Figure 1. Morphology of Phytophthora syringae. Upper row, Ovoid, nondeciduous sporangia formed sympodially on sporangiophores. Center row, Irregular, torulose mycelium. Lower row, Globose oogonia and paragynous antheridia (sometimes two antheridia per oogonium); inflated, catenulate hyphal swellings. (Courtesy A. Vaziri; Reproduced from Erwin and Ribeiro, 1996) Click image to see larger view.

 

Figure 2. Culture of Phytophthora syringae grown on V-8 juice agar. (Courtesy Jean B. Ristaino)

 

Figure 3. Semipapillate sporangia of Phytophthora syringae (×1,000). (Courtesy Jean B. Ristaino)

 

Figure 4. Comparison of sporangial and oogonial morphology of four Phytophthora species. 2–4, Sporangium, sporangial proliferation, and an oospore of Phytophthora idaei. 5–7, Phytophthora cactorum. 8–10, Phytophthora citricola. 11–13, Phytophthora syringae. (Reproduced, by permission of The British Mycological Society, from Kennedy and Duncan, 1995) Click image to see larger view.

 

Figure 5. Almond tree with Phytophthora syringae infection at pruning wounds. (Courtesy B. Teviotdale; Reproduced from APS Digital Image Collections, Diseases of Orchard Fruit and Nut Crops, American Phytopathological Society, St. Paul, MN)

 

Introduction

Phytophthora syringae  (Berk.) Kleb. (1909)

 

Phytophthora syringae was first isolated and described by Klebahn (1905; 1909) from diseased lilac trees, Syringa vulgaris, in Germany. Tucker reported that it was previously described by M. J. Berkeley as Ovularia syringae Berk. (1881). It is suggested that (Berk.) Kleb. not (Kleb.) Kleb. be used as the author citation (Cline et al., 2008). Other synonyms of P. syringae include Phloeophthora syringae Kleb. (1905), Nozemia syringae (Kleb.) Pethybr. (1913), P. cactorum subvar. syringae (Kleb.) Sarej. (1936), Pythiomorpha fischeriana Höhnk (1936), and P. fischeriana (Höhnk) Sparrow (1960). P. hibernalis was considered by Tucker (1931) to be synonymous with P. syringae but they are now considered distinct species (Ho and Jong, 1993). The name P. syringae has been applied to a root and collar rot of deciduous trees in Europe, which has now been described as a distinct species, P. pseudosyringae (Jung et al., 2003). P. syringae is best known as a pathogen of plants in the family Rosaceae. P. syringae is a group III Phytophthora species (Stamps et al., 1990) (Fig. 1).

Cultural Characteristics

The minimum temperature for growth is less than 5°C, and the maximum temperature for growth is 23°C (Fig. 2). The optimum temperature for growth is 15–20°C.

Reproductive Structures

Asexual Structures

 

Sporangiophores:

Sporangiophores form in a close monochasial sympodium with intercalary swellings.

 

Sporangia:

Sporangia are broadly ovoid or obpyriform, semipapillate, and noncaducous. Sporangia may have more than one apex and distortion and lateral attachment in some isolates (Gallegly and Hong, 2008). Sporangia form in succession from a single sporangium and average 36 × 57 µm (Figs. 3 and 4.11 and 4.12) (Waterhouse and Waterston, 1964). Size may vary depending on host and different dimensions can be found in Table 60.2 of Erwin and Ribeiro (1996).

 

Chlamydospores:

Waterhouse and Waterston (1964) and Ho and Jong (1993) did not report chlamydospore production, but Stamps et al. (1990) reported chlamydospores that were 25 µm in diameter.

 

Hyphae:

Hyphae can be up to 6 µm wide (Waterhouse and Waterston, 1964). Hyphal swellings are rounded, angular, often in chains, and occasionally delimited by septa. Hyphal coiling in old cultures is common (Fig. 1).

  

Sexual Structures

 

P. syringae is homothallic.

 

Antheridia:

Antheridia are predominately paragynous and occasionally amphigynous. Antheridia are 7 × 10 µm (Waterhouse and Waterston, 1964).

 

Oogonia:

Oogonia form abundantly in culture and host tissue and oogonium diameter averages 33 µm. Dimensions from different reports can be found in Table 60.2 of Erwin and Ribeiro (1996).

 

Oospores:

Oospores are plerotic, filling the entire oogonium. Oospore diameter averages 30 µm, but different reported dimensions can be found in Table 60.2 of Erwin and Ribeiro (1996) (Fig. 4.13). The oospore wall can be 2 µm thick (Waterhouse and Waterston, 1964).

Host Range and Distribution

P. syringae is responsible for collar and fruit rot in apple, leaf spot and shoot dieback in lilac, and pruning wound canker of almond. It can infect 24 genera in 14 families and has been reported in Africa, Asia, Australasia, Europe, North America, and South America (Cline et al., 2008).

Symptoms

Collar and Fruit Rot of Malus pumila (Apple):

In fruit rot, the flesh of infected tissue turns dark brown, but the rotted tissue remains firm. Collar rot occurs during late autumn, and symptoms include girdling of the trunk from the collar to several inches above the ground and exudation of gum from affected bark. During the spring, buds of young trees fail to open and mature trees put forth weak, small shoots that do not develop further. In nursery stocks, dark, slightly sunken cankers occur on stems, and in severe cases, the stem is girdled.

 

Leaf Spot and Shoot Dieback of Syringa vulgaris (Lilac):

P. syringae affects plants during the winter dormant season and leads to small, water-soaked lesions on leaves. The lesions gradually increase in size during periods of frequent rainfall and eventually become irregular in shape. The brown patches are surrounded by lighter-colored margins and entire leaves may be invaded. The fungus subsequently grows down the petioles into the cortex of the branches and dark brown or black cankers form in the bark. The vascular system is affected during advanced stages of the disease. Occasionally, disease may be limited to a single bud (Chester, 1932).

 

Pruning Wound Canker of Prunus dulcis (Almond):

P. syringae causes pruning wound cankers during the winter months. P. syringae causes gumming cankers at 2–20°C and infects plants with pruning wounds (Fig. 5).

References

Berkeley, M. J. 1881. Lilac fungus. Gard. Chron. II 16:665.

 

Chester, K. S. 1932. A comparative study of the three Phytophthora diseases of lilac and of their pathogens. J. Arnold Arbor. Harv. Univ. 13:232-269.

 

Cline, E. T., Farr, D. F., and Rossman, A. Y. 2008. A synopsis of Phytophthora with accurate scientific names, host range, and geographic distribution. Plant Health Progress doi:10.1094/PHP-2008-0318-01-RS.

 

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

 

Gallegly, M., and Hong, C. 2008. Phytophthora: Identifying Species by Morphology and DNA Fingerprints. American Phytopathological Society, St. Paul, MN.

 

Ho, H. H., and Jong, S. C. 1993. Phytophthora hibernalis and P. syringae. Mycotaxon 47:439-460.

 

Höhnk, W. 1936. On three pythiaceous oomycetes. Beih. Bot. Zentralbl. 55(Abt. A):89-99.

 

Jung, T., Nechwatal, J., Cooke, D. E. L., Hartmann, G. C., Blaschke, M., Oswald, W. F., Duncan, J. M., and Delatour, C. 2003. Phytophthora pseudosyringae sp. nov., a new species causing root and collar rot of deciduous tree species in Europe. Mycol. Res. 107: 772-789.

 

Klebahn, H. 1905. Eine neue Pilzkrankheit der Syringen (A new fungal disease of Syringae). Zentralbl. Bakt. 15(Abt. 2):335-336. (In German)

 

Klebahn, H. 1909. Die neue Zweig-und Knospenkrankheit (A new twig and bud disease). Pages 18-75 in: Krankheiten des Flieders. Verlag von Gebrüder Borntraeger, Berlin. (In German)

 

Kennedy, D. M., and Duncan, J. M. 1995. A papillate Phytophthora species with specificity to Rubus. Mycol. Res. 99:57-68.

 

Pethybridge, G. H. 1913. On the rotting of potato tubers by a new species of Phytophthora having a method of sexual reproduction hitherto undescribed. Sci. Proc. R. Dublin Soc. 13:529-565.

 

Sarejanni, J. A. 1936. La pourriture de Collet des Solanées cultivees et la classification du genre Phytophthora (A collar rot of cultivated Solanum and the classification of the genus Phytophthora). Inst. Phytopath. Benaki 2:35-52. (In French)

 

Sparrow, F. K., Jr. 1960. Aquatic Phycomycetes. University of Michigan Press, Ann Arbor, MI.

 

Stamps, D. J., Waterhouse, G. M., Newhook, F. J., and Hall, G. S. 1990. Revised tabular key to the species of Phytophthora. 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., and Waterston, J. M. 1964. Phytophthora syringae. CMI Descr. Pathog. Fungi Bact. 32.