African Journal of Microbiology Research Vol. 6(8), pp. 1782-1789, 29 February, 2012 Available online at http://www.academicjournals.org/AJMR DOI: 10.5897/ AJMR-11-1254 ISSN 1996-0808 ©2012 Academic Journals Full Length Research Paper Antagonism of actinomycete against Pestalotiopsis mangiferae, causal agent of mango brown rot in post harvest storage I. Ara*, H. Rizwana, M. R. Al-Othman and M. A. Bakir Department of Botany and Microbiology, College of Science, King Saud University, P.O. Box 22452, Riyadh-11495, Kingdom of Saudi Arabia. Accepted 13 January, 2012 For the preliminary screening eighty actinomycetes strains were selected as antagonists against Pestalotiopsis mangiferae, causal agent of brown rot of mango. Actinomycetes strains were cultured with P. mangiferae (dual culture) to determine their in vitro antagonistic ability. 17 strains that strongly inhibited hyphal growth of the pathogens were selected as potent antagonists. Green healthy fruits were treated with the test pathogens and potent antagonistic actinomycetes to determine their effect inhibition of pathogens. These isolates significantly reduced severity of brown rot on mango. Isolates CF-1(1), Dir-10(10), Dir-10(8) and Dir-10(3) reduced the size of the lesion as compared to control. These isolates exhibited disease inhibition of 70 to 89% in the inoculated mango fruits. However, maximum disease inhibition was observed with isolate CF-1(1) and this was the most potent isolate by inhibiting the disease by 89.06% in mango fruit. Key words: Post harvest disease, biological control, mango, actinomycetes, Pestalotiopsis mangiferae. INTRODUCTION Saudi Arabia is one of the largest fruit consuming markets, huge amounts of fruits are imported from different parts of the world. Mangoes (Mangifera indica L.) are imported in Saudi Arabia from tropical countries and are considered as most popular fruits (Abd-Elsalam et al., 2010). However, post harvest decay of fruits causes tremendous losses. It is estimated that 20 to 25% of harvested fruits are decayed by pathogens during post harvest handling even in developed countries (Droby, 2006; Zhu, 2006). In developing countries, postharvest losses are often more severe due to inadequate storage and transportation facilities (Rashad et al., 2011). Fungal fruit infections may occur during the growing season, harvesting, handling, transport, post-harvest storage and marketing conditions, or after purchasing by the consumer. Fruits due to their low pH, high moisture content and *Corresponding author. E-mail: ismetara@yahoo.com; iara@ksu.edu.sa. Tel: +966 1478 9585 Ext. 1639; +966534509242. nutritional composition are very susceptible to attack by pathogenic fungi which in addition to causing rots may also make them unfit for consumption by producing mycotoxins (Stinson et al., 1980; Philips,1984; Singh and Sharma, 2007). Microorganisms associated with post harvest spoilage of fruits have engaged the attention of mycologists for many years (Okigbo, 2001). Mangoes because of its delicious taste and high calorific value are ranked as the most popular fruits in international markets. Although bacteria, arthropods, nematodes and parasitic plants affect mango, diseases caused by fungi are most important and play a major role in post harvest rotting of mangoes (Ploetz et al., 1994). Different workers have reported various fungi from mango viz., Colletotrichum gleosporoides (Rawal, 1998; Savant and Raut, 2000; Ploetz et al., 1996; Sharma, 1993), P. mangiferae, Phoma spp. and Fusarium solani (Sharma, 1993; Sarvottam et al., 2009), as a cause of decline in quality of mango. P. mangiferae (Henn) Steyaert (Synonym Pestalotia mangiferae Henn) causes grey blight of leaves (Verma et al., 1991), grey leaf spots, stem end rots, brown spots or rots of mango fruits (Mordue, 1980). P. mangiferae produces abundant