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

Kunal Mandal and Satyabrata Maiti*

*satyabratamaiti@hotmail.com

Accepted for publication 16/02/05

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).

Figure 1: Initiation of bacterial soft rot symptoms in aloe	Figure 2: Bulging of epidermis due to gas formation during bacterial soft rotting in aloe

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.

Jin KS, Lee SW, Kim JJ, Ryu HY, 1994. Identification of bacterial isolates obtained from diseased orchid and aloe plants caused by Erwinia chrysanthemi. RDA Journal of Agricultural Science Crop Protection 36, 301-306.

Laat PCA de, Verhoeven JTW, Janse JD, 1994. Bacterial leaf rot of Aloe vera L., caused by Erwinia chrysanthemi biovar 3. European Journal of Plant Pathology 100, 81-84.

The British Society for Plant Pathology