The aim of this work was to identify genomic regions associated with northern leaf blight resistance (Exserohilum turcicum) in common maize lines and to study the control involved in the resistance. For association mapping, 72 maize lines were previously genotyped for SNP markers on the 650K platform (Affymetrix®), and their respective genotypic values were predicted by mixed models for northern leaf blight. In order to avoid spurious associations between SNP markers and the studied character, the analysis of population structure was initially performed. The analysis of association between the SNP and northern leaf blight markers was carried out using a linear mixed model. For the study of genetic control, the experiment was conducted in 2016 and it was composed of randomized blocks with three repetitions. Through the notes attributed to the lines and their respective generations, the genotypic data related to the inheritance of the studied disease were extracted. Analyzing the results, QTLs were found on chromosomes 1, 2, 3, 4, 6, 8, 9 and 10 for northern leaf blight in maize, which may increase, reduce or even override the effect of this attribute. Among the QTLs found, five genomic regions were detected for increased resistance to northern leaf blight with the use of SNP markers, found in chromosomes 3 (SNP210703), 8 (SNP507268 and SNP507269), 9 (SNP544616) and 10 (SNP610500). The genetic control of resistance to northern leaf blight is quantitative, with the additive effects being more important in the character determination. In addition, it presents high restricted heritability (88%), which allows good selection efficiency and selection gains.
Among the maize leaf diseases, white leaf spot, northern leaf blight, gray leaf spot, and southern rust are recognized not only by the potential for grain yield reduction but also by the widespread occurrence in the producing regions of Brazil and the world. The aim of this study was to characterize common maize lines for resistance to white leaf spot, northern leaf blight, gray leaf spot, and southern rust and suggest crosses based on the genetic diversity detected in SNP markers. The experiment was conducted in a randomized block design with three replications in order to characterize 72 maize lines. Genotypic values were predicted using the REML/BLUP procedure. These 72 lines were genotyped with SNP markers using the 650K platform (Affymetrix®) for the assessment of the genetic diversity. Genetic diversity was quantified using the Tocher and UPGMA methods. The existence of genetic variability for disease resistance was detected among maize lines, which made possible to classify them into three large groups (I, II, and III). The maize lines CD 49 and CD50 showed a good performance and can be considered sources of resistance to diseases. Therefore, their use as gene donors in maize breeding programs is recommended. Considering the information of genetic distance together with high heritability for leaf diseases, backcrossing of parent genotypes with different resistance levels, such as those of the lines CD49 x CD69 and CD50 x CD16, may result in new gene combinations, as they are divergent and meet good performances.
The viability of pollen grains is the essential precondition for obtaining enhanced or hybrid vigor genotypes and a good fixation of the fruit. It is a matter of great importance, especially for genetic improvement programs, which are used in various types of controlled pollination. This study aimed to evaluate the viability of the maize pollen grain through in vitro germination and stainability tests, collected at different times. The experimental design was a randomized block with factorial 2x5, two days of pollination at five times (9:00 a.m., 11:00 a.m., 1:00 p.m., 3:00 p.m. and 5:00 p.m.) with four replications. Each treatment consisted of 12 plants, which were taken randomly within each plot. The parameters evaluated were: germination percentage, the percentage of pollen grain stainability, the stigma receptivity and the best time for pollination. Through the analysis of variance, it was noted and interaction between the days and times of collection and highly significant differences for the following parameters: temperature percentage, humidity, germination and viability of the pollen grain, indicating that the days and times influenced the viability of pollen grains. We could observe that the best results of viable pollen grains were obtained at 09.00 a.m. regardless of the day. It was also noted that the ambient temperature and relative humidity were the main influencing factors on pollen viability, and not the collection times.
The experiment was conducted in a protected cultivation in the Marechal Cândido Rondon, PR, Brazil. The experimental design was constituted of randomized blocks with six piggery wastewater doses (0, 25, 50, 100, 200 and 400 m³ ha-1) in four repetitions. The variables evaluated were: number of tillers, plant height, dry matter, leaf area, leaf number, potassium content, phosphorus content and crude protein in the culture, leachate and soil analysis. The number of tillers increased linearly with the addition of SRW doses. At the beginning of the development of millet culture, swine raising wastewater (SRW) application causes a decrease in plant height; however, over the course of time, this management increases those values. There was an increase in the number of leaves at the beginning, and leaf area at the end of the development of millet crop. The SRW doses applied did not cause increase in phosphorus and potassium contents in plants, raising only the crude protein. The dry mass is highly influenced by the increase in SRW doses, with their highest levels in a dose of 319.75 m³ ha-1. The SRW doses cause reduction in soil pH and its constituents are not leached.
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