Cowpea genetic diversity and screening of drought tolerant genotypes
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2021-03-16
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A produção agrícola a nível mundial encontra-se ameaçada pelos efeitos das alterações climáticas. As projeções apontam para que estas alterações sejam bastante proeminentes na região Mediterrânica, havendo um aumento da temperatura e, um decréscimo e distribuição irregular dos níveis de precipitação. Consequentemente, torna-se necessário a procura de culturas adaptadas a estas alterações. O feijão-frade (Vigna unguiculata (L.) Walp.), pertencente à família Fabaceae, é uma cultura importante a nível económico e social, particularmente nos países em desenvolvimento. Esta leguminosa é altamente nutritiva, sendo que o seu grão seco pode conter em média 20 a 39% de proteína. Devido à sua tolerância a altas temperaturas e seca, o feijão-frade apresenta-se como uma cultura importante face às projeções para as alterações climáticas. Uma vez que a Europa é deficitária na produção de leguminosas, é necessário que se promova o aumento do cultivo, nomeadamente de feijão-frade. Para este estudo foram selecionados 29 genótipos de feijão-frade do cultigrupo unguiculata de diferentes países, com particular ênfase na Península Ibérica. A seleção destes genótipos teve por base uma série de trabalhos realizados no âmbito do projeto de investigação EUROLEGUME. Esta dissertação teve como objetivos principais: (1) a análise da diversidade genética e relações filogenéticas entre os genótipos através de marcadores moleculares microssatélites e; (2) a avaliação da tolerância à seca dos genótipos através de um ensaio de stresse hídrico onde as plantas cresceram em cilindros com diferentes profundidades (controlo: 30 cm e stresse: 90 cm) e foram sujeitas a stresse hídrico. Para avaliação da diversidade genética foram amplificados cinco loci microssatélites (VM31, VM35, VM37, VuUGM02 e VuUGM71) revelando-se todos polimórficos, com 6-12 alelos detetados por locus. Os resultados apontam para a proximidade genética entre genótipos dos cultigrupos unguiculata e sesquipedalis e da variedade spontanea estando separados das restantes subespécies. Os 29 acessos do cultigrupo unguiculata apresentam uma estreita relação filogenética, não sendo possível uma discriminação com base na sua origem geográfica. No entanto, verificou-se que as duas breeding lines da Nigéria (C59 e IT93K-503- 1) se encontram afastadas dos restantes genótipos do cultigrupo unguiculata. Relativamente ao ensaio de stresse hídrico, de um modo geral, os 29 genótipos de feijão-frade sofreram reduções significativas ao nível da altura da planta, da coloração do caule, do número de vagens, do número de sementes por planta e do peso seco da parte aérea e das vagens quando submetidos a condições de stresse hídrico. Ao nível fisiológico, estes genótipos também apresentaram reduções da área foliar, do teor relativo de clorofila, do diferencial de temperatura da folha e da atividade fotossintética. Em relação ao desenvolvimento radicular verificou-se um aumento destes parâmetros nas plantas sob condições de stresse hídrico. Com base na avaliação dos diferentes parâmetros, os genótipos C11 (Portugal), C39 (Grécia), C45 (Senegal), C47 (Irão), C57 (Portugal) e C58 (Portugal) podem ser considerados como mais tolerantes ao stresse hídrico. Estes genótipos poderão ser integrados em programas de melhoramento de forma a aumentar a resiliência do feijão-frade às alterações climáticas e, assim, contribuir para melhorar a produção de feijão-frade na Europa.
Agricultural production worldwide is threatened by the effects of climate change. These changes are expected to be particularly prominent in the Mediterranean region, pointing towards increased temperature and decreased precipitation levels with irregular distribution. Therefore, it is important to look for crops that are adapted to these constraints. Cowpea (Vigna unguiculata (L.) Walp.) is part of the Leguminosae family and presents high economic and social importance, particularly in the developing countries. This legume is highly nutritional, with the dry grain presenting 20 to 39% protein content. Due to its tolerance for drought and high temperatures, cowpea could become a key crop in the climate change scenario. With this set of characteristics, it could be interesting to increase cowpea’s cultivation in Europe and, at the same time, decrease the deficit production of grain legumes. In this study, a collection of 29 cowpea genotypes belonging to cultigroup unguiculata from worldwide regions with particular focus on Iberian Peninsula, was selected based on previous studies of the EUROLEGUME research project. The main aims of this dissertation were: (1) the analysis of the genetic diversity and phylogenetic relationships between genotypes using simple sequence repeats (SSRs) molecular markers; and (2) the screening of drought tolerant genotypes by conducting an experiment where plants were grown in pipes of different depths (control: 30 cm and stress: 90 cm) and submitted to drought stress. For the genetic diversity evaluation, a set of five SSR loci (VM31, VM35, VM37, VuUGM02 e VuUGM71) were amplified revealing to be all polymorphic with 6-12 alleles detected per locus. The results suggest a close genetic relationship between genotypes from the cultigroup unguiculata and sesquipedalis and the variety spontanea, which separates these from the genotypes of other species and subspecies. The 29 genotypes from cultigroup unguiculata show a narrow phylogenetic relationship, which did not allow the clustering of genotypes according to their geographic origin. Nonetheless, the two Nigerian breeding lines (C59 and IT93K-503-1) were clustered separately from the rest of the genotypes from cultigroup unguiculata. Regarding the drought stress experiment, overall, the 29 genotypes suffered significant reductions in plant height, stem greenness, total number of pods, total number of seeds and dry weight of shoot and pods under drought stress conditions. Moreover, drought stress also affected the cowpeas’ physiology, particularly by reducing foliar area, chlorophyll relative content, leaf temperature differential and photosynthetic activity. As for root development, an increase in most root parameters was observed in plants under drought stress conditions. Based on the evaluated parameters, genotypes C11 (Portugal), C39 (Greece), C45 (Senegal), C47 (Iran), C57 (Portugal) and C58 (Portugal) seemed to be the most tolerant to drought. These genotypes can be included in breeding programs to enhance cowpeas’ resilience to climate change and consequently contribute to the increase of cowpea production in Europe.
Agricultural production worldwide is threatened by the effects of climate change. These changes are expected to be particularly prominent in the Mediterranean region, pointing towards increased temperature and decreased precipitation levels with irregular distribution. Therefore, it is important to look for crops that are adapted to these constraints. Cowpea (Vigna unguiculata (L.) Walp.) is part of the Leguminosae family and presents high economic and social importance, particularly in the developing countries. This legume is highly nutritional, with the dry grain presenting 20 to 39% protein content. Due to its tolerance for drought and high temperatures, cowpea could become a key crop in the climate change scenario. With this set of characteristics, it could be interesting to increase cowpea’s cultivation in Europe and, at the same time, decrease the deficit production of grain legumes. In this study, a collection of 29 cowpea genotypes belonging to cultigroup unguiculata from worldwide regions with particular focus on Iberian Peninsula, was selected based on previous studies of the EUROLEGUME research project. The main aims of this dissertation were: (1) the analysis of the genetic diversity and phylogenetic relationships between genotypes using simple sequence repeats (SSRs) molecular markers; and (2) the screening of drought tolerant genotypes by conducting an experiment where plants were grown in pipes of different depths (control: 30 cm and stress: 90 cm) and submitted to drought stress. For the genetic diversity evaluation, a set of five SSR loci (VM31, VM35, VM37, VuUGM02 e VuUGM71) were amplified revealing to be all polymorphic with 6-12 alleles detected per locus. The results suggest a close genetic relationship between genotypes from the cultigroup unguiculata and sesquipedalis and the variety spontanea, which separates these from the genotypes of other species and subspecies. The 29 genotypes from cultigroup unguiculata show a narrow phylogenetic relationship, which did not allow the clustering of genotypes according to their geographic origin. Nonetheless, the two Nigerian breeding lines (C59 and IT93K-503-1) were clustered separately from the rest of the genotypes from cultigroup unguiculata. Regarding the drought stress experiment, overall, the 29 genotypes suffered significant reductions in plant height, stem greenness, total number of pods, total number of seeds and dry weight of shoot and pods under drought stress conditions. Moreover, drought stress also affected the cowpeas’ physiology, particularly by reducing foliar area, chlorophyll relative content, leaf temperature differential and photosynthetic activity. As for root development, an increase in most root parameters was observed in plants under drought stress conditions. Based on the evaluated parameters, genotypes C11 (Portugal), C39 (Greece), C45 (Senegal), C47 (Iran), C57 (Portugal) and C58 (Portugal) seemed to be the most tolerant to drought. These genotypes can be included in breeding programs to enhance cowpeas’ resilience to climate change and consequently contribute to the increase of cowpea production in Europe.
Descrição
Dissertação de Mestrado em Engenharia Agronómica
Palavras-chave
Vigna unguiculata (L.) Walp , tolerância à seca