Effectiveness of the R1-navajo embryo marker on sorting haploids in tropical maize germplasm

Modern maize breeding is currently based on Doubled Haploids (DH) technology. In following the steps to produce inbred lines by DH, sorting the haploids are the most important of them. Haploid inducers usually carry the R1 gene, responsible of purple pigmentation on seeds. Navajo is a typical phenotyping from this gene and leads to purple coloration on endosperm and embryo of the diploids but any pigmentation on haploid kernels. Aimed to analyze the effectiveness of R1-nj on sorting true haploids over tropical sources, two different experiments were conducted. In the first experiment, kernels analyzed came from the following induction cross (L47 x IL47), (P9 x IP9), (2B707 x IL47), and (2B707 x IP9) in which IL47 and IP9 were the tropical haploid inducers. In the second experiment, KHI (Krasnodar Haploid Inducer) was the haploid inducer and three commercial were adopting as sources. Putative haploids were sorted by R1-nj expression and the haploid level was checked by chromosome counting our phenotyping at the flowering stage. Overall, very low true haploid discovery rates were observed. 2B707 was the most reliable source in displaying true haploids. The ratio of this effectiveness among the two ex- periments to R1-nj marker ranged from 8.80 to 30.2%. These results can be explained by the presence of inhibitory genes on the tropical sources. Additionally, at the flowering stage, haploids plants had data of spontaneous doubling collected and summarized. Recovery on the female organs seems to be higher than male. Haploids from the IAC125 source exhibited best fully spontaneous doubling among the sources analyzed

Bias in the prediction of genetic gain due to mass and half-sib selection in random mating populations

The prediction of gains from selection allows the comparison of breeding methods and selection strategies, although these estimates may be biased. The objective of this study was to investigate the extent of such bias in predicting genetic gain. For this, we simulated 10 cycles of a hypothetical breeding program that involved seven traits, three population classes, three experimental conditions and two breeding methods (mass and half-sib selection). Each combination of trait, population, heritability, method and cycle was repeated 10 times. The predicted gains were biased, even when the genetic parameters were estimated without error. Gain from selection in both genders is twice the gain from selection in a single gender only in the absence of dominance. The use of genotypic variance or broad sense heritability in the predictions represented an additional source of bias. Predictions based on additive variance and narrow sense heritability were equivalent, as were predictions based on genotypic variance and broad sense heritability. The predictions based on mass and family selection were suitable for comparing selection strategies, whereas those based on selection within progenies showed the largest bias and lower association with the realized gain

Methods to classify maize cultivars in use efficiency and response to nitrogen

n plant breeding programs that aim to obtain cultivars with nitrogen (N) use efficiency, the focus is on methods of selection and experimental procedures that present low cost, fast response, high repeatability, and can be applied to a large number of cultivars. Thus, the objectives of this study were to classify maize cultivars regarding their use efficiency and response to N in a breeding program, and to validate the methodology with contrasting doses of the nutrient. The experimental design was a randomized block with the treatments arranged in a split-plot scheme with three replicates and five N doses (0, 30, 60, 120 and 200 kg ha-1) in the plots, and six cultivars in subplots. We compared a method examining the efficiency and response (ER) with two contrasting doses of N. After that, the analysis of variance, mean comparison and regression analysis were performed. In conclusion, the method of the use efficiency and response based on two N levels classifies the cultivars in the same way as the regression analysis, and it is appropriate in plant breeding routine. Thus, it is necessary to identify the levels of N required to discriminate maize cultivars in conditions of low and high N availability in plant breeding programs that aim to obtain efficient and responsive cultivars. Moreover, the analysis of the interaction genotype x environment at experiments with contrasting doses is always required, even when the interaction is not significant