New Disease Reports
New Disease Reports (2010) 20, 40.
Vol 21 > < Prev

First report of Phytophthora inundata associated with a latent infection of tobacco (Nicotiana tabacum) in Virginia

V. Parkunan 1*, C.S. Johnson 1, B.C. Bowman 1 and C.X. Hong 2

*venki@vt.edu

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Accepted: 16 Feb 2010

During a state-wide tobacco black shank survey in the summers of 2007 and 2009, we recovered four isolates (two each from stem pith and rhizosphere soil, respectively), that had a DNA fingerprint typical of Phytophthora inundata (Gallegly & Hong, 2008). These isolates were from a field producing flue-cured tobacco (cultivars K326 and NC71, respectively) in Nottoway County with approximately 50-75% incidence of plants showing typical symptoms of black shank (Fig. 1). All isolates produced non-papillate, ovoid to obpyriform sporangia, averaging 51 x 36 μm (Fig. 2), through internal proliferation. Isolates formed hyphal swellings (Fig. 3) but failed to produce oospores with testers. These morphological characters and the complete ribosomal DNA internal transcribed spacer sequences (GenBank Accession No. FJ959406) confirmed their identity as P. inundata. These isolates were tested against three tobacco entries (Hicks, L8 and NC1071), generally used to differentiate P. nicotianae races. Multi-cell trays with five plants of each entry were challenged with 3 x 104 zoospores/plant and maintained under greenhouse conditions for four weeks along with control plants. The test was repeated twice. No disease symptoms were observed on any plants after four weeks (Fig. 4). Symptomless root, stem and leaf tissue from inoculated and control plants were plated out separately on Phytophthora selective medium (PARPH-V8) after surface sterilization with 0.5% sodium hypochlorite and 70% ethanol.P. inundata was re-isolated from all inoculated plant samples, indicating that successful colonization occurred, as determined by direct colony-PCR single strand conformation polymorphism (Kong et al., 2005). 

Phytophthora inundata was reported as a pathogen of shrubs and trees in Europe and South America (Brasier et al., 2003) andisolatedfrom alfalfa roots in California (Ho et al., 2006). This pathogen was also documented to cause latent infection of Viburnum in Australia (Cunnington et al., 2006). To our knowledge, this is the first report of a latent infection of tobacco by P. inundata.Investigations into this infection mechanism and its interactions with other pathogens are warranted to elucidate the role of P. inundata in tobacco fields.

Figure1+
Figure 1: Flue-cured tobacco plants showing typical black shank symptoms, crown rot, yellowing and wilting of leaves in the field
Figure 1: Flue-cured tobacco plants showing typical black shank symptoms, crown rot, yellowing and wilting of leaves in the field
Figure2+
Figure 2: An ovoid and non-papillate sporangium of P. inundata
Figure 2: An ovoid and non-papillate sporangium of P. inundata
Figure3+
Figure 3: Hyphal swellings produced by P. inundata
Figure 3: Hyphal swellings produced by P. inundata
Figure4+
Figure 4: Symptomless seedlings of tobacco four weeks after P. inundata zoospores inoculation
Figure 4: Symptomless seedlings of tobacco four weeks after P. inundata zoospores inoculation

Acknowledgements

The authors would like to thank Altria Client Services and Philip Morris International for their funding of this research.

References

  1. Brasier CM, Sanchez-Hernandez E, Kirk SA, 2003. Phytophthora inundata sp. nov., a part heterothallic pathogen of trees and shrubs in wet or flooded soils. Mycological Research 107, 477-484.
  2. Cunnington JH, Jones RH, de Alwis S, Minchinton EJ, 2006. Two new Phytophthora records for Australia. Australasian Plant Pathology 35, 383-384.
  3. Gallegly ME, Hong CX, 2008. Phytophthora: Identifying Species by Morphology and DNA Fingerprints. St. Paul, MN, USA: APS Press, 20-21.
  4. Ho HH, Hong CX, Erwin DC, 2006. Phytophthora inundata isolated from diseased alfalfa roots in Southern California. Mycotaxon 97, 349-358.
  5. Kong P, Richardson PA, Hong CX, 2005. Direct colony PCR-SSCP for detection of multiple pythiaceous oomycetes in environmental samples. Journal of Microbiological Methods 61, 25-32.
This report was formally published in Plant Pathology

©2010 The Authors