Evaluation of plant oils for suppression of crown rot disease and improvement of shelf life of banana (Musa spp. AAA subgroup, cv. Robusta).

Banana (Musa acuminate L.) fruit is highly perishable and its storage life is often affected by number of postharvest diseases. Among these, crown rot is the most serious post-harvest disease in commercial bananas worldwide, as the disease shortens the storage life and spoils the appearance of fruit (Ranasinghe et al., 2003). Although the disease is reported to be caused by different pathogenic fungi such as Colletotrichum musae, Lasiodiplodia theobromae, Fusarium proliferatum and Verticillium theobromae (Finlay & Brown, 1993; Ploetz et al., 1994), the fungi L. theobromae and C. musae, have been reported to be the major pathogens associated with the cause of the crown rot disease in majority of banana producing countries (Anthony et al., 2003; Haque et al., 2003). Our earlier study also showed that in India too, L. theobromae and C. musae are the major pathogens causing this disease (Thangavelu et al., 2007). However, the research on the management of crown rot disease caused by these complex pathogens (L. theobromae and C. musae) is meagre. Moreover, crown rot disease is often controlled commercially by a post-harvest treatment, which involves submerging clusters of banana in solutions of thiobendazole (TBZ) or imazalil or benomyl fungicides (Krauss et al., 1998). Due to this intensive practice, the disease could not be controlled effectively as the pathogens have developed resistance ⁄tolerance to these fungicides (Johanson & Blazquez, 1992). In recent times, an increasing number of countries are also demanding fresh products not treated with agrochemicals, particularly those applied after harvest (Ranasinghe et al., 2003). Under these circumstances, an alternative method of controlling crown rot disease without the use of chemical is urgently required.Fourteen plant oils were evaluated to control the crown rot disease caused by Lasiodiplodia theobromae and Colletotrichum musae. Five of these, viz. Ocimum sanctum, Cymbopogan citratus, C. martinii, C. nardus and Pelargonium graveolens oils completely arrested the mycelial growth of both test pathogens at their lowest concentration compared to other oils. Besides, these plant oils have also inhibited the activity of cellulolytic and pectinolytic enzymes produced by these pathogens effectively under in vitro condition. The treatment of banana fruit var. Robusta (Cavendish-AAA) with oils of O. sanctum, C. citratus, C. nardus and C. martinii not only reduced the crown rot severity significantly, but also increased the shelf life of banana fruits. However, under low-temperature storage (14 C) condition, O. sanctum oil increased the shelf life of banana fruits up to 48 days without affecting their organoleptic properties. Hence, O. sanctum oil could be used as an alternative to chemical fungicides for the management of crown rot disease