Significant effects on the weight of the seedlings (F ¼ 69.59;
df1 ¼11, df2 ¼ 24; p 0.000) and of the roots (F ¼ 45.50; df1 ¼11,
df2 ¼ 24; p 0.000) were observed in this study and the results are
shown in Table 1. Addition of a zoospore suspension of P. ultimum
severely impaired growth of lettuce and the untreated, infected
treatment had significantly lower weight than the uninfected
control. The leaf area of a lettuce head, expressed as mean SD, of
the uninfected control was 1383 141 cm2. In comparison, pathogen
addition reduced leaf area by 64%. Addition of the purified
biosurfactant at a concentration of 50 mg mL1 of nutrient solution
protected the plants and no significant differences in plant weight
were observed compared with the uninfected control.