Response of Sugarbeet Lines to Isolates of Fusarium oxysporum f. sp. Betae from the United States

Nine isolates of Fusarium oxysporum Schlechtend.Fr. f. sp. betae (Stewart) Snyd & Hans, that cause Fusarium yel lows of sugarbeet ( Beta vulgaris L.), were tested for their interaction with different sugarbeet lines. two isolates were tested in the presence or absence of the sugarbeet cyst nematode, Heterodera schachtii (Schmidt). In the absence of the cyst nematode, differences in disease severity were detected in sugarbeet lines depending upon the isolates. A small number of lines showed reduced disease response to several isolates, but for the some lines, responses varied, depending upon the pathogen isolate. In the presence of H. schachtii, two isolates of F. oxysporum f. sp. betae increased disease severity in some lines and decreased it in others. this variability in host response may explain some of the variable results growers report after planting sugarbeet lines with resistance to Fusarium yellows.