DIFFERENTIAL ACCUMULATION OF ANTIFUNGAL COMPOUNDS DURING ONION SEED GERMINATION AND UPON INFECTION BY ASPERGILLUS NIGER VAN TIEGHEM

Abstract

Extracts from germinating seeds of two onion cultivars differing in susceptibility were fractionated by TLC for their content of antifungal compounds following inoculation with two Aspergillus niger isolates characterised by different degrees of virulence. Three antifungal fractions absorbing ultraviolet light were detected from healthy germinating seeds of the less susceptible cv. ‘Rossa Savonese’ whereas no fractions were observed from tissues of the more susceptible cv. ‘Bianca Agostana’. Inoculation with both isolates resulted in the induction of several fungitoxic compounds. The antifungal profile of ‘Rossa Savonese’ appeared to be more complex, suggesting a possible causal relationship between antifungal compound profile and resistance. Detected onion fractions exerted antifungal activity against both isolates. Our results suggest a role of fluorescent compounds in resistance to A. niger during onion seed germination, when the tissues are particularly exposed to attack by seed- and soilborne pathogens.