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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

CaracterizaÃÃo bioquÃmica, nutricional e funcional de genÃtipos elite de feijÃo-caupi [Vigna unguiculata (L.) Walp] / Biochemical, nutritional and functional characterization of elite genotypes of cowpea [Vigna unguiculata (L.) Walp]

Renalison Farias Pereira 13 September 2013 (has links)
FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / O melhoramento genÃtico convencional de feijÃo-caupi [Vigna unguiculata (L.) Walp] tem como proposta aperfeiÃoar suas propriedades agronÃmicas. Entretanto, a partir de uma preocupaÃÃo mundial, considerando alÃm das necessidades dos agricultores, empresÃrios e exportadores, tambÃm se busca desenvolver cultivares com maior qualidade nutricional para os consumidores. O objetivo geral deste trabalho foi analisar o efeito do melhoramento genÃtico convencional do feijÃo-caupi sobre os atributos nutricionais e propriedades funcionais de importÃncia industrial. Os atributos nutricionais foram avaliados inicialmente por meio da determinaÃÃo da composiÃÃo proximal e de minerais. As mÃdias (% base seca) dos valores de proteÃnas totais, lipÃdios, cinzas, fibra alimentar total e carboidratos digerÃveis foram 22,95; 1,60; 3,84; 17,80 e 53,87, respectivamente. Jà os teores de ferro e zinco foram em mÃdia 4,62 e 3,21 mg/100g de semente, respectivamente. Os genÃtipos com teor proteico acima de 25% apresentaram uma boa digestibilidade in vitro (cerca de 70%) e perfil de aminoÃcidos, inclusive os sulfurados, estando todos presentes em nÃveis acima do recomendado para crianÃas de 3 a 10 anos. Em comparaÃÃo com a soja, foram encontrados nÃveis baixos ou moderados de fatores tÃxicos e/ou antinutricionais nos genÃtipos com destaque em teor de proteÃna, ferro e zinco. Houve uma variaÃÃo no teor dos Ãcidos fenÃlicos (11,18 a 94,60 mg/g de semente), taninos (1,33 a 3,05 mg/g de semente), inibidores de tripsina (30,15 a 40,47 UI/mg de proteÃna), inibidores de quimotripsina (14,21 a 26,43 UI/mg de proteÃna) e lectinas (20.000 a 80.000 UH/Kg de semente). Ao se construir Ãndices de qualidade nutricional dos genÃtipos de feijÃo-caupi, verificou-se que os teores dos antinutrientes estudados podem modificar a classificaÃÃo dos mesmos. No entanto, quando os genÃtipos de feijÃo-caupi sÃo comparados com a soja, uma leguminosa amplamente consumida, percebe-se que esses fatores nÃo sÃo de grande relevÃncia, pois hà mÃtodos de inativaÃÃo e/ou remoÃÃo dos componentes indesejados. Propriedades funcionais promissoras foram encontradas para os genÃtipos avaliados, tais como capacidade de absorÃÃo de Ãgua e Ãleo, geleificaÃÃo e espumabilidade, as quais apontam para uma possÃvel aplicaÃÃo da farinha de feijÃo-caupi na indÃstria alimentÃcia. Baseando-se nos Ãndices de qualidade nutricional por meio das caracterÃsticas nutricionais e bioquÃmicas, os trÃs genÃtipos sugeridos para serem usados como parentais em programas de melhoramento genÃtico e produÃÃo de sementes sÃo: G17 (MNC02-682F-2-6), G03 (BRS ARACÃ) e G01 (BRS- JURUÃ). / Cowpea [Vigna unguiculata (L.) Walp] conventional breeding aims to improve its agricultural characteristics. However, there is a global concern that besides considering the needs of farmers, entrepreneurs and exporters, it is also necessary to develop cultivars with higher nutritional quality for consumers. The aim of this study was to evaluate the effects of conventional breeding of cowpeas upon their nutritional attributes and functional properties of industrial significance. The nutritional attributes were initially evaluated by determination of proximate and minerals composition. The means (% dry basis) of total proteins, lipids, ashes, total dietary fiber and digestible carbohydrates content were 22.95; 1.60; 3.84; 17.80 and 53.87, respectively. Mean values for iron and zinc contents were 4.62 and 3.21 mg/100g of seeds, respectively. Genotypes with protein content over 25% showed good in vitro digestibility (ca. 70%) and amino acid profile, including sulfur amino acids, all being in higher levels than the requirements for 3-10 years old children. The levels of toxic and/or antinutritional factors in the genotypes with better contents of protein, iron and zinc were low to moderate compared to those of soybeans. There were reasonable variations in phenolic acid contents (11.18 to 94.60 mg/g of seeds), tannin (1.33 to 3.05 mg/g of seeds), trypsin inhibitor (30.15 to 40.47 UI/mg protein), chymotrypsin inhibitor (14.21 to 26.43 UI/mg protein) and lectin (20,000 to 80,000UH/kg seeds). By using nutritional quality indexes of cowpea genotypes it was observed that the contents of antinutrients may change the ranking position. Nevertheless, when cowpea genotypes are compared to soybeans, it is observed that these factors are not so relevant considering that this legume seed is safely consumed by animals and humans since there are methods to inactivate or remove them. Promising functional properties were detected in the analyzed genotypes, such as water and oil absorption capacity, gelation and foaming properties. These properties point to a possible utilization of cowpea flour in the food industry. Based upon the nutritional quality indexes, we conclude that the top three genotypes suggested to be used as parentals in cowpea breeding programs are G17 (MNC02-682F-2-6), G03 (BRS-ARACÃ) and G01 (BRS-JURUÃ).
2

Caracterização bioquímica, nutricional e funcional de genótipos elite de feijão-caupi [Vigna unguiculata (L.) Walp] / Biochemical, nutritional and functional characterization of elite genotypes of cowpea [Vigna unguiculata (L.) Walp]

Pereira, Renalison Farias January 2013 (has links)
PEREIRA, Renalison Farias. Caracterização bioquímica, nutricional e funcional de genótipos elite de feijão-caupi [Vigna unguiculata (L.) Walp]. 2013. 78 f. : Dissertação (Mestrado) - Universidade Federal do Ceará, Centro de Ciências, Departamento de Bioquímica e Biologia Molecular, Programa de Pós-Graduação em Bioquímica. Fortaleza-CE, 2013. / Submitted by Eric Santiago (erichhcl@gmail.com) on 2016-07-04T14:04:11Z No. of bitstreams: 1 2013_dis_rfpereira.pdf: 2428841 bytes, checksum: 380801ff60fa7f467bb6148bfd418601 (MD5) / Approved for entry into archive by José Jairo Viana de Sousa (jairo@ufc.br) on 2016-07-05T17:38:50Z (GMT) No. of bitstreams: 1 2013_dis_rfpereira.pdf: 2428841 bytes, checksum: 380801ff60fa7f467bb6148bfd418601 (MD5) / Made available in DSpace on 2016-07-05T17:38:50Z (GMT). No. of bitstreams: 1 2013_dis_rfpereira.pdf: 2428841 bytes, checksum: 380801ff60fa7f467bb6148bfd418601 (MD5) Previous issue date: 2013 / Cowpea [Vigna unguiculata (L.) Walp] conventional breeding aims to improve its agricultural characteristics. However, there is a global concern that besides considering the needs of farmers, entrepreneurs and exporters, it is also necessary to develop cultivars with higher nutritional quality for consumers. The aim of this study was to evaluate the effects of conventional breeding of cowpeas upon their nutritional attributes and functional properties of industrial significance. The nutritional attributes were initially evaluated by determination of proximate and minerals composition. The means (% dry basis) of total proteins, lipids, ashes, total dietary fiber and digestible carbohydrates content were 22.95; 1.60; 3.84; 17.80 and 53.87, respectively. Mean values for iron and zinc contents were 4.62 and 3.21 mg/100g of seeds, respectively. Genotypes with protein content over 25% showed good in vitro digestibility (ca. 70%) and amino acid profile, including sulfur amino acids, all being in higher levels than the requirements for 3-10 years old children. The levels of toxic and/or antinutritional factors in the genotypes with better contents of protein, iron and zinc were low to moderate compared to those of soybeans. There were reasonable variations in phenolic acid contents (11.18 to 94.60 mg/g of seeds), tannin (1.33 to 3.05 mg/g of seeds), trypsin inhibitor (30.15 to 40.47 UI/mg protein), chymotrypsin inhibitor (14.21 to 26.43 UI/mg protein) and lectin (20,000 to 80,000UH/kg seeds). By using nutritional quality indexes of cowpea genotypes it was observed that the contents of antinutrients may change the ranking position. Nevertheless, when cowpea genotypes are compared to soybeans, it is observed that these factors are not so relevant considering that this legume seed is safely consumed by animals and humans since there are methods to inactivate or remove them. Promising functional properties were detected in the analyzed genotypes, such as water and oil absorption capacity, gelation and foaming properties. These properties point to a possible utilization of cowpea flour in the food industry. Based upon the nutritional quality indexes, we conclude that the top three genotypes suggested to be used as parentals in cowpea breeding programs are G17 (MNC02-682F-2-6), G03 (BRS-ARACÊ) and G01 (BRS-JURUÁ). / O melhoramento genético convencional de feijão-caupi [Vigna unguiculata (L.) Walp] tem como proposta aperfeiçoar suas propriedades agronômicas. Entretanto, a partir de uma preocupação mundial, considerando além das necessidades dos agricultores, empresários e exportadores, também se busca desenvolver cultivares com maior qualidade nutricional para os consumidores. O objetivo geral deste trabalho foi analisar o efeito do melhoramento genético convencional do feijão-caupi sobre os atributos nutricionais e propriedades funcionais de importância industrial. Os atributos nutricionais foram avaliados inicialmente por meio da determinação da composição proximal e de minerais. As médias (% base seca) dos valores de proteínas totais, lipídios, cinzas, fibra alimentar total e carboidratos digeríveis foram 22,95; 1,60; 3,84; 17,80 e 53,87, respectivamente. Já os teores de ferro e zinco foram em média 4,62 e 3,21 mg/100g de semente, respectivamente. Os genótipos com teor proteico acima de 25% apresentaram uma boa digestibilidade in vitro (cerca de 70%) e perfil de aminoácidos, inclusive os sulfurados, estando todos presentes em níveis acima do recomendado para crianças de 3 a 10 anos. Em comparação com a soja, foram encontrados níveis baixos ou moderados de fatores tóxicos e/ou antinutricionais nos genótipos com destaque em teor de proteína, ferro e zinco. Houve uma variação no teor dos ácidos fenólicos (11,18 a 94,60 mg/g de semente), taninos (1,33 a 3,05 mg/g de semente), inibidores de tripsina (30,15 a 40,47 UI/mg de proteína), inibidores de quimotripsina (14,21 a 26,43 UI/mg de proteína) e lectinas (20.000 a 80.000 UH/Kg de semente). Ao se construir índices de qualidade nutricional dos genótipos de feijão-caupi, verificou-se que os teores dos antinutrientes estudados podem modificar a classificação dos mesmos. No entanto, quando os genótipos de feijão-caupi são comparados com a soja, uma leguminosa amplamente consumida, percebe-se que esses fatores não são de grande relevância, pois há métodos de inativação e/ou remoção dos componentes indesejados. Propriedades funcionais promissoras foram encontradas para os genótipos avaliados, tais como capacidade de absorção de água e óleo, geleificação e espumabilidade, as quais apontam para uma possível aplicação da farinha de feijão-caupi na indústria alimentícia. Baseando-se nos índices de qualidade nutricional por meio das características nutricionais e bioquímicas, os três genótipos sugeridos para serem usados como parentais em programas de melhoramento genético e produção de sementes são: G17 (MNC02-682F-2-6), G03 (BRS ARACÊ) e G01 (BRS- JURUÁ).
3

Breeding cowpea (Vigna unguiculata (L.) walp.) for improved drought tolerance in Mozambique

Chiulele, Rogério Marcos. January 2010 (has links)
Cowpea yields in Mozambique can be increased through breeding farmers’ accepted cultivars with drought tolerance and stability across environments. A study was conducted in the southern region of Mozambique to: (1) determine farmers perceptions on major constraints limiting cowpea production and identify preferences regarding cultivars and traits, (2) determine the variability of selected cowpea germplasm for drought tolerance, (3) determine the gene action controlling drought tolerance, yield and yield components in cowpea, and (4) assess the genotype × environment interaction and yield stability of cowpea genotypes under drought-stressed and non-stressed conditions. The study on farmers’ perceptions about the major constraints limiting cowpea production and preferences regarding cowpea cultivars and traits established that cowpea was an important crop, cultivated for its grain, leaves and fresh pods for household consumption and the market. The study revealed that cowpea grain and leaves were equally important across the three districts in the study. Differences in accessibility to markets between districts influenced the ranking of grain and leaves among districts. Grain was more important in Bilene and Chibuto districts which are situated far from the major urban centre, Maputo, while leaves were more important in Boane district which is near the major market of Maputo. Fresh pods were important in Bilene district which is situated along the major highway connecting Maputo and other provinces. Drought was the most important production constraint followed by aphids, bruchids and viral diseases. The criteria used by farmers to select cowpea varieties included high grain and leaf yield, large seed size, earliness, smoothness of the testa and potential marketability of the variety. The implication of this study is that different types of varieties need to be developed for different areas. Dual-purpose or grain-type varieties need to be developed for areas situated far away from the major markets while varieties for leaf production need to be bred for areas near major markets. During the breeding process, a selection index needs to be adopted whereby drought tolerance, high grain and leaf yield, large seed size, smooth testa, earliness, aphids and bruchids resistance should be integrated as components of the index. High grain yield should receive high weight for varieties developed for areas located far from major markets while high leaf yield would receive high weight for varieties developed for areas located near major markets. The study on variability of cowpea germplasm collections for drought tolerance revealed wide genotypic variability among the tested germplasm. Biplot displays indicated that the genotypes could be grouped into four categories according to their drought tolerance and yielding ability as indicated below: high yielding-drought tolerant (group A), high yielding-drought susceptible (group B), low yielding-drought tolerant (group C), and low yielding-drought susceptible (group D). Examples of high yielding-drought tolerant genotypes were Sh-50, UC-524B, INIA-24, INIA-120, IT96D-610 and Tete-2. Stress tolerance index was the best criterion for assessing genotypes for variability in drought tolerance because it enabled the identification of high yielding and drought tolerant genotypes (group A). The assessment on gene action controlling drought tolerance (stay-green), yield and components indicated that both additive and non-additive effects were involved in controlling all of these traits. Additive gene action was more important than non-additive gene affects in controlling stay-green, days to flowering, number of pods per plant, number of seeds per pod and hundred seed weight. Under no-stress conditions, additive gene action was more important than non-additive gene action while under drought-stressed conditions, non-additive gene effects were more important than additive gene effects. Stay-green can easily be assessed visually in early segregating populations while yield and yield related traits cannot. Hence, selection for drought tolerance using the stay-green trait would be effective in early segregating generations while selection for yield and number of pods per plant would be effective in late segregating generations. Selection for yield could be conducted directly under no-stress conditions and indirectly using the number of pods per plant under drought stress conditions. Genotype INIA-41 would be the most desirable to use as a parent for drought tolerance and IT93K-503-1 would be the most desirable to use as a parent for drought tolerance and yield. The assessment on genotype × environment interaction and cowpea grain yield stability for forty-eight (48) cowpea genotypes grown under drought-stressed and non-stressed conditions indicated that cross-over genotype × environment interactions were present for yield indicating that genotypes responded differently to varying environmental conditions. Genotypes adapted to specific environmental conditions could be identified. Genotypes IT-18, INIA-51, INIA-51A and Nhavanca were adapted to non-stressed environments that were either drought stressed or non-stressed while VAR-11D was adapted to low yielding, stressful environments. Genotypes INIA-23A, INIA-81D, INIA-24, INIA-25, INIA-16 and INIA-76 were high yielding and stable while genotypes IT-18, INIA-51, INIA-51A, Nhavanca and VAR-11D were high yielding and unstable. Genotypes Bambey-21, INIA-36, INIA-12 and Monteiro were consistently low yielding and stable except INIA-12 that was consistently unstable. Chókwè was a high yielding environment and suitable for identifying high yielding genotypes but not ideal for selection because it was not representative of an average environment while Umbeluzi was low yielding and not ideal for selection. Overall, the study revealed that genetic improvement of drought tolerance and yield would be feasible. Potential parents for genetic improvement for yield and drought tolerance were identified. However, further studies for assessing yield stability of cowpea genotypes are necessary and could be achieved by including more seasons and sites to get a better understanding of the genotype × environment interaction and yield stability of cowpea in Mozambique. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.
4

Genetic study of cowpea (Vigna unguiculata (L.) Walp) resistance to Striga gesnerioides (Willd.) vatke in Burkina Faso.

Tignegre, Jean Baptiste De La Salle. January 2010 (has links)
In Burkina Faso, the existence of different races of Striga gesnerioides (Willd.) Vatke, with apparent variable aggressiveness on cowpea (Vigna unguiculata (L.) Walp) renders the breeding task very complex. Therefore, a number of studies was carried out from 2006 to 2009 in field, pot and ‘’in-vitro’’ to identify new sources of resistance to three prevailing Striga races, SR 1, SR 5 and a newly occurring Striga race named SR Kp and to understand the genetic pattern of the underlying resistance of cowpea germplasm to Striga races found in Burkina Faso. To achieve these objectives, the following investigations were initiated: (i) a participatory rural appraisal (PRA), a participatory variety selection (PVS) and grain quality survey were implemented to identify cowpea breeding priorities for Burkina Faso Striga hot-spots; (ii) the identification of sources of resistance in Burkina Faso germplasm, using three prevailing Striga races of S. gesnerioides as sources of inoculum; (iii) the identification of the mechanisms of resistance underlying the resistance to Striga in such genotypes; (iv) a study of combining abilities of selected parents through a diallel cross; (v) a study of the segregation patterns in crosses involving resistant and susceptible sources and a study of the allelic relationships between different resistance sources. The participatory studies conducted in 2007 and 2008 over three districts in Striga hotspots; there was no effective control method against Striga at farmers’ level. These investigations highlighted the importance of cowpea across all sites. Rain decline over time, low input use coupled with a poor extension system were the major constraints mentioned by farmers. Differential reactions of genotype KVx61-1 for Striga resistance suggested that different Striga races were prevailing in different areas. Farmers’ preferred traits in cowpea genotypes were oriented towards grain quality such as big sized grain, white seed colour and rough texture of cowpea grain, except in Northern-Burkina Faso, where farmers preferred brown-coloured grain for food. Cowpea was also seen as an income generating crop. An evaluation of 108 genotypes was done in 2007 in the field (rainy season) and in pots (off-season) for Striga resistance assessments. The screening trials enabled the identification of sources of resistance to S. gesnerioides. Genotypes KVx771-10, IT93K- 693-2, KVx775-33-2, Melakh and IT81D-994 are potential sources of resistance to all three Striga races with acceptable yield. Landraces were susceptible and late-maturing whilst most wild species were resistant but with unwanted shattering traits. A combining ability study for Striga resistance parameters conducted in pots and a resistance mechanism study conducted ‘’in-vitro’’ were performed using F1 populations from a 10 x 10 diallel cross. The general combining ability (GCA) effects were significant for the resistance parameters Striga emergence date (DSE), Striga height above soil (SH), cowpea grain weight (CGW), hundred grain weight (HGW) for all Striga races involved and Striga vigour (SVIG) for SR 5 and SR Kp. The pot-screening showed that, regardless of the SR used as inoculum, the additive genes were important in conferring Striga resistance for parameters DSE, SH, CGW and HGW. The selection of parents could therefore result in breeding advance. Complete dominance, partial, over-dominance and non-allelic interactions (epistasis or failure of some assumptions) were present for some parameters. The ‘’in-vitro’’ screening showed that additive genes were important, with high narrow sense heritability values for the resistance mechanisms Striga seed germination frequency (GR) for SR 1 and SR Kp, the frequency of Striga radicle necrosis before the penetration in cowpea rootlet (NBP) for SR 5, the frequency of Striga radicle necrosis after the penetration in cowpea rootlet (NAP) for SR 1 and SR Kp and the susceptibility ‘’in-vitro’’ (SIV) for SR 5 and SR Kp. The selection of parents can be useful in accumulating the genes for Striga resistance mechanisms in progenies. The F2 populations derived from crosses between Striga-resistant x susceptible genotypes were evaluated in Striga infested benches in 2008 and 2009. The segregation patterns suggest that single dominant genes govern Striga resistance. The test for allelism showed that two non-allelic genes were responsible for the resistance to S. gesnerioides in cowpea. A new Striga resistance gene seems to be involved in genotype KVx771-10 resistance to S. gesnerioides, which confers resistance to all studied Striga races. Gene 994-Rsg in genotype IT81D-994 which confers Striga resistance to SR 1 and gene Rsg 3 also conferring Striga resistance to SR 1 segregated differently for the resistance to SR 5 suggesting that they were different but both confer resistance to SR 5.
5

Occurrence of cowpea aphid-borne mosaic virus and prospects of improving resistance in local cowpea landraces in Uganda.

Orawu, Martin. January 2007 (has links)
Viral diseases are a major limiting factor to cowpea production in many countries of Africa. In Uganda, studies indicated that the cowpea aphid-borne mosaic virus (CABMV) is common and a potential threat to cowpea production in the region. There have been no efforts to develop cowpea cultivars with resistance to CABMV in Uganda. This work focused on the development of cultivars resistant to CABMV. Production of cowpea in Uganda is constrained by several factors, including a lack of awareness of diseases among the majority of farmers. A participatory rural appraisal (PRA) was conducted to elicit farmers’ indigenous knowledge of cowpea production and also to gain insight into their understanding of viral diseases affecting cowpea in Uganda. PRA tools such as group discussions, transect walks, problem listing and ranking were used to gather information. Insect pests, diseases, low yielding cultivars and the high cost of pesticides were perceived to be the most important production constraints. Farmers were not aware of the problem of virus diseases, but provided descriptive names of symptoms. Only three cowpea cultivars (Ebelat, Ecirikukwai and Blackcowpea) were produced in the area. Seed size and colour were seen as important traits in new varieties. Information about the occurrence, distribution and identity of cowpea viruses is limited in Uganda. The objective of this study was to identify the important cowpea virus diseases occurring naturally in the major cowpea growing regions of Uganda. Surveys were conducted to determine the incidence and severity of virus symptoms in four districts (Soroti, Kumi, Pallisa and Tororo) in 2004 and 2005. The incidence ranged from 40.5 to 94.4% and severity ranged from 15.0 to 30.6% (for Kumi and Pallisa districts, respectively) during the 2004 surveys. In 2005, the incidence ranged from 55.9 to 85.4% and severity ranged from 4.7 to 14.5% (for Tororo and Soroti districts, respectively). The CABMV, cowpea mild mottle virus (CPMMV), cowpea severe mosaic virus (CPSMV) and cucumber mosaic virus (CMV) were serologically detected by double antibody sandwich enzyme- linked immunosorbent assay (DAS-ELISA). Fifty four improved cowpea genotypes were screened for resistance to CABMV during the first season of 2004 at Serere Agricultural and Animal Production Research Institute in Uganda. Further screening was conducted in the second season of 2004 using 27 genotypes. The genotypes were planted in single rows between the rows of the susceptible cultivar, Ebelat. This was to provide high pressure of aphid vector (Aphis craccivora Koch) and CABMV inoculum. In addition, the test genotypes were artificially inoculated with a CABMV extract on fully expanded primary leaves of fourteen day-old seedlings. The CABMV incidence and severity was assessed. Disease severity was assessed on a 0-60% visual estimation scale where 0 = with no symptoms and 60 = with severe symptoms. Serological analysis was conducted using DAS-ELISA. Five genotypes showed good levels of resistance to CABMV, namely MU-93, IT82D-889, IT82D-516-2, IT85F-2841 and SECOW-2W. These resistant lines were crossed with three susceptible local landraces, namely Ebelat, Ecirikukwai and Blackcowpea in a North Carolina II mating design. The F1, F2 and BC1F1 populations and the parents were evaluated in the field to assess the response to CABMV and to study the inheritance of resistance to CABMV. The general combining ability (GCA) and specific combining ability (SCA) effects were significant, indicating that both additive and non-additive genetic factors are important in determining the control of CABMV in cowpea. The proportions (%) of the sum of squares for crosses attributable to GCA and SCA for CABMV severity were 51.4% for GCA due to females, 8.4% for GCA due to males and 40.2% for the SCA. The narrow-sense heritability estimates, obtained by regressing F1 on mid-parents was 0.87 and 0.84, F2 on F1 progenies 0.49 and 0.48, and F2 progenies on mid-parents 0.63 and 0.79, for AUDPC and final disease severity, respectively. Single gene conditioned resistance in seven populations, but resistance was quantitatively inherited and involved many genes in eight populations. Observation of transgressive segregation and moderate to high heritability suggests a quantitative mode of gene action and the importance of additive effects. The predominance of GCA variance, high heritability estimates and observation of transgressive segregation suggested that resistance could be improved by selection. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

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