A total disease-protective effect was observed when washed
cells were added in a concentration of log 7.5 cfu mL1. Addition of
a lower concentration of washed cells (log 5.2 cfu mL1) reduced
disease, but resulted in decreased root weight. Since lettuce is only
cultivated for a short period of time, the lower concentration of
cells could probably be used in practice. For other greenhouse crops
with a longer cultivation time, e.g. tomato and cucumber, the use of
a higher concentration of cells is probably more favourable in order
to protect the roots.