Research Projects

Population Genetics | Ecology and Epidemiology | Sustainable Agriculture

Ecology and Epidemiology
Dispersal of Phytophthora capsici in soils from conventional and organic production systems
P. capsici can cause a root and crown rot on pepper (Fig. 1) and also forms distinctive black lesions on the stem (Fig. 2). Root infections typically lead to wilting of the plant. P. capsici can also infect the leaves of the plant and causes lesions that are circular, greyish-brown and water-soaked (Fig. 3). Leaf lesions and stem lesions are common when inoculum is splash dispersed from the soil to lower portions of the plant. The pathogen can also infect fruit and causes lesions that are typically covered with white sporangia, a sign of the pathogen (Fig. 4). The pathogen causes a multicylic disease.

Fig. 1 Root and crown rot on bell pepper caused by Phytophthora capsici.	Fig. 2 Black stem lesion caused by Phytophthora capsici on bell pepper.
Fig. 3. Greyish brown water-soaked lesions on leaves of bell pepper caused by Phytophthora capsici.	Fig. 4. Lesion caused by Phytophthora capsici on bell pepper fruit. Note white mycelium and sporangia of the pathogen.

Several grants funded by the USDA NRI Programs on P. capsici research have been funded. Most recently, specific objectives of our research were to address the following questions 1) Are soils from organic agroecosystems more resistant than soils from conventional agroecosystems to invasion, dispersal and reproduction by the soilborne oomycete pathogen Phytophthora capsici; 2) Is species diversity, functional diversity, composition of the soil microflora, or soil physical and chemical factors most closely related to disease suppressiveness of soils to Phytophthora blight; and 3) Are soils from organic agroecosystems more resilient than soils from conventional agroecosystems to disturbance? How does the level of microbial biodiversity in these soils relate to resilience to disturbance?

Select papers
1. Liu, B.  Gumpertz, M. L.  Hu, S. and. Ristaino, J. B.  2007.   Effect of prior tillage and soil fertility amendments on dispersal of Phytophthora capsici and infection of pepper.  Eur. J. Plant Pathology. Accepted July 2007 Ristaino,
2. J.B. and Johnston, S.B. 1999. Ecologically- based management of Phytophthora blight on bell pepper. Plant Disease 83:1080-1089.
3. Sujkowski, L.S., Parra, G.R., Gumpertz, M.L., and Ristaino, J.B. 2000. Temporal Dynamics of Phytophthora blight in bell pepper in relation to the mechanisms of dispersal of primary inoculum of Phytophthora capsici in soil. Phytopathology 90:148-156.
4. Parra, G. and Ristaino, J.B. 2001. Resistance to mefenoxam and metalaxyl among field isolates of Phytophthora capsici causing Phytophthora blight of bell pepper. Plant Disease 85:1069-1075.
5. Ristaino, J.B. and Gumpertz, M.L. 2000. New frontiers in the study of dispersal and spatial analysis of epidemics caused by species in the genus Phytophthora. Annu. Rev.Phytopathology 38:541-576.
6 . Ristaino, J. B. and W. Thomas. 1997. Agriculture, Methyl bromide, and the ozone hole:Can we fill the gaps. Plant Disease 81:954-975. http://www.APSNET.org/online/feature/2-98_mb/top.html
http://www.apsnet.org/media/press/archive/methyl.asp
7. Café'-Filho, A. and Ristaino, J.B. 2002. Fitness of Phytophthora capsici isolates insensitive to mefenoxam from squash and pepper in North Carolina. Plant Health Progress:in review.