Dissertations / Theses on the topic 'Plant heterosis'

WRKY transcription factors (TFs) belong to a large family of regulatory proteins in plants that modulate many plant processes. Extensive studies have been conducted on WRKY-mediated defense response in Arabidopsis thaliana and many crop species. This study aims to investigate the potential roles and contributions of WRKY TFs regulation in improving defense response in the resynthesized Arabidopsis allotetraploids (Arabidopsis suecica) from two related autotetraploid progenitors, Arabidopsis thaliana (At4) and Arabidopsis arenosa (Aa). Upon infection by Pseudomonas syringae (Pst), the allotetraploids has showed enhanced resistance against the pathogen when compared to the parents. Rapid induction of WRKY18, WRKY40, WRKY38, WRKY53, WRKY6; MAP kinase pathway related genes, WRKY33, PAD3; SA-pathway related genes, ICS1, EDS1, PBS3, MYB31; was evident in response to Pst and salicylic acid treatment in the allotetraploids. Cleaved amplified polymorphic sequences analysis further revealed that the AtWRKY18, AaWRKY40, AtWRKY33, and AtWRKY60 alleles expressed at higher levels when compared to their respective homoeologs in the allotetraploids, suggesting potential altered protein-protein interaction networks in the hybrids. Therefore, a split-luciferase complementation assay was used to characterize and quantify protein-protein interaction among these homoeologous WRKYs in the allotetraploids. Results showed that preferential protein-protein interactions exist for the cis-interacting AtWRKY18/AtWRKY18 homodimer or trans-interacting AtWRKY18/AaWRKY40 heterodimer when compared to the respective interacting complexes. In addition, differential affinities of WRKY18 and WRKY40 homo- and hetero- dimers toward the W-boxes at the WRKY60 promoter were observed. In the allotetraploids, PR1 expression was repressed under basal state when compared to the progenitors. Although PR1 is expressed at a higher level in A. thaliana, its expression fold change was higher and faster in the all otetraploids upon salicylic acid treatment. Transient expression of WRKY18 or WRKY40 homodimer in various combinations induced differential expression of PR1 gene in their respective wrky18 and wrky40 Arabidopsis thaliana mutants. In contrast, similar PR1 induction by homodimer in various combinations was observed when they were transiently expressed in the allotetraploids. In addition, transgenic AtWRKY18 overexpression plant displayed enhanced disease resistance against Pst when compared to AaWRKY18 overexpression lines. Such enhanced disease resistance was found to associate with the higher expression of PR1 and PR2 in AtWRKY18 transgenic lines. Moreover, differential Pst-induced expression of the direct targets (ICS1, EDS1 and PBS3) of WRKY18 in the Arabidopsis AtWRKY18 and AaWRKY18 overexpressors supported a biological difference between the At and Aa homodimers in mediating the targets regulation, thus contributing to the difference in disease responses. Overall, our findings suggested that the rapid differential alleles expression and altered protein-protein or protein-DNA interactions of WRKY transcription factors could contribute to the improved defense in the allotetraploids, providing a molecular basis of for heterotic phenotype development in hybrids.

Improving protein quality and identifying superior inbreds and hybrids are significant challenges in commercial maize breeding programs. These two problems were addressed in separate studies on inbreds and hybrids from a complete diallel cross of 12 elite proprietary inbred lines of maize evaluated in field trials in two locations for two years. One of the inbreds (WI) was a novel source of high quality protein obtained from Wilson Seeds, Inc. in Harlan, Iowa. In the first study, diallel analyses were used to study combining ability and types of gene action important in the inheritance of protein content, grain yield, grain moisture at harvest, time to silk, kernel hardness, and density. General combining ability (GCA) and specific combining ability (SCA) effects were highly significant for all traits indicating presence of both additive and non-additive effects, respectively. Reciprocal effects (REe), often assumed to be absent in maize diallel studies, were significant for grain yield and protein concentration, suggesting that choice of female parent may be important for these traits. Ratios expressing the relative importance of GCA and SCA indicated that protein concentration is controlled primarily by additive gene action. In the second study, restriction fragment length polymorphism (RFLP) data were obtained for the 12 inbreds using 42 genomic clones each with four restriction enzymes. Modified Roger's distances were calculated and used in cluster analyses for heterotic grouping of the inbreds. Two measures of level of heterozygosity and hybrid value were evaluated as means of predicting Fl performance of hybrids in the complete diallel set of hybrids and in groups of hybrids representing crosses between and within heterotic groups. Results from this study confirm those of previous investigations with respect to prediction of hybrid performance when comparable groupings of crosses between related and unrelated lines were evaluated. This study further indicates that RFLPs may also be useful for prediction of hybrid performance in situations typical of early generations of many maize breeding programs where recombinant inbreds are testcrossed to a common tester inbred.
Ph. D.

Salinity is a challenge for crop productivity. Hence, plants exposed to saline environments reduce their vegetative and reproductive growth due to adverse effects of specific ions on metabolism and water relations. In order to cope with salinity, plants display physiological mechanisms based on three main aspects: i) source-sink relationships, ii) resource allocation and iii) alterations in endogenous hormone levels. The roles of developmental and hormonal mechanisms in salt response were investigated here. We employed mutants and transgenic tomato plants affecting different aspects of plant development and hormone response in the same genetic background (cultivar Micro-Tom). The following genotypes were used: Galapagos dwarf (Gdw), Lanata (Ln), lutescent (l), single flower truss (sft), sft heterozygous (sft/+), diageotropica (dgt), entire (e), Never ripe (Nr), epinastic (epi), procera (pro), notabilis (not), anti sense Chloroplastic carotenoid cleavage dioxygenase 7 (35S::asCCD7) and Salicylate hydroxylase (35S::nahG). Among the developmental genotypes studied, sft and l, involved in flower induction and senescence, respectively, were less affected when exposed to salt stress. Although l is considered deleterious due to its precocious senescence, it presented greater shoot biomass and leaf area during salinity. The heterozygous sft/+, whose high productivity was recently linked to an improved vegetative-to-reproductive balance, changed this balance and lowered its yield more than the control MT upon salt treatment. In the analysis of genotypes affecting hormonal status/signaling four kinds of salt responses among the genotypes were observed: i) High shoot growth in spite of high Na:K ratio presented by the strigolactone deficient and high branching CCD7 transgene; ii) High shoot growth and reduced accumulation of Na in tissues (probably due to dilution) presented by the auxin constitutive response e mutant; iii) The opposite response observed in \"ii\" presented by the low auxin sensitivity dgt mutant and iv) growth inhibition combined with reduced levels of Na and higher accumulation of K presented by the not mutant, which produces less ABA. Taken together, the results presented here points to novel developmental mechanisms, such as the promotion of moderate senescence and vegetative growth, and hormonal imbalances to be explored in the pursuing of crops resistant to salt stress.
A salinidade é um desafio para a produtividade agrícola, uma vez que plantas expostas à salinidade tem o crescimento vegetativo e reprodutivo reduzido devido aos efeitos adversos de íons específicos no metabolismo e nas relações hídricas. A fim de lidar com a salinidade, as plantas desempenham mecanismos fisiológicos baseados em três principais características: i) relações fonte-dreno; ii) alocação de reservas e iii) alterações nos níveis endógenos de hormônios. Nesse trabalho, investigamos a relação entre os processos de desenvolvimento e de regulação hormonal com a resposta à salinidade. Para tanto foram usados genótipos de tomateiro com alteração em diferentes vias de desenvolvimento e de produção ou sinalização de hormônios vegetais. Os seguintes genótipos foram usados: Galapagos dwarf (Gdw), Lanata (Ln), lutescent (l), single flower truss (sft), sft heterozygous (sft/+), diageotropica (dgt), entire (e), Never ripe (Nr), epinastic (epi), procera (pro), notabilis (not), anti sense Dioxigenase cloroplastídica de carotenoide 7 (35S::asCCD7) e Salicilato hidroxilase (35S::nahG). Entre os genótipos de desenvolvimento estudados, sft e l, relacionados à menor indução floral e senescência respectivamente, foram os menos afetados quando expostos à salinidade. O genótipo l acumulou maior biomassa e área foliar, apesar de ser considerado deletério devido à senescência precoce. As plantas heterozigotas, sft/+, cuja maior produtividade foi recentemente relacionada a um melhor balanço vegetativo/reprodutivo, alteraram esse balanço sob salinidade e reduziram sua produtividade mais que o controle MT sob estresse salino. Na análise dos genótipos com alteração hormonais foram observados quatro tipos de respostas à salinidade: i) elevado crescimento da parte aérea, apesar da razão Na:K ser alta no genótipo CCD7 cujo transgene induz deficiência de estrigolactona e excessiva ramificação; ii) elevado crescimento e acúmulo reduzido de Na nos tecidos (devido provavelmente a diluição) apresentada pelo mutante de resposta constitutiva a auxina e; iii) o oposto da resposta anterior foi apresentado pelo mutante pouco sensível à auxina , dgt; iv) inibição do crescimento combinado com nível reduzido de Na e alto acúmulo de K apresentada pelo mutante not que produz menos ácido abscísico. Considerados em conjunto, os resultados apresentaram temas para novos mecanismos de desenvolvimento, como a promoção moderada de senescência e do crescimento vegetativo além dos desbalanços hormonais, para serem explorados na busca de culturas resistentes ao estresse salino.

A introdução de genes Rht, oriundos principalmente de programas de melhoramento da Ásia, Europa, Estados Unidos e México permitiu o avanço da cultura do trigo (Triticum aestivum L.) para áreas consideradas marginais. Nesse contexto, este trabalho se propõe avaliar a capacidade de combinação, heterose e heterobeltiose em um dialelo 8x8 afim de verificar o efeito pleiotrópico (único gene controla diversas características do fenótipo), ou seja, além da estatura, quais os componentes de rendimento que estão sendo alterados quando cultivares de maior estatura são cruzados com as linhas anãs CD 0827, CD 0985 e UTF 0605 disponibilizadas por programas de melhoramento genético nacionais de trigo. O experimento foi conduzido em Pato Branco – PR, na safra agrícola de 2012, em delineamento experimental de blocos casualizados com três repetições. As hibridações foram realizadas com oito genitores, sendo três anões (CD 0827, CD 0985 e UTF 0605) e BRS Pardela, Safira, BRS Tangará, CD 111 e CD 108, escolhidos por apresentarem estatura de planta média à elevada, potencial produtivo e demais caracteres agronômicos de interesse. Os valores dos quadrados médios da capacidade geral de combinação (CGC) foram superiores à capacidade específica de combinação (CEC) para todos os caracteres estudados, demonstrando maior contribuição dos efeitos gênicos aditivos. A capacidade geral de combinação das linhagens anãs (CD 0827, CD 0985 e UTF 0605) indicou as maiores contribuições para a redução da estatura de planta, em ambas as gerações avaliadas, com destaque para a linhagem UTF 0605. A CGC também indica que os genitores UTF 0605, Safira e BRS Tangará maximizam o número de afilhos férteis por planta (AFPL) e CD 0985 e CD 111 se mostraram efetivos em aumentar o número de grãos por planta (NGE). Os genitores Safira, BRS Tangará, CD 108 e entre as anãs CD 0827 se destacaram com os mais elevados valores quanto a CGC para rendimento de grãos por planta (RGP). Os genitores anãos UTF 0605, CD 0985 e CD 0827 são fontes promissoras de genes aditivos para o desenvolvimento de progênies de menor estatura de planta e maior número de afilhos férteis por planta, grãos por espiga e massa de mil grãos. Os cruzamentos CD 0827 x Safira, UTF 0605 x Safira, CD 0985 x CD 111, CD 0985 x CD 108, UTF 0605 x CD 111, UTF 0605 x BRS Tangará destacaram-se com maiores valores de capacidade específica de combinação para rendimento de grãos, e os dois primeiros foram superiores quando se considera os valores de heterose e heterobeltiose e depressão endogâmica. Os resultados deste estudo demonstram a viabilidade de utilização de linhagens anãs em programas de melhoramento genético.
The introduction of Rht genes, mainly from breeding programs in Asia, Europe, United States and Mexico has allowed the advancement of wheat (Triticum aestivum L.) to marginal areas considered. In this context, this study aims to evaluate the combining ability, heterosis and heterosis in a 8x8 diallel order to verify the pleiotropic effect (single gene controls several features of the phenotype), in other words, beyond the stature which components of income that are being changed when taller cultivars are crossed with dwarf lines CD 0827, CD 0985 and UTF 0605 provided by national wheat breeding programs. The experiment was conducted in Pato Branco - PR in the 2012 harvest, in a randomized block design with three replications. Hybridizations were performed with eight parents, three of them dwarfs (CD 0827 , CD 0985 and UTF 0605), BRS Pardela, Safira , BRS Tangara, CD 111 and CD 108. The values of the mean squares for GCA were higher than SCA for all traits indicating higher contribution of additive genetic effects. The general combining ability of the dwarf lines (CD 0827 , CD 0985 and UTF 0605) indicated the greatest contributions to the reduction of plant height in both generations evaluated, highlighting the UTF 0605 lineage. The CGC also indicates that UTF 0605, Safira and BRS Tangará parents maximize the number of fertile tillers per plant (NFPP) and CD 0985 , CD 111 were effective in increasing the number of grains per spike (NGS). The Safira, BRS Tangará, CD 108 and CD 0827 between dwarf parents stood out with the highest values for GCA for grain yield per plant (GYP) . The dwarf parents UTF 0605, CD 0985 and CD 0827 are promising sources of additive genes for the development of progenies of lower plant height and increased number of fertile tillers per plant, grains per spike and thousand grain weight. The CD 0827 x Safira, UTF 0605 x Safira, CD 0985 x CD 111, CD 0985 x CD 108, UTF 0605 x CD 111, UTF 0605 x BRS Tangará stood out with higher values of specific combining ability for grain yield, and the first two were higher when considering the values of heterosis and heterosis and inbreeding depression. The results of this study demonstrate the feasibility of using plant population used in breeding programs.

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O trabalho teve como objetivo verificar a eficiência de diferentes testes de vigor para identificação do potencial fisiológico de quatro lotes de sementes de mutamba (Guazuma ulmifolia Lam.). O estudo foi desenvolvido no Laboratório de Análise de Sementes e no Viveiro Experimental de Plantas Ornamentais e Florestais - UNESP, Jaboticabal, SP. Foram utilizados quatro lotes de sementes provenientes de três localidades paulistas: lotes I e 11, coletados no município de Jaboticabal em 2000 e 2001, respectivamente, lote 111, coletado em Santa Rita do Passo Quatro, e lote IV, coletado em Luiz Antonio, os dois últimos em 2001. As sementes utilizadas em todos os testes foram escarificadas com ácido sulfúrico durante 50 minutos e lavadas em água corrente durante 15 minutos. Foram avaliados: teor de água, teste de germinação, teste de primeira contagem, índice de velocidade de germinação, emergência em viveiro, índice de velocidade de emergência, envelhecimento acelerado conduzido nas temperaturas de 410e e 450e, durante nove períodos de avaliação, e condutividade elétrica com diferentes números de sementes (50, 75, 100), postas para embeber em copos de plástico contendo 50, 75 e 100 mL de água desionizada, à temperatura de 250e, fazendo leituras freqüentes durante 72 horas. Os teores de água das sementes nos diferentes lotes apresentaram pequenas variações (9,2 a 10,0 %). Não foram verificadas diferenças estatísticas para a porcentagem de germinação, emergência em viveiro e índice de velocidade de emergência. Diante dos resultados obtidos, concluiu-se que o envelhecimento acelerado pode ser realizado na temperatura de 41°C por um período mínimo de 120 horas ou a 45°C durante 96 horas para avaliação do potencial fisiológico, e o teste de condutividade elétrica não se mostrou adequado para avaliação do potencial fisiológico das sementes...
The work had as objective to compare the efficiency of different vigor tests for identification of the physiologic potential in four lots of Guazuma ulmífolia seeds. The experiments were carried out at Jaboticabal, State of São Paulo, Brazil. Four seed lots from three places of São Paulo State were used: lots I and 11, collected in the municipal district of Jaboticabal in 2000 and 2001, lot 111, collected in Santa Rita do Passa Quatro, and lot IV, collected in Luiz Antonio, the last two in 2001. The seeds used in ali the tests were escarified with sulfuric acid during 50 minutes, and washed in running water during 15 minutes. The results were evaluated with base on seed moisture content, germination test, first count test, germination speed index, emergency in nursery, emergency speed index, accelerated aging at the temperatures of 41°C and 45°C (nine evaluation periods of time) and electric conductivity with different numbers of seeds (50,75, 100), put to soak in plastic boxes containing 50, 75 and 100 mL of water, at 25°C, with frequent observations during 72 hours. The seed moisture content in the different lots presented small variations (9,2 to 10,0%). Statistical differences were not verified for the germination percentage, emergency in nursery and emergency speed index. It was concluded that the accelerated aging at 41°C during a minimum period of 120 hours or at 45°C during 96 hours can be used for evaluation of the physiologic potential of the seeds, and the test of electric conductivity was not appropriate for this purpose. The test of first count and index of germination speed showed to be adequate for evaluation of the physiologic potential of the lots. The germination tests, emergency in nursery and index of emergency speed did not detect differences in the physiologic potential of the studied lots. The seeds lot from Santa Rita do Passa Quatro presented physiologic potential superior to the other lots.

Orientador: Rinaldo César de Paula
Banca: Miguel Luiz menezes Freitas
Banca: Sérgio Valiengo Valeri
Resumo: Handroanthus heptaphyllus (ipê-roxo) é uma árvore tropical da família Bignoniaceae, com ocorrência natural em diversas regiões fitoecológicas brasileiras. Apresenta alto valor econômico pela boa qualidade de sua madeira para produtos nobres, além do uso medicinal. Muito usada para a restauração de ecossistemas florestais e para fins paisagísticos. Este trabalho objetivou estudar a divergência genética entre árvores matrizes de H. heptaphyllus a partir de caracteres biométricos de frutos e sementes e de qualidade fisiológica de sementes. Foram coletadas sementes de 25 árvores matrizes localizadas no Câmpus da Faculdade de Ciências Agrárias e Veterinárias, da Universidade Estadual Paulista e na área urbana da cidade de Jaboticabal (SP). Ao todo, foram avaliados 19 caracteres sendo oito caracteres biométricos de frutos e sementes e 11 relacionados à qualidade fisiológica de sementes, aferida pelos testes de germinação, de condutividade elétrica, envelhecimento acelerado e de submersão. A divergência genética foi avaliada pelo método hierárquico de Ward e de dispersão por Componentes Principais, a partir da Distância Euclidiana calculada entre pares de árvores matrizes considerando-se três situações: i) apenas os caracteres biométricos; ii) apenas os caracteres de qualidade fisiológica das sementes e iii) os caracteres biométricos e de qualidade fisiológica das sementes simultaneamente. Para verificação da importância relativa de cada variável para a divergência genética usou-se ... (Resumo completo, clicar acesso eletrônico abaixo)
Mestre

Orientador: Maria Esmeralda Soares Payão Demattê
Banca: Teresinha de Jesus Deléo Rodrigues
Banca: Sonia Cristina Juliano Gualtieri de Andrade Perez
Banca: Rosiris Bergemann de Aguiar Silveira
Banca: Rinaldo Cesar de Paula
Resumo: O trabalho teve como objetivo verificar a eficiência de diferentes testes de vigor para identificação do potencial fisiológico de quatro lotes de sementes de mutamba (Guazuma ulmifolia Lam.). O estudo foi desenvolvido no Laboratório de Análise de Sementes e no Viveiro Experimental de Plantas Ornamentais e Florestais - UNESP, Jaboticabal, SP. Foram utilizados quatro lotes de sementes provenientes de três localidades paulistas: lotes I e 11, coletados no município de Jaboticabal em 2000 e 2001, respectivamente, lote 111, coletado em Santa Rita do Passo Quatro, e lote IV, coletado em Luiz Antonio, os dois últimos em 2001. As sementes utilizadas em todos os testes foram escarificadas com ácido sulfúrico durante 50 minutos e lavadas em água corrente durante 15 minutos. Foram avaliados: teor de água, teste de germinação, teste de primeira contagem, índice de velocidade de germinação, emergência em viveiro, índice de velocidade de emergência, envelhecimento acelerado conduzido nas temperaturas de 410e e 450e, durante nove períodos de avaliação, e condutividade elétrica com diferentes números de sementes (50, 75, 100), postas para embeber em copos de plástico contendo 50, 75 e 100 mL de água desionizada, à temperatura de 250e, fazendo leituras freqüentes durante 72 horas. Os teores de água das sementes nos diferentes lotes apresentaram pequenas variações (9,2 a 10,0 %). Não foram verificadas diferenças estatísticas para a porcentagem de germinação, emergência em viveiro e índice de velocidade de emergência. Diante dos resultados obtidos, concluiu-se que o envelhecimento acelerado pode ser realizado na temperatura de 41°C por um período mínimo de 120 horas ou a 45°C durante 96 horas para avaliação do potencial fisiológico, e o teste de condutividade elétrica não se mostrou adequado para avaliação do potencial fisiológico das sementes... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The work had as objective to compare the efficiency of different vigor tests for identification of the physiologic potential in four lots of Guazuma ulmífolia seeds. The experiments were carried out at Jaboticabal, State of São Paulo, Brazil. Four seed lots from three places of São Paulo State were used: lots I and 11, collected in the municipal district of Jaboticabal in 2000 and 2001, lot 111, collected in Santa Rita do Passa Quatro, and lot IV, collected in Luiz Antonio, the last two in 2001. The seeds used in ali the tests were escarified with sulfuric acid during 50 minutes, and washed in running water during 15 minutes. The results were evaluated with base on seed moisture content, germination test, first count test, germination speed index, emergency in nursery, emergency speed index, accelerated aging at the temperatures of 41°C and 45°C (nine evaluation periods of time) and electric conductivity with different numbers of seeds (50,75, 100), put to soak in plastic boxes containing 50, 75 and 100 mL of water, at 25°C, with frequent observations during 72 hours. The seed moisture content in the different lots presented small variations (9,2 to 10,0%). Statistical differences were not verified for the germination percentage, emergency in nursery and emergency speed index. It was concluded that the accelerated aging at 41°C during a minimum period of 120 hours or at 45°C during 96 hours can be used for evaluation of the physiologic potential of the seeds, and the test of electric conductivity was not appropriate for this purpose. The test of first count and index of germination speed showed to be adequate for evaluation of the physiologic potential of the lots. The germination tests, emergency in nursery and index of emergency speed did not detect differences in the physiologic potential of the studied lots. The seeds lot from Santa Rita do Passa Quatro presented physiologic potential superior to the other lots.
Doutor

Orientador: Cibele Chalita Martins
Coorientadora: Edna Ursulino Alves
Banca: Letícia Ane Sizuki Nociti Dezem
Banca: Silvelena Vanzolini Segato
Banca: Rita de Cássia Panizzi
Banca: Rinaldo Cesar de Paula
Resumo: Dentro de um programa de controle de qualidade, a avaliação da sanidade e do vigor das sementes é necessária para o sucesso da produção. Assim, o trabalho foi conduzido com o objetivo de identificar os fungos e verificar a eficiência de testes de vigor na diferenciação da qualidade dos lotes de sementes de Brachiaria brizantha cv. Marandú e Xaraés, visando obter informações sobre a qualidade sanitária das sementes e a emergência de plântulas em campo. Vinte lotes de sementes produzidas nos Estados de Mato Grosso do Sul, Mato Grosso, Goiás, Minas Gerais, São Paulo e Bahia foram submetidos à avaliação do teor de água, germinação e microflora fúngica, realizada pelo método do papel de filtro (blotter-test). Para avaliar o vigor e potencial fisiológico foram utilizados dezessete lotes de sementes, sendo oito da cultivar Marandú e nove da Xaraés, avaliados quanto ao teor de água, testes de germinação e vigor (primeira contagem de germinação, condutividade elétrica, emergência de plântulas, primeira contagem e índice de velocidade de emergência de plântulas em areia no laboratório e emergência de plântulas em campo). A microflora fúngica diagnosticada em sementes comerciais de capim marandú e xaraés é constituída por Helminthosporium sp., Fusarium sp., Phoma sp., Curvularia sp., Pyricularia grisea, Chaetomium sp., Nigrospora sp., Colletotrichum sp. e Aspergillus sp. não afeta a germinação de sementes de capim-marandú, no entanto, a incidência de Fusarium sp. e Aspergillus sp. reduz... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Within a quality control program, the evaluation of health and seeds vigor are fundamental and necessary for the successful production. Thus, this study was conducted in order to identify fungi and verify the efficiency of vigor tests in the quality differentiating of Brachiaria brizantha cv., Marandu and Xaraes seed lots, in order to obtain information that improve the sanitary quality of seeds and seedling emergence in the field. Twenty seed lots produced in the states of Mato Grosso do Sul, Mato Grosso, Goias, Minas Gerais, Sao Paulo and Bahia were evaluated for water content, germination and fungal microflora by the filter paper method (blotter-test). To evaluate the vigor and potential physiological were used seventeen seed lots, eight of the cultivar Marandu and nine of the Xaraes submitted to the germination test, first counting of germination test, electrical conductivity, seedling emergence, first germination count and seedling emergence speed index in the sand performed in the laboratory and emergency seedling tests in the field. The fungal microflora diagnosed in commercial seed lots of marandu and xaraes grasses consists of Helminthosporium sp., Fusarium sp., Phoma sp., Curvularia sp., Pyricularia grisea, Chaetomium sp., Nigrospora sp., Colletotrichum sp. and Aspergillus sp.. germination of marandu grass seeds was not affected by the incidence of fungi. The incidence of Fusarium sp. and Aspergillus sp reduces the germination of xaraes Regarding producing locations... (Complete abstract click electronic access below)
Doutor

Maize (Zea mays L.) is one of the most important food crops in sub-Saharan Africa (SSA); however its production is constrained by many factors. Grain yield is compromised by poor genetic performance and poor agronomic management. This calls for need to develop hybrids and exploiting heterosis of single crosses which are adapted to challenging environments. Currently, there is no popcorn hybrids developed in South Africa which is adapted to local conditions. As such, there is need to develop hybrids that cater for smallscale farmers in marginal environments. The objectives of the study were to determine i) standard heterosis, levels of variation and heritability for phenotypic traits in dent and flint maize hybrids; ii) the association between genetic distances and phenotypic traits in dent and flint maize hybrids; iii) mid-parent heterosis in popcorn hybrids, iv) the effect of secondary traits on grain yield in dent, flint and popcorn hybrids; v) genetic diversity and the relationship between traits in widely grown selected hybrids in Southern Africa; and vii) to compare effectiveness of phenotypic analysis models for determining genetic distances between hybrids. Popcorn, dent and flint hybrids were evaluated at two sites. The data was analysed using SAS, Genstat and Power marker statistical packages. The results revealed that the relationship between genetic distance and heterosis is dependent on the environment. Hybrids in top 10 at both sites were different indicating that there was a significant genotype x environment interaction. 13 new heterotic patterns that performed better than the controls can be utilized in heterosis breeding; however there is need to test them in different environments to check on their stability. Grain texture cannot be used to discriminate hybrids for yield because all patterns of dent x dent, dent x flint and flint x flint were present in the top 10 hybrids. Lines DXL124 and DXL158 dominated parentage of the top 10 hybrid rank for yield qualifying them as potential testers for specific combining ability in future studies. Heterosis in popcorn hybrids that performed better than the mid-parent can be utilized in heterosis breeding to exploit vigour, though there is need to test the hybrids in a number of different environments. The main direct factors contributing to yield were ear prolificacy, ear aspect, number of plants and shelling percentages qualifying them to be selected to boost grain yield. Phenotypic data and 91 SNP markers were used to estimate the genetic distance between the hybrids. The results indicated that hybrids that were in the same cluster belong to the same brand and were related in origin and pedigree. Both molecular and phenotypic data were effective in discriminating the hybrids into different clusters according to genetic background. SNP markers revealed nine clusters of hybrids, 12-trait model revealed eight clusters and five-trait model revealed six clusters at 85% genetic distance. The study indicates strategies that can be adopted to boost grain yield in dent, flint and popcorn hybrids.
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

There are few maize varieties that are drought tolerant in semi-arid eastern Kenya and farmer perceptions of drought tolerant maize cultivars have not been studied in this region. Farmers in this region use maize landraces that have not been studied for their potential future hybridization. The main objectives of this study were therefore to: (i) study farmer perceptions of drought and preference for maize varieties, (ii) improve drought tolerance in maize populations in the semi-arid eastern Kenya using S1 family recurrent selection, and (iii) classify maize landraces according to their heterotic patterns. A participatory rural appraisal (PRA) was conducted in Machakos and Makueni districts in semi-arid eastern Kenya. A total of 175 farmers were involved in focus group discussions. An open ended questionnaire and a checklist were used to guide the farmers during the discussion sessions. Scoring and ranking techniques were used to assess farmers’ preferences of maize varieties and constraints to maize production. The farmers grew maize as their major crop followed by beans. Nearly 60% of the farmers grew local maize landraces, whose seed they recycled from season to season; 40% grew improved varieties, but mainly composites rather than hybrids. The key farmers’ criteria for choosing a maize variety in order of importance were drought tolerance, early maturity, high yield, and disease resistance. The major constraints to maize production were drought, lack of technical know-how, pests, poor soils, and inadequate seed supply. Maize traits preferred by farmers in a drought tolerant variety included high yield, recovery after a dry spell and the stay green characteristic. Two maize landrace populations MKS and KTU from semi-arid eastern Kenya and three CIMMYT populations V032, ZM423, and ZM523 were subjected to two cycles of S1 progeny recurrent selection for drought tolerance in yield and traits indicative of drought tolerance were measured during flowering and grain filling from February 2005 to September 2007. Evaluation to determine selection gains was done in one trial replicated five times. It was laid out as a 4x4 lattice design and drought was imposed at reproductive stage by withholding irrigation one week before flowering and resumed during grain filling. The trial was repeated under well-watered conditions which served as a control experiment. After two cycles of selection under drought stress conditions, KTU population had a realized gain in yield of 0.2 t ha-1, MKS population 1.2 t ha-1 and ZM423 0.4 t ha-1, whereas in V032 and ZM523, grain yield reduced by 1.1 t ha-1 and 0.6 t ha-1, respectively. Under well watered conditions, the realized gains in grain yield were positive in all the populations except V032, where there was a reduction of 0.1 t ha-1. Selection increased the genetic variability and heritability estimates for yield in S1 lines of MKS and ZM423 populations, but decreased in KTU, V032 and ZM523 populations. The research to identify heterotic patterns was undertaken using ten maize landraces from the semi-arid eastern Kenya, six maize landraces from coastal Kenya, and three maize populations from CIMMYT. These populations were planted at Kiboko Research Farm during the short rains of October-December 2005 and crossed to two population testers, Embu 11 and Embu 12. The evaluation of the test crosses was done during the long rains of March-June 2006. Percentage heterosis for yield ranged from -17.7% to 397.4%, -79.4 to 22.2% for anthesis-silking interval, -23.9% to 29.2% for ear height, -0.1 to 1.1 for ear diameter, -7.1 to 21.2% for ear length and -5.9% to 30.3% for plant height. iii General combining ability (GCA) effects were significant (p=0.05) for all the traits, while specific combining ability (SCA) effects were not significant (p>0.05), implying that variation among these crosses was mainly due to additive rather than nonadditive gene effects. Since SCA was not significant (p>0.05) for yield, maize populations were classified based on percentage heterosis for yield alone. The maize populations therefore, were grouped into three different heterotic groups P, Q and R. Twelve landrace populations and two CIMMYT populations showed heterosis with Embu 11 and no heterosis with Embu 12 were put in one group P. Two landrace populations that showed no heterosis with either tester were put in group Q. Two landrace populations and one CIMMYT population showed heterosis with both testers were put in group R. None of the populations showed heterosis only with Embu 12 and no heterosis with Embu 11. The main constraint to maize production was drought and the farmers preferred their landraces whose seed they recycled season to season. After two cycles of recurrent selection, the landrace populations showed improved progress in yield. Thus, further selection will be beneficial in the populations where genetic variability increased. Therefore, these populations can further be improved per se and released as varieties and/or incorporated into the existing maize germplasm to broaden their genetic base, given that their heterotic patterns have been identified. Considering that farmers recycle seed, breeding should be towards the development of open-pollinated varieties which are drought tolerant.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

In Southern Africa and Mozambique, tropical lowland accounts for 22% and 65%, respectively, of area under maize production, but grain yield is compromised by downy mildew disease (DM, which is caused by Peronosclerospora sorghi (Weston and Uppal) Shaw), and lack of appropriate varieties, especially hybrids. Among other factors, productivity can be enhanced by deploying DM resistant hybrids, which are higher yielding than open pollinated varieties. Development of a viable hybrid-breeding programme requires knowledge of genetic effects governing yield and DM resistance in inbreds, and effective germplasm management requires heterotic groups and heterotic patterns to be established. In addition, knowledge of farmer-preferred traits is required. Currently, such information is not available to the hybrid-breeding programme in Mozambique. The objectives of this study were, therefore; i) to identify farmers’ preferred variety traits and major production constraints, ii) to determine combining ability effects of inbred maize S4 lines for grain yield and DM resistance, iii) to determine heterotic groups and heterotic patterns among the elite inbred maize lines, and iv) to investigate gene effects governing resistance to DM in breeding source inbred maize lines from the breeding programme in Mozambique. During 2007/08, 142 households were involved in a survey conducted in three districts representing two maize agro-ecological zones in Mozambique. Formal surveys and informal farmer-participatory methods were employed and data subjected to analysis in the SPSS computer programme. Results indicated that there was a low utilization of improved varieties, especially hybrids, with grain yield estimated at 0.7 t ha-1. Farmers were aware of the major production constraints and could discriminate constraints according to their importance for their respective communities. For the lowland environment, farmers identified downy mildew, drought, and cutworm and stem borer damage as the main constraints. In contrast, for the high altitude environments, they ranked ear rot, seed and fertilizer availability, turcicum leaf blight, grey leaf spot diseases and low soil fertility among the major constraints limiting productivity. The most important variety selection criteria were grain yield, short growth cycle, white and flint grain with stress tolerance to drought, low soil fertility, diseases, and grain weevils. These afore mentioned traits, would be priority for the breeding programmes for the lowland and mid altitude environments in Mozambique. To determine combining ability for downy mildew resistance, heterotic groups and heterotic patterns, two testers (open-pollinated varieties) ZM523 (Z) and Suwan-1 (S), were crossed with 18 lines to generate 36 top crosses for evaluation. Crosses were evaluated at two sites under DM. Preponderance of GCA effects indicated that additive gene effects were more important than non-additive gene effects in governing both grain yield and downy mildew resistance in the new maize lines. Based on specific combining ability (SCA) data, lines for yield were classified into two heterotic groups, S and Z; whereas based on heterosis data, lines were fitted into three heterotic groups (S, Z and SZ). Further heterotic patterns and gene action for yield were determined by subjecting nine inbred lines and the two testers, S and Z, to an 11 x 11 diallel-mating scheme. The diallel crosses, three hybrid checks and the two testers were evaluated in six environments in Mozambique. Results revealed that non-additive gene effects were predominant for yield components. In addition, high levels of heterosis for yield was observed and three heterotic groups identified (Z, S and S/Z), and five exceptional heterotic patterns among the inbred elite maize lines were observed. Topcrosses with yield levels comparable to single cross hybrids were also identified, and these would be advanced in the testing programme with potential for deployment as alternative cheaper and sustainable technology to conventional hybrids for the poor farming communities in Mozambique. To determine gene effects for downy mildew resistance in potential breeding lines, two maize populations were derived from crosses between downy mildew susceptible line LP67, and resistant lines DRAC and Suwan-L1. To generate F2 and backcross progenies (BCP1 and BCP2), F1 progenies were self-pollinated and simultaneously crossed to both inbred parents (P1 and P2). All the six generations (P1, P2, F1, F2, BCP1, and BCP2) of the populations were evaluated at two sites under downy mildew infection. A generation mean analysis was performed in SAS. It was revealed that downy mildew resistance was influenced by genes with additive and dominance effects, plus different types of epistatic effects such as additive x additive, and dominance x dominance. Overall results indicated that genes with predominantly non-additive effects controlled resistance in DRAC, whereas resistance in Suwan-L1 was largely influenced by additive gene effects. These findings have serious implications on the effective use of these downy mildew resistance sources in breeding programmes that aim to generate varieties with downy mildew resistance. Overall, results suggested that inbreeding and selection within heterotic groups, followed by hybridization between inbreds within and across heterotic groups would be effective to generate new hybrids. The breeding programme will consider development of conventional hybrids, such as single crosses and three way crosses, and top crosses. Implications of the findings of the study and recommendations are discussed.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.