allele frequencies was generally consistent with expectations based on known pedigrees. Results from this study suggest RFLP analysis as a potential alternative to field testing when attempting to assign maize inbred lines to heterotic groups.

Seasonal Factors of Correlation Between Climatic Factors, Photosynthetic and Agronomic Traits in Maize

AbstractThe dry matter accumulation and photosynthetic traits of upper leaves were studied twice weekly in 1983, under field conditions, for two early maturing maize cultivars. Analysis of correlation between climatic data and those traits were based on four week periods. Seasonal patterns of correlation coefficients were drawn by shifting the beginning of these four week periods from one sampling data to the next until four weeks before the end of the sampling period. Most traits were significantly correlated with climatic factors at one time or another; only those correlations which were of longer duration will be mentioned here. Net assimilation rate was positively correlated with maximum temperature during intensive leaf growth. The relative growth rate was closely correlated with photosynthetic photon irradiance (PPI) during the second half of June and with phosphofructokinase activity during the second part of July. The chlorophyll content showed a close and positive relationship with minimum temperature until the end of June and with PPI during most of August. The content of carotenoids was, for the most part, negatively correlated with climatic factors, the closest relationship existing with the PPI at the previous sampling date until the beginning of July. The activity of photosynthetic enzymes such as RuBP carboxylase, NADP malate dehydrogenase and PEP carboxylase was generally less closely correlated with climatic factors over longer periods. Patterns of correlation were remarkably similar for the two cultivars.

Effect of pollen storage by drying and deep-freezing on the expression of different agronomic traits in maize (Zea mays L.)

Pollen from the inbred maize line HMv 1645 was used to study the effect of pollen treatments (drying and deep-freezing) on the phenotypic performance of the next generation. Fresh and artificially dried pollen samples with different water contents (56%, 18%, 13% and 10%) were used for sib pollinations immediately after collection or drying. Samples containing low amounts of water were then stored in liquid nitrogen for 7 days. Fertilization ability of the samples with 13% water was the highest after storage. Plant characteristics of the next generation originated from the seeds set by differently treated (fresh, dried to 13% water and deep-frozen) pollen were examined and statistically analysed. Pollen treatments due to the pollen storage procedure did not cause detectable changes in quantitative characters of the next generation.

Effects of Puccinia sorghi Rust on Yield and Several Agronomic Traits of Maize in Hawaii1

Ten paired doublecross hybrids of maize (Zea mays L.), genetically similar except for the gene Rp‐d conferring resistance to Puccinia sorghi Schw., were studied under natural rust epiphytotics in an area with continuous corn production in Hawaii. Data on eight agronomic traits are summarized from April and November plantings, including grain yield, plant weight, ear length and diameter, 1,000‐kernel wt, plant and ear height, and days to silk. Rust was severe in both seasons, and slightly more so in winter (6.0 vs. 5.2 on a seven‐point scale). In this area, winter corn yields are characteristically about half those of summer, due to reduced light intensity and daylength.The rust affected all traits significantly when data combined over the two seasons were considered. Average reductions caused by rust were 35% for grain yield, 27% for fresh plant weight, 11% for ear length, 10% for kernel wt and ear diameter, and less than 5% for plant and ear height and days to silk. Highly significant interactions of season with treatment (resistant vs. susceptible hybrids) were detected in grain yield and plant height, with the rust effect generally enhanced in the winter planting. Grain yield reductions by rust were best correlated with changes in kernel weight (r = 0.78), but clearly reflected major effects on ear lengths and diameters as well. In areas of continuous corn production, uncontrolled P. sorghi rust can be a serious disease affecting essentially all components of yield.

Index Selection for Several Agronomic Traits in the BSSS2 Maize Population1

Expected genetic responses were used to compare the simultaneous improvement of several agronomic traits for three selection index methods in recurrent selection programs. Observations for various agronomic traits in maize (Zea mays L.) were obtained from 144 S1 lines of the BSSS2 maize population grown in several locations during the 1970‐72 growing seasons. These traits were European corn borer (Ostrinia nubilalis (Hubner)) resistance, cold tolerance (percentage of emergence, emergence index, and seedling dry weight), grain yield, grain moisture, root and stalk lodgings, and corn root worm (Diabrotica spp.) resistance (root damage, root size, and secondary root growth). Seven of them, grain yield, corn borer resistance, percentage emergence, emergence index, seedling dry weight, root size, and secondary root growth, were used to construct three types of index selection for S1 selection.The conventional indices constructed from two sets of arbitrarily assigned relative economic weights did not give satisfactory predicted improvement for all traits included in individual indices. Most of the predicted improvement went to grain yield and percentage of emergence. Base indices, in which relative economic weights were used as index coefficients, were 95 and 97% as efficient as conventional selection indices. Hence, the application of the base index would be preferable with S1 selection when precise relative economic values of the traits included in the indices are known. When modified selection indices (based on desired gains) were used, final goals from recurrent selection of the traits considered (S1 testing and 10% selection intensity) were predicted to be attained after 14 cycles or 28 years of selection. In another scheme of recurrent selection, corn borer resistance and cold tolerance traits would be evaluated in the S1 generation, and yield, root size, and secondary root growth would be tested hi the S2 generation. With 44 and 8% selection intensities in the S1 and S2 generations, respectively, improvement of all traits was expected to reach final goals after 10 cycles or 30 years of selection. Assuming that the two sets of the arbitrarily assigned relative economic weights were realistic, modified selection indices (based on their contributions to aggregate genetic advance) were shown to be only 46 and 61% as efficient as conventional indices for the specified desired gains and relative economic weights considered. Modified selection index with the S1 testing scheme was expected to give 53% of improvement for yield, compared with single trait selection based on yield alone. Use of the modified index selection is recommended for the simultaneous improvement of several agronomic traits in recurrent selection programs when the relative economic values of the traits are difficult to determine.Results from comparisons of predicted gain from recurrent selection with S1 testing and a combination of S1 and S2 testings suggested that S1 testing would be preferable, because fewer resources would be required and the construction of selection indices would be less complicated.