Figure 1. Culture of Phytophthora macrochlamydospora grown on V-8 juice agar. (Courtesy Jean B. Ristaino)

 

Figure 2. Morphology of Phytophthora macrochlamydospora. 1, Coralloid hyphal swellings. 2, Typical semipapillate sporangia. 3, Atypical sporangium displaying pronounced papilla (only rarely observed). 4, Catenulate hyphal swellings. 5, Intercalary immature chlamydospore. 6, Intercalary mature chlamydospore. All bars = 8.5 µm. (Reproduced, by permission of Mycologia, from Irwin, 1991; © The Mycological Society of America) Click image to see larger view.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Introduction

Phytophthora macrochlamydospora  J. A. G. Irwin (1991)

 

Phytophthora macrochlamydospora was isolated in 1974 from soybean, Glycine max cv. Hampton, that was affected by a stem and root rot. The absence of sexual structures makes this classification tentative, and it is not classified in Stamps et al. (1990). Cooke et al. (2000) placed this species into clade 9 and distinct from the species in clades 1–8.

Cultural Characteristics

The optimum temperature for growth is 23–30°C, the minimum temperature for growth is 6°C, and the maximum temperature for growth is 34°C (Fig. 1).

Reproductive Structures

Asexual Structures

Sporangiophores:

Sporangiophores can be up to 500 µm long and proliferate either internally or sympodially.

 

Sporangia:

Sporangia are formed terminally on sporangiophores and are semipapillate, ellipsoid to obpyriform, and 18–36 × 20–50 µm (Fig. 2.2 and 2.3).

 

Chlamydospores:

Chlamydospores that form on solid or liquid V-8 agar media are large, spherical, and terminal or intercalary. Chlamydospores are 24–84 µm in diameter (average 55 µm) and have walls that are 2.5–4.0 µm thick. The distinguishing feature is the abundant production of large, thick-walled chlamydospores (Fig. 2.5 and 2.6).

 

Hyphae:

Hyphal swellings are thin walled, spheroidal to ellipsoid, and often formed in chains (Fig. 2.1).

 

Sexual Structures

 

Sexual structures have not been found for P. macrochlamydospora.

Host Range and Distribution

Host

Common Name

Diseases

Geographical Distribution

Glycine max cv. Hampton

Soybean

Stem and root rot

Australia

Symptoms

P. macrochlamydospora causes stem and root rot in soybean.

References

Cooke, D. E. L., Drenth, A., Duncan, J. M., Wagels, G., and Brasier, C. M. 2000. A molecular phylogeny of Phytophthora and related oomycetes. Fungal Genet. Biol. 30:17-32.

 

Irwin, J. A. G. 1991. Phytophthora macrochlamydospora, a new species from Australia. Mycologia 83:517-519.

 

Stamps, D. J., Newhook, F. J., Waterhouse, G. M., and Hall, G. S. 1990. Revised tabular key to the species of Phytophthora de Bary. Mycol. Pap. 162. CAB International, Wallingford, United Kingdom; Commonwealth Mycological Institute, Kew, Surrey, England.