Genetic diversity is essential for crop breeding and one way to estimate it is through the concept of genetic base, which can be defined as the number of ancestors and their relative genetic contributions (RGC) to each cultivar. The RGC can be estimated through the coefficient of parentage between the ancestors and cultivars. Previous studies determined that the genetic base of Brazilian soybean was very narrow. The objective of this work was to evaluate the pedigree of 444 Brazilian soybean cultivars to estimate their genetic base. The cultivars were divided according to their release dates and according to their origin (public or private), and the genetic base for each group was also estimated. We found 60 ancestors, of which the top four (CNS, S-100, Roanoke and Tokyo, respectively) contribute 55.3% of the genetic base. Only 14 ancestors have an RGC over 1.0%, and they represent 92.4% of the genetic base. Analysis of the release dates indicated that there has been an increase in the number of ancestors over time, but the four main ancestors were the same over all periods, and their cumulative RGC increased from 46.6% to 57.6%, indicating a narrowing of the genetic base.

Soybean is one of the most valuable and profitable oil crop species and a thorough knowledge of the genetic structure of this crop is necessary for developing the best breeding strategies. In this study, a representative collection of soybean cultivars recommended for farming in all Brazilian regions was genotyped using 27 simple sequence repeat (SSR) loci. A total of 130 alleles were detected, with an average allelic number of 4.81 per locus. These alleles determined the core set that best represented this soybean germplasm. The Bayesian analysis revealed the presence of two clusters or subgroups within the whole collection (435 soybean cultivars) and the core set (31 entries). Cultivars of similar origin (ancestral) were clustered into the same groups in both analyses. The genetic diversity parameters, based on the SSR loci, revealed high similarity between the whole collection and core set. Differences between the two clusters detected in the core set were attributed more to the frequency of their ancestors than to their genetic base. In terms of ancestry, divergent groups were presented and a panel is shown which may foster efficient breeding programs and aid soybean breeders in planning reliable crossings in the development of new varieties.

Maize white spot (MWS) is a disease widely spread in maize production regions in Brazil and causes serious economic damages to the culture. Little is known about the dissemination, growth and development conditions of the MWS causal agent, the bacterium Pantoea ananatis. The objective of this work was to determine the viability of this bacterium, as well as its distribution in the plant. P. ananatis after isolated was stored in both, Nutrient Broth (NB) medium and in mineral oil. For the viability tests, the cultures stored in NB were maintained at 12ºC and –6ºC and the cultures stored in mineral oil were maintained at room temperature. The isolate remained viable for seven months in NB medium at the two temperatures assessed, and four months when stored in mineral oil. The presence of the P. ananatis bacteria was analyzed in, 1) soil samples collected close to rhizosphere, 2) in seeds from plants severely attacked by MWS, 3) foliar segments of healthy plants and 4) the stem of healthy plants. P. ananatis was found surviving epiphytically on the leaf surface and its population increased with plant age, air relative humidity, and decreasing of temperature. This agent was not found neither rhizosphere nor in seeds, but it was isolated in low quantity in maize stem. P. ananatis resides epiphytically on leaves and, due to several factors, may trigger injuries to its host. All epiphytic isolates were characterized in regards to ice nucleation activity, a characteristic of this pathogen.

Soybean is one of the most important crops worldwide. Brazil and the United States (US) are the world’s two biggest producers of this legume. The increase of publicly available DNA sequencing data as well as high-density genotyping data of multiple soybean germplasms has made it possible to understand the genetic relationships and identify genomics regions that underwent selection pressure during soy domestication and breeding. In this study, we analyzed the genetic relationships between Brazilian (N = 235) and US soybean cultivars (N = 675) released in different decades and screened for genomic signatures between Brazilian and US cultivars. The population structure analysis demonstrated that the Brazilian germplasm has a narrower genetic base than the US germplasm. The US cultivars were grouped according to maturity groups, while Brazilian cultivars were separated according to decade of release. We found 73 SNPs that differentiate Brazilian and US soybean germplasm. Maturity-associated SNPs showed high allelic frequency differences between Brazilian and US accessions. Other important loci were identified separating cultivars released before and after 1996 in Brazil. Our data showed important genomic regions under selection during decades of soybean breeding in Brazil and the US that should be targeted to adapt lines from different origins in these countries.

Selection of soybean experimental lines for tolerance to Asian rust and seed yield Soybean is an economically important culture and Brazil is among the largest world producers. Asian rust, caused by the fungus Phakopsora pachyrhizi, is a relatively new disease in Brazil and can cause large losses in this culture, represented by yield decreases and increases in costs for fungicide applications. There are some sources of vertical resistance genes for this disease, but there are also cases of resistance breakdown for some of these main genes. Tolerance, defined as the capacity of plants to endure a pathogen attack without significant losses, is a complementary strategy that can be used to control rust. The objective of this research was to study tolerance to Asian rust in experimental genotypes derived from 45 crosses in a 10 x 10 diallel design developed at the Sector of Applied Genetics to Self-Pollinated Crops, Department of Genetics/ESALQ/USP through methods of estimation of the rust effect and of phenotypic stability in combinations of fungicide managements, locations and years, besides identifing promising lines for inclusion in future breeding programs. The experimental designs used were Federer's augmented blocks in 2011/12 and 2012/13 and a randomized block design stratified in sets in 2013/14. In each year and location two experiments were performed: management 1, with the application of fungicides to control rust and other fungal diseases, including late season leaf diseases; management 2, only controlling other fungal disease, excluding rust. The contrast between these two managements allowed for an estimate of tolerance. Besides that, the stability based on the best genotype (Pi) and ecovalence (Wi) measurements were also used to estimate relative tolerance between genotypes. In 2011/12 225 F 2:7 progenies were evaluated; in 2012/13 675 F 7:8 lines were evaluated and the best 225 F 7:9 lines were evaluated in 2013/14. The results let to the following conclusions: a) there was clear evidence of tolerance to Asian rust among and within crosses; b) the strategy of comparing different fungicide managements to estimate tolerance (rust effect) was useful, but suffered instability, presenting low correlations among years; c) the methods of superiority or stability based on the best genotype (bmg) and ecovalence complemented the information based on the rust effect and aided in the selection of tolerant lines; d) initial evaluations for rust severity (rust score NF1) had low precision and it was recommended to concentrate on rust tolerance evaluations after longer periods of infection (NF2 and NF3); e) tolerance estimated by means of hundred-seed weights had low correlation with tolerance estimated by seed yield, therefore the combined use of both criteria improved the efficiency of selection for tolerance and seed yield; f) in the simulated selection 48 promising lines were identified for rust tolerance and seed yield, corresponding to approximately 22% selection percentage.