Submitted to: Plant Disease
Publication Type: Other
Publication Acceptance Date: 7/17/2004
Publication Date: 12/20/2004
Citation: Nishijima, K.A., Alvarez, A.M., Hepperly, P.R., Shintaku, M.H., Keith, L.M., Sato, D.M., Bushe, B.C., Armstrong, J.W., Zee, F.T. 2004. Association of enterobacter cloacae with rhizome rot of 'edible' ginger in hawaii. Plant Disease. Vol. 88 No. 12, pgs. 1318 - 1327. Interpretive Summary: An enteric bacterium identified as Enterobacter cloacae was isolated from healthy as well as decayed rhizomes of edible ginger (Zingiber officinale Roscoe). Our studies suggest that the bacterium exists in internal tissue of healthy rhizomes and becomes an opportunistic pathogen resulting in rhizome rot when conditions are ideal for bacterial growth or host susceptibility. Rot in the ginger rhizomes usually occurred in the center area of the rhizome and were characterized by yellowish-brown discoloration and spongy texture. In ginger inoculations, E. cloacae produced root rot and yellowing or 'burning' foliar symptoms on tissue-cultured ginger plantlets in test tubes, and rhizome rot symptoms on ginger slices and rhizome segments. The ginger strains of the bacterium also produced internal yellowing disease symptoms on the Kapoho Solo cultivar of papaya, and internal rot of onion bulbs. The association of E. cloacae with a rhizome rot of ginger is a new report. Two colony forms of the ginger strains of E. cloacae were also observed, which represents a new finding.
Technical Abstract: A Gram-negative, facultative anaerobic, rod-shaped bacterium was consistently isolated from decayed as well as symptomless ginger rhizomes. The bacterium was identified as Enterobacter cloacae by biochemical assays and 16S rDNA sequence analysis. Rot symptoms, which usually occurred in the central cylinder of the rhizome, were characterized by yellowish-brown to brown discolored tissue and firm to spongy texture. In inoculation experiments, ginger strains of E. cloacae produced basal stem and basal root rot, with foliar chlorosis and necrosis in tissue-cultured ginger plantlets, and discolored and spongy tissue in mature ginger rhizome slices and whole segments. In other hosts, ginger strains of E. cloacae caused internal yellowing of ripe papaya fruit and internal rot of onion bulbs. Three papaya cultivars responded differently to E. cloacae infection: 'Kapoho Solo' was highly susceptible, 'Rainbow' was mildly resistant, and 'Sun Up' was immune. All strains that caused symptoms in inoculated plants were reisolated and identified as E. cloacae. Our studies suggest that E. cloacae is an internal endophyte of ginger rhizomes that becomes an opportunistic pathogen that can cause rhizome rot when conditions favor bacterial growth or host susceptibility. The association of E. cloacae with a rhizome rot of ginger is a new finding.