White Maize Populations Research Articles

Screening of suitable genotype for Bangladesh conditions based on genetic variability and path analysis in F2 white maize populations

AbstractWhite maize is the new maize (Zea mays L.) cultivar in Bangladesh. The country needs high‐yielding white maize varieties for farmers’ cultivation, but developing such variety requires appropriate inbred lines. Here, nine F2 populations of white maize were evaluated through assessment of their genetic variability, heritability, and character association for selection of promising lines based on yield and growth parameters. Analysis of genetic variability showed that there were significant variations among the various genotypes of F2 populations. High heritability coupled with large genetic advances in percentage means were obtained in plant height, cob height, number of branches per tassel, number of cobs bearing node, leaf blade area, and grain yield per plant. The analysis of path coefficient indicated positive direct contribution towards yield per plant through days to 50% tasseling, days to 50% silking, cob height, days to maturity, number of branches of the tassel, cob breadth, and number of grains per row. The results thus indicated that indirect selection based on plant height, days to maturity, cob height, leaves per plants, cob length, number of rows per cob, and number of grains per row are reliable to select the appropriate lines for yield improvement in white maize. In view of the yield and its contributing characteristics, the population of KS 510 has a high yield potential for improvement of the varietal performance of white maize.

Improving Drought Tolerance in White Maize Population

Improving Drought Tolerance in White Maize Population

Efficiency of Index-Based Selection Methods for Stem Borer Resistance in Maize (Zea mays L.)

Breeders need a simple and reliable index that could be used to make selection quickly in a breeding program. A study was conducted at the International Institute of Tropical Agriculture, Nigeria, to compare efficiency of four selection indices in selecting the best genotypes in a population improvement program involving a yellow-grained (DMR ESR-Y) and white-grained (DMR ESR-W) maize (Zea mays L.) population under artificial stem borer infestation. Rank summation index (RSI), Base index (BSI), Multiplicative index (MI), and Optimum index that uses heritability as weight (OI) were compared using grain yield, plant aspect, ear aspect, stalk breakage, and tolerance to stem borer as selection criteria. The selection criteria had moderate to high narrow-sense heritability. Each of the traits had a significant correlation with all selection indices, except MI in DMR ESR-Y. The BSI had the highest selection differential (23.32%) followed by OI (21.45%) in the white maize population. It also had the highest (29.11%) followed by RSI (20.99%) in the yellow maize population. The BSI also had strongest correlation with RSI in the white (−0.95**) and the yellow maize population (−0.90**). Percentage similarity was highest between BSI and RSI in the white (82.6%) and yellow maize populations (72.3%). This suggested that both BSI and RSI are good selection indices that could be used in improvement programs for stem borer resistance in maize.

Genetic characterization and population structure of maize populations using SSR markers

Maize is a major staple food in sub-Saharan Africa. However, due to the threats posed by biotic and abiotic constraints to its production, it is a prerequisite to conserve germplasm with diverse genetic background and to seek for favourable genotypes with such background for improvement of superior genotypes. This study assessed the diversity of 70 white maize populations developed at CSIR-Savanna Agricultural Research Institute with resistance/tolerance to drought and low soil nitrogen (Low-N) using 31 SSR markers. A total of 288 alleles were detected among the germplasm used with a range of 4 to 17 alleles per locus and an average allele number of 9.60 alleles per locus. Polymorphic Information Content values for the SSR markers ranged from 0.32 to 0.85 with a mean value of 0.68. The average heterozygosity obtained from the markers was 0.54 and gene diversity ranged from 0.35 to 0.87 with a mean gene diversity value of 0.71 indicating a high level of polymorphism among the populations. Clustering based on Jaccard's similarity coefficient and an Unweighted Pair Group Method with Arithmetic Mean (UPGMA) revealed 5 clusters for the 70 populations. Evanno method for population structure clustering further revealed two sub-populations. Sub-population 1 was more genetically diverse with an Fst value of 0.18 than sub-population 2 which recorded an Fst value of 0.013. These results indicated that the SSR used were very polymorphic for diversity studies. Also, the studied maize populations are diverse and heterozygous, making them ideal source populations for extraction of drought and low-N tolerant inbred lines.

GENETIC REPEATABILITY, PHENOTYPIC AND GENOTYPIC COEFFICIENT OF VARIABILITY OFWHITE MAIZE (Zea mays L.) POPULATIONS

A plant breeder’s success in executing any breeding program depends greatly in the presence and amount of genetic variation including the genetic repeatability of the traits of interest. Fifteen white maize populations available at the Institute of Plant Breeding (IPB), University of the Philippines Los Baños (UPLB) were grown and evaluated at the Central Mindanao University (CMU) and UPLB on July and December 2011 respectively, to assess the genetic repeatability and the estimates of genetic coefficient. Different maize characters such as yield, days to anthesis , days to silking, plant and ear height, stand count, number of ears, ear length, ear diameter and shelling percentage were studied. The results revealed that in terms of repeatability, yield (31%), plant height (34.88), ear height (41.84%), and shelling percentage (35.54%) obtained moderate values while the rest of the traits indicated low values. Estimates of phenotypic coefficient of variation (PCV) exhibited moderate values for yield, stand count and number of ears while low values were indicated by all of the traits for genotypic coefficient of variation (GCV). Low magnitude of GCV as well as moderate genetic repeatability for the traits being investigated suggests that these parameters were under the control of environmental effects.Â

Changes in genetic variances and heritabilities in an early white maize population following S1 selection for grain yield, Striga resistance and drought tolerance

SUMMARYDrought is a major constraint to maize production in West and Central Africa (WCA). Assessment of genetic gain from S1 recurrent selection under drought is crucial for the development of drought tolerance breeding strategies. In an early white population, 60 S1 families each derived from the base population and three cycles of selection were evaluated under drought and well-watered conditions at two locations in Nigeria for 2 years to determine genetic variability, gains from selection and predict response to selection for grain yield and other traits. Genetic variances generally decreased for yield and other traits in advanced cycles under drought and well-watered conditions except yield and ear height under well-watered conditions. Similarly, heritabilities for yield and other traits decreased in advanced cycles under drought but increased in advanced cycles under well-watered conditions. Realized gain for yield was 0·291 t/ha, corresponding to 30·5% per cycle under drought and 0·352 kg/ha with a corresponding gain of 16·7% per cycle under well-watered conditions. Predicted gain based on C3 was 0·282 and 0·583 t/ha under drought and well-watered conditions. Low genetic variances, heritabilities and predicted gain for yield and other traits suggested a need to introgress drought tolerance genes into the population.

Evaluation of White Maize Populations for Quality and Agronomic Performance

Maize (Zea mays L.) used for food is mostly white, but studies involving white maize varieties are scarce. Furthermore, limited efforts have been devoted to improve white maize. We evaluated a wide collection of open‐pollinated white maize populations to identify the most suitable populations as base germplasm for a breeding program for bakery aptitude. There was large variability for growth cycle and other agronomic traits but not for grain moisture. Differences for quality traits were not significant except for grain hardness. Genotype × environment interaction was significant for days to anthesis and silking, and for other agronomic performance‐related traits, but not for grain moisture, interactions were due to magnitude rather than to rank changes. Flowering time and grain moisture were clearly associated to population origin, whereby populations from northern Spain were earlier than those from the south. Yield was moderate for these populations, and there were four northwestern Spanish and one American population with the best agronomic performances, medium growth cycle, and intermediate grain hardness. The maize population Rebordanes had the most promising value for yield and had high grain hardness. These white maize populations are potential valuable sources of base germplasm for breeding for traditional products.

Genetic Analysis and Identification of RAPD Markers Linked to Northern Corn Leaf Blight Disease Resistance in a White Maize Population

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Extent of Cross‐Fertilization in Maize by Pollen from Neighboring Transgenic Hybrids

There is an increasing concern about the preservation of genetic identity of conventional maize (Zea mays L.) and of distance required to segregate non‐genetically modified (non‐GM) from GM grain production since the introduction of Bacillus thuringiensis (Bt) and other transgenic events into commercial hybrids. Field experiments were conducted at three sites in Ottawa, Canada, for 3 yr to determine (i) the extent of cross‐fertilization of a maize genotype by foreign pollen of neighboring hybrids and (ii) the practical distance required to isolate conventional maize hybrids from neighboring GM maize fields. At each site, yellow‐kernel Bt maize was planted in the center (27 by 27 m) of a field surrounded in all directions by the distance equivalent to 24 or 48 rows (37 m) of white‐kernel maize, and a 200‐m non‐maize crop was maintained in all directions. Phenology and weather conditions were closely monitored during the tasseling and silking period. At maturity, a thorough examination on the cross‐fertilization was conducted in the white maize population. Our results showed that the rate of cross‐fertilization in maize was dependent upon the distance from the pollen source, wind direction and synchronization of silking and pollen shedding of the two genotypes involved. Up to 82% out‐cross was measured in the first row adjacent to the Bt maize. The level of out‐cross was <1% beyond the 37th border row (28 m) downwind and the 13th row (10 m) upwind in all site‐years. An exponential decline model was fitted well (P < 0.01) to the cross‐fertilization data as a function of distance from the yellow maize pollen source with R2 up to 0.64. Our data suggested that it is possible to produce non‐GM maize grains by removing the outside rows of non‐GM maize plants (about 30 m) neighboring the GM maize field in concern if the acceptance level is set at ≤1% out‐cross. The generally recommended 200‐m distance between two genotypes (inbreds, populations, hybrids, and wild relatives) appears to be appropriate for Bt or other GM maize, as well.

Effect of S3 Recurrent Selection in Four Tropical Maize Populations on Their Selfed and Randomly Mated Generations

Maize (Zea mays L.) breeders working with lowland tropical germplasm have experienced difficulties in developing good inbred lines. One limitation is moderate to drastic inbreeding depression (ID) these germplasms. In the present study, two cycles of S3 recurrent selection were conducted in four white maize populations (Pop. 21, Pop. 25, Pop. 29, Pop. 32) with tropical adaptation to improve them as hybrid‐oriented source germplasm, and the effect of selection was examined in the selfed (S1) and randomly mated (Syn‐2) generations. In each population, 200 to 250 S3 progenies were evaluated and 15 to 20 selected and intermated to form improved versions after cycle 1 (C1) and cycle 2 (C2). Selection was practiced for high grain yield, vigor, and other agronomic traits during inbreeding generations and in the S3‐progeny tests. The S1 and Syn‐2 generations of the C0, C1, and C2 of four populations were evaluated in three environments in Mexico, using split‐split plot design with populations in main plots, generations in subplots, and cycles in sub‐subplots. Selection improved the grain yield of the S1 generation, and the linear gain per cycle (Gc) was 12, 9, 4, and 4% in Pop. 21, Pop. 29, Pop. 32, and Pop. 25, respectively, being significant in Pop. 21 and Pop. 29. The C2 of Pop. 21 had the highest grain yield in both Syn‐2 and S1 generations. Generally, selection did not significantly affect grain moisture, days to silk, and anthesis‐silking interval, but it increased plant height in different populations. Combined over populations, however, grain moisture was significantly increased in addition to grain yield and plant height in both S1 and Syn‐2 generations. The linear Gc for grain yield across populations was 7.41 and 3.20% in the S1 and Syn‐2 generations, respectively. The effect of selection on grain yield and plant height was generally lower in the Syn‐2 than the S1 generation of Pop. 25, Pop. 29, and Pop. 32, but was comparable in two generations of Pop. 21. The ID for grain yield across populations decreased from 39% in CO to 35% in C2. The selection was effective in improving grain yield and reducing ID; and the improved populations would serve as better germplasm sources for the extraction of vigorous inbred lines.