POLANS, NEIL O.*, JEFFERY A. NELSON, DANA R. KURPIUS, and DAYLE E. SAAR. Department of Biological Sciences and Plant Molecular Biology Center, Northern Illinois University, DeKalb, IL 60115. - A phylogenetic study of pea.
Sixteen pea taxa representing both wild populations and cultivated
accessions of the genus Pisum are scored for morphological
characters, allozymes, RAPDs, ISSRs and ITS sequences. Tests of
skewness and partition homogeneity indicate that each of these
individual data sets contains strong phylogenetic signal and
sufficient congruence to support their combination in a single data
set. Using both the maximum parsimony and bootstrap methods from PAUP,
the small number of morphological characters precisely organizes the
species into traditional taxonomic groupings, perhaps in part
reflecting the role morphology plays historically in pea
classification. Individual and combined molecular data sets support
several of these same groupings. Decay indices and other branch values
for the data-rich ISSR and RAPD trees reveal particularly strong
support for three nodes that: 1) separate P. fulvum from the
P. humile, P. elatius and P. sativum ingroup; 2)
establish the northern humile, elatius and
sativum clade; and 3) define sativum as a monophyletic
group. The southern humile populations form a clade that is
distinct from elatius, sativum and even northern
humile in the combined molecular tree; although, this node is
supported only tenuously by the individual molecular trees. The RAPD
trees indicate that elatius is the sister taxon to the
cultivated sativum, a relationship that is observed in the
combined molecular tree. By comparison, the ISSR tree presents only
modest support for northern humile as the single closest
relative of the domesticated pea. A small number of polymorphic ITS
sites actually places northern humile further from
sativum and underscores the close affinity among all the
non-fulvum peas. Species fulvum is clearly the most
distinct of the pea taxa in every analysis.
Key words: ISSRs, ITS sequences, morphological characters, phylogenetics, Pisum, RAPDs