POLYGALACTURONASE PRODUCTION BY ASPERGILLUS NIGER: EXPRESSION IN ONION SEEDS AND POSSIBLE INVOLVEMENT IN VIRULENCE

Abstract

SUMMARY Nine Aspergillus niger isolates differing in virulence were assayed for polygalacturonase (PG) content and isoenzyme pattern in spores, liquid cultures and inoculated onion seeds of cultivar ‘Bianca Agostana’. The isolates differed in PG production quantitatively and in terms of isoenzyme pattern. Isolates An1 and An5, characterised by low PG production in liquid culture and low virulence, lacked detectable levels of three PG isoforms (PG3, PG4 and PG5). One acidic PG band (PG6) was detected only during growth in vitro by most of the isolates. Pectin lyase activity was not detected from spores, liquid cultures, or infected seeds. The ability of three isolates differing in virulence, An6, An7 and An14 to colonise five onion cultivars was also tested. The isolates differed in virulence and in quantitative and qualitative PG production. The results suggest that particular PGs from A. niger may contribute to virulence during onion seed colonisation.