The study aimed to address the optimal plant population density in maize that maximizes phenotypic expression and differentiation, and lessens environmental effects on genotypic expression in terms of the response to selection. A set of seven short-season hybrids (Rom set) was tested under rainfed conditions (2006, 2007) in Romania, and a set of seven long-season hybrids (Gr set) was tested with irrigation (2007) in Greece. Experimentation was conducted under ultra-low (ULD), low (LD), middle (MD), and high (HD) densities (0.74, 2.51, 4.20, 8.40 plants/m 2 for the Rom set, and 0.74, 3.13, 6.25, 8.33 plants/m 2 for the Gr set). Phenotypic expression and differentiation for grain yield were highest at the ULD. Coefficient of variation (CV) for grain yield, ear length and kernel row number decreased as density decreased. Environmental conditions and hybrid plant-yield potential (i.e., maximum yield per plant) were crucial for the optimal density that achieved the lowest environmental variance. For the Rom set the lowest CV for grain yield was obtained at the LD in the unfavourable season and at the ULD in the favourable season. The less acquired variance was achieved at the ULD for the highest yielding hybrids and at the LD for the lowest yielding hybrids, revealing a negative association between plant-yield potential and optimal density. Concluding, a density proximal to the ULD approximates absence of competition in maize, and optimizes three determinant parameters for successful selection: selection intensity, heritability and phenotypic differentiation.
The genomes of the two plant organelles encode for a relatively small number of proteins. Thus, nuclear genes encode the vast majority of their proteome. Organelle-to-nucleus communication takes place through retrograde signaling (RS) pathways. Signals relayed through RS pathways have an impact on nuclear gene expression but their target-genes remain elusive in a normal state of the cell (considering that only mutants and stress have been used so far). Here, we use maize cytolines as an alternative. The nucleus of a donor line was transferred into two other cytoplasmic environments through at least nine back-crosses, in a time-span of > 10 years. The transcriptomes of the resulting cytolines were sequenced and compared. There are 96 differentially regulated nuclear genes in two cytoplasm-donor lines when compared with their nucleus-donor. They are expressed throughout plant development, in various tissues and organs. One-third of the 96 proteins have a human homolog, stressing their potential role in mitochondrial RS. We also identified syntenic orthologous genes in four other grasses and homologous genes in Arabidopsis thaliana. These findings contribute to the paradigm we use to describe the RS in plants. The 96 nuclear genes identified here are not differentially regulated as a result of mutation, or any kind of stress. They are rather key players of the organelle-to-nucleus communication in a normal state of the cell.
During the process of maize seed production, in order to ensure the genetic purity of parental forms of hybrid maize, an important work performed is the removal of male inflorescences from plants on mother rows. Hand detasseling has high precision but is labor-intensive. Mechanical detasseling offers the possibility to cover large acreages in a short period of time, but the number of leaves removed has a varying influence on plant performance and seed yield. The aim of this study was to simulate three types of damages on plants similar to those induced through mechanical detasseling and to assess the effects for five inbred lines during the course of three years. Results show that when tassels alone were removed, the average seed yield decreased an average of 4–21%. When two leaves were removed with the tassel, yield decreased an average of 22–31%, while when plants were cut above the main ear, seed yield decreased an average of 31–66%. Environmental conditions influenced seed yield, especially high temperatures during flowering. Yield response to tassel and leaves removal varied between the inbred lines. Genotype controls maize ear and kernel characters, while environmental factors exercise a strong influence on seed yield, due to the succession of years with contrasting weather conditions in a key phenophase. Within the trend of full mechanization in agriculture, identification of inbred lines that cope better with plant damage can assist in optimizing seed production.
The influence of Fusarium ear infection on the maize yield and mycotoxin content (Transylvania-Romania) Maize is the host for a large number of pathogens, which invade all of its organs from the germination until being harvest, ear and grain infection often persistent even during storage. Diseases, through their symptoms reduce significantly the quantity and the quality of yield, estimated between 7-17% but, in the favorable years for this disease, they can be much greater. Fusarium diseases reduce yield value and quality by massive accumulation of Fusarium mycelium biomass (about 85%) on grain and ears and by mycotoxin contamination such as deoxynivalenol (DON), zearalenone (ZEA) and fumonisins (FUM). In this paper are presented aspects regarding the reaction of some maize hybrids under Fusarium spp. natural and artificial infections; the effect of Fusarium ear infection on yield, grain chemical composition, and mycotoxin content; the correlation between ear rot disease degree and yield ability, starch, protein and fat content. ANOVA evidenced the significant influence of experimental factors: infection conditions with Fusarium spp., maize genotypes, and their interaction on expression of the disease degree, yield capacity, protein, starch, fat and DON content. Average yield losses ranged between 7,0-9,3% during the experimental period. The hybrids Turda Star and Turda Favorit were more resistant to Fusarium ear rot, and Turda 165 was the most susceptible one. The artificial infection of ear with Fusarium spp. determined significantly decrease of starch and fat content and increases the protein and DON content for the most part of maize hybrids. Between rot diseased kernels and DON content a positive correlation was determined.
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