Bacterial soft rot of aloe caused by Pectobacterium chrysanthemi: a new report from India

A new leaf rot disease of Aloe vera was observed for the first time in 2000, at the National Research Centre for Medicinal and Aromatic Plants, India. The disease was serious when abundant moisture was available through irrigation and/or rain. The symptoms started as water soaked lesions at the base of the leaves (Fig. 1). The rotting progressed very fast and the whole plant died within two to three days. As the rotting progressed, the leaf epidermis bulged out due to gas formation and the leaf content was converted to a slimy mass, that was eventually released (Fig. 2).

A bacterium was isolated from the infected tissues. The organism was a non-spore forming, motile, short rod and usually single. It produced circular, convex, small (<1 mm) colonies without pigmentation by 24 h on nutrient agar. The bacterium produced positive reactions to catalase; levan production; gelatine liquefaction; anaerobic growth; fermentative utilisation of glucose and gas formation; utilisation and acid production from arabinose, ribose, xylose, galactose, sucrose, fructose, salicin, inocitol, manitol, cellobiose; and lypolytic activity. However, negative reactions were found to Gram staining; oxidase; starch hydrolysis; H2S production; acid production from methyl-α-D-glucoside, lactose, sorbitol, maltose, trehalose, dulcitol and adonitol; and production of reducing substance from sucrose. Pathogenicity was confirmed by inoculation of leaves in potted plants or excised leaves with bacterial suspension (6 x 10⁶ CFU per ml, approx.) either infiltrated or injected. Characteristic symptoms appeared within 24 h of inoculation.

The bacterium was identified as Pectobacterium chrysanthemi on the basis of the above characteristics and quantitative fatty acid methyl ester analysis and metabolic profiling (Biolog) at CABI Bioscience (IMI 389157). This disease was first reported from the Caribbean island of Aruba (Laat et al., 1994) and Korea (Jin et al., 1994). However, this is the first report of the disease from India.