Phytophthora nicotianae: A Pathogen of Herbaceous Ornamental Plants

1
Phytophthora Diseases of Ornamental Crops in
South Carolina
Steven N. Jeffers Clemson University Department
of Entomology, Soils, Plant Sciences Clemson, SC
2
Projects Students Funded

• PhD Student
• Chung-hang DuanPhD 2002
• Variations in fatty acid methyl ester profiles
  and amplified fragment length polymorphisms among
  and within species of Phytophthora from
  ornamental plants
• MS Student
• Jessica A. EisenmannMS 2003
• Identification, pathogenicity, and virulence of
  isolates of Phytophthora nicotianae from
  ornamental plants

3
Projects Students Funded

• Undergraduate students
• Christina PulasBS 2004
• morphological variation among P. citricola-like
  isolates
• Leigh Ann HarrisonBS 2004
• fatty acid methyl ester (FAME) profile analysis
  of Phytophthora cactorum
• Amanda WatsonBS 2006
• Phytophthora leaf blight of hosta (see poster)

4
Projects Students Funded

• Phytophthora Culture Collection
• collaboration with the CU Plant Problem Clinic
  colleagues around the country
• receive and store isolates of Phytophthora spp.
  from ornamental crops natural ecosystems
• Evaluate disease management strategies
• collaboration with SC growers and ag-chem
  industry representatives

5
Identification, Pathogenicity, and Virulence of
Isolates of Phytophthora nicotianae from
Ornamental Plants

• MS thesis project by J. A. Eisenmann

6
Differentiating P. nicotianae P. palmivora can
be difficult in a diagnostic lab

• Both attack herbaceous ornamental plants in the
  Southeast
• They tend to have similar morphological
  characters
• How can diagnosticians tell them apart??
• host range
• specific morphological physiological traits
• molecular fingerprints

7
Differentiating P. nicotianae P. palmivora

• P. nicotianae is the most common species on
  herbaceous ornamental crops in the SE
• attacks many different plantsincluding
  Antirrhinum, Buxus, Catharanthus, Daphne,
  Gardenia, Hemerocallis, Petunia, Phlox, Verbena,
  Vinca, many others
• P. palmivora attacks primarily Hedera spp. and
  the related plant Fatsia japonica
• both in the family Araliaceae
• but occasionally found on other hosts

8
Differentiating P. nicotianae P. palmivora
9
Differentiating P. nicotianae P. palmivora
P. palmivora
P. nicotianae
colonies on PAR-V8 selective medium are different
ITS-RFLP fingerprints clearly show a difference
between species!
10
Expanding the P. nicotianae Host Range

• Isolates were recovered from samples submitted to
  the CU Plant Problem Clinic between Aug 1995
  Dec 2001
• 114 plants in 42 genera that came from 32
  counties in South Carolina
• including many herbaceous several woody hosts
• Previously, only 16 genera reported as hosts and
  7 documented as hosts
• Therefore, at least 26 potentially new hosts!

11
Relative susceptibility of 16 ornamental plants
to Phytophthora nicotianae
12
Day Lily Stella dOro Tolerant
Pansy Susceptible
Gaura Resistant
13
Phytophthora root crown rot on Wave Petunia in
Tennessee
Alan Windham, UT-Extension
14
Conclusions

• New herbaceous ornamental crop hosts for P.
  nicotianae were identified
• Pn attacks more plants than previously known
• Plants used in these experiments varied from
  resistant to susceptible
• Tolerant plants were identified!
• these exhibit no symptoms yet are capable of
  supporting the pathogen and supplying inoculum to
  adjacent plants in nurseries landscapes
• Isolates of P. nicotianae varied in virulence
• host specialization occurs in pathogen population