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Poster: Biology & Disease Mgmt: Integrated Pest Mgmt


Evaluation of stem inoculation technique for assessing resistance to Phytophthora nicotianae in hydrangea cultivars
M. KABIR (1), T. Simmons (1), P. Liyanapathiranage (1), C. Curry (1), L. Alexander (2), F. Baysal-Gurel (1) (1) Tennessee State University, Nashville, TN, U.S.A.; (2) USDA-ARS, U.S. National Arboretum, McMinnville, TN, U.S.A.

Almost all hydrangeas, especially container-grown oakleaf hydrangeas (Hydrangea quercifolia) are more susceptible to Phytophthora root rot disease. Most economic and trading hydrangea cultivars are propagated as rooted cuttings. Reliable and rapid stem cutting-based screening technique to evaluate hydrangea cultivars for resistance to Phytophthora nicotianae is needed toward disease management. Hydrangea cvs. Queen of Hearts, Ruby Slippers and Munchkin stem cuttings were screened in a laboratory procedure by point inoculation with 5-day-old culture, #1 size (outside diameter 5 mm) plugs of P. nicotianae. Each stem cutting was evaluated for lesion area and lesion severity after 3, 5 and 7 days of incubation at 25°C with 16-hr-light/8-hr-dark cycle. The experiment was repeated twice. After comparing the lesion development on three hydrangea cultivars, the results showed that Queen of Hearts is most susceptible to P. nicotianae than other cultivars and five days observation is the optimal time for stem cutting-screening technique. This study will facilitate the ongoing large-scale screening for Phytophthora root rot resistance among hydrangea cultivars very easily and it is clear that described stem cutting-inoculation technique has the potential to play a significant role for simple, efficient and reproducible screening.