Submitted to: Sudden Oak Death Science Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 3/18/2009
Publication Date: 6/15/2009
Citation: Manter, D.K., Hansen, E., Parke, J. 2009. Effect of Plant Sterols and Tannins on Phytopthora ramorum growth and sporulations. 4th Sudden Oak Death Science Symposium. pp. 24. Interpretive Summary: Real-time PCR assays detected expression of both class I elicitins (Ram-a1 and Ram-a2) in all 15 isolates. Of the two elicitins, only the Ram-a2 differed between lineage (p = 0.000) with nearly 2-fold higher levels of expression in the EU1 and NA2 lineages as compared to the NA1 lineage. Ram-a2 expression showed a positive linear relationship with isolate virulence or lesion size (r2 = 0.71). The significant, positive, linearrelationship was also observed between Ram-a2 expression and sporulation although it was not as strong (r2 = 0.21). In conclusion, isolates belonging to clonal lineages EU1 and NA2 are generally more virulent, produce more sporangia, and produce more Ram-a2 elicitin in vitro than do isolates belonging to lineage NA1. This suggests that Ram-a2 may contribute to the fitness of Phytophthora ramorum. Further studies are needed to determine what quantities of Ram-a2 are produced in planta and any additional factors that may directly influence its activity.
Technical Abstract: Phytopthora ramorum populations are clonal and consist of three clonal lineages. EU1 is the only lineage found in Europe with a few isolated nursery infections in the USA, NA1 is associated with natural infestations in California and Oregon as well as some nursery infections in North America, and NA2 has a limited distribution and has only been isolated from a few nurseries in the USA. Recent studies have shown that the clonal lineages may have varying degrees of aggressiveness on some host species, such as Quercus rubra. In this study, we examined virulence, sporulation and elicitin production of five P. ramorum isolates from each of the three clonal lineages. Virulence (lesion size) and sporulation (sporangia production) were determined on inoculated detached leaves of rhododendron ‘Nova Zembla’. Elicitin production was determined in vitro. Lesion area differed between the clonal lineages (p < 0.001). Leaves inoculated with EU1 and NA2 isolates had significantly greater lesion area than NA1-inoculated leaves (ca. 4.2, 3.6, and 0.8 cm2 respectively). Similarly, sporangia production was greatest in the EU1 and NA2 isolates compared to the NA1 lineage; however considerable variation was noted between trials. In Trial 1, sporangia production was very low and there was no difference between clonal lineages (p = 0.20); however, there were significant differences among isolates (p = 0.04). Sporangia production was much greater in Trial 2 than in Trial 1, likely because the leaves were misted more frequently in the 1-2 days before processing to increase sporulation. In Trial 2, there were significant differences among clonal lineages and isolates (p = 0.0003). Lineages EU1 and NA2 produced significantly more sporangia per leaf (p < 0.001) than did lineage NA1 (ca. 800, 1000, and 300 sporangia per leaf respectively).