Screening short-day onion varieties for resistance to fusarium basal rot.

摘要

Fusarium basal rot (FBR) caused by Fusarium oxysporum f.sp. cepae, is a worldwide soil-borne fungal disease that affects bulb onions. Short-day onion germplasm were screened for FBR resistance in a growth chamber and in the field. In growth chambers, 42 short-day onion lines were sown in silica sand infested with 4.0x104 spores/g sand. At 2 weeks, the number of germinated seedlings was counted and the chamber temperature was increased from 22 to 28 degrees C. At 4 weeks, the number of surviving seedlings was counted and a percent survival rate was calculated for each line. The same onion lines were grown in a field known to produce a high incidence of fusarium-basal-rot-infected bulbs. When all the bulbs in a plot were mature, the basal plates of 30 bulbs were cut transversely and each plate was rated for disease severity on a scale of 1-9. The FBR incidence was calculated from the number of bulbs with FBR out of the total bulbs tested. In growth chamber studies, cultivars NuMex Luna and NMSU 00-32 had the highest seedling survival rate (23.6 and 20.4%, respectively). In field studies, cv. Cardinal was found to have the highest FBR incidence (90.8%) and the highest FBR severity (4.9). NMSU 00-13-1 had the lowest FBR incidence (10%) and the lowest FBR severity (1.11). A strong, positive correlation existed between FBR incidence and severity, whereas both traits were weakly correlated with seedling survival.