Improvement of Biological Control of White Rot of Onion and Variation

Onion plants infected with white rot are typically invaded through their root systems. The pathogen grows necrotrophically in the roots and may invade the bulbs or shoot bases causing a soft rot. Plants that are attacked early often die in the seedling stage. Since the root system are often completely rotted infected plants can easily be pulled out of the ground. Infected bulbs are at first covered with a fluffy white mycelium but this subsequently dies down to form a mat in which large numbers of sclerotia are embedded. Above-ground symptoms usually show first in onions as a yellowing of the older leaves which progressively wilt and fall over. If conditions are not ideal rotting of bulbs may continue in storage.