Figure 1. Morphology of Phytophthora richardiae. Upper row, Ovoid to ellipsoid, nonpapillate sporangia. Lower row, Globose oogonium with an amphigynous antheridium (often up to 20 µm wide). Oospore (not shown) has a thick (~5-μm) wall. Sporangium with a subterminal protuberance. Sporangia forming sympodially and proliferating externally. (Courtesy A. Vaziri; Reproduced from Erwin and Ribeiro, 1996) Click image to see larger view.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Introduction

Phytophthora richardiae  Buisman (1927)

 

Phytophthora richardiae was first described by Buisman in the Netherlands in 1927 as causing a disease of calla lilies (Buisman, 1927). It was named P. cryptogea var. richardiae (Buisman) by Ashby in 1929 (Ashby, 1929). Others have called the species P. richardiae (Stamps et al., 1990; Tucker, 1931; Waterhouse, 1963). It was named for the plant genus it infects, Richardia aethiopica (now known as Zantedeschia aethiopica). P. richardiae is a group VI Phytophthora species (Stamps et al., 1990) (Fig. 1).

Cultural Characteristics

The optimum temperature for growth is 24–25°C, the minimum temperature for growth is 10°C, and the maximum temperature for growth is 30–32°C (Erwin and Ribeiro, 1996). Tucker (1931) suggested that P. richardiae and P. cryptogea have similar growth parameters (minimum, 10°C; optimum, 20°C; and maximum, 30°C).

Reproductive Structures

Asexual Structures

 

Sporangiophores:

Sporangiophores are unbranched.

 

Sporangia:

Sporangia are nonpapillate, variable in shape, ovoid, obpyriform, obturbinate, and often with more than one apex, and occasionally have a lateral attachment. They are persistent on the stalk (noncaducous) and proliferate internally. They are 20–40 × 40–60 µm (average 33 × 52 µm) (Buisman, 1927) (Fig. 1).

 

Chlamydospores:

Chlamydospores are not produced.

 

Hyphae:

Hyphal swellings are large and spherical, rounded, or angular and in chains, often with radiating hyphae. 

 

Sexual Structures

 

P. richardiae is homothallic.

 

Antheridia:

Antheridia are mostly amphigynous and large (>20 µm) with characteristic protuberances and occasionally paragynous.

 

Oogonia:

Oogonia are 34–38 µm in diameter according to Buisman (1927), 29–48 µm (average 39 µm) according to Ashby (1929), and average 28.9 µm according to Tucker (1931).

 

Oospores:

Oospores are 19–41 µm in diameter (average 30.7 µm) according to Ashby (1929), average 25.4 µm according to Tucker (1931), and 29 µm according to Buisman (1927) (Fig. 1).

Host Range and Distribution

Host

Common Name

Disease

Geographical Distribution

Zantedeschia spp.

Calla lily

Leaf blight; root rot

Asia, Philippines, Australasia, Australia, Belgium, Czechoslovakia, Netherlands, United States, United Kingdom

Asparagus spp.

Asparagus

Root rot

Asia, Philippines, Australasia, Australia, Belgium, Czechoslovakia, Netherlands, United States, United Kingdom

Robinia spp.

Black locust

Root rot

Asia, Philippines, Australasia, Australia, Belgium, Czechoslovakia, Netherlands, United States, United Kingdom

Daucus carota

Carrot

Root rot

Asia, Philippines, Australasia, Australia, Belgium, Czechoslovakia, Netherlands, United States, United Kingdom

Lycopersicon esculentum

Tomato

Root rot

Asia, Philippines, Australasia, Australia, Belgium, Czechoslovakia, Netherlands, United States, United Kingdom

Symptoms

P. richardiae causes a destructive disease of calla lilies. Discoloration of leaves, chlorosis, and wilting occur. Infection of outer leaves occurs before inner leaves. Flowers are small and malformed. Brown discoloration of the spathe can occur. A root rot occurs and roots can have a reddish coloration. Infection usually begins at the point of attachment of the corm to the roots. The pathogen survives in the roots. Rotted corms are rarely infected but can become dry and spongy if infected. The pathogen may survive in roots and causes a progressive death of the plant over time. Oospores can form in diseased tissue (Erwin and Ribeiro, 1996).

References

Ashby, S. F. 1929. Further note on the production of sexual organs in paired cultures of species and strains of Phytophthora. Trans. Br. Mycol. Soc. 14:254-260.

 

Buisman, C. J. 1927. Root rots caused by Phycomycetes. Thesis. University of Utrecht. Meded. Phytopathol. Lab. Wille Commelin Scholten 11(7):1-51.

 

Erwin, D. C., and Ribeiro, O. K. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN.

 

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.

 

Tucker, C. M. 1931. Taxonomy of the genus Phytophthora de Bary. Univ. Mo. Agric. Exp. Stn. Bull. 153.

 

Waterhouse, G. M. 1963. Key to the species of Phytophthora de Bary. Mycol. Pap. 92. CAB International, Wallingford, United Kingdom; Commonwealth Mycological Institute, Kew, Surrey, England.