The taxonomy of the genus Vigna has been primarily based on morphological attributes. We have used 27 genomic clones from soybean, common bean, mungbean and cowpea to examine restriction fragment length polymorphism (RFLP) among 44 accessions of different species belonging to four subgenera of the genus Vigna. One accession each of common bean (Phaseolus vulgaris) and soybean (Glycine max) was included in the study. Total DNA from the various genotypes was digested with one restriction enzyme (Eco RV). Results of a numerical taxonomic analysis showed a high level of genetic variation within the genus with a remarkably higher amount of variation associated with Vigna sp. from Africa relative to those from Asia. The distinctness of the Asiatic grams in subgenus Ceratotropis, cowpea in section Catiang, bambara groundnut (V. subterranean) and members of the subgenus Plectotropis was elucidated by this study. Members of the subgenus Plectotropis were closer in genome homology to those of subgenus Vigna section Catiang than to those of subgenus Ceratotropis. The relative positions of some genotypes to one another on the dendrogram and minimum spanning tree were discussed in regard to hybridisations aimed generating well-saturated genomic maps and interspecies transfer of desirable genes.
Morphological studies and phylogenetic analyses of DNA sequences from three
genomic regions – the internal transcribed spacer (ITS) regions of the
nuclear ribosomal gene repeat, a partial sequence of RNA polymerase II subunit
(rpb2), and a partial sequence of translation elongation factor
(tef1) – were used to investigate the systematics of
Hypocrea citrina and related species. A neotype specimen is
designated for H. citrina that conforms to Persoon's description of a
yellow effuse fungus occurring on leaf litter. Historical information and
results obtained in this study provide the foundation for selection of a
lectotype specimen from Fries's herbarium for H. lactea. The results
indicate that (1) Hypocrea citrina and H. pulvinata are
distinct species; (2) H. lactea sensu Fries is a synonym of the older
name H. citrina; (3) H. pulvinata, H. protopulvinata, and
H. americana are phylogenetically distinct species that form a
well-supported polyporicolous clade; (4) H. citrina is situated in a
clade closely related to H. pulvinata; and (5) H.
microcitrina and H. pseudostraminea reside in a highly supported
clade phylogenetically distinct from H. citrina. Hypocrea protopulvinata,
H. microcitrina, H. megalocitrina, H. pseudostraminea, and a new species,
H. aurantiistroma, are reported and described from North America.
Variation in rpb2 and tef1 gene sequences suggests
geographical subgroupings between European and North American isolates of
H. pulvinata. The phylogenies inferred from ITS, rpb2, and
tef1 gene sequences are concordant. Hypocrea citrina var.
americana is elevated to species status, Hypocrea
americana.
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