Visando avaliar o potencial de populações segregantes de trigo obtidas de parentais portadores de características agronômicas contrastantes, quanto ao comprimento da raiz primária, produção de grãos e caracteres agronômicos; estimar a herdabilidade no sentido amplo e restrito para populações F2 obtidas, além das associações das características em estudo; confirmar os genitores mais promissores para utilização em programas de melhoramento de trigo e estimar a capacidade geral e específica de combinação dos genótipos de trigo, foram efetuados cruzamentos, em forma dialélica, entre quatro genótipos de trigo: BH-1146, Anahuac M-1, IAC-287/IAC-24 M-1 e MONS/ALDS// IAC-24 M-3. Foram obtidos híbridos em geração F1 e F2 e os retrocruzamentos RC1 e RC2, que foram avaliados quanto ao comprimento da raiz em solução nutritiva, conforme Camargo e Ferreira Filho (2005a). Após a medição das raízes, as plântulas foram transplantadas para telado do Centro de Grãos e Fibras do IAC sob delineamento de blocos ao acaso, com 28 tratamentos (os 4 parentais, os 6 F1s, F2s, RC1s e RC2s), com 6 repetições. Avaliaram-se os caracteres comprimento da raiz primária, altura das plantas, comprimento da espiga, número de espiguetas por espiga, grãos por espiga, grãos por espigueta, massa de cem grãos, comprimento do internódio da raque, número de espigas por planta, produção de grãos por planta e florescimento. Para análise dialélica foi utilizado o Modelo de Griffing (1956) Os valores estimados para a herdabilidade em sentido amplo, para os seis cruzamentos, foram altas para altura de plantas; médios, na maioria dos cruzamentos, para comprimento da raiz, comprimento da espiga, números de espigas por planta e grãos por espiga, produção de grãos por planta e florescimento; de médios a altos para comprimento do internódio da raque e número de espiguetas por espiga e de médios a baixos para massa de cem grãos e número de grãos por espigueta. Esses valores indicaram que grande parte das variações encontradas foi de origem genética. As estimativas de herdabilidade no sentido restrito (h2r) mostraram grande variação de magnitude nos diferentes cruzamentos para todos os caracteres avaliados. Ressaltou-se o cruzamento P1/P4, com parentais divergentes, com elevados valores de herdabilidade no sentido restrito. Altos valores de h2r foram estimados para altura de plantas em todos os cruzamentos, indicando que a seleção será efetiva nas primeiras gerações segregantes. As correlações fenotípicas revelaram haver uma tendência da seleção de plantas com maior comprimento da raiz primária estar associada com maior produção de grãos por planta e maior precocidade para o florescimento. BH-1146 demonstrou ser fonte genética de tolerância à seca no estádio inicial da cultura do trigo. As análises dialélicas corroboraram os resultados dos ensaios de genótipos, destacando os genótipos P4 como fonte de redução de altura das plantas e o P1 como fonte de aumento do comprimento da raiz; para produção de grãos evidenciaram-se P1 e P2 com elevados valores de capacidade geral de combinação. Detectaram-se efeitos significativos da CEC e CGC, evidenciando a ação de genes preponderantemente aditiva e de dominância na manifestação dos na maioria dos caracteres estudados / Diallel crossing was made with four wheat genotypes: BH-1146, Anahuac M-1, IAC-287/IAC-24 M-1 and MONS/ALDS// IAC-24 M-3, bearing agronomically contrasting characteristics, to evaluate the potential of segregating populations of wheat obtained from parents bearing contrasting agronomic characteristics for primary root length, grain yield and agronomic characteristics; to estimate the herdability, in the broad and narrow senses, for F2 obtained populations in addition to the association of the traits under study; to confirm the more promising parents for use in wheat improvement programs and to estimate the general and specific combining abilities of wheat genotypes. Hybrid were obtained in F1 and F2 generation of RC1 and RC2 backcrossing, which were evaluated for their root length in nutrient solution, according to Camargos and Ferreira Filhos method (2005a). After root measuring, plantules were transplanted to screens of the IAC Center for Grain and Fibers in blocks at random, with 28 treatments (4 parents, the 6 F1s, the 6 F2s, the 6 RC1s and the 6 RC2s), with 6 repetitions. Characteristics such as primary root length, plant length, and spike length, number of spikelet per spike, grains per spike, grains per spikelet, 100 grain weight, length of the rachis internode heigth, number of spike per plant, grain yield per plant and flowering were evaluated. The Griffing Model (1956) was used for the diallel analysis. Herdability estimates were obtained. The herdability estimates in the broad sense for the six crossings were high for plant height in all of them; moderate, in most of the crossings for root growth, spike heigth, number of spikes per plant and grain per spike, grain yield per plant and flowering; were moderate to high for rachis internode height and the number of spikelet per spike and moderate to low for 100 grain weight per spikelet. These values indicated that a large part of the variability found was of genetic origin. Herdability estimates in the narrow sense showed large variability in magnitude in the different crossings for the studied traits. P1/P4 crossing with different parents showed high herdability in the narrow sense. High herdability values in the narrow sense were estimated for plant heigth in all crossings, indicating that the selection will be effective for the first segregating generations. Phenotype correlations showed a tendency for the selection of plants with larger heigth for the primary root being associated with a higher grain yield per plant and higher early flowering. BH-1146 proved to be a genetic source of tolerance to drought in the initial stage of the wheat breeding. Diallel analysis confirm the results of experiments with genotypes, showing high values in the combining ability of P4 genotypes as being the source of reduction of plant heigth, and P1 as source of the increase in root length; P1 and P2 were found with high values of gi for the production of grain. CEC and CGC, showed the action of genes of major aditive effects and prevalence of the traits studies

Doctor of Philosophy / Department of Agronomy / Tesfaye Tesso / Sweet Sorghum [Sorghum bicolor (L.) Moench] is a type of cultivated sorghum grown primarily for its sugar-rich stalks. Because of its high fermentable sugar content, the crop is widely recognized as an alternative feedstock source for bio-fuel production. The extent to which stalk sugar accumulation occurs may be determined by several factors including the sink size. Grain is the most important sink in sorghum and other grain crops. Three experiments were conducted in this study to determine the extent to which the grain sink can reduce sugar accumulation in the stalks, to test and validate a genetic system that allows development of sterile sweet sorghum hybrids, and to assess the potential of sugar-rich hybrids to overcome stalk rot diseases. The first experiment, based on 22 sweet sorghum genotypes, was undertaken to study the effect of eliminating the grain sink (removing the head prior to anthesis) on stalk juice yield, sugar accumulation, and biomass. The data showed that the grain sink had a significant effect on all traits measured. Elimination of the grain sink significantly increased oBrix % (17.8%), dry biomass (27.8%), juice yield (23.9%), and total sugar yield (43.5%). The second experiment was aimed at validating the role of A3 genetic male sterility system for producing sterile sweet sorghum hybrids. Ten sweet sorghum pollinator lines of variable sugar content were selected among the entries included in the previous experiment. The lines were crossed to four A1 and A3 cytoplasmic male sterile (CMS) lines using a Design II mating scheme. The A3 females did not have effective restorers so that the hybrids were expected to be sterile. The parental lines and corresponding hybrids were evaluated for biomass production, oBrix, juice and sugar yield using a randomized complete block design. All A3 hybrids were sterile and did not produce seed when heads were covered prior to pollination. The effect of grain sink represented by the A1 vs. A3 CMS were highly significant for Brix%, biomass, juice, and sugar yield. Comparison of parents vs. crosses component was highly significant, indicating marked heterosis effect for the traits. Both general (GCA) and specific (SCA) combining ability effects were also significant for all traits, indicating the role of both additive and dominance genetic effects in the inheritance of the characters. Earlier studies have shown positive relationships between stalk sugar concentration and stalk rot disease resistance in sorghum. Thus, the objective of the third experiment was to study the effects of the CMS mediated differential accumulation of stalk sugar on severity of charcoal rot disease caused by Macrophomina phaseolina. The experiment provided an opportunity to test the effect of variable stalk sugar in the same genetic backgrounds. The data indicated that hybrids produced from A3 cytoplasm were more resistant to charcoal rot (7.1cm lesion length) compared to those produced from the A1 hybrids (9.5 cm lesion length). The enhanced resistance of hybrids with higher sugar yield could have significant agronomic advantage in sugar based bio-fuel feedstock production.

A utilização de genótipos de soja tolerantes é uma alternativa muito promissora no manejo da ferrugem asiática da soja (FAS), uma vez que a resistência qualitativa mostra-se instável devido à grande variabilidade do patógeno. Este estudo objetivou avaliar o potencial de populações formadas por 64 cruzamentos biparentais (gerações F2, F3 e F4) de um dialelo parcial 8 x 8 para produtividade de grãos (PG) e tolerância à ferrugem. Quinze genitores compreenderam linhagens experimentais desenvolvidas pelo Departamento de Genética/ESALQ/USP e um genitor envolveu uma cultivar comercial. Em 2012/13, dois experimentos foram conduzidos: o primeiro com as populações dos 64 cruzamentos (geração F2) e três testemunhas comuns, enquanto que o segundo envolveu os 16 genitores e as mesmas três testemunhas comuns. Em 2013/14 e 2014/15, a fim de se estimar o efeito ferrugem (EF), ou seja, o nível de tolerância dos genótipos, por meio da diferença entre as médias ajustadas de PG e peso de cem sementes (PCS), foram conduzidos quatro experimentos, sendo dois com as populações dos 64 cruzamentos (gerações F3 e F4) e outros dois com os 16 genitores; cada dupla de experimentos compreendeu dois manejos distintos de doenças com fungicidas. No manejo O&P foram feitas duas aplicações sucessivas de Opera e uma de Priori Xtra, para o controle da ferrugem e outras doenças de fim de ciclo (DFC); no manejo D foram feitas aplicações de Derosal para controle de DFC, exceto a ferrugem. No estádio R5, cinco plantas competitivas de cada parcela foram avaliadas para a severidade, enquanto que no estádio R8, cada parcela foi avaliada para caracteres agronômicos. Os dados obtidos foram analisados (programas computacionais R e Genes). A análise dialélica apresentou significância (p<0,001) dos quadrados médios de CGC e CEC. Para PG, considerando os parâmetros genéticos (heterose, herdabilidade, depressão por endogamia, CGC e CEC), os melhores genitores foram USP 02-16.122 (2), USP 04-17.027 (4), USP 04-17.039 (5), USP 231-4124-04 (6), USP 04-17.011 (10), USP 231-2228-01 (11), USP 231-2224-12 (13) e USP 231-2222-12 (16); tais genitores devem possuir maiores quantidades de genes favoráveis e com complementações genéticas apropriadas, com destaque de USP 04-17.027 (4). Oito (12,5%) cruzamentos sobressaíram com alto desempenho agronômico. A avaliação da severidade foi mais eficiente com o aumento da infecção (NF2). Os genitores USP 04-18.092 (1) e TMG INOX (9) foram resistentes à ferrugem. Com base nas perdas de PG e PCS, os genitores mais tolerantes foram USP 02-16.122 (2), USP 02-16.045 (3), USP 04-17.027 (4), USP 231-2132-04 (12), USP 231-1228-09 (15) e USP 231-2222-12 (16). Ao considerar em conjunto PG e PCS, quinze (23%) cruzamentos revelaram-se tolerantes ou resistentes de acordo com o contraste entre EF e NF2, respectivamente. Concluiu-se que houve forte associação entre CGC e CEC para os destaques reportados; a tolerância estimada pelo PCS e PG apresentaram baixa correlação entre si; assim, a combinação dos dois parâmetros melhorou a eficiência da seleção para tolerância. Ganhos adicionais em PG e tolerância à ferrugem poderão ser obtidos com a seleção entre e dentro de cruzamentos a partir da geração F5. / The use of tolerant soybean genotypes is a very promising alternative for the management of Asian soybean rust (FAS), since qualitative resistance proves to be unstable due to the high variability of the pathogen. This study aimed evaluate the potential of populations composed of 64 two-parental crosses (F2, F3 and F4 generations) of a partial diallel 8 x 8 to seed yield (PG) and tolerance to rust . Fifteen parents understood experimental lines developed by the Department of Genetics / ESALQ / USP and one parent involved a commercial cultivar. In 2012/13, two experiments were conducted: the first with the populations of the 64 crosses (F2) and three common checks, while the second involved 16 parents and the same three common checks. In 2013/14 and 2014/15, it was estimated the rust effect (EF), or the tolerance level of the genotypes using the difference between the adjusted mean of seed yield (PG) and one hundred-seeds weight (PCS), four experiments were conducted, two with populations of 64 crosses (generations F3 and F4) and two with 16 parents; each pair of experiments comprised two different managements of diseases with fungicides. In the management O&P has been made two successive applications of Opera and Priori Xtra in order to control rust and other late season leaf diseases (DFC). In the management D, applications of Derosal were made to control DFC, except rust. In R5 stage, five competitive plants from each plot were evaluated for rust severity, while at the R8 stage, each plot was evaluated for agronomic traits. The data were analyzed through the software R and Genes. The diallel analysis showed significance (p <0.001) of mean squares of GCA (general combining ability) and SCA (specific combining ability). For PG, considering the genetic parameters (heterosis, heritability, inbreeding depression, GCA and SCA), the best parents were USP 02-16.122 (2), USP 04-17.027 (4), USP 04-17.039 (5), USP 231-4124-04 (6), USP 04-17.011 (10), USP 231-2228-01 (11), USP 231-2224-12 (13) and USP 231-2222-12 (16); these parents must have larger amounts of favorable genes and appropriate genetic complementation, particularly USP 04-17.027 (4). Eight (12.5%) crosses stood out with high agronomic performance. The assessment of severity was more efficient with the increase of infection (NF2). The parents USP 04-18.092 (1) and TMG INOX (9) were resistant to FAS. Based on PG and PCS losses, the most tolerant parents were USP 04-18.092 (1), USP 02-16.122 (2), USP 02-16.045 (3), USP 04-17.027 (4), USP 231-3225-11 (7), USP 231-2132-04 (12) e USP 231-1228-09 (15). By considering together PG and PCS, fifteen (23%) crosses revealed tolerance or resistance to rust, according to the estimates of the EF and NF2, respectively. It was found a strong association between GCA and SCA for the reported genotypes. The estimated tolerance by PCS and PG showed low correlation between each other; thus, the combination of the two parameters improved selection efficiency for tolerance. Further gains in PG and rust tolerance may be obtained from the selection among and within crosses in the generation F5.

O trabalho iniciou um ciclo de seleção recombinando linhagens tolerantes à ferrugem asiática, com o intuito de estimar parâmetros genéticos úteis aos programas de melhoramento, incrementar a tolerância e predizer os cruzamentos mais promissores para extração de linhagens superiores. Foi realizado um dialelo completo, sem recíprocos, entre dez linhagens tolerantes à ferrugem, desenvolvidas pelo Setor de Genética Aplicada às Espécies Autógamas da ESALQ-USP. A geração F2 foi avaliada em covas, sendo estimados parâmetros relacionados aos caracteres agronômicos importantes, sem avaliação de reação à ferrugem. Na geração seguinte, progênies F2:3 foram avaliadas em três ambientes, Anhembi, Areão e ESALQ. A reação à ferrugem foi medida por dois caracteres: notas de reação à ferrugem e diferença de produtividade de grãos (PG) em experimentos com fungicidas distintos. Os resultados evidenciaram que os genitores possuíam alelos de resistência à ferrugem que podem garantir o sucesso da seleção recorrente. A metodologia do contraste de fungicidas discriminou eficientemente os genótipos com tolerância dos genótipos com suscetibilidade. O número de dias para a maturidade influenciou nas notas de reação à ferrugem; então, o grupo de maturação dos genótipos foi estimado para melhor avaliar o comportamento das progênies. Com base nos parâmetros da capacidade geral de combinação para PG e da reação à ferrugem, o genitor USP 191-104-11 (10) apresentou maior potencial de gerar progênies promissoras. Os cruzamentos USP 02-16.045 (2) x USP 16.015 (4), USP 16.015 (4) x USP 97-10.046 (6), USP 11-38 (5) x USP 97-10.046 (6) e USP 02- 16.045 (2) x USP 191-104-11 (10), destacaram-se pelo maior número de progênies com alta PG e tolerantes ou moderadamente tolerantes à ferrugem asiática. / This work started a cycle of selection throughout crosses among soybean lines with tolerance against soybean rust. The objectives were to increment the plant tolerance, to estimate useful genetic parameters for soybean breeding programs and to predict the most promising crosses to extract high yielding lines. A complete diallel, without reciprocal, among 10 rust tolerant lines was performed. Those lines were developed by the Sector of Genetics Applied to Autogamous Species from ESALQ-USP. The F2 generation was evaluated in hill plots and genetic parameters related to important agronomic traits were estimated, without evaluating the rust reaction. In the next generation, F2:3 progenies were evaluated in three environments, Anhembi, Areão and ESALQ. Rust reaction was evaluated throughout two main ways: according to the visual scores of rust reaction and contrasts in seed yield (PG) with fungicide experiments. The results showed that the parents have rust resistance alleles that can guarantee the success of the recurrent selection. The methodology of the fungicide contrasts efficiently discriminated the tolerant from the susceptible genotypes. The number of days to maturity influenced the rust reaction scores; so, the maturity groups of the genotypes were estimated for better evaluation of the performance of the progenies. According to the general combining ability (GCA) for yield and rust reaction, the parent USP 191-104- 11 (10) has the highest potential to generate high yielding lines. The crosses USP 02- 16.045 (2) x USP 16.015 (4), USP 16.015 (4) x USP 97-10.046 (6), USP 11-38 (5) x USP 97-10.046 (6) and USP 02-16.045 (2) x USP 191-104-11 (10) exceeded due the higher number of progenies with high yield and with tolerance or moderate tolerance to asian soybean rust.

O tomateiro (Solanum lycopersicum L.) é uma das plantas cultivadas de maior importância no mundo, sendo uma das principais hortaliças em importância econômica no Brasil. A murcha-bacteriana é uma doença dentre as mais limitantes para a cultura do tomateiro e o uso de cultivares resistentes à Ralstonia spp. é uma das únicas alternativas para evitar as perdas causadas por esse patógeno. Contudo, existem raríssimos estudos sobre a base genética de genótipos resistentes aos principais isolados de Ralstonia spp. Objetivou-se nesse trabalho estudar parâmetros genéticos da resistência à murcha-bacteriana em linhagens e híbridos usados como porta-enxertos de tomateiro, por meio de abordagens complementares que envolvem desde o ajuste das metodologias para indução artificial da doença, até estimativas das capacidades de combinação e a heterose entre linhagens, visando identificar cruzamentos promissores para o estabelecimento de um programa de melhoramento genético para resistência à murcha-bacteriana em tomateiro para porta-enxertos. Comparando-se quatro métodos de indução da resistência verificou-se que o método da lesão das raízes do torrão com objeto cortante (bisturi) e pulverização de 5 mL da suspensão bacteriana no torrão, comparativamente aos outros métodos avaliados, apresenta fácil execução, requer quantidades reduzidas de suspensão bacteriana e proporciona boas quantidades de plantas de tomateiro com sintomas de murcha-bacteriana, sendo o mais adequado entre os métodos testados. Foi estimada a heterose e capacidade de combinação entre linhagens de tomateiro para um isolado do biovar 2 de Ralstonia solanacearum em estágio de plântulas, em ambiente protegido, e em um solo naturalmente infestado por Ralstonia spp. Entre as linhagens avaliadas, apenas o genótipo Hawaii 7996 apresentou níveis aceitáveis de resistência, sendo necessário encontrar novas fontes de resistência para o início de um programa de melhoramento. Verificou-se que nenhuma das progênies derivadas dos cruzamentos desse estudo apresentaram resistência superior ao parental superior Além disso, foi verificada a importância dos efeitos aditivos e, consequentemente, os cruzamentos de genitores com alta CGC para o caráter e a seleção recorrente seriam as melhores alternativas no melhoramento para resistência à murcha-bacteriana. Finalmente, foram estudados os genitores e seus híbridos, utilizados como porta-enxerto em condições de campo e em ambiente protegido visando o aumento da resistência à murcha-bacteriana causada por Ralstonia spp., e incremento dos parâmetros produtivos de um híbrido comercial utilizado como copa. Verificou-se influência dos diferentes porta-enxertos em caracteres de produção e massa dos frutos e no desenvimento de copa. Caracteres relacionados ao sistema radicular dos porta-enxertos apresentaram heterose em relação aos seus genitores, com efeitos aditivos e não aditivos importantes, mostrando o desempenho das linhagens e sua contribuição para a produção de híbridos superiores. Por fim, este estudo possibilitou o melhor entendimento sobre a base genética da resistência em genótipos de tomateiro que possuem uso potencial como porta-enxertos resistentes à murcha-bacteriana. / The tomato (Solanum lycopersicum L.) is one of the most important cultivated plants in the world, being one of the main vegetables of economic importance in Brazil. The bacterial wilt is one of the most limiting diseases for the tomato crop and the use of resistant cultivars to Ralstonia spp. is one of the only alternatives to avoid losses caused by this pathogen. However, there are very few studies on the genetic basis of genotypes resistant to the main isolates of Ralstonia spp. The objective of this work was to study the genetic parameters of resistance to bacterial wilt in lines and hybrids used as tomato rootstocks, through complementary approaches that range from the adjustment of the methodologies for artificial induction of the disease, to estimates of the combining abilities and heterosis among lines, aiming to identify promising crosses for the establishment of a rootstock genetic breeding program for resistance to bacterial wilt in tomatoes. Comparing four resistance induction methods, it was verified that the method of injuring roots with cutting object (scalpel) and spraying 5 mL of the bacterial suspension in the clod compared to the other\'s methods evaluated, is easiest to perform, requires less amounts of bacterial suspension and provides good amounts of tomato plants with wilt symptoms, being the most suitable among the methods tested. The heterosis and combining ability of tomato lines for a strain of biovar 2 of Ralstonia solanacearum in greenhouse at seedling stage and in soil naturally infested by Ralstonia spp were estimated. Among the lines evaluated, only the Hawaii 7996 genotype showed acceptable levels of resistance, and it is necessary to find new sources of resistance for the beginning of a breeding program. It was verified that none of the progenies derived from the crosses of this study presented superior resistance to the superior parental. In addition, the importance of the additive effects was verified and, consequently, the crossings of parents with high CGC for the character and the recurrent selection would be the best alternatives in the improvement for resistance to bacterial wilt. Finally, we studied the parents and their hybrids, used as rootstocks under field conditions and in a protected environment aiming the increasing resistance to bacterial wilt caused by Ralstonia spp., and increasing of the yield parameters of a commercial hybrid used as a scion. The influence of the different rootstocks was verified in characters of yield and mass of the fruits and in the development of the scion. Characteristics related to the root system of rootstocks showed heterosis in relation to their parents, with important additive and non-additive effects, showing the performance of the lines and their contribution to the production of superior hybrids. Finally, this study allowed a better understanding of the genetic basis of resistance in tomato genotypes that have potential use as bacterial wilt resistant rootstocks.

O tomateiro (Solanum lycopersicum L.) é uma das plantas cultivadas de maior importância no mundo, sendo uma das principais hortaliças em importância econômica no Brasil. A murcha-bacteriana é uma doença dentre as mais limitantes para a cultura do tomateiro e o uso de cultivares resistentes à Ralstonia spp. é uma das únicas alternativas para evitar as perdas causadas por esse patógeno. Contudo, existem raríssimos estudos sobre a base genética de genótipos resistentes aos principais isolados de Ralstonia spp. Objetivou-se nesse trabalho estudar parâmetros genéticos da resistência à murcha-bacteriana em linhagens e híbridos usados como porta-enxertos de tomateiro, por meio de abordagens complementares que envolvem desde o ajuste das metodologias para indução artificial da doença, até estimativas das capacidades de combinação e a heterose entre linhagens, visando identificar cruzamentos promissores para o estabelecimento de um programa de melhoramento genético para resistência à murcha-bacteriana em tomateiro para porta-enxertos. Comparando-se quatro métodos de indução da resistência verificou-se que o método da lesão das raízes do torrão com objeto cortante (bisturi) e pulverização de 5 mL da suspensão bacteriana no torrão, comparativamente aos outros métodos avaliados, apresenta fácil execução, requer quantidades reduzidas de suspensão bacteriana e proporciona boas quantidades de plantas de tomateiro com sintomas de murcha-bacteriana, sendo o mais adequado entre os métodos testados. Foi estimada a heterose e capacidade de combinação entre linhagens de tomateiro para um isolado do biovar 2 de Ralstonia solanacearum em estágio de plântulas, em ambiente protegido, e em um solo naturalmente infestado por Ralstonia spp. Entre as linhagens avaliadas, apenas o genótipo Hawaii 7996 apresentou níveis aceitáveis de resistência, sendo necessário encontrar novas fontes de resistência para o início de um programa de melhoramento. Verificou-se que nenhuma das progênies derivadas dos cruzamentos desse estudo apresentaram resistência superior ao parental superior Além disso, foi verificada a importância dos efeitos aditivos e, consequentemente, os cruzamentos de genitores com alta CGC para o caráter e a seleção recorrente seriam as melhores alternativas no melhoramento para resistência à murcha-bacteriana. Finalmente, foram estudados os genitores e seus híbridos, utilizados como porta-enxerto em condições de campo e em ambiente protegido visando o aumento da resistência à murcha-bacteriana causada por Ralstonia spp., e incremento dos parâmetros produtivos de um híbrido comercial utilizado como copa. Verificou-se influência dos diferentes porta-enxertos em caracteres de produção e massa dos frutos e no desenvimento de copa. Caracteres relacionados ao sistema radicular dos porta-enxertos apresentaram heterose em relação aos seus genitores, com efeitos aditivos e não aditivos importantes, mostrando o desempenho das linhagens e sua contribuição para a produção de híbridos superiores. Por fim, este estudo possibilitou o melhor entendimento sobre a base genética da resistência em genótipos de tomateiro que possuem uso potencial como porta-enxertos resistentes à murcha-bacteriana. / The tomato (Solanum lycopersicum L.) is one of the most important cultivated plants in the world, being one of the main vegetables of economic importance in Brazil. The bacterial wilt is one of the most limiting diseases for the tomato crop and the use of resistant cultivars to Ralstonia spp. is one of the only alternatives to avoid losses caused by this pathogen. However, there are very few studies on the genetic basis of genotypes resistant to the main isolates of Ralstonia spp. The objective of this work was to study the genetic parameters of resistance to bacterial wilt in lines and hybrids used as tomato rootstocks, through complementary approaches that range from the adjustment of the methodologies for artificial induction of the disease, to estimates of the combining abilities and heterosis among lines, aiming to identify promising crosses for the establishment of a rootstock genetic breeding program for resistance to bacterial wilt in tomatoes. Comparing four resistance induction methods, it was verified that the method of injuring roots with cutting object (scalpel) and spraying 5 mL of the bacterial suspension in the clod compared to the other\'s methods evaluated, is easiest to perform, requires less amounts of bacterial suspension and provides good amounts of tomato plants with wilt symptoms, being the most suitable among the methods tested. The heterosis and combining ability of tomato lines for a strain of biovar 2 of Ralstonia solanacearum in greenhouse at seedling stage and in soil naturally infested by Ralstonia spp were estimated. Among the lines evaluated, only the Hawaii 7996 genotype showed acceptable levels of resistance, and it is necessary to find new sources of resistance for the beginning of a breeding program. It was verified that none of the progenies derived from the crosses of this study presented superior resistance to the superior parental. In addition, the importance of the additive effects was verified and, consequently, the crossings of parents with high CGC for the character and the recurrent selection would be the best alternatives in the improvement for resistance to bacterial wilt. Finally, we studied the parents and their hybrids, used as rootstocks under field conditions and in a protected environment aiming the increasing resistance to bacterial wilt caused by Ralstonia spp., and increasing of the yield parameters of a commercial hybrid used as a scion. The influence of the different rootstocks was verified in characters of yield and mass of the fruits and in the development of the scion. Characteristics related to the root system of rootstocks showed heterosis in relation to their parents, with important additive and non-additive effects, showing the performance of the lines and their contribution to the production of superior hybrids. Finally, this study allowed a better understanding of the genetic basis of resistance in tomato genotypes that have potential use as bacterial wilt resistant rootstocks.

Maize is susceptible to biotic and abiotic stresses. The most important abiotic stresses in Africa are drought and low soil fertility. Aflatoxin contamination is a potential problem in areas facing drought and low soil fertility. Three studies were conducted to evaluate maize germplasm for tolerance to stress. In the first study, fifteen maize inbred lines crossed in a diallel were evaluated under drought, low N stress, and well-watered conditions at six locations in three countries to estimate general (GCA) and specific combining ability (SCA), investigate genotype x environment interaction, and estimate genetic diversity and its relationship with grain yield and heterosis. GCA effects were not significant for grain yield across environments. Lines with good GCA effect for grain yield were P501 and CML258 across stresses. Lines CML339, CML341, and SPLC7-F had good GCA effects for anthesis silking interval across stresses. Additive genetic effects were more important for grain yield under drought and well-watered conditions. Heterosis estimates were highest in stress environments. Clustering based on genetic distance calculated using marker data from AFLP, RFLP, and SSRs grouped lines according to origin. Genetic distance was positively correlated with grain yield and specific combining ability. In the second study, synthetic hybrids were evaluated at seven locations in three countries to estimate GCA and SCA effects under low N stress and optimal conditions and investigate genotype x environment interaction. GCA effects were significant for all traits across low N stress and optimal conditions. The highest yielding synthetic hybrids involved synthetics developed from stress tolerant lines. Synthetics 99SADVIA-# and SYNA00F2 had good GCA for grain yield across low N stress conditions. Heterosis was highly correlated with grain yield. Optimal environments explained more variation than stress environments. The third study evaluated the agronomic performance and aflatoxin accumulation of single and three-way cross white maize hybrids at five locations in Texas. Inbreds CML343, Tx601W, and Tx110 showed positive GCA effects for grain yield. Significant GCA effects for reduced aflatoxin concentration were observed in lines CML269, CML270, and CML78 across locations. Differences in performance between single and three-way crosses hybrids were dependent mostly on the inbred lines.

Synthetic hexaploid wheats, created from a durum (Triticum durum) cross to Aegilops tauschii Coss. (McFadden and Sears, 1946), proved to be an efficient and beneficial source of new genes for common bread wheat (Triticum aestivum L). The purpose of this research was to evaluate the potential and performance of synthetic wheat in Texas. Ten elite primary synthetics from the International Maize and Wheat Improvement Center (CIMMYT), screened for desirable traits, were backcrossed to two Texas cultivars, TAM 111 and TAM 112. Populations were bulked and modified bulked to advance generations. Agronomic traits related to yield were determined on the F4 and F5 Improvement was observed in South Texas and the Blacklands, which have more disease pressure and fewer intermittent dry spells than another two locations at Chillicothe and Bushland in Texas Rolling and High Plains, respectively. Selected bulks were not superior to non-selected bulks. Head number per unit area had the highest correlation with yield and seed weight was the most heritable trait. Synthetic lines combined better with TAM 111 than TAM 112 in high yielding environments. populations across five Texas locations. Similar to crosses with spring wheat, synthetics contributed to yield through an increase in seed weight. Synthetic populations that produced higher grain yield than both TAM 111 and TAM 112 were able to maintain their large seed size and weight while improving their seed per head and head number traits. Poorer performance in environments with harsh winters could be due to a lack of winter-hardiness in the primary synthetics. This clearly demonstrates that improving yield, through utilization of common wheat by synthetic crosses, could result from selecting for larger seed per head and heads per unit area in lines driven from these populations. Introgression of new genes through synthetic backcrosses could contribute to the improvement of wheat in particular regions of Texas. Primary synthetics and recurrent parents combining for superior hybrids were identified.

Maize is susceptible to biotic and abiotic stresses. The most important abiotic stresses in Africa are drought and low soil fertility. Aflatoxin contamination is a potential problem in areas facing drought and low soil fertility. Three studies were conducted to evaluate maize germplasm for tolerance to stress. In the first study, fifteen maize inbred lines crossed in a diallel were evaluated under drought, low N stress, and well-watered conditions at six locations in three countries to estimate general (GCA) and specific combining ability (SCA), investigate genotype x environment interaction, and estimate genetic diversity and its relationship with grain yield and heterosis. GCA effects were not significant for grain yield across environments. Lines with good GCA effect for grain yield were P501 and CML258 across stresses. Lines CML339, CML341, and SPLC7-F had good GCA effects for anthesis silking interval across stresses. Additive genetic effects were more important for grain yield under drought and well-watered conditions. Heterosis estimates were highest in stress environments. Clustering based on genetic distance calculated using marker data from AFLP, RFLP, and SSRs grouped lines according to origin. Genetic distance was positively correlated with grain yield and specific combining ability. In the second study, synthetic hybrids were evaluated at seven locations in three countries to estimate GCA and SCA effects under low N stress and optimal conditions and investigate genotype x environment interaction. GCA effects were significant for all traits across low N stress and optimal conditions. The highest yielding synthetic hybrids involved synthetics developed from stress tolerant lines. Synthetics 99SADVIA-# and SYNA00F2 had good GCA for grain yield across low N stress conditions. Heterosis was highly correlated with grain yield. Optimal environments explained more variation than stress environments. The third study evaluated the agronomic performance and aflatoxin accumulation of single and three-way cross white maize hybrids at five locations in Texas. Inbreds CML343, Tx601W, and Tx110 showed positive GCA effects for grain yield. Significant GCA effects for reduced aflatoxin concentration were observed in lines CML269, CML270, and CML78 across locations. Differences in performance between single and three-way crosses hybrids were dependent mostly on the inbred lines.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2017-04-18T14:51:47Z No. of bitstreams: 2 Dissertação - Priscilla Neves de Santana - 2013.pdf: 2803001 bytes, checksum: 043adc84ee5ca3c6457e5e2475cee9c5 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-04-18T14:52:14Z (GMT) No. of bitstreams: 2 Dissertação - Priscilla Neves de Santana - 2013.pdf: 2803001 bytes, checksum: 043adc84ee5ca3c6457e5e2475cee9c5 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-04-18T14:52:14Z (GMT). No. of bitstreams: 2 Dissertação - Priscilla Neves de Santana - 2013.pdf: 2803001 bytes, checksum: 043adc84ee5ca3c6457e5e2475cee9c5 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2013-08-28 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / An adequate choice of genitors to be crossed to generate genetic variability is essential to increase the efficiency of sugarcane breeding program. The combining ability of genotypes in crosses constitutes a good measure of genetic potential in future crosses. The aim of this study was to evaluate the genetic potential of sugarcane genotypes based on biparental crosses of sugarcane breeding programs from the Interuniversity Network for the Development of Sugarcane Trade (PMGCA / RIDESA). The basic variable used was the rate of selection of each cross population (full sib family) in the initial phase of the program (T1), resulting from the selection practiced evaluating variables of primary importance for the species. The average selection rate of each family was predicted using BLUP methodology. Data analysis was performed using Method IV proposed by Griffing (1956), adapted to the set of crosses available, detailing the effects of General Combining Ability (GCA) and Specific Combining Ability (SCA). The predicted effects of SCA were correlated with genetic similarity estimates obtained using the Dice coefficient from SSR markers and the Malécot coancestry coefficient. It was detected significant effects of GCA, showing the possibility of selection of parents based on this parameter. Although not statistically tested, SCA showed determination coefficient higher than CGC. The genetic similarity obtained by coancestry coefficient showed a significant correlation with SCA, although of low magnitude. There was no significance for the correlation between genetic distance based on SSR marker and SCA. It was concluded that the rate of selection is efficient to select potentially promising parents in the first stage of selection in sugarcane. / A escolha adequada de genitores a serem cruzados para gerar variabilidade genética é condição essencial para aumentar a eficiência de um programa de melhoramento de cana-de-açúcar. A capacidade de combinação de genótipos em cruzamentos realizados constitui uma boa medida do potencial genético em cruzamentos futuros. O objetivo deste trabalho foi avaliar o potencial genético de genitores de cana-de-açúcar com base em cruzamentos biparentais utilizados nos programas de melhoramento genético de cana-deaçúcar da Rede Interuniversitária para o Desenvolvimento do Setor Sucroenergético (PMGCA/RIDESA). A variável básica usada para avaliação foi a taxa de seleção de cada cruzamento na fase inicial do programa (T1), resultante da seleção praticada avaliando variáveis primárias de importância para a espécie. A taxa de seleção média de cada cruzamento foi predita utilizando a metodologia BLUP. A análise dos dados foi realizada utilizando o método IV proposto por Griffing (1956), adaptado para o conjunto de cruzamentos disponível, detalhando os efeitos de Capacidade Geral de Combinação (CGC) e Capacidade Específica de Combinação (CEC). Os efeitos preditos de CEC foram correlacionados com estimativas de similaridade genética obtidas usando o coeficiente de Dice a partir de marcadores SSR e com o coeficiente de parentesco de Malècot. Foi detectada significância dos efeitos de CGC, mostrando a possibilidade de seleção de genitores com base neste parâmetro. Embora não testada estatisticamente, a CEC mostrou coeficiente de determinação superior à CGC. A similaridade genética obtida pelo coeficiente de parentesco mostrou uma correlação significativa, porém de baixa magnitude com CEC. Não houve significância para a correlação entre a distância genética estimada por marcadores e CEC. Concluiu-se que a taxa de seleção é eficiente para selecionar genitores potencialmente promissores na primeira fase de seleção de cana-de-açúcar.