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

 

Figure 2. Sporangia of Phytophthora ipomoeae. (Courtesy Peter Bonants; Reproduced, by permission, from Flier et al., 2002)

 

Figure 3. Oogonia of Phytophthora ipomoeae with amphigynous antheridia and oospores. (Courtesy Peter Bonants; Reproduced, by permission, from Flier et al., 2002)

 

Figure 4. Symptoms of Phytophthora ipomoeae on a morning glory (Ipomoea longipedunculata) leaf. (Courtesy Peter Bonants; Reproduced, by permission, from Flier et al., 2002)

 

Introduction

Phytophthora ipomoeae  Flier & Grünwald (2002)

 

Phytophthora ipomoeae was first described on morning glory in Toluca, Mexico (Flier et al., 2002). Internal transcribed spacer 1 and rDNA are similar between this species and P. infestans and P. mirabilis (Cooke et al., 2000). P. infestans has been reported previously on morning glory in India (Erwin and Ribeiro, 1996). However, the pathogen had different morphological characters and host specificity (Flier et al., 2002). Molecular characterization of other gene regions support the placement of P. ipomoeae in clade Ic (Cooke et al., 2000; Kroon et al., 2004). P. ipomoeae is a group IV species (Stamps et al., 1980; Waterhouse, 1963). Further work is needed to determine the evolutionary relatedness of this species to P. infestans. 

Cultural Characteristics

Mycelium grows well on rye A agar. The minimum temperature for growth is 11°C, the optimum temperature for growth is 20°C, and the maximum temperature for growth is 25°C (Fig. 1).

Reproductive Structures

Asexual Structures

Sporangiophores:

Sporangiophores are aerial and have compound sympodial and intermediate branches, with swellings where sporangia emerge.

 

Sporangia:

Sporangia are semipapillate and ellipsoid or semiovoid with caducous short pedicels. Sporangia are 35–47.5 µm long (average 39 µm). The length–breadth ratio is 1.9:1 (Fig. 2). Sporangia germinate directly with germ tubes or indirectly with zoospores.

 

Chlamydospores:

Chlamydospores have not been reported for P. ipomoeae.

 

Hyphae:

Hyphae are nonseptate, freely branching, and 4–7.5 µm in diameter. Hyphal swellings have not been reported for P. ipomoeae.

 

Sexual Structures

 

P. ipomoeae is homothallic.

 

Antheridia:

Antheridia are amphigynous and 19 µm long.

 

Oogonia:

Oogonia are smooth walled and 32.5 µm in diameter.

 

Oospores:

Oospores are smooth walled, colorless, and 28.8 µm in diameter (Fig. 3).

Host Range and Distribution

Host

Common Name

Disease

Geographical Distribution

Ipomoea longipedunculata

Morning glory

Leaf blight

Mexico

Ipomoea purpurea

Morning glory

Leaf blight

Mexico

Symptoms

Symptoms include blight on the leaves and stems of morning glory and other members of the family Convolvulaceae (Fig. 4).

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.

 

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

 

Flier, W. G., Grunwald, N. J., Kroon, L. P. N. M., van den Bosch, B. M., Garay-Serrano, E., Lozoya-Saldana, H., Bonants, P. J. M., and Turkensteen, L. J. 2002. Phytophthora ipomoeae sp. nov., a new homothallic species causing leaf blight on Ipomoea longipedunculata in the Toluca Valley of central Mexico. Mycol. Res. 106:848-856.

 

Kroon, L. P. N. M., Bakker, F. T., van den Bosch, G. B. M., Bonants, P. J. M., and Flier, W. G. 2004. Phylogenetic analysis of Phytophthora species based on mitochondrial and nuclear DNA sequences. Fungal Genet. Biol. 41:766-782.

 

Stamps, D. J., Waterhouse, G. M., Newhook, F. J., 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.

 

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.