STUDIES ON THE EFFECT OF FRUIT-COATING POLYMERS AND ORGANIC-ACIDS ON GROWTH OF COLLETOTRICHUM-MUSAE IN-VITRO AND ON POSTHARVEST CONTROL OF ANTHRACNOSE OF BANANAS

Twelve coating materials and their components which can be applied to fruit, and eight organic acids were incorporated into agar media to determine their ability to inhibit mycelial growth of Colletotrichum musae. Of the coating materials tested, two formulations based on a mixture of sucrose esters + fatty acids, Semperfresh F (SFS) and Semperfresh acid-stable (SFAS) at 0.1-1% concentrations were most effective at inhibiting mycelial growth of C. musae. The components used in fruit-coating materials which significantly inhibited growth were oleic, palmitic and lauric acids. Coating materials like chitosan, carboxymethyl cellulose and carboxymethyl chitosan were ineffective at concentrations up to 1%. The effect of organic acids and their salts on the growth of C. musae varied with concentration (1-3%). Malic, citric, oxalic and maleic acids all significantly (P < 0.05) reduced growth of C. musae. Complete inhibition of growth was achieved with potassium sorbate and sodium benzoate at 0.125% and oxalic and maleic acids at 0.5% (w/v). Organic acids also increased the lag time prior to growth initiation. Coating materials, alone or in combination with organic acids or a fungicide (benomyl), were compared for their ability to inhibit post-harvest lesion expansion of anthracnose symptoms on banana fruits at 25 degrees C and 85-90% r.h. SFAS at 1.5 or 3%, and SFAS + 2% potassium sorbate were the most effective treatments when intact skin of banana fruits was inoculated with spores of C. musae prior to application. When fruits were wound-inoculated with mycelium of C. musae, combinations of 3% SFAS with benomyl (250 or 500 mu g l(-1)) controlled lesion expansion more effectively than the fungicide alone. SFAS alone, or with potassium sorbate, or sodium benzoate significantly (P < 0.05) delayed lesion expansion for up to 7 d, but after II d incubation differences between treatments and the untreated control were less marked.