|BUSHE, BRIAN - University Of Hawaii|
|HELLER, WADE - University Of Hawaii|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2017
Publication Date: 3/13/2018
Citation: Sugiyama, L.S., Bushe, B., Heller, W., Keith, L.M. 2018. First report of pseudomonas cichorii causing bacterial leaf blight of plumeria pudica in Hawaii. Plant Disease. 102(5):1025. https://doi.org/10.1094/PDIS-11-17-1771-PDN.
Interpretive Summary: Bridal Bouquet Plumeria is a commonly grown ornamental in Hawaii. In November 2014, a nursery grower located in Panaewa on the eastern side of Hawaii Island noticed water-soaked, greyish-black leaf spots and leaf blight followed by defoliation on potted plants of P. pudica. The bacteria causing the disease was identified and its pathogenicity was proven. This is the first report of bacterial leaf blight caused by Pseudomonas cichorii on Plumeria pudica in Hawaii.
Technical Abstract: Bridal Bouquet Plumeria (Plumeria pudica) is a commonly grown ornamental in Hawaii. In November 2014, a nursery grower located in Panaewa on the eastern side of Hawai'i Island noticed water-soaked, greyish-black leaf spots and leaf blight followed by defoliation on potted plants of P. pudica. Leaf samples were submitted to the University of Hawaii Agricultural Diagnostic Center located at the Komohana Research and Extension Center in Hilo, HI for diagnosis. Bacteria were consistently isolated from diseased tissue. To differentiate the genera based on growth characteristics, bacteria were plated on NDA, YDC, KMB, CVP, and MS agar (Schaad et al. 2001). Culture plates of a fluorescent Pseudomonad were forwarded to the USDA-ARS-DKI-PBARC facility in Hilo, HI for further purification and molecular identification. A partial 16S rRNA gene sequence (1,355 bp) (accession no. MF536096) was 100% identical to multiple accessions of Pseudomonas cichorii (Swingle 1925) Stapp 1928 from chrysanthemum, okra and stevia in the NCBI database. To prove pathogenicity, four healthy P. pudica plants were inoculated with a bacterial suspension containing a drop of Tween 20 from 3-day-old cultures grown on LB at 27° C in the dark and adjusted to 1 x 10e8 CFU/ml. Plants were sprayed to run-off, placed in a clear plastic bag, and held at 24oC (Strayer et al. 2012). Four control plants were inoculated with sterile distilled water. After 24 h, plants were removed from the bag, placed on a greenhouse bench, and observed for disease development. After 1 day, numerous water soaked lesion were visible on the adaxial leaf surface and a few 1 to 2mm greyish-black leaf spots were visible on the abaxial leaf surface. Leaf spots continued to develop and by day 4 several had coalesced into large blighted areas covering 20 to 30% of the leaf surface. By day 7, 50 to 90% of each plant was defoliated. Bacterial colonies were consistently re-isolated from the inoculated plants and molecularly identified as P. cichorii, while no bacterial colonies were isolated from the control plants, thus fulfilling Koch’s postulates. The test was repeated twice. To our knowledge, this is the first report of bacterial leaf blight caused by P. cichorii on P. pudica in Hawaii. The nursery was notified of these findings. As recommended by Chase (2013), pruning, rouging and removal of diseased plant material, increased plant spacing and reduction of standing water were implemented. To date no additional samples have been submitted.