First Report of Pantoea stewartii subsp stewartii Causing Fruit Bronzing of Jackfruit (Artocarpus heterophyllus), a New Emerging Disease in Peninsular Malaysia

Jackfruit (Artocarpus heterophyllus) is one of the popular and the most widely grown fruit species in Malaysia (Department of Agriculture 2013). Under the Third National Agricultural Policy of Malaysia, jackfruit has been recognized as having the potential to meet domestic demand, for export and as a replacement for imports (Ministry of Agriculture 2011). Recently, a disease known as jackfruit bronzing, suspected to be caused by the bacterium Pantoea stewartii, has been constantly found in the jackfruit crop. Typical symptoms of infected jackfruits are characterized by yellowish-orange to reddish discoloration of the affected pulps and rags in the fruit (Gapasin et al. 2014). During April 2016, diseased samples with bronzing symptom of jackfruits were collected in Muadzam Shah plantation of Pahang state. These fruits were excised, rinsed with sterilized distilled water containing 1% sodium hypochlorite (NaClO), placed on nutrient agar (NA) medium using streak plate method, and incubated overnight at 28°C. Four representative bacterial colonies were obtained and selected for further characterization. Colonies were round, yellow-pigmented, smooth, and translucent. All strains were gram-negative, short, rod-shaped, and positive for oxidase, catalase, and indole production tests, which are the characteristics of Pantoea spp. For the pathogenicity test, 10 ml of 108 CFU/ml bacterial suspension of four selected strains were injected into healthy detached jackfruits of J33 (Tekam Yellow) variety. Fruits that were inoculated with sterile distilled water served as a negative control. Inoculations with all strains were performed in three replications, as well as the uninoculated control detached fruits. The inoculated fruits produced bronzing symptoms at 2 weeks post inoculation as observed on naturally diseased samples, whereas control fruits remained asymptomatic. Strain cultures were reisolated and possessed the morphological and biochemical characteristics as previously described. The PCR amplification with primers ES16 and ESIG2c showed all strains displaying a 920 bp amplicon (Coplin et al. 2002). The sequence data were deposited in GenBank (accession nos. KY195916 to KY195919). Bayesian analysis of the ES16/ESIG2c gene sequence clustered all strains into P. stewartii subsp. stewartii DC283 reference strain (AJ311838), with 100% posterior probability. To our knowledge, this is the first report of bronzing disease caused by P. stewartii subsp. stewartii in jackfruit in Malaysia. It is of significant importance to ensure the high quality and quantity of local jackfruit supplies in this country for domestic and international markets. © 2017, American Phytopathological Society. All rights reserved.