Maize has traditionally been the main staple diet in the Southern Asia and Sub-Saharan Africa and widely grown by millions of resource poor small scale farmers.
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Approximately, On the contrary to poor yields, the demand for maize as food, feed, and fuel is continuously increasing in these regions. Product added!
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Related Products. Add to cart Add to Wishlist. After this step, the markers that explain most of the genetic variance of a trait are selected. Efficient root systems enhance the relationship between the resources acquired and used for obtaining new resources and maintaining themselves ZHU et al. Plants typically respond to a nutrient deficiency by increasing the total length of both axial and lateral roots CHUN et al. Thus, studies investigating root morphology and plasticity when faced with environmental changes may be relevant for understanding the nutritional use efficiency of plants and, consequently, for helping select genotypes that are more tolerant to abiotic stresses RUTA et al.
The phenotype-based evaluation and selection of root traits uses methods that destroy the plant, which, depending on the genetic structure of the population, do not allow the use of the plants that were identified as superior in hybridizations. Consequently, there is a reduction in the potential gains that are obtained from the selection. In addition, some conventional breeding methods, such as recurrent selection, are very laborious and have shown low selection gains per unit time, often becoming uneconomical.
These facts can be mitigated with the use of GWS, which allows the early identification of superior genotypes without using destructive methods, thereby increasing the gains from selection and reducing the interval between generations. Prediction and selection may be performed at very early plant stages in this method, thus accelerating the breeding process. Additionally, the prediction tends to be more accurate because it considers the actual genetic relatedness of the evaluated individuals, rather than the mathematically calculated expected average relatedness.
Thus, the GWS enables a direct early selection because it acts on the genes that will be expressed in adulthood earlier than traditional early selection, which is indirect and acts via phenotypic assessment on the genes that are activated at an early age, hoping that it informs about its expression in adulthood RESENDE, Given the above, the objective of this study was to verify the accuracy of the GWS method when used in tropical maize breeding for root traits under conditions of nitrogen and phosphorus stress.
Two sources of germplasm were used in these experiments. The first consisted of seven inbred lines without any genetic variability in phosphorus use efficiency PUE , but with differing values of nitrogen use efficiency NUE Group I. Forty-one single-crosses were obtained by intergroup factorial mating unbalanced of the lines in these groups. These crosses were made reciprocally and involved the mixing of seeds of the same combination. The 41 single-crosses were evaluated in two experiments.
Genomic-based-breeding tools for tropical maize improvement.
The first experiment considered low nitrogen availability LN , and the second experiment considered low phosphorus availability LP. A randomized block design with two replicates was used in these experiments.
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The seeds were pre-germinated in a box with individual germination cells, with three seeds per inbred line. Soon after emergence, one seedling from each inbred line was transplanted to a cylindrical 4 dm 3 PVC pot 10 cm diameter x 50 cm height.
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The substrate for the N experiment was prepared by mixing sand and vermiculite in a ratio using the methodology described by Walk et al. The soil was used to absorb the phosphorus and prevent it from being readily available to the plant. The nutrient solution was replenished every two days starting on the seventh day after seedling emergence.
The solution described by Chun et al. Low P availability was simulated in the P experiment by addingonly 34 mg dm -3 of phosphorus in the form of triple superphosphate.
Quantitative Genetics, Genomics and Plant Breeding
The other nutrients were supplied by the nutrient solution without any added phosphorus addition. The seedlings were harvested at the vegetative stage with six completely expanded leaves V6 , which occurred 28 days after sowing. The seedling shoots were separated from the root system and stored in containers with water and alcohol solution The lateral and axial root lengths were extracted from all diameter classes d , and the lateral root lengths L LAT with a diameter less than or equal to 0.
X, Z W and T are incidence matrices that relate the effects of r, m, f, and c , respectively, to vector y. Eighty microsatellite markers SSR were used for genotyping. These markers were chosen for their informational content, location on chromosomes and, mainly, for their association with agronomic traits and abiotic stresses tolerance MAIZEGDB, The genotyping was only performed on the 14 parent lines, which had more than seven inbred generations.
Genetics, Genomics and Breeding of Maize
Thus, it was possible to extrapolate the marker results to single crosses. X and Z are the incidence matrices for b and h, respectively. Z has values of 0, 1 and 2 depending on the number of markers. Each locus is considered to explain in this method. In other words, equal parts of the genetic variance are assigned to all loci. The global genomic breeding value of the individual j is given by. Thus, the entire set of markers was first analyzed in all of the evaluated individuals the complete estimation population.
Nine marker subgroups that consisted of all markers , , , 50, 25, 10, 5, 2 and 1 marker s were generated from these results.