H. Forster et al., Phylogenetic relationships of Phytophthora species based on ribosomal ITS I DNA sequence analysis with emphasis on Waterhouse groups V and VI, MYCOL RES, 104, 2000, pp. 1055-1061
Phylogenetic relationships among Phytophthora species were investigated by
sequence analysis of the internal transcribed spacer region I of the riboso
mal DNA repeat unit. The extensive collection of isolates included taxa fro
m all six morphological groups recognized by Waterhouse (1963) including mo
lecular groups previously identified using isozymes and mtDNA restriction f
ragment length polymorphisms. Similar to previous studies, the inferred rel
ationships indicated that molecular groups of P. cryptooea/drechsleri-like
and P. megasperma-like taxa are polyphyletic. Morphological groups V and VI
, which are differentiated by the presence of amphigynous or paragynous ant
heridia, are not monophyletic: species of the two groups are interspersed i
n the tree. Species with papillate and semi-papillate sporangia (groups I-I
V) clustered together and this cluster was distinct from those of species w
ith non-papillate sporangia. There was no congruence between the mode of an
theridial attachment, sporangial caducity, or homo- or heterothallic habit
and the molecular grouping of the species. Our study provides evidence that
the antheridial position together with homo- or heterothallic habit does n
ot reflect phylogenetic relationships within Phytophthora. Consequently, co
nfirming studies done previously (Cooke & Duncan 1997), this study provides
evidence that the morphological characters used in Phytophthora taxonomy a
re of limited value for deducing phylogenetic relationships, because they e
xhibit convergent evolution.