Erwinia papayae
Erwinia papayae is a bacteria species causing bacterial crown rot, or bacterial canker, a noteworthy and grave disease of papaya ("Carica papaya"). Importance. "Erwinia papayae", the bacterial pathogen responsible for the disease, was first identified in 1931 in Java, Indonesia (Gardan "et al." 2004), and has since spread to papaya growing countries worldwide—from the Caribbean to South America to South East Asia (Ollitrault "et al." 2007). By the late 1960s, "E. papaya"e had appeared in the West Indies, where it obliterated all the yields of the papaya cultivar ‘Solo,’ which because of its high fruit yields and  quality was the only one grown in the fields (Ollitrault "et al." 2007). Papayas are significant cash crops for the papaya-growing countries because of their rapid generation, high yields, and large market demand both locally and internationally (Ollitrault "et al." 2007). In Malaysia, where the disease has plagued farmers for over a decade, papayas have an export value of approximately 24-28 million USD per year (Maktar "et al." 2008). With bacterial crown rot affecting approximately 800 hectares of papaya on the Malaysian Peninsula alone (Maktar "et al." 2008), this results in a huge loss in profit for the  agricultural industry. Host and symptoms. Although "Erwinia papayae" has been known to survive on leaves of cowpea, tomato, and rockmelon for a minimum of two weeks, the host range of bacterial crown rot is confined to papaya (Webb 1985). Inoculation with the pathogen of twenty-three common weed species and crops found in association with Philippine papaya fields found none of these species to be susceptible to the disease (Obrero 1980). Symptoms of bacterial crown rot begin as angular water-soaked lesions on leaf surfaces and eventually spread through veins and petioles to cause death to the canopy layer of  leaves. Water-soaked cankers also appear on the stem, causing it to collapse, and spread to meristems, killing the growing tips of the plant (Webb 1985; Fullerton "et al." 2011; Maktar "et al." 2008). Water-soaked lesions can also appear on unripe fruit, and although they start small, the lesions can turn into firm depressions (Webb 1985). Dry conditions can allow infected plants to recover and produce unaffected, fruit-producing branches. "Erwinia papayae" is a Gram-negative, straight rod bacterium with peritrichous flagella, so diagnosis can be made using a Gram stain. On King’s medium B, colonies are creamy  and mucoid with a non-diffusible blue pigment (Vawdrey 2011). Disease cycle. The pathogen can survive in the seed of infected papaya, even after drying, for approximately 30 days (Obrero 1980). Thus far, seed-borne transmission is the predominant method of spread and infection; in fact, studies indicate the pathogen has the ability for long-range dispersal via seed (Ramachandran "et al." 2015). Although symptoms can be seen year round, rain and splashing water aid in the transmission and exacerbate the disease (Webb 1985). The bacterium relies on wounds or natural plant openings to enter the papaya. Upon infection by  the pathogen, juvenile stem tissue initially shows dark green, water-soaked lesions, which develop into putrid wet rot on the stems (Vawdrey 2011). "E. papayae" causes a systemic infection—coalescing brown angular lesions spread from the stem lamina to the crown meristems. The firm depressed lesions that progress on unripe fruit penetrate seed cavities. The pathogen does not survive longer than two weeks in soil—instead, the pathogen survives inside the infected vascular bundles of diseased papaya (Vawdrey 2011). References. Fullerton RA, Taufa L, Vanneste JL, Yu J, Cornish DA, Park D. (2011). First record of bacterial crown rot of  papaya (Carica papaya) caused by an Erwinia papayae-like bacterium in the Kingdom of Tonga. Plant Disease 95, 70. Gardan, L., Christen, R., Achouak, W., & Prior, P. (2004). Erwinia papayae sp. nov., a pathogen of papaya (Carica papaya). International Journal of Systematic and Evolutionary Microbiology 54, 107-113. Maktar, N. H., Kamis, S., Mohd Yusof, F.Z., & Hussain, N.H. (2008). Erwinia papayae causing papaya dieback in Malaysia. Plant Pathology 57(4), 774. Obrero, F. P. (1991). Bacterial crown rot of papaya in the Philippines. In: Proceedings of First National Symposium/Workshop on Ring Spot and other diseases of papaya in the Philippines , The Philippine Phyt. Soc. Bureau of Plant Industry, San Andres, Malate, Manila, pp 20–23. Ollitrault, P., Bruyére, S., Ocampo, J., de Lapeyre, L., Gallard, A., Argoud, L., Duval, M.F., Coppens d’Eeckenbrugge, G., Le Bellec, F. (2007). Papaya breeding for tolerance to bacterial decline (Erwinia sp.) in the Caribbean region. Acta Horticulturae 740, 79-92 Ramachandran, K., Manaf, U. A., Zakaria, L. (2015) Molecular characterization and pathogenicity of Erwinia spp. Associated with pineapple [Ananas comosus (L.) Merr.] and papaya [Carica papaya L.). Journal of Plant Protection Research 55 (4), 396-404. Vawdrey, L. (2011). Threat Specific Contingency Plant, Bacterial Crown Rot : Erwinia papayae. In: Industry Biosecurity Plan for the Papaya Industry, Plant Health Australia, pp 1–25. Webb, R.R. (1985). Epidemiology and Control of Bacterial Canker of Papaya Caused by an Erwinia sp. on St. Croix, U.S. Virgin Islands. Plant Disease 69, 305-309.