The role of paragynous and amphigynous antheridia in sexual reproduction of Phytophthora cinnamomi

• Published in: Mycological research Vol. 101; no. 11; pp. 1383 - 1388
• Main Authors: HÜBERLI, DANIEL, TOMMERUP, I. C., HARDY, GILES E. ST J.
• Format: Journal Article
• Language: English
• Published: Oxford Cambridge University Press 01-11-1997; Elsevier Ltd; Elsevier
• Subjects: Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; Phytopathology. Animal pests. Plant and forest protection; Plant physiology and development; Sexual reproduction; Systematics. Morphology. Development cycle. Physiology; Vegetative and sexual reproduction, floral biology, fructification; Australia; Oceania; Fungi; Pathogenicity; Plant pathogen; Phytophthora cinnamomi; Morphology; Phycomycetes; Isolate; Male; Reproductive system; Sexual reproduction; Spores; Thallophyta
• ISSN: 0953-7562; 1469-8102
• DOI: 10.1017/S0953756296003413

The morphology of gametangia was examined in 43 pairs of isolates
(mating types A1×A2; 11 A1 and 24 A2 isolates; five
isozyme/electrophoretic types) of Phytophthora cinnamomi.
An amphigynous antheridium always formed with each oogonium.
However, in 41 of the crosses a proportion (39 had 0·2–10%
and
two had >30%) of oogonia also consistently had single or
multiple paragynous antheridia. Single or multiple paragynous antheridia
formed
concurrently with amphigynous ones during the
period of gametangial production in paired colonies. Where there were
multiple paragynous antheridia associated with an oogonium,
sometimes additional antheridia formed after fertilization or even after
oospores were visible. Developmental studies showed that
when meiosis in amphigynous and paragynous antheridia was simultaneous,
fertilization tubes developed synchronously from both.
However, cytological examination indicated that either a nucleus from an
amphigynous or a paragynous antheridium fertilized the
oosphere. Observations of paragynous and amphigynous, and amphigynous-only
associations suggested that fertilization from either
type of antheridium only occurred when meiosis in the oogonium was nearly
synchronous with that of the antheridium.
Asynchronous meiosis between oogonia and antheridia may contribute to failed
fertilization and aborted oospore development. This
appears to be the first description of paragynous antheridia in
P. cinnamomi and the second observation of oogonia with both
paragynous and amphigynous antheridia in a heterothallic Phytophthora
species. Moreover, the development of both paragynous and
amphigynous antheridia with an oogonium is rare in Phytophthora,
as
is the development of multiple antheridia. Antheridial variation
is a characteristic to be taken into account in isolate identification.
Nuclei from paragynous antheridia appear able to fertilize
oospheres and therefore, have a role in sexual reproduction.