Rye Bran Alkylresorcinols Inhibit Growth of Penicillium expansum and Neofabraea perennans In Vitro and In Vivo on Different Apple Cultivars

Apples (Malus domestica Borkh.) are highly susceptible to fungi causing rots, especially in organic orchards where these rots cause major economic losses. Since the use of conventional fungicides is prohibited or restricted in many countries and in organic production, altogether, one alternative is to make use of bioactive compounds that can inhibit fungal growth on apples. Antifungal effects of alkylresorcinols (ARs), isolated from rye bran, were used in two different bioactive emulsions and tested in vitro as well as in vivo against two fungi, Penicillium expansum and Neofabraea perennans, which cause important storage diseases in apple. For both fungi, application of AR emulsions produced a 50 % reduction in mycelial growth and spore germination. The in vivo tests were carried out on wound-inoculated fruit of four apple cultivars, 'Aroma', 'Ingrid Marie', Frida' and 'Gloster'. Spraying the inoculated fruit with ARs decreased lesion area diameter caused by P. expansum with 17-52 % and lesion area diameter caused by N. perennans with 31-77 %, depending on the apple cultivar. For each fungus, the inhibitory effect of ARs was stronger in those apple cultivars that appear to have the highest level of disease tolerance, i.e. the smallest lesions on the control fruit. The level of sun exposure of the fruit had neither significant influence on the decay nor in the inhibitory effect obtained with the postharvest application of ARs.