ABSTRACT. The aim of this study was to characterize maize lines tolerant to cold temperatures during the germination process. Seeds from lines with different levels of tolerance to low temperatures were used; 3 lines were classified as tolerant and 3 as susceptible to low germination temperatures. A field was set up to multiply seeds from selected lines. After the seeds were harvested and classified, we conducted physiological tests and analyzed fatty acid content of palmitic, stearic, oleic, linoleic, linolenic, and eicosenoic acids. In proteomic analysis, the expression of heat-resistant proteins, including catalase, peroxidase, esterase, superoxide dismutase, and α-amylase, were evaluated. Transcript analysis was used to measure the expression of the genes AOX1, AOX2, ZmMPK-17, and ZmAN-13. The material showing the highest susceptibility to low germination temperatures contained high saturated fatty acid content. Expression of α-amylase in seeds soaked for 72 h at a temperature of 10°C was lower than expression of α-amylase when soaked at 25°C for the same amount of time. We observed variation in the expression of heat-resistant proteins Gene expression related to temperature tolerance in maize in seeds of the lines evaluated. The genes AOX and Zm-AN13 were promising for use in identifying maize materials that are tolerant to low germination temperatures.

The importance of plant breeding in Brazilian agriculture has grown a lot in the last 50 years. This occurred mainly because of the: increase in graduate programs, which qualified hundreds of professionals; creation of EMBRAPA and other research institutes or state companies, with an emphasis on the production of new cultivars and; promulgation of the cultivar protection law, which stimulates investments in seed production. The retrospective of what happened, enabling the country to move from being an importer of grains, fruits, and fibers to one of the largest exporters of these products worldwide, was the focus of this work. Taking as reference some agricultural products, this article highlights the significant contribution of plant breeding in recent years. Also, some of the enormous challenges that still have to be overcome, in which the participation of Brazilian breeders will be fundamental to continue the progress of agriculture in the coming years.

Knowing genes related to water deficit is a valuable tool to assist and accelerate the selection process of maize genotypes more adapted to drought conditions. Therefore, this work aimed to evaluate genes expression related to tolerance to water deficit in maize lines, using proteomic and transcriptomic analyses. Two lines previously classified as tolerant (91-T) and non-tolerant (57-NT) to low water availability were used. Dried seeds, ears tips, and seedlings (collected at three, five, and seven days after sowing) of the two maize lines (91-T and 57-NT) were used in proteomic analyses. Seedlings were subject to two contrasting water-availability conditions (70% and 10% of the water retention capacity). The expression of catalase, peroxidase, and esterase enzymes and heat-resistant proteins were evaluated by electrophoresis. Dried seeds, ears tips, and seedlings (collected at seven days after sowing, subject to two contrasting water-availability conditions) of two maize lines (91-T and 57-NT) were used in the transcriptomic analyses. The expression of genes associated with tolerance to low water availability (ZmPP2C, ZmLEA3, and AOX2) was evaluated by the qRT-PCR technique. Results revealed that catalase, peroxidase, and esterase enzymes had a higher expression on the ears tips of the 91-T line. The expression of catalase and esterase enzymes reduced in seven-day-old seedlings in the two lines analyzed. Heat-resistant proteins had greater activity on the dried seeds of the 91-T line. The AOX2 gene was identified as a potential marker for the selection of maize genotypes tolerant to water deficit.

In conducting a recurrent selection (RS) program in tobacco (Nicotiana tabacum L.), inbred and noninbred progenies as well as double‐haploid (DH) progenies can be used. There is also the possibility of recombining the selected progenies using half‐sib (HS) or full‐sib (FS) progenies. To choose the best RS strategy, the breeder's equation can be used. When using inbred progenies with an allelic frequency other than 50%, one of the genetic variance components is the genetic covariance between additive effects and homozygous dominance effects (D1). This component may present negative values and is part of the numerator in the equation for gain from selection (GS). Thus, the objective of this study was to estimate the genetic variance components in a tobacco population and compare the different strategies to conduct RS. From an RS population, HS, FS, and S1:2 inbred progenies were evaluated in different experiments. The dominance variance was null. In this condition, the estimate of D1 is not significant, meaning that D1 does not influence the GS in the RS program. With the obtained estimates, the GS was estimated for the seven different strategies for conducting the RS program. The use of DH lines in tobacco RS represents the best strategy. Other strategies allow expressive GS, such as the alternate use of inbred and FS progenies, for evaluation and FS progenies for recombination.

The cycle of the common bean crop is shorter than that of other species. Nevertheless, in Brazil, researchers have been attempting to shorten the cycle even more to allow three crops a year and obtain greater flexibility in crop management. The aim of this study was to investigate the viability of selecting lines with a shorter cycle and that have good grain yield coming from the same segregating population. To that end, crosses were made between a short cycle and normal cycle cultivars. In the F2 and F2:3 generations, progenies were separated into two groups based on short or normal cycle. After that, the progenies selected were evaluated in the F2:4 and F2:5 generations for grain yield, cycle, and yield per day. The mean of the short cycle progenies was 15% lower for grain yield and 10% lower in yield per day in relation to the normal cycle progenies. Furthermore, selection of lines among those of short cycle that have grain yield equivalent to the best normal cycle lines is of very low probability.

Soybean seed production with high physiological quality is important for ensuring populations of recommended plants for each cultivar. It is also known that there is genetic variability for this characteristic among the soybean cultivars. The objective was to study the genes expressionof protein and gene transcript involved in the physiological quality of soybean seeds. The seeds of CD 206 and CD 201 cultivars were classified as high quality while Savana and Emgopa 316 cultivars were classified as low quality by germination and vigor tests. Physiological, enzymatic and transcripts analysis were held in seeds of each cultivar during two harvest seasons, R8 and R8 + 15 days; at protein level the alcohol dehydrogenase isoenzyme systems (ADH), phosphoglucoisomerase (PGI), superoxide dismutase (SOD), catalase (CAT), malate dehydrogenase (MDH) and isocitrate lyase (ICL). The PCR technique in real time (qRT-PCR) was used for transcritome studies for quantitative gene expression analysis. The method used was the comparative Ct considering the relative expression levels in relation to cultivar of high quality CD 201. It is concluded that there is higher enzymes expression involved in respiration, alcohol dehydrogenase (ADH), malate dehydrogenase (MDH) and phosphoglucoisomerase (PGI), in seeds with high physiological quality, especially when harvesting is delayed. The proteomic and transcriptomic profiles related to the genes involved in free radicals removing systems in soybeans varies among cultivars and the season of seed harvest.

The objective of this study was to evaluate gene expression related to water deficit tolerance in maize lines. For this, lines previously classified as tolerant (91-T and 32-T) and non-tolerant (24-NT and 57-NT) to water deficit were used. The seeds of the four lines were evaluated for emergence and emergence speed index, and the seedlings were evaluated for root and shoot length under two conditions of water availability (70 and 10% substrate water retention capacity). In transcript analysis, the expression of several genes associated with water deficit tolerance, ZmDBP3, ZmALDH9, ZmAN13, and ZmDREB2A, was evaluated by qRT-PCR for the 91-T and 57-NT lines. It can be concluded that soil water deficiency did not reduce root development. However, the shoot length was significantly lower under dry conditions. Through transcript analysis, the genes ZmDBP3 and ZmAN13 were identified as potential markers for the early selection of maize lines tolerant to water deficit.