Tolerance of onions (Allium cepa L.) to the pink root disease caused byPyrenochaeta terrestris

Abstract

The response of 11 onion cultivars (Allium cepa, L.) grown in flats containing soil infested withPyrenochaeta terrestris, the causal agent of pink root disease, was studied. In addition, four cultivars were tested in field trials. Pink roots were found on all the cultivars, including those considered to be resistant. The cultivars ‘Golden’ and ‘Yellow Creole’ were highly susceptible to pink root, whereas cvs. ‘Dessex’, ‘Granex’, ‘Laredo’, ‘Grano 502’ and ‘Grano’ (local) managed to grow and produce reasonable yields, despite having infected roots. Following infection, the growth period of early and intermediate maturing cultivars was shortened by 4–14 days, and that of late maturing cultivars by 18–45 days. A large percentage of small bulbs was produced by most of the susceptible cultivars, but no consistent results were obtained with the resistant cvs. ‘Granex’, ‘Dessex’, and ‘Laredo’. The resistant cultivars maintained an, extensive and viable root system which enabled them to tolerate the disease when grown in infested soils.