Erwinia papayae causing papaya dieback in Malaysia

A papaya die-back disease was first reported in Malaysia by the Johor State Department of Agriculture in 2003. By the end of 2006 it had spread to five other states on the west coast of the Malaysian peninsula, affecting ca. 800 ha and resulting in the destruction of ca. 1 million trees. Total yield losses were estimated at 200,000 metric tonnes, equivalent to US$ 58 million. The varieties affected were Eksotika, Solo, Hong Kong and Sekaki. Early symptoms included yellowing and necrosis along leaf edges followed by water-soaked areas on the bases of leaf stalks, crowns (Fig. 1) and along leaf mid-ribs. Fruit symptoms included dark spots on the skin and water-soaked flesh (Fig. 2). Later, necrotic and water-soaked areas developed on stems and spread to the internal tissues, followed by secondary fungal infections. In advanced stages bending of water-soaked leaf stalks occurs, leading to dieback, and death of trees (Fig. 3).

Hyaline bacterial colonies were consistently isolated on Luria Bertani agar from infected leaves, crowns, leaf midribs, fruits and leaf stalks after incubation for 48 h at 30°C. Isolates were Gram-negative rods, facultative anaerobes, oxidase negative and catalase positive. Six isolates were tested for tobacco hypersensitivity (Lelliot & Stead, 1987) and gave a strong response within 10-12 h. Pathogenicity was tested by inoculating suspensions into crowns and leaf stalks of five-month-old healthy papaya plants (cv. Eksotika). Sterile distilled water was used as a negative control. Characteristic symptoms were observed one week after inoculation. No symptoms were observed on control plants. The original bacterium was re-isolated from symptomatic plants and one isolate was sent to a commercial service for 16S rRNA gene sequencing. The isolate was identified as Erwinia papayae based on BLAST analyses of sequences in the NCBI database, with the highest similarity to E. papayae (GenBank acc no: AY131237.1) from the Caribbean (Gardan et al., 2004). PCR using phytoplasma specific primers, P1and P7 (Guthrie et al., 1998) ruled-out the involvement of phytoplasma.

This is the first report of E. papayae causing papaya dieback in Malaysia. The disease may have entered Malaysia via Johor, then spread to other states by human activity and possibly birds and insects. The first report of this disease in S.E. Asia was in Java in (von Rant, 1931). E. papayae was first reported as causing bacterial canker of papaya in the Caribbean by Gardan et al. (2004).