Earlier planting to escape summer drought and high temperature has increased the importance of cold tolerance in corn. The objectives of this study were to assess cold tolerance among the corn hybrids using morpho-physiological traits and to classify hybrids into different groups of tolerance. Corn hybrids were subjected to optimum, low, and very low temperatures during seed emergence and seedling growth and morphological and physiological traits were assessed. Variability existed among the corn hybrids for the measured traits. Total, leaf and root weights and cumulative length and length per unit volume were the most important morphological traits in describing hybrid variability. Principle component analysis and total low temperature response index methods were used to categorize hybrid tolerance to low temperature. Based on relative scores assigned in this study and their yield potential in the niche environment, producer could select hybrids to maximize corn production in an early planting production system.

Holistic and growth stage-specific screening is needed for identifying tolerant genotypes and for formulating strategies to mitigate the negative effects of abiotic stresses on crops. The objectives of this study were to characterize the genetic variability of 100 rice lines for early-season vigor, growth and physiological plasticity, and drought and temperature tolerance. Five studies were conducted to accomplish these objectives. In study 1 and 2, 100 rice genotypes consisting of several cultivars and experimental breeding lines were characterized for early-season vigor using several shoot and root morphological, physiological, and yield related traits. In study 3, low- and high-temperature tolerance assessed on select rice cultivars/hybrids during early-season. In study 4, genotypic variability in response to drought stress tolerance using morpo-physiological traits including roots was assessed under pot-culture conditions in a mini-greenhouse conditions. In study 5, the 100 rice genotypes were used to identify and validate SNP markers, and genome-wide association study (GWAS) to generate genotypic and phenotypic data with the objective of identifying new genetic loci controlling drought stress traits. Significant variability was recorded among rice genotypes and treatments for many traits measured. Early-season cumulative vigor response indices (CVRI) developed by summing individual responses indices for each trait varied among the rice genotypes, 21.36 (RU1404196) to 36.17 (N-22). Based on means and standard deviation of the CVRI, rice genotypes were classified as low- (43) and moderately low- (33), high- (16), and very high-vigor (5) groups. Total low-temperature response index values ranged from 18.48 to 23.15 whereas total high-temperature responses index values ranged from 42.01 to 48.82. Antonio, CLXL 745, and Mermentau were identified as sensitive to cold- and heat, and XL 753 was highly cold and heat tolerant genotypes tested. A cumulative drought stress response index (CDSRI) values varied between 14.7 (CHENIERE) and 27.9 (RU1402174) among the genotypes tested. This preliminary analysis of GWA indicated that substantial phenotypic and genotypic diversity exists in the 100 rice genotypes, despite their narrow genetic pool. The stress tolerant and high vigor rice genotypes will be valuable for rice breeders for developing new genotypes best suited under growing environments prone to early-season drought and temperature.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2017-12-27T10:27:35Z No. of bitstreams: 2 Tese - Arielle Elias Arantes - 2017.pdf: 12603465 bytes, checksum: d64f9bccc8dcafceb1f000629bf7f031 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-12-27T10:28:07Z (GMT) No. of bitstreams: 2 Tese - Arielle Elias Arantes - 2017.pdf: 12603465 bytes, checksum: d64f9bccc8dcafceb1f000629bf7f031 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-12-27T10:28:07Z (GMT). No. of bitstreams: 2 Tese - Arielle Elias Arantes - 2017.pdf: 12603465 bytes, checksum: d64f9bccc8dcafceb1f000629bf7f031 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-12-18 / Cattle ranching is the main land use activity in Brazil, with about 175 million hectares of cultivated pasture, with at least 50% of these being with some degree of degradation. Degraded pastures present low biomass production of little nutritional value, which leads to low animal weight gain in the rainy season and loss of weight in the dry season. Due to its low productive efficiency, if these areas were identified and recovered, they could be intensified, freeing pasture areas for other uses. In this context, the objective of this work was to evaluate the pasture vigor and the potential livestock intensification for Brazil. In order to obtain the vigor and productivity of Brazilian pastures, a Pasture Strength Index (PVI) was generated by integrating the α (intercept) and β (slope) coefficients, derived from the linear regression of the vegetation index (NDVI) over time (2000 to 2017). Pastures with low PVI values were located throughout the Caatinga biome, in the MATOPIBA region of the Cerrado biome, in the eastern portion of Mato Grosso do Sul, southeastern of Mato Grosso and northwestern of Goiás. These areas are associated to regions of higher water deficit, as shown by the relationship between the PVI and the total annual precipitation (R² = 0.40) and evapotranspiration. For the Cerrado biome, the PVI showed high spatial correspondence with the green biomass and percent green cover. Green biomass and percent green cover were generated from extrapolation of field data to the spatial resolution of MODIS images. The areas with lower PVI values in the Cerrado biome also had lower green biomass (< 6000 kg ha-1 ) and percent green cover (< 47%) during the growing season. Considering the accumulated green biomass in the growing season, it was observed that the Cerrado’s cattle stocking rate could increase from 1.11 AU ha-1 (real cattle stocking rate) to 2.56 AU ha-1 (potential cattle stocking rate). The real cattle stocking rate in 2015 was generated through the integration of the 2006 Livestock Census data with the Livestock Production data for the year 2015. The potential cattle stocking rate was obtained from the relationship between the forage production (green biomass and gross primary productivity - GPP) and the forage demand of one animal unit (1 AU = 450 kg). The potential of intensification was determined from the difference between the actual and the potential cattle stocking rates. For all of Brazil, the cattle stocking rate in 2015 was 0.97 AU ha-1 , reaching a potential of 3.60 AU ha-1 , that is, the potential for intensification was 2.63 AU ha-1 . The greatest potential of intensification occurred in the South region (3.62 AU ha-1 ), and the lowest in the North (2.13 AU ha-1 ) and Northeast (2.22 AU ha-1 ) regions of Brazil. / A pecuária é a principal atividade de uso da terra no Brasil, com cerca de 175 milhões de hectares de pastagens cultivadas, sendo que pelo menos 50% destas estão com algum nível de degradação. Pastagens degradadas apresentam baixa produção de biomassa de pouco valor nutritivo, o que leva a um menor ganho de peso animal na estação chuvosa e a perda de peso na estação seca. Pela sua baixa eficiência produtiva, caso haja a identificação e a recuperação destas áreas, estas poderiam ser intensificadas, liberando áreas para outros usos. Neste contexto, este trabalho teve por objetivo avaliar o vigor e o potencial de intensificação das pastagens brasileiras. Para obter o vigor das pastagens, gerou-se um Índice de Vigor do Pasto (PVI), por meio da integração dos coeficientes α (intercepto) e β (slope), obtidos da regressão linear do índice de vegetação (NDVI) ao longo do tempo (2000 a 2017). As pastagens com os menores valores de PVI localizaram-se em todo o bioma Caatinga, na região do MATOPIBA no bioma Cerrado, no leste do Mato Grosso do Sul, sudeste do Mato Grosso e noroeste de Goiás. Estas áreas estão associadas a regiões de maior déficit hídrico, como mostrado pela relação do PVI com a precipitação (R² = 0,40) e a evapotranspiração acumuladas durante o ano (R² = 0,30). Para o bioma Cerrado, o PVI apresentou alta correspondência espacial com a biomassa verde e com o percentual de cobertura verde. A biomassa verde e o percentual de cobertura verde foram geradas a partir da extrapolação de dados de campo para a resolução espacial das imagens MODIS. As áreas com menores valores de PVI no bioma Cerrado também tiveram pouca biomassa verde (< 6.000 kg ha-1 ) e porcentagem cobertura verde (< 47%) durante a estação de crescimento. Considerando o acúmulo de biomassa verde na estação de crescimento, percebeu-se que a lotação bovina do Cerrado poderia aumentar de 1,11 UA ha-1 (lotação real) para 2,56 UA ha-1 (lotação potencial). A lotação bovina real em 2015 foi estimada por meio da integração de dados do Censo Agropecuário de 2006 com dados da Produção Pecuária Municipal de 2015. Já a lotação potencial, foi obtida a partir da relação entre a produção de forragem (biomassa verde ou produtividade primária bruta – GPP) e a demanda de forragem de uma unidade animal (1 UA = 450 kg). A partir da diferença entre a lotação bovina real e potencial determinou-se o potencial de intensificação. Para todo o Brasil, a lotação bovina em 2015 foi de 0,97 UA ha-1 , podendo chegar a um potencial de 3,60 UA ha-1 , ou seja, o potencial de intensificação foi de 2,63 UA ha-1 . O maior potencial de intensificação se deu na região Sul (3,62 UA ha-1 ) e os menores nas regiões Norte (2,13 UA ha-1 ) e Nordeste (2,22 UA ha-1 ) do Brasil.