Source: https://repositorio.utad.pt/handle/10348/8823?locale=pt_PT
Timestamp: 2019-04-24 20:20:06+00:00

Document:
Cowpea (Vigna unguiculata L. Walp) belongs to the family Fabaceae and is native to Africa. It is a nutritious grain legume, able to tolerate different stresses, such as drought, high temperatures and tolerates most soil stresses, such as low fertility, acidic, basic and poorly drained soils. The study of genetic diversity is an important research area because only an evaluation as complete as possible of this variability allows the use of germplasm in plant breeding. Genetic diversity can be evaluated using morphological traits and molecular markers. There is a growing interest in the use of cloroplastidial DNA in studies of populations, because with the conservation of the gene in this genome, allows to design universal primers, which facilitates phylogenetic studies of populations of relatively remote individuals. In this study, a collection of cowpea landraces from Southern Europe was characterized by morphological and agronomic traits. The diversity and genetic relationships in this landraces comparatively with accessions from other parts of the world, and with other species of Vigna, were also studied through chloroplast microsatellite markers (cpSSRs). At the level of the qualitative traits evaluated in the landraces of Southern Europe, the erect and semi-erect growth habits were the most frequent (44% and 42%, respectively); subhastate shape (44%) was the most occurring terminal leaflet type; the two flower colours observed were white (72%) and purple (28%); and seeds had, mostly, cream colour (94%) with black hilum (58%) and kidney shape (69%). In relation to the quantitative characteristics, was verified that the total seed weight was the characteristic with the highest coefficient of variation (62.54%) and the pod length with the lowest coefficient of variation (15.29%). The 100 seeds weight presented a high value of heritability (h2 = 0.98). The cluster analysis performed using the Ward method based on 10 morphological and agronomic characteristics, divided the landraces of this collection in three distinct groups, and was not observed relationships between the landraces in each group and their geographical origin. Principal component analysis (PCA) showed that the first three major components accounted for 82.1% of the total variance. A set of 10 pairs of primers were used to analyse the genetic diversity of 108 accessions of Vigna unguiculata including alba, pubescens, tenuis and unguiculata subspecies (var. spontanea and var. unguiculata, cultigroup unguiculata and cultigroup sesquipedalis) and 5 accessions of other species of Vigna (V. racemosa, V. radiata and V. mungo), including mostly cultivated, but also wild. Eight of the 10 loci (ccmp3, ccmp7, VgcpSSR1, VgcpSSR10, VgcpSSR12, VgcpSSR14, ccSSR4, cSSR7) were polymorphic at the level of the various species studied. The set of 34 different detected alleles were combined into 10 different haplotypes, eight of which were unique. The most frequent haplotype (90.3%), putatively ancestral, included cultivated accessions of V. unguiculata ssp. unguiculata cultigroup unguiculata and V. unguiculata ssp. unguiculata cultigroup sesquipedalis, and wild species of V. unguiculata ssp. unguiculata var. spontanea and V. unguiculata ssp. tenuis. The present study allowed to show the great diversity still existing in cowpea in Portugal and other Southern Europe countries, despite the low polymorphism detected in its chloroplastidial genome. It was verified the existence of haplotypes shared by cultivated and wild material. The great variability detected in this collection of cowpea studied and the sharing of haplotypes is of great importance for breeding programs of this species.

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