Control of Rhizopus: Induced decay in watermelon (Citrullus lanatus L.) fruits using heat treatment

Oladele Oluwole Olakunle

Abstract
Control of Rhizopus, induced decay in watermelon (Citrullus lanatus) fruits using heat treatment was investigated. Watermelon fruits of uniform size and colour were selected, washed with clean water and disinfected after harvest. The fruits were then inoculated with spore suspension containing 3.02 x 10³ spores mL^-1 of Rhizopus sp. inoculated fruits were immersed separately in a water bath at 50 ^oC for 2, 3 and 5 min and 53 ^oC for 2 and 3 min. Control fruits were inoculated but not heat treated. Each set up was in 3 replicates. Control and treated fruits were then stored in cleaned transparent plastic containers at 28 ^oC + 2 ^oC and 75%-80% relative humidity and observed daily for disease severity. Result obtained on day 5 of storage showed there was no significance difference (p > 0.05) in the disease severities of control and all the treated fruits. The disease severity of both the control and all treated fruits was 1.00 + 0.28 which implied that the fruits were healthy (disease free). However as storage period progressed to day 25, only fruits treated at 53 ^oC for 3 min maintained disease severity of 1.00 + 0.00, which implied that the fruits were still disease free, recording mean appearance and taste index of 3.50 and 2.00, respectively, which thus indicated good appearance and sweet taste of the fruits. Other treatments recorded various degrees of rottenness. Hence, treatment at 53 ^oC for 3 min could be considered as the most effective for extending the shelf life of water melon fruits among all temperatures and time combinations experimented in the study.

Keywords
Disease severity; Hot water; Time; Pathogen; Spore suspension; Storage.

DOI
10.21472/bjbs.051035

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